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Sample records for pem fuel cel

  1. PEM regenerative fuel cells

    NASA Technical Reports Server (NTRS)

    Swette, Larry L.; Laconti, Anthony B.; Mccatty, Stephen A.

    1993-01-01

    This paper will update the progress in developing electrocatalyst systems and electrode structures primarily for the positive electrode of single-unit solid polymer proton exchange membrane (PEM) regenerative fuel cells. The work was done with DuPont Nafion 117 in complete fuel cells (40 sq cm electrodes). The cells were operated alternately in fuel cell mode and electrolysis mode at 80 C. In fuel cell mode, humidified hydrogen and oxygen were supplied at 207 kPa (30 psi); in electrolysis mode, water was pumped over the positive electrode and the gases were evolved at ambient pressure. Cycling data will be presented for Pt-Ir catalysts and limited bifunctional data will be presented for Pt, Ir, Ru, Rh, and Na(x)Pt3O4 catalysts as well as for electrode structure variations.

  2. PEM regenerative fuel cells

    NASA Astrophysics Data System (ADS)

    Swette, Larry L.; Laconti, Anthony B.; McCatty, Stephen A.

    1993-11-01

    This paper will update the progress in developing electrocatalyst systems and electrode structures primarily for the positive electrode of single-unit solid polymer proton exchange membrane (PEM) regenerative fuel cells. The work was done with DuPont Nafion 117 in complete fuel cells (40 sq cm electrodes). The cells were operated alternately in fuel cell mode and electrolysis mode at 80 C. In fuel cell mode, humidified hydrogen and oxygen were supplied at 207 kPa (30 psi); in electrolysis mode, water was pumped over the positive electrode and the gases were evolved at ambient pressure. Cycling data will be presented for Pt-Ir catalysts and limited bifunctional data will be presented for Pt, Ir, Ru, Rh, and Na(x)Pt3O4 catalysts as well as for electrode structure variations.

  3. PEM fuel cell degradation

    SciTech Connect

    Borup, Rodney L; Mukundan, Rangachary

    2010-01-01

    The durability of PEM fuel cells is a major barrier to the commercialization of these systems for stationary and transportation power applications. While significant progress has been made in understanding degradation mechanisms and improving materials, further improvements in durability are required to meet commercialization targets. Catalyst and electrode durability remains a primary degradation mode, with much work reported on understanding how the catalyst and electrode structure degrades. Accelerated Stress Tests (ASTs) are used to rapidly evaluate component degradation, however the results are sometimes easy, and other times difficult to correlate. Tests that were developed to accelerate degradation of single components are shown to also affect other component's degradation modes. Non-ideal examples of this include ASTs examining catalyst degradation performances losses due to catalyst degradation do not always well correlate with catalyst surface area and also lead to losses in mass transport.

  4. Corrosion resistant PEM fuel cell

    DOEpatents

    Fronk, Matthew Howard; Borup, Rodney Lynn; Hulett, Jay S.; Brady, Brian K.; Cunningham, Kevin M.

    2002-01-01

    A PEM fuel cell having electrical contact elements comprising a corrosion-susceptible substrate metal coated with an electrically conductive, corrosion-resistant polymer containing a plurality of electrically conductive, corrosion-resistant filler particles. The substrate may have an oxidizable metal first layer (e.g., stainless steel) underlying the polymer coating.

  5. Corrosion resistant PEM fuel cell

    DOEpatents

    Fronk, Matthew Howard; Borup, Rodney Lynn; Hulett, Jay S.; Brady, Brian K. NY); Cunningham, Kevin M.

    2011-06-07

    A PEM fuel cell having electrical contact elements comprising a corrosion-susceptible substrate metal coated with an electrically conductive, corrosion-resistant polymer containing a plurality of electrically conductive, corrosion-resistant filler particles. The substrate may have an oxidizable metal first layer (e.g., stainless steel) underlying the polymer coating.

  6. Corrosion resistant PEM fuel cell

    DOEpatents

    Li, Yang; Meng, Wen-Jin; Swathirajan, Swathy; Harris, Stephen Joel; Doll, Gary Lynn

    2002-01-01

    The present invention contemplates a PEM fuel cell having electrical contact elements (including bipolar plates/septums) comprising a titanium nitride coated light weight metal (e.g., Al or Ti) core, having a passivating, protective metal layer intermediate the core and the titanium nitride. The protective layer forms a barrier to further oxidation/corrosion when exposed to the fuel cell's operating environment. Stainless steels rich in CR, Ni, and Mo are particularly effective protective interlayers.

  7. Corrosion resistant PEM fuel cell

    DOEpatents

    Li, Yang; Meng, Wen-Jin; Swathirajan, Swathy; Harris, Stephen Joel; Doll, Gary Lynn

    2001-07-17

    The present invention contemplates a PEM fuel cell having electrical contact elements (including bipolar plates/septums) comprising a titanium nitride coated light weight metal (e.g., Al or Ti) core, having a passivating, protective metal layer intermediate the core and the titanium nitride. The protective layer forms a barrier to further oxidation/corrosion when exposed to the fuel cell's operating environment. Stainless steels rich in CR, Ni, and Mo are particularly effective protective interlayers.

  8. Corrosion resistant PEM fuel cell

    DOEpatents

    Li, Y.; Meng, W.J.; Swathirajan, S.; Harris, S.J.; Doll, G.L.

    1997-04-29

    The present invention contemplates a PEM fuel cell having electrical contact elements (including bipolar plates/septums) comprising a titanium nitride coated light weight metal (e.g., Al or Ti) core, having a passivating, protective metal layer intermediate the core and the titanium nitride. The protective layer forms a barrier to further oxidation/corrosion when exposed to the fuel cell`s operating environment. Stainless steels rich in Cr, Ni, and Mo are particularly effective protective interlayers. 6 figs.

  9. Corrosion resistant PEM fuel cell

    DOEpatents

    Li, Yang; Meng, Wen-Jin; Swathirajan, Swathy; Harris, Stephen J.; Doll, Gary L.

    1997-01-01

    The present invention contemplates a PEM fuel cell having electrical contact elements (including bipolar plates/septums) comprising a titanium nitride coated light weight metal (e.g., Al or Ti) core, having a passivating, protective metal layer intermediate the core and the titanium nitride. The protective layer forms a barrier to further oxidation/corrosion when exposed to the fuel cell's operating environment. Stainless steels rich in CR, Ni, and Mo are particularly effective protective interlayers.

  10. PEM fuel cell monitoring system

    DOEpatents

    Meltser, Mark Alexander; Grot, Stephen Andreas

    1998-01-01

    Method and apparatus for monitoring the performance of H.sub.2 --O.sub.2 PEM fuel cells. Outputs from a cell/stack voltage monitor and a cathode exhaust gas H.sub.2 sensor are corrected for stack operating conditions, and then compared to predetermined levels of acceptability. If certain unacceptable conditions coexist, an operator is alerted and/or corrective measures are automatically undertaken.

  11. PEM fuel cell monitoring system

    DOEpatents

    Meltser, M.A.; Grot, S.A.

    1998-06-09

    Method and apparatus are disclosed for monitoring the performance of H{sub 2}--O{sub 2} PEM fuel cells. Outputs from a cell/stack voltage monitor and a cathode exhaust gas H{sub 2} sensor are corrected for stack operating conditions, and then compared to predetermined levels of acceptability. If certain unacceptable conditions coexist, an operator is alerted and/or corrective measures are automatically undertaken. 2 figs.

  12. PEM fuel cell durability studies

    SciTech Connect

    Borup, Rodney L; Davey, John R; Ofstad, Axel B; Xu, Hui

    2008-01-01

    The durability of polymer electrolyte membrane (PEM) fuel cells is a major barrier to the commercialization for stationary and transportation power applications. For transportation applications, the durability target for fuel cell power systems is a 5,000 hour lifespan and able to function over a range of vehicle operating conditions (-40{sup o} to +40{sup o}C). However, durability is difficult to quantify and improve because of the quantity and duration of testing required, and also because the fuel cell stack contains many components, for which the degradation mechanisms, component interactions and effects of operating conditions are not fully understood. These requirements have led to the development of accelerated testing protocols for PEM fuel cells. The need for accelerated testing methodology is exemplified by the times required for standard testing to reach their required targets: automotive 5,000 hrs = {approx} 7 months; stationary systems 40,000 hrs = {approx} 4.6 years. As new materials continue to be developed, the need for relevant accelerated testing increases. In this investigation, we examine the durability of various cell components, examine the effect of transportation operating conditions (potential cycling, variable RH, shut-down/start-up, freeze/thaw) and evaluate durability by accelerated durability protocols. PEM fuel cell durability testing is performed on single cells, with tests being conducted with steady-state conditions and with dynamic conditions using power cycling to simulate a vehicle drive cycle. Component and single-cell characterization during and after testing was conducted to identify changes in material properties and related failure mechanisms. Accelerated-testing experiments were applied to further examine material degradation.

  13. Fuel Processors for PEM Fuel Cells

    SciTech Connect

    Levi T. Thompson

    2008-08-08

    Fuel cells are being developed to power cleaner, more fuel efficient automobiles. The fuel cell technology favored by many automobile manufacturers is PEM fuel cells operating with H2 from liquid fuels like gasoline and diesel. A key challenge to the commercialization of PEM fuel cell based powertrains is the lack of sufficiently small and inexpensive fuel processors. Improving the performance and cost of the fuel processor will require the development of better performing catalysts, new reactor designs and better integration of the various fuel processing components. These components and systems could also find use in natural gas fuel processing for stationary, distributed generation applications. Prototype fuel processors were produced, and evaluated against the Department of Energy technical targets. Significant advances were made by integrating low-cost microreactor systems, high activity catalysts, π-complexation adsorbents, and high efficiency microcombustor/microvaporizers developed at the University of Michigan. The microreactor system allowed (1) more efficient thermal coupling of the fuel processor operations thereby minimizing heat exchanger requirements, (2) improved catalyst performance due to optimal reactor temperature profiles and increased heat and mass transport rates, and (3) better cold-start and transient responses.

  14. Development of PEM fuel cell technology at international fuel cells

    SciTech Connect

    Wheeler, D.J.

    1996-04-01

    The PEM technology has not developed to the level of phosphoric acid fuel cells. Several factors have held the technology development back such as high membrane cost, sensitivity of PEM fuel cells to low level of carbon monoxide impurities, the requirement to maintain full humidification of the cell, and the need to pressurize the fuel cell in order to achieve the performance targets. International Fuel Cells has identified a hydrogen fueled PEM fuel cell concept that leverages recent research advances to overcome major economic and technical obstacles.

  15. Durability of PEM Fuel Cell Membranes

    NASA Astrophysics Data System (ADS)

    Huang, Xinyu; Reifsnider, Ken

    Durability is still a critical limiting factor for the commercialization of polymer electrolyte membrane (PEM) fuel cells, a leading energy conversion technology for powering future hydrogen fueled automobiles, backup power systems (e.g., for base transceiver station of cellular networks), portable electronic devices, etc. Ionic conducting polymer (ionomer) electrolyte membranes are the critical enabling materials for the PEM fuel cells. They are also widely used as the central functional elements in hydrogen generation (e.g., electrolyzers), membrane cell for chlor-alkali production, etc. A perfluorosulfonic acid (PFSA) polymer with the trade name Nafion® developed by DuPont™ is the most widely used PEM in chlor-alkali cells and PEM fuel cells. Similar PFSA membranes have been developed by Dow Chemical, Asahi Glass, and lately Solvay Solexis. Frequently, such membranes serve the dual function of reactant separation and selective ionic conduction between two otherwise separate compartments. For some applications, the compromise of the "separation" function via the degradation and mechanical failure of the electrolyte membrane can be the life-limiting factor; this is particularly the case for PEM in hydrogen/oxygen fuel cells.

  16. Brazed bipolar plates for PEM fuel cells

    DOEpatents

    Neutzler, Jay Kevin

    1998-01-01

    A liquid-cooled, bipolar plate separating adjacent cells of a PEM fuel cell comprising corrosion-resistant metal sheets brazed together so as to provide a passage between the sheets through which a dielectric coolant flows. The brazement comprises a metal which is substantially insoluble in the coolant.

  17. Brazed bipolar plates for PEM fuel cells

    DOEpatents

    Neutzler, J.K.

    1998-07-07

    A liquid-cooled, bipolar plate separating adjacent cells of a PEM fuel cell comprises corrosion-resistant metal sheets brazed together so as to provide a passage between the sheets through which a dielectric coolant flows. The brazement comprises a metal which is substantially insoluble in the coolant. 6 figs.

  18. Reversible (unitized) PEM fuel cell devices

    SciTech Connect

    Mitlitsky, F; Myers, B; Smith, W F; Weisberg, Molter, T M

    1999-06-01

    Regenerative fuel cells (RFCs) are enabling for many weight-critical portable applications, since the packaged specific energy (>400 Wh/kg) of properly designed lightweight RFC systems is several-fold higher than that of the lightest weight rechargeable batteries. RFC systems can be rapidly refueled (like primary fuel cells), or can be electrically recharged (like secondary batteries) if a refueling infrastructure is not conveniently available. Higher energy capacity systems with higher performance, reduced weight, and freedom from fueling infrastructure are the features that RFCs promise for portable applications. Reversible proton exchange membrane (PEM) fuel cells, also known as unitized regenerative fuel cells (URFCs), or reversible regenerative fuel cells, are RFC systems which use reversible PEM cells, where each cell is capable of operating both as a fuel cell and as an electrolyzer. URFCs further economize portable device weight, volume, and complexity by combining the functions of fuel cells and electrolyzers in the same hardware, generally without any system performance or efficiency reduction. URFCs are being made in many forms, some of which are already small enough to be portable. Lawrence Livermore National Laboratory (LLNL) has worked with industrial partners to design, develop, and demonstrate high performance and high cycle life URFC systems. LLNL is also working with industrial partners to develop breakthroughs in lightweight pressure vessels that are necessary for URFC systems to achieve the specific energy advantages over rechargeable batteries. Proton Energy Systems, Inc. (Proton) is concurrently developing and commercializing URFC systems (UNIGEN' product line), in addition to PEM electrolyzer systems (HOGEN' product line), and primary PEM fuel cell systems. LLNL is constructing demonstration URFC units in order to persuade potential sponsors, often in their own conference rooms, that advanced applications based on URFC s are feasible. Safety

  19. In situ PEM fuel cell water measurements

    SciTech Connect

    Borup, Rodney L; Mukundan, Rangachary; Davey, John R; Spendalow, Jacob S

    2008-01-01

    Efficient PEM fuel cell performance requires effective water management. The materials used, their durability, and the operating conditions under which fuel cells run, make efficient water management within a practical fuel cell system a primary challenge in developing commercially viable systems. We present experimental measurements of water content within operating fuel cells. in response to operational conditions, including transients and freezing conditions. To help understand the effect of components and operations, we examine water transport in operating fuel cells, measure the fuel cell water in situ and model the water transport within the fuel cell. High Frequency Resistance (HFR), AC Impedance and Neutron imaging (using NIST's facilities) were used to measure water content in operating fuel cells with various conditions, including current density, relative humidity, inlet flows, flow orientation and variable GDL properties. Ice formation in freezing cells was also monitored both during operation and shut-down conditions.

  20. Pattern recognition monitoring of PEM fuel cell

    DOEpatents

    Meltser, M.A.

    1999-08-31

    The CO-concentration in the H{sub 2} feed stream to a PEM fuel cell stack is monitored by measuring current and voltage behavior patterns from an auxiliary cell attached to the end of the stack. The auxiliary cell is connected to the same oxygen and hydrogen feed manifolds that supply the stack, and discharges through a constant load. Pattern recognition software compares the current and voltage patterns from the auxiliary cell to current and voltage signature determined from a reference cell similar to the auxiliary cell and operated under controlled conditions over a wide range of CO-concentrations in the H{sub 2} fuel stream. 4 figs.

  1. Pattern recognition monitoring of PEM fuel cell

    DOEpatents

    Meltser, Mark Alexander

    1999-01-01

    The CO-concentration in the H.sub.2 feed stream to a PEM fuel cell stack is monitored by measuring current and voltage behavior patterns from an auxiliary cell attached to the end of the stack. The auxiliary cell is connected to the same oxygen and hydrogen feed manifolds that supply the stack, and discharges through a constant load. Pattern recognition software compares the current and voltage patterns from the auxiliary cell to current and voltage signature determined from a reference cell similar to the auxiliary cell and operated under controlled conditions over a wide range of CO-concentrations in the H.sub.2 fuel stream.

  2. Design considerations for miniaturized PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Meyers, Jeremy P.; Maynard, Helen L.

    In this paper, we consider the design of a miniaturized proton-exchange membrane (PEM) fuel cell for powering 0.5-20 W portable telecommunication and computing devices. Our design is implemented on a silicon substrate to take advantage of advanced silicon processing technology in order to minimize production costs. The reduced length scales afforded by silicon processing allow us to consider designs that would be prohibited by excessive Ohmic losses in larger systems. We employ a mathematical model to quantify the effects of the secondary current distribution on two competing cell designs. In addition to the design of the cell itself, we discuss key integration issues and engineering trade-offs relevant to all miniaturized fuel cell systems: air movement, fuel delivery and water balance, thermal management and load handling.

  3. In situ PEM fuel cell water measurements

    SciTech Connect

    Borup, Rodney L; Mukundan, Rangachary; Davey, John R; Spendelow, Jacob S; Hussey, Daniel S; Jacobson, David L; Arif, Muhammad

    2009-01-01

    Efficient PEM (Polymer Electrolyte Membrane) fuel cell performance requires effective water management. To achieve a deeper understanding of water transport and performance issues associated with water management, we have conducted in situ water examinations to help understand the effects of components and operations. High Frequency Resistance (HFR), AC Impedance and Neutron imaging were used to measure water content in operating fuel cells, with various conditions, including current density, relative humidity, inlet flows, flow orientation and variable Gas Diffusion Layer (GDL) properties. High resolution neutron radiography was used to image fuel cells during a variety of conditions. The effect of specific operating conditions, including flow direction (co-flow or counter-flow) was examined. Counter-flow operation was found to result in higher water content than co-flow operation, which correlates to lower membrane resistivity. A variety of cells were used to quantify the membrane water in situ during exposure to saturated gases, during fuel cell operation, and during hydrogen pump operation. The quantitative results show lower membrane water content than previous results suggested.

  4. Recent Progress in Nanostructured Electrocatalysts for PEM Fuel Cells

    SciTech Connect

    Zhang, Sheng; Shao, Yuyan; Yin, Geping; Lin, Yuehe

    2013-03-30

    Polymer electrolyte membrane (PEM) fuel cells are attracting much attention as promising clean power sources and an alternative to conventional internal combustion engines, secondary batteries, and other power sources. Much effort from government laboratories, industry, and academia has been devoted to developing PEM fuel cells, and great advances have been achieved. Although prototype cars powered by fuel cells have been delivered, successful commercialization requires fuel cell electrocatalysts, which are crucial components at the heart of fuel cells, meet exacting performance targets. In this review, we present a brief overview of the recent progress in fuel cell electrocatalysts, which involves catalyst supports, Pt and Pt-based electrocatalysts, and non-Pt electrocatalysts.

  5. Dynamic behavior of PEM fuel cell and microturbine power plants

    NASA Astrophysics Data System (ADS)

    El-Sharkh, M. Y.; Sisworahardjo, N. S.; Uzunoglu, M.; Onar, O.; Alam, M. S.

    This paper presents a comparison between the dynamic behavior of a 250 kW stand-alone proton exchange membrane fuel cell power plant (PEM FCPP) and a 250 kW stand-alone microturbine (MT). Dynamic models for the two are introduced. To control the voltage and the power output of the PEM FCPP, voltage and power control loops are added to the model. For the MT, voltage, speed, and power control are used. Dynamic models are used to determine the response of the PEM FCPP and MT to a load step change. Simulation results indicate that the response of the MT to reach a steady state is about twice as fast as the PEM FCPP. For stand-alone operation of a PEM FCPP, a set of batteries or ultracapacitors is needed in order to satisfy the power mismatch during transient periods. Software simulation results are obtained by using MATLAB ®, Simulink ®, and SimPowerSystems ®.

  6. Bipolar plates for PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Middelman, E.; Kout, W.; Vogelaar, B.; Lenssen, J.; de Waal, E.

    The bipolar plates are in weight and volume the major part of the PEM fuel cell stack, and are also a significant contributor to the stack costs. The bipolar plate is therefore a key component if power density has to increase and costs must come down. Three cell plate technologies are expected to reach targeted cost price levels, all having specific advantages and drawbacks. NedStack has developed a conductive composite materials and a production process for fuel cell plates (bipolar and mono-polar). The material has a high electric and thermal conductivity, and can be processed into bipolar plates by a proprietary molding process. Process cycle time has been reduced to less than 10 s, making the material and process suitable for economical mass production. Other development work to increase material efficiency resulted in thin bipolar plates with integrated cooling channels, and integrated seals, and in two-component bipolar plates. Total thickness of the bipolar plates is now less than 3 mm, and will be reduced to 2 mm in the near future. With these thin integrated plates it is possible to increase power density up to 2 kW/l and 2 kW/kg, while at the same time reducing cost by integrating other functions and less material use.

  7. Materials Challenges for Automotive PEM Fuel Cells

    NASA Astrophysics Data System (ADS)

    Gasteiger, Hubert

    2004-03-01

    Over the past few years, significant R efforts aimed at meeting the challenging cost and performance targets required for the use of Polymer Electrolyte Membrane (PEM) fuel cells in automotive applications. Besides engineering advances in bipolar plate materials and design, the optimization of membrane-electrode assemblies (MEAs) was an important enabler in reducing the cost and performance gaps towards commercial viability for the automotive market. On the one hand, platinum loadings were reduced from several mgPt/cm2MEA [1] to values of 0.5-0.6 mgPt/cm2MEA in current applications and loadings as low as 0.25 mgPt/cm2MEA have been demonstrated on the research level [2]. On the other hand, implementation of thin membranes (20-30 micrometer) [3, 4] as well as improvements in diffusion medium materials, essentially doubled the achievable power density of MEAs to ca. 0.9 W/cm2MEA (at 0.65 V) [5], thereby not only reducing the size of a PEMFC fuel cell system, but also reducing its overall materials cost (controlled to a large extent by membrane and Pt-catalyst cost). While this demonstrated a clear path towards automotive applications, a renewed focus of R efforts is now required to develop materials and fundamental materials understanding to assure long-term durability of PEM fuel cells. This presentation therefore will discuss the state-of-the-art knowledge of catalyst, catalyst-support, and membrane degradation mechanisms. In the area of Pt-catalysts, experience with phosphoric acid fuel cells (PAFCs) has shown that platinum sintering leads to long-term performance losses [6]. While this is less critical at the lower PEMFC operating temperatures (<100C) compared to PAFCs (>200C), very little is known about the dependence of Pt-sintering on temperature, cell voltage, and catalyst type (i.e., Pt versus Pt-alloys) and will be discussed here. Similarly, carbon-support corrosion can contribute significantly to voltage degradation in PAFCs [7], and even in the PEMFC

  8. Sensor Development for PEM Fuel Cell Systems

    SciTech Connect

    Steve Magee; Richard Gehman

    2005-07-12

    This document reports on the work done by Honeywell Sensing and Control to investigate the feasibility of modifying low cost Commercial Sensors for use inside a PEM Fuel Cell environment. Both stationary and automotive systems were considered. The target environment is hotter (100 C) than the typical commercial sensor maximum of 70 C. It is also far more humid (100% RH condensing) than the more typical 95% RH non-condensing at 40 C (4% RH maximum at 100 C). The work focused on four types of sensors, Temperature, Pressure, Air Flow and Relative Humidity. Initial design goals were established using a market research technique called Market Driven Product Definition (MDPD). A series of interviews were conducted with various users and system designers in their facilities. The interviewing team was trained in data taking and analysis per the MDPD process. The final result was a prioritized and weighted list of both requirements and desires for each sensor. Work proceeded on concept development for the 4 types of sensors. At the same time, users were developing the actual fuel cell systems and gaining knowledge and experience in the use of sensors and controls systems. This resulted in changes to requirements and desires that were not anticipated during the MDPD process. The concepts developed met all the predicted requirements. At the completion of concept development for the Pressure Sensor, it was determined that the Fuel Cell developers were happy with off-the-shelf automotive pressure sensors. Thus, there was no incentive to bring a new Fuel Cell Specific Pressure Sensor into production. Work was therefore suspended. After the experience with the Pressure Sensor, the requirements for a Temperature Sensor were reviewed and a similar situation applied. Commercially available temperature sensors were adequate and cost effective and so the program was not continued from the Concept into the Design Phase.

  9. Materials Challenges for Automotive PEM Fuel Cells

    NASA Astrophysics Data System (ADS)

    Gasteiger, Hubert

    2004-03-01

    Over the past few years, significant R efforts aimed at meeting the challenging cost and performance targets required for the use of Polymer Electrolyte Membrane (PEM) fuel cells in automotive applications. Besides engineering advances in bipolar plate materials and design, the optimization of membrane-electrode assemblies (MEAs) was an important enabler in reducing the cost and performance gaps towards commercial viability for the automotive market. On the one hand, platinum loadings were reduced from several mgPt/cm2MEA [1] to values of 0.5-0.6 mgPt/cm2MEA in current applications and loadings as low as 0.25 mgPt/cm2MEA have been demonstrated on the research level [2]. On the other hand, implementation of thin membranes (20-30 micrometer) [3, 4] as well as improvements in diffusion medium materials, essentially doubled the achievable power density of MEAs to ca. 0.9 W/cm2MEA (at 0.65 V) [5], thereby not only reducing the size of a PEMFC fuel cell system, but also reducing its overall materials cost (controlled to a large extent by membrane and Pt-catalyst cost). While this demonstrated a clear path towards automotive applications, a renewed focus of R efforts is now required to develop materials and fundamental materials understanding to assure long-term durability of PEM fuel cells. This presentation therefore will discuss the state-of-the-art knowledge of catalyst, catalyst-support, and membrane degradation mechanisms. In the area of Pt-catalysts, experience with phosphoric acid fuel cells (PAFCs) has shown that platinum sintering leads to long-term performance losses [6]. While this is less critical at the lower PEMFC operating temperatures (<100C) compared to PAFCs (>200C), very little is known about the dependence of Pt-sintering on temperature, cell voltage, and catalyst type (i.e., Pt versus Pt-alloys) and will be discussed here. Similarly, carbon-support corrosion can contribute significantly to voltage degradation in PAFCs [7], and even in the PEMFC

  10. Transient analysis of water transport in PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Yan, Wei-Mon; Chu, Hsin-Sen; Chen, Jian-Yao; Soong, Chyi-Yeou; Chen, Falin

    This paper theoretically studies the water transport phenomena in PEM fuel cells, mainly investigating the transient behavior in the gas diffusion layer (GDL), catalyst layer (CL) and proton exchange membrane (PEM). In the PEM, both diffusion and electro-osmosis processes are considered, while in the GDL and CL, only diffusion process is taken into account. The process of water uptake is employed to account for the water transport at the interface between the PEM and CL. The results indicate that the water content in the PEM and the time for reaching the steady state in the start-up process are influenced by the humidification constant, k, the humidification, and the thickness of PEM. The rise of the k increases the water content in the membrane and shortens the time for reaching the steady state. Insufficient humidification causes relatively small water content and long steady time. When the PEM is thinner, the water is more uniformly distributed, the water content gets higher, and the time for reaching the steady state is distinctly shorter.

  11. PEM fuel cell applications and their development at International Fuel Cells

    SciTech Connect

    Fuller, T.F.; Gorman, M.E.; Van Dine, L.L.

    1996-12-31

    International Fuel Cells (IFC) is involved with the full spectrum of fuel cell power plants including the development of Proton Exchange Membrane (PEM) fuel cell systems. The extensive background in systems, design, materials and manufacturing technologies has been brought to bear on the development of highly competitive PEM power plants. IFC is aggressively pursuing these opportunities and is developing low-cost designs for a wide variety of PEM fuel cell applications with special emphasis on portable power and transportation. Experimental PEM power plants for each of these applications have been successfully tested.

  12. Proton Exchange Membrane (PEM) fuel Cell for Space Shuttle

    NASA Technical Reports Server (NTRS)

    Hoffman, William C., III; Vasquez, Arturo; Lazaroff, Scott M.; Downey, Michael G.

    1999-01-01

    Development of a PEM fuel cell powerplant (PFCP) for use in the Space Shuttle offers multiple benefits to NASA. A PFCP with a longer design life than is delivered currently from the alkaline fuel will reduce Space Shuttle Program maintenance costs. A PFCP compatible with zero-gravity can be adapted for future NASA transportation and exploration programs. Also, the commercial PEM fuel cell industry ensures a competitive environment for select powerplant components. Conceptual designs of the Space Shuttle PFCP have resulted in identification of key technical areas requiring resolution prior to development of a flight system. Those technical areas include characterization of PEM fuel cell stack durability under operational conditions and water management both within and external to the stack. Resolution of the above issues is necessary to adequately control development, production, and maintenance costs for a PFCP.

  13. Proton Exchange Membrane (PEM) Fuel Cells for Space Applications

    NASA Technical Reports Server (NTRS)

    Bradley, Karla

    2004-01-01

    This presentation will provide a summary of the PEM fuel cell development at the National Aeronautics and Space Administration, Johnson Space Center (NASA, JSC) in support of future space applications. Fuel cells have been used for space power generation due to their high energy storage density for multi-day missions. The Shuttle currently utilizes the alkaline fuel cell technology, which has highly safe and reliable performance. However, the alkaline technology has a limited life due to the corrosion inherent to the alkaline technology. PEM fuel cells are under development by industry for transportation, residential and commercial stationary power applications. NASA is trying to incorporate some of this stack technology development in the PEM fuel cells for space. NASA has some unique design and performance parameters which make developing a PEM fuel cell system more challenging. Space fuel cell applications utilize oxygen, rather than air, which yields better performance but increases the hazard level. To reduce the quantity of reactants that need to be flown in space, NASA also utilizes water separation and reactant recirculation. Due to the hazards of utilizing active components for recirculation and water separation, NASA is trying to develop passive recirculation and water separation methods. However, the ability to develop recirculation components and water separators that are gravity-independent and successfully operate over the full range of power levels is one of the greatest challenges to developing a safe and reliable PEM fuel cell system. PEM stack, accessory component, and system tests that have been performed for space power applications will be discussed.

  14. Cerium migration during PEM fuel cell accelerated stress testing

    SciTech Connect

    Baker, Andrew M.; Mukundan, Rangachary; Borup, Rodney L.; Spernjak, Dusan; Judge, Elizabeth J.; Advani, Suresh G.; Prasad, Ajay K.

    2016-01-01

    Cerium is a radical scavenger which improves polymer electrolyte membrane (PEM) fuel cell durability. During operation, however, cerium rapidly migrates in the PEM and into the catalyst layers (CLs). In this work, membrane electrode assemblies (MEAs) were subjected to accelerated stress tests (ASTs) under different humidity conditions. Cerium migration was characterized in the MEAs after ASTs using X-ray fluorescence. During fully humidified operation, water flux from cell inlet to outlet generated in-plane cerium gradients. Conversely, cerium profiles were flat during low humidity operation, where in-plane water flux was negligible, however, migration from the PEM into the CLs was enhanced. Humidity cycling resulted in both in-plane cerium gradients due to water flux during the hydration component of the cycle, and significant migration into the CLs. Fluoride and cerium emissions into effluent cell waters were measured during ASTs and correlated, which signifies that ionomer degradation products serve as possible counter-ions for cerium emissions. Fluoride emission rates were also correlated to final PEM cerium contents, which indicates that PEM degradation and cerium migration are coupled. Lastly, it is proposed that cerium migrates from the PEM due to humidification conditions and degradation, and is subsequently stabilized in the CLs by carbon catalyst supports.

  15. Cerium migration during PEM fuel cell accelerated stress testing

    DOE PAGESBeta

    Baker, Andrew M.; Mukundan, Rangachary; Borup, Rodney L.; Spernjak, Dusan; Judge, Elizabeth J.; Advani, Suresh G.; Prasad, Ajay K.

    2016-01-01

    Cerium is a radical scavenger which improves polymer electrolyte membrane (PEM) fuel cell durability. During operation, however, cerium rapidly migrates in the PEM and into the catalyst layers (CLs). In this work, membrane electrode assemblies (MEAs) were subjected to accelerated stress tests (ASTs) under different humidity conditions. Cerium migration was characterized in the MEAs after ASTs using X-ray fluorescence. During fully humidified operation, water flux from cell inlet to outlet generated in-plane cerium gradients. Conversely, cerium profiles were flat during low humidity operation, where in-plane water flux was negligible, however, migration from the PEM into the CLs was enhanced. Humiditymore » cycling resulted in both in-plane cerium gradients due to water flux during the hydration component of the cycle, and significant migration into the CLs. Fluoride and cerium emissions into effluent cell waters were measured during ASTs and correlated, which signifies that ionomer degradation products serve as possible counter-ions for cerium emissions. Fluoride emission rates were also correlated to final PEM cerium contents, which indicates that PEM degradation and cerium migration are coupled. Lastly, it is proposed that cerium migrates from the PEM due to humidification conditions and degradation, and is subsequently stabilized in the CLs by carbon catalyst supports.« less

  16. Advanced space power PEM fuel cell systems

    NASA Technical Reports Server (NTRS)

    Vanderborgh, N. E.; Hedstrom, J.; Huff, J. R.

    1989-01-01

    A model showing mass and heat transfer in proton exchange membrane (PEM) single cells is presented. For space applications, stack operation requiring combined water and thermal management is needed. Advanced hardware designs able to combine these two techniques are available. Test results are shown for membrane materials which can operate with sufficiently fast diffusive water transport to sustain current densities of 300 ma per square centimeter. Higher power density levels are predicted to require active water removal.

  17. Commercialization of proton exchange membrane (PEM) fuel cell technology

    NASA Astrophysics Data System (ADS)

    Goel, Navin; Pant, Alok; Sera, Gary

    1995-01-01

    The MCTTC performed a market assessment for PEM Fuel Cells for terrestrial applications for the Center for Space Power (CSP). The purpose of the market assessment was to gauge the market and commercial potential for PEM fuel cell technology. Further, the market assessment was divided into subsections of technical and market overview, competitive environment, political environment, barriers to market entry, and keys to market entry. The market assessment conducted by the MCTTC involved both secondary and primary research. The primary target markets for PEM fuel cells were transportation and utilities in the power range of 10 kW to 100 kW. The fuel cell vehicle market size was estimated under a pessimistic scenario and an optimistic scenario. The estimated size of the fuel cell vehicle market in dollar terms for the year 2005 is 17.3 billion for the pessimistic scenario and 34.7 billion for the optimistic scenario. The fundamental and applied research funded and conducted by the National Aeronautics and Space Administration (NASA) and DOE in the area of fuel cells presents an excellent opportunity to commercialize dual-use technology and enhance U.S. business competitiveness.

  18. Degradation mechanisms and accelerated testing in PEM fuel cells

    SciTech Connect

    Borup, Rodney L; Mukundan, Rangachary

    2010-01-01

    The durability of PEM fuel cells is a major barrier to the commercialization of these systems for stationary and transportation power applications. Although there has been recent progress in improving durability, further improvements are needed to meet the commercialization targets. Past improvements have largely been made possible because of the fundamental understanding of the underlying degradation mechanisms. By investigating component and cell degradation modes; defining the fundamental degradation mechanisms of components and component interactions new materials can be designed to improve durability. Various factors have been shown to affect the useful life of PEM fuel cells. Other issues arise from component optimization. Operational conditions (such as impurities in either the fuel and oxidant stream), cell environment, temperature (including subfreezing exposure), pressure, current, voltage, etc.; or transient versus continuous operation, including start-up and shutdown procedures, represent other factors that can affect cell performance and durability. The need for Accelerated Stress Tests (ASTs) can be quickly understood given the target lives for fuel cell systems: 5000 hours ({approx} 7 months) for automotive, and 40,000 hrs ({approx} 4.6 years) for stationary systems. Thus testing methods that enable more rapid screening of individual components to determine their durability characteristics, such as off-line environmental testing, are needed for evaluating new component durability in a reasonable turn-around time. This allows proposed improvements in a component to be evaluated rapidly and independently, subsequently allowing rapid advancement in PEM fuel cell durability. These tests are also crucial to developers in order to make sure that they do not sacrifice durability while making improvements in costs (e.g. lower platinum group metal [PGM] loading) and performance (e.g. thinner membrane or a GDL with better water management properties). To

  19. Degradation Mechanisms and Accelerated Testing in PEM Fuel Cells

    SciTech Connect

    Borup, Rodney L.

    2011-01-01

    The durability of PEM fuel cells is a major barrier to the commercialization of these systems for stationary and transportation power applications. Although there has been recent progress in improving durability, further improvements are needed to meet the commercialization targets. Past improvements have largely been made possible because of the fundamental understanding of the underlying degradation mechanisms. By investigating component and cell degradation modes; defining the fundamental degradation mechanisms of components and component interactions new materials can be designed to improve durability. Various factors have been shown to affect the useful life of PEM fuel cells. Other issues arise from component optimization. Operational conditions (such as impurities in either the fuel or oxidant stream), cell environment, temperature (including subfreezing exposure), pressure, current, voltage, etc.; or transient versus continuous operation, including start-up and shutdown procedures, represent other factors that can affect cell performance and durability.

  20. PEM fuel cell bipolar plate material requirements for transportation applications

    SciTech Connect

    Borup, R.L.; Stroh, K.R.; Vanderborgh, N.E.

    1996-04-01

    Cost effective bipolar plates are currently under development to help make proton exchange membrane (PEM) fuel cells commercially viable. Bipolar plates separate individual cells of the fuel cell stack, and thus must supply strength, be electrically conductive, provide for thermal control of the fuel stack, be a non-porous materials separating hydrogen and oxygen feed streams, be corrosion resistant, provide gas distribution for the feed streams and meet fuel stack cost targets. Candidate materials include conductive polymers and metal plates with corrosion resistant coatings. Possible metals include aluminium, titanium, iron/stainless steel and nickel.

  1. Method of monitoring CO concentrations in hydrogen feed to a PEM fuel cell

    DOEpatents

    Grot, Stephen Andreas; Meltser, Mark Alexander; Gutowski, Stanley; Neutzler, Jay Kevin; Borup, Rodney Lynn; Weisbrod, Kirk

    2000-01-01

    The CO concentration in the H.sub.2 feed stream to a PEM fuel cell stack is monitored by measuring current and/or voltage behavior patterns from a PEM-probe communicating with the reformate feed stream. Pattern recognition software may be used to compare the current and voltage patterns from the PEM-probe to current and voltage telltale outputs determined from a reference cell similar to the PEM-probe and operated under controlled conditions over a wide range of CO concentrations in the H.sub.2 fuel stream. The PEM-probe is intermittently purged of any CO build-up on the anode catalyst (e.g., by (1) flushing the anode with air, (2) short circuiting the PEM-probe, or (3) reverse biasing the PEM-probe) to keep the PEM-probe at peak performance levels.

  2. The importance of water control to PEM fuel cell performance

    SciTech Connect

    Cisar, A.; Murphy, O.J.; Simpson, S.F.

    1996-12-31

    All membranes currently in use in polymer electrolyte membrane (PEM) fuel cells have sulfonate (-SO{sub 3}{sup -}) groups as the anionic functionalities attached to the backbone of the polymer electrolyte. As a consequence of this fact, all PEM membranes depend on the presence of water in the electrolyte to facilitate proton transport. This includes perfluorinated membranes, such as Nafion{reg_sign} (DuPont), and Gore Select{trademark} (W. L. Gore), partially fluorinated membranes, such as the Ballard membrane, which is a derivatized trifluorostyrene, non-fluorinated membranes, including both sulfonated polyparaphenylene (Maxdem`s Poly-X{trademark}) and sulfonated styrene-butadiene (DAIS), and the various grafted materials that have been described in the literature. In every case, without water, the proton conductivity of the membrane is insufficient to support fuel cell operation.

  3. The influence of carbon dioxide on PEM fuel cell anodes

    NASA Astrophysics Data System (ADS)

    de Bruijn, F. A.; Papageorgopoulos, D. C.; Sitters, E. F.; Janssen, G. J. M.

    The influence of CO 2 on the performance of PEM fuel cells was investigated by means of fuel cell experiments and cyclic voltammetry. Depending on the composition and microstructure of the fuel cell anode, the effect varies from small to significant. Adsorbed hydrogen plays a dominant role in the formation of CO-like species via the reverse water-gas shift reaction. Platinum sites which are not utilized in the electrochemical oxidation of hydrogen are thought to catalyze this reverse-shift reaction. Alloying with ruthenium suppresses the reverse-shift reaction.

  4. Hydrogen-Oxygen PEM Regenerative Fuel Cell Energy Storage System

    NASA Technical Reports Server (NTRS)

    Bents, David J.; Scullin, Vincent J.; Chang, Bei-Jiann; Johnson, Donald W.; Garcia, Christopher P.

    2005-01-01

    An introduction to the closed cycle hydrogen-oxygen polymer electrolyte membrane (PEM) regenerative fuel cell (RFC), recently constructed at NASA Glenn Research Center, is presented. Illustrated with explanatory graphics and figures, this report outlines the engineering motivations for the RFC as a solar energy storage device, the system requirements, layout and hardware detail of the RFC unit at NASA Glenn, the construction history, and test experience accumulated to date with this unit.

  5. Commercial ballard PEM fuel cell natural gas power plant development

    SciTech Connect

    Watkins, D.S.; Dunnison, D.; Cohen, R.

    1996-12-31

    The electric utility industry is in a period of rapid change. Deregulation, wholesale and retail wheeling, and corporate restructuring are forcing utilities to adopt new techniques for conducting their business. The advent of a more customer oriented service business with tailored solutions addressing such needs as power quality is a certain product of the deregulation of the electric utility industry. Distributed and dispersed power are fundamental requirements for such tailored solutions. Because of their modularity, efficiency and environmental benefits, fuel cells are a favored solution to implement distributed and dispersed power concepts. Ballard Power Systems has been working to develop and commercialize Proton Exchange Membrane (PEM) fuel cell power plants for stationary power markets. PEM`s capabilities of flexible operation and multiple market platforms bodes well for success in the stationary power market. Ballard`s stationary commercialization program is now in its second phase. The construction and successful operation of a 10 kW natural gas fueled, proof-of-concept power plant marked the completion of phase one. In the second phase, we are developing a 250 kW market entry power plant. This paper discusses Ballard`s power plant development plan philosophy, the benefits from this approach, and our current status.

  6. PEM Fuel Cells Redesign Using Biomimetic and TRIZ Design Methodologies

    NASA Astrophysics Data System (ADS)

    Fung, Keith Kin Kei

    Two formal design methodologies, biomimetic design and the Theory of Inventive Problem Solving, TRIZ, were applied to the redesign of a Proton Exchange Membrane (PEM) fuel cell. Proof of concept prototyping was performed on two of the concepts for water management. The liquid water collection with strategically placed wicks concept demonstrated the potential benefits for a fuel cell. Conversely, the periodic flow direction reversal concepts might cause a potential reduction water removal from a fuel cell. The causes of this water removal reduction remain unclear. In additional, three of the concepts generated with biomimetic design were further studied and demonstrated to stimulate more creative ideas in the thermal and water management of fuel cells. The biomimetic design and the TRIZ methodologies were successfully applied to fuel cells and provided different perspectives to the redesign of fuel cells. The methodologies should continue to be used to improve fuel cells.

  7. The use of experimental design to find the operating maximum power point of PEM fuel cells

    SciTech Connect

    Crăciunescu, Aurelian; Pătularu, Laurenţiu; Ciumbulea, Gloria; Olteanu, Valentin; Pitorac, Cristina; Drugan, Elena

    2015-03-10

    Proton Exchange Membrane (PEM) Fuel Cells are difficult to model due to their complex nonlinear nature. In this paper, the development of a PEM Fuel Cells mathematical model based on the Design of Experiment methodology is described. The Design of Experiment provides a very efficient methodology to obtain a mathematical model for the studied multivariable system with only a few experiments. The obtained results can be used for optimization and control of the PEM Fuel Cells systems.

  8. Numerical Simulations of Droplet Dynamics in PEM Fuel Cell Microchannels

    NASA Astrophysics Data System (ADS)

    Cauble, Eric; Owkes, Mark

    2015-11-01

    Proton exchange membrane (PEM) fuel cells are of beneficial interest due to their capability of producing clean energy with zero emissions. An important design challenge hindering the performance of fuel cells is controlling water removal to maintain a hydrated membrane while avoiding excess water that may lead to channel blockage. Fuel cell water management requires a detailed knowledge of multiphase flow dynamics within microchannels. Direct observation of gas-liquid flows is difficult due to the small scale and viewing obstructions of the channels within the fuel cell. Instead, this work uses a CFD approach to compute the formation and dynamics of droplets in fuel cell channels. The method leverages a conservative volume-of-fluid (VOF) formulation coupled with a novel methodology to track dynamic contact angles. We present details of the numerical approach and simulation results relevant to water management in PEM fuel cells. In particular, it is shown that variation of the contact hysteresis angle influences the wetting properties of the droplet and significantly impacts water transport throughout the a fuel cell channel.

  9. Numerical modeling and simulation of PEM fuel cells: Progress and perspective

    NASA Astrophysics Data System (ADS)

    Song, Guang-Hua; Meng, Hua

    2013-06-01

    This paper provides a comprehensive review on the research and development in multi-scale numerical modeling and simulation of PEM fuel cells. An overview of recent progress in PEM fuel cell modeling has been provided. Fundamental transport phenomena in PEM fuel cells and the corresponding mathematical formulation of macroscale models are analyzed. Various important issues in PEM fuel cell modeling and simulation are examined in detail, including fluid flow and species transport, electron and proton transport, heat transfer and thermal management, liquid water transport and water management, transient response behaviors, and cold-start processes. Key areas for further improvements have also been discussed.

  10. PEM fuel cell stack development for automotive applications

    SciTech Connect

    Ernst, W.D.

    1996-12-31

    Presently, the major challenges to the introduction of fuel cell power systems for automotive applications are to maximize the effective system power density and minimize cost. The material cost, especially for Platinum, had been a significant factor until recent advances by Los Alamos National Laboratory and others in low Platinum loading electrode design has brought these costs within control. Since the initiation of its PEM stack development efforts, MTI has focused on applying its system and mechanical engineering heritage on both increasing power density and reducing cost. In May of 1995, MTI was selected (along with four other companies) as a subcontractor by the Ford Motor Company to participate in Phase I of the DOE Office of Transportation Technology sponsored PNGV Program entitled: {open_quotes}Direct-Hydrogen-Fueled Proton-Exchange-Membrane (PEM) Fuel Cell System for Transportation Applications{close_quotes}. This Program was instituted to: (1) Advance the performance and economic viability of a direct-hydrogen-fueled PEM fuel cell system, (2) Identify the critical problems that must be resolved before system scale-up and vehicle integration, and (3) Integrate the fuel cell power system into a sub-scale vehicle propulsion system. The Phase I objective was to develop and demonstrate a nominal 10 kW stack meeting specific criteria. Figure I is a photograph of the stack used for these demonstrations. After completion of Phase I, MTI was one of only two companies selected to continue into Phase II of the Program. This paper summarizes Phase I stack development and results.

  11. Process simulation of a PEM fuel cell system

    SciTech Connect

    Ledjeff-Hey, K.; Roes, J.; Formanski, V.; Gieshoff, J.; Vogel, B.

    1996-01-01

    The thermodynamic performance of a PEM fuel cell system for producing electrical power from natural gas is investigated by considering the flows of energy and energy through the various steps of the whole system. The flows of energy are evaluated using a computer code for energy and energy analyses. The fuel cell system is designed to produce a hydrogen volumetric flow of nearly 5.0 m{sup 3} {sub NTP}/h, provided to the fuel cell at an absolute pressure of 2.9 bar. The fuel cell itself is working with an efficiency of about 60 % at an operating temperature of 65 - 75{degrees} C with an air ratio of four and provides a maximum electric power of 9 kW. Taking into consideration only the produced electric power as useful output of the fuel cell system a total efficiency of 42.2 % is calculated using the simulation results.

  12. Gold Nanoparticles-Enhanced Proton Exchange Membrane (PEM) Fuel Cell

    NASA Astrophysics Data System (ADS)

    Li, Hongfei; Pan, Cheng; Liu, Ping; Zhu, Yimei; Adzic, Radoslav; Rafailovich, Miriam

    Proton exchange membrane fuel cells have drawn great attention and been taken as a promising alternated energy source. One of the reasons hamper the wider application of PEM fuel cell is the catalytic poison effect from the impurity of the gas flow. Haruta has predicted that gold nanoparticles that are platelet shaped and have direct contact with the metal oxide substrate to be the perfect catalysts of the CO oxidization, yet the synthesis method is difficult to apply in the Fuel Cell. In our approach, thiol-functionalized gold nanoparticles were synthesized through two-phase method developed by Brust et al. We deposit these Au particles with stepped surface directly onto the Nafion membrane in the PEM fuel cell by Langmuir-Blodgett method, resulting in over 50% enhancement of the efficiency of the fuel cell. DFT calculations were conducted to understand the theory of this kind of enhancement. The results indicated that only when the particles were in direct surface contact with the membrane, where AuNPs attached at the end of the Nafion side chains, it could reduce the energy barrier for the CO oxidation that could happen at T<300K.

  13. Method of making MEA for PEM/SPE fuel cell

    DOEpatents

    Hulett, Jay S.

    2000-01-01

    A method of making a membrane-electrode-assembly (MEA) for a PEM/SPE fuel cell comprising applying a slurry of electrode-forming material directly onto a membrane-electrolyte film. The slurry comprises a liquid vehicle carrying catalyst particles and a binder for the catalyst particles. The membrane-electrolyte is preswollen by contact with the vehicle before the electrode-forming slurry is applied to the membrane-electrolyte. The swollen membrane-electrolyte is constrained against shrinking in the "x" and "y" directions during drying. Following assembly of the fuel cell, the MEA is rehydrated inside the fuel cell such that it swells in the "z" direction for enhanced electrical contact with contiguous electrically conductive components of the fuel cell.

  14. Novel Hydrogen Purification Device Integrated with PEM Fuel Cells

    SciTech Connect

    Joseph Schwartz; Hankwon Lim; Raymond Drnevich

    2010-12-31

    A prototype device containing twelve membrane tubes was designed, built, and demonstrated. The device produced almost 300 scfh of purified hydrogen at 200 psig feed pressure. The extent of purification met the program target of selectively removing enough impurities to enable industrial-grade hydrogen to meet purity specifications for PEM fuel cells. An extrusion process was developed to produce substrate tubes. Membranes met several test objectives, including completing 20 thermal cycles, exceeding 250 hours of operating life, and demonstrating a flux of 965 scfh/ft2 at 200 psid and 400 C.

  15. H2S removal with ZnO during fuel processing for PEM fuel cell applications

    SciTech Connect

    Li, Liyu; King, David L.

    2006-09-15

    The possibility of using ZnO as a H2S absorbent to protect catalysts in the gasoline and diesel fuel processor for PEM fuel cell applications was studied. It is possible to use commercial ZnO absorbent as a guard bed to protect the PROX catalyst and PEM fuel cell. However, it is not feasible to use ZnO to protect high and low temperature WGS catalysts, most likely due to COS formation via reactions CO + H2S = COS + H2 and CO2 + H2S = COS + H2O.

  16. New electroplated aluminum bipolar plate for PEM fuel cell

    NASA Astrophysics Data System (ADS)

    El-Enin, Sanaa A. Abo; Abdel-Salam, Omar E.; El-Abd, Hammam; Amin, Ashraf M.

    Further improvement in the performance of the polymer electrolyte membrane fuel cells as a power source for automotive applications may be achieved by the use of a new material in the manufacture of the bipolar plate. Several nickel alloys were applied on the aluminum substrate, the use of aluminum as a bipolar plate instead of graphite is to reduce the bipolar plate cost and weight and the ease of machining. The electroplated nickel alloys on aluminum substrate produced a new metallic bipolar plate for PEM fuel cell with a higher efficiency and longer lifetime than the graphite bipolar plate due to its higher electrical conductivity and its lower corrosion rate. Different pretreatment methods were tested; the optimum method for pretreatment consists of dipping the specimen in a 12.5% NaOH for 3 min followed by electroless zinc plating for 2 min, then the specimen is dipped quickly in the electroplating bath after rinsing with distilled water. The produced electroplate was tested with different measurement techniques, chosen based on the requirement for a PEM fuel cell bipolar plate, including X-ray diffraction, EDAX, SEM, corrosion resistance, thickness measurement, microhardness, and electrical conductivity.

  17. Fatigue and Mechanical Damage Propagation in Automotive PEM Fuel Cells

    NASA Astrophysics Data System (ADS)

    Banan, Roshanak

    Polymer electrolyte membrane (PEM) fuel cells are generally exposed to high magnitude road-induced vibrations and impact loads, frequent humidity-temperature loading cycles, and freeze/thaw stresses when employed in automotive applications. The resultant mechanical stresses can play a significant role in the evolution of mechanical defects in the membrane electrode assembly (MEA). The focus of this research is to investigate fatigue challenges due to humidity-temperature (hygrothermal) cycles and vibrations and their effects on damage evolution in PEM fuel cells. To achieve this goal, this thesis is divided into three parts that provide insight into damage propagation in the MEA under i) hygrothermal cycles, ii) external applied vibrations, and iii) a combination of both to simulate realistic automotive conditions. A finite element damage model based on cohesive zone theory was developed to simulate the propagation of micro-scale defects (cracks and delaminations) in the MEA under fuel cell operating conditions. It was found that the micro-defects can propagate to critical states under start-up and shut-down cycles, prior to reaching the desired lifespan of the fuel cell. The simultaneous presence of hygrothermal cycles and vibrations severely intensified damage propagation and resulted in considerably large defects within 75% of the fuel cell life expectancy. However, the order of generated damage was found to be larger under hygrothermal cycles than vibrations. Under hygrothermal cycles, membrane crack propagation was more severe compared to delamination propagation. Conversely, the degrading influence of vibrations was more significant on delaminations. The presence of an anode/cathode channel offset under the combined loadings lead to a 2.5-fold increase in the delamination length compared to the aligned-channel case. The developed model can be used to investigate the damage behaviour of current materials employed in fuel cells as well as to evaluate the

  18. Development of Novel PEM Membrane and Multiphase CD Modeling of PEM Fuel Cell

    SciTech Connect

    K. J. Berry; Susanta Das

    2009-12-30

    To understand heat and water management phenomena better within an operational proton exchange membrane fuel cell's (PEMFC) conditions, a three-dimensional, two-phase computational fluid dynamic (CFD) flow model has been developed and simulated for a complete PEMFC. Both liquid and gas phases are considered in the model by taking into account the gas flow, diffusion, charge transfer, change of phase, electro-osmosis, and electrochemical reactions to understand the overall dynamic behaviors of species within an operating PEMFC. The CFD model is solved numerically under different parametric conditions in terms of water management issues in order to improve cell performance. The results obtained from the CFD two-phase flow model simulations show improvement in cell performance as well as water management under PEMFCs operational conditions as compared to the results of a single phase flow model available in the literature. The quantitative information obtained from the two-phase model simulation results helped to develop a CFD control algorithm for low temperature PEM fuel cell stacks which opens up a route in designing improvement of PEMFC for better operational efficiency and performance. To understand heat and water management phenomena better within an operational proton exchange membrane fuel cell's (PEMFC) conditions, a three-dimensional, two-phase computational fluid dynamic (CFD) flow model has been developed and simulated for a complete PEMFC. Both liquid and gas phases are considered in the model by taking into account the gas flow, diffusion, charge transfer, change of phase, electro-osmosis, and electrochemical reactions to understand the overall dynamic behaviors of species within an operating PEMFC. The CFD model is solved numerically under different parametric conditions in terms of water management issues in order to improve cell performance. The results obtained from the CFD two-phase flow model simulations show improvement in cell performance as well

  19. Test of a PEM fuel cell with low voltage static converter

    NASA Astrophysics Data System (ADS)

    Thounthong, Phatiphat; Raël, Stéphane; Davat, Bernard

    This paper presents a test of a 500 W polymer electrolyte membrane (PEM) fuel cell connected with a power electronic converter. The aim of this device is to develop fuel cell dynamic models and to study converter structure and control to adapt fuel cell to an electrical power train. The design of the converter is first discussed before presenting different experimental results involving thermodynamic and mechanical phenomena of the PEM fuel cell.

  20. Small Portable PEM Fuel Cell Systems for NASA Exploration Missions

    NASA Technical Reports Server (NTRS)

    Burke, Kenneth A.

    2005-01-01

    Oxygen-Hydrogen PEM-based fuel cell systems are being examined as a portable power source alternative in addition to advanced battery technology. Fuel cell power systems have been used by the Gemini, Apollo, and Space Shuttle programs. These systems have not been portable, but have been integral parts of their spacecraft, and have used reactants from a separate cryogenic supply. These systems typically have been higher in power. They also have had significant ancillary equipment sections that perform the pumping of reactants and coolant through the fuel cell stack and the separation of the product water from the unused reactant streams. The design of small portable fuel cell systems will be a significant departure from these previous designs. These smaller designs will have very limited ancillary equipment, relying on passive techniques for reactant and thermal management, and the reactant storage will be an integral part of the fuel cell system. An analysis of the mass and volume for small portable fuel cell systems was done to evaluate and quantify areas of technological improvement. A review of current fuel cell technology as well as reactant storage and management technology was completed to validate the analysis and to identify technology challenges

  1. A portable power system using PEM fuel cells

    SciTech Connect

    Long, E.

    1997-12-31

    Ball has developed a proof-of-concept, small, lightweight, portable power system. The power system uses a proton exchange membrane (PEM) fuel cell stack, stored hydrogen, and atmospheric oxygen as the oxidant to generate electrical power. Electronics monitor the system performance to control cooling air and oxidant flow, and automatically do corrective measures to maintain performance. With the controller monitoring the system health, the system can operate in an ambient environment from 0 C to +50 C. The paper describes system testing, including load testing, thermal and humidity testing, vibration and shock testing, field testing, destructive testing of high-pressure gas tanks, and test results on the fuel cell power system, metal hydride hydrogen storage, high-pressure hydrogen gas storage, and chemical hydride hydrogen storage.

  2. Cerium migration during PEM fuel cell assembly and operation

    DOE PAGESBeta

    Baker, Andrew M.; Torraco, Dennis; Judge, Elizabeth J.; Spernjak, Dusan; Mukundan, Rangachary; Borup, Rod L.; Advani, Suresh G.; Prasad, Ajay K.

    2015-10-02

    Cerium migration between PEM fuel cell components is influenced by potential-driven mobility, ionic diffusion, and gradients in water content. These factors were investigated in ex situ experiments and in operating fuel cells. Potential-induced migration was measured ex situ in hydrated window cells. Cerium-containing MEAs were also fabricated and tested under ASTs. MEA disassembly and subsequent XRF analysis were used to observe rapid cerium migration during cell assembly and operation. During MEA hot pressing, humidification, and low RH operation at OCV, ionic diffusion causes uniform migration from the membrane into the catalyst layers. During high RH operation at OCV, in-plane ceriummore » gradients arise due to variations in water content. These gradients may diminish the scavenging efficacy of cerium by reducing its proximity to generated radicals.« less

  3. Cerium migration during PEM fuel cell assembly and operation

    SciTech Connect

    Baker, Andrew M.; Torraco, Dennis; Judge, Elizabeth J.; Spernjak, Dusan; Mukundan, Rangachary; Borup, Rod L.; Advani, Suresh G.; Prasad, Ajay K.

    2015-09-14

    Cerium migration between PEM fuel cell components is influenced by potential-driven mobility, ionic diffusion, and gradients in water content. These factors were investigated in ex situ experiments and in operating fuel cells. Potential-induced migration was measured ex situ in hydrated window cells. Cerium-containing MEAs were also fabricated and tested under ASTs. MEA disassembly and subsequent XRF analysis were used to observe rapid cerium migration during cell assembly and operation. During MEA hot pressing, humidification, and low RH operation at OCV, ionic diffusion causes uniform migration from the membrane into the catalyst layers. During high RH operation at OCV, in-plane cerium gradients arise due to variations in water content. These gradients may diminish the scavenging efficacy of cerium by reducing its proximity to generated radicals.

  4. Novel Polyoxometalate Containing Membranes for PEM Fuel Cells

    SciTech Connect

    Mason K. Harrup; Frederick F. Stewart; Thomas A Luther; Tammy Trowbridge

    2009-03-01

    Current proton exchange membrane (PEM) technologies are inadequate to address the projected needs for fuel cell performance above 80 ºC. Continuing research into traditional ion carriers in novel membrane materials offers the promise of marginal improvement, representing only an evolutionary increase in performance. This conclusion is supported by the role of water in conduction. Thus, the key to better PEMs is not to eliminate water, but to change the role of water by developing ion carriers that will bind water more tightly than traditional sulfur or phosphorus based carriers resulting in materials that will conduct at higher temperatures. This change entails having a carrier structure that interacts more intimately with water and by increasing the ion carrier anionic charge to result in more tightly held inner shell protonated waters of hydration. Both of these factors synergistically act to maintain a critical water concentration at the carrier necessary for conduction. In this work, polyoxometalate (POM) clusters were selected to serve as these different proton carriers.

  5. Parallel operation characteristics of PEM fuel cell and microturbine power plants

    NASA Astrophysics Data System (ADS)

    Uzunoglu, M.; Onar, O.; El-Sharkh, M. Y.; Sisworahardjo, N. S.; Rahman, A.; Alam, M. S.

    This paper reports on the dynamic behavior of a 250 kW proton exchange membrane fuel cell power plant (PEM FCPP) and a 250 kW microturbine (MT) when operating in parallel. A load sharing control scheme is used to distribute the load equally between the PEM FCPP and the MT. For stand alone operation of a PEM FCPP, a set of batteries or ultracapacitors are needed in order to satisfy the power mismatch during transient periods. Using MT in parallel with the PEM FCPP helps in eliminating the need for storage devices. Models for the PEM FCPP and the MT with power, voltage and speed controls are used to determine the dynamic response of the system to a step change in the load. Simulation results indicate viability of parallel operation of the PEM FCPP and the MT. These results are obtained using MATLAB ®, Simulink ®, and SimPowerSystems ®.

  6. Optimum design of bipolar plates for separate air flow cooling system of PEM fuel cells stacks

    NASA Astrophysics Data System (ADS)

    Franco, Alessandro

    2015-12-01

    The paper discusses about thermal management of PEM fuel cells. The objective is to define criteria and guidelines for the design of the air flow cooling system of fuel cells stacks for different combination of power density, bipolar plates material, air flow rate, operating temperature It is shown that the optimization of the geometry of the channel permits interesting margins for maintaining the use of separate air flow cooling systems for high power density PEM fuel cells.

  7. Non-Kinetic Losses Caused by Electrochemical Carbon Corrosion in PEM Fuel Cells

    SciTech Connect

    Park, Seh Kyu; Shao, Yuyan; Viswanathan, Vilayanur V.; Liu, Jun; Wang, Yong

    2012-05-01

    This paper presented non-kinetic losses in PEM fuel cells under an accelerated stress test of catalyst support. The cathode with carbon-supported Pt catalyst was prepared and characterized with potential hold at 1.2 V vs. SHE in PEM fuel cells. Irreversible losses caused by carbon corrosion were evaluated using a variety of electrochemical characterizations including cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, and polarization technique. Ohmic losses at the cathode with potential hold were determined using its capacitive responses. Concentration losses in PEM fuel cells were analyzed in terms of Tafel behavior and thin film/flooded-agglomerate dynamics.

  8. Characterization of PEM fuel cell degradation by polarization change curves

    NASA Astrophysics Data System (ADS)

    Bezmalinovic, Dario; Simic, Boris; Barbir, Frano

    2015-10-01

    Polarization change curves, defined as a difference between the polarization curve at the beginning of life and the actual polarization curve after the cell has been operational for some time, were used to analyze degradation of a PEM fuel cell exposed to voltage cycling as an accelerated stress test for electrocatalyst degradation. Degradation, i.e., loss of voltage was due to increase of activation losses and increase of resistance in the catalyst layer, both most likely due to the loss of catalyst electrochemically active area. The results of the polarization change curves analysis correspond to the findings of the periodic individual tests performed during the accelerated stress test, such as electrochemical impedance spectroscopy, cyclic voltammetry and linear sweep voltammetry. Therefore, this method has potential to be used as a relatively quick and simple, yet effective, degradation diagnostic tool.

  9. Engineered nano-scale ceramic supports for PEM fuel cells

    SciTech Connect

    Brosha, Eric L; Blackmore, Karen J; Burrell, Anthony K; Henson, Neil J; Phillips, Jonathan

    2010-01-01

    Catalyst support durability is currently a technical barrier for commercialization of polymer electrolyte membrane (PEM) fuel cells, especially for transportation applications. Degradation and corrosion of the conventional carbon supports leads to losses in active catalyst surface area and, consequently, reduced performance. As a result, the major aim of this work is to develop support materials that interact strongly with Pt, yet sustain bulk-like catalytic activities with very highly dispersed particles. This latter aspect is key to attaining the 2015 DOE technical targets for platinum group metal (PGM) loadings (0.20 mg/cm{sup 2}). The benefits of the use of carbon-supported catalysts to drastically reduce Pt loadings from the early, conventional Pt-black technology are well known. The supported platinum catalyzed membrane approach widely used today for fabrication of membrane electrode assemblies (MEAs) was developed shortly thereafter these early reports. Of direct relevance to this present work, are the investigations into Pt particle growth in PEM fuel cells, and subsequent follow-on work showing evidence of Pt particles suspended free of the support within the catalyst layer. Further, durability work has demonstrated the detrimental effects of potential cycling on carbon corrosion and the link between electrochemical surface area and particle growth. To avoid the issues with carbon degradation altogether, it has been proposed by numerous fuel cell research groups to replace carbon supports with conductive materials that are ceramic in nature. Intrinsically, these many conductive oxides, carbides, and nitrides possess the prerequisite electronic conductivity required, and offer corrosion resistance in PEMFC environments; however, most reports indicate that obtaining sufficient surface area remains a significant barrier to obtaining desirable fuel ceU performance. Ceramic materials that exhibit high electrical conductivity and necessary stability under fuel

  10. Real life testing of a Hybrid PEM Fuel Cell Bus

    NASA Astrophysics Data System (ADS)

    Folkesson, Anders; Andersson, Christian; Alvfors, Per; Alaküla, Mats; Overgaard, Lars

    Fuel cells produce low quantities of local emissions, if any, and are therefore one of the most promising alternatives to internal combustion engines as the main power source in future vehicles. It is likely that urban buses will be among the first commercial applications for fuel cells in vehicles. This is due to the fact that urban buses are highly visible for the public, they contribute significantly to air pollution in urban areas, they have small limitations in weight and volume and fuelling is handled via a centralised infrastructure. Results and experiences from real life measurements of energy flows in a Scania Hybrid PEM Fuel Cell Concept Bus are presented in this paper. The tests consist of measurements during several standard duty cycles. The efficiency of the fuel cell system and of the complete vehicle are presented and discussed. The net efficiency of the fuel cell system was approximately 40% and the fuel consumption of the concept bus is between 42 and 48% lower compared to a standard Scania bus. Energy recovery by regenerative braking saves up 28% energy. Bus subsystems such as the pneumatic system for door opening, suspension and brakes, the hydraulic power steering, the 24 V grid, the water pump and the cooling fans consume approximately 7% of the energy in the fuel input or 17% of the net power output from the fuel cell system. The bus was built by a number of companies in a project partly financed by the European Commission's Joule programme. The comprehensive testing is partly financed by the Swedish programme "Den Gröna Bilen" (The Green Car). A 50 kW el fuel cell system is the power source and a high voltage battery pack works as an energy buffer and power booster. The fuel, compressed hydrogen, is stored in two high-pressure stainless steel vessels mounted on the roof of the bus. The bus has a series hybrid electric driveline with wheel hub motors with a maximum power of 100 kW. Hybrid Fuel Cell Buses have a big potential, but there are

  11. Transient response of high temperature PEM fuel cell

    NASA Astrophysics Data System (ADS)

    Peng, J.; Shin, J. Y.; Song, T. W.

    A transient three-dimensional, single-phase and non-isothermal numerical model of polymer electrolyte membrane (PEM) fuel cell with high operating temperature has been developed and implemented in computational fluid dynamic (CFD) code. The model accounts for transient convective and diffusive transport, and allows prediction of species concentration. Electrochemical charge double-layer effect is considered. Heat generation according to electrochemical reaction and ohmic loss are involved. Water transportation across membrane is ignored due to low water electro-osmosis drag force of polymer polybenzimidazole (PBI) membrane. The prediction shows transient in current density which overshoots (undershoots) the stabilized state value when cell voltage is abruptly decreased (increased). The result shows that the peak of overshoot (undershoot) is related with cathode air stoichiometric mass flow rate instead of anode hydrogen stoichiometric mass flow rate. Current is moved smoothly and there are no overshoot or undershoot with the influence of charge double-layer effect. The maximum temperature is located in cathode catalyst layer and both fuel cell average temperature and temperature deviation are increased with increasing of current load.

  12. Proton Exchange Membrane (PEM) Fuel Cell Status and Remaining Challenges for Manned Space-Flight Applications

    NASA Technical Reports Server (NTRS)

    Reaves, Will F.; Hoberecht, Mark A.

    2003-01-01

    The Fuel Cell has been used for manned space flight since the Gemini program. Its power output and water production capability over long durations for the mass and volume are critical for manned space-flight requirements. The alkaline fuel cell used on the Shuttle, while very reliable and capable for it s application, has operational sensitivities, limited life, and an expensive recycle cost. The PEM fuel cell offers many potential improvements in those areas. NASA Glenn Research Center is currently leading a PEM fuel cell development and test program intended to move the technology closer to the point required for manned space-flight consideration. This paper will address the advantages of PEM fuel cell technology and its potential for future space flight as compared to existing alkaline fuel cells. It will also cover the technical hurdles that must be overcome. In addition, a description of the NASA PEM fuel cell development program will be presented, and the current status of this effort discussed. The effort is a combination of stack and ancillary component hardware development, culminating in breadboard and engineering model unit assembly and test. Finally, a detailed roadmap for proceeding fiom engineering model hardware to qualification and flight hardware will be proposed. Innovative test engineering and potential payload manifesting may be required to actually validate/certify a PEM fuel cell for manned space flight.

  13. Final Report - MEA and Stack Durability for PEM Fuel Cells

    SciTech Connect

    Yandrasits, Michael A.

    2008-02-15

    Proton exchange membrane fuel cells are expected to change the landscape of power generation over the next ten years. For this to be realized one of the most significant challenges to be met for stationary systems is lifetime, where 40,000 hours of operation with less than 10% decay is desired. This project conducted fundamental studies on the durability of membrane electrode assemblies (MEAs) and fuel cell stack systems with the expectation that knowledge gained from this project will be applied toward the design and manufacture of MEAs and stack systems to meet DOE’s 2010 stationary fuel cell stack systems targets. The focus of this project was PEM fuel cell durability – understanding the issues that limit MEA and fuel cell system lifetime, developing mitigation strategies to address the lifetime issues and demonstration of the effectiveness of the mitigation strategies by system testing. To that end, several discoveries were made that contributed to the fundamental understanding of MEA degradation mechanisms. (1) The classically held belief that membrane degradation is solely due to end-group “unzipping” is incorrect; there are other functional groups present in the ionomer that are susceptible to chemical attack. (2) The rate of membrane degradation can be greatly slowed or possibly eliminated through the use of additives that scavenge peroxide or peroxyl radicals. (3) Characterization of GDL using dry gases is incorrect due to the fact that fuel cells operate utilizing humidified gases. The proper characterization method involves using wet gas streams and measuring capillary pressure as demonstrated in this project. (4) Not all Platinum on carbon catalysts are created equally – the major factor impacting catalyst durability is the type of carbon used as the support. (5) System operating conditions have a significant impact of lifetime – the lifetime was increased by an order of magnitude by changing the load profile while all other variables remain

  14. Intergovernmental Advanced Stationary PEM Fuel Cell System Demonstration Final Report

    SciTech Connect

    Rich Chartrand

    2011-08-31

    A program to complete the design, construction and demonstration of a PEMFC system fuelled by Ethanol, LPG or NG for telecom applications was initiated in October 2007. Early in the program the economics for Ethanol were shown to be unfeasible and permission was given by DOE to focus on LPG only. The design and construction of a prototype unit was completed in Jun 2009 using commercially available PEM FC stack from Ballard Power Systems. During the course of testing, the high pressure drop of the stack was shown to be problematic in terms of control and stability of the reformer. Also, due to the power requirements for air compression the overall efficiency of the system was shown to be lower than a similar system using internally developed low pressure drop FC stack. In Q3 2009, the decision was made to change to the Plug power stack and a second prototype was built and tested. Overall net efficiency was shown to be 31.5% at 3 kW output. Total output of the system is 6 kW. Using the new stack hardware, material cost reduction of 63% was achieved over the previous Alpha design. During a November 2009 review meeting Plug Power proposed and was granted permission, to demonstrate the new, commercial version of Plug Power's telecom system at CERL. As this product was also being tested as part of a DOE Topic 7A program, this part of the program was transferred to the Topic 7A program. In Q32008, the scope of work of this program was expanded to include a National Grid demonstration project of a micro-CHP system using hightemperature PEM technology. The Gensys Blue system was cleared for unattended operation, grid connection, and power generation in Aug 2009 at Union College in NY state. The system continues to operate providing power and heat to Beuth House. The system is being continually evaluated and improvements to hardware and controls will be implemented as more is learned about the system's operation. The program is instrumental in improving the efficiency and

  15. Advanced Materials for PEM-Based Fuel Cell Systems

    SciTech Connect

    James E. McGrath; Donald G. Baird; Michael von Spakovsky

    2005-10-26

    Proton exchange membrane fuel cells (PEMFCs) are quickly becoming attractive alternative energy sources for transportation, stationary power, and small electronics due to the increasing cost and environmental hazards of traditional fossil fuels. Two main classes of PEMFCs include hydrogen/air or hydrogen/oxygen fuel cells and direct methanol fuel cells (DMFCs). The current benchmark membrane for both types of PEMFCs is Nafion, a perfluorinated sulfonated copolymer made by DuPont. Nafion copolymers exhibit good thermal and chemical stability, as well as very high proton conductivity under hydrated conditions at temperatures below 80 degrees C. However, application of these membranes is limited due to their high methanol permeability and loss of conductivity at high temperatures and low relative humidities. These deficiencies have led to the search for improved materials for proton exchange membranes. Potential PEMs should have good thermal, hydrolytic, and oxidative stability, high proton conductivity, selective permeability, and mechanical durability over long periods of time. Poly(arylene ether)s, polyimides, polybenzimidazoles, and polyphenylenes are among the most widely investigated candidates for PEMs. Poly(arylene ether)s are a promising class of proton exchange membranes due to their excellent thermal and chemical stability and high glass transition temperatures. High proton conductivity can be achieved through post-sulfonation of poly(arylene ether) materials, but this most often results in very high water sorption or even water solubility. Our research has shown that directly polymerized poly(arylene ether) copolymers show important advantages over traditional post-sulfonated systems and also address the concerns with Nafion membranes. These properties were evaluated and correlated with morphology, structure-property relationships, and states of water in the membranes. Further improvements in properties were achieved through incorporation of inorganic

  16. Advanced Materials for PEM-Based Fuel Cell Systems

    SciTech Connect

    James E. McGrath

    2005-10-26

    Proton exchange membrane fuel cells (PEMFCs) are quickly becoming attractive alternative energy sources for transportation, stationary power, and small electronics due to the increasing cost and environmental hazards of traditional fossil fuels. Two main classes of PEMFCs include hydrogen/air or hydrogen/oxygen fuel cells and direct methanol fuel cells (DMFCs). The current benchmark membrane for both types of PEMFCs is Nafion, a perfluorinated sulfonated copolymer made by DuPont. Nafion copolymers exhibit good thermal and chemical stability, as well as very high proton conductivity under hydrated conditions at temperatures below 80 °C. However, application of these membranes is limited due to their high methanol permeability and loss of conductivity at high temperatures and low relative humidities. These deficiencies have led to the search for improved materials for proton exchange membranes. Potential PEMs should have good thermal, hydrolytic, and oxidative stability, high proton conductivity, selective permeability, and mechanical durability over long periods of time. Poly(arylene ether)s, polyimides, polybenzimidazoles, and polyphenylenes are among the most widely investigated candidates for PEMs. Poly(arylene ether)s are a promising class of proton exchange membranes due to their excellent thermal and chemical stability and high glass transition temperatures. High proton conductivity can be achieved through post-sulfonation of poly(arylene ether) materials, but this most often results in very high water sorption or even water solubility. Our research has shown that directly polymerized poly(arylene ether) copolymers show important advantages over traditional post-sulfonated systems and also address the concerns with Nafion membranes. These properties were evaluated and correlated with morphology, structure-property relationships, and

  17. High resolution neutron imaging of water in PEM fuel cells

    SciTech Connect

    Mukundan, Rangachary; Borup, Rodney L; Davey, John R; Spendelow, Jacob S

    2008-01-01

    Optimal water management in Polymer Electrolyte Membrane (PEM) fuel cells is critical to improving the performance and durability of fuel cell systems especially during transient, start-up and shut-down operations. For example, while a high water content is desirable for improved membrane and catalyst ionomer conductivity, high water content can also block gas access to the triple-phase boundary resulting in lowered performance due to catalyst and gas diffusion layer (GDL) flooding. Visualizing liquid water by neutron imaging has been used over the past decade to study the water distribution inside operating fuel cells. In this paper, the results from our imaging at NIST using their recently installed higher resolution ({approx} 25 mm) Microchannel Plate (MCP) detector with a pixel pitch of 14.7 mm are presented. This detector is capable of quantitatively imaging the water inside the MEA (Membrane Electrode Assembly)/GDL (Gas Diffusion Layer) of working fuel cells and can provide the water profiles within these various components in addition to the channel water. Specially designed fuel cells (active area = 2.25 cm{sup 2}) have been used in order to take advantage of the full detector resolution. The cell design is illustrated in a figure where one of the current collector/end plates is shown. The serpentine pattern was machined into a block of aluminum and plated with nickel and then gold to form the flow field. The measurements were performed using beam no. 1 and aperture no. 2 with a fluence rate of 1.9 x 10{sup 6} neutrons cm{sup -2} sec{sup -1}. The cells were assembled with Gore{sup TM} Primea{sup R} MEAs and SGL Sigracet {sup R} 24 series GDLs (PRIMEA, GORE-SELECT and GORE are trademarks of W. L. Gore & Associates, Inc). All the cells were tested at 80 {sup o}C with 1.2 stoichiometry H{sub 2} and 2.0 stoichiometry air flows.

  18. Understanding of ammonia transport in PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Jung, Myunghee

    This dissertation investigates ammonia (NH3) as a fuel contaminant to the anode in Proton Exchange Membrane Fuel Cells (PEMFCs). Since NH 3 is fed to the anode in a gas phase and transferred to the cathode, the effect of a contaminant is distributed through MEA and quite complicated. This study is focused on the investigation of mechanism of NH3 transport and the isolation of multiple effects to degrade the performance of fuel cell. An External Reference Electrode (ERE) was employed to decouple the effect of individual electrode and explain the mechanism of NH3 contamination. A mechanism of NH3 transport is proposed and supported by data for various inlet conditions in a N2/N2 laboratory-scale fuel cell at Open Circuit Conditions (OCC). With a commercialized GORE(TM) PRIMEA RTM 5631 MEAs at 70°C, data were obtained utilizing a material balance technique, which uses an ion selective electrode (ISE) to determine the concentration of ammonium ion in the process streams. The results indicate that ammonia is not transported across the membrane when the feeds to both electrodes are dry. However, with humidified feeds ammonia was transported from the anode to the cathode. The data also indicate the water content of in the MEA is the critical factor that causes NH3 crossover in the MEA. Diffusion coefficients of NH3 in MEA are also calculated at different relative humilities. An ERE was developed for PEM fuel cell by using a NafionRTM strip which was used to understand contamination mechanism. The voltage of anode electrode relative to ERE was measured during a polarization curve. The data showed the measurement of individual electrode potential was extremely affected by the misalignment between two electrodes. We compare the overpotential measured from the reference electrode and the calculated overpotential from subtracting the cell voltages between neat hydrogen and a 25 ppm CO in H 2 stream at same current. The studies indicated that the overpotentials obtained from

  19. PEM fuel cell cost minimization using ``Design For Manufacture and Assembly`` techniques

    SciTech Connect

    Lomax, F.D. Jr.; James, B.D.; Mooradian, R.P.

    1997-12-31

    Polymer Electrolyte Membrane (PEM) fuel cells fueled with direct hydrogen have demonstrated substantial technical potential to replace Internal Combustion Engines (ICE`s) in light duty vehicles. Such a transition to a hydrogen economy offers the potential of substantial benefits from reduced criteria and greenhouse emissions as well as reduced foreign fuel dependence. Research conducted for the Ford Motor Co. under a US Department of Energy contract suggests that hydrogen fuel, when used in a fuel cell vehicle (FCV), can achieve a cost per vehicle mile less than or equal to the gasoline cost per mile when used in an ICE vehicle. However, fuel cost parity is not sufficient to ensure overall economic success: the PEM fuel cell power system itself must be of comparable cost to the ICE. To ascertain if low cost production of PEM fuel cells is feasible, a powerful set of mechanical engineering tools collectively referred to as Design for Manufacture and Assembly (DFMA) has been applied to several representative PEM fuel cell designs. The preliminary results of this work are encouraging, as presented.

  20. Next Generation Bipolar Plates for Automotive PEM Fuel Cells

    SciTech Connect

    Adrianowycz, Orest; Norley, Julian; Stuart, David J; Flaherty, David; Wayne, Ryan; Williams, Warren; Tietze, Roger; Nguyen, Yen-Loan H; Zawodzinski, Tom; Pietrasz, Patrick

    2010-04-15

    The results of a successful U.S. Department of Energy (DoE) funded two-year $2.9 MM program lead by GrafTech International Inc. (GrafTech) are reported and summarized. The program goal was to develop the next generation of high temperature proton exchange membrane (PEM) fuel cell bipolar plates for use in transportation fuel cell applications operating at temperatures up to 120 °C. The bipolar plate composite developed during the program is based on GrafTech’s GRAFCELL resin impregnated flexible graphite technology and makes use of a high temperature Huntsman Advanced Materials resin system which extends the upper use temperature of the composite to the DoE target. High temperature performance of the new composite is achieved with the added benefit of improvements in strength, modulus, and dimensional stability over the incumbent resin systems. Other physical properties, including thermal and electrical conductivity of the new composite are identical to or not adversely affected by the new resin system. Using the new bipolar plate composite system, machined plates were fabricated and tested in high temperature single-cell fuel cells operating at 120 °C for over 1100 hours by Case Western Reserve University. Final verification of performance was done on embossed full-size plates which were fabricated and glued into bipolar plates by GrafTech. Stack testing was done on a 10-cell full-sized stack under a simulated drive cycle protocol by Ballard Power Systems. Freeze-thaw performance was conducted by Ballard on a separate 5-cell stack and shown to be within specification. A third stack was assembled and shipped to Argonne National Laboratory for independent performance verification. Manufacturing cost estimate for the production of the new bipolar plate composite at current and high volume production scenarios was performed by Directed Technologies Inc. (DTI). The production cost estimates were consistent with previous DoE cost estimates performed by DTI for the

  1. EFFECTS OF FUEL IMPURITIES ON PEM FUEL CELL PERFORMANCE.

    SciTech Connect

    Uribe, F. A.; Zawodzinski, T. A. , Jr.

    2001-01-01

    Power generation with polymer electrolyte membrane fuel cells (PEMFC), particularly those designed for domestic and transportation applications, will likely operate on hydrogen reformed from hydrocarbons. The primary sources of H{sub 2} can be methane (from natural gas), gasoline or diesel fuel. Unfortunately, the reforming process generates impurities that may negatively affect FC performance. The effects of CO impurity have received most of the attention. However, there are other impurities that also may be detrimental to FC: operation. Here we present the effects of ammonia, hydrogen sulfide, methane and ethylene. Two structural domains of the membrane and electrode assembly (MEA) are usually affected by the presence of a harmful impurity. First, the impurity may decrease the ionic conductivity in the catalyst layer or in the bulk membrane. Second, the impurity may chemisorb onto the anode catalyst surface, suppressing the catalyst activity for H{sub 2} oxidation. Catalyst poisoning by CO is the best known example of this kind of effect. Fuel reforming processes [1] generally involve the reaction of a fuel source with air. The simultaneous presence of N{sub 2} and H{sub 2} may generate NH{sub 3} in concentrations of 30 to 90 ppm [1]. The effect of NH{sub 3} on performance depends on the impurity concentration and the time of anode exposure [2]. Higher concentrations result in more rapid performance decreases. If the cell is exposed to ammonia for about 1 hour and then returned to neat H{sub 2}, it will recover its original performance very slowly (about 12 hrs). This behavior is quite different from that of CO, which can be quickly purged from the anode with pure H{sub 2}, resulting in complete performance restoration within a few minutes. Longer exposure times (e.g. >15 hrs) to ammonia result in severe and irreversible losses in performance. It seems that replacement of H{sup +} ions by NH{sub 4}{sup +} ions, first within the anode catalyst layer and then in

  2. Phase 1 feasibility study of an integrated hydrogen PEM fuel cell system. Final report

    SciTech Connect

    Luczak, F.

    1998-03-01

    Evaluated in the report is the use of hydrogen fueled proton exchange membrane (PEM) fuel cells for devices requiring less than 15 kW. Metal hydrides were specifically analyzed as a method of storing hydrogen. There is a business and technical part to the study that were developed with feedback from each other. The business potential of a small PEM product is reviewed by examining the markets, projected sales, and required investment. The major technical and cost hurdles to a product are also reviewed including: the membrane and electrode assembly (M and EA), water transport plate (WTP), and the metal hydrides. It was concluded that the best potential stationary market for hydrogen PEM fuel cell less than 15 kW is for backup power use in telecommunications applications.

  3. NASA's PEM Fuel Cell Power Plant Development Program for Space Applications

    NASA Technical Reports Server (NTRS)

    Hoberecht, Mark A.

    2008-01-01

    A three-center NASA team led by the Glenn Research Center in Cleveland, Ohio is completing a five-year PEM fuel cell power plant development program for future space applications. The focus of the program has been to adapt commercial PEM fuel cell technology for space applications by addressing the key mission requirements of using pure oxygen as an oxidant and operating in a multi-gravity environment. Competing vendors developed breadboard units in the 1 to 5 kW power range during the first phase of the program, and a single vendor developed a nominal 10-kW engineering model power pant during the second phase of the program. Successful performance and environmental tests conducted by NASA established confidence that PEM fuel cell technology will be ready to meet the electrical power needs of future space missions.

  4. NASA Non-Flow-Through PEM Fuel Cell System for Aerospace Applications

    NASA Technical Reports Server (NTRS)

    Araghi, Koorosh R.

    2011-01-01

    NASA is researching passive NFT Proton Exchange Membrane (PEM) fuel cell technologies for primary fuel cell power plants in air-independent applications. NFT fuel cell power systems have a higher power density than flow through systems due to both reduced parasitic loads and lower system mass and volume. Reactant storage still dominates system mass/volume considerations. NFT fuel cell stack testing has demonstrated equivalent short term performance to flow through stacks. More testing is required to evaluate long-term performance.

  5. Water Transport Characteristics of Gas Diffusion Layer in a PEM Fuel Cell

    SciTech Connect

    Damle, Ashok S; Cole, J Vernon

    2008-11-01

    A presentation addressing the following: Water transport in PEM Fuel Cells - a DoE Project 1. Gas Diffusion Layer--Role and Characteristics 2. Capillary Pressure Determinations of GDL Media 3. Gas Permeability Measurements of GDL Media 4. Conclusions and Future Activities

  6. Simulation and system analysis of an ethanol fuel processor/PEM fuel cell power plant

    SciTech Connect

    Amphlett, J.C.; Leclerc, S.; Mann, R.F.; Peppley, B.A.; Roberge, P.R.

    1998-07-01

    Proton-exchange membrane (PEM) fuel cell systems offer a potential power source for utility and mobile applications. Currently, practical fuel cell systems use fuel processors for the production of a hydrogen-rich gas for the fuel cell anode. Liquid fuels such as ethanol, which can be produced from renewable feed stocks, are attractive options as feeds to a fuel processor. The generation of hydrogen gas for fuel cells, in most cases, becomes the crucial design issue with respect to weight and volume in these applications. Furthermore, these fuel processors require a gas clean-up system to ensure that the fuel quality meets the demands of the cell anode. The endothermic nature of the reformer will have a significant effect on the overall system efficiency. The gas clean-up system may also significantly affect the overall heat balance. A model of a methanol steam reformer that was previously developed has been used as the basis for a model for an ethanol steam reformer. Similarly, a steady-state electrochemical fuel cell model (SSEM) that was previously developed was used. A palladium diffuser purifier simulation was used for gas clean-up. The ethanol fuel processor model and the SSEM have been incorporated into a process simulation and system analysis of an ethanol-fueled reformer/fuel cell system. The performance of this complete system has been investigated for a variety of operating conditions. Assuming that ethanol reforming could be done at 400 C, a net electrical efficiency based on the LHV of ethanol of approximately 54% was calculated. The efficiency, however, is very sensitive to reforming temperature and drops rapidly as the reformer temperature increases. The fractional recovery of hydrogen by the gas clean-up system is also an important factor. The net thermal efficiency passes through a maximum at the point when the heating value in the retentate from the purifier just meets the endothermic heating requirements of the reformer.

  7. Degradation and reliability modelling of polymer electrolyte membrane (PEM) fuel cells

    NASA Astrophysics Data System (ADS)

    Fowler, Michael William

    To date there has been very little reliability or end of life analysis conducted for polymer electrolyte membrane (PEM) fuel cell systems. Voltage degradation as a fuel cell ages is a widely observed phenomenon, but little systematic information has been reported, nor has this phenomenon been included in electrochemical models. This work documents and classifies the failure modes that can be experienced in PEM fuel cells. A test station was adapted for the long term operation of a single, 50 cm2, internally hydrated, PEM fuel cell. An endurance test was conducted to age the cell under normal operating conditions for 1350 hours, at which time membrane failure was experienced. Changes in the polarization curve predicted by the Generalized Steady State Electrochemical Degradation Model (GSSEDM) are demonstrated from the data for the performance of typical PEM fuel cell hardware. This work develops and applies the generalized steady state electrochemical model for a PEM cell, and introduces two new terms to account for membrane electrode assembly (MEA) ageing, specifically the ageing of the MEA materials. One term is based on the concept that the water carrying capacity of the membrane deteriorates with time-in-service. The second term involves intrinsic rate constants associated with the reactions on the anode and cathode side, and the changes in catalytic activity due to catalyst degradation. The resulting model is largely mechanistic with most terms being derived from theory or including coefficients that have a theoretical basis, but also includes empirical parameters to deal with the changing performance. The value of such a generic model to predict or correlate PEM fuel cell stack voltages over the life of the fuel cell is demonstrated in this work. From the experimental data a membrane conductivity degradation rate, lambdaDR, was determined, and the value for lambdaDR was found to be -0.0007 hr -1. A term was introduced for degradation rate of the fuel cell due

  8. Magnetic Resonance Imaging (MRI) of PEM Dehydration and Gas Manifold Flooding During Continuous Fuel Cell Operation

    SciTech Connect

    Minard, Kevin R.; Vishwanathan, Vilanyur V.; Majors, Paul D.; Wang, Li Q.; Rieke, Peter C.

    2006-10-27

    The methods, apparatus, and results are reported for in-situ, near real time, magnetic resonance imaging (MRI) of MEA dehydration and gas manifold flooding in an operating PEM fuel cell. To acquire high-resolution, artifact-free images for visualizing water distribution, acquisition parameters for a standard, two-dimensional (2D), spin-echo sequence were first optimized for the measured magnetic field heterogeneity induced by fuel cell components. 2D images of water inside the fuel cell were then acquired every 128 seconds during 11.4 hours of continuous operation under constant load. Collected images revealed that MEA dehydration proceeded non-uniformly across its plane, starting from gas inlets and ending at gas outlets, and that upon completion of this dehydration process manifold flooding began. To understand these observations, acquired images were correlated to the current output and operating characteristics of the fuel cell. Results demonstrate the power of MRI for in-situ, near real-time imaging of water distribution and non-uniformity in operating PEM fuel cells, and highlight its utility for understanding PEM fuel cell operation, the causes of cell failure, and for developing new strategies of water management.

  9. Analysis of on-board fuel processing designs for PEM fuel cell vehicles

    SciTech Connect

    Kartha, S.; Fischer, S.; Kreutz, T.

    1996-12-31

    As a liquid fuel with weight and volume energy densities comparable to those of gasoline, methanol is an attractive energy carrier for mobile power systems. It is available without contaminants such as sulfur, and can be easily reformed at relatively low temperatures with inexpensive catalysts. This study is concerned with comparing the net efficiencies of PEM fuel cell vehicles fueled with methanol and hydrogen, using fuel cell system models developed using ASPEN chemical process simulation software. For both the methanol and hydrogen systems, base case designs are developed and several variations are considered that differ with respect to the degree of system integration for recovery of heat and compressive work. The methanol systems are based on steam reforming with the water-gas shift reaction and preferential oxidation, and the hydrogen systems are based on compressed hydrogen. This analysis is an exercise in optimizing the system design for each fuel, which ultimately entails balancing system efficiency against a host of other considerations, including system complexity, performance, cost, reliability, weight and volume.

  10. Predicted emissions from a methanol-fueled ``electrochemical automobile engine`` based on a PEM fuel cell

    SciTech Connect

    Amphlett, J.C.; Mann, R.F.; Peppley, B.A.

    1995-12-31

    A simulation of a fuel cell engine (FCE) based on a proton exchange membrane (PEM) fuel-cell stack was developed using a process simulation software package. Rates of emissions of unburned methanol, formaldehyde, CO and NO{sub x}, were calculated based on chemical equilibria. The predicted rates of emissions for unburned methanol, formaldehyde and CO were found to all be less than 1 {micro}g/km. This is considerably less than has been reported in the literature but represents a theoretical limit which should be achievable as effective catalytic-combustion systems are developed for hydrogen/methanol fueled burners. The worst-case rate of NO{sub x}, emissions was shown to be less than 0.03 g/km (0.05 g/mi.). It was found that increasing the rate of heat transfer in the steam reformer, which converts the methanol to a hydrogen-rich gas, significantly reduced the rate of NO{sub x}, emission due to the lower burner temperatures which could be used. The results indicate that, in terms of emissions reduction, a methanol fueled FCE is an excellent long-term alternative to the ICE.

  11. Fuel processing for PEM fuel cells: transport and kinetic issues of system design

    NASA Astrophysics Data System (ADS)

    Zalc, J. M.; Löffler, D. G.

    In light of the distribution and storage issues associated with hydrogen, efficient on-board fuel processing will be a significant factor in the implementation of PEM fuel cells for automotive applications. Here, we apply basic chemical engineering principles to gain insight into the factors that limit performance in each component of a fuel processor. A system consisting of a plate reactor steam reformer, water-gas shift unit, and preferential oxidation reactor is used as a case study. It is found that for a steam reformer based on catalyst-coated foils, mass transfer from the bulk gas to the catalyst surface is the limiting process. The water-gas shift reactor is expected to be the largest component of the fuel processor and is limited by intrinsic catalyst activity, while a successful preferential oxidation unit depends on strict temperature control in order to minimize parasitic hydrogen oxidation. This stepwise approach of sequentially eliminating rate-limiting processes can be used to identify possible means of performance enhancement in a broad range of applications.

  12. Final Scientific Report, New Proton Conductive Composite Materials for PEM Fuel Cells

    SciTech Connect

    Lvov, Serguei

    2010-11-08

    This project covered one of the main challenges in present-day PEM fuel cell technology: to design a membrane capable of maintaining high conductivity and mechanical integrity when temperature is elevated and water vapor pressure is severely reduced. The DOE conductivity milestone of 0.1 S cm-1 at 120 degrees C and 50 % relative humidity (RH) for designed membranes addressed the target for the project. Our approach presumed to develop a composite membrane with hydrophilic proton-conductive inorganic material and the proton conductive polymeric matrix that is able to “bridge” the conduction paths in the membrane. The unique aspect of our approach was the use of highly functionalized inorganic additives to benefit from their water retention properties and high conductivity as well. A promising result turns out that highly hydrophilic phosphorsilicate gels added in Nafion matrix improved PEM fuel cell performance by over 50% compared with bare Nafion membrane at 120 degrees C and 50 % RH. This achievement realizes that the fuel cell operating pressure can be kept low, which would make the PEM fuel cell much more cost efficient and adaptable to practical operating conditions and facilitate its faster commercialization particularly in automotive and stationary applications.

  13. Three-wheel air turbocompressor for PEM fuel cell systems

    DOEpatents

    Rehg, Tim; Gee, Mark; Emerson, Terence P.; Ferrall, Joe; Sokolov, Pavel

    2003-08-19

    A fuel cell system comprises a compressor and a fuel processor downstream of the compressor. A fuel cell stack is in communication with the fuel processor and compressor. A combustor is downstream of the fuel cell stack. First and second turbines are downstream of the fuel processor and in parallel flow communication with one another. A distribution valve is in communication with the first and second turbines. The first and second turbines are mechanically engaged to the compressor. A bypass valve is intermediate the compressor and the second turbine, with the bypass valve enabling a compressed gas from the compressor to bypass the fuel processor.

  14. Investigating Methods of Heat Recovery from Low-Temperature PEM Fuel Cells in CHP Applications

    SciTech Connect

    Jalalzadeh-Azar, A. A.

    2004-01-01

    Heat recovery from low-temperature proton exchange membrane (PEM) fuel cells poses a number of challenges. In response to these challenges, thermodynamic assessments of proposed heat recovery methods are studied in the context of combined heat and power (CHP) for building applications. Preheating combustion air in conjunction with desiccant dehumidification and absorption cooling technologies is one of the two strategies examined in this study. The other approach integrates the PEM fuel cell with a water-loop heat pump (WLHP) for direct heat recovery. As the primary objective, energy-saving potentials of the adopted heat recovery strategies are estimated with respect to various benchmarks. The quantified energy-saving potentials are translated into effective CHP performance indices and compared with those typically specified by the manufacturers for service hot water applications. The need for developing CHP performance protocols is also discussed in light of the proposed energy recovery techniques - thereby, accomplishing the secondary objective.

  15. Online soft sensor of humidity in PEM fuel cell based on dynamic partial least squares.

    PubMed

    Long, Rong; Chen, Qihong; Zhang, Liyan; Ma, Longhua; Quan, Shuhai

    2013-01-01

    Online monitoring humidity in the proton exchange membrane (PEM) fuel cell is an important issue in maintaining proper membrane humidity. The cost and size of existing sensors for monitoring humidity are prohibitive for online measurements. Online prediction of humidity using readily available measured data would be beneficial to water management. In this paper, a novel soft sensor method based on dynamic partial least squares (DPLS) regression is proposed and applied to humidity prediction in PEM fuel cell. In order to obtain data of humidity and test the feasibility of the proposed DPLS-based soft sensor a hardware-in-the-loop (HIL) test system is constructed. The time lag of the DPLS-based soft sensor is selected as 30 by comparing the root-mean-square error in different time lag. The performance of the proposed DPLS-based soft sensor is demonstrated by experimental results. PMID:24453923

  16. Online Soft Sensor of Humidity in PEM Fuel Cell Based on Dynamic Partial Least Squares

    PubMed Central

    Long, Rong; Chen, Qihong; Zhang, Liyan; Ma, Longhua; Quan, Shuhai

    2013-01-01

    Online monitoring humidity in the proton exchange membrane (PEM) fuel cell is an important issue in maintaining proper membrane humidity. The cost and size of existing sensors for monitoring humidity are prohibitive for online measurements. Online prediction of humidity using readily available measured data would be beneficial to water management. In this paper, a novel soft sensor method based on dynamic partial least squares (DPLS) regression is proposed and applied to humidity prediction in PEM fuel cell. In order to obtain data of humidity and test the feasibility of the proposed DPLS-based soft sensor a hardware-in-the-loop (HIL) test system is constructed. The time lag of the DPLS-based soft sensor is selected as 30 by comparing the root-mean-square error in different time lag. The performance of the proposed DPLS-based soft sensor is demonstrated by experimental results. PMID:24453923

  17. Novel, low-cost separator plates and flow-field elements for use in PEM fuel cells

    SciTech Connect

    Edlund, D.J.

    1996-12-31

    PEM fuel cells offer promise for a wide range of applications including vehicular (e.g., automotive) and stationary power generation. The performance and cost targets that must be met for PEM technology to be commercially successful varies to some degree with the application. However, in general the cost of PEM fuel cell stacks must be reduced substantially if they are to see widespread use for electrical power generation. A significant contribution to the manufactured cost of PEM fuel cells is the machined carbon plates that traditionally serve as bipolar separator plates and flow-field elements. In addition, carbon separator plates are inherently brittle and suffer from breakage due to shock, vibration, and improper handling. This report describes a bifurcated separator device with low resistivity, low manufacturing cost, compact size and durability.

  18. Process for recycling components of a PEM fuel cell membrane electrode assembly

    DOEpatents

    Shore, Lawrence

    2012-02-28

    The membrane electrode assembly (MEA) of a PEM fuel cell can be recycled by contacting the MEA with a lower alkyl alcohol solvent which separates the membrane from the anode and cathode layers of the assembly. The resulting solution containing both the polymer membrane and supported noble metal catalysts can be heated under mild conditions to disperse the polymer membrane as particles and the supported noble metal catalysts and polymer membrane particles separated by known filtration means.

  19. On-board removal of CO and other impurities in hydrogen for PEM fuel cell applications

    NASA Astrophysics Data System (ADS)

    Huang, Cunping; Jiang, Ruichun; Elbaccouch, Mohamed; Muradov, Nazim; Fenton, James M.

    Carbon monoxide (CO) in the hydrogen (H 2) stream can cause severe performance degradation for an H 2 polymer electrolyte membrane (PEM) fuel cell. The on-board removal of CO from an H 2 stream requires a process temperature less than 80 °C, and a fast reaction rate in order to minimize the reactor volume. At the present time, few technologies have been developed that meet these two requirements. This paper describes a concept of electrochemical water gas shift (EWGS) process to remove low concentration CO under ambient conditions for on-board applications. No on-board oxygen or air supply is needed for CO oxidation. Experimental work has been carried out to prove the concept of EWGS and the results indicate that the process can completely remove low level CO and improve the performance of a PEM fuel cell to the level of a pure H 2 stream. Because the EWGS electrolyzer can be modified from a humidifier for a PEM fuel cell system, no additional device is needed for the CO removal. More experimental data are needed to determine the rate of CO electrochemical removal and to explore the mechanism of the proposed process.

  20. PEM fuel cell stack performance using dilute hydrogen mixture. Implications on electrochemical engine system performance and design

    SciTech Connect

    Inbody, M.A.; Vanderborgh, N.E.; Hedstrom, J.C.; Tafoya, J.I.

    1996-12-31

    Onboard fuel processing to generate a hydrogen-rich fuel for PEM fuel cells is being considered as an alternative to stored hydrogen fuel for transportation applications. If successful, this approach, contrasted to operating with onboard hydrogen, utilizes the existing fuels infrastructure and provides required vehicle range. One attractive, commercial liquid fuels option is steam reforming of methanol. However, expanding the liquid methanol infrastructure will take both time and capital. Consequently technology is also being developed to utilize existing transportation fuels, such as gasoline or diesel, to power PEM fuel cell systems. Steam reforming of methanol generates a mixture with a dry gas composition of 75% hydrogen and 25% carbon dioxide. Steam reforming, autothermal reforming, and partial oxidation reforming of C{sub 2} and larger hydrocarbons produces a mixture with a more dilute hydrogen concentration (65%-40%) along with carbon dioxide ({approx}20%) and nitrogen ({approx}10%-40%). Performance of PEM fuel cell stacks on these dilute hydrogen mixtures will affect the overall electrochemical engine system design as well as the overall efficiency. The Los Alamos Fuel Cell Stack Test facility was used to access the performance of a PEM Fuel cell stack over the range of gas compositions chosen to replicate anode feeds from various fuel processing options for hydrocarbon and alcohol fuels. The focus of the experiments was on the anode performance with dilute hydrogen mixtures with carbon dioxide and nitrogen diluents. Performance with other anode feed contaminants, such as carbon monoxide, are not reported here.

  1. Modeling efficiency and water balance in PEM fuel cell systems with liquid fuel processing and hydrogen membranes

    NASA Astrophysics Data System (ADS)

    Pearlman, Joshua B.; Bhargav, Atul; Shields, Eric B.; Jackson, Gregory S.; Hearn, Patrick L.

    Integrating PEM fuel cells effectively with liquid hydrocarbon reforming requires careful system analysis to assess trade-offs associated with H 2 production, purification, and overall water balance. To this end, a model of a PEM fuel cell system integrated with an autothermal reformer for liquid hydrocarbon fuels (modeled as C 12H 23) and with H 2 purification in a water-gas-shift/membrane reactor is developed to do iterative calculations for mass, species, and energy balances at a component and system level. The model evaluates system efficiency with parasitic loads (from compressors, pumps, and cooling fans), system water balance, and component operating temperatures/pressures. Model results for a 5-kW fuel cell generator show that with state-of-the-art PEM fuel cell polarization curves, thermal efficiencies >30% can be achieved when power densities are low enough for operating voltages >0.72 V per cell. Efficiency can be increased by operating the reformer at steam-to-carbon ratios as high as constraints related to stable reactor temperatures allow. Decreasing ambient temperature improves system water balance and increases efficiency through parasitic load reduction. The baseline configuration studied herein sustained water balance for ambient temperatures ≤35 °C at full power and ≤44 °C at half power with efficiencies approaching ∼27 and ∼30%, respectively.

  2. Final Report: Development of a Thermal and Water Management System for PEM Fuel Cell

    SciTech Connect

    Zia Mirza, Program Manager

    2011-12-06

    This final program report is prepared to provide the status of program activities performed over the period of 9 years to develop a thermal and water management (TWM) system for an 80-kW PEM fuel cell power system. The technical information and data collected during this period are presented in chronological order by each calendar year. Balance of plant (BOP) components of a PEM fuel cell automotive system represents a significant portion of total cost based on the 2008 study by TIAX LLC, Cambridge, MA. The objectives of this TWM program were two-fold. The first objective was to develop an advanced cooling system (efficient radiator) to meet the fuel cell cooling requirements. The heat generated by the fuel cell stack is a low-quality heat (small difference between fuel cell stack operating temperature and ambient air temperature) that needs to be dissipated to the ambient air. To minimize size, weight, and cost of the radiator, advanced fin configurations were evaluated. The second objective was to evaluate air humidification systems which can meet the fuel cell stack inlet air humidity requirements. The moisture from the fuel cell outlet air is transferred to inlet air, thus eliminating the need for an outside water source. Two types of humidification devices were down-selected: one based on membrane and the other based on rotating enthalpy wheel. The sub-scale units for both of these devices have been successfully tested by the suppliers. This project addresses System Thermal and Water Management.

  3. On-board diesel autothermal reforming for PEM fuel cells: Simulation and optimization

    SciTech Connect

    Cozzolino, Raffaello Tribioli, Laura

    2015-03-10

    Alternative power sources are nowadays the only option to provide a quick response to the current regulations on automotive pollutant emissions. Hydrogen fuel cell is one promising solution, but the nature of the gas is such that the in-vehicle conversion of other fuels into hydrogen is necessary. In this paper, autothermal reforming, for Diesel on-board conversion into a hydrogen-rich gas suitable for PEM fuel cells, has investigated using the simulation tool Aspen Plus. A steady-state model has been developed to analyze the fuel processor and the overall system performance. The components of the fuel processor are: the fuel reforming reactor, two water gas shift reactors, a preferential oxidation reactor and H{sub 2} separation unit. The influence of various operating parameters such as oxygen to carbon ratio, steam to carbon ratio, and temperature on the process components has been analyzed in-depth and results are presented.

  4. NEW MATERIAL NEEDS FOR HYDROCARBON FUEL PROCESSING: Generating Hydrogen for the PEM Fuel Cell

    NASA Astrophysics Data System (ADS)

    Farrauto, R.; Hwang, S.; Shore, L.; Ruettinger, W.; Lampert, J.; Giroux, T.; Liu, Y.; Ilinich, O.

    2003-08-01

    The hydrogen economy is fast approaching as petroleum reserves are rapidly consumed. The fuel cell promises to deliver clean and efficient power by combining hydrogen and oxygen in a simple electrochemical device that directly converts chemical energy to electrical energy. Hydrogen, the most plentiful element available, can be extracted from water by electrolysis. One can imagine capturing energy from the sun and wind and/or from the depths of the earth to provide the necessary power for electrolysis. Alternative energy sources such as these are the promise for the future, but for now they are not feasible for power needs across the globe. A transitional solution is required to convert certain hydrocarbon fuels to hydrogen. These fuels must be available through existing infrastructures such as the natural gas pipeline. The present review discusses the catalyst and adsorbent technologies under development for the extraction of hydrogen from natural gas to meet the requirements for the proton exchange membrane (PEM) fuel cell. The primary market is for residential applications, where pipeline natural gas will be the source of H2 used to power the home. Other applications including the reforming of methanol for portable power applications such as laptop computers, cellular phones, and personnel digital equipment are also discussed. Processing natural gas containing sulfur requires many materials, for example, adsorbents for desulfurization, and heterogeneous catalysts for reforming (either autothermal or steam reforming) water gas shift, preferential oxidation of CO, and anode tail gas combustion. All these technologies are discussed for natural gas and to a limited extent for reforming methanol.

  5. Teledyne Energy Systems, Inc., Proton Exchange Member (PEM) Fuel Cell Engineering Model Powerplant. Test Report: Initial Benchmark Tests in the Original Orientation

    NASA Technical Reports Server (NTRS)

    Loyselle, Patricia; Prokopius, Kevin

    2011-01-01

    Proton Exchange Membrane (PEM) fuel cell technology is the leading candidate to replace the alkaline fuel cell technology, currently used on the Shuttle, for future space missions. During a 5-yr development program, a PEM fuel cell powerplant was developed. This report details the initial performance evaluation test results of the powerplant.

  6. EXPERIMENTAL AND NUMERICAL ANALYSIS OF SUBFREEZING OPERATION IN PEM FUEL CELLS

    SciTech Connect

    Mukherjee, Partha P

    2010-01-01

    In this work, we present the neutron radiography and analysis, as well as modeling predictions of cold-start operation of PEM fuel cells. Fuel cells with Gore or LANL MEAs and SGL or E-Tek ELAT GDLs are tested in varying subfreezing temperatures (-40 to 0 C) to determine time to failure, amount of water formation, and place of water formation. Theoretical modeling is also conducted and model predictions are compared with the cell voltage evolution during subfreezing operation. A higher PTFE-loading in the MPL is found to decrease loss in ESCA in our case.

  7. Hydrogen as fuel carrier in PEM fuelcell for automobile applications

    NASA Astrophysics Data System (ADS)

    Sk, Mudassir Ali; Venkateswara Rao, K.; Ramana Rao, Jagirdar V.

    2015-02-01

    The present work focuses the application of nanostructured materials for storing of hydrogen in different carbon materials by physisorption method. To market a hydrogen-fuel cell vehicle as competitively as the present internal combustion engine vehicles, there is a need for materials that can store a minimum of 6.5wt% of hydrogen. Carbon materials are being heavily investigated because of their promise to offer an economical solution to the challenge of safe storage of large hydrogen quantities. Hydrogen is important as a new source of energy for automotive applications. It is clear that the key challenge in developing this technology is hydrogen storage. Combustion of fossil fuels and their overuse is at present a serious concern as it is creates severe air pollution and global environmental problems; like global warming, acid rains, ozone depletion in stratosphere etc. This necessitated the search for possible alternative sources of energy. Though there are a number of primary energy sources available, such as thermonuclear energy, solar energy, wind energy, hydropower, geothermal energy etc, in contrast to the fossil fuels in most cases, these new primary energy sources cannot be used directly and thus they must be converted into fuels, that is to say, a new energy carrier is needed. Hydrogen fuel cells are two to three times more efficient than combustion engines. As they become more widely available, they will reduce dependence on fossil fuels. In a fuel cell, hydrogen and oxygen are combined in an electrochemical reaction that produces electricity and, as a byproduct, water.

  8. 160 C PROTON EXCHANGE MEMBRANE (PEM) FUEL CELL SYSTEM DEVELOPMENT

    SciTech Connect

    L.G. Marianowski

    2001-12-21

    The objectives of this program were: (a) to develop and demonstrate a new polymer electrolyte membrane fuel cell (PEMFC) system that operates up to 160 C temperatures and at ambient pressures for stationary power applications, and (b) to determine if the GTI-molded composite graphite bipolar separator plate could provide long term operational stability at 160 C or higher. There are many reasons that fuel cell research has been receiving much attention. Fuel cells represent environmentally friendly and efficient sources of electrical power generation that could use a variety of fuel sources. The Gas Technology Institute (GTI), formerly Institute of Gas Technology (IGT), is focused on distributed energy stationary power generation systems. Currently the preferred method for hydrogen production for stationary power systems is conversion of natural gas, which has a vast distribution system in place. However, in the conversion of natural gas into a hydrogen-rich fuel, traces of carbon monoxide are produced. Carbon monoxide present in the fuel gas will in time cumulatively poison, or passivate the active platinum catalysts used in the anodes of PEMFC's operating at temperatures of 60 to 80 C. Various fuel processors have incorporated systems to reduce the carbon monoxide to levels below 10 ppm, but these require additional catalytic section(s) with sensors and controls for effective carbon monoxide control. These CO cleanup systems must also function especially well during transient load operation where CO can spike 300% or more. One way to circumvent the carbon monoxide problem is to operate the fuel cell at a higher temperature where carbon monoxide cannot easily adsorb onto the catalyst and poison it. Commercially available polymer membranes such as Nafion{trademark} are not capable of operation at temperatures sufficiently high to prevent this. Hence this project investigated a new polymer membrane alternative to Nafion{trademark} that is capable of operation at

  9. Cost Analysis of Fuel Cell Systems for Transportation Compressed Hydrogen and PEM Fuel Cell System

    SciTech Connect

    Eric J. Carlson

    2004-10-20

    PEMFC technology for transportation must be competitive with internal combustion engine powertrains in a number of key metrics, including performance, life, reliability, and cost. Demonstration of PEMFC cost competitiveness has its own challenges because the technology has not been applied to high volume automotive markets. The key stack materials including membranes, electrodes, bipolar plates, and gas diffusion layers have not been produced in automotive volumes to the exacting quality requirements that will be needed for high stack yields and to the evolving property specifications of high performance automotive stacks. Additionally, balance-of-plant components for air, water, and thermal management are being developed to meet the unique requirements of fuel cell systems. To address the question of whether fuel cells will be cost competitive in automotive markets, the DOE has funded this project to assess the high volume production cost of PEM fuel cell systems. In this report a historical perspective of our efforts in assessment of PEMFC cost for DOE is provided along with a more in-depth assessment of the cost of compressed hydrogen storage is provided. Additionally, the hydrogen storage costs were incorporated into a system cost update for 2004. Assessment of cost involves understanding not only material and production costs, but also critical performance metrics, i.e., stack power density and associated catalyst loadings that scale the system components. We will discuss the factors influencing the selection of the system specification (i.e., efficiency, reformate versus direct hydrogen, and power output) and how these have evolved over time. The reported costs reflect internal estimates and feedback from component developers and the car companies. Uncertainty in the cost projection was addressed through sensitivity analyses.

  10. Start-up analysis for automotive PEM fuel cell systems

    NASA Astrophysics Data System (ADS)

    De Francesco, M.; Arato, E.

    The development of fuel cell cars can play an important role in resolving transport problems, due to the high environmental compatibility and high efficiency of this kind of vehicle. Among the different types of fuel cells, proton-exchange membrane fuel cells (PEMFCs) are considered the best solution for automotive applications at the moment. In this work, constructive criteria are discussed with the aim of obtaining a power generation module adaptable to a wide range of cars. A particular problem in accomplishing the overall project is represented by the definition of the compressor system for air feeding. In this work, the design approach to the problem will be delineated: some options are reviewed and the best solution is analysed. The transient response of the system (fuel cell and compressor) is investigated in order to optimise the start-up running through a model of a fuel cell stack and a compressor simulation. The model and its results are proposed as a work procedure to solve the problem, by varying external conditions: in fact, to perform the system start-up under stable conditions, the air relative humidity and temperature must be maintained in a proper range of values. The approach here presented has been utilised for the definition of the characteristics of the power module and layout of a middle-size hybrid city bus in the framework of a project promoted by the European Union.

  11. Low Cost PEM Fuel Cell Metal Bipolar Plates

    SciTech Connect

    Wang, Conghua

    2013-05-30

    Bipolar plate is an important component in fuel cell stacks and accounts for more than 75% of stack weight and volume. The technology development of metal bipolar plates can effectively reduce the fuel cells stack weight and volume over 50%. The challenge is the metal plate corrosion protection at low cost for the broad commercial applications. This project is aimed to develop innovative technological solutions to overcome the corrosion barrier of low cost metal plates. The feasibility of has been demonstrated and patented (US Patent 7,309,540). The plan is to further reduce the cost, and scale up the technology. The project is built on three pillars: 1) robust experimental evidence demonstrating the feasibility of our technology, 2) a team that consists of industrial leaders in fuel cell stack application, design, and manufactures; 3) a low-risk, significant-milestone driven program that proves the feasibility of meeting program objectives The implementation of this project will reduce the fuel cell stack metal bipolar separator plate cost which accounts 15-21% of the overall stack cost. It will contribute to the market adoption of fuel cell technologies. In addition, this corrosion protection technology can be used similar energy devices, such as batteries and electrolyzers. Therefore, the success of the project will be benefit in broad markets.

  12. Carbon support oxidation in PEM fuel cell cathodes

    NASA Astrophysics Data System (ADS)

    Maass, S.; Finsterwalder, F.; Frank, G.; Hartmann, R.; Merten, C.

    Oxidation of the cathode carbon catalyst support in polymer electrolyte fuel cells (PEMFC) has been examined. For this purpose platinum supported electrodes and pure carbon electrodes were fabricated and tested in membrane-electrode-assemblies (MEAs) in air and nitrogen atmosphere. The in situ experiments account for the fuel cell environment characterized by the presence of a solid electrolyte and water in the gas and liquid phases. Cell potential transients occurring during automotive fuel cell operation were simulated by dynamic measurements. Corrosion rates were calculated from CO 2 and CO concentrations in the cathode exhaust measured by non-dispersive infrared spectroscopy (NDIR). Results from these potentiodynamic measurements indicate that different potential regimes relevant for carbon oxidation can be distinguished. Carbon corrosion rates were found to be higher under dynamic operation and to strongly depend on electrode history. These characteristics make it difficult to predict corrosion rates accurately in an automotive drive cycle.

  13. System Design of a Natural Gas PEM Fuel Cell Power Plant for Buildings

    SciTech Connect

    Joe Ferrall, Tim Rehg, Vesna Stanic

    2000-09-30

    The following conclusions are made based on this analysis effort: (1) High-temperature PEM data are not available; (2) Stack development effort for Phase II is required; (3) System results are by definition preliminary, mostly due to the immaturity of the high-temperature stack; other components of the system are relatively well defined; (4) The Grotthuss conduction mechanism yields the preferred system characteristics; the Grotthuss conduction mechanism is also much less technically mature than the vehicle mechanism; (5) Fuel processor technology is available today and can be procured for Phase II (steam or ATR); (6) The immaturity of high-temperature membrane technology requires that a robust system design be developed in Phase II that is capable of operating over a wide temperature and pressure range - (a) Unpressurized or Pressurized PEM (Grotthuss mechanism) at 140 C, Highest temperature most favorable, Lowest water requirement most favorable, Pressurized recommended for base loaded operation, Unpressurized may be preferred for load following; (b) Pressurized PEM (vehicle mechanism) at about 100 C, Pressure required for saturation, Fuel cell technology currently available, stack development required. The system analysis and screening evaluation resulted in the identification of the following components for the most promising system: (1) Steam reforming fuel processor; (2) Grotthuss mechanism fuel cell stack operating at 140 C; (3) Means to deliver system waste heat to a cogeneration unit; (4) Pressurized system utilizing a turbocompressor for a base-load power application. If duty cycling is anticipated, the benefits of compression may be offset due to complexity of control. In this case (and even in the base loaded case), the turbocompressor can be replaced with a blower for low-pressure operation.

  14. Transport Studies and Modeling in PEM Fuel Cells

    SciTech Connect

    Mittelsteadt, Cortney K.; Xu, Hui; Brawn, Shelly

    2014-07-30

    This project’s aim was to develop fuel cell components (i.e. membranes, gas-diffusion media (GDM), bipolar plates and flow fields) that possess specific properties (i.e. water transport and conductivity). A computational fluid dynamics model was developed to elucidate the effect of certain parameters on these specific properties. Ultimately, the model will be used to determine sensitivity of fuel cell performance to component properties to determine limiting components and to guide research. We have successfully reached our objectives and achieved most of the milestones of this project. We have designed and synthesized a variety of hydrocarbon block polymer membranes with lower equivalent weight, structure, chemistry, phase separation and process conditions. These membranes provide a broad selection with optimized water transport properties. We have also designed and constructed a variety of devices that are capable of accurately measuring the water transport properties (water uptake, water diffusivity and electro-osmatic drag) of these membranes. These transport properties are correlated to the membranes’ structures derived from X-ray and microscopy techniques to determine the structure-property relationship. We successfully integrated hydrocarbon membrane MEAs with a current distribution board (CBD) to study the impact of hydrocarbon membrane on water transport in fuel cells. We have designed and fabricated various GDM with varying substrate, diffusivity and micro-porous layers (MPL) and characterized their pore structure, tortuosity and hydrophobicity. We have derived a universal chart (MacMullin number as function of wet proofing and porosity) that can be used to characterize various GDM. The abovementioned GDMs have been evaluated in operating fuel cells; their performance is correlated to various pore structure, tortuosity and hydrophobicity of the GDM. Unfortunately, determining a universal relationship between the MacMullin number and these properties

  15. Performance of PEM Liquid-Feed Direct Methanol-Air Fuel Cells

    NASA Technical Reports Server (NTRS)

    Narayanan, S. R.

    1995-01-01

    A direct methanol-air fuel cell operating at near atmospheric pressure, low-flow rate air, and at temperatures close to 60oC would tremendously enlarge the scope of potential applications. While earlier studies have reported performance with oxygen, the present study focuses on characterizing the performance of a PEM liquid feed direct methanol-air cell consisting of components developed in house. These cells employ Pt-Ru catalyst in the anode, Pt at the cathode and Nafion 117 as the PEM. The effect of pressure, flow rate of air and temperature on cell performance has been studied. With air, the performance level is as high as 0.437 V at 300 mA/cm2 (90oC, 20 psig, and excess air flow) has been attained. Even more significant is the performance level at 60oC, 1 atm and low flow rates of air (3-5 times stoichiometric), which is 0.4 V at 150 mA/cm2. Individual electrode potentials for the methanol and air electrode have been separated and analyzed. Fuel crossover rates and the impact of fuel crossover on the performance of the air electrode have also been measured. The study identifies issues specific to the methanol-air fuel cell and provides a basis for improvement strategies.

  16. Evaluation of microbial triglyceride oil purification requirements for the CelTherm process: an efficient biochemical pathway to renewable fuels and chemicals.

    PubMed

    Linnen, Michael; Seames, Wayne; Kubatova, Alena; Menon, Suresh; Alisala, Kashinatham; Hash, Sara

    2014-10-01

    CelTherm is a biochemical process to produce renewable fuels and chemicals from lignocellulosic biomass. The present study's objective was to determine the level of treatment/purity of the microbial triacylglyceride oil (TAG) necessary to facilitate fuel production. After a unique microbe aerobically synthesizes TAG from biomass-derived sugars, the microbes were harvested and dried then crude TAG was chemically extracted from the residual biomass. Some TAGs were further purified to hydrotreating process requirements. Both grades were then noncatalytically cracked into a petroleum-like intermediate characterized by gas chromatography. Experiments were repeated using refined soybean oil for comparison to previous studies. The products from crude microbial TAG cracking were then further refined into a jet fuel product. Fuel tests indicate that this jet fuel corresponds to specifications for JP-8 military turbine fuel. It was thus concluded that the crude microbial TAG is a suitable feedstock with no further purification required, demonstrating CelTherm's commercial potential. PMID:24781206

  17. Improved Membrane Materials for PEM Fuel Cell Application

    SciTech Connect

    Kenneth A. Mauritz; Robert B. Moore

    2008-06-30

    The overall goal of this project is to collect and integrate critical structure/property information in order to develop methods that lead to significant improvements in the durability and performance of polymer electrolyte membrane fuel cell (PEMFC) materials. This project is focused on the fundamental improvement of PEMFC membrane materials with respect to chemical, mechanical and morphological durability as well as the development of new inorganically-modified membranes.

  18. Development Status of PEM Non-Flow-Through Fuel Cell System Technology for NASA Applications

    NASA Technical Reports Server (NTRS)

    Hoberecht, Mark A.; Jakupca, Ian J.

    2011-01-01

    Today s widespread development of proton-exchange-membrane (PEM) fuel cell technology for commercial users owes its existence to NASA, where fuel cell technology saw its first applications. Beginning with the early Gemini and Apollo programs, and continuing to this day with the Shuttle Orbiter program, fuel cells have been a primary source of electrical power for many NASA missions. This is particularly true for manned missions, where astronauts are able to make use of the by-product of the fuel cell reaction, potable water. But fuel cells also offer advantages for unmanned missions, specifically when power requirements exceed several hundred watts and primary batteries are not a viable alternative. In recent years, NASA s Exploration Technology Development Program (ETDP) funded the development of fuel cell technology for applications that provide both primary power and regenerative fuel cell energy storage for planned Exploration missions that involved a return to the moon. Under this program, the Altair Lunar Lander was a mission requiring fuel cell primary power. There were also various Lunar Surface System applications requiring regenerative fuel cell energy storage, in which a fuel cell and electrolyzer combine to form an energy storage system with hydrogen, oxygen, and water as common reactants. Examples of these systems include habitat modules and large rovers. In FY11, the ETDP has been replaced by the Enabling Technology Development and Demonstration Program (ETDDP), with many of the same technology goals and requirements applied against NASA s revised Exploration portfolio.

  19. PEM Fuel Cell Freeze Durability and Cold Start Project

    SciTech Connect

    Patterson, T.; O'Neill, Jonathan

    2008-01-02

    UTC has taken advantage of the unique water management opportunities inherent in micro-porous bipolar-plates to improve the cold-start performance of its polymer electrolyte fuel cells (PEFC). Diagnostic experiments were used to determine the limiting factors in micro-porous plate PEFC freeze performance and the causes of any performance decay. Alternative cell materials were evaluated for their freeze performance. Freeze-thaw cycling was also performed to determine micro-porous plate PEFC survivability. Data from these experiments has formed the basis for continuing development of advanced materials capable of supporting DOE's cold-start and durability objectives.

  20. 2004 DOE Hydrogen, Fuel Cells & Infrastructure Technologies Program Review Presentation COST AND PERFORMANCE ENHANCEMENTS FOR A PEM FUEL CELL TURBOCOMPRESSOR

    SciTech Connect

    Mark K. Gee

    2004-04-01

    The objective is to assist the Department of Energy in the development of a low cost, reliable and high performance air compressor/expander. Technical Objective 1: Perform a turbocompressor systems PEM fuel cell trade study to determine the enhanced turbocompressor approach. Technical Objective 2: Using the results from technical objective 1, an enhanced turbocompressor will be fabricated. The design may be modified to match the flow requirements of a selected fuel cell system developer. Technical Objective 3: Design a cost and performance enhanced compact motor and motor controller. Technical Objective 4: Turbocompressor/motor controller development.

  1. Development of a 10 kW hydrogen/air PEM fuel cell stack

    SciTech Connect

    Barbir, F.; Marken, F.; Bahar, B.; Kolde, J.A.

    1996-12-31

    PEM fuel cells have potential for meeting automotive industry`s power density and cost requirements, such as 0.8 kW/kg, 0.8 kW/1 and $30/kW. For automotive applications, the fuel cell power requirements are in the 10-100 kW range. As the first phase in reaching this power output, a 10 kW PEM fuel cell stack has been developed at Energy Partners. The stack consists of 50 cells with relatively large active area of 780 cm{sup 2}. The main feature of the stack is the advanced membrane electrode assembly (MEA) developed by W.L. Gore & Associates, Inc. These novel MEAs consist of a thin composite perfluorinated polymer membrane with a catalyst layer with platinum loading of 0.3 Mg/cm{sup 2} on each side. The combination of reinforcement and thinness provides high membrane conductance and improved water distribution in the operating cell. In addition, the membrane has excellent mechanical properties (particularly when it is hydrated) and dimensional stability.

  2. A new state-observer of the inner PEM fuel cell pressures for enhanced system monitoring

    NASA Astrophysics Data System (ADS)

    Bethoux, Olivier; Godoy, Emmanuel; Roche, Ivan; Naccari, Bruno; Amira Taleb, Miassa; Koteiche, Mohamad; Nassif, Younane

    2014-06-01

    In embedded systems such as electric vehicles, Proton exchange membrane fuel cell (PEMFC) has been an attractive technology for many years especially in automotive applications. This paper deals with PEMFC operation monitoring which is a current target for improvement for attaining extended durability. In this paper, supervision of the PEMFC is done using knowledge-based models. Without extra sensors, it enables a clear insight of state variables of the gases in the membrane electrode assembly (MEA) which gives the PEMFC controller the ability to prevent abnormal operating conditions and associated irreversible degradations. First, a new state-observer oriented model of the PEM fuel cell is detailed. Based on this model, theoretical and practical observability issues are discussed. This analysis shows that convection phenomena can be considered negligible from the dynamic point of view; this leads to a reduced model. Finally a state-observer enables the estimation of the inner partial pressure of the cathode by using only the current and voltage measurements. This proposed model-based approach has been successfully tested on a PEM fuel cell simulator using a set of possible fault scenarios.

  3. PEM fuel cell fault detection and identification using differential method: simulation and experimental validation

    NASA Astrophysics Data System (ADS)

    Frappé, E.; de Bernardinis, A.; Bethoux, O.; Candusso, D.; Harel, F.; Marchand, C.; Coquery, G.

    2011-05-01

    PEM fuel cell performance and lifetime strongly depend on the polymer membrane and MEA hydration. As the internal moisture is very sensitive to the operating conditions (temperature, stoichiometry, load current, water management…), keeping the optimal working point is complex and requires real-time monitoring. This article focuses on PEM fuel cell stack health diagnosis and more precisely on stack fault detection monitoring. This paper intends to define new, simple and effective methods to get relevant information on usual faults or malfunctions occurring in the fuel cell stack. For this purpose, the authors present a fault detection method using simple and non-intrusive on-line technique based on the space signature of the cell voltages. The authors have the objective to minimize the number of embedded sensors and instrumentation in order to get a precise, reliable and economic solution in a mass market application. A very low number of sensors are indeed needed for this monitoring and the associated algorithm can be implemented on-line. This technique is validated on a 20-cell PEMFC stack. It demonstrates that the developed method is particularly efficient in flooding case. As a matter of fact, it uses directly the stack as a sensor which enables to get a quick feedback on its state of health.

  4. Surface modified stainless steels for PEM fuel cell bipolar plates

    DOEpatents

    Brady, Michael P [Oak Ridge, TN; Wang, Heli [Littleton, CO; Turner, John A [Littleton, CO

    2007-07-24

    A nitridation treated stainless steel article (such as a bipolar plate for a proton exchange membrane fuel cell) having lower interfacial contact electrical resistance and better corrosion resistance than an untreated stainless steel article is disclosed. The treated stainless steel article has a surface layer including nitrogen-modified chromium-base oxide and precipitates of chromium nitride formed during nitridation wherein oxygen is present in the surface layer at a greater concentration than nitrogen. The surface layer may further include precipitates of titanium nitride and/or aluminum oxide. The surface layer in the treated article is chemically heterogeneous surface rather than a uniform or semi-uniform surface layer exclusively rich in chromium, titanium or aluminum. The precipitates of titanium nitride and/or aluminum oxide are formed by the nitriding treatment wherein titanium and/or aluminum in the stainless steel are segregated to the surface layer in forms that exhibit a low contact resistance and good corrosion resistance.

  5. Simulation of gas and water management strategies in PEM fuel cells for UAV power

    NASA Astrophysics Data System (ADS)

    Wade, Nasir; Smith, Sonya

    2008-11-01

    Proton exchange membrane fuel cells (PEMFC) a involve a number of complex fluid phenomena that are not well understood. The focus of this research is to design a fuel cell that addresses the issues of gas and water management for the power requirements for an Unmanned Arial Vehicle (UAV). Often in conventional stack design, PEM fuel cells are connected electrically in series to create the desired voltage and feed from a common fuel or oxidant stream. This method of fueling, often leads to an uneven distribution of fluid within the stack, causing issues such as cell flooding, dehydration of membrane and inevitably poor fuel cell performance. Generally, fuel cell designers and developers incorporate higher stoichiometric gas flow rates and use flow field designs with high pressure drops in order to counter this phenomenon, ensuring even gas distribution. This method, although effective for water removal, leads to added cost and higher levels of wasted fuel. Using a simulation based approach we demonstrate the feasibility and effectiveness of an individual fuel and oxidant flow distribution, integrated with an individual sequential exhaust technique for a 6-8 cell stack which outputs 300-500 Watts of power. Using varied exhaust configurations the most optimal active gas management strategy will be outlined and recommended to give the best stack performance.

  6. Vessel Cold-Ironing Using a Barge Mounted PEM Fuel Cell: Project Scoping and Feasibility.

    SciTech Connect

    Pratt, Joseph William; Harris, Aaron P

    2013-01-01

    A barge-mounted hydrogen-fueled proton exchange membrane (PEM) fuel cell system has the potential to reduce emissions and fossil fuel use of maritime vessels in and around ports. This study determines the technical feasibility of this concept and examines specific options on the U.S. West Coast for deployment practicality and potential for commercialization.The conceptual design of the system is found to be straightforward and technically feasible in several configurations corresponding to various power levels and run times.The most technically viable and commercially attractive deployment options were found to be powering container ships at berth at the Port of Tacoma and/or Seattle, powering tugs at anchorage near the Port of Oakland, and powering refrigerated containers on-board Hawaiian inter-island transport barges. Other attractive demonstration options were found at the Port of Seattle, the Suisun Bay Reserve Fleet, the California Maritime Academy, and an excursion vessel on the Ohio River.

  7. Research and Development of a PEM Fuel Cell, Hydrogen Reformer, and Vehicle Refueling Facility

    SciTech Connect

    Edward F. Kiczek

    2007-08-31

    Air Products and Chemicals, Inc. has teamed with Plug Power, Inc. of Latham, NY, and the City of Las Vegas, NV, to develop, design, procure, install and operate an on-site hydrogen generation system, an alternative vehicle refueling system, and a stationary hydrogen fuel cell power plant, located in Las Vegas. The facility will become the benchmark for validating new natural gas-based hydrogen systems, PEM fuel cell power generation systems, and numerous new technologies for the safe and reliable delivery of hydrogen as a fuel to vehicles. Most important, this facility will serve as a demonstration of hydrogen as a safe and clean energy alternative. Las Vegas provides an excellent real-world performance and durability testing environment.

  8. On the influence of temperature on PEM fuel cell operation

    NASA Astrophysics Data System (ADS)

    Coppo, M.; Siegel, N. P.; Spakovsky, M. R. von

    The 3D implementation of a previously developed 2D PEMFC model [N.P. Siegel, M.W. Ellis, D.J. Nelson, M.R. von Spakovsky, A two-dimensional computational model of a PEMFC with liquid water transport, J. Power Sources 128 (2) (2004) 173-184; N.P. Siegel, M.W. Ellis, D.J. Nelson, M.R. von Spakovsky, Single domain PEMFC model based on agglomerate catalyst geometry, J. Power Sources 115 (2003) 81-89] has been used to analyze the various pathways by which temperature affects the operation of a proton exchange membrane fuel cell [M. Coppo, CFD analysis and experimental investigation of proton exchange membrane fuel cells, Ph.D. Dissertation, Politecnico di Torino, Turin, Italy, 2005]. The original model, implemented in a specially modified version of CFDesign ® [CFDesign ® V5.1, Blue Ridge Numerics, 2003] , accounts for all of the major transport processes including: (i) a three-phase model for water transport in the liquid, vapor and dissolved phases, (ii) proton transport, (iii) gaseous species transport and reaction, (iv) an agglomerate model for the catalyst layers and (v) gas phase momentum transport. Since the details of it have been published earlier [N.P. Siegel, M.W. Ellis, D.J. Nelson, M.R. von Spakovsky, A two-dimensional computational model of a PEMFC with liquid water transport, J. Power Sources 128 (2) (2004) 173-184; N.P. Siegel, M.W. Ellis, D.J. Nelson, M.R. von Spakovsky, Single domain PEMFC model based on agglomerate catalyst geometry, J. Power Sources 115 (2003) 81-89; N.P. Siegel, Development and validation of a computational model for a proton exchange membrane fuel cell, Ph.D. Dissertation, Virginia Polytechnic Institute and State University, Blacksburg, VA, 2003], only new features are briefly discussed in the present work. In particular, the model has been extended in order to account for the temperature dependence of all of the physical properties involved in the model formulation. Moreover, a novel model has been developed to describe liquid

  9. Degradation of Ionic Pathway in PEM Fuel Cell Cathode

    SciTech Connect

    Park, Seh Kyu; Shao, Yuyan; Wan, Haiying; Viswanathan, Vilayanur V.; Towne, Silas A.; Rieke, Peter C.; Liu, Jun; Wang, Yong

    2011-11-12

    The degradation of the ionic pathway throughout the catalyst layer in proton exchange membrane fuel cells was studied under an accelerated stress test of catalyst support (potential hold at 1.2 V). Electrochemical behaviors of the cathode based on graphitic mesoporous carbon supported Pt catalyst were examined using electrochemical impedance spectroscopy and cyclic voltammetry. Impedance data were plotted and expressed in the complex capacitance form to determine useful parameters in the transmission line model: the double-layer capacitance, peak frequency, and ionic resistance. Electrochemical surface area and hydrogen crossover current through the membrane were estimated from cyclic voltammogram, while cathode Faradaic resistance was compared with ionic resistance as a function of test time. It was observed that during an accelerated stress test of catalyst support, graphitic mesoporous carbon becomes hydrophilic which increases interfacial area between the ionomer and the catalyst up to 100 h. However, the ionic resistance in the catalyst layer drastically increases after 100 h with further carbon support oxidation. The underlying mechanism has been studied and it was found that significant degradation of ionic pathway throughout the catalyst layer due to catalyst support corrosion induces uneven hydration and mechanical stress in the ionomer.

  10. Dependence of high-temperature PEM fuel cell performance on Nafion ® content

    NASA Astrophysics Data System (ADS)

    Song, Ying; Xu, Hui; Wei, Yu; Kunz, H. Russell; Bonville, Leonard J.; Fenton, James M.

    Operating a proton exchange membrane (PEM) fuel cell at elevated temperatures (above 100 °C) has significant advantages, such as reduced CO poisoning, increased reaction rates, faster heat rejection, easier and more efficient water management and more useful waste heat. Catalyst materials and membrane electrode assembly (MEA) structure must be considered to improve PEM fuel cell performance. As one of the most important electrode design parameters, Nafion ® content was optimized in the high-temperature electrodes in order to achieve high performance. The effect of Nafion ® content on the electrode performance in H 2/air or H 2/O 2 operation was studied under three different operation conditions (cell temperature (°C)/anode (%RH)/cathode (%RH)): 80/100/75, 100/70/70 and 120/35/35, all at atmospheric pressure. Different Nafion ® contents in the cathode catalyst layers, 15-40 wt%, were evaluated. For electrodes with 0.5 mg cm -2 Pt loading, cell voltages of 0.70, 0.68 and 0.60 V at a current density of 400 mA cm -2 were obtained at 35 wt% Nafion ® ionomer loading, when the cells were operated at the three test conditions, respectively. Cyclic voltammetry was conducted to evaluate the electrochemical surface area. The experimental polarization curves were analyzed by Tafel slope, catalyst activity and diffusion capability to determine the influence of the Nafion ® loading, mainly associated with the cathode.

  11. Development and demonstration of a higher temperature PEM fuel cell stack

    NASA Astrophysics Data System (ADS)

    Bonville, Leonard J.; Kunz, H. Russell; Song, Ying; Mientek, Anthony; Williams, Minkmas; Ching, Albert; Fenton, James M.

    Research and development was conducted on a proton exchange membrane (PEM) fuel cell stack to demonstrate the capabilities of Ionomem Corporation's composite membrane to operate at 120 °C and ambient pressure for on-site electrical power generation with useful waste heat. The membrane was a composite of polytetrafluoroethylene (PTFE), Nafion ®, and phosphotungstic acid. Studies were first performed on the membrane, cathode catalyst layer, and gas diffusion layer to improve performance in 25 cm 2, subscale cells. This technology was then scaled-up to a commercial 300 cm 2 size and evaluated in multi-cell stacks. The resulting stack obtained a performance near that of the subscale cells, 0.60 V at 400 mA cm -2 at near 120 °C and ambient pressure with hydrogen and air reactants containing water at 35% relative humidity. The water used for cooling the stack resulted in available waste heat at 116 °C. The performance of the stack was verified. This was the first successful test of a higher-temperature, PEM, fuel-cell stack that did not use phosphoric acid electrolyte.

  12. NASA's PEM Fuel Cell Power Plant Development Program for Space Applications

    NASA Technical Reports Server (NTRS)

    Hoberecht, Mark

    2006-01-01

    NASA embarked on a PEM fuel cell power plant development program beginning in 2001. This five-year program was conducted by a three-center NASA team of Glenn Research Center (lead), Johnson Space Center, and Kennedy Space Center. The program initially was aimed at developing hardware for a Reusable Launch Vehicle (RLV) application, but more recently had shifted to applications supporting the NASA Exploration Program. The first phase of the development effort, to develop breadboard hardware in the 1-5 kW power range, was conducted by two competing vendors. The second phase of the effort, to develop Engineering Model hardware at the 10 kW power level, was conducted by the winning vendor from the first phase of the effort. Both breadboard units and the single engineering model power plant were delivered to NASA for independent testing. This poster presentation will present a summary of both phases of the development effort, along with a discussion of test results of the PEM fuel cell engineering model under simulated mission conditions.

  13. Numerical study of changing the geometry of the flow field of a PEM fuel cell

    NASA Astrophysics Data System (ADS)

    Khazaee, I.; Sabadbafan, H.

    2016-05-01

    The geometry of channels of a PEM fuel cell is an important parameter that affects the performance of it that the lower voltage loss in polarization curve can indicate the better performance. In this study a complete three-dimensional and single phase model is used to investigate the effect of increasing the number of serpentine channels in the bipolar plates and also increasing the area (depth) of channels of a PEM fuel cell with rectangular, triangular and elliptical cross-section geometry. A single set of conservation equations which are valid for the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane region is developed and numerically solved using a finite volume based computational fluid dynamics technique. The results show that there are good agreement with the numerical results and experimental results of the previous work of authors. Also the results show that by increasing the number of channels from one to four and eight, the performance improved about 18 % and by decreasing the area of channels from 2 to 1 mm2 the performance improved about 13 %.

  14. Design and fabrication of miniaturized PEM fuel cell combined microreactor with self-regulated hydrogen mechanism

    NASA Astrophysics Data System (ADS)

    Balakrishnan, A.; Frei, M.; Kerzenmacher, S.; Reinecke, H.; Mueller, C.

    2015-12-01

    In this work we present the design and fabrication of the miniaturized PEM fuel cell combined microreactor system with hydrogen regulation mechanism and testing of prototype microreactor. The system consists of two components (i) fuel cell component and (ii) microreactor component. The fuel cell component represents the miniaturized PEM fuel cell system (combination of screen printed fuel cell assembly and an on-board hydrogen storage medium). Hydrogen production based on catalytic hydrolysis of chemical hydride takes place in the microreactor component. The self-regulated hydrogen mechanism based on the gaseous hydrogen produced from the catalytic hydrolysis of sodium borohydride (NaBH4) gets accumulated as bubbles at the vicinity of the hydrophobic coated hydrogen exhaust holes. When the built up hydrogen bubbles pressure exceeds the burst pressure at the hydrogen exhaust holes the bubble collapses. This collapse causes a surge of fresh NaBH4 solution onto the catalyst surface leading to the removal of the reaction by-products formed at the active sites of the catalyst. The catalyst used in the system is platinum deposited on a base substrate. Nickel foam, carbon porous medium (CPM) and ceramic plate were selected as candidates for base substrate for developing a robust catalyst surface. For the first time the platinum layer fabricated by pulsed electrodeposition and dealloying (EPDD) technique is used for hydrolysis of NaBH4. The major advantages of such platinum catalyst layers are its high surface area and their mechanical stability. Prototype microreactor system with self-regulated hydrogen mechanism is demonstrated.

  15. Durability of Membrane Electrode Assemblies (MEAs) in PEM Fuel Cells Operated on Pure Hydrogen and Oxygen

    NASA Technical Reports Server (NTRS)

    Stanic, Vesna; Braun, James; Hoberecht, Mark

    2003-01-01

    Proton exchange membrane (PEM) fuel cells are energy sources that have the potential to replace alkaline fuel cells for space programs. Broad power ranges, high peak-to-nominal power capabilities, low maintenance costs, and the promise of increased life are the major advantages of PEM technology in comparison to alkaline technology. The probability of PEM fuel cells replacing alkaline fuel cells for space applications will increase if the promise of increased life is verified by achieving a minimum of 10,000 hours of operating life. Durability plays an important role in the process of evaluation and selection of MEAs for Teledyne s Phase I contract with the NASA Glenn Research Center entitled Proton Exchange Membrane Fuel cell (PEMFC) Power Plant Technology Development for 2nd Generation Reusable Launch Vehicles (RLVs). For this contract, MEAs that are typically used for H2/air operation were selected as potential candidates for H2/O2 PEM fuel cells because their catalysts have properties suitable for O2 operation. They were purchased from several well-established MEA manufacturers who are world leaders in the manufacturing of diverse products and have committed extensive resources in an attempt to develop and fully commercialize MEA technology. A total of twelve MEAs used in H2/air operation were initially identified from these manufacturers. Based on the manufacturers specifications, nine of these were selected for evaluation. Since 10,000 hours is almost equivalent to 14 months, it was not possible to perform continuous testing with each MEA selected during Phase I of the contract. Because of the lack of time, a screening test on each MEA was performed for 400 hours under accelerated test conditions. The major criterion for an MEA pass or fail of the screening test was the gas crossover rate. If the gas crossover rate was higher than the membrane intrinsic permeability after 400 hours of testing, it was considered that the MEA had failed the test. Three types of

  16. Experimental and theoretical study of a dual-layer gas diffusion layer in PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Park, Sehkyu

    2008-07-01

    The gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs) functions as a diffuser and a current collector. The GDL typically consists of the microporous layer (MPL) and the macroporous substrate (MPS). The MPL reduces the ohmic losses and facilitates water removal in the MEA. In this study, a novel method was developed to prepare a dual-layer GDL that enhances the catalyst utilization and the overall fuel cell performance. Several characterization techniques, including mercury porosimetry, water permeation measurement, electrochemical polarization and ac impedance spectroscopy were performed to investigate how carbon loading (or MPL thickness) and PTFE content in the MPL and in the MPS control the water management in PEM fuel cells. An experimental study on carbon loading in the MPL showed that a relatively low carbon loading (0.5 mg cm-2 in this study) results in a balancing of water saturations in the catalyst layer and the GDL, thus improving the oxygen diffusion kinetics. Experimental studies on PTFE content in the MPL and in the MPS indicated that effective water management is attributed to the trade-off between the pore volume and the hydrophobic property of each diffusion layer. A theoretical study of a dual-layer GDL in PEM fuel cells demonstrated that saturation in the MPS is intimately coupled with both the fraction of hydrophilic surface and the average pore diameter. A thin and more hydrophobic MPL altered the pore geometry and the hydrophobic property of a MPS, resulting in better mass transport of reactants and products in the MEA.

  17. Performance and durability of PEM fuel cells operated at sub-freezing temperatures

    SciTech Connect

    Mukundan, Rangachary; Davey, John R; Lujan, Roger W; Spendelow, Jacob S

    2008-01-01

    The durability of polymer electrolyte membrane (PEM) fuel cells operated at sub-freezing temperatures has received increasing attention in recent years. The Department of Energy's PEM fuel cell stack technical targets for the year 2010 include unassisted start-up from -40 {sup o}C and startup from -20 {sup o}C ambient in as low as 30 seconds with < 5 MJ energy consumption. Moreover, the sub-freezing operations should not have any impact on acieving other technical targets including 5000 hours durability. The effect of MEA preparation on the performance of single-PEM fuel cells operated at sub-freezing temperatures is presented. The cell performance and durability are dependent on the MEA and are probably influenced by the porosity of the catalyst layers. When a cell is operated isothermally at -10 {sup o}C in constant current mode, the voltage gradually decreases over time and eventually drops to zero. AC impedance analysis indicated that the rate of voltage loss is initially due to an increase in the charge transfer resistance and is gradual. After a period, the rate of decay accelerates rapidly due to mass transport limitations at the catalyst and/or gas diffusion layers. The high frequency resistance also increases over time during the isothermal operation at sub-freezing temperatures and was a function of the initial membrane water content. LANL prepared MEAs showed very little loss in the catalyst surface area with multiple sub-freezing operations, whereas the commercial MEAs exhibited significant loss in cathode surface area with the anode being unaffected. These results indicate that catalyst layer ice formation is influenced strongly by the MEA and is responsible for the long-term degradation of fuel cells operated at sub-freezing temperatures. This ice formation was monitored using neutron radiography and was found to be concentrated near cell edges at the flow field turns. The water distribution also indicated that ice may be forming mainly in the GDLs at

  18. Bootstrapping a Sustainable North American PEM Fuel Cell Industry: Could a Federal Acquisition Program Make a Difference?

    SciTech Connect

    Greene, David L; Duleep, Dr. K. G.

    2008-10-01

    The North American Proton Exchange Membrane (PEM) fuel cell industry may be at a critical juncture. A large-scale market for automotive fuel cells appears to be several years away and in any case will require a long-term, coordinated commitment by government and industry to insure the co-evolution of hydrogen infrastructure and fuel cell vehicles (Greene et al., 2008). The market for non-automotive PEM fuel cells, on the other hand, may be much closer to commercial viability (Stone, 2006). Cost targets are less demanding and manufacturers appear to be close, perhaps within a factor of two, of meeting them. Hydrogen supply is a significant obstacle to market acceptance but may not be as great a barrier as it is for hydrogen-powered vehicles due to the smaller quantities of hydrogen required. PEM fuel cells appear to be potentially competitive in two markets: (1) Backup power (BuP) supply, and (2) electrically-powered MHE (Mahadevan et al., 2007a, 2007b). There are several Original Equipment Manufacturers (OEMs) of PEM fuel cell systems for these applications but production levels have been quite low (on the order of 100-200 per year) and cumulative production experience is also limited (on the order of 1,000 units to date). As a consequence, costs remain above target levels and PEM fuel cell OEMs are not yet competitive in these markets. If cost targets can be reached and acceptable solutions to hydrogen supply found, a sustainable North American PEM fuel cell industry could be established. If not, the industry and its North American supply chain could disappear within a year or two. The Hydrogen Fuel Cell and Infrastructure Technologies (HFCIT) program of the U.S. Department of Energy (DOE) requested a rapid assessment of the potential for a government acquisition program to bootstrap the market for non-automotive PEM fuel cells by driving down costs via economies of scale and learning-by-doing. The six week study included in-depth interviews of three manufacturers

  19. WaterTransport in PEM Fuel Cells: Advanced Modeling, Material Selection, Testing and Design Optimization

    SciTech Connect

    J. Vernon Cole; Abhra Roy; Ashok Damle; Hari Dahr; Sanjiv Kumar; Kunal Jain; Ned Djilai

    2012-10-02

    Water management in Proton Exchange Membrane, PEM, Fuel Cells is challenging because of the inherent conflicts between the requirements for efficient low and high power operation. Particularly at low powers, adequate water must be supplied to sufficiently humidify the membrane or protons will not move through it adequately and resistance losses will decrease the cell efficiency. At high power density operation, more water is produced at the cathode than is necessary for membrane hydration. This excess water must be removed effectively or it will accumulate in the Gas Diffusion Layers, GDLs, between the gas channels and catalysts, blocking diffusion paths for reactants to reach the catalysts and potentially flooding the electrode. As power density of the cells is increased, the challenges arising from water management are expected to become more difficult to overcome simply due to the increased rate of liquid water generation relative to fuel cell volume. Thus, effectively addressing water management based issues is a key challenge in successful application of PEMFC systems. In this project, CFDRC and our partners used a combination of experimental characterization, controlled experimental studies of important processes governing how water moves through the fuel cell materials, and detailed models and simulations to improve understanding of water management in operating hydrogen PEM fuel cells. The characterization studies provided key data that is used as inputs to all state-of-the-art models for commercially important GDL materials. Experimental studies and microscopic scale models of how water moves through the GDLs showed that the water follows preferential paths, not branching like a river, as it moves toward the surface of the material. Experimental studies and detailed models of water and airflow in fuel cells channels demonstrated that such models can be used as an effective design tool to reduce operating pressure drop in the channels and the associated

  20. Hydrogen-Oxygen PEM Regenerative Fuel Cell Development at the NASA Glenn Research Center

    NASA Technical Reports Server (NTRS)

    Bents, David J.; Scullin, Vincent J.; Chang, Bei-Jiann; Johnson, Donald W.; Garcia, Christoher P.; Jakupca, Ian J.

    2005-01-01

    The closed-cycle hydrogen-oxygen PEM regenerative fuel cell (RFC) at the NASA Glenn Research Center has successfully demonstrated closed cycle operation at rated power for multiple charge-discharge cycles. During charge cycle the RFC has absorbed input electrical power simulating a solar day cycle ranging from zero to 15 kWe peak, and delivered steady 5 kWe output power for periods exceeding 8 hr. Orderly transitions from charge to discharge mode, and return to charging after full discharge, have been accomplished without incident. Continuing test operations focus on: (1) Increasing the number of contiguous uninterrupted charge discharge cycles; (2) Increasing the performance envelope boundaries; (3) Operating the RFC as an energy storage device on a regular basis; (4) Gaining operational experience leading to development of fully automated operation; and (5) Developing instrumentation and in situ fluid sampling strategies to monitor health and anticipate breakdowns.

  1. Nanostructured Electrocatalysts for PEM Fuel Cells and Redox Flow Batteries: A Selected Review

    SciTech Connect

    Shao, Yuyan; Cheng, Yingwen; Duan, Wentao; Wang, Wei; Lin, Yuehe; Wang, Yong; Liu, Jun

    2015-12-04

    PEM fuel cells and redox flow batteries are two very similar technologies which share common component materials and device design. Electrocatalysts are the key components in these two devices. In this Review, we discuss recent progress of electrocatalytic materials for these two technologies with a focus on our research activities at Pacific Northwest National Laboratory (PNNL) in the past years. This includes (1) nondestructive functionalization of graphitic carbon as Pt support to improve its electrocatalytic performance, (2) triple-junction of metal–carbon–metal oxides to promote Pt performance, (3) nitrogen-doped carbon and metal-doped carbon (i.e., metal oxides) to improve redox reactions in flow batteries. A perspective on future research and the synergy between the two technologies are also discussed.

  2. Separate in situ measurements of ECA under land and channel in PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Higier, Andrew; Liu, Hongtan

    2012-10-01

    Separate in situ measurements of electrochemical areas (ECA) under land and channel areas in proton exchange membrane (PEM) fuel cells are realized using cyclic voltammetry. Experiments are carried out using special membrane electrode assemblies (MEA) in single-channel serpentine flow fields with different widths of channels and lands. The experimental results show that ECAs are significantly higher in the areas under the land than that under the channel. ECA-normalized polarization curves show that ECA is the most significant factor causing higher current density under the land than under the channel in the high cell potential region, and the true concentration polarization under the land in the low potential region is actually much greater than what can be seen in conventional polarization curves. Further experimental results show that, within the compression pressure range examined, ECA increases with compression pressure significantly.

  3. Iron-based alloy and nitridation treatment for PEM fuel cell bipolar plates

    DOEpatents

    Brady, Michael P [Oak Ridge, TN; Yang, Bing [Oak Ridge, TN; Maziasz, Philip J [Oak Ridge, TN

    2010-11-09

    A corrosion resistant electrically conductive component that can be used as a bipolar plate in a PEM fuel cell application is composed of an alloy substrate which has 10-30 wt. % Cr, 0.5 to 7 wt. % V, and base metal being Fe, and a continuous surface layer of chromium nitride and vanadium nitride essentially free of base metal. A oxide layer of chromium vanadium oxide can be disposed between the alloy substrate and the continuous surface nitride layer. A method to prepare the corrosion resistant electrically conductive component involves a two-step nitridization sequence by exposing the alloy to a oxygen containing gas at an elevated temperature, and subsequently exposing the alloy to an oxygen free nitrogen containing gas at an elevated temperature to yield a component where a continuous chromium nitride layer free of iron has formed at the surface.

  4. Analytical Investigation and Improvement of Performance of a Proton Exchange Membrane (Pem) Fuel Cell in Mobile Applications

    NASA Astrophysics Data System (ADS)

    Khazaee, I.

    2015-05-01

    In this study, the performance of a proton exchange membrane fuel cell in mobile applications is investigated analytically. At present the main use and advantages of fuel cells impact particularly strongly on mobile applications such as vehicles, mobile computers and mobile telephones. Some external parameters such as the cell temperature (Tcell ) , operating pressure of gases (P) and air stoichiometry (λair ) affect the performance and voltage losses in the PEM fuel cell. Because of the existence of many theoretical, empirical and semi-empirical models of the PEM fuel cell, it is necessary to compare the accuracy of these models. But theoretical models that are obtained from thermodynamic and electrochemical approach, are very exact but complex, so it would be easier to use the empirical and smi-empirical models in order to forecast the fuel cell system performance in many applications such as mobile applications. The main purpose of this study is to obtain the semi-empirical relation of a PEM fuel cell with the least voltage losses. Also, the results are compared with the existing experimental results in the literature and a good agreement is seen.

  5. Analysis of liquid water formation in polymer electrolyte membrane (PEM) fuel cell flow fields with a dry cathode supply

    NASA Astrophysics Data System (ADS)

    Gößling, Sönke; Klages, Merle; Haußmann, Jan; Beckhaus, Peter; Messerschmidt, Matthias; Arlt, Tobias; Kardjilov, Nikolay; Manke, Ingo; Scholta, Joachim; Heinzel, Angelika

    2016-02-01

    PEM fuel cells can be operated within a wide range of different operating conditions. In this paper, the special case of operating a PEM fuel cell with a dry cathode supply and without external humidification of the cathode, is considered. A deeper understanding of the water management in the cells is essential for choosing the optimal operation strategy for a specific system. In this study a theoretical model is presented which aims to predict the location in the flow field at which liquid water forms at the cathode. It is validated with neutron images of a PEM fuel cell visualizing the locations at which liquid water forms in the fuel cell flow field channels. It is shown that the inclusion of the GDL diffusion resistance in the model is essential to describe the liquid water formation process inside the fuel cell. Good agreement of model predictions and measurement results has been achieved. While the model has been developed and validated especially for the operation with a dry cathode supply, the model is also applicable to fuel cells with a humidified cathode stream.

  6. Hydrogen-Oxygen PEM Regenerative Fuel Cell at NASA Glenn Research Center

    NASA Technical Reports Server (NTRS)

    Bents, David J.

    2004-01-01

    The NASA Glenn Research Center has constructed a closed-cycle hydrogen-oxygen PEM regenerative fuel cell (RFC) to explore its potential use as an energy storage device for a high altitude solar electric aircraft. Built up over the last 2 years from specialized hardware and off the shelf components the Glenn RFC is a complete "brassboard" energy storage system which includes all the equipment required to (1) absorb electrical power from an outside source and store it as pressurized hydrogen and oxygen and (2) make electrical power from the stored gases, saving the product water for re-use during the next cycle. It consists of a dedicated hydrogen-oxygen fuel cell stack and an electrolyzer stack, the interconnecting plumbing and valves, cooling pumps, water transfer pumps, gas recirculation pumps, phase separators, storage tanks for oxygen (O2) and hydrogen (H2), heat exchangers, isolation valves, pressure regulators, nitrogen purge provisions, instrumentation, and other components. It specific developmental functions include: (1) Test fuel cells and fuel cell components under repeated closed-cycle operation (nothing escapes; everything is used over and over again). (2) Simulate diurnal charge-discharge cycles (3) Observe long-term system performance and identify degradation and loss mechanisms. (4) Develop safe and convenient operation and control strategies leading to the successful development of mission-capable, flight-weight RFC's.

  7. Long term testing of start-stop cycles on high temperature PEM fuel cell stack

    NASA Astrophysics Data System (ADS)

    Kannan, Arvind; Kabza, Alexander; Scholta, Joachim

    2015-03-01

    A PEM fuel cell with an operating temperature above 100 °C is desired for increasing the kinetics of reactions, reduced sensitivity to impurities of the fuel, as well as for the reduction of the requirements on thermal and water management systems. High Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFC) can effectively be combined with CHP systems to offer a simple system design and higher overall system efficiencies. For HT-PEMFC systems, the development of elaborated start/stop strategies is essential in mitigation of fuel cell degradation during these events. A 5 cell co-flow stack is assembled with BASF P1100W membrane electrode assembly (MEA) with an active area of 163.5 cm2. Continuous operation and more than 1500 start stop cycles have been performed in order to study the degradation effects of both continuous operation and of repeated start stops using a protective start-stop algorithm, which is designed to avoid the formation of aggressive cell potentials. The repeated use of this procedure led to a degradation of 26 μV/cycle at a current density of 0.25 A cm-2 and 11 μV/cycle at a current density of 0.03 A cm-2. At open circuit voltage (OCV), a higher degradation rate of 133 μV/cycle was observed.

  8. Test of Hydrogen-Oxygen PEM Fuel Cell Stack at NASA Glenn Research Center

    NASA Technical Reports Server (NTRS)

    Bents, David J.; Scullin, Vincent J.; Chang, Bei-Jiann; Johnson, Donald W.; Garcia, Christopher P.; Jakupca, Ian J.

    2003-01-01

    This paper describes performance characterization tests of a 64 cell hydrogen oxygen PEM fuel cell stack at NASA Glenn Research Center in February 2003. The tests were part of NASA's ongoing effort to develop a regenerative fuel cell for aerospace energy storage applications. The purpose of the tests was to verify capability of this stack to operate within a regenerative fuel cell, and to compare performance with earlier test results recorded by the stack developer. Test results obtained include polarization performance of the stack at 50 and 100 psig system pressure, and a steady state endurance run at 100 psig. A maximum power output of 4.8 kWe was observed during polarization runs, and the stack sustained a steady power output of 4.0 kWe during the endurance run. The performance data obtained from these tests compare reasonably close to the stack developer's results although some additional spread between best to worst performing cell voltages was observed. Throughout the tests, the stack demonstrated the consistent performance and repeatable behavior required for regenerative fuel cell operation.

  9. Nanostructured catalyst materials for next generation polymer electrolyte membrane (PEM) fuel cells

    NASA Astrophysics Data System (ADS)

    Khudhayer, Wisam J.

    Polymer electrolyte membrane (PEM) fuel cells are electrochemical energy conversion devices which have demonstrated great promise as future energy sources for electric vehicles, as they convert chemical energy to electrical energy with a significantly higher efficiency and lower environmental impact than in standard combustion processes. However, the commercialization of PEM fuel cells for transportation applications has been hindered by several factors such as high cost of Pt, low Pt utilization, poor long-term durability of the conventional PEM fuel cell catalyst (Pt nanoparticels supported on carbon black; Pt/C), and poor thermal and chemical stability of the electrocatalyst supports (carbon black). The goal of this research was to fabricate high performance, durable, carbon-free, controllable porosity, and low cost (low Pt loading) sputtered-nanostructured electrocatalysts and investigate their morphologies, crystal properties, and electrocatalytic activities. First, the electrocatalytic oxygen reduction reaction (ORR) activity of vertically-aligned solid Pt nanorods was evaluated. A glancing angle deposition (GLAD) technique was used to fabricate Pt nanorod arrays directly on glassy carbon (GC) electrodes. It was found that Pt-nanorod electrocatalysts exhibit higher area-specific activity, greater electrochemical stability, higher electron-transfer rate constant, and comparable activation energy for ORR than those of Pt/C due to their larger crystallite size, single-crystal property, and dominance of the preferred crystal orientations (Pt[110]) for ORR. However, Pt nanorods show lower mass specific activity than that of Pt/C electrocatalyst due to the large diameter of nanorods. Second, to further enhance the mass-specific activity of solid GLAD Pt nanorods, the GLAD chromium (Cr) nanorods were used as low-cost catalyst supports for conformal Pt thin film coating achieved by a small angle deposition (SAD) technique as a potential catalyst electrode for oxygen

  10. Mechanical and transport properties of NafionRTM for PEM fuel cells; temperature and hydration effects

    NASA Astrophysics Data System (ADS)

    Majsztrik, Paul William

    This work investigates the mechanical and water transport properties of Nafion, a fully fluorinated ion conducting polymer used as a membrane material in proton exchange membrane fuel cells (PEMFCs). Both of these properties are extremely important to the short and long term operation of fuel cells. Nafion is a viscoelastic material, responding to stress in a time-dependant manner. The result is that Nafion flows under stress and responds dynamically to changes in hydration and stress. Stresses applied to the membrane of a PEM fuel cell, both from clamping as well as strain from changing levels of hydration, cause Nafion to flow. This results in thinning in spots and sometimes leads to the development of pinholes or contact problems between membrane and electrode. Temperature and water content strongly affect Nafion's viscoelastic response, of direct importance for operating PEM fuel cells. The viscoelastic response of Nafion was measured over a range of temperature and hydration using viscoelastic creep. A specially designed creep apparatus with environmental controls was used. It was found that the effects of temperature and hydration on Nafion's viscoelastic response are very complicated. Around room temperature, water acts to plasticize Nafion; elastic modulus and resistance to creep decrease with increasing hydration. As temperature increases, water has the opposite effect on mechanical response; hydration acts to stabilize the material. Mechanical property values are reported over a range of temperature and hydration germane to the operation of PEMFCs. Additionally, the data is used to infer molecular level interactions and the effects of temperature and hydration on microstructure. Hydration of Nafion and other PEMFC materials is required for the high proton conductivity needed for fuel cell operation. Uptake of water by Nafion results in volumetric swelling. Water transport through Nafion was directly measured by permeation. Both liquid and vapor phase

  11. Lattice Boltzmann Simulation of Multiphase Transport in Nanostructured PEM Fuel Cells

    NASA Astrophysics Data System (ADS)

    Stiles, Christopher D.

    As the fossil fuel crisis becomes more critical, it is imperative to develop renewable sources of power generation. Polymer electrolyte membrane (PEM) fuel cells are considered a viable option. However, the cost of the platinum catalyst has hindered their commercialization. PEM fuel cells with platinum loading of >0.4 mg cm2 are common. Efforts towards further reducing this loading are currently underway utilizing nanostructured electrodes. A consequence of increased platinum utilization per unit area and thinner nanostructured electrodes is flooding, which is detrimental to fuel cell performance. Flooding causes a two-fold impact on cell performance: a drop in cell voltage and a rise in parasitic pumping power to overcome the increased pressure drop, which together result in a significant reduction in system efficiency. Proper water management is therefore crucial for optimum performance of the fuel cell and also for enhancing membrane durability. The goal of this thesis is to simulate the multiphase fluid transport in the nanostructured PEMFC of H2O in air with realistic density ratios. In order to pursue this goal, the ability of the pseudopotential based multiphase lattice Boltzmann method to realistically model the coexistence of the gas and liquid phases of H2O at low temperatures is explored. This method is expanded to include a gas mixture of O2 and N 2 into the multiphase H2O systems. Beginning with the examination of the phase transition region described by the current implementation of the multiphase pseudopotential lattice Boltzmann model. Following this, a modified form of the pressure term with the use of a scalar multiplier kappa for the Peng-Robinson equation of state is thoroughly investigated. This method proves to be very effective at enabling numerically stable simulations at low temperatures with large density ratios. It is found that for decreasing values of kappa, this model leads to an increase in multiphase interface thickness and a

  12. Experimental study of humidity changes on the performance of an elliptical single four-channel PEM fuel cell

    NASA Astrophysics Data System (ADS)

    Gholizadeh, Mohammad; Ghazikhani, Mohsen; Khazaee, Iman

    2016-04-01

    Humidity and humidification in a proton exchange membrane fuel cells (PEM) can significantly affect the performance of these energy generating devices. Since protons (H+) needs to be accompanied by water molecules to pass from the anode side to the cathode side, the PEM fuel cell membrane should be sufficiently wet. Low or high amount of water in the membrane can interrupt the flow of protons and thus reduce the efficiency of the fuel cell. In this context, several experimental studies and modeling have been carried out on PEM fuel cell and interesting results have been achieved. In this paper, the humidity and flow rate of gas in the anode and cathode are modified to examine its effect on fuel cell performance. The results show that the effect of humidity changing in the anode side is greater than that of the cathode so that at zero humidity of anode and 70 % humidity of the cathode, a maximum current flow of 0.512 A/cm2 for 0.12 V was obtained. However, at 70 % anode humidity and zero cathode humidity, a maximum flow of 0.86 A/cm2 for 0.13 V was obtained.

  13. Hydrogen-Oxygen PEM Regenerative Fuel Cell Development at NASA Glenn Research Center

    NASA Technical Reports Server (NTRS)

    Bents, David J.; Scullin, Vincent J.; Chang, B. J.; Johnson, Donald W.; Garcia, Christopher P.; Jakupca, Ian J.

    2006-01-01

    The closed-cycle hydrogen-oxygen PEM regenerative fuel cell (RFC) at NASA Glenn Research Center has demonstrated multiple back to back contiguous cycles at rated power, and round trip efficiencies up to 52 percent. It is the first fully closed cycle regenerative fuel cell ever demonstrated (entire system is sealed: nothing enters or escapes the system other than electrical power and heat). During FY2006 the system has undergone numerous modifications and internal improvements aimed at reducing parasitic power, heat loss and noise signature, increasing its functionality as an unattended automated energy storage device, and in-service reliability. It also serves as testbed towards development of a 600 W-hr/kg flight configuration, through the successful demonstration of lightweight fuel cell and electrolyser stacks and supporting components. The RFC has demonstrated its potential as an energy storage device for aerospace solar power systems such as solar electric aircraft, lunar and planetary surface installations; any airless environment where minimum system weight is critical. Its development process continues on a path of risk reduction for the flight system NASA will eventually need for the manned lunar outpost.

  14. Performance evaluation and characterization of metallic bipolar plates in a proton exchange membrane (PEM) fuel cell

    NASA Astrophysics Data System (ADS)

    Hung, Yue

    Bipolar plate and membrane electrode assembly (MEA) are the two most repeated components of a proton exchange membrane (PEM) fuel cell stack. Bipolar plates comprise more than 60% of the weight and account for 30% of the total cost of a fuel cell stack. The bipolar plates perform as current conductors between cells, provide conduits for reactant gases, facilitate water and thermal management through the cell, and constitute the backbone of a power stack. In addition, bipolar plates must have excellent corrosion resistance to withstand the highly corrosive environment inside the fuel cell, and they must maintain low interfacial contact resistance throughout the operation to achieve optimum power density output. Currently, commercial bipolar plates are made of graphite composites because of their relatively low interfacial contact resistance (ICR) and high corrosion resistance. However, graphite composite's manufacturability, permeability, and durability for shock and vibration are unfavorable in comparison to metals. Therefore, metals have been considered as a replacement material for graphite composite bipolar plates. Since bipolar plates must possess the combined advantages of both metals and graphite composites in the fuel cell technology, various methods and techniques are being developed to combat metallic corrosion and eliminate the passive layer formed on the metal surface that causes unacceptable power reduction and possible fouling of the catalyst and the electrolyte. The main objective of this study was to explore the possibility of producing efficient, cost-effective and durable metallic bipolar plates that were capable of functioning in the highly corrosive fuel cell environment. Bulk materials such as Poco graphite, graphite composite, SS310, SS316, incoloy 800, titanium carbide and zirconium carbide were investigated as potential bipolar plate materials. In this work, different alloys and compositions of chromium carbide coatings on aluminum and SS316

  15. Modeling the cathode pressure dynamics in the Buckeye Bullet II 540 kW hydrogen PEM fuel cell system

    NASA Astrophysics Data System (ADS)

    Hillstrom, Edward T.; Canova, Marcello; Guezennec, Yann; Rizzoni, Giorgio

    2013-11-01

    The Buckeye Bullet 2 (BB2) is the world's fastest hydrogen fuel cell vehicle, with an international speed record of 302.9 mph. In order to achieve the power levels necessary for reaching the top speed, a unique gas supply system was designed to feed the PEM fuel cell modules. Stored Heliox with 40% oxygen content was used as the oxidizer and supplied to the cathode at high pressure. The high oxygen concentration at the cathode leads to a high rate of water formation in the GDL, with considerable influence on the pressure dynamics. For this reason, a precise monitoring of the pressure and water formation is required so that the cathode can operate at the maximum allowable pressure. This paper presents a novel control-oriented modeling approach to predict the cathode pressure dynamics of the BB2 PEM fuel cell system, developed for system optimization, monitoring and control. A distributed-parameter model was designed to characterize the liquid water formation and transport in the cathode channels, starting from the conservation laws for viscous fluid flow. The model was validated against a set of laboratory tests and actual race data. In this context, the proposed model is compared to a well known control-oriented PEM fuel cell model, to illustrate how the ability to predict the water transport at high reaction rates allows for an improved prediction of the pressure dynamics.

  16. Drinking water purification by electrosynthesis of hydrogen peroxide in a power-producing PEM fuel cell.

    PubMed

    Li, Winton; Bonakdarpour, Arman; Gyenge, Előd; Wilkinson, David P

    2013-11-01

    The industrial anthraquinone auto-oxidation process produces most of the world's supply of hydrogen peroxide. For applications that require small amounts of H2 O2 or have economically difficult transportation means, an alternate, on-site H2 O2 production method is needed. Advanced drinking water purification technologies use neutral-pH H2 O2 in combination with UV treatment to reach the desired water purity targets. To produce neutral H2 O2 on-site and on-demand for drinking water purification, the electroreduction of oxygen at the cathode of a proton exchange membrane (PEM) fuel cell operated in either electrolysis (power consuming) or fuel cell (power generating) mode could be a possible solution. The work presented here focuses on the H2 /O2 fuel cell mode to produce H2 O2 . The fuel cell reactor is operated with a continuous flow of carrier water through the cathode to remove the product H2 O2 . The impact of the cobalt-carbon composite cathode catalyst loading, Teflon content in the cathode gas diffusion layer, and cathode carrier water flowrate on the production of H2 O2 are examined. H2 O2 production rates of up to 200 μmol h(-1)  cmgeometric (-2) are achieved using a continuous flow of carrier water operating at 30 % current efficiency. Operation times of more than 24 h have shown consistent H2 O2 and power production, with no degradation of the cobalt catalyst. PMID:24039111

  17. Performance evaluation and characterization of metallic bipolar plates in a proton exchange membrane (PEM) fuel cell

    NASA Astrophysics Data System (ADS)

    Hung, Yue

    Bipolar plate and membrane electrode assembly (MEA) are the two most repeated components of a proton exchange membrane (PEM) fuel cell stack. Bipolar plates comprise more than 60% of the weight and account for 30% of the total cost of a fuel cell stack. The bipolar plates perform as current conductors between cells, provide conduits for reactant gases, facilitate water and thermal management through the cell, and constitute the backbone of a power stack. In addition, bipolar plates must have excellent corrosion resistance to withstand the highly corrosive environment inside the fuel cell, and they must maintain low interfacial contact resistance throughout the operation to achieve optimum power density output. Currently, commercial bipolar plates are made of graphite composites because of their relatively low interfacial contact resistance (ICR) and high corrosion resistance. However, graphite composite's manufacturability, permeability, and durability for shock and vibration are unfavorable in comparison to metals. Therefore, metals have been considered as a replacement material for graphite composite bipolar plates. Since bipolar plates must possess the combined advantages of both metals and graphite composites in the fuel cell technology, various methods and techniques are being developed to combat metallic corrosion and eliminate the passive layer formed on the metal surface that causes unacceptable power reduction and possible fouling of the catalyst and the electrolyte. The main objective of this study was to explore the possibility of producing efficient, cost-effective and durable metallic bipolar plates that were capable of functioning in the highly corrosive fuel cell environment. Bulk materials such as Poco graphite, graphite composite, SS310, SS316, incoloy 800, titanium carbide and zirconium carbide were investigated as potential bipolar plate materials. In this work, different alloys and compositions of chromium carbide coatings on aluminum and SS316

  18. An experimental study of a PEM fuel cell power train for urban bus application

    NASA Astrophysics Data System (ADS)

    Corbo, P.; Migliardini, F.; Veneri, O.

    An experimental study was carried out on a fuel cell propulsion system for minibus application with the aim to investigate the main issues of energy management within the system in dynamic conditions. The fuel cell system (FCS), based on a 20 kW PEM stack, was integrated into the power train comprising DC-DC converter, Pb batteries as energy storage systems and asynchronous electric drive of 30 kW. As reference vehicle a minibus for public transportation in historical centres was adopted. A preliminary experimental analysis was conducted on the FCS connected to a resistive load through a DC-DC converter, in order to verify the stack dynamic performance varying its power acceleration from 0.5 kW s -1 to about 4 kW s -1. The experiments on the power train were conducted on a test bench able to simulate the vehicle parameters and road characteristics on specific driving cycles, in particular the European R40 cycle was adopted as reference. The "soft hybrid" configuration, which permitted the utilization of a minimum size energy storage system and implied the use of FCS mainly in dynamic operation, was compared with the "hard hybrid" solution, characterized by FCS operation at limited power in stationary conditions. Different control strategies of power flows between fuel cells, electric energy storage system and electric drive were adopted in order to verify the two above hybrid approaches during the vehicle mission, in terms of efficiencies of individual components and of the overall power train. The FCS was able to support the dynamic requirements typical of R40 cycle, but an increase of air flow rate during the fastest acceleration phases was necessary, with only a slight reduction of FCS efficiency. The FCS efficiency resulted comprised between 45 and 48%, while the overall power train efficiency reached 30% in conditions of constant stack power during the driving cycle.

  19. Ice formation in PEM fuel cells operated isothermally at sub-freezing temperatures

    SciTech Connect

    Mukundan, Rangachary; Luhan, Roger W; Davey, John R; Spendelow, Jacob S; Borup, Rodney L; Hussey, Daniel S; Jacobson, David L; Arif, Muhammad

    2009-01-01

    The effect of MEA and GDL structure and composition on the performance of single-PEM fuel cells operated isothermally at subfreezing temperatures is presented. The cell performance and durability are not only dependent on the MEA/GDL materials used but also on their interfaces. When a cell is operated isothermally at sub-freezing temperatures in constant current mode, the water formation due to the current density initially hydrates the membrane/ionomer and then forms ice in the catalyst layer/GDL. An increase in high frequency resistance was also observed in certain MEAs where there is a possibility of ice formation between the catalyst layer and GDL leading to a loss in contact area. The total water/ice holding capacity for any MEA was lower at lower temperatures and higher current densities. The durability of MEAs subjected to multiple isothermal starts was better for LANL prepared MEAs as compared to commercial MEAs, and cloth GDLs when compared to paper GDLs. The ice formation was monitored using high-resolution neutron radiography and was found to be concentrated near the cathode catalyst layer. However, there was significant ice formation in the GDLs especially at the higher temperature ({approx} -10 C) and lower current density (0.02 A/cm{sup 2}) operations. These results are consistent with the longer-term durability observations that show more severe degradation at the lower temperatures.

  20. Deformation of PEM fuel cell gas diffusion layers under compressive loading: An analytical approach

    NASA Astrophysics Data System (ADS)

    Norouzifard, Vahid; Bahrami, Majid

    2014-10-01

    In the PEM fuel cell stack, the fibrous porous gas diffusion layer (GDL) provides mechanical support for the membrane assembly against the compressive loads imposed by bipolar plates. In this study, a new mechanistic model is developed using fundamental beam theory that can accurately predict the mechanical deflection of GDL under compressive loads. The present analytical model is built on a unit cell approach, which assumes a simplified geometry for the complex and random GDL microstructure. The model includes salient microstructural parameters and properties of the fibrous porous medium including: carbon fiber diameter, fiber elastic modulus, pore size distribution, and porosity. Carbon fiber bending is proved to be the main deformation mechanism at the unit cell level. A comprehensive optical measurement study with statistical analysis is performed to determine the geometrical parameters of the model for a number of commercially available GDL samples. A comparison between the present model and our experimental stress-strain data shows a good agreement for the linear deformation region, where the compressive pressure is higher than 1 MPa.

  1. Analytical and numerical study on cooling flow field designs performance of PEM fuel cell with variable heat flux

    NASA Astrophysics Data System (ADS)

    Afshari, Ebrahim; Ziaei-Rad, Masoud; Jahantigh, Nabi

    2016-06-01

    In PEM fuel cells, during electrochemical generation of electricity more than half of the chemical energy of hydrogen is converted to heat. This heat of reactions, if not exhausted properly, would impair the performance and durability of the cell. In general, large scale PEM fuel cells are cooled by liquid water that circulates through coolant flow channels formed in bipolar plates or in dedicated cooling plates. In this paper, a numerical method has been presented to study cooling and temperature distribution of a polymer membrane fuel cell stack. The heat flux on the cooling plate is variable. A three-dimensional model of fluid flow and heat transfer in cooling plates with 15 cm × 15 cm square area is considered and the performances of four different coolant flow field designs, parallel field and serpentine fields are compared in terms of maximum surface temperature, temperature uniformity and pressure drop characteristics. By comparing the results in two cases, the constant and variable heat flux, it is observed that applying constant heat flux instead of variable heat flux which is actually occurring in the fuel cells is not an accurate assumption. The numerical results indicated that the straight flow field model has temperature uniformity index and almost the same temperature difference with the serpentine models, while its pressure drop is less than all of the serpentine models. Another important advantage of this model is the much easier design and building than the spiral models.

  2. Fault detection and isolation of PEM fuel cell system based on nonlinear analytical redundancy. An application via parity space approach

    NASA Astrophysics Data System (ADS)

    Aitouche, A.; Yang, Q.; Ould Bouamama, B.

    2011-05-01

    This paper presents a procedure dealing with the issue of fault detection and isolation (FDI) using nonlinear analytical redundancy (NLAR) technique applied in a proton exchange membrane (PEM) fuel cell system based on its mathematic model. The model is proposed and simplified into a five orders state space representation. The transient phenomena captured in the model include the compressor dynamics, the flow characteristics, mass and energy conservation and manifold fluidic mechanics. Nonlinear analytical residuals are generated based on the elimination of the unknown variables of the system by an extended parity space approach to detect and isolate actuator and sensor faults. Finally, numerical simulation results are given corresponding to a faults signature matrix.

  3. Analysis of an energy recovery system for reformate-based PEM fuel cells involving a binary two-phase mixture

    NASA Astrophysics Data System (ADS)

    Cao, Yiding

    A comprehensive analysis on a novel energy recovery system for reformate-based proton exchange membrane (PEM) fuel cell systems is presented. The energy recovery system includes a throttling valve, a heat exchanger, a compressor, and is coupled with a coolant loop for the fuel cell stack. The feed stock of the fuel reformer, which is primarily a mixture of water and fuel, is vaporized in the heat exchanger and is then compressed to a sufficiently high pressure before it is ducted into the fuel reformer. The analysis includes the throttling of two-phase fuel/water mixture and vaporization in the heat exchanger to obtain the temperature and pressure of the mixture at the inlet of the compressor. The results indicate that the power plant efficiency with the energy recovery system can be increased by more than 20% compared to that of a fuel cell power plant without the energy recovery system. Additionally, more than 25% of the waste heat generated by the fuel cell stack can be removed due to the energy recovery system, and the fuel burned for the fuel reforming purpose is reduced by more than 70%.

  4. Research and development of proton-exchange membrane (PEM) fuel cell system for transportation applications. Phase I final report

    SciTech Connect

    1996-01-01

    Objective during Phase I was to develop a methanol-fueled 10-kW fuel cell power source and evaluate its feasibility for transportation applications. This report documents research on component (fuel cell stack, fuel processor, power source ancillaries and system sensors) development and the 10-kW power source system integration and test. The conceptual design study for a PEM fuel cell powered vehicle was documented in an earlier report (DOE/CH/10435-01) and is summarized herein. Major achievements in the program include development of advanced membrane and thin-film low Pt-loaded electrode assemblies that in reference cell testing with reformate-air reactants yielded performance exceeding the program target (0.7 V at 1000 amps/ft{sup 2}); identification of oxidation catalysts and operating conditions that routinely result in very low CO levels ({le} 10 ppm) in the fuel processor reformate, thus avoiding degradation of the fuel cell stack performance; and successful integrated operation of a 10-kW fuel cell stack on reformate from the fuel processor.

  5. Radiation grafted and sulfonated (FEP-g-polysterene) - An alternative to perfluorinated membranes for PEM fuel cells?

    NASA Astrophysics Data System (ADS)

    Buechi, F. N.; Gupta, B.; Rouilly, M.; Hauser, P. C.; Chapiro, A.; Scherer, G. G.

    Partially fluorinated proton exchange membranes (PEMs) were synthesized for fuel cell applications by simultaneous radiation grafting of styrene on FEP films followed by sulfonation. Properties of the synthesized membranes can be tailored by varying the degree of grafting and crosslinking. The performance of these membranes was tested in H2/O2 fuel cells. Long time testing showed steady performance for high grafted membranes over periods of more than 300 h at a cell temperature of 60 C. Low grafted membranes and the Morgane CDS membrane showed considerable decay of cell power on the same time scale. A fast degradation of all membranes occurred at a cell temperature of 80 C. It is noted that grafting in film form makes this process a potentially cheap and easy technique for the preparation of solid polymer fuel cell electrolytes.

  6. PEM fuel cell stack testing in the framework of an EU-harmonized fuel cell testing protocol: Results for an 11 kW stack

    NASA Astrophysics Data System (ADS)

    Bove, Roberto; Malkow, Thomas; Saturnio, Antonio; Tsotridis, Georgios

    Fuel cell testing and standardization thematic network (FCTESTNET) was a Thematic Network funded by the European Commission under the Fifth Framework Program (FP5), which was comprised of 55 European partners. The project concluded in 2006 and the main output was the collection and compilation of agreed testing procedures for different fuel cell technologies (PEM, SOFC, MCFC), applications (stationary, portable, transport), as well as balance of plant. Experimental validation of such testing procedures is the next necessary step for obtaining reliable harmonized testing procedures. The Joint Research Centre (JRC), Institute for Energy (IE) has started the validation process on selected PEM testing procedures. One of the FCTESTNET procedures applied at JRC-IE is the polarization curve for a PEM stack. Results show that the harmonization of some parameters, such as the acquisition and equilibrium time for each value of the current density, and the control of the stack coolant temperature, is a necessary action for an objective and trustworthy comparison of the performance data.

  7. PEM (Proton exchange membrane) fuel cell stack heat and mass measurement

    SciTech Connect

    Vanderborgh, N.E.; Kimble, M.C.; Huff, J.R.; Hedstrom, J.C.

    1992-08-01

    PEM stacks are under evaluation as candidates for future space power technology. Results of long-term operation on a set of contemporary stacks fitted with different proton exchange membrane materials are given. Data on water balances show effects of membrane materials on stack performance. 15 refs.

  8. PEM (Proton exchange membrane) fuel cell stack heat and mass measurement

    SciTech Connect

    Vanderborgh, N.E.; Kimble, M.C.; Huff, J.R.; Hedstrom, J.C.

    1992-01-01

    PEM stacks are under evaluation as candidates for future space power technology. Results of long-term operation on a set of contemporary stacks fitted with different proton exchange membrane materials are given. Data on water balances show effects of membrane materials on stack performance. 15 refs.

  9. Diesel fuel processor for PEM fuel cells: Two possible alternatives (ATR versus SR)

    NASA Astrophysics Data System (ADS)

    Cutillo, A.; Specchia, S.; Antonini, M.; Saracco, G.; Specchia, V.

    There are large efforts in exploring the on-board reforming technologies, which would avoid the actual lack of hydrogen infrastructure and related safety issues. From this view point, the present work deals with the comparison between two different 10 kW e fuel processors (FP) systems for the production of hydrogen-rich fuel gas starting from diesel oil, based respectively on autothermal (ATR) and steam-reforming (SR) process and related CO clean-up technologies; the obtained hydrogen rich gas is fed to the PEMFC stack of an auxiliary power unit (APU). Based on a series of simulations with Matlab/Simulink, the two systems were compared in terms of FP and APU efficiency, hydrogen concentration fed to the FC, water balance and process scheme complexity. Notwithstanding a slightly higher process scheme complexity and a slightly more difficult water recovery, the FP based on the SR scheme, as compared to the ATR one, shows higher efficiency and larger hydrogen concentration for the stream fed to the PEMFC anode, which represent key issues for auxiliary power generation based on FCs as compared, e.g. to alternators.

  10. Engineered Nano-scale Ceramic Supports for PEM Fuel Cells. Tech Team Meeting Presentaion

    SciTech Connect

    Brosha, Eric L.; Elbaz Alon, Lior; Henson, Neil J.; Rockward, Tommy; Roy, Aaron; Serov, Alexey; Ward, Timothy

    2012-08-13

    Catalyst support durability is currently a technical barrier for commercialization of polymer electrolyte membrane (PEM) fuel cells, especially for transportation applications. Degradation and corrosion of the conventional carbon supports leads to losses in active catalyst surface area and, consequently, reduced performance. As a result, the goal of this work is to develop support materials that interact strongly with Pt, yet sustain bulk-like catalytic activities with very highly dispersed particles. Ceramic materials that are prepared using conventional solid-state methods have large grain sizes and low surface areas that can only be minimally ameliorated through grinding and ball milling. Other synthesis routes to produce ceramic materials must be investigated and utilized in order to obtain desired surface areas. In this work, several different synthesis methods are being utilized to prepare electronically conductive ceramic boride, nitride, and oxide materials with high surface areas and have the potential for use as PEMFC catalyst supports. Polymer-assisted deposition (PAD) and aerosol-through plasma (A-T-P) torch are among several methods used to obtain ceramic materials with surface areas that are equal to, or exceed Vulcan XC-72R supports. Cubic Mo-based ceramic phases have been prepared with average XRD-determined crystallite sizes as low as 1.6 nm (from full profile, XRD fitting) and a BET surface area exceeding 200 m{sup 2}/g. Additionally, black, sub-stoichiometric TiO{sub 2-x}, have been prepared with an average crystallite size in the 4 nm range and surface areas exceeding 250 m{sup 2}/gr. Pt disposition using an incipient wetness approach produced materials with activity for hydrogen redox reactions and ORR. Cyclic voltammetry data will be shown for a variety of potential Pt/ceramic catalysts. Initial experiments indicate enhanced Pt metal-support interactions as well. Plane wave periodic density functional calculations (VASP) are being used to

  11. 2005 DOE Hydrogen Program Review PresentationCOST AND PERFORMANCE ENHANCEMENTS FOR A PEM FUEL CELL TURBOCOMPRESSOR

    SciTech Connect

    Mark K. Gee

    2005-04-01

    The objectives of the program during the past year was to complete Technical Objectives 2 and 3 and initiate Technical Objective 4 are described. To assist the Department of Energy in the development of a low cost, reliable and high performance air compressor/expander. Technical Objective 1: Perform a turbocompressor systems PEM fuel cell trade study to determine the enhanced turbocompressor approach. Technical Objective 2: Using the results from technical objective 1, an enhanced turbocompressor will be fabricated. The design may be modified to match the flow requirements of a selected fuel cell system developer. Technical Objective 3: Design a cost and performance enhanced compact motor and motor controller. Technical Objective 4: Turbocompressor/motor controller development.

  12. Properties of graphite-stainless steel composite in bipolar plates in simulated anode and cathode environments of PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Włodarczyk, Renata

    2014-09-01

    The use of a graphite-stainless steel composite as bipolar plates (BP) in polymer electrolyte membrane fuel cells (PEMFCs) has been evaluated. The study covers measurements of mechanical properties, microstructural examination, analysis of surface profile, wettability, porosity and corrosion resistance of the composite. The corrosion properties of the composite were examined in 0.1 mol·dm-3 H2SO4 + 2 ppm F- saturated with H2 or with O2 and in solutions with different pH: in Na2SO4+ 2 ppm F- (pH = 1.00, 3.00, 5.00) at 80 °C. The performed tests indicate that the graphite modified with stainless steel can be a good choice to be used as a bipolar plate in PEM fuel cells.

  13. Micro reactor integrated μ-PEM fuel cell system: a feed connector and flow field free approach

    NASA Astrophysics Data System (ADS)

    Balakrishnan, A.; Mueller, C.; Reinecke, H.

    2013-12-01

    A system level microreactor concept for hydrogen generation with Sodium Borohydride (NaBH4) is demonstrated. The uniqueness of the system is the transport and distribution feature of fuel (hydrogen) to the anode of the fuel cell without any external feed connectors and flow fields. The approach here is to use palladium film instead of feed connectors and the flow fields; palladium's property to adsorb and desorb the hydrogen at ambient and elevated condition. The proof of concept is demonstrated with a polymethyl methacrylate (PMMA) based complete system integration which includes microreactor, palladium transport layer and the self-breathing polymer electrolyte membrane (PEM) fuel cell. The hydrolysis of NaBH4 was carried out in the presence of platinum supported by nickel (NiPt). The prototype functionality is tested with NaBH4 chemical hydride. The characterization of the integrated palladium layer and fuel cell is tested with constant and switching load. The presented integrated fuel cell is observed to have a maximum power output and current of 60 mW and 280 mA respectively.

  14. Direct-hydrogen-fueled proton-exchange-membrane (PEM) fuel cell system for transportation applications. Quarterly technical progress report No. 4, April 1, 1995--June 30, 1995

    SciTech Connect

    Oei, D.

    1995-08-03

    This is the fourth Technical Progress Report for DOE Contract No. DE-AC02-94CE50389 awarded to Ford Motor Company on July 1, 1994. The overall objective of this contract is to advance the Proton-Exchange-Membrane (PEM) fuel cell technology for automotive applications. Specifically, the objectives resulting from this contract are to: (1) Develop and demonstrate on a laboratory propulsion system within 2-1/2 years a fully functional PEM Fuel Cell Power System (including fuel cell peripherals, peak power augmentation and controls). This propulsion system will achieve, or will be shown to have the growth potential to achieve, the weights, volumes, and production costs which are competitive with those same attributes of equivalently performing internal combustion engine propulsion systems; (2) Select and demonstrate a baseline onboard hydrogen storage method with acceptable weight, volume, cost, and safety features and analyze future alternatives; and (3) Analyze the hydrogen infrastructure components to ensure that hydrogen can be safely supplied to vehicles at geographically widespread convenient sites and at prices which are less than current gasoline prices per vehicle-mile; (4) Identify any future R&D needs for a fully integrated vehicle and for achieving the system cost and performance goals.

  15. Evolutionary programming-based methodology for economical output power from PEM fuel cell for micro-grid application

    NASA Astrophysics Data System (ADS)

    El-Sharkh, M. Y.; Rahman, A.; Alam, M. S.

    This paper presents a methodology for finding the optimal output power from a PEM fuel cell power plant (FCPP). The FCPP is used to supply power to a small micro-grid community. The technique used is based on evolutionary programming (EP) to find a near-optimal solution of the problem. The method incorporates the Hill-Climbing technique (HCT) to maintain feasibility during the solution process. An economic model of the FCPP is used. The model considers the production cost of energy and the possibility of selling and buying electrical energy from the local grid. In addition, the model takes into account the thermal energy output from the FCPP and the thermal energy requirement for the micro-grid community. The results obtained are compared against a solution based on genetic algorithms. Results are encouraging and indicate viability of the proposed technique.

  16. Design, Fabrication and Prototype testing of a Chip Integrated Micro PEM Fuel Cell Accumulator combined On-Board Range Extender

    NASA Astrophysics Data System (ADS)

    Balakrishnan, A.; Mueller, C.; Reinecke, H.

    2014-11-01

    In this work we present the design, fabrication and prototype testing of Chip Integrated Micro PEM Fuel Cell Accumulator (CIμ-PFCA) combined On-Board Range Extender (O-BRE). CIμ-PFCA is silicon based micro-PEM fuel cell system with an integrated hydrogen storage feature (palladium metal hydride), the run time of CIμ-PFCA is dependent on the stored hydrogen, and in order to extend its run time an O-BRE is realized (catalytic hydrolysis of chemical hydride, NaBH4. Combining the CIμ-PFCA and O-BRE on a system level have few important design requirements to be considered; hydrogen regulation, gas -liquid separator between the CIμ-PFCA and the O-RE. The usage of traditional techniques to regulate hydrogen (tubes), gas-liquid phase membranes (porous membrane separators) are less desirable in the micro domain, due to its space constraint. Our approach is to use a passive hydrogen regulation and gas-liquid phase separation concept; to use palladium membrane. Palladium regulates hydrogen by concentration diffusion, and its property to selectively adsorb only hydrogen is used as a passive gas-liquid phase separator. Proof of concept is shown by realizing a prototype system. The system is an assembly of CIμ-PFCA, palladium membrane and the O-BRE. The CIμ-PFCA consist of 2 individually processed silicon chips, copper supported palladium membrane realized by electroplating followed by high temperature annealing process under inter atmosphere and the O-BRE is realized out of a polymer substrate by micromilling process with platinum coated structures, which functions as a catalyst for the hydrolysis of NaBH4. The functionality of the assembled prototype system is demonstrated by the measuring a unit cell (area 1 mm2) when driven by the catalytic hydrolysis of chemical hydride (NaBH4 and the prototype system shows run time more than 15 hours.

  17. In-situ diagnostic tools for hydrogen transfer leak characterization in PEM fuel cell stacks part II: Operational applications

    NASA Astrophysics Data System (ADS)

    Niroumand, Amir M.; Homayouni, Hooman; DeVaal, Jake; Golnaraghi, Farid; Kjeang, Erik

    2016-08-01

    This paper describes a diagnostic tool for in-situ characterization of the rate and distribution of hydrogen transfer leaks in Polymer Electrolyte Membrane (PEM) fuel cell stacks. The method is based on reducing the air flow rate from a high to low value at a fixed current, while maintaining an anode overpressure. At high air flow rates, the reduction in air flow results in lower oxygen concentration in the cathode and therefore reduction in cell voltages. Once the air flow rate in each cell reaches a low value at which the cell oxygen-starves, the voltage of the corresponding cell drops to zero. However, oxygen starvation results from two processes: 1) the electrochemical oxygen reduction reaction which produces current; and 2) the chemical reaction between oxygen and the crossed over hydrogen. In this work, a diagnostic technique has been developed that accounts for the effect of the electrochemical reaction on cell voltage to identify the hydrogen leak rate and number of leaky cells in a fuel cell stack. This technique is suitable for leak characterization during fuel cell operation, as it only requires stack air flow and voltage measurements, which are readily available in an operational fuel cell system.

  18. Performance Evaluation of Electrochem's PEM Fuel Cell Power Plant for NASA's 2nd Generation Reusable Launch Vehicle

    NASA Technical Reports Server (NTRS)

    Kimble, Michael C.; Hoberecht, Mark

    2003-01-01

    NASA's Next Generation Launch Technology (NGLT) program is being developed to meet national needs for civil and commercial space access with goals of reducing the launch costs, increasing the reliability, and reducing the maintenance and operating costs. To this end, NASA is considering an all- electric capability for NGLT vehicles requiring advanced electrical power generation technology at a nominal 20 kW level with peak power capabilities six times the nominal power. The proton exchange membrane (PEM) fuel cell has been identified as a viable candidate to supply this electrical power; however, several technology aspects need to be assessed. Electrochem, Inc., under contract to NASA, has developed a breadboard power generator to address these technical issues with the goal of maximizing the system reliability while minimizing the cost and system complexity. This breadboard generator operates with dry hydrogen and oxygen gas using eductors to recirculate the gases eliminating gas humidification and blowers from the system. Except for a coolant pump, the system design incorporates passive components allowing the fuel cell to readily follow a duty cycle profile and that may operate at high 6:1 peak power levels for 30 second durations. Performance data of the fuel cell stack along with system performance is presented to highlight the benefits of the fuel cell stack design and system design for NGLT vehicles.

  19. Platinized Graphene/ceramics Nano-sandwiched Architectures and Electrodes with Outstanding Performance for PEM Fuel Cells.

    PubMed

    Chen, Xu; He, Daping; Wu, Hui; Zhao, Xiaofeng; Zhang, Jian; Cheng, Kun; Wu, Peng; Mu, Shichun

    2015-01-01

    For the first time a novel oxygen reduction catalyst with a 3D platinized graphene/nano-ceramic sandwiched architecture is successfully prepared by an unusual method. Herein the specific gravity of graphene nanosheets (GNS) is tailored by platinizing graphene in advance to shorten the difference in the specific gravity between carbon and SiC materials, and then nano-SiC is well intercalated into GNS interlayers. This nano-architecture with highly dispersed Pt nanoparticles exhibits a very high oxygen reduction reaction (ORR) activity and polymer electrolyte membrane (PEM) fuel cell performance. The mass activity of half cells is 1.6 times of that of the GNS supported Pt, and 2.4 times that of the commercial Pt/C catalyst, respectively. Moreover, after an accelerated stress test our catalyst shows a predominantly electrochemical stability compared with benchmarks. Further fuel cell tests show a maximum power density as high as 747 mW/cm(2) at low Pt loading, which is more than 2 times higher than that of fuel cells with the pristine graphene electrode. PMID:26538366

  20. Platinized Graphene/ceramics Nano-sandwiched Architectures and Electrodes with Outstanding Performance for PEM Fuel Cells

    NASA Astrophysics Data System (ADS)

    Chen, Xu; He, Daping; Wu, Hui; Zhao, Xiaofeng; Zhang, Jian; Cheng, Kun; Wu, Peng; Mu, Shichun

    2015-11-01

    For the first time a novel oxygen reduction catalyst with a 3D platinized graphene/nano-ceramic sandwiched architecture is successfully prepared by an unusual method. Herein the specific gravity of graphene nanosheets (GNS) is tailored by platinizing graphene in advance to shorten the difference in the specific gravity between carbon and SiC materials, and then nano-SiC is well intercalated into GNS interlayers. This nano-architecture with highly dispersed Pt nanoparticles exhibits a very high oxygen reduction reaction (ORR) activity and polymer electrolyte membrane (PEM) fuel cell performance. The mass activity of half cells is 1.6 times of that of the GNS supported Pt, and 2.4 times that of the commercial Pt/C catalyst, respectively. Moreover, after an accelerated stress test our catalyst shows a predominantly electrochemical stability compared with benchmarks. Further fuel cell tests show a maximum power density as high as 747 mW/cm2 at low Pt loading, which is more than 2 times higher than that of fuel cells with the pristine graphene electrode.

  1. Platinized Graphene/ceramics Nano-sandwiched Architectures and Electrodes with Outstanding Performance for PEM Fuel Cells

    PubMed Central

    Chen, Xu; He, Daping; Wu, Hui; Zhao, Xiaofeng; Zhang, Jian; Cheng, Kun; Wu, Peng; Mu, Shichun

    2015-01-01

    For the first time a novel oxygen reduction catalyst with a 3D platinized graphene/nano-ceramic sandwiched architecture is successfully prepared by an unusual method. Herein the specific gravity of graphene nanosheets (GNS) is tailored by platinizing graphene in advance to shorten the difference in the specific gravity between carbon and SiC materials, and then nano-SiC is well intercalated into GNS interlayers. This nano-architecture with highly dispersed Pt nanoparticles exhibits a very high oxygen reduction reaction (ORR) activity and polymer electrolyte membrane (PEM) fuel cell performance. The mass activity of half cells is 1.6 times of that of the GNS supported Pt, and 2.4 times that of the commercial Pt/C catalyst, respectively. Moreover, after an accelerated stress test our catalyst shows a predominantly electrochemical stability compared with benchmarks. Further fuel cell tests show a maximum power density as high as 747 mW/cm2 at low Pt loading, which is more than 2 times higher than that of fuel cells with the pristine graphene electrode. PMID:26538366

  2. Electrochemical energy storage using PEM systems

    SciTech Connect

    Vanderborgh, N.E.; Hedstrom, J.C.; Huff, J.R.

    1991-01-01

    This paper gives the results of an engineering assessment for future, long-lived space power systems for extraterrestrial applications. Solar-based, regenerative fuel cell power plants formed from either alkaline or PEM components are the focus. Test results on advanced PEM fuel cell stack components are presented. 7 refs., 4 figs., 1 tab.

  3. Experimental investigation of water droplet-air flow interaction in a non-reacting PEM fuel cell channel

    NASA Astrophysics Data System (ADS)

    Esposito, Angelo; Montello, Aaron D.; Guezennec, Yann G.; Pianese, Cesare

    It has been well documented that water production in PEM fuel cells occurs in discrete locations, resulting in the formation and growth of discrete droplets on the gas diffusion layer (GDL) surface within the gas flow channels (GFCs). This research uses a simulated fuel cell GFC with three transparent walls in conjunction with a high speed fluorescence photometry system to capture videos of dynamically deforming droplets. Such videos clearly show that the droplets undergo oscillatory deformation patterns. Although many authors have previously investigated the air flow induced droplet detachment, none of them have studied these oscillatory modes. The novelty of this work is to process and analyze the recorded videos to gather information on the droplets induced oscillation. Plots are formulated to indicate the dominant horizontal and vertical deformation frequency components over the range of sizes of droplets from formation to detachment. The system is also used to characterize droplet detachment size at a variety of channel air velocities. A simplified model to explain the droplet oscillation mechanism is provided as well.

  4. Measurement of effective gas diffusion coefficients of catalyst layers of PEM fuel cells with a Loschmidt diffusion cell

    NASA Astrophysics Data System (ADS)

    Shen, Jun; Zhou, Jianqin; Astrath, Nelson G. C.; Navessin, Titichai; Liu, Zhong-Sheng (Simon); Lei, Chao; Rohling, Jurandir H.; Bessarabov, Dmitri; Knights, Shanna; Ye, Siyu

    In this work, using an in-house made Loschmidt diffusion cell, we measure the effective coefficient of dry gas (O 2-N 2) diffusion in cathode catalyst layers of PEM fuel cells at 25 °C and 1 atmosphere. The thicknesses of the catalyst layers under investigation are from 6 to 29 μm. Each catalyst layer is deposited on an Al 2O 3 membrane substrate by an automated spray coater. Diffusion signal processing procedure is developed to deduce the effective diffusion coefficient, which is found to be (1.47 ± 0.05) × 10 -7 m 2 s -1 for the catalyst layers. Porosity and pore size distribution of the catalyst layers are also measured using Hg porosimetry. The diffusion resistance of the interface between the catalyst layer and the substrate is found to be negligible. The experimental results show that the O 2-N 2 diffusion in the catalyst layers is dominated by the Knudsen effect.

  5. SYSTEMS MODELING OF AMMONIA BORANE BEAD REACTOR FOR OFF-BOARD REGENERABLE HYDROGEN STORAGE IN PEM FUEL CELL APPLICATIONS

    SciTech Connect

    Brooks, Kriston P.; Devarakonda, Maruthi N.; Rassat, Scot D.; King, Dale A.; Herling, Darrell R.

    2010-06-01

    Out of the materials available for chemical hydrogen storage in PEM fuel cell applications, ammonia borane (AB, NH3BH3) has a high hydrogen storage capacity (upto 19.6% by weight for the release of three hydrogen molecules). Therefore, AB was chosen in our chemical hydride simulation studies. A model for the AB bead reactor system was developed to study the system performance and determine the energy, mass and volume requirements for off-board regenerable hydrogen storage. The system includes hot and cold augers, ballast tank and reactor, product tank, H2 burner and a radiator. One dimensional models based on conservation of mass, species and energy were used to predict important state variables such as reactant and product concentrations, temperatures of various components, flow rates, along with pressure in the reactor system. Control signals to various components are governed by a control system which is modeled as an independent subsystem. Various subsystem components in the models were coded as C language S-functions and implemented in Matlab/Simulink environment. Preliminary system simulation results for a start-up case and for a transient drive cycle indicate accurate trends in the reactor system dynamics.

  6. Magnetic resonance imaging of water content across the Nafion membrane in an operational PEM fuel cell.

    PubMed

    Zhang, Ziheng; Martin, Jonathan; Wu, Jinfeng; Wang, Haijiang; Promislow, Keith; Balcom, Bruce J

    2008-08-01

    Water management is critical to optimize the operation of polymer electrolyte membrane fuel cells. At present, numerical models are employed to guide water management in such fuel cells. Accurate measurements of water content variation in polymer electrolyte membrane fuel cells are required to validate these models and to optimize fuel cell behavior. We report a direct water content measurement across the Nafion membrane in an operational polymer electrolyte membrane fuel cell, employing double half k-space spin echo single point imaging techniques. The MRI measurements with T2 mapping were undertaken with a parallel plate resonator to avoid the effects of RF screening. The parallel plate resonator employs the electrodes inherent to the fuel cell to create a resonant circuit at RF frequencies for MR excitation and detection, while still operating as a conventional fuel cell at DC. Three stages of fuel cell operation were investigated: activation, operation and dehydration. Each profile was acquired in 6 min, with 6 microm nominal resolution and a SNR of better than 15. PMID:18555714

  7. A practical PEM fuel cell model for simulating vehicle power sources

    SciTech Connect

    Amphlett, J.C.; Mann, R.F.; Peppley, B.A.; Roberge, P.R.; Rodrigues, A.

    1995-07-01

    The interest in fuel cell technology as an alternative to internal combustion engines is growing rapidly with the increased concern with environmental issues such s reducing vehicle emissions. Fuel cells offer a power source which produces electrical energy from fuel and oxidant which produce little or no emissions. Fuel cell power sources are being considered for both terrestrial and marine applications. The research and commercialization of such systems require system modeling to determine performance levels and fuel and oxidant requirements. A practical model will have to be flexible in its calculations depending on the information available. A model predicting the performance of a proton exchange membrane fuel cell has been developed for a Ballard Mark V 5 kW 35-cell stack. The parametric model combining both empirical and mechanistic qualities was developed to calculate the cell voltage output in terms of complex relationships between current, stack temperature, and inlet partial pressure of hydrogen and oxygen. The model utilizes an iterative computer solution to obtain a practical flexible model which could calculate any variable in terms of the others. This paper illustrates the use of a practical model to determine the fuel and oxidant requirements to achieve various levels of power required for different vehicle power supplies. Applications to automobiles, buses, locomotives, ships, submarines, and unmanned underwater vehicles with power supplies of 3--3,000 kW were investigated.

  8. Development of a 10 kW PEM fuel cell for stationary applications

    SciTech Connect

    Barthels, H.; Mergel, J.; Oetjen, H.F.

    1996-12-31

    A 10 kW Proton Exchange Membrane Fuel Cell (PEMFC) is being developed as part of a long-term energy storage path for electricity in the photovoltaic demonstration plant called PHOEBUS at the Forschungszentrum Julich.

  9. Synthesis and Characterization of CO- and H2S-Tolerant Electrocatalysts for PEM Fuel Cell

    SciTech Connect

    Shamsuddin Ilias

    2006-05-18

    The present state-of-art Proton Exchange Membrane Fuel Cell (PEMFC) technology is based on platinum (Pt) as a catalyst for both the fuel (anode) and air (cathode) electrodes. This catalyst is highly active but susceptible to poisoning by CO, which may be present in the H{sub 2}-fuel used or may be introduced during the fuel processing. Presence of trace amount of CO and H{sub 2}S in the H{sub 2}-fuel poisons the anode irreversibly and decreases the performance of the PEMFCs. In an effort to reduce the Pt-loading and improve the PEMFC performance, we propose to synthesize a number of Pt-based binary, ternary, and quaternary electrocatalysts using Ru, Mo, Ir, Ni, and Co as a substitute for Pt. By fine-tuning the metal loadings and compositions of candidate electrocatalysts, we plan to minimize the cost and optimize the catalyst activity and performance in PEMFC. The feasibility of the novel electrocatalysts will be demonstrated in the proposed effort with gas phase CO and H{sub 2}S concentrations typical of those found in reformed fuel gas with coal/natural gas/methanol feedstocks. During this reporting period we used four Pt-based electrocatalysts (Pt/Ru/Mo/Se, Pt/Ru/Mo/Ir, Pt/Ru/Mo/W, Ptr/Ru/Mo/Co) in MEAs and these were evaluated for CO-tolerance with 20 and 100 ppm CO concentration in H{sub 2}-fuel. From current-voltage performance study, the catalytic activity was found in the increasing order of Pt/Ru/Mo/Ir > Pt/Ru/Mo/W > Pt/Ru/Mo/Co > Pt/Ru/MO/Se. From preliminary cost analysis it appears that could of the catalyst metal loading can reduced by 40% to 60% depending on the selection of metal combinations without compromising the fuel cell performance.

  10. Synthesis and Characterization of CO- and H2S-Tolerant Electrocatalysts for PEM Fuel Cell

    SciTech Connect

    Shamsuddin Ilias

    2006-09-30

    The present state-of-art Proton Exchange Membrane Fuel Cell (PEMFC) technology is based on platinum (Pt) as a catalyst for both the fuel (anode) and air (cathode) electrodes. This catalyst is highly active but susceptible to poisoning by CO, which may be present in the H{sub 2}-fuel used or may be introduced during the fuel processing. Presence of trace amount of CO and H{sub 2}S in the H{sub 2}-fuel poisons the anode irreversibly and decreases the performance of the PEMFCs. In an effort to reduce the Pt-loading and improve the PEMFC performance, we propose to synthesize a number of Pt-based binary, ternary, and quaternary electrocatalysts using Ru, Mo, Ir, Ni, and Co as a substitute for Pt. By fine-tuning the metal loadings and compositions of candidate electrocatalysts, we plan to minimize the cost and optimize the catalyst activity and performance in PEMFC. The feasibility of the novel electrocatalysts will be demonstrated in the proposed effort with gas phase CO and H{sub 2}S concentrations typical of those found in reformed fuel gas with coal/natural gas/methanol feedstocks. In this work binary, ternary, and quaternary platinum-based electrocatalysts were synthesized for the purpose of lowering the cost and increasing the CO tolerance of the membrane electrode assembly (MEA) in the fuel cell. The metals Ru, Mo, W, Ir, Co and Se were alloyed with platinum on a carbon support using a modified reduction method. These catalysts were fabricated into MEAs and evaluated for electrical performance and CO tolerance with polarization experiments. The quaternary system Pt/Ru/Mo/Ir system is the most CO tolerant in the PEMFC and has a low total metal loading of 0.4 mg/cm{sup 2} in the electrode of the cell.

  11. Inorganic-based proton conductive composite membranes for elevated temperature and reduced relative humidity PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Wang, Chunmei

    Proton exchange membrane (PEM) fuel cells are regarded as highly promising energy conversion systems for future transportation and stationary power generation and have been under intensive investigations for the last decade. Unfortunately, cutting edge PEM fuel cell design and components still do not allow economically commercial implementation of this technology. The main obstacles are high cost of proton conductive membranes, low-proton conductivity at low relative humidity (RH), and dehydration and degradation of polymer membranes at high temperatures. The objective of this study was to develop a systematic approach to design a high proton conductive composite membrane that can provide a conductivity of approximately 100 mS cm-1 under hot and dry conditions (120°C and 50% RH). The approach was based on fundamental and experimental studies of the proton conductivity of inorganic additives and composite membranes. We synthesized and investigated a variety of organic-inorganic Nafion-based composite membranes. In particular, we analyzed their fundamental properties, which included thermal stability, morphology, the interaction between inorganic network and Nafion clusters, and the effect of inorganic phase on the membrane conductivity. A wide range of inorganic materials was studied in advance in order to select the proton conductive inorganic additives for composite membranes. We developed a conductivity measurement method, with which the proton conductivity characteristics of solid acid materials, zirconium phosphates, sulfated zirconia (S-ZrO2), phosphosilicate gels, and Santa Barbara Amorphous silica (SBA-15) were discussed in detail. Composite membranes containing Nafion and different amounts of functionalized inorganic additives (sulfated inorganics such as S-ZrO2, SBA-15, Mobil Composition of Matter MCM-41, and S-SiO2, and phosphonated inorganic P-SiO2) were synthesized with different methods. We incorporated inorganic particles within Nafion clusters

  12. Studies on Methanol Crossover in Liquid-Feed Direct Methanol Pem Fuel Cells

    NASA Technical Reports Server (NTRS)

    Narayanan, S. R.

    1995-01-01

    The performance of liquid feed direct methanol fuel cells using various types of Nafion membranes as the solid polymer electrolyte have been studied. The rate of fuel crossover and electrical performance has been measured for cells with Nafion membranes of various thicknesses and equivalent weights. The crossover rate is found to decrease with increasing thickness and applied current. The dependence of crossover rate on current density can be understood in terms of a simple linear diffusion model which suggests that the crossover rate can be influenced by the electrode structure in addition to the membrane. The studies suggest that Nafion EW 1500 is a very promising alternate to Nafion EW 1100 for direct methanol fuel cells.

  13. Materials, Proton Conductivity and Electrocatalysis in High-Temperature PEM Fuel Cells

    NASA Astrophysics Data System (ADS)

    Daletou, Maria K.; Kallitsis, Joannis; Neophytides, Stylianos G.

    Fuel cells (FCs) are interesting alternatives to existing power conversion systems since they combine high efficiency with the usage of renewable fuels. Fuel cells can generate power from a fraction of a watt to hundreds of kilowatts and can be used in automotive, stationary or portable applications.1,2,3,4,5,6 A FC is an electrochemical device that converts in a continuous manner the free energy of a chemical reaction into electrical energy (via an electrical current). This galvanic cell consists of an electrolyte (liquid or solid) sandwiched between two porous electrodes. In order to reach desirable amounts of energy power, single cell assemblies can be mechanically compressed across electrically conductive separators to fabricate stacks.

  14. Analysis of the energy efficiency of an integrated ethanol processor for PEM fuel cell systems

    NASA Astrophysics Data System (ADS)

    Francesconi, Javier A.; Mussati, Miguel C.; Mato, Roberto O.; Aguirre, Pio A.

    The aim of this work is to investigate the energy integration and to determine the maximum efficiency of an ethanol processor for hydrogen production and fuel cell operation. Ethanol, which can be produced from renewable feedstocks or agriculture residues, is an attractive option as feed to a fuel processor. The fuel processor investigated is based on steam reforming, followed by high- and low-temperature shift reactors and preferential oxidation, which are coupled to a polymeric fuel cell. Applying simulation techniques and using thermodynamic models the performance of the complete system has been evaluated for a variety of operating conditions and possible reforming reactions pathways. These models involve mass and energy balances, chemical equilibrium and feasible heat transfer conditions (Δ T min). The main operating variables were determined for those conditions. The endothermic nature of the reformer has a significant effect on the overall system efficiency. The highest energy consumption is demanded by the reforming reactor, the evaporator and re-heater operations. To obtain an efficient integration, the heat exchanged between the reformer outgoing streams of higher thermal level (reforming and combustion gases) and the feed stream should be maximized. Another process variable that affects the process efficiency is the water-to-fuel ratio fed to the reformer. Large amounts of water involve large heat exchangers and the associated heat losses. A net electric efficiency around 35% was calculated based on the ethanol HHV. The responsibilities for the remaining 65% are: dissipation as heat in the PEMFC cooling system (38%), energy in the flue gases (10%) and irreversibilities in compression and expansion of gases. In addition, it has been possible to determine the self-sufficient limit conditions, and to analyze the effect on the net efficiency of the input temperatures of the clean-up system reactors, combustion preheating, expander unit and crude ethanol as

  15. Synthesis and Characterization of CO- and H2S- Tolerant Electrocatalysts for PEM Fuel Cell

    SciTech Connect

    Shamsuddin Ilias

    2006-12-31

    The present state-of-art Proton Exchange Membrane Fuel Cell (PEMFC) technology is based on platinum (Pt) as a catalyst for both the fuel (anode) and air (cathode) electrodes. This catalyst is highly active but susceptible to poisoning by CO, which may be present in the H{sub 2}-fuel used or may be introduced during the fuel processing. Presence of trace amount of CO in the H{sub 2}-fuel poisons the anode irreversibly and decreases the performance of the PEMFCs. In an effort to reduce the Pt-loading and improve the PEMFC performance, we have synthesized a number of Pt-based binary, ternary, and quaternary electrocatalysts using Ru, Mo, Ir, Ni, and Co as a substitute for Pt. Co-catalytic activities were found for the elements Mo, Ru, and Ir. Both the ternary (Pt/Ru/Mo/C) and quaternary (Pt/Ru/Mo/Ir/C) metal catalysts in membrane electrode assemblies (MEA) outperformed pure Pt/C catalysts at all levels in presence of CO up to 100 ppm. Preliminary results suggest that by substituting Mo, Ru, and Ir in catalyst formulation, it is possible to reduce Pt-loading and increase CO-tolerance in PEMFC application. Comparison studies showed that the newly developed ternary and quaternary catalysts with lower Pt outperformed pure Pt catalyst in presence of CO-contaminated H{sub 2} fuel. High performance at low Pt loading of less than 0.4 mg/cm{sup 2} was achieved, thus exceeding the initial targets.

  16. Synthesis and Characterization of CO- and H2S-Tolerant Electrocatalysts for PEM Fuel Cell

    SciTech Connect

    Shamsuddin Ilias

    2005-07-20

    The present state-of-art Proton Exchange Membrane Fuel Cell (PEMFC) technology is based on platinum (Pt) as a catalyst for both the fuel (anode) and air (cathode) electrodes. This catalyst is highly active but susceptible to poisoning by CO, which may be present in the H{sub 2}-fuel used or may be introduced during the fuel processing. Presence of trace amount of CO and H{sub 2}S in the H{sub 2}-fuel poisons the anode irreversibly and decreases the performance of the PEMFCs. In an effort to reduce the Pt-loading and improve the PEMFC performance, we propose to synthesize a number of Pt-based binary, ternary, and quaternary electrocatalysts using Ru, Mo, Ir, Ni, and Co as a substitute for Pt. By fine-tuning the metal loadings and compositions of candidate electrocatalysts, we plan to minimize the cost and optimize the catalyst activity and performance in PEMFC. The feasibility of the novel electrocatalysts will be demonstrated in the proposed effort with gas phase CO and H{sub 2}S concentrations typical of those found in reformed fuel gas with coal/natural gas/methanol feedstocks. During this reporting period we synthesized several tri-metallic electrocatalysts catalysts (Pt/Ru/Mo, Pt/Ru/Ir, Pt/Ru/W, Ptr/Ru/Co, and Pt/Ru/Se on Vulcan XG72 Carbon) by ultrasonication method. These catalysts were tested in MEAs for CO tolerance at 20 and 100 ppm CO concentrations. From Galvonstatic study the catalytic activity was found in the order of: Pt/Ru/Mo/C > Pt/Ru/Ir/C > Pt/Ru/W/C > Ptr/Ru/Co/C > and Pt/Ru/Se. The catalysts performed very well at 20 ppm CO but at 100 ppm CO performance dropped significantly.

  17. A PEMS study of the emissions of gaseous pollutants and ultrafine particles from gasoline- and diesel-fueled vehicles

    NASA Astrophysics Data System (ADS)

    Huang, Cheng; Lou, Diming; Hu, Zhiyuan; Feng, Qian; Chen, Yiran; Chen, Changhong; Tan, Piqiang; Yao, Di

    2013-10-01

    On-road emission measurements of gasoline- and diesel-fueled vehicles were conducted by a portable emission measurement system (PEMS) in Shanghai, China. Horiba OBS 2200 and TSI EEPS 3090 were employed to detect gaseous and ultrafine particle emissions during the tests. The driving-based emission factors of gaseous pollutants and particle mass and number were obtained on various road types. The average NOx emission factors of the diesel bus, diesel car, and gasoline car were 8.86, 0.68, and 0.17 g km-1, all of which were in excess of their emission limits. The particle number emission factors were 7.06 × 1014, 6.08 × 1014, and 1.57 × 1014 km-1, generally higher than the results for similar vehicle types reported in the previous studies. The size distributions of the particles emitted from the diesel vehicles were mainly concentrated in the accumulation mode, while those emitted from the gasoline car were mainly distributed in the nucleation mode. Both gaseous and particle emission rates exhibit significant correlations with the change in vehicle speed and power demand. The lowest emission rates for each vehicle type were produced during idling. The highest emission rates for each vehicle type were generally found in high-VSP bins. The particle number emission rates of the gasoline car show the strongest growth trend with increasing VSP and speed. The particle number emission for the gasoline car increased by 3 orders of magnitude from idling to the highest VSP and driving speed conditions. High engine power caused by aggressive driving or heavy loads is the main contributor to high emissions for these vehicles in real-world situations.

  18. Investigation on "saw-tooth" behavior of PEM fuel cell performance during shutdown and restart cycles

    NASA Astrophysics Data System (ADS)

    Qi, Zhigang; Tang, Hao; Guo, Qunhui; Du, Bin

    It was sometimes observed that the performance of a proton-exchange membrane fuel cell improved after the cell went through shutdown and restart cycles. Such a performance recovery led to a "saw-tooth" performance pattern when multiple shutdowns and restarts occurred during the endurance test of a fuel cell. The shutdowns included both planned shutdowns and unintended ones due to station trips or emergency stops (E-stops). The length of the shutdown periods ranged from a few minutes to several weeks. Although such a "saw-tooth" behavior could be attributed to multiple reasons such as: (1) catalyst surface oxidation state change; (2) catalyst surface cleansing; or (3) water management, we found that it was mainly related to water management in our cases after a systematic investigation employing both single cells and stacks.

  19. Using Heteropolyacids in the Anode Catalyst Layer of Dimethyl Ether PEM Fuel Cells

    SciTech Connect

    Ferrell III, J. R.; Turner, J. A.; Herring, A. M.

    2008-01-01

    In this study, polarization experiments were performed on a direct dimethyl ether fuel cell (DMEFC). The experimental setup allowed for independent control of water and DME flow rates. Thus the DME flow rate, backpressure, and water flow rate were optimized. Three heteropoly acids, phosphomolybdic acid (PMA), phosphotungstic acid (PTA), and silicotungstic acid (STA) were incorporated into the anode catalyst layer in combination with Pt/C. Both PTA-Pt and STA-Pt showed higher performance than the Pt control at 30 psig of backpressure. Anodic polarizations were also performed, and Tafel slopes were extracted from the data. The trends in the Tafel slope values are in agreement with the polarization data. The addition of phosphotungstic acid more than doubled the power density of the fuel cell, compared to the Pt control.

  20. The formation of protective nitride surfaces for PEM fuel cell metallic bipolar plates

    NASA Astrophysics Data System (ADS)

    Brady, M. P.; Yang, B.; Wang, H.; Turner, J. A.; More, K. L.; Wilson, M.; Garzon, F.

    2006-08-01

    The selective gas nitridation of model nickel-based alloys was used to form dense, electrically conductive and corrosion-resistant nitride surface layers, including TiN, VN, CrN, Cr2N, as wellas a complex NiNbVN phase. Evaluation for use as a protective surface for metallic bipolar plates in proton exchange membrane fuel cells (PEMFC) indicated that CrN/Cr2N based surfaces holdpromise to meet U.S. Department of Energy (DOE) performance goals for automative applications. The thermally grown CrN/Cr2N surface formed on model Ni-Cr based alloys exhibited good stability and low electrical resistance in single-cell fuel cell testing under simulated drive-cycle conditions. Recent results indicate that similar protective chromium nitride surfaces can be formed on less expensive Fe-Cr based alloys potentially capable of meeting DOE cost goals.

  1. Multiscale Structured and Functionally Graded Gas Diffusion Electrodes for PEM-Fuel Cells and Electrodialysis

    NASA Astrophysics Data System (ADS)

    Wolf, H.; Franz, M.; Bienhüls, C.; Willert-Porada, M.

    2008-02-01

    In the presented work, different methods of preparation of functionally graded gas diffusion electrodes (GDE) for fuel cell and electrodialysis application were investigated. High electrochemical performance with a low platinum catalyst content of only 0.1 mg/cm2 was achieved. The new GDEs are superior to commercial ones with five times higher platinum content, due to their optimized pore structure and improved distribution of catalyst and ion conductive polymer.

  2. "Dedicated To The Continued Education, Training and Demonstration of PEM Fuel Cell Powered Lift Trucks In Real-World Applications."

    SciTech Connect

    Dever, Thomas J.

    2011-11-29

    The project objective was to further assist in the commercialization of fuel cell and H2 technology by building further upon the successful fuel cell lift truck deployments that were executed by LiftOne in 2007, with longer deployments of this technology in real-world applications. We involved facilities management, operators, maintenance personnel, safety groups, and Authorities Having Jurisdiction. LiftOne strived to educate a broad group from many areas of industry and the community as to the benefits of this technology. Included were First Responders from the local areas. We conducted month long deployments with end-users to validate the value proposition and the market requirements for fuel cell powered lift trucks. Management, lift truck operators, Authorities Having Jurisdiction and the general public experienced 'hands on' fuel cell experience in the material handling applications. We partnered with Hydrogenics in the execution of the deployment segment of the program. Air Products supplied the compressed H2 gas and the mobile fueler. Data from the Fuel Cell Power Packs and the mobile fueler was sent to the DOE and NREL as required. Also, LiftOne conducted the H2 Education Seminars on a rotating basis at their locations for lift trucks users and for other selected segments of the community over the project's 36 month duration. Executive Summary The technology employed during the deployments program was not new, as the equipment had been used in several previous demos and early adoptions within the material handling industry. This was the case with the new HyPx Series PEM - Fuel Cell Power Packs used, which had been demo'd before during the 2007 Greater Columbia Fuel Cell Challenge. The Air Products HF-150 Fueler was used outdoors during the deployments and had similarly been used for many previous demo programs. The methods used centered on providing this technology as the power for electric sit-down lift trucks at high profile companies operating large

  3. A segmented model for studying water transport in a PEM fuel cell

    NASA Astrophysics Data System (ADS)

    Chen, Yong-Song

    Fuel Cells are devices that generate electricity by electrochemically combining hydrogen and oxygen. Water management plays an important role in the durability and efficiency of a proton exchange membrane fuel cell (PEMFC). In this study, single cells are modeled as lumped models consisting of 15 interconnected segments, which are linked according to the flow field patterns of the anode and cathode but they are treated as individual lumped elements. Parameters of this model were calibrated based on neutron radiography experimental results obtained at the NIST Center for Neutron Research (NCNR). Three special single cells were designed for the purpose of detecting liquid water and water vapor simultaneously. The major difference between our design and traditional flow field designs is the fact the anode channels and cathode channels were shifted sideways, so that the anode and cathode channels do not overlap in the majority of the active areas. The liquid water is measured by using neutron radiography. The water vapor is measured by the twenty relative humidity sensors embedded in the anode and the cathode flow field plates. The effects of relative humidity and stoichiometry of cathode inlet on relative humidity distribution in the channels and on water accumulation in the GDLs were investigated in this study. The liquid water accumulation at steady-state was calculated by using imaging mask techniques and least-squares method. It is demonstrated that liquid water tends to accumulates in the gas diffusion layers under the rib. Modeling results suggest that opposite flow direction improve the cell performance at low humidity conditions. Accordingly, this segmented model is useful in designing flow field patterns and comparing the influence of different flow field patterns before they are machined on the flow field plates. That reduces the cost of developing and designing a fuel cell.

  4. Design of graphene sheets-supported Pt catalyst layer in PEM fuel cells

    SciTech Connect

    Park, Seh K.; Shao, Yuyan; Wan, Haiying; Rieke, Peter C.; Viswanathan, Vilayanur V.; Towne, Silas A.; Saraf, Laxmikant V.; Liu, Jun; Lin, Yuehe; Wang, Yong

    2011-03-01

    A series of cathodes using Pt supported onto graphene sheets with different contents of carbon black in the catalyst layer were prepared and characterized. Carbon black was added as a spacer between two-dimensional graphene sheets in the catalyst layer to study its effect on the performances of proton exchange membrane fuel cell. Electrochemical properties and surface morphology of the cathodes with and without carbon black were characterized using cyclic voltammetry, ac-impedance spectroscopy, electrochemical polarization technique, and scanning electron microscopy. The results indicated that carbon black effectively modifies the array of graphene supports, resulting in more Pt nanoparticles available for electrochemical reaction and better mass transport in the catalyst layer.

  5. Evaluation of the effect of impregnated platinum on PFSA degradation for PEM fuel cells.

    SciTech Connect

    Rodgers, Marianne; Pearman, Benjamin P; Bonville, Leonard J.; Cullen, David A; Mohajeri, Nahid; Slattery, Darlene

    2013-01-01

    One of the main sources of membrane degradation in fuel cells is attack by radicals formed wherever Pt, H2, and O2 are present. The effect of Pt precipitated in the membrane is under debate. Although Pt can provide another site for radical formation, it can also scavenge hydrogen peroxide and radicals in the membrane and improve durability. In this work, the effects of Pt particles within the membrane are evaluated and related to membrane degradation. Membranes were ex situ impregnated with 0, 10, 30, and 50 mol% Pt and then tested for 100 h in a fuel cell, at 90 C/100% relative humidity. The highest degradation was observed with the membranes containing 10 mol% Pt, with fluoride emissions of the same magnitude as those of catalyst coated membranes containing Pt/C. Membranes containing 0, 30, and 50 mol% Pt resulted in very low fluoride emission. The high degradation in the 10 mol% membrane was attributed to the low density of platinum particles, which allows generated radicals to attack the membrane before being deactivated. In the 30 mol% and 50 mol% membranes, where the platinum particles were denser, the generated radicals became deactivated on neighboring particles before they attacked the membrane.

  6. Dynamic Model and Experimental Validation of a PEM Fuel Cell System

    NASA Astrophysics Data System (ADS)

    Nassif, Younane; Godoy, Emmanuel; Bethoux, Olivier; Roche, Ivan

    Fuel cells are expected to become a challenging technology in terms of efficiency, and fitting the emission reduction schedules [Lemons, J. Power Sources, 29:251, 1] for the automotive application. Their fundamental component consists of two electrodes separated by a membrane. Fuel cells convert chemical energy into electrical energy while producing water and heat. To not disturb the transportation of the reactant gas, a proper membrane hydration needs to be maintained. Two different conditions can occur facing an inadequate water balance which decreases the performance of the stack. An insufficient removal of the accumulated water causes water flooding, decreasing reactant transport rate. Similarly, excessive water removal dries the membrane. To monitor the amount of water inside the cell, dynamic model based on the mass conservation principles and thermodynamic properties is developed in the form of nonlinear state space representation. Fick's law and Maxwell-Stefan model are used to describe multicomponent diffusion. Darcy's law is used to define the porous medium permeability. To demonstrate the accuracy of the proposed model, obtained results are compared with measured data at steady states operation mode. Investigation of the steady-state behavior is discussed in this paper.

  7. Liquid-Water Uptake and Removal in PEM Fuel-Cell Components

    SciTech Connect

    Das, Prodip K.; Gunterman, Haluna P.; Kwong, Anthony; Weber, Adam Z.

    2011-09-23

    Management of liquid water is critical for optimal fuel-cell operation, especially at low temperatures. It is therefore important to understand the wetting properties and water holdup of the various fuel-cell layers. While the gas-diffusion layer is relatively hydrophobic and exhibits a strong intermediate wettability, the catalyst layer is predominantly hydrophilic. In addition, the water content of the ionomer in the catalyst layer is lower than that of the bulk membrane, and is affected by platinum surfaces. Liquid-water removal occurs through droplets on the surface of the gas-diffusion layer. In order to predict droplet instability and detachment, a force balance is used. While the pressure or drag force on the droplet can be derived, the adhesion or surface-tension force requires measurement using a sliding-angle approach. It is shown that droplets produced by forcing water through the gas-diffusion layer rather than placing them on top of it show much stronger adhesion forces owing to the contact to the subsurface water.

  8. Microwave-assisted synthesis of Pt/CNT nanocomposite electrocatalysts for PEM fuel cells.

    PubMed

    Zhang, Weimin; Chen, Jun; Swiegers, Gerhard F; Ma, Zi-Feng; Wallace, Gordon G

    2010-02-01

    Microwave-assisted heating of functionalized, single-wall carbon nanotubes (FCNTs) in ethylene glycol solution containing H(2)PtCl(6), led to the reductive deposition of Pt nanoparticles (2.5-4 nm) over the FCNTs, yielding an active catalyst for proton-exchange membrane fuel cells (PEMFCs). In single-cell testing, the Pt/FCNT composites displayed a catalytic performance that was superior to Pt nanoparticles supported by raw (unfunctionalized) CNTs (RCNTs) or by carbon black (C), prepared under identical conditions. The supporting single-wall carbon nanotubes (SWNTs), functionalized with carboxyl groups, were studied by thermogravimetric analysis (TGA), cyclic voltammetry (CV), and Raman spectroscopy. The loading level, morphology, and crystallinity of the Pt/SWNT catalysts were determined using TGA, SEM, and XRD. The electrochemically active catalytic surface area of the Pt/FCNT catalysts was 72.9 m(2)/g-Pt. PMID:20644806

  9. Mechanism of Pinhole Formation in Membrane Electrode Assemblies for PEM Fuel Cells

    NASA Technical Reports Server (NTRS)

    Stanic, Vesna; Hoberecht, Mark

    2004-01-01

    The pinhole formation mechanism was studied with a variety of MEAs using ex-situ and in-situ methods. The ex-situ tests included the MEA aging in oxygen and MEA heat of ignition. In-situ durability tests were performed in fuel cells at different operating conditions with hydrogen and oxygen. After the in-situ failure, MEAs were analyzed with an Olympus BX 60 optical microscope and Cambridge 120 scanning electron microscope. MEA chemical analysis was performed with an IXRF EDS microanalysis system. The MEA failure analyses showed that pinholes and tears were the MEA failure modes. The pinholes appeared in MEA areas where the membrane thickness was drastically reduced. Their location coincided with the stress concentration points, indicating that membrane creep was responsible for their formation. Some of the pinholes detected had contaminant particles precipitated within the membrane. This mechanism of pinhole formation was correlated to the polymer blistering.

  10. Investigation of aligned carbon nanotubes as a novel catalytic electrodes for PEM fuel cells.

    SciTech Connect

    Liu, D. J.; Yang, J.; Gosztola, D. J.

    2007-01-01

    Recent progress in synthesizing and characterizing aligned carbon nanotubes (ACNT) as the electrode catalyst material for proton exchange membrane fuel cells (PEMFC) is reported. Catalytically functionalized ACNT active towards the electrocatalytic reduction of oxygen were prepared by a chemical vapor deposition method. The electrocatalytic activities and the nanostructures of the ACNT layers were investigated by cyclic voltammetry and scanning electron microscopy. To understand the nature of the transition metal as the catalytically active site in the ACNT, we also conducted an in situ X-ray absorption spectroscopic investigation at the Advanced Photon Source at Argonne National Laboratory. The oxidation state and coordination structure of the transition metals embedded inside the nanotubes were monitored by examining the EXAFS spectra collected under different polarization potentials. We clearly observed the change in the electronic and coordinational structures during the oxygen reduction reaction.

  11. Cathode pressure modeling of the Buckeye Bullet II 500kW PEM fuel cell system

    NASA Astrophysics Data System (ADS)

    Hillstrom, Edward T.

    This dissertation details the development of a model that simulates the pressure dynamics of the cathode supply system for the Buckeye Bullet 2, the worlds fastest hydrogen fuel cell vehicle. Due to the extreme power levels of the BB2 system, and the unique use of heliox as the oxidant supply, it is shown that existing system level models for predicting the fuel cell pressure dynamics do not adequately capture the dynamics of the BB2 system. Several modeling attempts are evaluated, and eventually the most robust model is a model which is derived from a rational system decomposition of the cathode system. By separating the major losses of the cathode system into an upstream and downstream resistance, the performance of the model is significantly improved. It is shown that the rate at which water exits the cathode plays a significant role accurately capturing the pressure dynamics. With this in mind, a distributed parameter model is developed to provide estimates of how the rate of liquid water removal from cathode changes with time. The results of this model are validated through physical testing. The resulting model relies on five empirically tunable parameters to tune the model performance to match that of the system. The method of calibrating these parameters is outlined, and the resulting model developed with stationary test data is compared to data from the actual BB2 race data. Only a few parameters need to be recalibrated, which is due to physical system differences between the data from the stationary tests and the race data.

  12. Statistic analysis of operational influences on the cold start behaviour of PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Oszcipok, M.; Riemann, D.; Kronenwett, U.; Kreideweis, M.; Zedda, M.

    For portable fuel cell systems a multitude of applications have been presented over the past few years. Most of these applications were developed for indoor use, and not optimised for outdoor conditions. The key problem concerning this case is the cold start ability of the polymer electrolyte membrane fuel cell (PEMFC). This topic was first investigated by the automotive industry, which has the same requirements for alternative traction systems as for conventional combustion engines. The technical challenge is the fact that produced water freezes to ice after shut-down of the PEMFC and during start-up when the temperature is below 0 °C. To investigate the basic cold start behaviour isothermal, potentiostatic single cell experiments were performed and the results are presented. The cold start behaviour is evaluated using the calculated cumulated charge transfer through the membrane which directly corresponds with the amount of produced water in the PEMFC. The charge transfer curves were mathematically fitted to obtain only three parameters describing the cold start-up with the cumulated charge transfer density and the results are analysed using the statistical software Cornerstone 4.0. The results of the statistic regression analyses are used to establish a statistic-based prediction model of the cold start behaviour which describes the behaviour of the current density during the experiment. The regression shows that the initial start current mainly depends on the membrane humidity and the operation voltage. After the membrane humidity has reached its maximum, the current density drops down to zero. The current decay also depends on the constant gas flows of the reactant gases. Ionic conductivity of the membrane and charge transfer resistance were investigated by a series of ac impedance spectra during potentiostatic operation of the single cell at freezing temperatures. Cyclic voltammetry and polarisation curves between cold start experiments show degradation

  13. Final Project Report: Development of Micro-Structural Mitigation Strategies for PEM Fuel Cells: Morphological Simulations and Experimental Approaches

    SciTech Connect

    Wessel, Silvia; Harvey, David

    2013-06-28

    The durability of PEM fuel cells is a primary requirement for large scale commercialization of these power systems in transportation and stationary market applications that target operational lifetimes of 5,000 hours and 40,000 hours by 2015, respectively. Key degradation modes contributing to fuel cell lifetime limitations have been largely associated with the platinum-based cathode catalyst layer. Furthermore, as fuel cells are driven to low cost materials and lower catalyst loadings in order to meet the cost targets for commercialization, the catalyst durability has become even more important. While over the past few years significant progress has been made in identifying the underlying causes of fuel cell degradation and key parameters that greatly influence the degradation rates, many gaps with respect to knowledge of the driving mechanisms still exist; in particular, the acceleration of the mechanisms due to different structural compositions and under different fuel cell conditions remains an area not well understood. The focus of this project was to address catalyst durability by using a dual path approach that coupled an extensive range of experimental analysis and testing with a multi-scale modeling approach. With this, the major technical areas/issues of catalyst and catalyst layer performance and durability that were addressed are: 1. Catalyst and catalyst layer degradation mechanisms (Pt dissolution, agglomeration, Pt loss, e.g. Pt in the membrane, carbon oxidation and/or corrosion). a. Driving force for the different degradation mechanisms. b. Relationships between MEA performance, catalyst and catalyst layer degradation and operational conditions, catalyst layer composition, and structure. 2. Materials properties a. Changes in catalyst, catalyst layer, and MEA materials properties due to degradation. 3. Catalyst performance a. Relationships between catalyst structural changes and performance. b. Stability of the three-phase boundary and its effect on

  14. A Semi-Empirical Two Step Carbon Corrosion Reaction Model in PEM Fuel Cells

    SciTech Connect

    Young, Alan; Colbow, Vesna; Harvey, David; Rogers, Erin; Wessel, Silvia

    2013-01-01

    The cathode CL of a polymer electrolyte membrane fuel cell (PEMFC) was exposed to high potentials, 1.0 to 1.4 V versus a reversible hydrogen electrode (RHE), that are typically encountered during start up/shut down operation. While both platinum dissolution and carbon corrosion occurred, the carbon corrosion effects were isolated and modeled. The presented model separates the carbon corrosion process into two reaction steps; (1) oxidation of the carbon surface to carbon-oxygen groups, and (2) further corrosion of the oxidized surface to carbon dioxide/monoxide. To oxidize and corrode the cathode catalyst carbon support, the CL was subjected to an accelerated stress test cycled the potential from 0.6 VRHE to an upper potential limit (UPL) ranging from 0.9 to 1.4 VRHE at varying dwell times. The reaction rate constants and specific capacitances of carbon and platinum were fitted by evaluating the double layer capacitance (Cdl) trends. Carbon surface oxidation increased the Cdl due to increased specific capacitance for carbon surfaces with carbon-oxygen groups, while the second corrosion reaction decreased the Cdl due to loss of the overall carbon surface area. The first oxidation step differed between carbon types, while both reaction rate constants were found to have a dependency on UPL, temperature, and gas relative humidity.

  15. Simulation and experimental validation of droplet dynamics in microchannels of PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Ashrafi, Moosa; Shams, Mehrzad; Bozorgnezhad, Ali; Ahmadi, Goodarz

    2016-02-01

    In this study, dynamics of droplets in the channels of proton exchange membrane fuel cells with straight and serpentine flow-fields was investigated. Tapered and filleted channels were suggested for the straight and serpentine flow-fields respectively in order to improve water removal in channels. Surface tension and wall adhesion forces were applied by using the volume of fluid method. The hydrophilic walls and hydrophobic gas diffusion layer were considered. The mechanism of droplets movement with different diameters was studied by using the Weber and capillary numbers in simple and tapered straight channels. It was illustrated that the flooding was reduced in tapered channel due to increase of water removal rate, and available reaction sites improved subsequently. In addition, film flow was formed in the tapered channel more than the simple channel, so pressure fluctuation was decreased in the tapered channel. Moreover, the water coverage ratio of hydrophilic tapered surface was more than the simple channel, which enhanced water removal from the channel. The filleted serpentine channel was introduced to improve water removal from the simple serpentine channel. It was shown by observation of the unsteady and time-averaged two-phase pressure drop that in the filleted serpentine channels, the two-phase pressure drop was far less than the simple serpentine channel, and also the accumulation of water droplets in the elbows was less leading to lower pressure fluctuation. The numerical simulation results were validated by experiments.

  16. Characterization of PEM fuel cell membrane-electrode-assemblies by electrochemical methods and microanalysis

    SciTech Connect

    Borup, R.L.; Vanderborgh, N.E.

    1995-09-01

    Characterization of Membrane Electrode Assemblies (MEAs) is used to help optimize construction of the MEA. Characterization techniques include electron microscopies (SEM and TEM), and electrochemical evaluation of the catalyst. Electrochemical hydrogen adsorption/desorption (HAD) and CO oxidation are used to evaluate the active Pt surface area of fuel cell membrane electrode assemblies. Electrochemical surface area measurements have observed large active Pt surface areas, on the order of 50 m{sup 2}/g for 20% weight Pt supported on graphite. Comparison of the hydrogen adsorption/desorption with CO oxidation indicates that on the supported catalysts, the saturation coverage of CO/Pt is about 0.90, the same as observed in H{sub 2}SO{sub 4}. The catalyst surface area measurements are nearly a factor of 2 lower than the Pt surface area calculated from the 30 {angstrom} average particle size observed by TEM. The electrochemical measurements combined with microanalysis of membrane electrode assemblies, allow a greater understanding and optimization of process variables.

  17. Study of a small heat and power PEM fuel cell system generator

    NASA Astrophysics Data System (ADS)

    Hubert, Charles-Emile; Achard, Patrick; Metkemeijer, Rudolf

    A micro-cogenerator based on a natural gas reformer and a PEMFC is studied in its entirety, pointing out the links between different sub-systems. The study is conducted within the EPACOP project, which aims at testing PEMFC systems on user sites to evaluate development and acceptance of this technology for small stationary applications. Five units were installed from November 2002 to May 2003 and have been operated until now, in real life conditions. They deliver up to 4 kW of AC power and about 6 kW of heat. Center for Energy and Processes (CEP), one of the scientific partners, processes and analyses the experimental data from the five units, running in different regions of France. This database and the study of the flowsheet enable to propose changes to enhance the efficiency of the system composed of a steam reforming, a shift and a preferential oxidation reactor, a fuel cell stack and heat exchangers. The steady state modelling and optimisation of the system is done with Thermoptim ®, a software developed within CEP for applied thermodynamics. At constant power, main targets are to decrease natural gas consumption, to increase heat recovery and to improve the water balance. This study is made using the pinch point analysis, at full load and partial load. Main results of this study are different system configurations that allow improvement of gross electrical and thermal efficiency and enable to obtain a positive water balance.

  18. PEM Degradation Investigation Final Technical Report

    SciTech Connect

    Dan Stevenson; Lee H Spangler

    2010-10-18

    This project conducted fundamental studies of PEM MEA degradation. Insights gained from these studies were disseminated to assist MEA manufacturers in understanding degradation mechanisms and work towards DOE 2010 fuel cell durability targets.

  19. Artificial Neural Network Modeling of Pt/C Cathode Degradation in PEM Fuel Cells

    NASA Astrophysics Data System (ADS)

    Maleki, Erfan; Maleki, Nasim

    2016-08-01

    Use of computational modeling with a few experiments is considered useful to obtain the best possible result for a final product, without performing expensive and time-consuming experiments. Proton exchange membrane fuel cells (PEMFCs) can produce clean electricity, but still require further study. An oxygen reduction reaction (ORR) takes place at the cathode, and carbon-supported platinum (Pt/C) is commonly used as an electrocatalyst. The harsh conditions during PEMFC operation result in Pt/C degradation. Observation of changes in the Pt/C layer under operating conditions provides a tool to study the lifetime of PEMFCs and overcome durability issues. Recently, artificial neural networks (ANNs) have been used to solve, predict, and optimize a wide range of scientific problems. In this study, several rates of change at the cathode were modeled using ANNs. The backpropagation (BP) algorithm was used to train the network, and experimental data were employed for network training and testing. Two different models are constructed in the present study. First, the potential cycles, temperature, and humidity are used as inputs to predict the resulting Pt dissolution rate of the Pt/C at the cathode as the output parameter of the network. Thereafter, the Pt dissolution rate and Pt ion diffusivity are regarded as inputs to obtain values of the Pt particle radius change rate, Pt mass loss rate, and surface area loss rate as outputs. The networks are finely tuned, and the modeling results agree well with experimental data. The modeled responses of the ANNs are acceptable for this application.

  20. Graphene-Supported Platinum Catalyst-Based Membrane Electrode Assembly for PEM Fuel Cell

    NASA Astrophysics Data System (ADS)

    Devrim, Yilser; Albostan, Ayhan

    2016-08-01

    The aim of this study is the preparation and characterization of a graphene-supported platinum (Pt) catalyst for proton exchange membrane fuel cell (PEMFC) applications. The graphene-supported Pt catalysts were prepared by chemical reduction of graphene and chloroplatinic acid (H2PtCl6) in ethylene glycol. X-ray powder diffraction, thermogravimetric analysis (TGA) and scanning electron microscopy have been used to analyze structure and surface morphology of the graphene-supported catalyst. The TGA results showed that the Pt loading of the graphene-supported catalyst was 31%. The proof of the Pt particles on the support surfaces was also verified by energy-dispersive x-ray spectroscopy analysis. The commercial carbon-supported catalyst and prepared Pt/graphene catalysts were used as both anode and cathode electrodes for PEMFC at ambient pressure and 70°C. The maximum power density was obtained for the Pt/graphene-based membrane electrode assembly (MEA) with H2/O2 reactant gases as 0.925 W cm2. The maximum current density of the Pt/graphene-based MEA can reach 1.267 and 0.43 A/cm2 at 0.6 V with H2/O2 and H2/air, respectively. The MEA prepared by the Pt/graphene catalyst shows good stability in long-term PEMFC durability tests. The PEMFC cell voltage was maintained at 0.6 V without apparent voltage drop when operated at 0.43 A/cm2 constant current density and 70°C for 400 h. As a result, PEMFC performance was found to be superlative for the graphene-supported Pt catalyst compared with the Pt/C commercial catalyst. The results indicate the graphene-supported Pt catalyst could be utilized as the electrocatalyst for PEMFC applications.

  1. Graphene-Supported Platinum Catalyst-Based Membrane Electrode Assembly for PEM Fuel Cell

    NASA Astrophysics Data System (ADS)

    Devrim, Yilser; Albostan, Ayhan

    2016-06-01

    The aim of this study is the preparation and characterization of a graphene-supported platinum (Pt) catalyst for proton exchange membrane fuel cell (PEMFC) applications. The graphene-supported Pt catalysts were prepared by chemical reduction of graphene and chloroplatinic acid (H2PtCl6) in ethylene glycol. X-ray powder diffraction, thermogravimetric analysis (TGA) and scanning electron microscopy have been used to analyze structure and surface morphology of the graphene-supported catalyst. The TGA results showed that the Pt loading of the graphene-supported catalyst was 31%. The proof of the Pt particles on the support surfaces was also verified by energy-dispersive x-ray spectroscopy analysis. The commercial carbon-supported catalyst and prepared Pt/graphene catalysts were used as both anode and cathode electrodes for PEMFC at ambient pressure and 70°C. The maximum power density was obtained for the Pt/graphene-based membrane electrode assembly (MEA) with H2/O2 reactant gases as 0.925 W cm2. The maximum current density of the Pt/graphene-based MEA can reach 1.267 and 0.43 A/cm2 at 0.6 V with H2/O2 and H2/air, respectively. The MEA prepared by the Pt/graphene catalyst shows good stability in long-term PEMFC durability tests. The PEMFC cell voltage was maintained at 0.6 V without apparent voltage drop when operated at 0.43 A/cm2 constant current density and 70°C for 400 h. As a result, PEMFC performance was found to be superlative for the graphene-supported Pt catalyst compared with the Pt/C commercial catalyst. The results indicate the graphene-supported Pt catalyst could be utilized as the electrocatalyst for PEMFC applications.

  2. Analysis and modeling of PEM fuel cell stack performance: Effect of in situ reverse water gas shift reaction and oxygen bleeding

    NASA Astrophysics Data System (ADS)

    Karimi, G.; Li, Xianguo

    In this study the performance of a polymer electrolyte membrane (PEM) fuel cell stack is analyzed with a mathematical model when the stack operates on hydrocarbon reformate gas as the anode feed stream. It is shown that the effect of carbon dioxide dilution of the hydrogen dominated reformate gas has a minimal impact on the stack performance. However, the CO-poisoning effect due to the in situ reverse water gas shift reaction in the anode feed stream could have a very serious adverse impact on the stack performance, especially at high current densities. Thermodynamic calculations indicate that the equilibrium concentrations of CO could be as high as 100 ppm, generated by the in situ reverse water gas shift reaction, under the typical conditions of PEM fuel cell operation; and are influenced by the stack operating temperature and water content of the reformate anode feed. This CO-poisoning of the stack performance is shown mitigated effectively by introducing about 0.5-1% oxygen to the anode feed.

  3. Water Management In PEM Fuel Cell -“ A Lattice-Boltzmann Modeling Approach

    SciTech Connect

    Mukherjee, Shiladitya; Cole, James Vernon; Jain, Kunal; Gidwani, Ashok

    2009-06-01

    In Proton Exchange Membrane Fuel Cells (PEMFCs), water management and the effective transport of water through the gas-diffusion-layer (GDL) are key issues for improved performance at high power density and for durability during freeze-thaw cycles. The diffusion layer is a thin (~150-350{micro}m), porous material typically composed of a web of carbon fibers and particles, and is usually coated with hydrophobic Teflon to remove the excess water through capillary action. In-situ diagnostics of water movement and gas-reactant transport through this thin opaque substrate is challenging. Numerical analyses are typically based on simplified assumptions, such as Darcy's Law and Leverett functions for the capillary pressure. The objective of this work is to develop a high fidelity CFD modeling and analysis tool to capture the details of multiphase transport through the porous GDL. The tool can be utilized to evaluate GDL material design concepts and optimize systems based on the interactions between cell design, materials, and operating conditions. The flow modeling is based on the Lattice Boltzmann Method (LBM). LBM is a powerful modeling tool to simulate multiphase flows. Its strength is in its kinetic theory based foundation, which provides a fundamental basis for incorporating intermolecular forces that lead to liquid-gas phase separation and capillary effects without resorting to expensive or ad-hoc interface reconstruction schemes. At the heart of the solution algorithm is a discrete form of the well-known Boltzmann Transport Equation (BTE) for molecular distribution, tailored to recover the continuum Navier-Stokes flow. The solution advances by a streaming and collision type algorithm, mimicking actual molecular physics, which makes it suitable for porous media involving complex boundaries. We developed a numerical scheme to reconstruct various porous GDL microstructures including Teflon loading. Single and multiphase LBM models are implemented to compute

  4. Investigation of water droplet dynamics in PEM fuel cell gas channels

    NASA Astrophysics Data System (ADS)

    Gopalan, Preethi

    Water management in Proton Exchange Membrane Fuel Cell (PEMFC) has remained one of the most important issues that need to be addressed before its commercialization in automotive applications. Accumulation of water on the gas diffusion layer (GDL) surface in a PEMFC introduces a barrier for transport of reactant gases through the GDL to the catalyst layer. Despite the fact that the channel geometry is one of the key design parameters of a fluidic system, very limited research is available to study the effect of microchannel geometry on the two-phase flow structure. In this study, the droplet-wall dynamics and two-phase pressure drop across the water droplet present in a typical PEMFC channel, were examined in auto-competitive gas channel designs (0.4 x 0.7 mm channel cross section). The liquid water flow pattern inside the gas channel was analyzed for different air velocities. Experimental data was analyzed using the Concus-Finn condition to determine the wettability characteristics in the corner region. It was confirmed that the channel angle along with the air velocity and the channel material influences the water distribution and holdup within the channel. Dynamic contact angle emerged as an important parameter in controlling the droplet-wall interaction. Experiments were also performed to understand how the inlet location of the liquid droplet on the GDL surface affects the droplet dynamic behavior in the system. It was found that droplets emerging near the channel wall or under the land lead to corner filling of the channel. Improvements in the channel design has been proposed based on the artificial channel roughness created to act as capillary grooves to transport the liquid water away from the land area. For droplets emerging near the center of the channel, beside the filling and no-filling behavior reported in the literature, a new droplet jumping behavior was observed. As droplets grew and touched the sidewalls, they jumped off to the sidewall leaving the

  5. Synthesis of proton conducting mesoporous materials and composite membranes for high temperature proton exchange membrane (PEM) fuel cells

    NASA Astrophysics Data System (ADS)

    Feng, Fangxia

    ), and bis(trifluoromethanesulfonyl)imide (HTFSI). The effect of TMOS/template content and the acid on the conductivity as well as H2/O2 performance were investigated. The results indicated that the incorporation of TMOs/surfactant/acid could increase the proton conductivity and the fuel cell performance. Sulfonated silica/heteropolyacid (HPA) composite membranes were investigated for high temperature proton exchange membrane (PEM) fuel cells. HPAs included tungstosilicic acid (WSA) and tungstophosphoric acid (WPA). The influence of the HPA type, and HPA content on the proton conductivity and fuel cell performance was investigated. (Abstract shortened by UMI.)

  6. Cooling channels design analysis with chaotic laminar trajectory for closed cathode air-cooled PEM fuel cells using non-reacting numerical approach

    NASA Astrophysics Data System (ADS)

    N, W. Mohamed W. A.

    2015-09-01

    The thermal management of Polymer Electrolyte Membrane (PEM) fuel cells contributes directly to the overall power output of the system. For a closed cathode PEM fuel cell design, the use of air as a cooling agent is a non-conventional method due to the large heat load involved, but it offers a great advantage for minimizing the system size. Geometrical aspects of the cooling channels have been identified as the basic parameter for improved cooling performance. Numerical investigation using STAR-CCM computational fluid dynamics platform was applied for non-reacting cooling effectiveness study of various channel geometries for fuel cell application. The aspect ratio of channels and the flow trajectory are the parametric variations. A single cooling plate domain was selected with an applied heat flux of 2400 W/m2 while the cooling air are simulated at Reynolds number of 400 that corresponds to normal air flow velocities using standard 6W fans. Three channel designs of similar number of channels (20 channels) are presented here to analyze the effects of having chaotic laminar flow trajectory compared to the usual straight path trajectory. The total heat transfer between the cooling channel walls and coolant were translated into temperature distribution, maximum temperature gradient, average plate temperature and overall cooling effectiveness analyses. The numerical analysis shows that the chaotic flow promotes a 5% to 10% improvement in cooling effectiveness, depending on the single-axis or multi-axis flow paths applied. Plate temperature uniformity is also more realizable using the chaotic flow designs.

  7. Alleviating product inhibition in cellulase enzyme Cel7A.

    PubMed

    Atreya, Meera E; Strobel, Kathryn L; Clark, Douglas S

    2016-02-01

    Enzymes that degrade cellulose into glucose are one of the most expensive components of processes for converting cellulosic biomass to fuels and chemicals. Cellulase enzyme Cel7A is the most abundant enzyme naturally employed by fungi to depolymerize cellulose, and like other cellulases is inhibited by its product, cellobiose. There is thus great economic incentive for minimizing the detrimental effects of product inhibition on Cel7A. In this work, we experimentally generated 10 previously proposed site-directed mutant Cel7A enzymes expected to have reduced cellobiose binding energies (the majority of mutations were to alanine). We then tested their resilience to cellobiose as well as their hydrolytic activities on microcrystalline cellulose. Although every mutation tested conferred reduced product inhibition (and abolished it for some), our results confirm a trade-off between Cel7A tolerance to cellobiose and enzymatic activity: Reduced product inhibition was accompanied by lower overall enzymatic activity on crystalline cellulose for the mutants tested. The tempering effect of mutations on inhibition was nearly constant despite relatively large differences in activities of the mutants. Our work identifies an amino acid in the Cel7A product binding site of interest for further mutational studies, and highlights both the challenge and the opportunity of enzyme engineering toward improving product tolerance in Cel7A. PMID:26302366

  8. A distinct model of synergism between a processive endocellulase (TfCel9A) and an exocellulase (TfCel48A) from Thermobifida fusca.

    PubMed

    Kostylev, Maxim; Wilson, David

    2014-01-01

    Lignocellulosic biomass is digested in nature by the synergistic activities of enzymes with complementary properties, and understanding synergistic interactions will improve the efficiency of industrial biomass use for sustainable fuels and chemicals. Cel9A and Cel48A from a model bacterium, Thermobifida fusca (TfCel9A and TfCel48A, respectively), are two cellulases with different properties and have previously been shown to synergize well with each other. TfCel9A is a processive endocellulase with relatively high activity on crystalline cellulose. TfCel48A is a reducing end-directed exocellulase with very low activity on crystalline cellulose. Neither enzyme fits its respective role in the classical synergism model of enzymatic cellulose digestion. Using the results of time course, endpoint, and sequential addition activity assays, we propose a model of synergistic cooperation between the two cellulases. TfCel9A is most effective on fresh bacterial cellulose with a presumably uniform surface at the molecular level. Its processive activity likely erodes the surface and thus reduces its own activity. TfCel48A is able to hydrolyze the TfCel9A-modified substrate efficiently and replenish the uniform surface required by TfCel9A, creating a feedback mechanism. The model of synergistic interactions is comparable to an earlier proposed model for Trichoderma reesei Cel7A and Cel7B, but the roles of endo- and exocellulases are reversed, a finding which suggests that bacteria and fungi may have evolved different approaches to efficient biomass degradation. PMID:24162578

  9. Highly porous PEM fuel cell cathodes based on low density carbon aerogels as Pt-support: Experimental study of the mass-transport losses

    NASA Astrophysics Data System (ADS)

    Marie, Julien; Chenitz, Regis; Chatenet, Marian; Berthon-Fabry, Sandrine; Cornet, Nathalie; Achard, Patrick

    Carbon aerogels exhibiting high porous volumes and high surface areas, differentiated by their pore-size distributions were used as Pt-supports in the cathode catalytic layer of H 2/air-fed PEM fuel cell. The cathodes were tested as 50 cm 2 membrane electrode assemblies (MEAs). The porous structure of the synthesized catalytic layers was impacted by the nanostructure of the Pt-doped carbon aerogels (Pt/CAs). In this paper thus we present an experimental study aiming at establishing links between the porous structure of the cathode catalytic layers and the MEAs performances. For that purpose, the polarization curves of the MEAs were decomposed in 3 contributions: the kinetic loss, the ohmic loss and the mass-transport loss. We showed that the MEAs made with the different carbon aerogels had similar kinetic activities (low current density performance) but very different mass-transport voltage losses. It was found that the higher the pore-size of the initial carbon aerogel, the higher the mass-transport voltage losses. Supported by our porosimetry (N 2-adsorption and Hg-porosimetry) measurement, we interpret this apparent contradiction as the consequence of the more important Nafion penetration into the carbon aeorogel with larger pore-size. Indeed, the catalytic layers made from the larger pore-size carbon aerogel had lower porosities. We thus show in this work that carbon aerogels are materials with tailored nanostructured structure which can be used as model materials for experimentally testing the optimization of the PEM fuel cell catalytic layers.

  10. On-board reforming of biodiesel and bioethanol for high temperature PEM fuel cells: Comparison of autothermal reforming and steam reforming

    NASA Astrophysics Data System (ADS)

    Martin, Stefan; Wörner, Antje

    2011-03-01

    In the 21st century biofuels will play an important role as alternative fuels in the transportation sector. In this paper different reforming options (steam reforming (SR) and autothermal reforming (ATR)) for the on-board conversion of bioethanol and biodiesel into a hydrogen-rich gas suitable for high temperature PEM (HTPEM) fuel cells are investigated using the simulation tool Aspen Plus. Special emphasis is placed on thermal heat integration. Methyl-oleate (C19H36O2) is chosen as reference substance for biodiesel. Bioethanol is represented by ethanol (C2H5OH). For the steam reforming concept with heat integration a maximum fuel processing efficiency of 75.6% (76.3%) is obtained for biodiesel (bioethanol) at S/C = 3. For the autothermal reforming concept with heat integration a maximum fuel processing efficiency of 74.1% (75.1%) is obtained for biodiesel (bioethanol) at S/C = 2 and λ = 0.36 (0.35). Taking into account the better dynamic behaviour and lower system complexity of the reforming concept based on ATR, autothermal reforming in combination with a water gas shift reactor is considered as the preferred option for on-board reforming of biodiesel and bioethanol. Based on the simulation results optimum operating conditions for a novel 5 kW biofuel processor are derived.

  11. Gene Integration and Expression and Extracellular Secretion of Erwinia chrysanthemi Endoglucanase CelY (celY) and CelZ (celZ) in Ethanologenic Klebsiella oxytoca P2†

    PubMed Central

    Zhou, Shengde; Davis, F. C.; Ingram, L. O.

    2001-01-01

    The development of methods to reduce costs associated with the solubilization of cellulose is essential for the utilization of lignocellulose as a renewable feedstock for fuels and chemicals. One promising approach is the genetic engineering of ethanol-producing microorganisms that also produce cellulase enzymes during fermentation. By starting with an ethanologenic derivative (strain P2) of Klebsiella oxytoca M5A1 with the native ability to metabolize cellobiose, the need for supplemental β-glucosidase was previously eliminated. In the current study, this approach has been extended by adding genes encoding endoglucanase activities. Genes celY and celZ from Erwinia chrysanthemi have been functionally integrated into the chromosome of P2 using surrogate promoters from Zymomonas mobilis for expression. Both were secreted into the extracellular milieu, producing more than 20,000 endoglucanase units (carboxymethyl cellulase activity) per liter of fermentation broth. During the fermentation of crystalline cellulose with low levels of commercial cellulases of fungal origin, these new strains produced up to 22% more ethanol than unmodified P2. Most of the beneficial contribution was attributed to CelY rather than to CelZ. These results suggest that fungal enzymes with substrate profiles resembling CelY (preference for long-chain polymers and lack of activity on soluble cello-oligosaccharides of two to five glucosyl residues) may be limiting in commercial cellulase preparations. PMID:11133422

  12. A structural study of Hypocrea jecorina Cel5A

    PubMed Central

    Lee, Toni M; Farrow, Mary F; Arnold, Frances H; Mayo, Stephen L

    2011-01-01

    Interest in generating lignocellulosic biofuels through enzymatic hydrolysis continues to rise as nonrenewable fossil fuels are depleted. The high cost of producing cellulases, hydrolytic enzymes that cleave cellulose into fermentable sugars, currently hinders economically viable biofuel production. Here, we report the crystal structure of a prevalent endoglucanase in the biofuels industry, Cel5A from the filamentous fungus Hypocrea jecorina. The structure reveals a general fold resembling that of the closest homolog with a high-resolution structure, Cel5A from Thermoascus aurantiacus. Consistent with previously described endoglucanase structures, the H. jecorina Cel5A active site contains a primarily hydrophobic substrate binding groove and a series of hydrogen bond networks surrounding two catalytic glutamates. The reported structure, however, demonstrates stark differences between side-chain identity, loop regions, and the number of disulfides. Such structural information may aid efforts to improve the stability of this protein for industrial use while maintaining enzymatic activity through revealing nonessential and immutable regions. PMID:21898652

  13. A structural study of Hypocrea jecorina Cel5A.

    PubMed

    Lee, Toni M; Farrow, Mary F; Arnold, Frances H; Mayo, Stephen L

    2011-11-01

    Interest in generating lignocellulosic biofuels through enzymatic hydrolysis continues to rise as nonrenewable fossil fuels are depleted. The high cost of producing cellulases, hydrolytic enzymes that cleave cellulose into fermentable sugars, currently hinders economically viable biofuel production. Here, we report the crystal structure of a prevalent endoglucanase in the biofuels industry, Cel5A from the filamentous fungus Hypocrea jecorina. The structure reveals a general fold resembling that of the closest homolog with a high-resolution structure, Cel5A from Thermoascus aurantiacus. Consistent with previously described endoglucanase structures, the H. jecorina Cel5A active site contains a primarily hydrophobic substrate binding groove and a series of hydrogen bond networks surrounding two catalytic glutamates. The reported structure, however, demonstrates stark differences between side-chain identity, loop regions, and the number of disulfides. Such structural information may aid efforts to improve the stability of this protein for industrial use while maintaining enzymatic activity through revealing nonessential and immutable regions. PMID:21898652

  14. Development of a brazing process for the production of water- cooled bipolar plates made of chromium-coated metal foils for PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Mueller, M.; Hoehlich, D.; Scharf, I.; Lampke, T.; Hollaender, U.; Maier, H. J.

    2016-03-01

    Beside lithium batteries, PEM fuel cells are the most promising strategy as a power source to achieve the targets for introducing and increasing the usage of electric vehicles. Due to limited space and weight problems, water cooled, metallic bipolar plates in a fuel cell metal stack are preferred in motor vehicles. These plates are stamped metal sheets with a complex structure, interconnected media-tight. To meet the multiple tasks and requirements in use, complex and expensive combinations of materials are currently in use (carbon fiber composites, graphite, gold-plated nickel, stainless and acid resistant steel). The production of such plates is expensive as it is connected with considerable effort or the usage of precious metals. As an alternative, metalloid nitrides (CrN, VN, W2N, etc.) show a high chemical resistance, hardness and a good conductivity. So this material category meets the basic requirements of a top layer. However, the standard methods for their production (PVD, CVD) are expensive and have a slow deposition rate and a lower layer thicknesses. Because of these limitations, a full functionality over the life cycle of a bipolar plate is not guaranteed. The contribution shows the development and quantification of an alternative production process for bipolar plates. The expectation is to get significant advantages from the combination of chromium electrodeposition and thermochemical treatment to form chromium nitrides. Both processes are well researched and suitable for series production. The thermochemical treatment of the chromium layer also enables a process-integrated brazing.

  15. Nb-doped TiO2/carbon composite supports synthesized by ultrasonic spray pyrolysis for proton exchange membrane (PEM) fuel cell catalysts

    NASA Astrophysics Data System (ADS)

    Senevirathne, Keerthi; Neburchilov, Vladimir; Alzate, Vanesa; Baker, Ryan; Neagu, Roberto; Zhang, Jiujun; Campbell, Stephen; Ye, Siyu

    2012-12-01

    In this paper we report the use of both ultrasonic spray pyrolysis and microwave-assisted polyol reduction methods to synthesize Nb-doped TiO2/carbon (25 wt% Nb0.07Ti0.93O2/75 wt% carbon) composite supports and Pt0.62Pd0.38 alloy catalysts, respectively. The physicochemical properties of the synthesized supports and their Pt0.62Pd0.38 supported catalysts are evaluated using several methods including XRD, TEM, BET surface area analysis, TGA, as well as ICP-MS elemental analysis. The electronic conductivities and thermal/chemical stabilities of the supports are also evaluated with respect to their possible use as catalyst supports. Electrochemical measurements for oxygen reduction activity of the Pt0.62Pd0.38 alloy catalysts supported on oxide/carbon composites are also carried out in order to check their suitability for possible PEM fuel cell applications. The results show that 20wt%Pt0.62Pd0.38/25 wt%(Nb0.07Ti0.93O2)-75 wt%C catalysts exhibit enhanced mass activities compared to those of commercially available 48wt% Pt/C and home-made 20wt% Pt62Pd38/C catalysts.

  16. Mass Production Cost Estimation For Direct H2 PEM Fuel Cell Systesm for Automotive Applications. 2010 Update

    SciTech Connect

    James, Brian D.; Kalinoski, Jeffrey A.; Baum, Kevin N.

    2010-09-30

    This report is the fourth annual update of a comprehensive automotive fuel cell cost analysis. It contains estimates for material and manufacturing costs of complete 80 kWnet direct-hydrogen proton exchange membrane fuel cell systems suitable for powering light-duty automobiles.

  17. Mass Production Cost Estimation for Direct H2 PEM Fuel Cell Systems for Automotive Applications. 2009 Update

    SciTech Connect

    James, Brian D.; Kalinoski, Jeffrey A.; Baum, Kevin N.

    2010-01-01

    This report is the third annual update of a comprehensive automotive fuel cell cost analysis. It contains estimates for material and manufacturing cost of complete 80 kWnet direct hydrogen proton exchange membrane fuel cell systems suitable for powering light duty automobiles.

  18. SYNTHESIS AND CHARACTERIZATION OF CO-AND H2S-TOLERANT ELECTROCATALYSTS FOR PEM FUEL CELL

    SciTech Connect

    Shamsuddin Ilias

    2005-03-29

    The present state-of-art Proton Exchange Membrane Fuel Cell (PEMFC) technology is based on platinum (Pt) as a catalyst for both the fuel (anode) and air (cathode) electrodes. This catalyst is highly active but susceptible to poisoning by CO, which may be present in the H{sub 2}-fuel used or may be introduced during the fuel processing. Presence of trace amount of CO and H{sub 2}S in the H{sub 2}-fuel poisons the anode irreversibly and decreases the performance of the PEMFCs. In an effort to reduce the Pt-loading and improve the PEMFC performance, we propose to synthesize a number of Pt-based binary, ternary, and quaternary electrocatalysts using Ru, Mo, Ir, Ni, and Co as a substitute for Pt. By fine-tuning the metal loadings and compositions of candidate electrocatalysts, we plan to minimize the cost and optimize the catalyst activity and performance in PEMFC. The feasibility of the novel electrocatalysts will be demonstrated in the proposed effort with gas phase CO and H{sub 2}S concentrations typical of those found in reformed fuel gas with coal/natural gas/methanol feedstocks. During this reporting period several bi-metallic electrocatalysts were synthesized using ultra-sonication. These catalysts (Pt/Ru, Pt/Mo and Pt/Ir) were tested in MEAs. From Galvonstatic study the catalytic activity was found in the order of: Pt/Ru/C > Pt/Mo/C > Pt/Ir/C. It appears that electrocatalysts prepared by ultra-sonication process are more active compared to the conventional technique. Work is in progress to further study these catalysts for CO-tolerance in PEMFC and identify potential candidate metals for synthesis of tri-metallic electrocatalysts.

  19. Synthesis and Characterization of CO-and H2S-Tolerant Electrocatalysts for PEM Fuel Cell

    SciTech Connect

    Shamsuddin Ilias

    2005-12-22

    The present state-of-art Proton Exchange Membrane Fuel Cell (PEMFC) technology is based on platinum (Pt) as a catalyst for both the fuel (anode) and air (cathode) electrodes. This catalyst is highly active but susceptible to poisoning by CO, which may be present in the H{sub 2}-fuel used or may be introduced during the fuel processing. Presence of trace amount of CO and H{sub 2}S in the H{sub 2}-fuel poisons the anode irreversibly and decreases the performance of the PEMFCs. In an effort to reduce the Pt-loading and improve the PEMFC performance, we propose to synthesize a number of Pt-based binary, ternary, and quaternary electrocatalysts using Ru, Mo, Ir, Ni, and Co as a substitute for Pt. By fine-tuning the metal loadings and compositions of candidate electrocatalysts, we plan to minimize the cost and optimize the catalyst activity and performance in PEMFC. The feasibility of the novel electrocatalysts will be demonstrated in the proposed effort with gas phase CO and H{sub 2}S concentrations typical of those found in reformed fuel gas with coal/natural gas/methanol feedstocks. During this reporting period we synthesized four Pt-based electrocatalysts catalysts (Pt/Ru/Mo/Se, Pt/Ru/Mo/Ir, Pt/Ru/Mo/W, Ptr/Ru/Mo/Co) on Vulcan XG72 Carbon support by both conventional and ultra-sonication method. From current-voltage performance study, the catalytic activity was found in the increasing order of Pt/Ru/Mo/Ir > Pt/Ru/Mo/W > Pt/Ru/Mo/Co > Pt/Ru/MO/Se. Sonication method appears to provide better dispersion of catalysts on carbon support.

  20. SYNTHESIS AND CHARACTERIZATION OF CO-AND H2S-TOLERANT ELECTROCATALYSTS FOR PEM FUEL CELL

    SciTech Connect

    Shamsuddin Ilias

    2004-03-31

    The present state-of-art Proton Exchange Membrane Fuel Cell (PEMFC) technology is based on platinum (Pt) as a catalyst for both the fuel (anode) and air (cathode) electrodes. This catalyst is highly active but susceptible to poisoning by CO, which may be present in the H{sub 2}-fuel used or may be introduced during the fuel processing. Presence of trace amount of CO and H{sub 2}S in the H{sub 2}-fuel poisons the anode irreversibly and decreases the performance of the PEMFCs. In an effort to reduce the Pt-loading and improve the PEMFC performance, we propose to synthesize a number of Pt-based binary, ternary, and quaternary electrocatalysts using Ru, Mo, Ir, Ni, and Co as a substitute for Pt. By fine-tuning the metal loadings and compositions of candidate electrocatalysts, we plan to minimize the cost and optimize the catalyst activity and performance in PEMFC. The feasibility of the novel electrocatalysts will be demonstrated in the proposed effort with gas phase CO and H{sub 2}S concentrations typical of those found in reformed fuel gas with coal/natural gas/methanol feedstocks. During this reporting period several bi-metallic electrocatalysts were synthesized and tested in MEAs. From Galvonstatic study the catalytic activity was found in the order of: Pt/Ru/C > Pt/Mo/C > Pt/Ir/C > Pt/Ni/C > Pt/Cr/C. Work in progress to further study these catalysts for CO-tolerance in PEMFC and identify potential candidate metals for synthesis of trimetallic electrocatalysts.

  1. SYNTHESIS AND CHARACTERIZATION OF CO- AND H{sub 2}S-TOLERANT ELECTROCATALYSTS FOR PEM FUEL CELL

    SciTech Connect

    Shamsuddin Ilias

    2005-04-05

    The present state-of-art Proton Exchange Membrane Fuel Cell (PEMFC) technology is based on platinum (Pt) as a catalyst for both the fuel (anode) and air (cathode) electrodes. This catalyst is highly active but susceptible to poisoning by CO, which may be present in the H{sub 2}-fuel used or may be introduced during the fuel processing. Presence of trace amount of CO and H{sub 2}S in the H{sub 2}-fuel poisons the anode irreversibly and decreases the performance of the PEMFCs. In an effort to reduce the Pt-loading and improve the PEMFC performance, we propose to synthesize a number of Pt-based binary, ternary, and quaternary electrocatalysts using Ru, Mo, Ir, Ni, and Co as a substitute for Pt. By fine-tuning the metal loadings and compositions of candidate electrocatalysts, we plan to minimize the cost and optimize the catalyst activity and performance in PEMFC. The feasibility of the novel electrocatalysts will be demonstrated in the proposed effort with gas phase CO and H{sub 2}S concentrations typical of those found in reformed fuel gas with coal/natural gas/methanol feedstocks. During this reporting period several tri-metallic electrocatalysts were synthesized using both ultra-sonication and conventional method. These catalysts (Pt/Ru/Mo, Pt/Ru/Ir, Pt/Ru/W, Ptr/Ru/Co, and Pt/Ru/Se on carbon) were tested in MEAs. From Galvonstatic study the catalytic activity was found in the order of: Pt/Ru/Mo/C > Pt/Ru/Ir/C > Pt/Ru/W/C > Ptr/Ru/Co/C > and Pt/Ru/Se. It appears that electrocatalysts prepared by ultra-sonication process are more active compared to the conventional technique. Work is in progress to further study these catalysts for CO-tolerance in PEMFC.

  2. Research and Development of Proton-Exchange Membrane (PEM) Fuel Cell System for Transportation Applications: Initial Conceptual Design Report

    SciTech Connect

    Not Available

    1993-11-30

    This report addresses Task 1.1, model development and application, and Task 1.2, vehicle mission definition. Overall intent is to produce a methanol-fueled 10-kW power source, and to evaluate electrochemical engine (ECE) use in transportation. Major achievements include development of an ECE power source model and its integration into a comprehensive power source/electric vehicle propulsion model, establishment of candidate FCV (fuel cell powered electric vehicle) mission requirements, initial FCV studies, and a candidate FCV recommendation for further study.

  3. Research and development of Proton-Exchange Membrane (PEM) fuel cell system for transportation applications: Initial conceptual design report

    NASA Astrophysics Data System (ADS)

    1993-11-01

    This report addresses Task 1.1, model development and application, and Task 1.2, vehicle mission definition. Overall intent is to produce a methanol-fueled 10-kW power source and to evaluate electrochemical engine (ECE) use in transportation. Major achievements include development of an ECE power source model and its integration into a comprehensive power source/electric vehicle propulsion model, establishment of candidate FCV (fuel cell powered electric vehicle) mission requirements, initial FCV studies, and a candidate FCV recommendation for further study.

  4. Polarization Losses under Accelerated Stress Test Using Multiwalled Carbon Nanotube Supported Pt Catalyst in PEM Fuel Cells

    SciTech Connect

    Park, Seh K.; Shao, Yuyan; Kou, Rong; Viswanathan, Vilayanur V.; Towne, Silas A.; Rieke, Peter C.; Liu, Jun; Lin, Yuehe; Wang, Yong

    2011-03-01

    The electrochemical behavior for Pt catalysts supported on multiwalled carbon nanotubes and Vulcan XC-72 in proton exchange membrane fuel cells under accelerated stress test was examined by cyclic voltammetry, electrochemical impedance spectroscopy, and polarization technique. Pt catalyst supported on multiwalled carbon nanotubes exhibited highly stable electrochemical surface area, oxygen reduction kinetics, and fuel cell performance at a highly oxidizing condition, indicating multiwalled carbon nanotubes show high corrosion resistance and strong interaction with Pt nanoparticles. The Tafel slope, ohmic resistances, and limiting current density determined were used to differentiate kinetic, ohmic, mass-transfer polarization losses from the actual polarization curve. Kinetic contribution to the total overpotential was larger throughout the stress test. However, the fraction of kinetic overpotential decreased and mass-transfer overpotential portion remained quite constant during accelerated stress test, whereas the fraction of ohmic overpotential primarily originating from severe proton transport limitation in the catalyst layer increased under the anodic potential hold.

  5. Potential Usage of Thermoelectric Devices in a High-Temperature Polymer Electrolyte Membrane (PEM) Fuel Cell System: Two Case Studies

    NASA Astrophysics Data System (ADS)

    Gao, Xin; Chen, Min; Andreasen, Søren Juhl; Kær, Søren Knudsen

    2012-06-01

    Methanol-fueled, high-temperature polymer electrolyte membrane fuel cell (HTPEMFC) power systems are promising as the next generation of vehicle engines, efficient and environmentally friendly. Currently, their performance still needs to be improved, and they still rely on a large Li-ion battery for system startup. In this article, to handle these two issues, the potential of thermoelectric (TE) devices applied in a HTPEMFC power system has been preliminarily evaluated. First, right after the fuel cell stack or the methanol reformer, thermoelectric generators (TEGs) are embedded inside a gas-liquid heat exchanger to form a heat recovery subsystem jointly for electricity production. It is calculated that the recovered power can increase the system efficiency and mitigate the dependence on Li-ion battery during system startup. To improve the TEG subsystem performance, a finite-difference model is then employed and two main parameters are identified. Second, TE coolers are integrated into the methanol steam reformer to regulate heat fluxes herein and improve the system dynamic performance. Similar modification is also done on the evaporator to improve its dynamic performance as well as to reduce the heat loss during system startup. The results demonstrate that the TE-assisted heat flux regulation and heat-loss reduction can also effectively help solve the abovementioned two issues. The preliminary analysis in this article shows that a TE device application inside HTPEMFC power systems is of great value and worthy of further study.

  6. Heterologous expression of codon optimized Trichoderma reesei Cel6A in Pichia pastoris.

    PubMed

    Sun, Fubao Fuelbiol; Bai, Renhui; Yang, Huimin; Wang, Fei; He, Jing; Wang, Chundi; Tu, Maobing

    2016-10-01

    The Cel6A deficiency has become one of the limiting factors for cellulose saccharification in biochemical conversion of cellulosic biomass to fuels and chemicals. The work attempted to use codon optimization to enhance Trichoderma reesei Cel6A expression in Pichia pastoris. Two recombinants P. pastoris GS115 containing AOX1 and GAP promotors were successfully constructed, respectively. The optimal temperatures and pHs of the expressed Cel6A from two recombinants were consistent with each other, were also in the extremely similar range to that reported on the native Cel6A from T. reesei. Based on the shake flask fermentation, AOX1 promotor enabled the recombinant to produce 265U/L and 300mg/L of the Cel6A enzyme, and the GAP promotor resulted in 145U/L and 200mg/L. High cell density fed batch (HCDFB) fermentation significantly improved the enzyme titer (1100U/L) and protein yield (2.0g/L) for the recombinant with AOX1 promotor. Results have showed that the AOX1 promotor is more suitable than the GAP for the Cel6A expression in P. pastoris. And the HCDFB cultivation is a favorable way to express the Cel6A highly in the methanol inducible yeast. PMID:27542751

  7. Cost related sensitivity analysis for optimal operation of a grid-parallel PEM fuel cell power plant

    NASA Astrophysics Data System (ADS)

    El-Sharkh, M. Y.; Tanrioven, M.; Rahman, A.; Alam, M. S.

    Fuel cell power plants (FCPP) as a combined source of heat, power and hydrogen (CHP&H) can be considered as a potential option to supply both thermal and electrical loads. Hydrogen produced from the FCPP can be stored for future use of the FCPP or can be sold for profit. In such a system, tariff rates for purchasing or selling electricity, the fuel cost for the FCPP/thermal load, and hydrogen selling price are the main factors that affect the operational strategy. This paper presents a hybrid evolutionary programming and Hill-Climbing based approach to evaluate the impact of change of the above mentioned cost parameters on the optimal operational strategy of the FCPP. The optimal operational strategy of the FCPP for different tariffs is achieved through the estimation of the following: hourly generated power, the amount of thermal power recovered, power trade with the local grid, and the quantity of hydrogen that can be produced. Results show the importance of optimizing system cost parameters in order to minimize overall operating cost.

  8. Determination of polymer electrolyte membrane (PEM) degradation products in fuel cell water using electrospray ionization tandem mass spectrometry.

    PubMed

    Zedda, Marco; Tuerk, Jochen; Peil, Stefan; Schmidt, Torsten C

    2010-12-30

    Within the scope of research of membrane degradation phenomena during fuel cell operation a reliable analytical procedure for the extraction, detection and quantification of possible membrane oxidation products has been developed. These oxidation products originate from the attack of hydroxyl or peroxyl radicals on the membrane polymer. Such radicals are formed in situ (during fuel cell operation) or ex situ (Fenton test as oxidative stress simulation). The analysis of membrane oxidation products was carried out by electrospray ionization tandem mass spectrometry. Five potential membrane oxidation products (4-hydroxybenzoic acid (4-HBA), 4-hydroxybenzaldehyde (4-HBAD), 4,4-biphenol (4,4-BP), 4-hydroxybenzenesulfonate (4-HBS), and 4,4-sulfonylbiphenol (4,4-SBP)) were selected based on the molecular structure of the sulfonated polyarylether membrane used. In conjunction with the development of a multiple reaction monitoring (MRM) method, the ionization and fragmentation of the selected compounds were investigated. For 4,4-BP a molecular ion (M(+•) ) was observed in the positive ionization mode and used for MRM method development. Reproducible extraction of the model compounds was achieved using a mixed-mode sorbent material with both weak anion-exchange and reversed-phase retention properties. By using the developed analytical procedure, the identities of two membrane degradation products (4-HBA and 4-HBAD) were determined in situ and ex situ. In addition to the investigation of membrane degradation phenomena, the combination of extraction on a mixed-mode sorbent material and tandem mass spectrometric detection is attractive for the analysis of aromatic sulfonic acids, phenolic acids and phenols. PMID:21080505

  9. ExCELS--The Next Step.

    ERIC Educational Resources Information Center

    Fox, John N.; And Others

    1994-01-01

    ExCELS is a program that supports teachers interested in the use of computer interfacing at the secondary school level. This paper describes an ExCEL-based course developed for science education majors, presents an overview of interface apparatus and how it is used in schools, and gives examples of experiments performed. (LZ)

  10. PEM Degradation Investigation Final Technical Report

    SciTech Connect

    Dan Stevenson; Lee H Spangler

    2007-11-02

    The objectives of this paper are: (1) Develop a system capable of measuring current and voltage performance for each membrane in a Polymer Electrolyte Membranes (PEM) fuel cell stack and record the performance of each individual cell; (2) Develop a single cell PEM FC to allow in situ synchrotron x-ray measurements of the cell in operation and to perform spatially resolved x-ray measurements on fuel cell elements before and after degradation; and (3) Perform initial magnetic resonance microimaging experiments on membrane materials. The Montana State University PEM Membrane Degradation program is geared towards determining how and why membranes in fuel cells degrade and fail. By monitoring every individual membrane in a fuel cell 2000 times/sec while the cell is subjected to real-world type use, we hope to: (1) cause the types of degradation users see, but in a controlled environment; (2) determine an electrical signature that will identify what causes failure, or at least warns of impending failure; (3) allows us to perform advanced x-ray and MRI characterization of the degraded membranes to provide information that may result in improvements of the membrane material; and (4) perhaps allow design of electronic control systems that will prevent fuel cells from operating under conditions where damage is likely to occur.

  11. Microstructural analysis of mass transport phenomena in gas diffusion media for high current density operation in PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Kotaka, Toshikazu; Tabuchi, Yuichiro; Mukherjee, Partha P.

    2015-04-01

    Cost reduction is a key issue for commercialization of fuel cell electric vehicles (FCEV). High current density operation is a solution pathway. In order to realize high current density operation, it is necessary to reduce mass transport resistance in the gas diffusion media commonly consisted of gas diffusion layer (GDL) and micro porous layer (MPL). However, fundamental understanding of the underlying mass transport phenomena in the porous components is not only critical but also not fully understood yet due to the inherent microstructural complexity. In this study, a comprehensive analysis of electron and oxygen transport in the GDL and MPL is conducted experimentally and numerically with three-dimensional (3D) microstructural data to reveal the structure-transport relationship. The results reveal that the mass transport in the GDL is strongly dependent on the local microstructural variations, such as local pore/solid volume fractions and connectivity. However, especially in the case of the electrical conductivity of MPL, the contact resistance between carbon particles is the dominant factor. This suggests that reducing the contact resistance between carbon particles and/or the number of contact points along the transport pathway can improve the electrical conductivity of MPL.

  12. Numerical investigation of interfacial mass transport resistance and two-phase flow in PEM fuel cell air channels

    NASA Astrophysics Data System (ADS)

    Koz, Mustafa

    Proton exchange membrane fuel cells (PEMFCs) are efficient and environmentally friendly electrochemical engines. The performance of a PEMFC is adversely affected by oxygen (O2) concentration loss from the air flow channel to the cathode catalyst layer (CL). Oxygen transport resistance at the gas diffusion layer (GDL) and air channel interface is a non-negligible component of the O2 concentration loss. Simplified PEMFC performance models in the available literature incorporate the O2 resistance at the GDL-channel interface as an input parameter. However, this parameter has been taken as a constant so far in the available literature and does not reflect variable PEMFC operating conditions and the effect of two-phase flow in the channels. This study numerically calculates the O2 transport resistance at the GDL-air channel interface and expresses this resistance through the non-dimensional Sherwood number (Sh). Local Sh is investigated in an air channel with multiple droplets and films inside. These water features are represented as solid obstructions and only air flow is simulated. Local variations of Sh in the flow direction are obtained as a function of superficial air velocity, water feature size, and uniform spacing between water features. These variations are expressed with mathematical expressions for the PEMFC performance models to utilize and save computational resources. The resulting mathematical correlations for Sh can be utilized in PEMFC performance models. These models can predict cell performance more accurately with the help of the results of this work. Moreover, PEMFC performance models do not need to use a look-up table since the results were expressed through correlations. Performance models can be kept simplified although their predictions will become more realistic. Since two-phase flow in channels is experienced mostly at lower temperatures, performance optimization at low temperatures can be done easier.

  13. Lattice-Boltzmann Simulations of Multiphase Flows in Gas-Diffusion-Layer (GDL) of a PEM Fuel Cell

    SciTech Connect

    Mukherjeea, Shiladitya; Cole, J Vernon; Jainb, Kunal; Gidwania, Ashok

    2008-11-01

    Improved power density and freeze-thaw durability in automotive applications of Proton Exchange Membrane Fuel Cells (PEMFCs) requires effective water management at the membrane. This is controlled by a porous hydrophobic gas-diffusion-layer (GDL) inserted between the membrane catalyst layer and the gas reactant channels. The GDL distributes the incoming gaseous reactants on the catalyst surface and removes excess water by capillary action. There is, however, limited understanding of the multiphase, multi-component transport of liquid water, vapor and gaseous reactants within these porous materials. This is due primarily to the challenges of in-situ diagnostics for such thin (200 -“ 300 {microns}), optically opaque (graphite) materials. Transport is typically analyzed by fitting Darcy's Law type expressions for permeability, in conjunction with capillary pressure relations based on formulations derived for media such as soils. Therefore, there is significant interest in developing predictive models for transport in GDLs and related porous media. Such models could be applied to analyze and optimize systems based on the interactions between cell design, materials, and operating conditions, and could also be applied to evaluating material design concepts. Recently, the Lattice Boltzmann Method (LBM) has emerged as an effective tool in modeling multiphase flows in general, and flows through porous media in particular. This method is based on the solution of a discrete form of the well-known Boltzmann Transport Equation (BTE) for molecular distribution, tailored to recover the continuum Navier-Stokes flow. The kinetic theory basis of the method allows simple implementation of molecular forces responsible for liquid-gas phase separation and capillary effects. The solution advances by a streaming and collision type algorithm that makes it suitable to implement for domains with complex boundaries. We have developed both single and multiphase LB models and applied them to

  14. Cel vinyls: materials and methods.

    PubMed

    Harrison, S J

    1983-12-01

    Many commercial uses of media are applicable to medical/scientific media production and illustration, not the least of which are techniques pioneered in the commercial cartooning field. Whether or not the illustrative effort culminates in a "cartoon," the production techniques of the cartooning industry cannot be overlooked by the illustrator faced with providing projection graphics, whether animated or still, for slides, motion pictures, television or even print media. When Walt Disney introduced Mickey Mouse as "Steamboat Willie" in 1928, his technology opened the door for exploration of cartooning media by all artists. Only in comparatively recent years have these tools been used by the scientific illustrator. In this article cel vinyl acrylics or cartoon colors will be discussed: the rationale for the use of this medium, materials and methods, and considerations related to the photography of this art form. PMID:6677644

  15. Research and development of Proton-Exchange-Membrane (PEM) fuel cell system for transportation applications. Fuel cell infrastructure and commercialization study

    SciTech Connect

    1996-11-01

    This paper has been prepared in partial fulfillment of a subcontract from the Allison Division of General Motors under the terms of Allison`s contract with the U.S. Department of Energy (DE-AC02-90CH10435). The objective of this task (The Fuel Cell Infrastructure and Commercialization Study) is to describe and prepare preliminary evaluations of the processes which will be required to develop fuel cell engines for commercial and private vehicles. This report summarizes the work undertaken on this study. It addresses the availability of the infrastructure (services, energy supplies) and the benefits of creating public/private alliances to accelerate their commercialization. The Allison prime contract includes other tasks related to the research and development of advanced solid polymer fuel cell engines and preparation of a demonstration automotive vehicle. The commercialization process starts when there is sufficient understanding of a fuel cell engine`s technology and markets to initiate preparation of a business plan. The business plan will identify each major step in the design of fuel cell (or electrochemical) engines, evaluation of the markets, acquisition of manufacturing facilities, and the technical and financial resources which will be required. The process will end when one or more companies have successfully developed and produced fuel cell engines at a profit. This study addressed the status of the information which will be required to prepare business plans, develop the economic and market acceptance data, and to identify the mobility, energy and environment benefits of electrochemical or fuel cell engines. It provides the reader with information on the status of fuel cell or electrochemical engine development and their relative advantages over competitive propulsion systems. Recommendations and descriptions of additional technical and business evaluations that are to be developed in more detail in Phase II, are included.

  16. Binding and Movement of Individual Cel7A Cellobiohydrolases on Crystalline Cellulose Surfaces Revealed by Single-molecule Fluorescence Imaging*

    PubMed Central

    Jung, Jaemyeong; Sethi, Anurag; Gaiotto, Tiziano; Han, Jason J.; Jeoh, Tina; Gnanakaran, Sandrasegaram; Goodwin, Peter M.

    2013-01-01

    The efficient catalytic conversion of biomass to bioenergy would meet a large portion of energy requirements in the near future. A crucial step in this process is the enzyme-catalyzed hydrolysis of cellulose to glucose that is then converted into fuel such as ethanol by fermentation. Here we use single-molecule fluorescence imaging to directly monitor the movement of individual Cel7A cellobiohydrolases from Trichoderma reesei (TrCel7A) on the surface of insoluble cellulose fibrils to elucidate molecular level details of cellulase activity. The motion of multiple, individual TrCel7A cellobiohydrolases was simultaneously recorded with ∼15-nm spatial resolution. Time-resolved localization microscopy provides insights on the activity of TrCel7A on cellulose and informs on nonproductive binding and diffusion. We measured single-molecule residency time distributions of TrCel7A bound to cellulose both in the presence of and absence of cellobiose the major product and a potent inhibitor of Cel7A activity. Combining these results with a kinetic model of TrCel7A binding provides microscopic insight into interactions between TrCel7A and the cellulose substrate. PMID:23818525

  17. Binding and movement of individual Cel7A cellobiohydrolases on crystalline cellulose surfaces revealed by single-molecule fluorescence imaging.

    PubMed

    Jung, Jaemyeong; Sethi, Anurag; Gaiotto, Tiziano; Han, Jason J; Jeoh, Tina; Gnanakaran, Sandrasegaram; Goodwin, Peter M

    2013-08-16

    The efficient catalytic conversion of biomass to bioenergy would meet a large portion of energy requirements in the near future. A crucial step in this process is the enzyme-catalyzed hydrolysis of cellulose to glucose that is then converted into fuel such as ethanol by fermentation. Here we use single-molecule fluorescence imaging to directly monitor the movement of individual Cel7A cellobiohydrolases from Trichoderma reesei (TrCel7A) on the surface of insoluble cellulose fibrils to elucidate molecular level details of cellulase activity. The motion of multiple, individual TrCel7A cellobiohydrolases was simultaneously recorded with ∼15-nm spatial resolution. Time-resolved localization microscopy provides insights on the activity of TrCel7A on cellulose and informs on nonproductive binding and diffusion. We measured single-molecule residency time distributions of TrCel7A bound to cellulose both in the presence of and absence of cellobiose the major product and a potent inhibitor of Cel7A activity. Combining these results with a kinetic model of TrCel7A binding provides microscopic insight into interactions between TrCel7A and the cellulose substrate. PMID:23818525

  18. CEL_INTERROGATOR: A FREE AND OPEN SOURCE PACKAGE FOR AFFYMETRIX CEL FILE PARSING

    Technology Transfer Automated Retrieval System (TEKTRAN)

    CEL_Interrogator Package is a suite of programs designed to extract the average probe intensity and other information for each probe sequence from an Affymetrix GeneChip CEL file and unite them with their human-readable Affymetrix consensus sequence names. The resulting text file is suitable for di...

  19. Cloning and DNA sequence of the gene coding for Clostridium thermocellum cellulase Ss (CelS), a major cellulosome component.

    PubMed Central

    Wang, W K; Kruus, K; Wu, J H

    1993-01-01

    Clostridium thermocellum ATCC 27405 produces an extracellular cellulase system capable of hydrolyzing crystalline cellulose. The enzyme system involves a multicomponent protein aggregate (the cellulosome) with a total molecular weight in the millions, impeding mechanistic studies. However, two major components of the aggregate, SS (M(r) = 82,000) and SL (M(r) = 250,000), which act synergistically to hydrolyze crystalline cellulose, have been identified (J. H. D. Wu, W. H. Orme-Johnson, and A. L. Demain, Biochemistry 27:1703-1709, 1988). To further study this synergism, we cloned and sequenced the gene (celS) coding for the SS (CelS) protein by using a degenerate, inosine-containing oligonucleotide probe whose sequence was derived from the N-terminal amino acid sequence of the CelS protein. The open reading frame of celS consisted of 2,241 bp encoding 741 amino acid residues. It encoded the N-terminal amino acid sequence and two internal peptide sequences determined for the native CelS protein. A putative ribosome binding site was identified at the 5' end of the gene. A putative signal peptide of 27 amino acid residues was adjacent to the N terminus of the CelS protein. The predicted molecular weight of the secreted protein was 80,670. The celS gene contained a conserved reiterated sequence encoding 24 amino acid residues found in proteins encoded by many other clostridial cel or xyn genes. A palindromic structure was found downstream from the open reading frame. The celS gene is unique among the known cel genes of C. thermocellum. However, it is highly homologous to the partial open reading frame found in C. cellulolyticum and in Caldocellum saccharolyticum, indicating that these genes belong to a new family of cel genes. Images PMID:8444792

  20. Orpinomyces cellulase CelE protein and coding sequences

    DOEpatents

    Li, Xin-Liang; Ljungdahl, Lars G.; Chen, Huizhong

    2000-08-29

    A CDNA designated celE cloned from Orpinomyces PC-2 encodes a polypeptide (CelE) of 477 amino acids. CelE is highly homologous to CelB of Orpinomyces (72.3% identity) and Neocallimastix (67.9% identity), and like them, it has a non-catalytic repeated peptide domain (NCRPD) at the C-terminal end. The catalytic domain of CelE is homologous to glycosyl hydrolases of Family 5, found in several anaerobic bacteria. The gene of celE is devoid of introns. The recombinant proteins CelE and CelB of Orpinomyces PC-2 randomly hydrolyze carboxymethylcellulose and cello-oligosaccharides in the pattern of endoglucanases.

  1. Analysis and Test of a Proton Exchange Membrane Fuel Cell Power System for Space Power Applications

    NASA Technical Reports Server (NTRS)

    Vasquez, Arturo; Varanauski, Donald; Clark, Robert, Jr.

    2000-01-01

    An effort is underway to develop a prototype Proton Exchange Membrane (PEM) Fuel Cell breadboard system for fuhlre space applications. This prototype will be used to develop a comprehensive design basis for a space-rated PEM fuel cell powerplant. The prototype system includes reactant pressure regulators, ejector-based reactant pumps, a 4-kW fuel cell stack and cooling system, and a passive, membranebased oxygen / water separator. A computer model is being developed concurrently to analytically predict fluid flow in the oxidant reactant system. Fuel cells have historically played an important role in human-rated spacecraft. The Gemini and Apollo spacecraft used fuel cells for vehicle electrical power. The Space Shuttle currently uses three Alkaline Fuel Cell Powerplants (AFCP) to generate all of the vehicle's 15-20kW electrical power. Engineers at the Johnson Space Center have leveraged off the development effort ongoing in the commercial arena to develop PEM fuel cel ls for terrestrial uses. The prototype design originated from efforts to develop a PEM fuel cell replacement for the current Space Shuttle AFCP' s. In order to improve on the life and an already excellent hi storical record of reliability and safety, three subsystems were focused on. These were the fuel cell stack itself, the reactant circulation devices, and reactant / product water separator. PEM fuel cell stack performance is already demonstrating the potential for greater than four times the useful life of the current Shuttle's AFCP. Reactant pumping for product water removal has historically been accomplished with mechanical pumps. Ejectors offer an effective means of reactant pumping as well as the potential for weight reduction, control simplification, and long life. Centrifugal water separation is used on the current AFCP. A passive, membrane-based water separator offers compatibility with the micro-gravity environment of space, and the potential for control simplification, elimination of

  2. Fuel cell CO sensor

    DOEpatents

    Grot, Stephen Andreas; Meltser, Mark Alexander; Gutowski, Stanley; Neutzler, Jay Kevin; Borup, Rodney Lynn; Weisbrod, Kirk

    1999-12-14

    The CO concentration in the H.sub.2 feed stream to a PEM fuel cell stack is monitored by measuring current and/or voltage behavior patterns from a PEM-probe communicating with the reformate feed stream. Pattern recognition software may be used to compare the current and voltage patterns from the PEM-probe to current and voltage telltale outputs determined from a reference cell similar to the PEM-probe and operated under controlled conditions over a wide range of CO concentrations in the H.sub.2 fuel stream. A CO sensor includes the PEM-probe, an electrical discharge circuit for discharging the PEM-probe to monitor the CO concentration, and an electrical purging circuit to intermittently raise the anode potential of the PEM-probe's anode to at least about 0.8 V (RHE) to electrochemically oxidize any CO adsorbed on the probe's anode catalyst.

  3. Catalytic Mechanism of Cellulose Degradation by a Cellobiohydrolase, CelS

    SciTech Connect

    Saharay, Moumita; Guo, Hong; Smith, Jeremy C

    2010-08-01

    The hydrolysis of cellulose is the bottleneck in cellulosic ethanol production. The cellobiohydrolase CelS from Clostridium thermocellum catalyzes the hydrolysis of cello-oligosaccharides via inversion of the anomeric carbon. Here, to examine key features of the CelS-catalyzed reaction, QM/MM (SCCDFTB/MM) simulations are performed. The calculated free energy profile for the reaction possesses a 19 kcal/mol barrier. The results confirm the role of active site residue Glu87 as the general acid catalyst in the cleavage reaction and show that Asp255 may act as the general base. A feasible position in the reactant state of the water molecule responsible for nucleophilic attack is identified. Sugar ring distortion as the reaction progresses is quantified. The results provide a computational approach that may complement the experimental design of more efficient enzymes for biofuel production.

  4. Distribution and Seasonality of Selected Hydrocarbons and Halocarbons over the Western Pacific Basin During PEM-West A and PEM-West B

    NASA Technical Reports Server (NTRS)

    Blake, Nicola J.; Blake, Donald R.; Chen, Tai-Yih; Collins, James E., Jr.; Sachse, Glen W.; Anderson, Bruce E.; Rowland, F. Sherwood

    1997-01-01

    Nonmethane hydrocarbons (NMHCs) and halocarbons were measured in the troposphere over the northwestern Pacific as part of the airborne component of NASA's Pacific Exploratory Mission-West Phase B (PEM-West B). This study took place in late winter of 1994, a period characterized by maximum outflow from the Asian continent. The results are compared to those from Pacific Exploratory Mission-West Phase A (PEM-West A), which was flown in the same region during late summer of 1991, when flow from the subtropical western Pacific dominated the lower troposphere. Mixing ratios of NMHCs, tetrachloroethene (C2Cl4), and methyl bromide (CH3Br) were significantly higher during PEM-West B than during PEM-West A, particularly at latitudes north of 25 deg N and altitudes lower than 6 km. The primary reasons for these higher ambient concentrations were the seasonal increase in the atmospheric lifetimes of trace gases controlled by HO radical reactions, and the more frequent input of continental air masses. During PEM-West B, air masses of continental origin observed north of 25 deg N latitude were augmented with urban signature gases such as C2Cl4. By contrast, more southerly continental outflow had characteristics associated with combustion sources such as biomass burning, including wood fuel burning. During the summer PEM-West A period, the spatial distribution of methyl iodide (CH3I) was consistent with effective oceanic sources at all latitudes, being especially strong in tropical and subtropical regions. At low latitudes, PEM-West B CH3I mixing ratios in the lower troposphere were similar to PEM-West A, but at latitudes greater than about 25 deg N PEM-West B concentrations were significantly reduced. Equatorial regions exhibited enhanced CH3I mixing ratios extending into the upper tropical troposphere, consistent with fast vertical transport of air from the tropical marine boundary layer.

  5. A Total Cost of Ownership Model for Low Temperature PEM Fuel Cells in Combined Heat and Power and Backup Power Applications

    SciTech Connect

    University of California, Berkeley; Wei, Max; Lipman, Timothy; Mayyas, Ahmad; Chien, Joshua; Chan, Shuk Han; Gosselin, David; Breunig, Hanna; Stadler, Michael; McKone, Thomas; Beattie, Paul; Chong, Patricia; Colella, Whitney; James, Brian

    2014-06-23

    A total cost of ownership model is described for low temperature proton exchange membrane stationary fuel cell systems for combined heat and power (CHP) applications from 1-250kW and backup power applications from 1-50kW. System designs and functional specifications for these two applications were developed across the range of system power levels. Bottom-up cost estimates were made for balance of plant costs, and detailed direct cost estimates for key fuel cell stack components were derived using design-for-manufacturing-and-assembly techniques. The development of high throughput, automated processes achieving high yield are projected to reduce the cost for fuel cell stacks to the $300/kW level at an annual production volume of 100 MW. Several promising combinations of building types and geographical location in the U.S. were identified for installation of fuel cell CHP systems based on the LBNL modelling tool DER CAM. Life-cycle modelling and externality assessment were done for hotels and hospitals. Reduced electricity demand charges, heating credits and carbon credits can reduce the effective cost of electricity ($/kWhe) by 26-44percent in locations such as Minneapolis, where high carbon intensity electricity from the grid is displaces by a fuel cell system operating on reformate fuel. This project extends the scope of existing cost studies to include externalities and ancillary financial benefits and thus provides a more comprehensive picture of fuel cell system benefits, consistent with a policy and incentive environment that increasingly values these ancillary benefits. The project provides a critical, new modelling capacity and should aid a broad range of policy makers in assessing the integrated costs and benefits of fuel cell systems versus other distributed generation technologies.

  6. Research and development of a proton-exchange-membrane (PEM) fuel cell system for transportation applications. Progress report for Quarter 4 of the Phase II report

    SciTech Connect

    1995-10-20

    This 4th quarter report summarizes activity from July 1, 1995 through October 1, 1995; the report is organized as usual into sections describing background information and work performed under the main WBS categories: The Fuel Processor (WBS 1.0) team activity during this quarter focused on the continued design/development of the full scale fuel processing hardware. The combustor test stand has been completed allowing more detailed testing of the various parts of the combustor subsystem; this subsystem is currently being evaluated using the dual fuel (methanol/hydrogen) option to gain a better understanding of the control issues. The Fuel Cell Stack (WBS 2.0) team activity focused on material analysis and testing to determine the appropriate approach for the first GM stack. Five hundred hours of durability was achieved on a single cell fixture using coated titanium plates (anode and cathode) with no appreciable voltage degradation of the SEL (Stack Engineering Lab) produced MEA. Additionally, the voltage level drop across each of the plates remained low (<5mv) over the full test period; The system integration and control team focused on the initial layout and configuration of the system; and the Reference powertrain and commercialization studies are currently under review.

  7. PEMS (PORTABLE EMISSONS MEASUREMENT SYSTEM)

    EPA Science Inventory

    PEMS is a generic term that encompasses all portable emissions measurement systems. Two EPA-developed examples are ROVER (Real-time On-Vehicle Emissions Reporter) for on-highway applications, and SPOT (Simple Portable On-vehicle Tester) for non-road applications. Now, however, ...

  8. An autoantibody against N{sup {epsilon}}-(carboxyethyl)lysine (CEL): Possible involvement in the removal of CEL-modified proteins by macrophages

    SciTech Connect

    Mera, Katsumi; Nagai, Ryoji; Takeo, Kazuhiro; Izumi, Miyoko; Maruyama, Toru; Otagiri, Masaki

    2011-04-08

    Highlights: {yields} A higher amount of autoantibody against CEL than that of other AGEs was observed in human plasma. {yields} The purified human anti-CEL autoantibody specifically reacted with CEL. {yields} Anti-CEL antibody accelerated the uptake of {sup 125}I-CEL-HSA by macrophage in vitro. {yields} Endocytic uptake of {sup 125}I-CEL-HSA by mice liver was accelerated in the presence of anti-CEL antibody. -- Abstract: Advanced glycation end products (AGEs) are believed to play a significant role in the development of diabetic complications. In this study, we measured the levels of autoantibodies against several AGE structures in healthy human plasma and investigated the physiological role of the autoantibodies. A high titer of the autoantibody against N{sup {epsilon}}-(carboxyethyl)lysine (CEL) was detected in human plasma compared with other AGE structures such as CML and pentosidine. The purified human anti-CEL autoantibody reacted with CEL-modified human serum albumin (CEL-HSA), but not CML-HSA. A rabbit polyclonal anti-CEL antibody, used as a model autoantibody against CEL, accelerated the uptake of CEL-HSA by macrophages, but did not enhance the uptake of native HSA. Furthermore, when {sup 125}I-labeled CEL-HSA was injected into the tail vein of mice, accumulation of {sup 125}I-CEL-HSA in the liver was accelerated by co-injection of the rabbit anti-CEL antibody. These results demonstrate that the autoantibody against CEL in plasma may play a role in the macrophage uptake of CEL-modified proteins.

  9. Evaluation of a 2.5 kWel automotive low temperature PEM fuel cell stack with extended operating temperature range up to 120 °C

    NASA Astrophysics Data System (ADS)

    Ruiu, Tiziana; Dreizler, Andreas M.; Mitzel, Jens; Gülzow, Erich

    2016-01-01

    Nowadays, the operating temperature of polymer electrolyte membrane fuel cell stacks is typically limited to 80 °C due to water management issues of membrane materials. In the present work, short-term operation at elevated temperatures up to 120 °C and long-term steady-state operation under automotive relevant conditions at 80 °C are examined using a 30-cell stack developed at DLR. The high temperature behavior is investigated by using temperature cycles between 90 and 120 °C without adjustment of the gases dew points, to simulate a short-period temperature increase, possibly caused by an extended power demand and/or limited heat removal. This galvanostatic test demonstrates a fully reversible performance decrease of 21 ± 1% during each thermal cycle. The irreversible degradation rate is about a factor of 6 higher compared to the one determined by the long-term test. The 1200-h test at 80 °C demonstrates linear stack voltage decay with acceptable degradation rate, apart from a malfunction of the air compressor, which results in increased catalyst degradation effects on individual cells. This interpretation is based on an end-of-life characterization, aimed to investigate catalyst, electrode and membrane degradation, by determining hydrogen crossover rates, high frequency resistances, electrochemically active surface areas and catalyst particle sizes.

  10. Unveiling N-protonation and anion-binding effects on Fe/N/C-catalysts for O2 reduction in PEM fuel cells

    PubMed Central

    Herranz, Juan; Jaouen, Frédéric; Lefèvre, Michel; Kramm, Ulrike I.; Proietti, Eric; Dodelet, Jean-Pol; Bogdanoff, Peter; Fiechter, Sebastian; Abs-Wurmbach, Irmgard; Bertrand, Patrick; Arruda, Thomas M.; Mukerjee, Sanjeev

    2013-01-01

    The high cost of proton-exchange-membrane fuel cells would be considerably reduced if platinumbased catalysts were replaced by iron-based substitutes, which have recently demonstrated comparable activity for oxygen reduction, but whose cause of activity decay in acidic medium has been elusive. Here, we reveal that the activity of Fe/N/C-catalysts prepared through a pyrolysis in NH3 is mostly imparted by acid-resistant FeN4-sites whose turnover frequency for the O2 reduction can be regulated by fine chemical changes of the catalyst surface. We show that surface N-groups protonate at pH 1 and subsequently bind anions. This results in decreased activity for the O2 reduction. The anions can be removed chemically or thermally, which restores the activity of acid-resistant FeN4-sites. These results are interpreted as an increased turnover frequency of FeN4-sites when specific surface N-groups protonate. These unprecedented findings provide new perspective for stabilizing the most active Fe/N/C-catalysts known to date. PMID:24179561

  11. Application of a composite structure of carbon nanoparticles and Nb-TiO2 nanofibers as electrocatalyst support for PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Bauer, Alex; Hui, Rob; Ignaszak, Anna; Zhang, Jiujun; Jones, Deborah J.

    2012-07-01

    Platinum catalyst nanoparticles (20 wt.%) were deposited on a mixed support, which consisted of 25 at.% Nb doped TiO2 nanofibers and carbon agglomerates. XRD analysis revealed that titania was present in the rutile phase. The catalyst was characterized electrochemically with respect to durability and oxygen reduction activity. Based on cyclic voltammetry tests, the Nb-TiO2/C supported catalyst was more stable compared to a commercially available carbon supported Pt catalyst (E-tek) over 1000 cycles. The apparent active Pt area decreased by 5% due to cycling, whereas in the case of Pt/C the decrease was 23%. The oxygen reduction performance was comparable for both cases. For example, during the anodic sweep the mass activity at 0.9 V vs. the reversible hydrogen electrode (RHE) was 19 A gPt-1 and 20 A gPt-1 for the freshly prepared in-house prepared and commercial catalysts, respectively. After the durability experiment both types of catalysts yielded a mass activity of 17 A gPt-1. Fuel cell tests with a single cell configuration were also carried out with the Nb-TiO2/C supported catalyst on the cathode side (gas diffusion electrode), yielding a peak power density of 0.34 W cm-2 at 75 °C when pure oxygen was supplied on the cathode side.

  12. A catalyst layer optimisation approach using electrochemical impedance spectroscopy for PEM fuel cells operated with pyrolysed transition metal-N-C catalysts

    NASA Astrophysics Data System (ADS)

    Malko, Daniel; Lopes, Thiago; Ticianelli, Edson A.; Kucernak, Anthony

    2016-08-01

    The effect of the ionomer to carbon (I/C) ratio on the performance of single cell polymer electrolyte fuel cells is investigated for three different types of non-precious metal cathodic catalysts. Polarisation curves as well as impedance spectra are recorded at different potentials in the presence of argon or oxygen at the cathode and hydrogen at the anode. It is found that a optimised ionomer content is a key factor for improving the performance of the catalyst. Non-optimal ionomer loading can be assessed by two different factors from the impedance spectra. Hence this observation could be used as a diagnostic element to determine the ideal ionomer content and distribution in newly developed catalyst-electrodes. An electrode morphology based on the presence of inhomogeneous resistance distribution within the porous structure is suggested to explain the observed phenomena. The back-pressure and relative humidity effect on this feature is also investigated and supports the above hypothesis. We give a simple flowchart to aid optimisation of electrodes with the minimum number of trials.

  13. Operation of Nafion ®-based PEM fuel cells with no external humidification: influence of operating conditions and gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Williams, Minkmas V.; Kunz, H. Russell; Fenton, James M.

    Polarization tests were conducted on proton exchange membrane fuel cells (PEMFCs) at cell temperatures between 60 and 80 °C with various reactant humidification levels; varied from no external humidification to fully saturated on both the anode and the cathode. Elimination of cathode external humidification, while maintaining a fully humidified anode inlet, resulted in cell performance loss of only 5% or 33 mV (from 0.674 to 0.641 V) at 400 mA/cm 2 at an anode stoichiometry of 3 and a cathode stoichiometry of 4. When both the anode and the cathode humidification were removed ("dry operation"), cell performance strongly depended on the cell operating temperature and the inlet gas stoichiometric flow rates. High performance of non-humidified PEMFCs was demonstrated by optimizing the operating cell temperature and the inlet gas stoichiometric flow rates, to find a balance between cell "flooding", oxygen mole fraction, and proton conductivity. Performance of a cell with an in-house cathode gas diffusion layer (GDL) showed a loss of only 4% or 29 mV (from 0.674 to 0.645 V) compared to the near-saturated condition, at 400 mA/cm 2 and optimum stoichiometry. Using a commercial E-TEK_V.2.11 carbon cloth cathode GDL showed significantly greater loss when operated with no external humidification at the same optimized condition. An overall system analysis suggested that at optimum stoichiometric flow rates and cell temperatures, with the in-house GDL, while the net power output might be reduced by at most 17% under dry operation the total required non-stack energy duty would be cut by over 46% when compared to operation with saturated inlet gases.

  14. 40 CFR 1065.915 - PEMS instruments.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 32 2010-07-01 2010-07-01 false PEMS instruments. 1065.915 Section 1065.915 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Field Testing and Portable Emission Measurement Systems § 1065.915 PEMS instruments. (a) Instrument specifications....

  15. Absence of the endo-beta-1,4-glucanases Cel1 and Cel2 reduces susceptibility to Botrytis cinerea in tomato.

    PubMed

    Flors, Víctor; Leyva, María de la O; Vicedo, Begonya; Finiti, Ivan; Real, María Dolores; García-Agustín, Pilar; Bennett, Alan B; González-Bosch, Carmen

    2007-12-01

    Cel1 and Cel2 are members of the tomato (Solanum lycopersicum Mill) endo-beta-1,4-glucanase (EGase) family that may play a role in fruit ripening and organ abscission. This work demonstrates that Cel1 protein is present in other vegetative tissues and accumulates during leaf development. We recently reported the downregulation of both the Cel1 mRNA and protein upon fungal infection, suggesting the involvement of EGases in plant-pathogen interactions. This hypothesis was confirmed by assessing the resistance to Botrytis cinerea infection of transgenic plants expressing both genes in an antisense orientation (Anti-Cel1, Anti-Cel2 and Anti-Cel1-Cel2). The Anti-Cel1-Cel2 plants showed enhanced resistance to this fungal necrotroph. Microscopical analysis of infected leaves revealed that tomato plants accumulated pathogen-inducible callose within the expanding lesion. Anti-Cel1-Cel2 plants presented a faster and enhanced callose accumulation against B. cinerea than wild-type plants. The inhibitor 2-deoxy-d-glucose, a callose synthesis inhibitor, showed a direct relationship between faster callose accumulation and enhanced resistance to B. cinerea. EGase activity appears to negatively modulate callose deposition. The absence of both EGase genes was associated with changes in the expression of the pathogen-related genes PR1 and LoxD. Interestingly, Anti-Cel1-Cel2 plants were more susceptible to Pseudomonas syringae, displaying severe disease symptoms and enhanced bacterial growth relative to wild-type plants. Analysis of the involvement of Cel1 and Cel2 in the susceptibility to B. cinerea in fruits was done with the ripening-impaired mutants Never ripe (Nr) and Ripening inhibitor (rin). The data reported in this work support the idea that enzymes involved in cell wall metabolism play a role in susceptibility to pathogens. PMID:17916112

  16. Synergistic Hydrolysis of Carboxymethyl Cellulose and Acid-Swollen Cellulose by Two Endoglucanases (CelZ and CelY) from Erwinia chrysanthemi†

    PubMed Central

    Zhou, Shengde; Ingram, Lonnie O.

    2000-01-01

    Erwinia chrysanthemi produces a battery of hydrolases and lyases which are very effective in the maceration of plant cell walls. Although two endoglucanases (CelZ and CelY; formerly EGZ and EGY) are produced, CelZ represents approximately 95% of the total carboxymethyl cellulase activity. In this study, we have examined the effectiveness of CelY and CelZ alone and of combinations of both enzymes using carboxymethyl cellulose (CMC) and amorphous cellulose (acid-swollen cellulose) as substrates. Synergy was observed with both substrates. Maximal synergy (1.8-fold) was observed for combinations containing primarily CelZ; the ratio of enzyme activities produced was similar to those produced by cultures of E. chrysanthemi. CelY and CelZ were quite different in substrate preference. CelY was unable to hydrolyze soluble cellooligosaccharides (cellotetraose and cellopentaose) but hydrolyzed CMC to fragments averaging 10.7 glucosyl units. In contrast, CelZ readily hydrolyzed cellotetraose, cellopentaose, and amorphous cellulose to produce cellobiose and cellotriose as dominant products. CelZ hydrolyzed CMC to fragments averaging 3.6 glucosyl units. In combination, CelZ and CelY hydrolyzed CMC to products averaging 2.3 glucosyl units. Synergy did not require the simultaneous presence of both enzymes. Enzymatic modification of the substrate by CelY increased the rate and extent of hydrolysis by CelZ. Full synergy was retained by the sequential hydrolysis of CMC, provided CelY was used as the first enzyme. A general mechanism is proposed to explain the synergy between these two enzymes based primarily on differences in substrate preference. PMID:11004164

  17. CelG from Clostridium cellulolyticum: a multidomain endoglucanase acting efficiently on crystalline cellulose.

    PubMed Central

    Gal, L; Gaudin, C; Belaich, A; Pages, S; Tardif, C; Belaich, J P

    1997-01-01

    The gene coding for CelG, a family 9 cellulase from Clostridium cellulolyticum, was cloned and overexpressed in Escherichia coli. Four different forms of the protein were genetically engineered, purified, and studied: CelGL (the entire form of CelG), CelGcat1 (the catalytic domain of CelG alone), CelGcat2 (CelGcat1 plus 91 amino acids at the beginning of the cellulose binding domain [CBD]), and GST-CBD(CelG) (the CBD of CelG fused to glutathione S-transferase). The biochemical properties of CelG were compared with those of CelA, an endoglucanase from C. cellulolyticum which was previously studied. CelG, like CelA, was found to have an endo cutting mode of activity on carboxymethyl cellulose (CMC) but exhibited greater activity on crystalline substrates (bacterial microcrystalline cellulose and Avicel) than CelA. As observed with CelA, the presence of the nonhydrolytic miniscaffolding protein (miniCipC1) enhanced the activity of CelG on phosphoric acid swollen cellulose (PASC), but to a lesser extent. The absence of the CBD led to the complete inactivation of the enzyme. The abilities of CelG and GST-CBD(CelG) to bind various substrates were also studied. Although the entire enzyme is able to bind to crystalline cellulose at a limited number of sites, the chimeric protein GST-CBD(CelG) does not bind to either of the tested substrates (Avicel and PASC). The lack of independence between the two domains and the weak binding to cellulose suggest that this CBD-like domain may play a special role and be either directly or indirectly involved in the catalytic reaction. PMID:9352905

  18. Xylella fastidiosa plasmid-encoded PemK toxin is an endoribonuclease.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Stable inheritance of pXF-RIV11 in Xylella fastidiosa is conferred by the pemI/pemK plasmid addiction system. PemK serves as a toxin inhibiting bacterial growth; PemI is the corresponding antitoxin that blocks activity of PemK toxin by direct binding. PemK toxin and PemI antitoxin were over-expre...

  19. Applications and development of high pressure PEM systems

    SciTech Connect

    Leonida, A; Militsky, F; Myers, B; Weisberg, A H

    1999-06-01

    Many portable fuel cell applications require high pressure hydrogen, oxygen, or both. High pressure PEM systems that were originally designed and developed primarily for aerospace applications are being redesigned for use in portable applications. Historically, applications can be broken into weight sensitive and weight insensitive cell stack designs. Variants of the weight sensitive designs have been considered to refill oxygen bottles for space suits, to provide oxygen for space shuttle, to provide oxygen and/or reboost propellants to the space station, and to recharge oxygen bottles for commercial aviation. A long operating history has been generated for weight insensitive designs that serve as oxygen generators for submarines. Exciting future vehicle concepts and portable applications are enabled by carefully designing lightweight stacks which do not require additional pressure containment. These include high altitude long endurance solar rechargeable aircraft and airships, water refuelable spacecraft, and a variety of field portable systems. High pressure electrolyzers can refill compressed hydrogen storage tanks for fuel cell powered vehicles or portable fuel cells. Hamilton Standard has demonstrated many high pressure PEM water electrolyzer designs for a variety of applications. Electrolyzers with operational pressures up to 3000 psi (20.7 MPa) are currently used for US Navy submarine oxygen generators. An aerospace version has been demonstrated in the Integrated Propulsion Test Article (IPTA) program. Electrolyzers with operational pressures up to 6000 psi (41.4 MPa) have also been demonstrated in the High Pressure Oxygen Recharge System (HPORS). Onboard oxygen generator systems (OBOGS) that generate up to 2000 psi (13.8 MPa) oxygen and refill breathable oxygen tanks for commercial aviation have been designed and successfully demonstrated. Other hardware applications that require high pressure PEM devices are related to these proven applications.

  20. Applicability of the PEMS technique for simplified NO X monitoring on board ships

    NASA Astrophysics Data System (ADS)

    Cooper, D. A.; Ekström, M.

    The performance of a predictive emission monitoring system (PEMS) as a technique for NO x monitoring on medium speed marine diesel engines has been evaluated for 16 similar engines on four different ships. The PEMS function tested measured O 2 concentration in the exhaust gas, engine load, combustion air temperature and humidity, and barometric pressure to calculate the NO x concentration. Emission measurements were carried out by means of a conventional continuous emission monitoring system (CEMS) and the measured NO x concentrations were compared with those calculated by the PEMS function. For 11 of the 16 engines, the average error between measured and calculated NO x concentration was <10% of the calibration range (1725 ppm). In addition, 10 of the engines displayed correlation coefficients between measured and calculated NO x as 0.90 or higher. For two of the ships, the predicted NO x concentrations from all engines on board gave good agreement with those measured (2.6-4.7% and 2.6-8.0% average error). In other cases however, the performance of the PEMS function was poor e.g. the four engines of ship D showed average errors of 10.3-17.7%. Although similar engine models, fuel and load characteristics were compared in the tests, the specific NO x emissions at steady-state loads used varied from 12.6 up to 15.8 g k -1Wh corr. Although a single PEMS function may prove universal and adequate for calculating NO x emissions from similar engines on board the same ship, an engine specific PEMS function is recommended. The form of the PEMS function, i.e. using exhaust O 2 and engine load as inputs, is however likely to be applicable to most propeller-law diesel engines. Bearing in mind the performance criteria for using PEMS at land-based installations, the results from this study are promising. Viewed as a single data set of 56 h with 16 separate engine comparisons between CEMS and PEMS, the data set shows a relative accuracy of 14.5% i.e. within the 20% requirement of

  1. Adaptive Process Controls and Ultrasonics for High Temperature PEM MEA Manufacture

    SciTech Connect

    Walczyk, Daniel F.

    2015-08-26

    The purpose of this 5-year DOE-sponsored project was to address major process bottlenecks associated with fuel cell manufacturing. New technologies were developed to significantly reduce pressing cycle time for high temperature PEM membrane electrode assembly (MEA) through the use of novel, robust ultrasonic (U/S) bonding processes along with low temperature (<100°C) PEM MEAs. In addition, greater manufacturing uniformity and performance was achieved through (a) an investigation into the causes of excessive variation in ultrasonically and thermally bonded MEAs using more diagnostics applied during the entire fabrication and cell build process, and (b) development of rapid, yet simple quality control measurement techniques for use by industry.

  2. Preventing CO poisoning in fuel cells

    DOEpatents

    Gottesfeld, Shimshon

    1990-01-01

    Proton exchange membrane (PEM) fuel cell performance with CO contamination of the H.sub.2 fuel stream is substantially improved by injecting O.sub.2 into the fuel stream ahead of the fuel cell. It is found that a surface reaction occurs even at PEM operating temperatures below about 100.degree. C. to oxidatively remove the CO and restore electrode surface area for the H.sub.2 reaction to generate current. Using an O.sub.2 injection, a suitable fuel stream for a PEM fuel cell can be formed from a methanol source using conventional reforming processes for producing H.sub.2.

  3. Evaluation of carbon-supported Pt and Pd nanoparticles for the hydrogen evolution reaction in PEM water electrolysers

    NASA Astrophysics Data System (ADS)

    Grigoriev, S. A.; Millet, P.; Fateev, V. N.

    Carbon-supported Pt and Pd nanoparticles (CSNs) were synthesized and electrochemically characterized in view of potential application in proton exchange membrane (PEM) water electrolysers. Electroactive metallic nanoparticles were obtained by chemical reduction of precursor salts adsorbed to the surface of Vulcan XC-72 carbon carrier, using ethylene glycol as initial reductant and with final addition of formaldehyde. CSNs were then coated over the surface of electron-conducting working electrodes using an alcoholic solution of perfluorinated polymer. Their electrocatalytic activities with regard to the hydrogen evolution reaction (HER) were measured in sulfuric acid solution using cyclic voltammetry, and in a PEM cell during water electrolysis. Results obtained show that palladium can be advantageously used as an alternative electrocatalyst to platinum for the HER in PEM water electrolysers. Developed electrocatalysts could also be used in PEM fuel cells.

  4. Regenerative fuel cells

    NASA Technical Reports Server (NTRS)

    Swette, Larry L.; Kackley, Nancy D.; Laconti, Anthony B.

    1992-01-01

    A development status evaluation is presented for moderate-temperature, single-unit, regenerative fuel cells using either alkaline or solid polymer proton-exchange membrane (PEM) electrolytes. Attention is given to the results thus far obtained for Pt, Ir, Rh, and Na(x)Pt3O4 catalysts. Alkaline electrolyte tests have been performed on a half-cell basis with a floating-electrode cell; PEM testing has been with complete fuel cells, using Nafion 117.

  5. 40 CFR 1065.915 - PEMS instruments.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... to calculate test results for a single test. If you use redundant systems, use good engineering... as temperature, pressure, humidity, physical orientation, mechanical shock and vibration..., according to PEMS manufacturer instructions and using good engineering judgment. (4) ECM signals...

  6. Economics of Direct Hydrogen Polymer Electrolyte Membrane Fuel Cell Systems

    SciTech Connect

    Mahadevan, Kathyayani

    2011-10-04

    Battelle's Economic Analysis of PEM Fuel Cell Systems project was initiated in 2003 to evaluate the technology and markets that are near-term and potentially could support the transition to fuel cells in automotive markets. The objective of Battelle?s project was to assist the DOE in developing fuel cell systems for pre-automotive applications by analyzing the technical, economic, and market drivers of direct hydrogen PEM fuel cell adoption. The project was executed over a 6-year period (2003 to 2010) and a variety of analyses were completed in that period. The analyses presented in the final report include: Commercialization scenarios for stationary generation through 2015 (2004); Stakeholder feedback on technology status and performance status of fuel cell systems (2004); Development of manufacturing costs of stationary PEM fuel cell systems for backup power markets (2004); Identification of near-term and mid-term markets for PEM fuel cells (2006); Development of the value proposition and market opportunity of PEM fuel cells in near-term markets by assessing the lifecycle cost of PEM fuel cells as compared to conventional alternatives used in the marketplace and modeling market penetration (2006); Development of the value proposition of PEM fuel cells in government markets (2007); Development of the value proposition and opportunity for large fuel cell system application at data centers and wastewater treatment plants (2008); Update of the manufacturing costs of PEM fuel cells for backup power applications (2009).

  7. Characterization and Nucleotide Sequence of the Cryptic Cel Operon of Escherichia Coli K12

    PubMed Central

    Parker, L. L.; Hall, B. G.

    1990-01-01

    Wild-type Escherichia coli are not able to utilize β-glucoside sugars because the genes for utilization of these sugars are cryptic. Spontaneous mutations in the cel operon allow its expression and enable the organism to ferment cellobiose, arbutin and salicin. In this report we describe the structure and nucleotide sequence of the cel operon. The cel operon consists of five genes: celA, whose function is unknown; celB and celC which encode phosphoenolpyruvate-dependent phosphotransferase system enzyme II(cel) and enzyme III(cel), respectively, for the transport and phosphorylation of β-glucoside sugars; celD, which encodes a negative regulatory protein; and celF, which encodes a phospho-β-glucosidase that acts on phosphorylated cellobiose, arbutin and salicin. The mutationally activated cel operon is induced in the presence of its substrates, and is repressed in their absence. A comparison of proteins encoded by the cel operon with functionally equivalent proteins of the bgl operon, another cryptic E. coli gene system responsible for the catabolism of β-glucoside sugars, revealed no significant homology between these two systems despite common functional characteristics. The celD and celF encoded repressor and phospho-β-glucosidase proteins are homologous to the melibiose regulatory protein and to the melA encoded α-galactosidase of E. coli, respectively. Furthermore, the celC encoded PEP-dependent phosphotransferase system enzyme III(cel) is strikingly homologous to an enzyme III(lac) of the Gram-positive organism Staphylococcus aureus. We conclude that the genes for these two enzyme IIIs diverged much more recently than did their hosts, indicating that E. coli and S. aureus have undergone relatively recent exchange of chromosomal genes. PMID:2179047

  8. Effects of Ca2+ on refolding of the recombinant hemolytic lectin CEL-III.

    PubMed

    Hisamatsu, Keigo; Unno, Hideaki; Goda, Shuichiro; Hatakeyama, Tomomitsu

    2009-05-01

    CEL-III is a hemolytic lectin isolated from Cucumaria echinata. Although recombinant CEL-III (rCEL-III) expressed in Escherichia coli showed very weak hemolytic activity compared with native protein, it was considerably enhanced by refolding in the presence of Ca(2+). This suggests that Ca(2+) supported correct folding of the carbohydrate-binding domains of rCEL-III, leading to effective binding to the cell surface and subsequent self-oligomerization. PMID:19420692

  9. Nonhumidified High-Temperature Membranes Developed for Proton Exchange Membrane Fuel Cells

    NASA Technical Reports Server (NTRS)

    Kinder, James D.

    2005-01-01

    Fuel cells are being considered for a wide variety of aerospace applications. One of the most versatile types of fuel cells is the proton-exchange-membrane (PEM) fuel cell. PEM fuel cells can be easily scaled to meet the power and space requirements of a specific application. For example, small 100-W PEM fuel cells are being considered for personal power for extravehicular activity suit applications, whereas larger PEM fuel cells are being designed for primary power in airplanes and in uninhabited air vehicles. Typically, PEM fuel cells operate at temperatures up to 80 C. To increase the efficiency and power density of the fuel cell system, researchers are pursuing methods to extend the operating temperature of the PEM fuel cell to 180 C. The most widely used membranes in PEM fuel cells are Nafion 112 and Nafion 117--sulfonated perfluorinated polyethers that were developed by DuPont. In addition to their relatively high cost, the properties of these membranes limit their use in a PEM fuel cell to around 80 C. The proton conductivity of Nafion membranes significantly decreases above 80 C because the membrane dehydrates. The useful operating range of Nafion-based PEM fuel cells can be extended to over 100 C if ancillary equipment, such as compressors and humidifiers, is added to maintain moisture levels within the membrane. However, the addition of these components reduces the power density and increases the complexity of the fuel cell system.

  10. Laser Ablation Increases PEM/Catalyst Interfacial Area

    NASA Technical Reports Server (NTRS)

    Whitacre, Jay; Yalisove, Steve

    2009-01-01

    An investigational method of improving the performance of a fuel cell that contains a polymer-electrolyte membrane (PEM) is based on the concept of roughening the surface of the PEM, prior to deposition of a thin layer of catalyst, in order to increase the PEM/catalyst interfacial area and thereby increase the degree of utilization of the catalyst. The roughening is done by means of laser ablation under carefully controlled conditions. Next, the roughened membrane surface is coated with the thin layer of catalyst (which is typically platinum), then sandwiched between two electrode/catalyst structures to form a membrane/ele c t - rode assembly. The feasibility of the roughening technique was demonstrated in experiments in which proton-conducting membranes made of a perfluorosulfonic acid-based hydrophilic, protonconducting polymer were ablated by use of femtosecond laser pulses. It was found that when proper combinations of the pulse intensity, pulse-repetition rate, and number of repetitions was chosen, the initially flat, smooth membrane surfaces became roughened to such an extent as to be converted to networks of nodules interconnected by filaments (see Figure 1). In further experiments, electrochemical impedance spectroscopy (EIS) was performed on a pristine (smooth) membrane and on two laser-roughened membranes after the membranes were coated with platinum on both sides. Some preliminary EIS data were interpreted as showing that notwithstanding the potential for laser-induced damage, the bulk conductivities of the membranes were not diminished in the roughening process. Other preliminary EIS data (see Figure 2) were interpreted as signifying that the surface areas of the laser-roughened membranes were significantly greater than those of the smooth membrane. Moreover, elemental analyses showed that the sulfur-containing molecular groups necessary for proton conduction remained intact, even near the laser-roughened surfaces. These preliminary results can be taken

  11. PEM-INST-001: Instructions for Plastic Encapsulated Microcircuit (PEM) Selection, Screening, and Qualification

    NASA Technical Reports Server (NTRS)

    Teverovsky, Alexander; Sahu, Kusum

    2003-01-01

    Potential users of plastic encapsulated microcircuits (PEMs) need to be reminded that unlike the military system of producing robust high-reliability microcircuits that are designed to perform acceptably in a variety of harsh environments, PEMs are primarily designed for use in benign environments where equipment is easily accessed for repair or replacement. The methods of analysis applied to military products to demonstrate high reliability cannot always be applied to PEMs. This makes it difficult for users to characterize PEMs for two reasons: 1. Due to the major differences in design and construction, the standard test practices used to ensure that military devices are robust and have high reliability often cannot be applied to PEMs that have a smaller operating temperature range and are typically more frail and susceptible to moisture absorption. In contrast, high-reliability military microcircuits usually utilize large, robust, high-temperature packages that are hermetically sealed. 2. Unlike the military high-reliability system, users of PEMs have little visibility into commercial manufacturers proprietary design, materials, die traceability, and production processes and procedures. There is no central authority that monitors PEM commercial product for quality, and there are no controls in place that can be imposed across all commercial manufacturers to provide confidence to high-reliability users that a common acceptable level of quality exists for all PEMs manufacturers. Consequently, there is no guaranteed control over the type of reliability that is built into commercial product, and there is no guarantee that different lots from the same manufacturer are equally acceptable. And regarding application, there is no guarantee that commercial products intended for use in benign environments will provide acceptable performance and reliability in harsh space environments. The qualification and screening processes contained in this document are intended to

  12. A retrospective on the LBNL PEM project

    SciTech Connect

    Huber, J.S.; Moses, W.W.; Wang, G.C.; Derenzo, S.E.; Huesman,R.H.; Qi, J.; Virador, P.; Choong, W.S.; Mandelli, E.; Beuville, E.; Pedrali-Noy, M.; Krieger, B.; Meddeler, G.

    2004-11-15

    We present a retrospective on the LBNL Positron EmissionMammography (PEM) project, looking back on our design and experiences.The LBNL PEM camera utilizes detector modules that are capable ofmeasuring depth of interaction (DOI) and places them into 4 detectorbanks in a rectangular geometry. In order to build this camera, we had todevelop the DOI detector module, LSO etching, Lumirror-epoxy reflectorfor the LSO array (to achieve optimal DOI), photodiode array, custom IC,rigid-flex readout board, packaging, DOI calibration and reconstructionalgorithms for the rectangular camera geometry. We will discuss thehighlights (good and bad) of these developments.

  13. A retrospective on the LBNL PEM project.

    PubMed

    Huber, Jennifer S; Moses, William W; Wang, Gin-Chung; Derenzo, Stephen E; Huesman, Ronald H; Qi, Jinyi; Virador, Patrick; Choong, Woon-Seng; Mandelli, Emanuele; Beuville, Eric; Pedrali-Noy, Marzio; Krieger, Brad; Meddeler, Gerrit J

    2006-01-01

    We present a retrospective on the LBNL Positron Emission Mammography (PEM) project, looking back on our design and experiences. The LBNL PEM camera utilizes detector modules that are capable of measuring depth of interaction (DOI) and places them into 4 detector banks in a rectangular geometry. In order to build this camera, we had to develop the DOI detector module, LSO etching, Lumirror-epoxy reflector for the LSO array (to achieve optimal DOI), photodiode array, custom IC, rigid-flex readout board, packaging, DOI calibration and reconstruction algorithms for the rectangular camera geometry. We will discuss the high-lights (good and bad) of these developments. PMID:17645996

  14. Tuning surface hydrophilicity/hydrophobicity of hydrocarbon proton exchange membranes (PEMs).

    PubMed

    He, Chenfeng; Mighri, Frej; Guiver, Michael D; Kaliaguine, Serge

    2016-03-15

    The effect of annealing on the surface hydrophilicity of various representative classes of hydrocarbon-based proton exchange membranes (PEMs) is investigated. In all cases, a more hydrophilic membrane surface develops after annealing at elevated temperatures. The annealing time also had some influence, but in different ways depending on the class of PEM. Longer annealing times resulted in more hydrophilic membrane surfaces for copolymerized sulfonated poly(ether ether ketone) (SPEEK-HQ), while the opposite behavior occurred in sulfonated poly(aryl ether ether ketone) (Ph-SPEEK), sulfonated poly(aryl ether ether ketone ketone) (Ph-m-SPEEKK) and sulfonated poly (aryl ether ether nitrile) (SPAEEN-B). Increased surface hydrophilicity upon annealing results from ionic cluster decomposition, according to the "Eisenberg-Hird-Moore model" (EHM). The increased surface hydrophilicity is supported by contact angle (CA) measurements, and the cluster decomposition is auxiliarily supported by probing the level of atomic sulfur (sulfonic acid) within different surface depths using angle-dependent XPS as well as ATR-FTIR. Membrane acidification leads to more hydrophilic surfaces by elimination of the hydrogen bonding that occurs between strongly-bound residual solvent (dimethylacetamide, DMAc) and PEM sulfonic acid groups. The study of physicochemical tuning of surface hydrophilicity/hydrophobicity of PEMs by annealing and acidification provides insights for improving membrane electrode assembly (MEA) fabrication in fuel cell (FC). PMID:26722798

  15. PemK Toxin of Bacillus anthracis Is a Ribonuclease

    PubMed Central

    Agarwal, Shivangi; Mishra, Neeraj Kumar; Bhatnagar, Sonika; Bhatnagar, Rakesh

    2010-01-01

    Bacillus anthracis genome harbors a toxin-antitoxin (TA) module encoding pemI (antitoxin) and pemK (toxin). This study describes the rPemK as a potent ribonuclease with a preference for pyrimidines (C/U), which is consistent with our previous study that demonstrated it as a translational attenuator. The in silico structural modeling of the PemK in conjunction with the site-directed mutagenesis confirmed the role of His-59 and Glu-78 as an acid-base couple in mediating the ribonuclease activity. The rPemK is shown to form a complex with the rPemI, which is in line with its function as a TA module. This rPemI-rPemK complex becomes catalytically inactive when both the proteins interact in a molar stoichiometry of 1. The rPemI displays vulnerability to proteolysis but attains conformational stability only upon rPemK interaction. The pemI-pemK transcript is shown to be up-regulated upon stress induction with a concomitant increase in the amount of PemK and a decline in the PemI levels, establishing the role of these modules in stress. The artificial perturbation of TA interaction could unleash the toxin, executing bacterial cell death. Toward this end, synthetic peptides are designed to disrupt the TA interaction. The peptides are shown to be effective in abrogating TA interaction in micromolar range in vitro. This approach can be harnessed as a potential antibacterial strategy against anthrax in the future. PMID:20022964

  16. Plastic Encapsulated Microcircuits (PEMs) Reliability Guide

    NASA Technical Reports Server (NTRS)

    Sandor, M.

    2000-01-01

    It is reported by some users and has been demonstrated by others via testing and qualification that the quality and reliability of plastic-encapsulated microcircuits (PEMs) manufactured today are excellent in commercial applications and closely equivalent, and in some cases superior to their hemetic counterparts.

  17. No Association Between CEL-HYB Hybrid Allele and Chronic Pancreatitis in Asian Populations.

    PubMed

    Zou, Wen-Bin; Boulling, Arnaud; Masamune, Atsushi; Issarapu, Prachand; Masson, Emmanuelle; Wu, Hao; Sun, Xiao-Tian; Hu, Liang-Hao; Zhou, Dai-Zhan; He, Lin; Fichou, Yann; Nakano, Eriko; Hamada, Shin; Kakuta, Yoichi; Kume, Kiyoshi; Isayama, Hiroyuki; Paliwal, Sumit; Mani, K Radha; Bhaskar, Seema; Cooper, David N; Férec, Claude; Shimosegawa, Tooru; Chandak, Giriraj R; Chen, Jian-Min; Li, Zhao-Shen; Liao, Zhuan

    2016-06-01

    A hybrid allele between the carboxyl ester lipase gene (CEL) and its pseudogene, CELP (called CEL-HYB), generated by nonallelic homologous recombination between CEL intron 10 and CELP intron 10', was found to increase susceptibility to chronic pancreatitis in a case-control study of patients of European ancestry. We attempted to replicate this finding in 3 independent cohorts from China, Japan, and India, but failed to detect the CEL-HYB allele in any of these populations. The CEL-HYB allele might therefore be an ethnic-specific risk factor for chronic pancreatitis. An alternative hybrid allele (CEL-HYB2) was identified in all 3 Asian populations (1.7% combined carrier frequency), but was not associated with chronic pancreatitis. PMID:26946345

  18. Research and development of a Proton-Exchange-Membrane (PEM) fuel cell system for transportation applications. Progress report for Quarter 8 of the Phase II effort, July 1, 1996--September 30, 1996

    SciTech Connect

    1996-11-08

    This eighth quarterly report summarizes activity from July 1, 1996 through September 30, 1996. The report is organized in sections describing background information and work performed under the main work breakdown structure (WBS) categories. The WBS categories included are fuel processor, fuel cell stack, and system integration and controls. Program scheduling and task progress are presented in the appendix.

  19. Cellulose hydrolysis and binding with Trichoderma reesei Cel5A and Cel7A and their core domains in ionic liquid solutions.

    PubMed

    Wahlström, Ronny; Rahikainen, Jenni; Kruus, Kristiina; Suurnäkki, Anna

    2014-04-01

    Ionic liquids (ILs) dissolve lignocellulosic biomass and have a high potential as pretreatment prior to total enzymatic hydrolysis. ILs are, however, known to inactivate cellulases. In this article, enzymatic hydrolysis of microcrystalline cellulose (MCC) and enzyme binding onto the cellulosic substrate were studied in the presence of cellulose-dissolving ILs. Two different ILs, 1,3-dimethylimidazolium dimethylphosphate ([DMIM]DMP) and 1-ethyl-3-methylimidazolium acetate ([EMIM]AcO), and two monocomponent cellulases, Trichoderma reesei cellobiohydrolase Cel7A and endoglucanase Cel5A, were used in the study. The role and IL sensitivity of the carbohydrate-binding module (CBM) were studied by performing hydrolysis and binding experiments with both the intact cellulases, and their respective core domains (CDs). Based on hydrolysis yields and substrate binding experiments for the intact enzymes and their CDs in the presence of ILs, the function of the CBM appeared to be very IL sensitive. Binding data suggested that the CBM was more important for the substrate binding of endoglucanase Cel5A than for the binding of cellobiohydrolase Cel7A. The CD of Cel7A was able to bind well to cellulose even without a CBM, whereas Cel5A CD had very low binding affinity. Hydrolysis also occurred with Cel5A CD even if this protein had very low binding affinity in all the studied matrices. Binding and hydrolysis were less affected by the studied ILs for Cel7A than for Cel5A. To our knowledge, this is the first systematic study of IL effects on cellulase substrate binding. PMID:24258388

  20. Nucleotide sequence of the celG gene of Clostridium thermocellum and characterization of its product, endoglucanase CelG.

    PubMed Central

    Lemaire, M; Béguin, P

    1993-01-01

    The nucleotide sequence of the celG gene of Clostridium thermocellum, encoding endoglucanase CelG, was determined. The open reading frame extended over 1,698 bp and encoded a 566-amino-acid polypeptide (molecular weight of 63,128) similar to the C. thermocellum endoglucanase CelB (51.5% identical residues). The N terminus displayed a typical signal peptide, followed by a catalytic domain. The C terminus, which was separated from the catalytic domain by a 25-amino-acid segment rich in Pro, Thr, and Ser, contained two conserved stretches of 22 amino acids closely similar to those previously described in other cellulases from the same organism. Expression of the gene in Escherichia coli was increased by fusing the fragment coding for the catalytic domain in frame with the start of the lacZ' gene present in the vector. A low- and a high-M(r) form of the protein were purified. The two forms displayed identical enzymatic properties. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that both forms consist of a major polypeptide of M(r) 50,000 and two minor polypeptides of M(r)s 49,000 and 48,000, resulting from heterogeneous proteolytic cleavage at the C terminus. An antiserum raised against the forms purified from E. coli reacted with an immunoreactive polypeptide of M(r) 66,000, which was associated with the extracellular cellulolytic complex of C. thermocellum known as the cellulosome. Images PMID:8501039

  1. ExCEL, Exploring Careers Through Experiential Learning: Year One Evaluation Report.

    ERIC Educational Resources Information Center

    Buttram, Joan L.; Blair, Mark W.

    A third-party evaluation was conducted of the first year of the Exploring Careers through Experiential Learning project (ExCEL). ExCEL is a planned adaptation of the Northwest Regional Education Laboratory model (NWREL) to meet the needs of students in Prince William County, Virginia, and to assist high school students in successful transition to…

  2. Quality Assessment and Development in the Course of the EFMD CEL Programme Accreditation

    ERIC Educational Resources Information Center

    Meier, C.; Seufert, S.; Euler, D.

    2012-01-01

    This paper reviews the experiences and learnings derived from the European Foundation for Management Development's programme accreditation teChnology-Enhanced Learning (EFMD CEL) programme accreditation. The EFMD CEL quality framework is briefly described, and an overview of the programmes that have pursued accreditation is presented.…

  3. CEL-Seq2: sensitive highly-multiplexed single-cell RNA-Seq.

    PubMed

    Hashimshony, Tamar; Senderovich, Naftalie; Avital, Gal; Klochendler, Agnes; de Leeuw, Yaron; Anavy, Leon; Gennert, Dave; Li, Shuqiang; Livak, Kenneth J; Rozenblatt-Rosen, Orit; Dor, Yuval; Regev, Aviv; Yanai, Itai

    2016-01-01

    Single-cell transcriptomics requires a method that is sensitive, accurate, and reproducible. Here, we present CEL-Seq2, a modified version of our CEL-Seq method, with threefold higher sensitivity, lower costs, and less hands-on time. We implemented CEL-Seq2 on Fluidigm's C1 system, providing its first single-cell, on-chip barcoding method, and we detected gene expression changes accompanying the progression through the cell cycle in mouse fibroblast cells. We also compare with Smart-Seq to demonstrate CEL-Seq2's increased sensitivity relative to other available methods. Collectively, the improvements make CEL-Seq2 uniquely suited to single-cell RNA-Seq analysis in terms of economics, resolution, and ease of use. PMID:27121950

  4. Improved activity of a thermophilic cellulase, Cel5A, from Thermotoga maritima on ionic liquid pretreated switchgrass.

    PubMed

    Chen, Zhiwei; Pereira, Jose H; Liu, Hanbin; Tran, Huu M; Hsu, Nathan S Y; Dibble, Dean; Singh, Seema; Adams, Paul D; Sapra, Rajat; Hadi, Masood Z; Simmons, Blake A; Sale, Kenneth L

    2013-01-01

    Ionic liquid pretreatment of biomass has been shown to greatly reduce the recalcitrance of lignocellulosic biomass, resulting in improved sugar yields after enzymatic saccharification. However, even under these improved saccharification conditions the cost of enzymes still represents a significant proportion of the total cost of producing sugars and ultimately fuels from lignocellulosic biomass. Much of the high cost of enzymes is due to the low catalytic efficiency and stability of lignocellulolytic enzymes, especially cellulases, under conditions that include high temperatures and the presence of residual pretreatment chemicals, such as acids, organic solvents, bases, or ionic liquids. Improving the efficiency of the saccharification process on ionic liquid pretreated biomass will facilitate reduced enzyme loading and cost. Thermophilic cellulases have been shown to be stable and active in ionic liquids but their activity is typically at lower levels. Cel5A_Tma, a thermophilic endoglucanase from Thermotoga maritima, is highly active on cellulosic substrates and is stable in ionic liquid environments. Here, our motivation was to engineer mutants of Cel5A_Tma with higher activity on 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) pretreated biomass. We developed a robotic platform to screen a random mutagenesis library of Cel5A_Tma. Twelve mutants with 25-42% improvement in specific activity on carboxymethyl cellulose and up to 30% improvement on ionic-liquid pretreated switchgrass were successfully isolated and characterized from a library of twenty thousand variants. Interestingly, most of the mutations in the improved variants are located distally to the active site on the protein surface and are not directly involved with substrate binding. PMID:24244549

  5. Improved Activity of a Thermophilic Cellulase, Cel5A, from Thermotoga maritima on Ionic Liquid Pretreated Switchgrass

    PubMed Central

    Chen, Zhiwei; Pereira, Jose H.; Liu, Hanbin; Tran, Huu M.; Hsu, Nathan S. Y.; Dibble, Dean; Singh, Seema; Adams, Paul D.; Sapra, Rajat; Hadi, Masood Z.; Simmons, Blake A.; Sale, Kenneth L.

    2013-01-01

    Ionic liquid pretreatment of biomass has been shown to greatly reduce the recalcitrance of lignocellulosic biomass, resulting in improved sugar yields after enzymatic saccharification. However, even under these improved saccharification conditions the cost of enzymes still represents a significant proportion of the total cost of producing sugars and ultimately fuels from lignocellulosic biomass. Much of the high cost of enzymes is due to the low catalytic efficiency and stability of lignocellulolytic enzymes, especially cellulases, under conditions that include high temperatures and the presence of residual pretreatment chemicals, such as acids, organic solvents, bases, or ionic liquids. Improving the efficiency of the saccharification process on ionic liquid pretreated biomass will facilitate reduced enzyme loading and cost. Thermophilic cellulases have been shown to be stable and active in ionic liquids but their activity is typically at lower levels. Cel5A_Tma, a thermophilic endoglucanase from Thermotoga maritima, is highly active on cellulosic substrates and is stable in ionic liquid environments. Here, our motivation was to engineer mutants of Cel5A_Tma with higher activity on 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) pretreated biomass. We developed a robotic platform to screen a random mutagenesis library of Cel5A_Tma. Twelve mutants with 25–42% improvement in specific activity on carboxymethyl cellulose and up to 30% improvement on ionic-liquid pretreated switchgrass were successfully isolated and characterized from a library of twenty thousand variants. Interestingly, most of the mutations in the improved variants are located distally to the active site on the protein surface and are not directly involved with substrate binding. PMID:24244549

  6. Synergistic activity of Paenibacillus sp. BP-23 cellobiohydrolase Cel48C in association with the contiguous endoglucanase Cel9B and with endo- or exo-acting glucanases from Thermobifida fusca.

    PubMed

    Sánchez, Marta M; Irwin, Diana C; Pastor, F I Javier; Wilson, David B; Diaz, Pilar

    2004-07-20

    Cellobiohydrolase Cel48C from Paenibacillus sp. BP-23, an enzyme displaying limited activity on most cellulosic substrates, was assayed for activity in the presence of other bacterial endo- or exocellulases. Significant enhanced activity was observed when Cel48C was incubated in the presence of Paenibacillus sp. BP-23 endoglucanase Cel9B or Thermobifida fusca cellulases Cel6A and Cel6B, indicating that Cel48C acts synergistically with them. Maximum synergism rates on bacterial microcrystalline cellulose or filter paper were obtained with a mixture of Paenibacillus cellulases Cel9B and Cel48C, accompanied by T. fusca exocellulase Cel6B. Synergism was also observed in cell extracts from recombinant clone E. coli pUCel9-Cel48 expressing the two contiguous Paenibacillus cellulases Cel9B and Cel48C. The enhanced cellulolytic activity displayed by the cellulase mixtures assayed could be used as an efficient tool for biotechnological applications like pulp and paper manufacturing. PMID:15236244

  7. Biochemical genetics of the circadian rhythm in Neurospora crassa: studies on the cel strain

    SciTech Connect

    Lakin-Thomas, P.L.

    1985-01-01

    In Neurospora crassa, the cel mutation lengthens the period of the circadian rhythm when the medium is supplemented with linoleic acid (18:2). Double mutant strains were constructed between cel and the clock mutants prd-1 and four alleles at the frq locus. It was found that: (1) the effect of 18:2 on cel was blocked by prd-1, i.e., prd-1 is epistatic to cel. (2) cel and frq interact such that the percent increase in the period produced by 18:2 was inversely proportional to the period of the frq parent. (3) Data from the literature on period effects in double mutant strains support a multiplicative rather than an additive model. A biochemical interpretation of these interactions is discussed, based on the control of flux through metabolic pathways. Because the cel strain is known to be deficient in the pantothenate derivative normally attached to the fatty acid synthetase (FAS) complex, the possibility that cel may affect other pantothenate-modified proteins was investigated. It was found that in the cel/sup +/ strain, five proteins of molecular weights (M/sub r/) 9000, 19,000, 22,000, 140,000, and 200,000 were labelled with (/sup 14/C)pantothenate. In the cel strain, only the 200 k (FAS) label was reduced in amount. Therefore, there is no evidence that cel affects circadian rhythmicity through any deficiency other than FAS. A biochemical model for circadian rhythmicity in Neurospora is presented. Oscillations in cytoplasmic and mitochondrial Ca/sup 2 +/ are proposed; clock mutations are postulated to affect Ca/sup 2 +/ transporters and the mitochondrial membrane; and phase-shifting effects are accounted for by changes in Ca/sup 2 +/ or ATP levels.

  8. Cytotoxicity of a GalNAc-specific C-type lectin CEL-I toward various cell lines.

    PubMed

    Kuramoto, Takuya; Uzuyama, Hitomi; Hatakeyama, Tomomitsu; Tamura, Tadashi; Nakashima, Takuji; Yamaguchi, Kenichi; Oda, Tatsuya

    2005-01-01

    We found that CEL-I was a potent cytotoxic lectin. MDCK, HeLa, and XC cells were highly sensitive to CEL-I cytotoxicity and killed in a dose-dependent manner, whereas CHO, L929, and RAW264.7 cells were relatively resistant to CEL-I, and no significant toxicity was observed up to 10 microg/ml. Among these cell lines, MDCK cells showed the highest susceptibility to CEL-I cytotoxicity. A binding study using FITC-labeled CEL-I (F-CEL-I) revealed that the amounts of bound F-CEL-I on the sensitive cell lines were evidently greater than those on the resistant cell lines, suggesting that the different susceptibility of the cell lines to CEL-I cytotoxicity is partly explained by different efficiencies of binding of CEL-I to these cell lines. Interestingly, the cytotoxicity of CEL-I toward MDCK cells was more potent than those of other lectins such as WGA, PHA-L, and Con A, even though these lectins were capable of binding to MDCK cells at comparable levels to CEL-I. Since the cytotoxicity of CEL-I was strongly inhibited by GalNAc, the binding to cell surface specific carbohydrates is essential for the CEL-I cytotoxicity. The trypan blue dye exclusion test indicated that CEL-I caused a disorder of plasma membrane integrity as a relatively early event. CEL-I failed to induce the release of carboxyfluorescein (CF) from CF-loaded MDCK cells as seen for pore-forming hemolytic isolectin CEL-III, suggesting that the primary cellular target of CEL-I may be the plasma membrane, but its action mechanism differs from that of CEL-III. Although CEL-I induced dramatic cellular morphological changes in MDCK cells, neither typical apoptotic nuclear morphological changes nor DNA fragmentation was observed in CEL-I-treated MDCK cells even after such cellular changes. Our results demonstrated that CEL-I showed a potent cytotoxic effect, especially on MDCK cells, by causing plasma membrane disorder without induction of apoptosis. PMID:15713882

  9. 40 CFR 1065.920 - PEMS calibrations and verifications.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 33 2014-07-01 2014-07-01 false PEMS calibrations and verifications. 1065.920 Section 1065.920 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Field Testing and Portable Emission Measurement Systems § 1065.920 PEMS calibrations and verifications....

  10. 40 CFR 1065.925 - PEMS preparation for field testing.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 33 2014-07-01 2014-07-01 false PEMS preparation for field testing. 1065.925 Section 1065.925 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Field Testing and Portable Emission Measurement Systems § 1065.925 PEMS preparation for field testing....

  11. PEM Electrolysis H2A Production Case Study Documentation

    SciTech Connect

    James, Brian; Colella, Whitney; Moton, Jennie; Saur, G.; Ramsden, T.

    2013-12-31

    This report documents the development of four DOE Hydrogen Analysis (H2A) case studies for polymer electrolyte membrane (PEM) electrolysis. The four cases characterize PEM electrolyzer technology for two hydrogen production plant sizes (Forecourt and Central) and for two technology development time horizons (Current and Future).

  12. Characteristics of bifunctional acidic endoglucanase (Cel5B) from Gloeophyllum trabeum.

    PubMed

    Kim, Ho Myeong; Lee, Yoon Gyo; Patel, Darshan H; Lee, Kwang Ho; Lee, Dae-Seok; Bae, Hyeun-Jong

    2012-07-01

    The endoglucanase (Cel5B) from the filamentous fungus Gloeophyllum trabeum was cloned and expressed without a signal peptide, and alanine residue 22 converted to glutamine in Pichia pastoris GS115. The DNA sequence of Cel5B had an open reading frame of 1,077 bp, encoding a protein of 359 amino acid residues with a molecular weight of 47 kDa. On the basis of sequence similarity, Cel5B displayed active site residues at Glu-175 and Glu-287. Both residues lost full hydrolytic activity when replaced with alanine through point mutation. The purified recombinant Cel5B showed very high specific activity, about 80- to 1,000-fold and 13- to 70-fold in comparison with other endoglucanases and cellobiohydrolase, on carboxymethylcellulose and filter paper, respectively, at pH 3.5 and 55°C. Cel5B displayed bifunctional characteristics under acidic conditions. The kinetic properties of the enzyme determined using a Lineweaver-Burk plot indicated that Cel5B is a catalytically efficient cellulolytic enzyme. These results suggest that Cel5B has high bifunctional endo- and exoglucanase activity under acidic conditions and is a good candidate for bioconversion of lignocellulose. PMID:22395898

  13. Extreme Thermophilic Enzyme CelB-m Efficiently Degrades the Cellulose in Transgenic Arabidopsis thaliana.

    PubMed

    Wu, Jiandong; Wang, Meng; Zhang, Hui; Liu, Ruoxue

    2015-09-01

    Agricultural and forestry wastes abundant in the plant biomass are an important resource of green energy. However, little is known about how to exploit efficiently the resource. In this study, we isolated the CelB gene that encodes the extremely thermophilic cellulose-degrading enzyme from Thermotoga maritime. The enzyme-encoding gene CelB was optimized and reconstructed in N' codes by the code adaptability in Arabidopsis thaliana. Then, the optimized gene (CelB-m) or the recombinant gene (CBD-CelB) was fused with the plant binary vector which harbors the β-glucuronidase (GUS) gene that was transferred into Arabidopsis, respectively. GUS assay results showed CelB gene ubiquitous expression in transgenic plants. The enzyme-activity assays exhibited that the cellulase activity in the leaves of CelB-m transgenic plants were significantly higher than that of wild-type plants. The highest amount of enzymatic activity obtained was 131.2 U for every gram of fresh leaves in CBD-CelB plants. In addition, the enzymatic activity was stable at the temperature of 90 °C. These results suggested that the ectopic expression of pertinent biomass-degrading enzymes in transgenic plants can degrade effectively the plant biomass and lay a foundation on the application for the transgenic technique to crops. PMID:26186956

  14. Nanocrystalline cerium oxide materials for solid fuel cell systems

    DOEpatents

    Brinkman, Kyle S

    2015-05-05

    Disclosed are solid fuel cells, including solid oxide fuel cells and PEM fuel cells that include nanocrystalline cerium oxide materials as a component of the fuel cells. A solid oxide fuel cell can include nanocrystalline cerium oxide as a cathode component and microcrystalline cerium oxide as an electrolyte component, which can prevent mechanical failure and interdiffusion common in other fuel cells. A solid oxide fuel cell can also include nanocrystalline cerium oxide in the anode. A PEM fuel cell can include cerium oxide as a catalyst support in the cathode and optionally also in the anode.

  15. PEM public key certificate cache server

    NASA Astrophysics Data System (ADS)

    Cheung, T.

    1993-12-01

    Privacy Enhanced Mail (PEM) provides privacy enhancement services to users of Internet electronic mail. Confidentiality, authentication, message integrity, and non-repudiation of origin are provided by applying cryptographic measures to messages transferred between end systems by the Message Transfer System. PEM supports both symmetric and asymmetric key distribution. However, the prevalent implementation uses a public key certificate-based strategy, modeled after the X.509 directory authentication framework. This scheme provides an infrastructure compatible with X.509. According to RFC 1422, public key certificates can be stored in directory servers, transmitted via non-secure message exchanges, or distributed via other means. Directory services provide a specialized distributed database for OSI applications. The directory contains information about objects and then provides structured mechanisms for accessing that information. Since directory services are not widely available now, a good approach is to manage certificates in a centralized certificate server. This document describes the detailed design of a centralized certificate cache serve. This server manages a cache of certificates and a cache of Certificate Revocation Lists (CRL's) for PEM applications. PEMapplications contact the server to obtain/store certificates and CRL's. The server software is programmed in C and ELROS. To use this server, ISODE has to be configured and installed properly. The ISODE library 'libisode.a' has to be linked together with this library because ELROS uses the transport layer functions provided by 'libisode.a.' The X.500 DAP library that is included with the ELROS distribution has to be linked in also, since the server uses the DAP library functions to communicate with directory servers.

  16. Characterization of modular bifunctional processive endoglucanase Cel5 from Hahella chejuensis KCTC 2396.

    PubMed

    Ghatge, Sunil Subhash; Telke, Amar Anandrao; Kang, Seo-Hee; Arulalapperumal, Venkatesh; Lee, Keun-Woo; Govindwar, Sanjay Prabhu; Um, Youngsoon; Oh, Doo-Byoung; Shin, Hyun-Dong; Kim, Seon-Won

    2014-05-01

    Cel5 from marine Hahella chejuensis is composed of glycoside hydrolase family-5 (GH5) catalytic domain (CD) and two carbohydrate binding modules (CBM6-2). The enzyme was expressed in Escherichia coli and purified to homogeneity. The optimum endoglucanase and xylanase activities of recombinant Cel5 were observed at 65 °C, pH 6.5 and 55 °C, pH 5.5, respectively. It exhibited K m of 1.8 and 7.1 mg/ml for carboxymethyl cellulose and birchwood xylan, respectively. The addition of Ca(2+) greatly improved thermostability and endoglucanase activity of Cel5. The Cel5 retained 90 % of its endoglucanase activity after 24 h incubation in presence of 5 M concentration of NaCl. Recombinant Cel5 showed production of cellobiose after hydrolysis of cellulosic substrates (soluble/insoluble) and methylglucuronic acid substituted xylooligosaccharides after hydrolysis of glucuronoxylans by endo-wise cleavage. These results indicated that Cel5 as bifunctional enzyme having both processive endoglucanase and xylanase activities. The multidomain structure of Cel5 is clearly distinguished from the GH5 bifunctional glycoside hydrolases characterized to date, which are single domain enzymes. Sequence analysis and homology modeling suggested presence of two conserved binding sites with different substrate specificities in CBM6-2 and a single catalytic site in CD. Residues Glu132 and Glu219 were identified as key catalytic amino acids by sequence alignment and further verified by using site directed mutagenesis. CBM6-2 plays vital role in catalytic activity and thermostability of Cel5. The bifunctional activities and multiple substrate specificities of Cel5 can be utilized for efficient hydrolysis of cellulose and hemicellulose into soluble sugars. PMID:24343767

  17. DOE/FORD fuel cell contract for automotive application

    SciTech Connect

    Djong-Gie Oei

    1995-08-01

    The objectives of the contract are twofold. The first objective is to assess the feasibility of using a direct hydrogen fueled PEM fuel cell engine to power a midsize passenger car through the various drive cycles and test such a propulsion system on a test bed. The second objective is to study the supply infrastructure and safety aspects of hydrogen for future practical implementation of PEM fuel cells.

  18. Design of Current Source Dc/Dc Converter for Interfacing a 5 Kw Pem Fuel Cell / Paaugstinošā Strāvas Avota Līdzsprieguma Pārveidotāja Izstrāde 5 Kw Ūdeņraža Degvielas Elementam

    NASA Astrophysics Data System (ADS)

    Andreičiks, A.; Steiks, I.; Krievs, O.

    2013-08-01

    In domestic applications the low DC output voltage of a hydrogen fuel cell used as the main power supply or a backup power source has to be matched to the level and frequency of the AC voltage of utility grid. The interfacing power converter system usually consists of a DC/DC converter and an inverter. In this work, a DC/DC step-up converter stage is designed for interfacing a 5kW proton exchange membrane (PEM) fuel cell. The losses of DC/DC conversion are estimated and, basing on the relevant analysis, the most appropriate configuration of converter modules is selected for a DC/DC converter stage of increased efficiency. The authors present the results of experimental analysis and simulation for the selected configuration of four double inductor step-up push-pull converter modules Ūdeņraža degvielas elementa invertoru sistēmas mājsaimniecības pielietojumiem parasti sastāv no līdzsprieguma paaugstināšanas un invertēšanas mezgliem. Šis raksts ir veltīts paaugstinošā līdzsprieguma pārveidotāja izstrādei 5 kW protonu apmaiņas membrānas degvielas elementam. Rakstā izpētīts divu induktoru divtaktu strāvas avota paaugstinošais līdzsprieguma pārveidotājs, aplūkojot gan datormodelēšanas, gan eksperimentālos rezultātus. Lai palielinātu DC/DC pārveidotāja efektivitāti var izmantot vairākus pārveidotāja moduļus, kam ieejas savienotas paralēli un izejās - virkne. Analīze Šajā raksta ir veikta analīze, balstoties uz kuras var izvēlieties skaitu pārveidotāj moduļu skaitu, kuri nodrošina vislabāko efektivitāti DC/DC pārveidotāja posmā. Kopējais eksperimentāli noteiktais izstrādātās degvielas elementa pārveidotāju sistēmas fizikālā modeļa lietderības koeficients ir 93%

  19. Biochemical characterization and crystal structures of a fungal family 3 β-glucosidase, Cel3A from Hypocrea jecorina.

    PubMed

    Karkehabadi, Saeid; Helmich, Kate E; Kaper, Thijs; Hansson, Henrik; Mikkelsen, Nils-Egil; Gudmundsson, Mikael; Piens, Kathleen; Fujdala, Meredith; Banerjee, Goutami; Scott-Craig, John S; Walton, Jonathan D; Phillips, George N; Sandgren, Mats

    2014-11-01

    Cellulase mixtures from Hypocrea jecorina are commonly used for the saccharification of cellulose in biotechnical applications. The most abundant β-glucosidase in the mesophilic fungus Hypocrea jecorina is HjCel3A, which hydrolyzes the β-linkage between two adjacent molecules in dimers and short oligomers of glucose. It has been shown that enhanced levels of HjCel3A in H. jecorina cellulase mixtures benefit the conversion of cellulose to glucose. Biochemical characterization of HjCel3A shows that the enzyme efficiently hydrolyzes (1,4)- as well as (1,2)-, (1,3)-, and (1,6)-β-D-linked disaccharides. For crystallization studies, HjCel3A was produced in both H. jecorina (HjCel3A) and Pichia pastoris (Pp-HjCel3A). Whereas the thermostabilities of HjCel3A and Pp-HjCel3A are the same, Pp-HjCel3A has a higher degree of N-linked glycosylation. Here, we present x-ray structures of HjCel3A with and without glucose bound in the active site. The structures have a three-domain architecture as observed previously for other glycoside hydrolase family 3 β-glucosidases. Both production hosts resulted in HjCel3A structures that have N-linked glycosylations at Asn(208) and Asn(310). In H. jecorina-produced HjCel3A, a single N-acetylglucosamine is present at both sites, whereas in Pp-HjCel3A, the P. pastoris-produced HjCel3A enzyme, the glycan chains consist of 8 or 4 saccharides. The glycosylations are involved in intermolecular contacts in the structures derived from either host. Due to the different sizes of the glycosylations, the interactions result in different crystal forms for the two protein forms. PMID:25164811

  20. Novel proton exchange membrane fuel cell electrodes to improve performance of reversible fuel cell systems

    NASA Astrophysics Data System (ADS)

    Brown, Tim Matthew

    Proton exchange membrane (PEM) fuel cells react fuel and oxidant to directly and efficiently produce electrical power, without the need for combustion, heat engines, or motor-generators. Additionally, PEM fuel cell systems emit zero to virtually zero criteria pollutants and have the ability to reduce CO2 emissions due to their efficient operation, including the production or processing of fuel. A reversible fuel cell (RFC) is one particular application for a PEM fuel cell. In this application the fuel cell is coupled with an electrolyzer and a hydrogen storage tank to complete a system that can store and release electrical energy. These devices can be highly tailored to specific energy storage applications, potentially surpassing the performance of current and future secondary battery technology. Like all PEM applications, RFCs currently suffer from performance and cost limitations. One approach to address these limitations is to improve the cathode performance by engineering more optimal catalyst layer geometry as compared to the microscopically random structure traditionally used. Ideal configurations are examined and computer modeling shows promising performance improvements are possible. Several novel manufacturing methods are used to build and test small PEM fuel cells with novel electrodes. Additionally, a complete, dynamic model of an RFC system is constructed and the performance is simulated using both traditional and novel cathode structures. This work concludes that PEM fuel cell microstructures can be tailored to optimize performance based on design operating conditions. Computer modeling results indicate that novel electrode microstructures can improve fuel cell performance, while experimental results show similar performance gains that bolster the theoretical predictions. A dynamic system model predicts that novel PEM fuel cell electrode structures may enable RFC systems to be more competitive with traditional energy storage technology options.

  1. Fuel cell and membrane therefore

    DOEpatents

    Aindow, Tai-Tsui

    2016-08-09

    A fuel cell includes first and second flow field plates, and an anode electrode and a cathode electrode between the flow field plates. A polymer electrolyte membrane (PEM) is arranged between the electrodes. At least one of the flow field plates influences, at least in part, an in-plane anisotropic physical condition of the PEM that varies in magnitude between a high value direction and a low value direction. The PEM has an in-plane physical property that varies in magnitude between a high value direction and a low value direction. The PEM is oriented with its high value direction substantially aligned with the high value direction of the flow field plate.

  2. Two cellulases, CelA and CelC, from the polycentric anaerobic fungus Orpinomyces strain PC-2 contain N-terminal docking domains for a cellulase-hemicellulase complex.

    PubMed Central

    Li, X L; Chen, H; Ljungdahl, L G

    1997-01-01

    Two cDNAs encoding two cellulases, CelA and CelC, were isolated from a cDNA library of the polycentric anaerobic fungus Orpinomyces sp. strain PC-2 constructed in Escherichia coli. Nucleotide sequencing revealed that the celA cDNA (1,558 bp) and celC cDNA (1,628 bp) had open reading frames encoding polypeptides of 459 (CelA) and 449 (CelC) amino acids, respectively. The two cDNAs were 76.9 and 67.7% identical at the nucleotide and amino acid levels, respectively. Analysis of the deduced amino acid sequences showed that starting from the N termini, both CelA and CelC had signal peptides, which were followed by noncatalytic repeated peptide domains (NCRPD) containing two repeated sequences of 33 to 40 amino acid residues functioning as docking domains. The NCRPDs and the catalytic domains were separated by linker sequences. The NCRPDs were homologous to those found in several hydrolases of anaerobic fungi, whereas the catalytic domains were homologous to the catalytic domains of fungal cellobiohydrolases and bacterial endoglucanases. The linker sequence of CelA contained predominantly glutamine and proline residues, while that of CelC contained mainly threonine residues. CelA and CelC did not have a typical cellulose binding domain (CBD). CelA and CelC expressed in E. coli rapidly decreased the viscosity of carboxymethyl cellulose (CMC), indicating that there was endoglucanase activity. In addition, they produced cellobiose from CMC, acid-swollen cellulose, and cellotetraose, suggesting that they had cellobiohydrolase activity. The optimal activity conditions with CMC as the substrate were pH 4.3 to 6.8 and 50 degrees C for CelA and pH 4.6 to 7.0 and 40 degrees C for CelC. Despite the lack of a CBD, CelC displayed a high affinity for microcrystalline cellulose, whereas CelA did not. PMID:9406391

  3. Processivity, Synergism, and Substrate Specificity of Thermobifida fusca Cel6B ▿

    PubMed Central

    Vuong, Thu V.; Wilson, David B.

    2009-01-01

    A relationship between processivity and synergism has not been reported for cellulases, although both characteristics are very important for hydrolysis of insoluble substrates. Mutation of two residues located in the active site tunnel of Thermobifida fusca exocellulase Cel6B increased processivity on filter paper. Surprisingly, mixtures of the Cel6B mutant enzymes and T. fusca endocellulase Cel5A did not show increased synergism or processivity, and the mutant enzyme which had the highest processivity gave the poorest synergism. This study suggests that improving exocellulase processivity might be not an effective strategy for producing improved cellulase mixtures for biomass conversion. The inverse relationship between the activities of many of the mutant enzymes with bacterial microcrystalline cellulose and their activities with carboxymethyl cellulose indicated that there are differences in the mechanisms of hydrolysis for these substrates, supporting the possibility of engineering Cel6B to target selected substrates. PMID:19734341

  4. Intronless celB from the anaerobic fungus Neocallimastix patriciarum encodes a modular family A endoglucanase.

    PubMed Central

    Zhou, L; Xue, G P; Orpin, C G; Black, G W; Gilbert, H J; Hazlewood, G P

    1994-01-01

    The cDNA designated celB from the anaerobic rumen fungus Neocallimastix patriciarum contained a single open reading frame of 1422 bp coding for a protein (CelB) of M(r) 53,070. CelB expressed by Escherichia coli harbouring the full-length gene hydrolysed carboxymethylcellulose in the manner of an endoglucanase, but was most active against barley beta-glucan. It also released reducing sugar from xylan and lichenan, but was inactive against crystalline cellulose, laminarin, mannan, galactan and arabinan. The rate of hydrolysis of cellulo-oligosaccharides by CelB increased with increasing chain length from cellotriose to cellopentaose. The predicted structure of CelB contained features indicative of modular structure. The first 360 residues of CelB constituted a fully functional catalytic domain that was homologous with bacterial endoglucanases belonging to cellulase family A, including five which originate from three different species of anaerobic rumen bacteria. Downstream from this domain, and linked to it by a serine/threonine-rich hinge, was a non-catalytic domain containing short tandem repeats, homologous to the C-terminal repeats contained in xylanase A from the same anaerobic fungus. Unlike previous fungal cellulases, genomic celB was devoid of introns. This lack of introns and the homology of its encoded product with rumen bacterial endoglucanases suggest that acquisition of celB by the fungus may at some stage have involved horizontal gene transfer from a prokaryote to N. particiarum. Images Figure 4 PMID:8297343

  5. Homologous expression of the Caldicellulosiruptor bescii CelA reveals that the extracellular protein is glycosylated.

    PubMed

    Chung, Daehwan; Young, Jenna; Bomble, Yannick J; Vander Wall, Todd A; Groom, Joseph; Himmel, Michael E; Westpheling, Janet

    2015-01-01

    Members of the bacterial genus Caldicellulosiruptor are the most thermophilic cellulolytic microbes described with ability to digest lignocellulosic biomass without conventional pretreatment. The cellulolytic ability of different species varies dramatically and correlates with the presence of the multimodular cellulase CelA, which contains both a glycoside hydrolase family 9 endoglucanase and a glycoside hydrolase family 48 exoglucanase known to be synergistic in their activity, connected by three cellulose-binding domains via linker peptides. This architecture exploits the cellulose surface ablation driven by its general cellulase processivity as well as excavates cavities into the surface of the substrate, revealing a novel paradigm for cellulase activity. We recently reported that a deletion of celA in C. bescii had a significant effect on its ability to utilize complex biomass. To analyze the structure and function of CelA and its role in biomass deconstruction, we constructed a new expression vector for C. bescii and were able, for the first time, to express significant quantities of full-length protein in vivo in the native host. The protein, which contains a Histidine tag, was active and excreted from the cell. Expression of CelA protein with and without its signal sequence allowed comparison of protein retained intracellularly to protein transported extracellularly. Analysis of protein in culture supernatants revealed that the extracellular CelA protein is glycosylated whereas the intracellular CelA is not, suggesting that either protein transport is required for this post-translational modification or that glycosylation is required for protein export. The mechanism and role of protein glycosylation in bacteria is poorly understood and the ability to express CelA in vivo in C. bescii will allow the study of the mechanism of protein glycosylation in this thermophile. It will also allow the study of glycosylation of CelA itself and its role in the structure

  6. Homologous Expression of the Caldicellulosiruptor bescii CelA Reveals that the Extracellular Protein Is Glycosylated

    PubMed Central

    Bomble, Yannick J.; Vander Wall, Todd A.; Groom, Joseph; Himmel, Michael E.; Westpheling, Janet

    2015-01-01

    Members of the bacterial genus Caldicellulosiruptor are the most thermophilic cellulolytic microbes described with ability to digest lignocellulosic biomass without conventional pretreatment. The cellulolytic ability of different species varies dramatically and correlates with the presence of the multimodular cellulase CelA, which contains both a glycoside hydrolase family 9 endoglucanase and a glycoside hydrolase family 48 exoglucanase known to be synergistic in their activity, connected by three cellulose-binding domains via linker peptides. This architecture exploits the cellulose surface ablation driven by its general cellulase processivity as well as excavates cavities into the surface of the substrate, revealing a novel paradigm for cellulase activity. We recently reported that a deletion of celA in C. bescii had a significant effect on its ability to utilize complex biomass. To analyze the structure and function of CelA and its role in biomass deconstruction, we constructed a new expression vector for C. bescii and were able, for the first time, to express significant quantities of full-length protein in vivo in the native host. The protein, which contains a Histidine tag, was active and excreted from the cell. Expression of CelA protein with and without its signal sequence allowed comparison of protein retained intracellularly to protein transported extracellularly. Analysis of protein in culture supernatants revealed that the extracellular CelA protein is glycosylated whereas the intracellular CelA is not, suggesting that either protein transport is required for this post-translational modification or that glycosylation is required for protein export. The mechanism and role of protein glycosylation in bacteria is poorly understood and the ability to express CelA in vivo in C. bescii will allow the study of the mechanism of protein glycosylation in this thermophile. It will also allow the study of glycosylation of CelA itself and its role in the structure

  7. Homologous expression of the Caldicellulosiruptor bescii CelA reveals that the extracellular protein is glycosylated

    DOE PAGESBeta

    Chung, Daehwan; Young, Jenna; Bomble, Yannick J.; Vander Wall, Todd A.; Groom, Joseph; Himmel, Michael E.; Westpheling, Janet

    2015-03-23

    Members of the bacterial genus Caldicellulosiruptor are the most thermophilic cellulolytic microbes described with ability to digest lignocellulosic biomass without conventional pretreatment. The cellulolytic ability of different species varies dramatically and correlates with the presence of the multimodular cellulase CelA, which contains both a glycoside hydrolase family 9 endoglucanase and a glycoside hydrolase family 48 exoglucanase known to be synergistic in their activity, connected by three cellulose-binding domains via linker peptides. This architecture exploits the cellulose surface ablation driven by its general cellulase processivity as well as excavates cavities into the surface of the substrate, revealing a novel paradigm formore » cellulase activity. We recently reported that a deletion of celA in C. bescii had a significant effect on its ability to utilize complex biomass. To analyze the structure and function of CelA and its role in biomass deconstruction, we constructed a new expression vector for C. bescii and were able, for the first time, to express significant quantities of full-length protein in vivo in the native host. The protein, which contains a Histidine tag, was active and excreted from the cell. Expression of CelA protein with and without its signal sequence allowed comparison of protein retained intracellularly to protein transported extracellularly. Analysis of protein in culture supernatants revealed that the extracellular CelA protein is glycosylated whereas the intracellular CelA is not, suggesting that either protein transport is required for this post-translational modification or that glycosylation is required for protein export. The mechanism and role of protein glycosylation in bacteria is poorly understood and the ability to express CelA in vivo in C. bescii will allow the study of the mechanism of protein glycosylation in this thermophile. Finally, it will also allow the study of glycosylation of CelA itself and its role

  8. Heterologous expression of cellobiohydrolase II (Cel6A) in maize endosperm.

    PubMed

    Devaiah, Shivakumar Pattada; Requesens, Deborah Vicuna; Chang, Yeun-Kyung; Hood, Kendall R; Flory, Ashley; Howard, John A; Hood, Elizabeth E

    2013-06-01

    The technology of converting lignocellulose to biofuels has advanced swiftly over the past few years, and enzymes are a significant constituent of this technology. In this regard, cost effective production of cellulases has been the focus of research for many years. One approach to reach cost targets of these enzymes involves the use of plants as bio-factories. The application of this technology to plant biomass conversion for biofuels and biobased products has the potential for significantly lowering the cost of these products due to lower enzyme production costs. Cel6A, one of the two cellobiohydrolases (CBH II) produced by Hypocrea jecorina, is an exoglucanase that cleaves primarily cellobiose units from the non-reducing end of cellulose microfibrils. In this work we describe the expression of Cel6A in maize endosperm as part of the process to lower the cost of this dominant enzyme for the bioconversion process. The enzyme is active on microcrystalline cellulose as exponential microbial growth was observed in the mixture of cellulose, cellulases, yeast and Cel6A, Cel7A (endoglucanase), and Cel5A (cellobiohydrolase I) expressed in maize seeds. We quantify the amount accumulated and the activity of the enzyme. Cel6A expressed in maize endosperm was purified to homogeneity and verified using peptide mass finger printing. PMID:23080294

  9. Computational Investigations of Trichoderma Reesei Cel7A Suggest New Routes for Enzyme Activity Improvements

    SciTech Connect

    Beckham, G. T.; Payne, C. M.; Bu, L.; Taylor, C. B.; McCabe, C.; Chu, J. W.; Himmel, M. E.; Crowley, M. F.

    2012-01-01

    The Trichoderma reesei Family 7 cellulase (Cel7A) is a key industrial enzyme in the production of biofuels from lignocellulosic biomass. It is a multi-modular enzyme with a Family 1 carbohydrate-binding module, a flexible O-glycosylated linker, and a large catalytic domain. We have used simulation to elucidate new functions for the 3 sub-domains, which suggests new routes to increase the activity of this central enzyme. These findings include new roles for glycosylation, which we have shown can be used to tune the binding affinity. We have also examined the structures of the catalytically-active complex of Cel7A and its non-processive counterpart, Cel7B, engaged on cellulose, which suggests allosteric mechanisms involved in chain binding when these cellulases are complexed on cellulose. Our computational results also suggest that product inhibition varies significantly between Cel7A and Cel7B, and we offer a molecular-level explanation for this observation. Finally, we discuss simulations of the absolute and relative binding free energy of cellulose ligands and various mutations along the CD tunnel, which will affect processivity and the ability of Cel7A (and related enzymes) to digest cellulose. These results highlight new considerations in protein engineering for processive and non-processive cellulases for production of lignocellulosic biofuels.

  10. The celC gene, a new phylogenetic marker useful for taxonomic studies in Rhizobium.

    PubMed

    Robledo, Marta; Velázquez, Encarna; Ramírez-Bahena, Martha Helena; García-Fraile, Paula; Pérez-Alonso, Ana; Rivas, Raúl; Martínez-Molina, Eustoquio; Mateos, Pedro F

    2011-09-01

    The celC gene codifies for a cellulase that fulfils a very significant role in the infection process of clover by Rhizobium leguminosarum. This gene is located in the celABC operon present in the chromosome of strains representing R. leguminosarum, Rhizobium etli and Rhizobium radiobacter whose genomes have been completely sequenced. Nevertheless, the existence of this gene in other species of the genus Rhizobium had not been investigated to date. In this study, the celC gene was analysed for the first time in several species of this genus isolated from legume nodules and plant tumours, in order to compare the celC phylogeny to those of other chromosomal and plasmidic genes. The results obtained showed that phylogenies of celC and chromosomal genes, such as rrs, recA and atpD, were completely congruent, whereas no relation was found with symbiotic or virulence genes. Therefore, the suitability and usefulness of the celC gene to differentiate species of the genus Rhizobium, especially those with closely related rrs genes, was highlighted. Consequently, the taxonomic status of several strains of the genus Rhizobium with completely sequenced genomes is also discussed. PMID:21621937

  11. CelR, an Ortholog of the Diguanylate Cyclase PleD of Caulobacter, Regulates Cellulose Synthesis in Agrobacterium tumefaciens

    PubMed Central

    Barnhart, D. Michael; Su, Shengchang; Baccaro, Brenna E.; Banta, Lois M.

    2013-01-01

    Cellulose fibrils play a role in attachment of Agrobacterium tumefaciens to its plant host. While the genes for cellulose biosynthesis in the bacterium have been identified, little is known concerning the regulation of the process. The signal molecule cyclic di-GMP (c-di-GMP) has been linked to the regulation of exopolysaccharide biosynthesis in many bacterial species, including A. tumefaciens. In this study, we identified two putative diguanylate cyclase genes, celR (atu1297) and atu1060, that influence production of cellulose in A. tumefaciens. Overexpression of either gene resulted in increased cellulose production, while deletion of celR, but not atu1060, resulted in decreased cellulose biosynthesis. celR overexpression also affected other phenotypes, including biofilm formation, formation of a polar adhesion structure, plant surface attachment, and virulence, suggesting that the gene plays a role in regulating these processes. Analysis of celR and Δcel mutants allowed differentiation between phenotypes associated with cellulose production, such as biofilm formation, and phenotypes probably resulting from c-di-GMP signaling, which include polar adhesion, attachment to plant tissue, and virulence. Phylogenetic comparisons suggest that species containing both celR and celA, which encodes the catalytic subunit of cellulose synthase, adapted the CelR protein to regulate cellulose production while those that lack celA use CelR, called PleD, to regulate specific processes associated with polar localization and cell division. PMID:24038703

  12. The cel3 gene of Agaricus bisporus codes for a modular cellulase and is transcriptionally regulated by the carbon source.

    PubMed Central

    Chow, C M; Yagüe, E; Raguz, S; Wood, D A; Thurston, C F

    1994-01-01

    A 52-kDa protein, CEL3, has been separated from the culture filtrate of Agaricus bisporus during growth on cellulose. A PCR-derived probe was made, with a degenerate oligodeoxynucleotide derived from the amino acid sequence of a CEL3 CNBr cleavage product and was used to select cel3 cDNA clones from an A. bisporus cDNA library. Two allelic cDNAs were isolated. They showed 98.8% identity of their nucleotide sequences. The deduced amino acid sequence and domain architecture of CEL3 showed a high degree of similarity to those of cellobiohydrolase II of Trichoderma reesei. Functional expression of cel3 cDNA in Saccharomyces cerevisiae was achieved by placing it under the control of a constitutive promoter and fusing it to the yeast invertase signal sequence. Recombinant CEL3 secreted by yeast showed enzymatic activity towards crystalline cellulose. At long reaction times, CEL3 was also able to degrade carboxymethyl cellulose. Northern (RNA) analysis showed that cel3 gene expression was induced by cellulose and repressed by glucose, fructose, 2-deoxyglucose, and lactose. Glycerol, mannitol, sorbitol, and maltose were neutral carbon sources. Nuclear run-on analysis showed that the rate of synthesis of cel3 mRNA in cellulose-grown cultures was 13 times higher than that in glucose-grown cultures. A low basal rate of cel3 mRNA synthesis was observed in the nuclei isolated from glucose-grown mycelia. Images PMID:8085821

  13. Overexpression, purification and crystallization of the two C-terminal domains of the bifunctional cellulase ctCel9D-Cel44A from Clostridium thermocellum

    SciTech Connect

    Najmudin, Shabir; Guerreiro, Catarina I. P. D.; Ferreira, Luís M. A.; Romão, Maria J. C.; Fontes, Carlos M. G. A.; Prates, José A. M.

    2005-12-01

    The two C-terminal domains of the cellulase ctCel9D-Cel44A from C. thermocellum cellulosome have been crystallized in tetragonal space group P4{sub 3}2{sub 1}2 and X-ray diffraction data have been collected to 2.1 and 2.8 Å from native and seleno-l-methionine-derivative crystals, respectively. Clostridium thermocellum produces a highly organized multi-enzyme complex of cellulases and hemicellulases for the hydrolysis of plant cell-wall polysaccharides, which is termed the cellulosome. The bifunctional multi-modular cellulase ctCel9D-Cel44A is one of the largest components of the C. thermocellum cellulosome. The enzyme contains two internal catalytic domains belonging to glycoside hydrolase families 9 and 44. The C-terminus of this cellulase, comprising a polycystic kidney-disease module (PKD) and a carbohydrate-binding module (CBM44), has been crystallized. The crystals belong to the tetragonal space group P4{sub 3}2{sub 1}2, containing a single molecule in the asymmetric unit. Native and seleno-l-methionine-derivative crystals diffracted to 2.1 and 2.8 Å, respectively.

  14. Proton exchange membrane fuel cell technology for transportation applications

    SciTech Connect

    Swathirajan, S.

    1996-04-01

    Proton Exchange Membrane (PEM) fuel cells are extremely promising as future power plants in the transportation sector to achieve an increase in energy efficiency and eliminate environmental pollution due to vehicles. GM is currently involved in a multiphase program with the US Department of Energy for developing a proof-of-concept hybrid vehicle based on a PEM fuel cell power plant and a methanol fuel processor. Other participants in the program are Los Alamos National Labs, Dow Chemical Co., Ballard Power Systems and DuPont Co., In the just completed phase 1 of the program, a 10 kW PEM fuel cell power plant was built and tested to demonstrate the feasibility of integrating a methanol fuel processor with a PEM fuel cell stack. However, the fuel cell power plant must overcome stiff technical and economic challenges before it can be commercialized for light duty vehicle applications. Progress achieved in phase I on the use of monolithic catalyst reactors in the fuel processor, managing CO impurity in the fuel cell stack, low-cost electrode-membrane assembles, and on the integration of the fuel processor with a Ballard PEM fuel cell stack will be presented.

  15. The anchorage function of CipA (CelL), a scaffolding protein of the Clostridium thermocellum cellulosome.

    PubMed Central

    Kruus, K; Lua, A C; Demain, A L; Wu, J H

    1995-01-01

    Enzymatic cellulose degradation is a heterogeneous reaction requiring binding of soluble cellulase molecules to the solid substrate. Based on our studies of the cellulase complex of Clostridium thermocellum (the cellulosome), we have previously proposed that such binding can be brought about by a special "anchorage subunit." In this "anchor-enzyme" model, CipA (a major subunit of the cellulosome) enhances the activity of CelS (the most abundant catalytic subunit of the cellulosome) by anchoring it to the cellulose surface. We have subsequently reported that CelS contains a conserved duplicated sequence at its C terminus and that CipA contains nine repeated sequences with a cellulose binding domain (CBD) in between the second and third repeats. In this work, we reexamined the anchor-enzyme mechanism by using recombinant CelS (rCelS) and various CipA domains, CBD, R3 (the repeat next to CBD), and CBD/R3, expressed in Escherichia coli. As analyzed by non-denaturing gel electrophoresis, rCelS, through its conserved duplicated sequence, formed a stable complex with R3 or CBD/R3 but not with CBD. Although R3 or CBD alone did not affect the binding of rCelS to cellulose, such binding was dependent on CBD/R3, indicating the anchorage role of CBD/R3. Such anchorage apparently increased the rCelS activity toward crystalline cellulose. These results substantiate the proposed anchor-enzyme model and the expected roles of individual CipA domains and the conserved duplicated sequence of CelS. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 PMID:7568112

  16. Ionic liquid and deep eutectic solvent-activated CelA2 variants generated by directed evolution.

    PubMed

    Lehmann, Christian; Bocola, Marco; Streit, Wolfgang R; Martinez, Ronny; Schwaneberg, Ulrich

    2014-06-01

    Chemoenzymatic cellulose degradation is one of the key steps for the production of biomass-based fuels under mild conditions. An effective cellulose degradation process requires diverse physico-chemical dissolution of the biomass prior to enzymatic degradation. In recent years, "green" solvents, such as ionic liquids and, more recently, deep eutectic liquids, have been proposed as suitable alternatives for biomass dissolution by homogenous catalysis. In this manuscript, a directed evolution campaign of an ionic liquid tolerant β-1,4-endoglucanase (CelA2) was performed in order to increase its performance in the presence of choline chloride/glycerol (ChCl:Gly) or 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), as a first step to identify residues which govern ionic strength resistance and obtaining insights for employing cellulases on the long run in homogenous catalysis of lignocellulose degradation. After mutant library screening, variant M4 (His288Phe, Ser300Arg) was identified, showing a dramatically reduced activity in potassium phosphate buffer and an increased activity in the presence of ChCl:Gly or [BMIM]Cl. Further characterization showed that the CelA2 variant M4 is activated in the presence of these solvents, representing a first report of an engineered enzyme with an ionic strength activity switch. Structural analysis revealed that Arg300 could be a key residue for the ionic strength activation through a salt bridge with the neighboring Asp287. Experimental and computational results suggest that the salt bridge Asp287-Arg300 generates a nearly inactive CelA2 variant and activity is regained when ChCl:Gly or [BMIM]Cl are supplemented (~5-fold increase from 0.64 to 3.37 μM 4-MU/h with the addition ChCl:Gly and ~23-fold increase from 3.84 to 89.21 μM 4-pNP/h with the addition of [BMIM]Cl). Molecular dynamic simulations further suggest that the salt bridge between Asp287 and Arg300 in variant M4 (His288Phe, Ser300Arg) modulates the observed salt

  17. Kinetic studies of Thermobifida fusca Cel9A active site mutant enzymes.

    PubMed

    Zhou, Weilin; Irwin, Diana C; Escovar-Kousen, Jose; Wilson, David B

    2004-08-01

    Thermobifida fusca Cel9A-90, an unusual family 9 enzyme, is a processive endoglucanase containing a catalytic domain closely linked to a family 3c cellulose binding domain (Cel9A-68) followed by a fibronectin III-like domain and a family 2 cellulose binding domain. To study its catalytic mechanism, 12 mutant genes with changes in five conserved residues of Cel9A-68 were constructed, cloned, and expressed in Escherichia coli. The purified mutant enzymes were assayed for their activities on (carboxymethyl)cellulose, phosphoric acid-swollen cellulose, bacterial microcrystalline cellulose, and 2,4-dinitrophenyl beta-D-cellobioside. They were also tested for ligand binding, enzyme processivity, and thermostability. The results clearly show that E424 functions as the catalytic acid, D55 and D58 are both required for catalytic base activity, and Y206 plays an important role in binding, catalysis, and processivity, while Y318 plays an important role in binding of crystalline cellulose substrates and is required for processivity. Several amino acids located in a loop at the end of the catalytic cleft (T245-L251) were deleted from Cel9A-68, and this enzyme showed slightly improved filter paper activity and binding to BMCC but otherwise behaved like the wild-type enzyme. The FnIII-like domain was deleted from Cel9A-90, reducing BMCC activity to 43% of the wild type. PMID:15274620

  18. Oligomerization process of the hemolytic lectin CEL-III purified from a sea cucumber, Cucumaria echinata.

    PubMed

    Kuwahara, Hiromiki; Yamasaki, Takayuki; Hatakeyama, Tomomitsu; Aoyagi, Haruhiko; Fujisawa, Tetsuro

    2002-05-01

    CEL-III is a Ca(2+)-dependent lectin purified from a sea cucumber, Cucumaria echinata. This protein exhibits strong hemolytic activity as well as cytotoxicity toward some cultured cell lines. Hemolysis is caused by CEL-III oligomers formed in the cell membrane after binding to specific carbohydrate chains on the cell surface. We have found that the oligomerization of CEL-III is also induced by the binding of simple carbohydrates, such as lactose, in aqueous solution under high pH and high ionic strength conditions. From gel filtration analysis of the oligomerization of CEL-III, it was found that the formation of the CEL-III oligomer is effectively induced by the binding of lactose and lactulose, disaccharides containing a beta-galactoside structure. Electron micrographs of the resulting oligomers revealed them to exist as particles with a size of approximately 20-30 nm. The oligomerization process required more than 1 h, which is consistent with the increase in surface hydrophobicity as measured using a fluorescent probe, 8-anilinonaphthalene-1-sulfonate. However, a change in the far-UV CD spectra as well as small-angle X-ray scattering occurred within a few minutes, suggesting that a structural change in the protein takes place rapidly, but the following growth of the oligomer is a much slower process. PMID:11983084

  19. Fuel cell development for transportation: Catalyst development

    SciTech Connect

    Doddapaneni, N.

    1996-04-01

    Fuel cells are being considered as alternate power sources for transportation and stationary applications. With proton exchange membrane (PEM) fuel cells the fuel crossover to cathodes causes severe thermal management and cell voltage drop due to oxidation of fuel at the platinized cathodes. The main goal of this project was to design, synthesize, and evaluate stable and inexpensive transition metal macrocyclic catalysts for the reduction of oxygen and be electrochemically inert towards anode fuels such as hydrogen and methanol.

  20. Final Report - Effects of Impurities on Fuel Cell Performance and Durability

    SciTech Connect

    Trent Molter

    2012-08-18

    This program is focused on the experimental determination of the effects of key hydrogen side impurities on the performance of PEM fuel cells. Experimental data has been leveraged to create mathematical models that predict the performance of PEM fuel cells that are exposed to specific impurity streams. These models are validated through laboratory experimentation and utilized to develop novel technologies for mitigating the effects of contamination on fuel cell performance. Results are publicly disseminated through papers, conference presentations, and other means.

  1. Different Approaches for Ensuring Performance/Reliability of Plastic Encapsulated Microcircuits (PEMs) in Space Applications

    NASA Technical Reports Server (NTRS)

    Gerke, R. David; Sandor, Mike; Agarwal, Shri; Moor, Andrew F.; Cooper, Kim A.

    1999-01-01

    This paper presents viewgraphs on Plastic Encapsulated Microcircuits (PEMs). Different approaches are addressed to ensure good performance and reliability of PEMs. The topics include: 1) Mitigating Risk; and 2) Program results.

  2. Xylan oligosaccharides and cellobiohydrolase I (TrCel7A) interaction and effect on activity

    PubMed Central

    2011-01-01

    Background The well-studied cellulase mixture secreted by Trichoderma reesei (anamorph to Hypocrea jecorina) contains two cellobiohydolases (CBHs), cellobiohydrolase I (TrCel7A) and cellobiohydrolase II (TrCeI6A), that are core enzymes for the solubilisation of cellulose. This has attracted significant research interest because of the role of the CBHs in the conversion of biomass to fermentable sugars. However, the CHBs are notoriously slow and susceptible to inhibition, which presents a challenge for the commercial utilisation of biomass. The xylans and xylan fragments that are also present in the biomass have been suggested repeatedly as one cause of the reduced activity of CHBs. Yet, the extent and mechanisms of this inhibition remain poorly elucidated. Therefore, we studied xylan oligosaccharides (XOSs) of variable lengths with respect to their binding and inhibition of both TrCel7A and an enzyme variant without the cellulose-binding domain (CBM). Results We studied the binding of XOSs to TrCel7A by isothermal titration calorimetry. We found that XOSs bind to TrCel7A and that the affinity increases commensurate with XOS length. The CBM, on the other hand, did not affect the affinity significantly, which suggests that XOSs may bind to the active site. Activity assays of TrCel7A clearly demonstrated the negative effect of the presence of XOSs on the turnover number. Conclusions On the basis of these binding data and a comparison of XOS inhibition of the activity of the two enzyme variants towards, respectively, soluble and insoluble substrates, we propose a competitive mechanism for XOS inhibition of TrCel7A with phosphoric swollen cellulose as a substrate. PMID:22035059

  3. Preferential oxidation of methanol and carbon monoxide for gas cleanup during methanol fuel processing

    SciTech Connect

    Birdsell, S.A.; Vanderborgh, N.E.; Inbody, M.A.

    1993-07-01

    Methanol fuel processing generates hydrogen for low-temperature, PEM fuel cell systems now being considered for transportation and other applications. Although liquid methanol fuel is convenient for this application, existing fuel processing techniques generate contaminants that degrade fuel cell performance. Through mathematical models and laboratory experiments chemical processing is described that removes CO and other contaminants from the anode feed stream.

  4. Interaction between the endoglucanase CelA and the scaffolding protein CipC of the Clostridium cellulolyticum cellulosome.

    PubMed Central

    Pagès, S; Belaich, A; Tardif, C; Reverbel-Leroy, C; Gaudin, C; Belaich, J P

    1996-01-01

    The 5' end of the cipC gene, coding for the N-terminal part of CipC, the scaffolding protein of Clostridium cellulolyticum ATCC 35319, was cloned and sequenced. It encodes a 586-amino-acid peptide, including several domains: a cellulose-binding domain, a hydrophilic domain, and two hydrophobic domains (cohesin domains). Sequence alignments showed that the N terminus of CipC and CbpA of C. cellulovorans ATCC 35296 have the same organization. The mini-CipC polypeptide, containing a cellulose-binding domain, hydrophilic domain 1, and cohesin domain 1, was overexpressed in Escherichia coli and purified. The interaction between endoglucanase CelA, with (CelA2) and without (CelA3) the characteristic clostridial C-terminal domain called the duplicated-segment or dockerin domain, and the mini-CipC polypeptide was monitored by two different methods: the interaction Western blotting (immunoblotting) method and binding assays with biotin-labeled protein. Among the various forms of CelA (CelA2, CelA3, and an intermediary form containing only part of the duplicated segment), only CelA2 was found to interact with cohesin domain 1 of CipC. The apparent equilibrium dissociation constant of the CelA2-mini-CipC complex was 7 x 10(-9)M, which indicates that there exists a high affinity between these two proteins. PMID:8636029

  5. High performance robust F-doped tin oxide based oxygen evolution electro-catalysts for PEM based water electrolysis

    SciTech Connect

    Datta, Moni Kanchan; Kadakia, Karan; Velikokhatnyi, Oleg I; Jampani, Prashanth H; Chung, Sung Jae; Poston, James A; Manivannan, Ayyakkannu; Kumta, Prashant N

    2013-01-01

    Identification and development of non-noble metal based electro-catalysts or electro-catalysts comprising compositions with significantly reduced amounts of expensive noble metal contents (e.g. IrO{sub 2}, Pt) with comparable electrochemical performance to the standard noble metal/metal oxide for proton exchange membrane (PEM) based water electrolysis would signify a major breakthrough in hydrogen generation via water electrolysis. Development of such systems would lead to two primary outcomes: first, a reduction in the overall capital costs of PEM based water electrolyzers, and second, attainment of the targeted hydrogen production costs (<$3.00/gge delivered by 2015) comparable to conventional liquid fuels. In line with these goals, by exploiting a two-pronged theoretical first principles and experimental approach herein, we demonstrate for the very first time a solid solution of SnO{sub 2}:10 wt% F containing only 20 at.% IrO{sub 2} [e.g. (Sn{sub 0.80}Ir{sub 0.20})O{sub 2}:10F] displaying remarkably similar electrochemical activity and comparable or even much improved electrochemical durability compared to pure IrO{sub 2}, the accepted gold standard in oxygen evolution electro-catalysts for PEM based water electrolysis. We present the results of these studies.

  6. A Novel Unitized Regenerative Proton Exchange Membrane Fuel Cell

    NASA Technical Reports Server (NTRS)

    Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

    1996-01-01

    A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel single cell unitized regenerative fuel cell and results obtained on testing it are presented.

  7. A novel unitized regenerative proton exchange membrane fuel cell

    NASA Technical Reports Server (NTRS)

    Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

    1995-01-01

    A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed in work performed at Lynntech. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel unitized regenerative fuel cell and results obtained on testing it will be presented.

  8. A novel unitized regenerative proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

    1995-04-01

    A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed in work performed at Lynntech. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel unitized regenerative fuel cell and results obtained on testing it will be presented.

  9. Regenerative fuel cell systems for project pathfinder

    NASA Technical Reports Server (NTRS)

    Huff, J. R.; Hedstrom, J.; Vanderborgh, N. E.; Prokopius, P.

    1989-01-01

    The objectives of a surface power program, an element of the exploration thrust of the Pathfinder project, and plans for meeting them are outlined. Technological assessment and tradeoff studies of fuel cell and electrolyzer technologies suitable for use in a regenerative fuel cell are described. The viability of proton exchange membranes (PEM) in meeting the system requirements is discussed.

  10. Polybenzimidazole film containing phosphoric acid as proton exchange membrane (PEM)

    NASA Astrophysics Data System (ADS)

    Ameri, Roya

    , phosphoric acid, TFA/Hsb3POsb4,\\ TFA/Hsb2O, and phenol-water and form different crystal structures. The crystalline structure varies depending on the doping procedure. Employment of PBI doped with phosphoric acid as polymer electrolyte membranes in fuel cells opened a new prospect in PEM fuel cell applications. It shows promising properties from the polymer point of view.

  11. Navy fuel cell demonstration project.

    SciTech Connect

    Black, Billy D.; Akhil, Abbas Ali

    2008-08-01

    This is the final report on a field evaluation by the Department of the Navy of twenty 5-kW PEM fuel cells carried out during 2004 and 2005 at five Navy sites located in New York, California, and Hawaii. The key objective of the effort was to obtain an engineering assessment of their military applications. Particular issues of interest were fuel cell cost, performance, reliability, and the readiness of commercial fuel cells for use as a standalone (grid-independent) power option. Two corollary objectives of the demonstration were to promote technological advances and to improve fuel performance and reliability. From a cost perspective, the capital cost of PEM fuel cells at this stage of their development is high compared to other power generation technologies. Sandia National Laboratories technical recommendation to the Navy is to remain involved in evaluating successive generations of this technology, particularly in locations with greater environmental extremes, and it encourages their increased use by the Navy.

  12. 40 CFR 1065.915 - PEMS instruments.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... max. Engine torque estimator, BSFC (This is a signal from an engine's ECM) T or BSFC 1 s 1 Hz means 8... engine speed, torque, brake-specific fuel consumption (BSFC, in units of mass of fuel per kW-hr), and... any speed, torque, or BSFC estimator should meet the performance specifications in Table 1 of...

  13. Molecular cloning, functional expression, and characterization of isolectin genes of hemolytic lectin CEL-III from the marine invertebrate Cucumaria echinata.

    PubMed

    Shimizu, Yoshiki; Yamazaki, Hiroshi; Yoshida, Shigeto; Yonekura, Masami; Kouzuma, Yoshiaki

    2012-01-01

    CEL-III is a hemolytic lectin purified from the marine invertebrate Cucumaria echinata. Previous research has indictated that CEL-III is composed of several isoforms. Here we identified five CEL-III isolectin genes, designated CEL-III-L1, CEL-III-L2, CEL-III-S1, CEL-III-S2, and CEL-III-LS1, by cDNA cloning. The deduced amino acid sequences suggested they shared 94.0-99.8% identical residues. Among the amino acid residues involved in carbohydrate binding, the His residue, which contributes to stacking with sugar, in subdomain 1α was replaced by Tyr in CEL-III-L2. The recombinant proteins were expressed in Escherichia coli or insect cells. rCEL-III-L2 showed higher hemolytic activity than those of the other isolectins. Furthermore, an apparent oligomer band of rCEL-III-L2 was detected on erythrocyte membranes, although the other isolectins showed smear bands. These results suggest that Tyr36 of CEL-III-L2 is important for the expression of hemolytic activity and oligomerization. PMID:22313748

  14. PemK toxin encoded by the Xylella fastidiosa IncP-1 plasmid pXF-RIV11 is a ribonuclease

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Stable inheritance of the IncP-1 plasmid pXF-RIV11 in Xylella fastidiosa is conferred by the pemI/pemK plasmid addiction system. PemK serves as a toxin inhibiting bacterial growth; PemI is the corresponding antitoxin that blocks activity of PemK toxin by direct binding. Here, PemK toxin and PemI ant...

  15. ExCEL, Exploring Careers through Experiential Learning: Year Three Evaluation Report.

    ERIC Educational Resources Information Center

    Buttram, Joan L.

    Career development, life skills, and basic skills were important emphases in the experience-based career education program installed at two Virginia high schools. The program, call ExCEL (Exploring Careers through Experiential Learning), aimed to provide student experience in community learning sites and to integrate this with acquisition of…

  16. Amino terminal region of Phytophthora sojae cel12 endoglucanase confers tissue collapse function in Nicotiana

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Phytophthora encodes an unusually large number of glycosyl hydrolases (GH), with many large gene families resulting from duplication events. There are ten copies of GH 12 (cel12) present in Phytophthora sojae. This is the only pathogen endoglucanase family to which plants produce an inhibitory pr...

  17. Fuel cell development at McDermott Technology, Inc.

    SciTech Connect

    Tharp, M.R.; Privette, R.M.; Rowley, D.R.; Khandkar, A.

    1999-07-01

    McDermott Technology, Inc. (MTI) has been involved with the development of a wide variety of fuel cell technologies since 1990. Current programs include the development of planar solid fuel cell (pSOFC) stacks and systems and fuel processing and balance of plant development for proton exchange membrane (PEM) systems. These programs are described.

  18. PEM-based polarimeters for industrial applications

    NASA Astrophysics Data System (ADS)

    Wang, Baoliang

    2010-11-01

    polarimetry have established their own scientific communities, within which regular conferences are held.2-6 Tens of thousands of articles have been published on polarimeters and their applications, including books and many review articles.1, 7-15 In this paper, I will focus on polarimeters using the photoelastic modulator (PEM).16-18

  19. Engineering of Family-5 Glycoside Hydrolase (Cel5A) from an Uncultured Bacterium for Efficient Hydrolysis of Cellulosic Substrates

    PubMed Central

    Telke, Amar A.; Zhuang, Ningning; Ghatge, Sunil S.; Lee, Sook-Hee; Ali Shah, Asad; Khan, Haji; Um, Youngsoon; Shin, Hyun-Dong; Chung, Young Ryun; Lee, Kon Ho; Kim, Seon-Won

    2013-01-01

    Cel5A, an endoglucanase, was derived from the metagenomic library of vermicompost. The deduced amino acid sequence of Cel5A shows high sequence homology with family-5 glycoside hydrolases, which contain a single catalytic domain but no distinct cellulose-binding domain. Random mutagenesis and cellulose-binding module (CBM) fusion approaches were successfully applied to obtain properties required for cellulose hydrolysis. After two rounds of error-prone PCR and screening of 3,000 mutants, amino acid substitutions were identified at various positions in thermotolerant mutants. The most heat-tolerant mutant, Cel5A_2R2, showed a 7-fold increase in thermostability. To enhance the affinity and hydrolytic activity of Cel5A on cellulose substrates, the family-6 CBM from Saccharophagus degradans was fused to the C-terminus of the Cel5A_2R2 mutant using overlap PCR. The Cel5A_2R2-CBM6 fusion protein showed 7-fold higher activity than the native Cel5A on Avicel and filter paper. Cellobiose was a major product obtained from the hydrolysis of cellulosic substrates by the fusion enzyme, which was identified by using thin layer chromatography analysis. PMID:23785445

  20. Galactose recognition by a tetrameric C-type lectin, CEL-IV, containing the EPN carbohydrate recognition motif.

    PubMed

    Hatakeyama, Tomomitsu; Kamiya, Takuro; Kusunoki, Masami; Nakamura-Tsuruta, Sachiko; Hirabayashi, Jun; Goda, Shuichiro; Unno, Hideaki

    2011-03-25

    CEL-IV is a C-type lectin isolated from a sea cucumber, Cucumaria echinata. This lectin is composed of four identical C-type carbohydrate-recognition domains (CRDs). X-ray crystallographic analysis of CEL-IV revealed that its tetrameric structure was stabilized by multiple interchain disulfide bonds among the subunits. Although CEL-IV has the EPN motif in its carbohydrate-binding sites, which is known to be characteristic of mannose binding C-type CRDs, it showed preferential binding of galactose and N-acetylgalactosamine. Structural analyses of CEL-IV-melibiose and CEL-IV-raffinose complexes revealed that their galactose residues were recognized in an inverted orientation compared with mannose binding C-type CRDs containing the EPN motif, by the aid of a stacking interaction with the side chain of Trp-79. Changes in the environment of Trp-79 induced by binding to galactose were detected by changes in the intrinsic fluorescence and UV absorption spectra of WT CEL-IV and its site-directed mutants. The binding specificity of CEL-IV toward complex oligosaccharides was analyzed by frontal affinity chromatography using various pyridylamino sugars, and the results indicate preferential binding to oligosaccharides containing Galβ1-3/4(Fucα1-3/4)GlcNAc structures. These findings suggest that the specificity for oligosaccharides may be largely affected by interactions with amino acid residues in the binding site other than those determining the monosaccharide specificity. PMID:21247895

  1. Fuel cells - from the laboratory to the road

    SciTech Connect

    Fronk, M.H.

    1996-12-31

    The polymer electrolyte membrane (PEM) Fuel Cell faces stiff competition from existing automotive powerplants and other Hybrid APUs. To be successful, the Fuel Cell will have to demonstrate real customer advantages such as fuel economy and emissions. The PEM technology has an inherent advantage over other powerplants in both thermal efficiency and emission performance, and as such fits in very well with the future regulations that strive to clean up the environment. In addition, it will need to be cost competitive and provide acceptable performance. The majority of development activity on PEM Fuel Cells to date has concentrated primarily in the area of Stack refinement and optimization with improvements coming in higher power densities and higher specific power. To make the Fuel Cell compatible with an automotive environment the entire system will need to be analyzed, understood, and then engineered to work together in an efficient manner.

  2. USER'S GUIDE FOR PEM-2: POLLUTION EPISODIC MODEL (VERSION 2)

    EPA Science Inventory

    The Pollution Episodic Model Version 2 (PEM-2) is an urban-scale model designed to predict short term average ground-level concentrations and deposition fluxes of one or two gaseous or particulate pollutants at multiple receptors. The two pollutants may be non-reactive, or chemic...

  3. 40 CFR 1065.925 - PEMS preparation for field testing.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    .... 1065.925 Section 1065.925 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... purge any gaseous sampling PEMS instruments with ambient air until sampling begins to prevent system contamination from excessive cold-start emissions. (e) Conduct calibrations and verifications. (f) Operate...

  4. 40 CFR 1065.920 - PEMS calibrations and verifications.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 34 2012-07-01 2012-07-01 false PEMS calibrations and verifications. 1065.920 Section 1065.920 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... meet applicable validation requirements, such as drift validation, hydrocarbon contamination...

  5. 40 CFR 1065.920 - PEMS calibrations and verifications.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 34 2013-07-01 2013-07-01 false PEMS calibrations and verifications. 1065.920 Section 1065.920 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... meet applicable validation requirements, such as drift validation, hydrocarbon contamination...

  6. 40 CFR 1065.925 - PEMS preparation for field testing.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    .... 1065.925 Section 1065.925 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... purge any gaseous sampling PEMS instruments with ambient air until sampling begins to prevent system contamination from excessive cold-start emissions. (e) Conduct calibrations and verifications. (f) Operate...

  7. 7. Credit PEM. Interior of Martinsburg Plant, showing Warren 500 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Credit PEM. Interior of Martinsburg Plant, showing Warren 500 KW, 2200 Volt generator, with horizontal rode driven sheave wheel to right, belt-driven exciter in center, and switchboard on left. Photo c. 1907. - Dam No. 4 Hydroelectric Plant, Potomac River, Martinsburg, Berkeley County, WV

  8. 2. Credit PEM. View of Martinsburg Power Company steam generating ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Credit PEM. View of Martinsburg Power Company steam generating plant. From right to left: original 1889 generating building, transformer room, new generating room and, adjacent to draft stack is boiler room addition. Photo c. 1911. - Dam No. 4 Hydroelectric Plant, Potomac River, Martinsburg, Berkeley County, WV

  9. 5. Credit PEM. Interior of Martinsburg Plant, showing Atlas Corliss ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Credit PEM. Interior of Martinsburg Plant, showing Atlas Corliss 1000 hp steam engine and sheave wheel which powered a Warren 500 KW revolving field generator (which doesn't appear in this photo). Photo c. 1907. - Dam No. 4 Hydroelectric Plant, Potomac River, Martinsburg, Berkeley County, WV

  10. 6. Credit PEM. Interior of Martinsburg Plant, showing installation of ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. Credit PEM. Interior of Martinsburg Plant, showing installation of Warren 500 KW, 2200 Volt revolving field a.c. generator and sheave wheel, to be connected to Atlas Corliss 1000 hp steam engine (which doesn't appear in this photo). Photo c. 1907 - Dam No. 4 Hydroelectric Plant, Potomac River, Martinsburg, Berkeley County, WV

  11. 40 CFR 1065.920 - PEMS Calibrations and verifications.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 32 2010-07-01 2010-07-01 false PEMS Calibrations and verifications. 1065.920 Section 1065.920 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... validation, hydrocarbon contamination validation, and proportional validation. (4) Determine the...

  12. 40 CFR 1065.925 - PEMS preparation for field testing.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    .... 1065.925 Section 1065.925 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... purge any gaseous sampling PEMS instruments with ambient air until sampling begins to prevent system contamination from excessive cold-start emissions. (e) Conduct calibrations and verifications. (f) Operate...

  13. Clear-PEM system counting rates: a Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Rodrigues, P.; Trindade, A.; Varela, J.

    2007-01-01

    Positron Emission Mammography (PEM) with 18F-Fluorodeoxyglucose (18F-FDG) is a functional imaging technique for breast cancer detection. The development of dedicated imaging systems with high sensitivity and spatial resolution are crucial for early breast cancer diagnosis and an efficient therapy. Clear-PEM is a dual planar scanner designed for high-resolution breast cancer imaging under development by the Portuguese PET Mammography consortium within the Crystal Clear Collaboration. It brings together a favorable combination of high-density scintillator crystals coupled to compact photodetectors, arranged in a double readout scheme capable of providing depth-of-interaction information. A Monte Carlo study of the Clear-PEM system counting rates is presented in this paper. Hypothetical breast exam scenarios were simulated to estimate the single event rates, true and random coincidence rates. A realistic description of the patient and detector geometry, radiation environment, physics and instrumentation factors was adopted in this work. Special attention was given to the 18F-FDG accumulation in the patient torso organs which, for the Clear-PEM scanner, represent significant activity outside the field-of-view (FOV) contributing to an increase of singles, randoms and scattered coincidences affecting the overall system performance. The potential benefits of patient shielding to minimize the influence of the out-of-field background was explored. The influence of LYSO:Ce crystal intrinsic natural activity due to the presence of the 176Lu isotope on the counting rate performance of the proposed scanner, was also investigated.

  14. Comparison of scintillators for positron emission mammography (PEM) systems

    SciTech Connect

    Raymond Raylman; Stanislaw Majewski; Mark Smith; Randolph Wojcik; Andrew Weisenberger; Brian Kross; Vladimir Popov; Jamal J. Derakhshan

    2003-02-01

    Positron emission mammography (PEM) has promise as an effective method for the detection of breast lesions. Perhaps the most significant design feature of a PEM system is the choice of scintillator material. In this investigation we compared three scintillators for use in PEM: NaI(Tl), gadolinium oxyorthosilicate (GSO), and lutetium-gadolinium oxyorthosilicate (LGSO). The PEM systems consisted of two 30/spl times/30 arrays of pixelated scintillators (3/spl times/3/spl times/10 mm/sup 3/ for GSO and LGSO and 3/spl times/3/spl times/19 mm/sup 3/ for NaI(Tl)) coupled to arrays of square position-sensitive photomultiplier tubes. The Compton scatter fraction, system energy resolution, spatial resolution, spatial resolution uniformity, and detection sensitivity were compared. Compton scatter fractions for the systems were comparable, between 8% and 9%. The NaI(Tl) system produced the best system energy resolution (18.2%), the GSO system had the worst system energy resolution (28.7%).

  15. Dynamic first principles model of a complete reversible fuel cell system

    NASA Astrophysics Data System (ADS)

    Brown, Tim M.; Brouwer, Jacob; Samuelsen, G. Scott; Holcomb, Franklin H.; King, Joel

    A dynamic model of a discrete reversible fuel cell (RFC) system has been developed in a Matlab Simulink ® environment. The model incorporates first principles dynamic component models of a proton exchange membrane (PEM) fuel cell, a PEM electrolyzer, a metal hydride hydrogen storage tank, and a cooling system radiator, as well as empirical models of balance of plant components. Dynamic simulations show unique charging and discharging control issues and highlight factors contributing to overall system efficiency.

  16. PTS regulation domain-containing transcriptional activator CelR and sigma factor σ(54) control cellobiose utilization in Clostridium acetobutylicum.

    PubMed

    Nie, Xiaoqun; Yang, Bin; Zhang, Lei; Gu, Yang; Yang, Sheng; Jiang, Weihong; Yang, Chen

    2016-04-01

    The phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) regulation domain (PRD)-containing enhancer binding proteins (EBPs) are an important class of σ(54) -interacting transcriptional activators. Although PRD-containing EBPs are present in many Firmicutes, most of their regulatory functions remain unclear. In this study, the transcriptional regulons of about 50 PRD-containing EBPs in diverse Firmicutes species are reconstructed by using a comparative genomic approach, which contain the genes associated with utilization of β-glucosides, fructose/levan, mannose/glucose, pentitols, and glucosamine/fructosamine. We then present experimental evidence that the cel operon involved in cellobiose utilization is directly regulated by CelR and σ(54) (SigL) in Clostridium acetobutylicum. The predicted three CelR-binding sites and σ(54) promoter elements upstream of the cel operon are verified by in vitro binding assays. We show that CelR has an ATPase activity, which is strongly stimulated by the presence of DNA containing the CelR-binding sites. Moreover, mutations in any one of the three CelR-binding sites significantly decreased the cel promoter activity probably due to the need for all three DNA sites for maximal ATPase activity of CelR. It is suggested that CelR is regulated by PTS-mediated phosphorylation at His-551 and His-829, which exerts a positive effect and an inhibitory effect, respectively, on the CelR activity. PMID:26691835

  17. Insights from the Molecular Dynamics Simulation of Cellobiohydrolase Cel6A Molecular Structural Model from Aspergillus fumigatus NITDGPKA3.

    PubMed

    Dodda, Subba Reddy; Sarkar, Nibedita; Aikat, Kaustav; Krishnaraj, Navanietha R; Bhattacharjee, Sanchari; Bagchi, Angshuman; Mukhopadhyay, Sudit S

    2016-01-01

    Global demand for bioethanol is increasing tremendously as it could help to replace the conventional fossil fuel and at the same time supporting the bioremediation of huge volume of cellulosic wastes generated from different sources. Ideal genetic engineering approaches are essential to improve the efficacy of the bioethanol production processes for real time applications. A locally isolated fungal strain Aspergillus fumigatus NITDGPKA3 was used in our laboratory for the hydrolysis of lignocellulose with good cellulolytic activity when compared with other contemporary fungal strains. An attempt is made to sequence the cellobiohydrolases (CBHs) of A. fumigatus NITDGPKA3, model its structure to predict its catalytic activity towards improving the protein by genetic engineering approaches. Herein, the structure of the sequenced Cellobiohydrolases (CBHs) of A. fumigatus NITDGPKA3, modelled by homology modelling and its validation is reported. Further the catalytic activity of the modelled CBH enzyme was assessed by molecular docking analysis. Phylogenetic analysis showed that CBH from A. fumigatus NITDGPKA3 belongs to the Glycohydro 6 (Cel6A) super family. Molecular modeling and molecular dynamics simulation suggest the structural and functional mechanism of the enzyme. The structures of both the cellulose binding (CBD) and catalytic domain (CD) have been compared with most widely studied CBH of Trichoderma reesei. The molecular docking with cellulose suggests that Gln 248, Pro 287, Val236, Asn284, and Ala288 are the main amino acids involved in the hydrolysis of the β, 1-4, glycosidic bonds of cellulose. PMID:27109185

  18. Fundamental study of nanostructured electro-catalysts with reduced noble metal content for PEM based water electrolysis

    NASA Astrophysics Data System (ADS)

    Kadakia, Sandeep Karan

    Identification and development of non-noble metal based electro-catalysts or electro-catalysts with significant reduction of expensive noble metal contents (E.g. IrO2, Pt) with comparable electrochemical performance as the standard noble metal/metal oxide for proton exchange membrane (PEM) based water electrolysis would constitute a major breakthrough in the generation of hydrogen by water electrolysis. Accomplishing such a system would not only result reduction of the overall capital costs of PEM based water electrolyzers, but also help attain the targeted hydrogen production cost [< $ 3.0 / gallon gasoline equivalent (gge)] comparable to conventional liquid fuels. In line with these goals, it was demonstrated that fluorine doped IrO 2 thin films and nanostructured high surface area powders display remarkably higher electrochemical activity, and comparable durability as pure IrO 2 electro-catalyst for the oxygen evolution reaction (OER) in PEM based water electrolysis. Furthermore, corrosion resistant SnO2 and NbO 2 support has been doped with F and coupled with IrO2 or RuO2 for use as an OER electro-catalyst. A solid solution of SnO 2:F or NbO2:F with only 20 - 30 mol.% IrO2 or RuO2 yielding a rutile structure in the form of thin films and bulk nanoparticles displays similar electrochemical activity and stability as pure IrO2/RuO2. This would lead to more than 70 mol.% reduction in the noble metal oxide content. Novel nanostructured ternary (Ir,Sn,Nb)O 2 thin films of different compositions have also been studied. It has been shown that (Ir0.40Sn0.30Nb 0.30)O2 shows similar electrochemical activity and enhanced chemical robustness as compared to pure IrO2. F doping of the ternary (Ir,Sn,Nb)O2 catalyst helps in further decreasing the noble metal oxide content of the catalyst. As a result, these reduced noble metal oxide catalyst systems would potentially be preferred as OER electro-catalysts for PEM electrolysis. The excellent performance of the catalysts coupled

  19. Characterization of recombinant CEL-I, a GalNAc-specific C-type lectin, expressed in Escherichia coli using an artificial synthetic gene.

    PubMed

    Hatakeyama, Tomomitsu; Shiba, Kouhei; Matsuo, Noriaki; Fujimoto, Tokiko; Oda, Tatsuya; Sugawara, Hajime; Aoyagi, Haruhiko

    2004-01-01

    CEL-I is a C-type lectin isolated from the Holothuroidea Cucumaria echinata. This lectin shows very high N-acetylgalactosamine-binding specificity. We constructed an artificial gene encoding recombinant CEL-I (rCEL-I) using a combination of synthetic oligonucleotides, and expressed it in Escherichia coli cells. Since the recombinant protein was obtained as inclusion bodies, the latter were solubilized using urea and 2-mercaptoethanol, and the protein was refolded during the purification and dialysis steps. The purified rCEL-I showed comparable hemagglutinating activity to that of native CEL-I at relatively high Ca(2+)-concentrations, whereas it was weaker at lower Ca(2+)-concentrations due to decreased Ca(2+)-binding affinity. rCEL-I exhibited similar carbohydrate-binding specificity to native CEL-I, including strong GalNAc-binding specificity, as examined by hemagglutination inhibition assay. Comparison of the far UV-CD spectra of recombinant and native CEL-I revealed that the two proteins undergo a similar conformational change upon binding of Ca(2+). Single crystals of rCEL-I were also obtained under the same conditions as those used for the native protein, suggesting that they have similar tertiary structures. Although native CEL-I exhibited strong cytotoxicity toward cultured cells, rCEL-I showed low cytotoxicity. These results indicate that rCEL-I has a tertiary structure and carbohydrate-binding specificity similar to those of native CEL-I. Howeger, there is a subtle difference in the properties between the two proteins probably due to the additional methionine residue at the N-terminus of rCEL-I. PMID:14999015

  20. Characterization of a recombinant C-type lectin, rCEL-IV, expressed in Escherichia coli cells using a synthetic gene.

    PubMed

    Hatakeyama, Tomomitsu; Hozawa, Takao; Hirotani, Iyo; Tsuda, Nobuaki; Kusunoki, Masami; Shiba, Kohei

    2006-03-01

    The body fluid of marine invertebrate Cucumaria echinata (Holothuroidea) contains four Ca2+-dependent galactose-specific lectins. One of these lectins, CEL-IV, is composed of a C-type carbohydrate-recognition domain homotetramer. CEL-IV exhibits higher specificity for alpha-galactosides than for beta-galactosides, while other C. echinata lectins show preferential binding of beta-galactosides. We constructed an artificial synthetic gene for recombinant CEL-IV (rCEL-IV) based on the amino acid sequence previously determined from the purified protein. rCEL-IV was expressed in Escherichia coli cells as inclusion bodies. After the refolding process, most of rCEL-IV spontaneously formed a homotetramer structure having interchain disulfide bonds. The secondary structure of rCEL-IV was similar to that of the native one, as judged by the comparison of the far UV-circular dichroism spectra of rCEL-IV and native CEL-IV (nCEL-IV). Carbohydrate-binding specificity of rCEL-IV was confirmed to be similar to that of nCEL-IV from the results of the binding-inhibition assay using liposomes composed of rabbit erythrocyte lipids. Crystals of rCEL-IV were obtained in a few days by the sitting drop vapor diffusion method. These results indicate that rCEL-IV achieved essentially correct three-dimensional structure, including the carbohydrate-binding sites, and it would be very useful for further study on the carbohydrate-recognition mechanism by mutational and X-ray crystallographic analyses. PMID:16503091

  1. Crystallization and preliminary crystallographic study of oligomers of the haemolytic lectin CEL-III from the sea cucumber Cucumaria echinata.

    PubMed

    Unno, Hideaki; Hisamatsu, Keigo; Nagao, Tomonao; Tateya, Yuki; Matsumoto, Naoki; Goda, Shuichiro; Hatakeyama, Tomomitsu

    2013-04-01

    CEL-III is a Ca(2+)-dependent haemolytic lectin isolated from the marine invertebrate Cucumaria echinata. This lectin binds to Gal/GalNAc-containing carbohydrate chains on the cell surface and, after conformational changes, oligomerizes to form ion-permeable pores in cell membranes. CEL-III also forms soluble oligomers similar to those formed in cell membranes upon binding of specific carbohydrates in high-pH and high-salt solutions. These soluble and membrane CEL-III oligomers were crystallized and X-ray diffraction data were collected. Crystals of soluble oligomers and membrane oligomers diffracted X-rays to 3.3 and 4.2 Å resolution, respectively, using synchrotron radiation and the former was found to belong to space group C2. Self-rotation functional analysis of the soluble oligomer crystal suggested that it might be composed of heptameric CEL-III. PMID:23545649

  2. Crystallization and preliminary crystallographic study of oligomers of the haemolytic lectin CEL-III from the sea cucumber Cucumaria echinata

    PubMed Central

    Unno, Hideaki; Hisamatsu, Keigo; Nagao, Tomonao; Tateya, Yuki; Matsumoto, Naoki; Goda, Shuichiro; Hatakeyama, Tomomitsu

    2013-01-01

    CEL-III is a Ca2+-dependent haemolytic lectin isolated from the marine invertebrate Cucumaria echinata. This lectin binds to Gal/GalNAc-containing carbohydrate chains on the cell surface and, after conformational changes, oligomerizes to form ion-permeable pores in cell membranes. CEL-III also forms soluble oligomers similar to those formed in cell membranes upon binding of specific carbohydrates in high-pH and high-salt solutions. These soluble and membrane CEL-III oligomers were crystallized and X-ray diffraction data were collected. Crystals of soluble oligomers and membrane oligomers diffracted X-rays to 3.3 and 4.2 Å resolution, respectively, using synchrotron radiation and the former was found to belong to space group C2. Self-rotation functional analysis of the soluble oligomer crystal suggested that it might be composed of heptameric CEL-III. PMID:23545649

  3. The NASA fuel cell upgrade program for the Space Shuttle Orbiter

    SciTech Connect

    Warshay, M.; Prokopius, P.; Le, M.; Voecks, G.

    1997-12-31

    As part of NASA`s overall efforts to improve the Space Shuttle operations, a program to upgrade the existing fuel cell powerplant has begun. The upgrade will involve replacing the alkaline fuel cell (AFC) system with a proton exchange membrane (PEM) fuel cell system, resulting in a much lower life cycle cost of the powerplant. The program is being implemented by a team comprised of NASA/JSC, NASA/LeRC, and JPL personnel, with support from NASA/KSC. With extremely high annual maintenance costs and subsystem replacement costs, the need for a lower cost Orbiter fuel cell powerplant is obvious. Earlier NASA plant to upgrade the shuttle fuel cell were not adequately funded and only focused upon upgrading the existing AFC. For the current program, the PEM fuel cell system will be implemented because the projected long life (10,000 hrs. vs. 2,000 hrs. for AFC), high power density (PEM projected to produce 50% more power), and enhanced system reliability and safety all lead to significantly lower life cycle powerplant costs. And in addition to the Orbiter application, PEM fuel cell development would support a number of important space applications that the AFC would not, such as Lunar/Mars transportation, the Reusable Launch Vehicle (RLV), Space Station emergency power and/or future energy storage applications, and various portable applications. NASA is also leveraging all of the large scale PEM fuel cell development activities that are ongoing for DOE, DOD, and commercial applications. There is no activity in the AFC area. The Shuttle Fuel Cell Upgrade plan of the JSC/LeRC/JPL team includes the following key elements: (1) Systems Analyses to assure compatibility/maximum utilization by shuttle of the best PEM fuel cell characteristics; (2) Short Stack Testing of the leading PEM fuel cell contractors` hardware; (3) Detailed Task Objective (DTO) Flight Experiment to verify PEM system water management and thermal management under zero-g operation; (4) A Downselect to the best

  4. ARPA advanced fuel cell development

    SciTech Connect

    Dubois, L.H.

    1995-08-01

    Fuel cell technology is currently being developed at the Advanced Research Projects Agency (ARPA) for several Department of Defense applications where its inherent advantages such as environmental compatibility, high efficiency, and low noise and vibration are overwhelmingly important. These applications range from man-portable power systems of only a few watts output (e.g., for microclimate cooling and as direct battery replacements) to multimegawatt fixed base systems. The ultimate goal of the ARPA program is to develop an efficient, low-temperature fuel cell power system that operates directly on a military logistics fuel (e.g., DF-2 or JP-8). The absence of a fuel reformer will reduce the size, weight, cost, and complexity of such a unit as well as increase its reliability. In order to reach this goal, ARPA is taking a two-fold, intermediate time-frame approach to: (1) develop a viable, low-temperature proton exchange membrane (PEM) fuel cell that operates directly on a simple hydrocarbon fuel (e.g., methanol or trimethoxymethane) and (2) demonstrate a thermally integrated fuel processor/fuel cell power system operating on a military logistics fuel. This latter program involves solid oxide (SOFC), molten carbonate (MCFC), and phosphoric acid (PAFC) fuel cell technologies and concentrates on the development of efficient fuel processors, impurity scrubbers, and systems integration. A complementary program to develop high performance, light weight H{sub 2}/air PEM and SOFC fuel cell stacks is also underway. Several recent successes of these programs will be highlighted.

  5. A kinetic study of Trichoderma reesei Cel7B catalyzed cellulose hydrolysis.

    PubMed

    Song, Xiangfei; Zhang, Shujun; Wang, Yefei; Li, Jingwen; He, Chunyan; Yao, Lishan

    2016-06-01

    One prominent feature of Trichoderma reesei (Tr) endoglucanases catalyzed cellulose hydrolysis is that the reaction slows down quickly after it starts (within minutes). But the mechanism of the slowdown is not well understood. A structural model of Tr- Cel7B catalytic domain bound to cellulose was built computationally and the potentially important binding residues were identified and tested experimentally. The 13 tested mutants show different binding properties in the adsorption to phosphoric acid swollen cellulose and filter paper. Though the partitioning parameter to filter paper is about 10 times smaller than that to phosphoric acid swollen cellulose, a positive correlation is shown for two substrates. The kinetic studies show that the reactions slow down quickly for both substrates. This slowdown is not correlated to the binding constant but anticorrelated to the enzyme initial activity. The amount of reducing sugars released after 24h by Cel7B in phosphoric acid swollen cellulose, Avicel and filter paper cellulose hydrolysis is correlated with the enzyme activity against a soluble substrate p-nitrophenyl lactoside. Six of the 13 tested mutants, including N47A, N52D, S99A, N323D, S324A, and S346A, yield ∼15-35% more reducing sugars than the wild type (WT) Cel7B in phosphoric acid swollen cellulose and filter paper hydrolysis. This study reveals that the slowdown of the reaction is not due to the binding of the enzyme to cellulose. The activity of Tr- Cel7B against the insoluble substrate cellulose is determined by the enzyme's capability in hydrolyzing the soluble substrate. PMID:27178789

  6. Measurement of Species Distributions in Operating Fuel Cells

    SciTech Connect

    Partridge Jr, William P; Toops, Todd J; Parks, II, James E; Armstrong, Timothy R.

    2004-10-01

    Measurement and understanding of transient species distributions across and within fuel cells is a critical need for advancing fuel cell technology. The Spatially Resolved Capillary Inlet Mass Spectrometer (SpaciMS) instrument has been applied for in-situ measurement of transient species distributions within operating reactors; including diesel catalyst, air-exhaust mixing systems, and non-thermal plasma reactors. The work described here demonstrates the applicability of this tool to proton exchange membrane (PEM) and solid oxide fuel cells (SOFC) research. Specifically, we have demonstrated SpaciMS measurements of (1) transient species dynamics across a PEM fuel cell (FC) associated with load switching, (2) intra-PEM species distributions, and transient species dynamics at SOFC temperatures associated with FC load switching.

  7. Homologous expression of the Caldicellulosiruptor bescii CelA reveals that the extracellular protein is glycosylated

    SciTech Connect

    Chung, Daehwan; Young, Jenna; Bomble, Yannick J.; Vander Wall, Todd A.; Groom, Joseph; Himmel, Michael E.; Westpheling, Janet

    2015-03-23

    Members of the bacterial genus Caldicellulosiruptor are the most thermophilic cellulolytic microbes described with ability to digest lignocellulosic biomass without conventional pretreatment. The cellulolytic ability of different species varies dramatically and correlates with the presence of the multimodular cellulase CelA, which contains both a glycoside hydrolase family 9 endoglucanase and a glycoside hydrolase family 48 exoglucanase known to be synergistic in their activity, connected by three cellulose-binding domains via linker peptides. This architecture exploits the cellulose surface ablation driven by its general cellulase processivity as well as excavates cavities into the surface of the substrate, revealing a novel paradigm for cellulase activity. We recently reported that a deletion of celA in C. bescii had a significant effect on its ability to utilize complex biomass. To analyze the structure and function of CelA and its role in biomass deconstruction, we constructed a new expression vector for C. bescii and were able, for the first time, to express significant quantities of full-length protein in vivo in the native host. The protein, which contains a Histidine tag, was active and excreted from the cell. Expression of CelA protein with and without its signal sequence allowed comparison of protein retained intracellularly to protein transported extracellularly. Analysis of protein in culture supernatants revealed that the extracellular CelA protein is glycosylated whereas the intracellular CelA is not, suggesting that either protein transport is required for this post-translational modification or that glycosylation is required for protein export. The mechanism and role of protein glycosylation in bacteria is poorly understood and the ability to express CelA in vivo in C. bescii will allow the study of the mechanism of protein glycosylation in this thermophile. Finally, it will also allow the study of glycosylation of CelA itself and its role in the

  8. Improving the activity of Trichoderma reesei cel7B through stabilizing the transition state.

    PubMed

    Wang, Yefei; Song, Xiangfei; Zhang, Shujun; Li, Jingwen; Shu, Zhiyu; He, Chunyan; Huang, Qingshan; Yao, Lishan

    2016-06-01

    Trichoderma reesei (Tr.) cellulases, which convert cellulose to reducing sugars, are a promising catalyst used in the lignocellulosic biofuel production. Improving Tr. cellulases activity, though very difficult, is highly desired due to the recalcitrance of lignocellulose. Meanwhile, it is preferable to enhance the cellulase's promiscuity so that substrates other than cellulose can also be hydrolyzed. In this work, an attempt is made to improve the catalytic activity of a major endogluanase Tr. Cel7B against xylan which crosslinks with cellulose in lignocellulose. By using quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations, the transition state of the xylo-oligosaccharide hydrolysis is identified. Then, mutations are introduced and their effect on the transition state stabilization is ranked based on the free energy calculations. Seven top ranked mutants are evaluated experimentally. Three mutants A208Q, A222D, and G230R show a higher activity than the wild-type Tr. Cel7B in the hydrolysis of xylan (by up to 47%) as well as filter paper (by up to 50%). The combination of the single mutants can further improve the enzyme activity. Our work demonstrates that the free energy method is effective in engineering the Tr. Cel7B activity against xylan and cellulose, and thus may also be useful for improving the activity of other Tr. cellulases. Biotechnol. Bioeng. 2016;113: 1171-1177. © 2015 Wiley Periodicals, Inc. PMID:26616246

  9. celB, a gene coding for a bifunctional cellulase from the extreme thermophile "Caldocellum saccharolyticum".

    PubMed Central

    Saul, D J; Williams, L C; Grayling, R A; Chamley, L W; Love, D R; Bergquist, P L

    1990-01-01

    "Caldocellum saccharolyticum" is an obligatory anaerobic thermophilic bacterium. A gene from this organism, designated celB, has been cloned in Escherichia coli as part of a bacteriophage lambda gene library. This gene produces a thermostable cellulase that shows both endoglucanase and exoglucanase activities on test substrates and is able to degrade crystalline cellulose to glucose. The sequence of celB has homology with both exo- and endoglucanases described by others. It appears to have a central domain without enzymatic activity which is joined to the enzymatic domains by runs of amino acids rich in proline and threonine (PT boxes). Deletion analysis shows that the exoglucanase activity is located in the amino-terminal domain of the enzyme and that endoglucanase activity is located in the carboxy-terminal domain. There are internal transcriptional and translational start sites within the gene. The intact gene has been cloned into a temperature-inducible expression vector, pJLA602, and overexpressed in E. coli. Polyacrylamide gel electrophoresis showed that celB produced a protein with a molecular weight of 118,000 to 120,000. A number of smaller proteins with activity against carboxymethyl cellulose and 4-methyl umbelliferyl-beta-D-cellobioside were also produced. These are believed to be the result of alternative translational start sites and/or proteolytic degradation products of the translated gene product. Images PMID:2126700

  10. Rhizobium cellulase CelC2 is essential for primary symbiotic infection of legume host roots

    PubMed Central

    Robledo, M.; Jiménez-Zurdo, J. I.; Velázquez, E.; Trujillo, M. E.; Zurdo-Piñeiro, J. L.; Ramírez-Bahena, M. H.; Ramos, B.; Díaz-Mínguez, J. M.; Dazzo, F.; Martínez-Molina, E.; Mateos, P. F.

    2008-01-01

    The rhizobia–legume, root-nodule symbiosis provides the most efficient source of biologically fixed ammonia fertilizer for agricultural crops. Its development involves pathways of specificity, infectivity, and effectivity resulting from expressed traits of the bacterium and host plant. A key event of the infection process required for development of this root-nodule symbiosis is a highly localized, complete erosion of the plant cell wall through which the bacterial symbiont penetrates to establish a nitrogen-fixing, intracellular endosymbiotic state within the host. This process of wall degradation must be delicately balanced to avoid lysis and destruction of the host cell. Here, we describe the purification, biochemical characterization, molecular genetic analysis, biological activity, and symbiotic function of a cell-bound bacterial cellulase (CelC2) enzyme from Rhizobium leguminosarum bv. trifolii, the clover-nodulating endosymbiont. The purified enzyme can erode the noncrystalline tip of the white clover host root hair wall, making a localized hole of sufficient size to allow wild-type microsymbiont penetration. This CelC2 enzyme is not active on root hairs of the nonhost legume alfalfa. Microscopy analysis of the symbiotic phenotypes of the ANU843 wild type and CelC2 knockout mutant derivative revealed that this enzyme fulfils an essential role in the primary infection process required for development of the canonical nitrogen-fixing R. leguminosarum bv. trifolii-white clover symbiosis. PMID:18458328

  11. Structural insights into the affinity of Cel7A carbohydrate-binding module for lignin.

    PubMed

    Strobel, Kathryn L; Pfeiffer, Katherine A; Blanch, Harvey W; Clark, Douglas S

    2015-09-11

    The high cost of hydrolytic enzymes impedes the commercial production of lignocellulosic biofuels. High enzyme loadings are required in part due to their non-productive adsorption to lignin, a major component of biomass. Despite numerous studies documenting cellulase adsorption to lignin, few attempts have been made to engineer enzymes to reduce lignin binding. In this work, we used alanine-scanning mutagenesis to elucidate the structural basis for the lignin affinity of Trichoderma reesei Cel7A carbohydrate binding module (CBM). T. reesei Cel7A CBM mutants were produced with a Talaromyces emersonii Cel7A catalytic domain and screened for their binding to cellulose and lignin. Mutation of aromatic and polar residues on the planar face of the CBM greatly decreased binding to both cellulose and lignin, supporting the hypothesis that the cellulose-binding face is also responsible for lignin affinity. Cellulose and lignin affinity of the 31 mutants were highly correlated, although several mutants displayed selective reductions in lignin or cellulose affinity. Four mutants with increased cellulose selectivity (Q2A, H4A, V18A, and P30A) did not exhibit improved hydrolysis of cellulose in the presence of lignin. Further reduction in lignin affinity while maintaining a high level of cellulose affinity is thus necessary to generate an enzyme with improved hydrolysis capability. This work provides insights into the structural underpinnings of lignin affinity, identifies residues amenable to mutation without compromising cellulose affinity, and informs engineering strategies for family one CBMs. PMID:26209638

  12. Mechanisms of Activation of the Cryptic Cel Operon of Escherichia Coli K12

    PubMed Central

    Parker, L. L.; Hall, B. G.

    1990-01-01

    The cel (cellobiose utilization) operon of Escherichia coli K12 is not expressed in the wild-type organism. However, mutants that can express the operon and thereby utilize the β-glucoside sugars cellobiose, arbutin and salicin are easily isolated. Two kinds of mutations are capable of activating the operon. The first involves mutations that allow the repressor to recognize the substrates cellobiose, arbutin and salicin as inducers. We have identified the sequence changes in five different active alleles and found those differences to be single base pair changes at one of two lysine codons in the repressor gene. The second kind of mutation involves the integration of the insertion sequences IS1, IS2 or IS5 into a 108-bp region 72-180 bp upstream of the start of transcription. Integration occurs at several different sites and in different orientations. Transcription of the cel operon begins at the same base pair in all mutants examined. Of 44 independent cel(+) mutants, 27 were activated by point mutations and 17 were activated by insertion sequences. The preferred mechanism of activation appears to be strain dependent, since one of the parents yielded 94% insertionally activated alleles, while another yielded 100% point mutation activated alleles. PMID:2179048

  13. Structural Insights into the Affinity of Cel7A Carbohydrate-binding Module for Lignin*

    PubMed Central

    Strobel, Kathryn L.; Pfeiffer, Katherine A.; Blanch, Harvey W.; Clark, Douglas S.

    2015-01-01

    The high cost of hydrolytic enzymes impedes the commercial production of lignocellulosic biofuels. High enzyme loadings are required in part due to their non-productive adsorption to lignin, a major component of biomass. Despite numerous studies documenting cellulase adsorption to lignin, few attempts have been made to engineer enzymes to reduce lignin binding. In this work, we used alanine-scanning mutagenesis to elucidate the structural basis for the lignin affinity of Trichoderma reesei Cel7A carbohydrate binding module (CBM). T. reesei Cel7A CBM mutants were produced with a Talaromyces emersonii Cel7A catalytic domain and screened for their binding to cellulose and lignin. Mutation of aromatic and polar residues on the planar face of the CBM greatly decreased binding to both cellulose and lignin, supporting the hypothesis that the cellulose-binding face is also responsible for lignin affinity. Cellulose and lignin affinity of the 31 mutants were highly correlated, although several mutants displayed selective reductions in lignin or cellulose affinity. Four mutants with increased cellulose selectivity (Q2A, H4A, V18A, and P30A) did not exhibit improved hydrolysis of cellulose in the presence of lignin. Further reduction in lignin affinity while maintaining a high level of cellulose affinity is thus necessary to generate an enzyme with improved hydrolysis capability. This work provides insights into the structural underpinnings of lignin affinity, identifies residues amenable to mutation without compromising cellulose affinity, and informs engineering strategies for family one CBMs. PMID:26209638

  14. Breaking down the barriers to commercialization of fuel cells in transportation through Government - industry R&D programs

    SciTech Connect

    Chalk, S.G.; Venkateswaran, S.R.

    1996-12-31

    PEM fuel cell technology is rapidly emerging as a viable propulsion alternative to the internal combustion engine. Fuel cells offer the advantages of low emissions, high efficiency, fuel flexibility, quiet and continuous operation, and modularity. Over the last decade, dramatic advances have been achieved in the performance and cost of PEM fuel cell technologies for automotive applications. However, significant technical barriers remain to making fuel cell propulsion systems viable alternatives to the internal combustion engine. This paper focuses on the progress achieved and remaining technical barriers while highlighting Government-industry R&D efforts that are accelerating fuel cell technology toward commercialization.

  15. Experimental characterization of the Clear-PEM scanner spectrometric performance

    NASA Astrophysics Data System (ADS)

    Bugalho, R.; Carriço, B.; Ferreira, C. S.; Frade, M.; Ferreira, M.; Moura, R.; Ortigão, C.; Pinheiro, J. F.; Rodrigues, P.; Rolo, I.; Silva, J. C.; Trindade, A.; Varela, J.

    2009-10-01

    In the framework of the Clear-PEM project for the construction of a high-resolution and high-specificity scanner for breast cancer imaging, a Positron Emission Mammography tomograph has been developed and installed at the Instituto Português de Oncologia do Porto hospital. The Clear-PEM scanner is mainly composed by two planar detector heads attached to a robotic arm, trigger/data acquisition electronics system and computing servers. The detector heads hold crystal matrices built from 2 × 2 × 20 mm3 LYSO:Ce crystals readout by Hamamatsu S8550 APD arrays. The APDs are optically coupled to both ends of the 6144 crystals in order to extract the DOI information for each detected event. Each one of 12288 APD's pixels is read and controlled by Application Specific Integrated Circuits water-cooled by an external cooling unit. The Clear-PEM frontend boards innovative design results in a unprecedented integration of the crystal matrices, APDs and ASICs, making Clear-PEM the PET scanner with the highest number of APD pixels ever integrated so far. In this paper, the scanner's main technical characteristics, calibration strategies and the first spectrometric performance evaluation in a clinical environment are presented. The first commissioning results show 99.7% active channels, which, after calibration, have inter-pixel and absolute gain distributions with dispersions of, respectively, 12.2% and 15.3%, demonstrating that despite the large number of channels, the system is uniform. The mean energy resolution at 511 keV is of 15.9%, with a 8.8% dispersion, and the mean CDOI-1 is 5.9%/mm, with a 7.8% dispersion. The coincidence time resolution, at 511 keV, for a energy window between 400 and 600 keV, is 5.2 ns FWHM.

  16. Operation of the 25kW NASA Lewis Research Center Solar Regenerative Fuel Cell Tested Facility

    NASA Technical Reports Server (NTRS)

    Moore, S. H.; Voecks, G. E.

    1997-01-01

    Assembly of the NASA Lewis Research Center(LeRC)Solar Regenerative Fuel Cell (RFC) Testbed Facility has been completed and system testing has proceeded. This facility includes the integration of two 25kW photovoltaic solar cell arrays, a 25kW proton exchange membrane (PEM) electrolysis unit, four 5kW PEM fuel cells, high pressure hydrogen and oxygen storage vessels, high purity water storage containers, and computer monitoring, control and data acquisition.

  17. Essentials of PEM Fellowship Part 2: The Profession in Entrustable Professional Activities.

    PubMed

    Hsu, Deborah; Nypaver, Michele; Fein, Daniel M; McAneney, Constance; Santen, Sally; Nagler, Joshua; Zuckerbraun, Noel; Roskind, Cindy Ganis; Reynolds, Stacy; Zaveri, Pavan; Stankovic, Curt; House, Joseph B; Langhan, Melissa; Titus, M Olivia; Dahl-Grove, Deanna; Klasner, Ann E; Ramirez, Jose; Chang, Todd; Jacobs, Elizabeth; Chapman, Jennifer; Lumba-Brown, Angela; Thompson, Tonya; Mittiga, Matthew; Eldridge, Charles; Heffner, Viday; Herman, Bruce E; Kennedy, Christopher; Madhok, Manu; Kou, Maybelle

    2016-06-01

    This article is the second in a 7-part series that aims to comprehensively describe the current state and future directions of pediatric emergency medicine (PEM) fellowship training from the essential requirements to considerations for successfully administering and managing a program to the careers that may be anticipated upon program completion. This article describes the development of PEM entrustable professional activities (EPAs) and the relationship of these EPAs with existing taxonomies of assessment and learning within PEM fellowship. It summarizes the field in concepts that can be taught and assessed, packaging the PEM subspecialty into EPAs. PMID:27253361

  18. Performance and quality control of Clear-PEM detector modules

    NASA Astrophysics Data System (ADS)

    Amaral, Pedro; Carriço, Bruno; Ferreira, Miguel; Moura, Rui; Ortigão, Catarina; Rodrigues, Pedro; Da Silva, José C.; Trindade, Andreia; Varela, João

    2007-10-01

    Clear-PEM is a dedicated PET scanner for breast and axilla cancer diagnosis, under development within the framework of the Crystal Clear Collaboration at CERN, aiming at the detection of tumors down to 2 mm in diameter. The camera consists of two planar detector heads with active dimensions 16.0×14.5 cm 2. Each head has 96 Clear-PEM detector modules consisting of 32 LYSO:Ce pixels with dimensions 2×2×20 mm 3 packed in a 4×8 BaSO 4 reflector matrix compressed between two Hamamatsu S8550 APD arrays in a double-readout configuration for Depth-of-Interaction (DoI) determination. The modules are individually measured and characterized before being grouped into Supermodules (comprised of 24 modules). Measured properties include photo-peak position, relative gain dispersion, energy resolution, cross-talk and DoI resolution. Optical inspection of matrices was also performed with the aid of a microscope, to search for pixel misalignments and matrix defects. Modules' performance was thoroughly evaluated with a 511 keV collimated beam to exactly determine DoI resolution. In addition, a fast quality control (QC) procedure using flood irradiations from a 137Cs source was applied systematically. The overall performance of the 24 detector modules complies with the design goals of the Clear-PEM detector, showing energy resolution around 15%, DoI resolution of about 2 mm and gain dispersion among pixels of 15%.

  19. FUEL CELL BUS DEMONSTRATION IN MEXICO CITY

    EPA Science Inventory

    The report discusses the performance of a cull-size, zero-emission, Proton Exchange Membrane (PEM) fuel-cell-powered transit bus in the atmospheric environment of Mexico City. To address the air quality problems caused by vehicle emissions in Mexico City, a seminar on clean vehic...

  20. Fuel cell flooding detection and correction

    DOEpatents

    DiPierno Bosco, Andrew; Fronk, Matthew Howard

    2000-08-15

    Method and apparatus for monitoring an H.sub.2 -O.sub.2 PEM fuel cells to detect and correct flooding. The pressure drop across a given H.sub.2 or O.sub.2 flow field is monitored and compared to predetermined thresholds of unacceptability. If the pressure drop exists a threshold of unacceptability corrective measures are automatically initiated.

  1. Expression, crystal structure and cellulase activity of the thermostable cellobiohydrolase Cel7A from the fungus Humicola grisea var. thermoidea.

    PubMed

    Momeni, Majid Haddad; Goedegebuur, Frits; Hansson, Henrik; Karkehabadi, Saeid; Askarieh, Glareh; Mitchinson, Colin; Larenas, Edmundo A; Ståhlberg, Jerry; Sandgren, Mats

    2014-09-01

    Glycoside hydrolase family 7 (GH7) cellobiohydrolases (CBHs) play a key role in biomass recycling in nature. They are typically the most abundant enzymes expressed by potent cellulolytic fungi, and are also responsible for the majority of hydrolytic potential in enzyme cocktails for industrial processing of plant biomass. The thermostability of the enzyme is an important parameter for industrial utilization. In this study, Cel7 enzymes from different fungi were expressed in a fungal host and assayed for thermostability, including Hypocrea jecorina Cel7A as a reference. The most stable of the homologues, Humicola grisea var. thermoidea Cel7A, exhibits a 10°C higher melting temperature (T(m) of 72.5°C) and showed a 4-5 times higher initial hydrolysis rate than H. jecorina Cel7A on phosphoric acid-swollen cellulose and showed the best performance of the tested enzymes on pretreated corn stover at elevated temperature (65°C, 24 h). The enzyme shares 57% sequence identity with H. jecorina Cel7A and consists of a GH7 catalytic module connected by a linker to a C-terminal CBM1 carbohydrate-binding module. The crystal structure of the H. grisea var. thermoidea Cel7A catalytic module (1.8 Å resolution; R(work) and R(free) of 0.16 and 0.21, respectively) is similar to those of other GH7 CBHs. The deviations of several loops along the cellulose-binding path between the two molecules in the asymmetric unit indicate higher flexibility than in the less thermostable H. jecorina Cel7A. PMID:25195749

  2. Cel5I, a SLH-Containing Glycoside Hydrolase: Characterization and Investigation on Its Role in Ruminiclostridium cellulolyticum.

    PubMed

    Franche, Nathalie; Tardif, Chantal; Ravachol, Julie; Harchouni, Seddik; Ferdinand, Pierre-Henri; Borne, Romain; Fierobe, Henri-Pierre; Perret, Stéphanie

    2016-01-01

    Ruminiclostridium cellulolyticum (Clostridium cellulolyticum) is a mesophilic cellulolytic anaerobic bacterium that produces a multi-enzymatic system composed of cellulosomes and non-cellulosomal enzymes to degrade plant cell wall polysaccharides. We characterized one of the non-cellulosomal enzymes, Cel5I, composed of a Family-5 Glycoside Hydrolase catalytic module (GH5), a tandem of Family-17 and -28 Carbohydrate Binding Modules (CBM), and three S-layer homologous (SLH) modules, where the latter are expected to anchor the protein on the cell surface. Cel5I is the only putative endoglucanase targeting the cell surface as well as the only putative protein in R. cellulolyticum containing CBM17 and/or CBM28 modules. We characterized different recombinant structural variants from Cel5I. We showed that Cel5I has an affinity for insoluble cellulosic substrates through its CBMs, that it is the most active endoglucanase on crystalline cellulose of R. cellulolyticum characterized to date and mostly localized in the cell envelope of R. cellulolyticum. Its role in vivo was analyzed using a R. cellulolyticum cel5I mutant strain. Absence of Cel5I in the cell envelope did not lead to a significant variation of the phenotype compared to the wild type strain. Neither in terms of cell binding to cellulose, nor for its growth on crystalline cellulose, thus indicating that the protein has a rather subtle role in tested conditions. Cel5I might be more important in a natural environment, at low concentration of degradable glucose polymers, where its role might be to generate higher concentration of short cellodextrins close to the cell surface, facilitating their uptake or for signalization purpose. PMID:27501457

  3. Cel5I, a SLH-Containing Glycoside Hydrolase: Characterization and Investigation on Its Role in Ruminiclostridium cellulolyticum

    PubMed Central

    Franche, Nathalie; Tardif, Chantal; Ravachol, Julie; Harchouni, Seddik; Ferdinand, Pierre-Henri; Borne, Romain; Fierobe, Henri-Pierre; Perret, Stéphanie

    2016-01-01

    Ruminiclostridium cellulolyticum (Clostridium cellulolyticum) is a mesophilic cellulolytic anaerobic bacterium that produces a multi-enzymatic system composed of cellulosomes and non-cellulosomal enzymes to degrade plant cell wall polysaccharides. We characterized one of the non-cellulosomal enzymes, Cel5I, composed of a Family-5 Glycoside Hydrolase catalytic module (GH5), a tandem of Family-17 and -28 Carbohydrate Binding Modules (CBM), and three S-layer homologous (SLH) modules, where the latter are expected to anchor the protein on the cell surface. Cel5I is the only putative endoglucanase targeting the cell surface as well as the only putative protein in R. cellulolyticum containing CBM17 and/or CBM28 modules. We characterized different recombinant structural variants from Cel5I. We showed that Cel5I has an affinity for insoluble cellulosic substrates through its CBMs, that it is the most active endoglucanase on crystalline cellulose of R. cellulolyticum characterized to date and mostly localized in the cell envelope of R. cellulolyticum. Its role in vivo was analyzed using a R. cellulolyticum cel5I mutant strain. Absence of Cel5I in the cell envelope did not lead to a significant variation of the phenotype compared to the wild type strain. Neither in terms of cell binding to cellulose, nor for its growth on crystalline cellulose, thus indicating that the protein has a rather subtle role in tested conditions. Cel5I might be more important in a natural environment, at low concentration of degradable glucose polymers, where its role might be to generate higher concentration of short cellodextrins close to the cell surface, facilitating their uptake or for signalization purpose. PMID:27501457

  4. GREENHOUSE GAS (GHG) VERIFICATION GUIDELINE SERIES: ANR Pipeline Company PARAMETRIC EMISSIONS MONITORING SYSTEM (PEMS) VERSION 1.0

    EPA Science Inventory

    The Environmental Technology Verification report discusses the technology and performance of the Parametric Emissions Monitoring System (PEMS) manufactured by ANR Pipeline Company, a subsidiary of Coastal Corporation, now El Paso Corporation. The PEMS predicts carbon doixide (CO2...

  5. Emerging Fuel Cell Technology Being Developed: Offers Many Benefits to Air Vehicles

    NASA Technical Reports Server (NTRS)

    Walker, James F.; Civinskas, Kestutis C.

    2004-01-01

    Fuel cells, which have recently received considerable attention for terrestrial applications ranging from automobiles to stationary power generation, may enable new aerospace missions as well as offer fuel savings, quiet operations, and reduced emissions for current and future aircraft. NASA has extensive experience with fuel cells, having used them on manned space flight systems over four decades. Consequently, the NASA Glenn Research Center has initiated an effort to investigate and develop fuel cell technologies for multiple aerospace applications. Two promising fuel cell types are the proton exchange membrane (PEM) and solid oxide fuel cell (SOFC). PEM technology, first used on the Gemini spacecraft in the sixties, remained unutilized thereafter until the automotive industry recently recognized the potential. PEM fuel cells are low-temperature devices offering quick startup time but requiring relatively pure hydrogen fuel. In contrast, SOFCs operate at high temperatures and tolerate higher levels of impurities. This flexibility allows SOFCs to use hydrocarbon fuels, which is an important factor considering our current liquid petroleum infrastructure. However, depending on the specific application, either PEM or SOFC can be attractive. As only NASA can, the Agency is pursuing fuel cell technology for civil uninhabited aerial vehicles (UAVs) because it offers enhanced scientific capabilities, including enabling highaltitude, long-endurance missions. The NASA Helios aircraft demonstrated altitudes approaching 100,000 ft using solar power in 2001, and future plans include the development of a regenerative PEM fuel cell to provide nighttime power. Unique to NASA's mission, the high-altitude aircraft application requires the PEM fuel cell to operate on pure oxygen, instead of the air typical of terrestrial applications.

  6. [The Study of Large OPD's PEM Based on Micro Trapezoidal Photo-Elastic Crystals].

    PubMed

    Zhang, Rui; Wang, Zhi-bin; Wang, Yao-li; Chen, You-hua; Chen, Yuan-yuan

    2015-07-01

    Existing Photoelastic Modulator (PEM), whose optical path difference (OPD) is small, has strict requirements on the incident spot size and is poor in the aspect of light use efficiency under multiple reflections. What's more, Photoelastic Modulator based Fourier transform spectrometer (PEM-FTS) spectral resolution is relatively poor. Because there are these disadvantages in the PEM, this paper presents a method of large optical path difference whose PEM is based on micro trapezoidal photoelastic crystals. By improving the structure of photoelastic crystal, the PEM becomes micro trapezoidal octagonal structure. And two transmission surfaces are changed slightly into a certain angle. Therefore, the PEM improved can not only increase the optical path difference of the PEM, but also have less requirements on the incident spot size. Firstly, a detailed analysis of the maximum modulation optical path difference was made in this paper. Secondly, the equation of maximum optical path difference was deduced under any angle and any position of incident light, vibration displacement and stress distribution of PEM are analyzed by the way of COMSOL Multiphysics 4.3a. Again, a method was analyzed to find the best angle of incidence, combining with maximum optical path difference and energy efficiency. Then the large OP's PEM is designed and processed, including two parts: photoelastic crystal and piezoelectric crystal. Moreover, ZnSe crystal is used as photoelastic crystal, and piezoelectric quartz crystal is used as piezoelectric crystal. With experiment analyzed by 632. 8 nm He-Ne laser, the results show that under the same driving voltage, the optical path difference of the PEM improved is about 19. 25 times bigger than the normal PEM, and the relative error is 1.3%. PMID:26717731

  7. Molecular and Biochemical Analyses of CbCel9A/Cel48A, a Highly Secreted Multi-Modular Cellulase by Caldicellulosiruptor bescii during Growth on Crystalline Cellulose

    PubMed Central

    Yi, Zhuolin; Su, Xiaoyun; Revindran, Vanessa; Mackie, Roderick I.; Cann, Isaac

    2013-01-01

    During growth on crystalline cellulose, the thermophilic bacterium Caldicellulosiruptor bescii secretes several cellulose-degrading enzymes. Among these enzymes is CelA (CbCel9A/Cel48A), which is reported as the most highly secreted cellulolytic enzyme in this bacterium. CbCel9A/Cel48A is a large multi-modular polypeptide, composed of an N-terminal catalytic glycoside hydrolase family 9 (GH9) module and a C-terminal GH48 catalytic module that are separated by a family 3c carbohydrate-binding module (CBM3c) and two identical CBM3bs. The wild-type CbCel9A/Cel48A and its truncational mutants were expressed in Bacillus megaterium and Escherichia coli, respectively. The wild-type polypeptide released twice the amount of glucose equivalents from Avicel than its truncational mutant that lacks the GH48 catalytic module. The truncational mutant harboring the GH9 module and the CBM3c was more thermostable than the wild-type protein, likely due to its compact structure. The main hydrolytic activity was present in the GH9 catalytic module, while the truncational mutant containing the GH48 module and the three CBMs was ineffective in degradation of either crystalline or amorphous cellulose. Interestingly, the GH9 and/or GH48 catalytic modules containing the CBM3bs form low-density particles during hydrolysis of crystalline cellulose. Moreover, TM3 (GH9/CBM3c) and TM2 (GH48 with three CBM3 modules) synergistically hydrolyze crystalline cellulose. Deletion of the CBM3bs or mutations that compromised their binding activity suggested that these CBMs are important during hydrolysis of crystalline cellulose. In agreement with this observation, seven of nine genes in a C. bescii gene cluster predicted to encode cellulose-degrading enzymes harbor CBM3bs. Based on our results, we hypothesize that C. bescii uses the GH48 module and the CBM3bs in CbCel9A/Cel48A to destabilize certain regions of crystalline cellulose for attack by the highly active GH9 module and other endoglucanases

  8. Structural and functional studies of the glycoside hydrolase family 3 β-glucosidase Cel3A from the moderately thermophilic fungus Rasamsonia emersonii.

    PubMed

    Gudmundsson, Mikael; Hansson, Henrik; Karkehabadi, Saeid; Larsson, Anna; Stals, Ingeborg; Kim, Steve; Sunux, Sergio; Fujdala, Meredith; Larenas, Edmund; Kaper, Thijs; Sandgren, Mats

    2016-07-01

    The filamentous fungus Hypocrea jecorina produces a number of cellulases and hemicellulases that act in a concerted fashion on biomass and degrade it into monomeric or oligomeric sugars. β-Glucosidases are involved in the last step of the degradation of cellulosic biomass and hydrolyse the β-glycosidic linkage between two adjacent molecules in dimers and oligomers of glucose. In this study, it is shown that substituting the β-glucosidase from H. jecorina (HjCel3A) with the β-glucosidase Cel3A from the thermophilic fungus Rasamsonia emersonii (ReCel3A) in enzyme mixtures results in increased efficiency in the saccharification of lignocellulosic materials. Biochemical characterization of ReCel3A, heterologously produced in H. jecorina, reveals a preference for disaccharide substrates over longer gluco-oligosaccharides. Crystallographic studies of ReCel3A revealed a highly N-glycosylated three-domain dimeric protein, as has been observed previously for glycoside hydrolase family 3 β-glucosidases. The increased thermal stability and saccharification yield and the superior biochemical characteristics of ReCel3A compared with HjCel3A and mixtures containing HjCel3A make ReCel3A an excellent candidate for addition to enzyme mixtures designed to operate at higher temperatures. PMID:27377383

  9. Structural and functional studies of the glycoside hydrolase family 3 β-glucosidase Cel3A from the moderately thermophilic fungus Rasamsonia emersonii

    PubMed Central

    Gudmundsson, Mikael; Hansson, Henrik; Karkehabadi, Saeid; Larsson, Anna; Stals, Ingeborg; Kim, Steve; Sunux, Sergio; Fujdala, Meredith; Larenas, Edmund; Kaper, Thijs; Sandgren, Mats

    2016-01-01

    The filamentous fungus Hypocrea jecorina produces a number of cellulases and hemicellulases that act in a concerted fashion on biomass and degrade it into monomeric or oligomeric sugars. β-Glucosidases are involved in the last step of the degradation of cellulosic biomass and hydrolyse the β-glycosidic linkage between two adjacent molecules in dimers and oligomers of glucose. In this study, it is shown that substituting the β-glucosidase from H. jecorina (HjCel3A) with the β-glucosidase Cel3A from the thermophilic fungus Rasamsonia emersonii (ReCel3A) in enzyme mixtures results in increased efficiency in the saccharification of lignocellulosic materials. Biochemical characterization of ReCel3A, heterologously produced in H. jecorina, reveals a preference for disaccharide substrates over longer gluco-oligosaccharides. Crystallographic studies of ReCel3A revealed a highly N-glycosylated three-domain dimeric protein, as has been observed previously for glycoside hydrolase family 3 β-glucosidases. The increased thermal stability and saccharification yield and the superior biochemical characteristics of ReCel3A compared with HjCel3A and mixtures containing HjCel3A make ReCel3A an excellent candidate for addition to enzyme mixtures designed to operate at higher temperatures. PMID:27377383

  10. Primary and secondary electrical space power based on advanced PEM systems

    NASA Technical Reports Server (NTRS)

    Vanderborgh, N. E.; Hedstrom, J. C.; Stroh, K. R.; Huff, J. R.

    1993-01-01

    For new space ventures, power continues to be a pacing function for mission planning and experiment endurance. Although electrochemical power is a well demonstrated space power technology, current hardware limitations impact future mission viability. In order to document and augment electrochemical technology, a series of experiments for the National Aeronautics and Space Administration Lewis Research Center (NASA LeRC) are underway at the Los Alamos National Laboratory that define operational parameters on contemporary proton exchange membrane (PEM) hardware operating with hydrogen and oxygen reactants. Because of the high efficiency possible for water electrolysis, this hardware is also thought part of a secondary battery design built around stored reactants - the so-called regenerative fuel cell. An overview of stack testing at Los Alamos and of analyses related to regenerative fuel cell systems are provided in this paper. Finally, this paper describes work looking at innovative concepts that remove complexity from stack hardware with the specific intent of higher system reliability. This new concept offers the potential for unprecedented electrochemical power system energy densities.

  11. Carbon monoxide poisoning of proton-exchange membrane fuel cells

    SciTech Connect

    Rodrigues, A.; Amphlett, J.C.; Mann, R.F.; Peppley, B.A.; Roberge, P.R.

    1997-12-31

    The platinum-alloy catalyst used in proton-exchange membrane (PEM) fuel cell anodes is highly susceptible to carbon monoxide (CO) poisoning. CO reduces the catalyst activity by blocking active catalyst sites normally available for hydrogen chemisorption and dissociation. The reaction kinetics at the anode catalyst surface can be used to estimate the decrease in cell voltage due to various levels of CO contamination in the inlet fuel streams on PEM fuel cell performance have been reviewed and analyzed in an attempt to further understand the electrochemical properties of the CO adsorption process. A fuel cell performance model of bipolar, Nafion 117 PEM fuel cell stack has been developed which predicts equilibrium cell output voltage as a function of current density and partial pressure of CO. The model contains both empirical and mechanistic parameters and evolved from a steady-state electrochemical model for a PEM fuel cell fed with a CO-free anode gas. Reaction kinetics and equilibrium surface coverage have been incorporated into the electrochemical model to predict the decrease in fuel cell performance at equilibrium. The effects of CO were studied at various concentrations of CO in hydrogen as the anode feed gas. Literature data were used to develop the model parameters and the resulting model is used to compare the model-predicted voltages, with and without CO, to data found in the literature.

  12. Mechanism of product inhibition for cellobiohydrolase Cel7A during hydrolysis of insoluble cellulose.

    PubMed

    Olsen, Johan P; Alasepp, Kadri; Kari, Jeppe; Cruys-Bagger, Nicolaj; Borch, Kim; Westh, Peter

    2016-06-01

    The cellobiohydrolase cellulase Cel7A is extensively utilized in industrial treatment of lignocellulosic biomass under conditions of high product concentrations, and better understanding of inhibition mechanisms appears central in attempts to improve the efficiency of this process. We have implemented an electrochemical biosensor assay for product inhibition studies of cellulases acting on their natural substrate, cellulose. Using this method we measured the hydrolytic rate of Cel7A as a function of both product (inhibitor) concentration and substrate load. This data enabled analyses along the lines of conventional enzyme kinetic theory. We found that the product cellobiose lowered the maximal rate without affecting the Michaelis constant, and this kinetic pattern could be rationalized by two fundamentally distinct molecular mechanisms. One was simple reversibility, that is, an increasing rate of the reverse reaction, lowering the net hydrolytic velocity as product concentrations increase. Strictly this is not a case of inhibition, as no catalytically inactive is formed. The other mechanism that matched the kinetic data was noncompetitive inhibition with an inhibition constant of 490 ± 40 μM. Noncompetitive inhibition implies that the inhibitor binds with comparable strength to either free enzyme or an enzymesubstrate complex, that is, that association between enzyme and substrate has no effect on the binding of the inhibitor. This mechanism is rarely observed, but we argue, that the special architecture of Cel7A with numerous subsites for binding of both substrate and product could give rise to a true noncompetitive inhibition mechanism. Biotechnol. Bioeng. 2016;113: 1178-1186. © 2015 Wiley Periodicals, Inc. PMID:26636743

  13. Numerical simulations of two-phase flow in proton exchange membrane fuel cells using the volume of fluid method - A review

    NASA Astrophysics Data System (ADS)

    Ferreira, Rui B.; Falcão, D. S.; Oliveira, V. B.; Pinto, A. M. F. R.

    2015-03-01

    Water management in proton exchange membrane (PEM) fuel cells, i.e., balance between membrane drying and liquid water flooding, is a major aspect in the operation of these devices. Flooding results in gas-liquid two-phase flow that causes high pressure drops, flow maldistribution and poor cell performances. Limitations related to the experimental techniques dedicated to investigate the dynamics of liquid water in a PEM fuel cell have motivated researchers to conduct computational modeling and simulation to better understand the two-phase flow and its implications. Among different mathematical models employed, the volume of fluid (VOF) method is the most popular approach. This paper reviews the VOF numerical simulations of two-phase flow in PEM fuel cells. The focus of the study, numerical details, and main outcomes of each research work are discussed during this review. Moreover, recommendations for future simulations as well as challenges of applying the VOF method to PEM fuel cells are presented.

  14. The characterization of the endoglucanase Cel12A from Gloeophyllum trabeum reveals an enzyme highly active on β-glucan.

    PubMed

    Miotto, Lis Schwartz; de Rezende, Camila Alves; Bernardes, Amanda; Serpa, Viviane Isabel; Tsang, Adrian; Polikarpov, Igor

    2014-01-01

    The basidiomycete fungus Gloeophyllum trabeum causes a typical brown rot and is known to use reactive oxygen species in the degradation of cellulose. The extracellular Cel12A is one of the few endo-1,4-β-glucanase produced by G. trabeum. Here we cloned cel12A and heterologously expressed it in Aspergillus niger. The identity of the resulting recombinant protein was confirmed by mass spectrometry. We used the purified GtCel12A to determine its substrate specificity and basic biochemical properties. The G. trabeum Cel12A showed highest activity on β-glucan, followed by lichenan, carboxymethylcellulose, phosphoric acid swollen cellulose, microcrystalline cellulose, and filter paper. The optimal pH and temperature for enzymatic activity were, respectively, 4.5 and 50 °C on β-glucan. Under these conditions specific activity was 239.2 ± 9.1 U mg(-1) and the half-life of the enzyme was 84.6 ± 3.5 hours. Thermofluor studies revealed that the enzyme was most thermal stable at pH 3. Using β-glucan as a substrate, the Km was 3.2 ± 0.5 mg mL(-1) and the Vmax was 0.41 ± 0.02 µmol min(-1). Analysis of the effects of GtCel12A on oat spelt and filter paper by scanning electron microscopy revealed the morphological changes taking place during the process. PMID:25251390

  15. Management of PEM public key certificates using X.500 directory service: Some problems and solutions

    SciTech Connect

    Cheung, Terry C.

    1993-08-01

    Internet Privacy Enhanced Mail (PEM) provides security services to users of Internet electronic mail. While the prevalent PEM implementation uses a public key certificate-based strategy, certificates are mostly distributed vie e-mail exchanges, which raises several security and performance issues. This paper discusses some problems with this strategy, explores the relevant issues, and develops an approach to address them.

  16. 40 CFR 1065.910 - PEMS auxiliary equipment for field testing.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 32 2010-07-01 2010-07-01 false PEMS auxiliary equipment for field...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Field Testing and Portable Emission Measurement Systems § 1065.910 PEMS auxiliary equipment for field testing. For field testing you may use various...

  17. 40 CFR 1065.910 - PEMS auxiliary equipment for field testing.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 33 2014-07-01 2014-07-01 false PEMS auxiliary equipment for field...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Field Testing and Portable Emission Measurement Systems § 1065.910 PEMS auxiliary equipment for field testing. For field testing you may use various...

  18. 40 CFR 1065.910 - PEMS auxiliary equipment for field testing.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 34 2013-07-01 2013-07-01 false PEMS auxiliary equipment for field...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Field Testing and Portable Emission Measurement Systems § 1065.910 PEMS auxiliary equipment for field testing. For field testing you may use various...

  19. "Masking Effect" And "Internal CEL" New Design Concepts For A Positive Working Photoresist

    NASA Astrophysics Data System (ADS)

    Miura, Konoe; Ochiai, Tameichi; Kameyama, Yasuhiro; Kashi, Chie; Uoya, Shigeo; Nakajima, Masayuki; Kawai, Akira; Kishimura, Shinji

    1988-01-01

    Two new concepts,"masking effect" and "internal CEL", are proposed to design a high resolution quinonediazide-novolak type photoresist. On the basis of these two design concepts, we optimized the composition of the resist, and succeeded in developing a high resolution resist, which is composed of m-cresol/p-cresol/xylenol/formaldehyde novolak resin and 2 ,3 ,4 , 4' -tetrahydroxybenzophenone 1 , 2 -naphtoquinonediaz ide-5 -sulfonate. This resist can resolve as small as 0.6 um lines & spaces with aspect ratio of 2.7 (NA.0.42) and has the gamma value of 2.0.

  20. Development and testing of a PEM SO2-depolarized electrolyzer and an operating method that prevents sulfur accumulation

    DOE PAGESBeta

    Steimke, John L.; Steeper, Timothy J.; Colon-Mercado, Hector R.; Gorensek, Maximilian B.

    2015-09-02

    The hybrid sulfur (HyS) cycle is being developed as a technology to generate hydrogen by splitting water, using heat and electrical power from a nuclear or solar power plant. A key component is the SO2-depolarized electrolysis (SDE) cell, which reacts SO2 and water to form hydrogen and sulfuric acid. SDE could also be used in once-through operation to consume SO2 and generate hydrogen and sulfuric acid for sale. A proton exchange membrane (PEM) SDE cell based on a PEM fuel cell design was fabricated and tested. Measured cell potential as a function of anolyte pressure and flow rate, sulfuric acidmore » concentration, and cell temperature are presented for this cell. Sulfur accumulation was observed inside the cell, which could have been a serious impediment to further development. A method to prevent sulfur formation was subsequently developed. As a result, this was made possible by a testing facility that allowed unattended operation for extended periods.« less

  1. Opportunities for portable Ballard Fuel Cells

    SciTech Connect

    Voss, H.H.; Huff, J.R.

    1996-12-31

    With the increasing proliferation and sophistication of portable electronic devices in both commercial and military markets, the need has arisen for small, lightweight power supplies that can provide increased operating life over those presently available. A solution to this power problem is the development of portable Ballard Fuel Cell power systems that operate with a hydrogen fuel source and air. Ballard has developed PEM fuel cell stacks and power systems in the 25 to 100 watt range for both of these markets. For military use, Ballard has teamed with Ball Corporation and Hydrogen Consultants, Inc. and has provided the Ballard Fuel Cell stack for an ambient PEM fuel cell power system for the DoD. The system provides power from idle to I 00 watts and has the capability of delivering overloads of 125 watts for short periods of time. The system is designed to operate over a wide range of temperature, relative humidity and altitude. Hydrogen is supplied as a compressed gas, metal hydride or chemical hydride packaged in a unit that is mated to the power/control unit. The hydrogen sources provide 1.5, 5 and 15 kWh of operation, respectively. The design of the fuel cell power system enables the unit to operate at 12 volts or 24 volts depending upon the equipment being used. For commercial applications, as with the military, fuel cell power sources in the 25 to 500 watt range will be competing with advanced batteries. Ambient PEM fuel cell designs and demonstrators are being developed at 25 watts and other low power levels. Goals are minimum stack volume and weight and greatly enhanced operating life with reasonable system weight and volume. This paper will discuss ambient PEM fuel cell designs and performance and operating parameters for a number of power levels in the multiwatt range.

  2. Development of ClearPEM-Sonic, a multimodal mammography system for PET and Ultrasound

    NASA Astrophysics Data System (ADS)

    Cucciati, G.; Auffray, E.; Bugalho, R.; Cao, L.; Di Vara, N.; Farina, F.; Felix, N.; Frisch, B.; Ghezzi, A.; Juhan, V.; Jun, D.; Lasaygues, P.; Lecoq, P.; Mensah, S.; Mundler, O.; Neves, J.; Paganoni, M.; Peter, J.; Pizzichemi, M.; Siles, P.; Silva, J. C.; Silva, R.; Tavernier, S.; Tessonnier, L.; Varela, J.

    2014-03-01

    ClearPEM-Sonic is an innovative imaging device specifically developed for breast cancer. The possibility to work in PEM-Ultrasound multimodality allows to obtain metabolic and morphological information increasing the specificity of the exam. The ClearPEM detector is developed to maximize the sensitivity and the spatial resolution as compared to Whole-Body PET scanners. It is coupled with a 3D ultrasound system, the SuperSonic Imagine Aixplorer that improves the specificity of the exam by providing a tissue elasticity map. This work describes the ClearPEM-Sonic project focusing on the technological developments it has required, the technical merits (and limits) and the first multimodal images acquired on a dedicated phantom. It finally presents selected clinical case studies that confirm the value of PEM information.

  3. Characterization of PM-PEMS for in-use measurements conducted during validation testing for the PM-PEMS measurement allowance program

    NASA Astrophysics Data System (ADS)

    Khan, M. Yusuf; Johnson, Kent C.; Durbin, Thomas D.; Jung, Heejung; Cocker, David R.; Bishnu, Dipak; Giannelli, Robert

    2012-08-01

    This study provides an evaluation of the latest Particulate Matter-Portable Emissions Measurement Systems (PM-PEMS) under different environmental and in-use conditions. It characterizes four PM measurement systems based on different measurement principles. At least three different units were tested for each PM-PEMS to account for variability. These PM-PEMS were compared with a UC Riverside's mobile reference laboratory (MEL). PM measurements were made from a class 8 truck with a 2008 Cummins diesel engine with a diesel particulate filter (DPF). A bypass around the DPF was installed in the exhaust to achieve a brake specific PM (bsPM) emissions level of 25 mg hp-1h-1. PM was dominated by elemental carbon (EC) during non-regeneration conditions and by hydrated sulfate (H2SO4.6H2O) during regeneration. The photo-acoustic PM-PEMS performed best, with a linear regression slope of 0.90 and R2 of 0.88 during non-regenerative conditions. With the addition of a filter, the photo-acoustic PM-PEMS slightly over reported than the total PM mass (slope = 1.10, R2 = 0.87). Under these same non-regeneration conditions, a PM-PEMS equipped with a quartz crystal microbalance (QCM) technology performed the poorest, and had a slope of 0.22 and R2 of 0.13. Re-tests performed on upgraded QCM PM-PEMS showed a better slope (0.66), and a higher R2 of 0.25. In the case of DPF regeneration, all PM-PEMS performed poorly, with the best having a slope of 0.20 and R2 of 0.78. Particle size distributions (PSD) showed nucleation during regeneration, with a shift of particle size to smaller diameters (˜64 nm to ˜13 nm) with elevated number concentrations when compared to non-regeneration conditions.

  4. The processive endocellulase CelF, a major component of the Clostridium cellulolyticum cellulosome: purification and characterization of the recombinant form.

    PubMed Central

    Reverbel-Leroy, C; Pages, S; Belaich, A; Belaich, J P; Tardif, C

    1997-01-01

    The recombinant form of the cellulase CelF of Clostridium cellulolyticum, tagged by a C-terminal histine tail, was overproduced in Escherichia coli. The fusion protein was purified by affinity chromatography on a Ni-nitrilotriacetic acid column. The intact form of CelF (Mr, 79,000) was rapidly degraded at the C terminus, giving a shorter stable form, called truncated CelF (Mr, 71,000). Both the entire and the truncated purified forms degraded amorphous cellulose (kcat = 42 and 30 min(-1), respectively) and microcrystalline cellulose (kcat = 13 and 10 min(-1), respectively). The high ratio of soluble reducing ends to insoluble reducing ends released by truncated CelF from amorphous cellulose showed that CelF is a processive enzyme. Nevertheless, the diversity of the cellodextrins released by truncated CelF from phosphoric acid-swollen cellulose at the beginning of the reaction indicated that the enzyme might randomly hydrolyze beta-1,4 bonds. This hypothesis was supported by viscosimetric measurements and by the finding that CelF and the endoglucanase CelA are able to degrade some of the same cellulose sites. CelF was therefore called a processive endocellulase. The results of immunoblotting analysis showed that CelF was associated with the cellulosome of C. cellulolyticum. It was identified as one of the three major components of cellulosomes. The ability of the entire form of CelF to interact with CipC, the cellulosome integrating protein, or mini-CipC1, a recombinant truncated form of CipC, was monitored by interaction Western blotting (immunoblotting) and by binding assays using a BIAcore biosensor-based analytical system. PMID:8981979

  5. Glovebox for GeoLab Subsystem in HDU1-PEM

    NASA Technical Reports Server (NTRS)

    Evans, Cynthia; Calaway, Michael J.; Bell, Mary

    2012-01-01

    The GeoLab glovebox was designed to enable the preliminary examination, by astronauts, of geological samples collected from the surface of another planetary body. The collected information would then aid scientists in making decisions about sample curation and prioritization for return to Earth for study. This innovation was designed around a positive- pressure-enriched nitrogen environment glovebox to reduce sample handling contamination. The structure was custom-designed to fit in section H of NASA s Habitat Demonstration Unit 1 Pressurized Excursion Module (HDU1- PEM). In addition, the glovebox was designed to host analytical instruments in a way that prevents sample contamination.

  6. 4. Credit PEM. Interior of Martinsburg Plant; on right showing ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. Credit PEM. Interior of Martinsburg Plant; on right showing Taylor 150 hp steam engine belt-connected to a Warren 150 KW, 2200 Volt a.c. generator. On left, a Fisher 400 hp steam engine belt-connected to a Warren 200 KW, 2200 Volt a.c. generator. In center, also belt-connected to Fisher 400 hp engine is a Bail 120 light, arc-light generator. Photo c. 1905. - Dam No. 4 Hydroelectric Plant, Potomac River, Martinsburg, Berkeley County, WV

  7. Mitochondrially-targeted bacterial phosphatidylethanolamine methyltransferase sustained phosphatidylcholine synthesis of a Saccharomyces cerevisiae Δpem1 Δpem2 double mutant without exogenous choline supply.

    PubMed

    Kobayashi, Shingo; Mizuike, Aya; Horiuchi, Hiroyuki; Fukuda, Ryouichi; Ohta, Akinori

    2014-09-01

    In eukaryotic cells, phospholipids are synthesized exclusively in the defined organelles specific for each phospholipid species. To explain the reason for this compartmental specificity in the case of phosphatidylcholine (PC) synthesis, we constructed and characterized a Saccharomyces cerevisiae strain that lacked endogenous phosphatidylethanolamine (PE) methyltransferases but had a recombinant PE methyltransferase from Acetobacter aceti, which was fused with a mitochondrial targeting signal from yeast Pet100p and a 3×HA epitope tag. This fusion protein, which we named as mitopmt, was determined to be localized to the mitochondria by fluorescence microscopy and subcellular fractionation. The expression of mitopmt suppressed the choline auxotrophy of a double deletion mutant of PEM1 and PEM2 (pempem2Δ) and enabled it to synthesize PC in the absence of choline. This growth suppression was observed even if the Kennedy pathway was inactivated by the repression of PCT1 encoding CTP:phosphocholine cytidylyltransferase, suggesting that PC synthesized in the mitochondria is distributed to other organelles without going through the salvage pathway. The pempem2Δ strain deleted for PSD1 encoding the mitochondrial phosphatidylserine decarboxylase was able to grow because of the expression of mitopmt in the presence of ethanolamine, implying that PE from other organelles, probably from the ER, was converted to PC by mitopmt. These results suggest that PC could move out of the mitochondria, and raise the possibility that its movement is not under strict directional limitations. PMID:24832487

  8. Characterization of Leishmania major phosphatidylethanolamine methyltransferases LmjPEM1 and LmjPEM2 and their inhibition by choline analogs.

    PubMed

    Bibis, Stergios S; Dahlstrom, Kelly; Zhu, Tongtong; Zufferey, Rachel

    2014-09-01

    Phosphatidylcholine (PC) is the most abundant phospholipid in the membranes of the human parasite Leishmania. It is synthesized via two metabolic routes, the de novo pathway that starts with the uptake of choline, and the threefold methylation of phosphatidylethanolamine. Choline was shown to be dispensable for Leishmania; thus, the methylation pathway likely represents the primary route for PC production. Here, we have identified and characterized two phosphatidylethanolamine methyltransferases, LmjPEM1 and LmjPEM2. Both enzymes are expressed in promastigotes as well as in the vertebrate form amastigotes, suggesting that these methyltransferases are important for the development of the parasite throughout its life cycle. These enzymes are maximally expressed during the log phase of growth which correlates with the demand of PC synthesis during cell multiplication. Immunofluorescence studies combined with cell fractionation have shown that both methyltransferases are localized at the endoplasmic reticulum membrane. Heterologous expression in yeast has demonstrated that LmjPEM1 and LmjPEM2 complement the choline auxotrophy phenotype of a yeast double null mutant lacking phosphatidylethanolamine methyltransferase activity. LmjPEM1 catalyzes the first, and to a lesser extent, the second methylation reaction. In contrast, LmjPEM2 has the capacity to add the second and third methyl group onto phosphatidylethanolamine to yield (lyso)PC; it can also add the first methyl group, albeit with very low efficiency. Finally, we have demonstrated using inhibition studies with choline analogs that miltefosine and octadecyltrimethylammonium bromide are potent inhibitors of this metabolic pathway. PMID:25176160

  9. Characterization of functional domains of the hemolytic lectin CEL-III from the marine invertebrate Cucumaria echinata.

    PubMed

    Kouzuma, Yoshiaki; Suzuki, Yota; Nakano, Masahiro; Matsuyama, Kayo; Tojo, Sumiki; Kimura, Makoto; Yamasaki, Takayuki; Aoyagi, Haruhiko; Hatakeyama, Tomomitsu

    2003-09-01

    CEL-III is a Ca(2+)-dependent, galactose/N-acetylgalactosamine (GalNAc)-specific lectin isolated from the marine invertebrate Cucumaria echinata. This lectin exhibits strong hemolytic activity and cytotoxicity through pore formation in target cell membranes. The amino acid sequence of CEL-III revealed the N-terminal two-thirds to have homology to the B-chains of ricin and abrin, which are galactose-specific plant toxic lectins; the C-terminal one-third shows no homology to any known proteins. To examine the carbohydrate-binding ability of the N-terminal region of CEL-III, the protein comprising Pyr1-Phe283 was expressed in Escherichia coli cells. The expressed protein showed both the ability to bind to a GalNAc-immobilized column as well as hemagglutinating activity for rabbit erythrocytes, confirming that the N-terminal region has binding activity for specific carbohydrates. Since the C-terminal region could not be expressed in E. coli cells, a fragment containing this region was produced by limited proteolysis of the native protein by trypsin. The resulting C-terminal 15 kDa fragment of CEL-III exhibited a tendency to self-associate, forming an oligomer. When mixed with erythrocytes, the oligomer of the C-terminal fragment caused hemagglutination, probably due to hydrophobic interaction with cell membranes, while the monomeric fragment did not. Chymotryptic digestion of the preformed CEL-III oligomer induced upon lactose binding also yielded an oligomer of the C-terminal fragment comprising six molecules of the 16 kDa fragment. These results suggest that after binding to cell surface carbohydrate chains, CEL-III oligomerizes through C-terminal domains, leading to the formation of ion-permeable pores by hydrophobic interaction with the cell membrane. PMID:14561725

  10. Expression of Recombinant Cellulase Cel5A from Trichoderma reesei in Tobacco Plants

    PubMed Central

    Garvey, Megan; Fischer, Rainer; Commandeur, Ulrich

    2014-01-01

    Cellulose degrading enzymes, cellulases, are targets of both research and industrial interests. The preponderance of these enzymes in difficult-to-culture organisms, such as hyphae-building fungi and anaerobic bacteria, has hastened the use of recombinant technologies in this field. Plant expression methods are a desirable system for large-scale production of enzymes and other industrially useful proteins. Herein, methods for the transient expression of a fungal endoglucanase, Trichoderma reesei Cel5A, in Nicotiana tabacum are demonstrated. Successful protein expression is shown, monitored by fluorescence using an mCherry-enzyme fusion protein. Additionally, a set of basic tests are used to examine the activity of transiently expressed T. reesei Cel5A, including SDS-PAGE, Western blotting, zymography, as well as fluorescence and dye-based substrate degradation assays. The system described here can be used to produce an active cellulase in a short time period, so as to assess the potential for further production in plants through constitutive or inducible expression systems. PMID:24962636

  11. Improving Trichoderma reesei Cel7B thermostability by targeting the weak spots.

    PubMed

    Zhang, Shujun; Wang, Yefei; Song, Xiangfei; Hong, Jingbo; Zhang, Yu; Yao, Lishan

    2014-10-27

    For proteins that denature irreversibly, the denaturation is typically triggered by a partial unfolding, followed by a permanent change (e.g., aggregation). The regions that initiate the partial unfolding are named "weak spots". In this work, a molecular dynamics (MD) simulation and data analysis protocol is developed to identify the weak spots of Trichoderma reesei Cel7B, an important endoglucanase in cellulose hydrolysis, through assigning the local melting temperature (Tmp) to individual residue pairs. To test the predicted weak spots, a total of eight disulfide bonds were designed in these regions and all enhanced the enzyme thermostability. The increased stability, quantified by ΔT50 (which is the T50 difference between the mutant and the wild type enzyme), is negatively correlated with the MD-predicted Tmp, demonstrating the effectiveness of the protocol and highlighting the importance of the weak spots. Strengthening interactions in these regions proves to be a useful strategy in improving the thermostability of Tr. Cel7B. PMID:25286389

  12. Expression of recombinant cellulase Cel5A from Trichoderma reesei in tobacco plants.

    PubMed

    Garvey, Megan; Klinger, Johannes; Klose, Holger; Fischer, Rainer; Commandeur, Ulrich

    2014-01-01

    Cellulose degrading enzymes, cellulases, are targets of both research and industrial interests. The preponderance of these enzymes in difficult-to-culture organisms, such as hyphae-building fungi and anaerobic bacteria, has hastened the use of recombinant technologies in this field. Plant expression methods are a desirable system for large-scale production of enzymes and other industrially useful proteins. Herein, methods for the transient expression of a fungal endoglucanase, Trichoderma reesei Cel5A, in Nicotiana tabacum are demonstrated. Successful protein expression is shown, monitored by fluorescence using an mCherry-enzyme fusion protein. Additionally, a set of basic tests are used to examine the activity of transiently expressed T. reesei Cel5A, including SDS-PAGE, Western blotting, zymography, as well as fluorescence and dye-based substrate degradation assays. The system described here can be used to produce an active cellulase in a short time period, so as to assess the potential for further production in plants through constitutive or inducible expression systems. PMID:24962636

  13. Preliminary X-ray analysis of cellobiohydrolase Cel7B from Melanocarpus albomyces

    SciTech Connect

    Parkkinen, Tarja; Koivula, Anu; Vehmaanperä, Jari; Rouvinen, Juha

    2007-09-01

    The crystallization and preliminary X-ray diffraction analysis of cellobiohydrolase from M. albomyces is reported. Cellobiohydrolases are enzymes that cleave off cellobiose units from cellulose chains in a processive manner. Melanocarpus albomyces Cel7B is a thermostable single-module cellobiohydrolase that has relatively low activity on small soluble substrates at room temperature. It belongs to glycoside hydrolase family 7, which includes endo-β-1,4-glucanases and cellobiohydrolases. Cel7B was crystallized using the hanging-drop vapour-diffusion method and streak-seeding. The crystals belonged to space group P2{sub 1}, with unit-cell parameters a = 50.9, b = 94.5, c = 189.8 Å, β = 90.0° and four monomers in the asymmetric unit. Analysis of the intensity statistics showed that the crystals were pseudo-merohedrally twinned, with a twinning fraction of 0.37. X-ray diffraction data were collected at 1.6 Å resolution using synchrotron radiation.

  14. Deletion of Caldicellulosiruptor bescii CelA reveals its crucial role in the deconstruction of lignocellulosic biomass

    SciTech Connect

    Young, Jenna; Chung, Daehwan; Bomble, Yannick J.; Himmel, Michael E.; Westpheling, Janet

    2014-10-09

    Background: Members of the bacterial genus Caldicellulosiruptor are the most thermophilic cellulolytic organisms described to date, and have the ability to grow on lignocellulosic biomass without conventional pretreatment. Different species vary in their abilities to degrade cellulose, and the presence of CelA, a bifunctional glycoside hydrolase that contains a Family 48 and a Family 9 catalytic domain, correlates well with cellulolytic ability in members of this genus. For example, C. hydrothermalis, which does not contain a CelA homolog, or a GH48 Family or GH9 Family glycoside hydrolase, is the least cellulolytic of the Caldicellulosiruptor species so far described. C. bescii, which contains CelA and expresses it constitutively, is among the most cellulolytic. In fact, CelA is the most abundant extracellular protein produced in C. bescii. The enzyme contains two catalytic units, a Family 9A-CBM3c processive endoglucanase and a Family 48 exoglucanase, joined by two Family 3b carbohydrate-binding domains. Although there are two non-reducing end-specific Family 9 and three reducing end-specific Family 48 glycoside hydrolases (producing primarily glucose and cellobiose; and cellobiose and cellotriose, respectively) in C. bescii, CelA is the only protein that combines both enzymatic activities. Results: A deletion of the celA gene resulted in a dramatic reduction in the microorganism’s ability to grow on crystalline cellulose (Avicel) and diminished growth on lignocellulosic biomass. A comparison of the overall endoglucanase and exoglucanase activities of the mutant compared with the wild-type suggests that the loss of the endoglucanase activity provided by the GH9 family domain is perhaps compensated for by other enzymes produced by the cell. In contrast, it appears that no other enzymes in the C. bescii secretome can compensate for the loss of exoglucanase activity. The change in enzymatic activity in the celA mutant resulted in a 15-fold decrease in sugar

  15. Deletion of Caldicellulosiruptor bescii CelA reveals its crucial role in the deconstruction of lignocellulosic biomass

    DOE PAGESBeta

    Young, Jenna; Chung, Daehwan; Bomble, Yannick J.; Himmel, Michael E.; Westpheling, Janet

    2014-10-09

    Background: Members of the bacterial genus Caldicellulosiruptor are the most thermophilic cellulolytic organisms described to date, and have the ability to grow on lignocellulosic biomass without conventional pretreatment. Different species vary in their abilities to degrade cellulose, and the presence of CelA, a bifunctional glycoside hydrolase that contains a Family 48 and a Family 9 catalytic domain, correlates well with cellulolytic ability in members of this genus. For example, C. hydrothermalis, which does not contain a CelA homolog, or a GH48 Family or GH9 Family glycoside hydrolase, is the least cellulolytic of the Caldicellulosiruptor species so far described. C. bescii,more » which contains CelA and expresses it constitutively, is among the most cellulolytic. In fact, CelA is the most abundant extracellular protein produced in C. bescii. The enzyme contains two catalytic units, a Family 9A-CBM3c processive endoglucanase and a Family 48 exoglucanase, joined by two Family 3b carbohydrate-binding domains. Although there are two non-reducing end-specific Family 9 and three reducing end-specific Family 48 glycoside hydrolases (producing primarily glucose and cellobiose; and cellobiose and cellotriose, respectively) in C. bescii, CelA is the only protein that combines both enzymatic activities. Results: A deletion of the celA gene resulted in a dramatic reduction in the microorganism’s ability to grow on crystalline cellulose (Avicel) and diminished growth on lignocellulosic biomass. A comparison of the overall endoglucanase and exoglucanase activities of the mutant compared with the wild-type suggests that the loss of the endoglucanase activity provided by the GH9 family domain is perhaps compensated for by other enzymes produced by the cell. In contrast, it appears that no other enzymes in the C. bescii secretome can compensate for the loss of exoglucanase activity. The change in enzymatic activity in the celA mutant resulted in a 15-fold decrease in

  16. Mirrored serpentine flow channels for fuel cell

    DOEpatents

    Rock, Jeffrey Allan

    2000-08-08

    A PEM fuel cell having serpentine flow field channels wherein the input/inlet legs of each channel border the input/inlet legs of the next adjacent channels in the same flow field, and the output/exit legs of each channel border the output/exit legs of the next adjacent channels in the same flow field. The serpentine fuel flow channels may be longer, and may contain more medial legs, than the serpentine oxidant flow channels.

  17. The Excellence-Commitment-and-Effective-Learning (ExCEL) Group: An Integrated Approach for First-Year College Students' Success.

    ERIC Educational Resources Information Center

    Ting, Siu-Man Raymond; Grant, Susan; Plenert, Sheri L.

    2000-01-01

    Presents research findings that evaluate the study skills, academic performance, and retention of students who participated in an Excellence-Commitment-and-Effective-Learning (ExCEL) group. Results indicate that the ExCEL groups appear to have enhanced the participants' study skills, GPAs, and social and cultural adjustment during the first year.…

  18. Roles of the valine clusters in domain 3 of the hemolytic lectin CEL-III in its oligomerization and hemolytic abilities.

    PubMed

    Hisamatsu, Keigo; Unno, Hideaki; Goda, Shuichiro; Hatakeyama, Tomomitsu

    2009-01-01

    The hemolytic lectin CEL-III and its site-directed mutants were expressed in Escherichia coli cells. Replacement of the valine clusters in domain 3 with alanine residues led to increased self-oligomerization in solution and higher hemolytic activity. The results suggest the involvement of these valine clusters in CEL-III oligomerization and hemolytic activity. PMID:19356139

  19. CEL-I, an N-acetylgalactosamine (GalNAc)-specific C-type lectin, induces nitric oxide production in RAW264.7 mouse macrophage cell line.

    PubMed

    Yamanishi, Tomohiro; Hatakeyama, Tomomitsu; Yamaguchi, Kenichi; Oda, Tatsuya

    2009-08-01

    We found that CEL-I, a GalNAc-specific C-type lectin isolated from the marine invertebrate Holothuroidea (Cucumaria echinata), induces inducible nitric oxide synthase (iNOS) expression and NO production in RAW264.7 cells. The NO production was inhibited by an iNOS inhibitor, L-NAME, but was not by a lipopolysaccharide (LPS) inhibitor, polymyxin B. In the presence of 0.1-M GalNAc, increased NO production by CEL-I-treated RAW264.7 cells was observed rather than the inhibition. Bovine serum albumin (BSA) significantly inhibited the CEL-I-induced NO production as well as the binding of FITC-labelled CEL-I on RAW264.7 cells. Three MAP kinase inhibitors (specific to extra-cellular regulated kinase, c-jun NH(2)-terminal kinase and p38 MAP kinase) inhibited CEL-I-induced NO production with different extents. Heat-treatment of CEL-I resulted in a decreased activity of CEL-I depending on the temperature. These results suggest that CEL-I induces NO production in RAW264.7 cells through the protein-cell interaction rather than the binding to the specific carbohydrate chains on the cell surface. PMID:19351706

  20. HDU Pressurized Excursion Module (PEM) Prototype Systems Integration

    NASA Technical Reports Server (NTRS)

    Gill, Tracy R.; Kennedy, Kriss; Tri, Terry; Toups, Larry; Howe, A. Scott

    2010-01-01

    The Habitat Demonstration Unit (HDU) project team constructed an analog prototype lunar surface laboratory called the Pressurized Excursion Module (PEM). The prototype unit subsystems were integrated in a short amount of time, utilizing a skunk-works approach that brought together over 20 habitation-related technologies from a variety of NASA centers. This paper describes the system integration strategies and lessons learned, that allowed the PEM to be brought from paper design to working field prototype using a multi-center team. The system integration process included establishment of design standards, negotiation of interfaces between subsystems, and scheduling fit checks and installation activities. A major tool used in integration was a coordinated effort to accurately model all the subsystems using CAD, so that conflicts were identified before physical components came together. Some of the major conclusions showed that up-front modularity that emerged as an artifact of construction, such as the eight 45 degree "pie slices" making up the module whose steel rib edges defined structural mounting and loading points, dictated much of the configurational interfaces between the major subsystems and workstations. Therefore, 'one of the lessons learned included the need to use modularity as a tool for organization in advance, and to work harder to prevent non-critical aspects of the platform from dictating the modularity that may eventually inform the fight system.

  1. Fuel Cell System for Transportation -- 2005 Cost Estimate

    SciTech Connect

    Wheeler, D.

    2006-10-01

    Independent review report of the methodology used by TIAX to estimate the cost of producing PEM fuel cells using 2005 cell stack technology. The U.S. Department of Energy (DOE) Hydrogen, Fuel Cells and Infrastructure Technologies Program Manager asked the National Renewable Energy Laboratory (NREL) to commission an independent review of the 2005 TIAX cost analysis for fuel cell production. The NREL Systems Integrator is responsible for conducting independent reviews of progress toward meeting the DOE Hydrogen Program (the Program) technical targets. An important technical target of the Program is the proton exchange membrane (PEM) fuel cell cost in terms of dollars per kilowatt ($/kW). The Program's Multi-Year Program Research, Development, and Demonstration Plan established $125/kW as the 2005 technical target. Over the last several years, the Program has contracted with TIAX, LLC (TIAX) to produce estimates of the high volume cost of PEM fuel cell production for transportation use. Since no manufacturer is yet producing PEM fuel cells in the quantities needed for an initial hydrogen-based transportation economy, these estimates are necessary for DOE to gauge progress toward meeting its targets. For a PEM fuel cell system configuration developed by Argonne National Laboratory, TIAX estimated the total cost to be $108/kW, based on assumptions of 500,000 units per year produced with 2005 cell stack technology, vertical integration of cell stack manufacturing, and balance-of-plant (BOP) components purchased from a supplier network. Furthermore, TIAX conducted a Monte Carlo analysis by varying ten key parameters over a wide range of values and estimated with 98% certainty that the mean PEM fuel cell system cost would be below DOE's 2005 target of $125/kW. NREL commissioned DJW TECHNOLOGY, LLC to form an Independent Review Team (the Team) of industry fuel cell experts and to evaluate the cost estimation process and the results reported by TIAX. The results of this

  2. Expression of endo-1,4-beta-glucanase (cel1) in Arabidopsis thaliana is associated with plant growth, xylem development and cell wall thickening.

    PubMed

    Shani, Ziv; Dekel, Mara; Roiz, Levava; Horowitz, Miri; Kolosovski, Natalia; Lapidot, Shaul; Alkan, Sari; Koltai, Hinanit; Tsabary, Galit; Goren, Raphael; Shoseyov, Oded

    2006-10-01

    Arabidopsis thaliana CEL1 protein was detected in young expanding tissues. Immunostaining revealed that CEL1 accumulated mostly in xylem cells. The primary, as well as the secondary xylem showed considerable CEL1 staining. CEL1 was also observed in young epidermal cells, in which the thicker lateral and tangential walls stained more intensely than the inner walls. In newly formed cell walls, the lateral tangential walls were labeled more intensively than the inner walls. Cellulase activity was found to be significantly higher in growing tissue compared to mature parts of the plant. Cel1 expression concurrently with cellulase activity could be restored in detached matured leaves by sucrose treatment after 48 h in the culture medium. PMID:16758197

  3. Mitogenic activity of CEL-I, an N-acetylgalactosamine (GalNAc)-specific C-type lectin, isolated from the marine invertebrate Cucumaria echinata (Holothuroidea).

    PubMed

    Jiang, Zedong; Kim, Daekyung; Yamasaki, Yasuhiro; Yamanishi, Tomohiro; Hatakeyama, Tomomitsu; Yamaguchi, Kenichi; Oda, Tatsuya

    2010-01-01

    An N-acetylgalactosamine (GalNAc)-specific Ca(2+)-dependent lectin (C-type lectin), isolated from the marine invertebrate Holothuroidea (Cucumaria echinata), CEL-I, showed potent mitogenic activity toward normal mouse spleen cells. The mitogenic activity of CEL-I, which reached a maximum at 100 microg/ml, was inhibited by GalNAc in a concentration-dependent manner. The mitogenic effect of CEL-I at 10 microg/ml on T cell- enriched splenocytes was at a similar level due to a well-known T cell mitogen, concanavalin A (Con A), at 10 microg/ml. Furthermore, CEL-I evoked a mitogenic response from nude mouse spleen cells, while no significant effects of Con A on this cell population were observed over a wide range of concentrations. These results suggest that CEL-I is a potent mitogenic lectin with the ability to stimulate both T and B cells. PMID:20699569

  4. Automotive Fuel Processor Development and Demonstration with Fuel Cell Systems

    SciTech Connect

    Nuvera Fuel Cells

    2005-04-15

    The potential for fuel cell systems to improve energy efficiency and reduce emissions over conventional power systems has generated significant interest in fuel cell technologies. While fuel cells are being investigated for use in many applications such as stationary power generation and small portable devices, transportation applications present some unique challenges for fuel cell technology. Due to their lower operating temperature and non-brittle materials, most transportation work is focusing on fuel cells using proton exchange membrane (PEM) technology. Since PEM fuel cells are fueled by hydrogen, major obstacles to their widespread use are the lack of an available hydrogen fueling infrastructure and hydrogen's relatively low energy storage density, which leads to a much lower driving range than conventional vehicles. One potential solution to the hydrogen infrastructure and storage density issues is to convert a conventional fuel such as gasoline into hydrogen onboard the vehicle using a fuel processor. Figure 2 shows that gasoline stores roughly 7 times more energy per volume than pressurized hydrogen gas at 700 bar and 4 times more than liquid hydrogen. If integrated properly, the fuel processor/fuel cell system would also be more efficient than traditional engines and would give a fuel economy benefit while hydrogen storage and distribution issues are being investigated. Widespread implementation of fuel processor/fuel cell systems requires improvements in several aspects of the technology, including size, startup time, transient response time, and cost. In addition, the ability to operate on a number of hydrocarbon fuels that are available through the existing infrastructure is a key enabler for commercializing these systems. In this program, Nuvera Fuel Cells collaborated with the Department of Energy (DOE) to develop efficient, low-emission, multi-fuel processors for transportation applications. Nuvera's focus was on (1) developing fuel processor

  5. A review of radiation-grafted polymer electrolyte membranes for alkaline polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Zhou, Tianchi; Shao, Rong; Chen, Song; He, Xuemei; Qiao, Jinli; Zhang, Jiujun

    2015-10-01

    The past two decades have witnessed many efforts to develop radiation-grafted alkaline membranes for alkaline PEM fuel cell applications, as such membranes have certain advantages over other kinds of alkaline membranes, including well-controlled composition, functionality, and other promising properties. To facilitate research and development in this area, the present paper reviews radiation-grafted alkaline membranes. We examine their synthesis/fabrication/characterization, membrane material selection, and theoretical approaches for fundamental understanding. We also present detailed examinations of their application in fuel cell in terms of the working principles of the radiation grafting process, the fabrication of MEAs using radiation-grafted membranes, the membranes' corresponding performance in alkaline PEM fuel cells, as well as performance optimization. The paper also summarizes the challenges and mitigation strategies for radiation-grafted alkaline membranes and their application in PEM fuel cells, presenting an overall picture of the technology as it presently stands.

  6. Compact Single-Stage Fuel Processor for PEM Fuel Cells. Final report

    SciTech Connect

    Rhine, Wendell E.; Ye, Neng

    2000-01-01

    Based on observations during the steam reforming of ethanol, the authors conclude that carbon was forming in the steam generator due to the thermal decomposition of ethanol. Since ethanol is being thermally decomposed, they were operating the steam generator at too high of a temperature. The thermal degradation of ethanol was confirmed by using a GC with a flame ionization detector. They observed trace amounts of additional hydrocarbons other than methane in the effluent which we assume maybe ethane and ethylene. We identified the operating conditions that allowed us to steam reform ethanol for an acceptable amount of time. These conditions were a steam temperature of 200 C and a wall temperature of 400 C at the center of the reactor. The calculated ratios of CO{sub 2}/CO indicate that we can lower the potential for carbon deposition from the Boudouard further by reducing the pressure.

  7. Advanced proton-exchange materials for energy efficient fuel cells.

    SciTech Connect

    Fujimoto, Cy H.; Grest, Gary Stephen; Hickner, Michael A.; Cornelius, Christopher James; Staiger, Chad Lynn; Hibbs, Michael R.

    2005-12-01

    The ''Advanced Proton-Exchange Materials for Energy Efficient Fuel Cells'' Laboratory Directed Research and Development (LDRD) project began in October 2002 and ended in September 2005. This LDRD was funded by the Energy Efficiency and Renewable Energy strategic business unit. The purpose of this LDRD was to initiate the fundamental research necessary for the development of a novel proton-exchange membranes (PEM) to overcome the material and performance limitations of the ''state of the art'' Nafion that is used in both hydrogen and methanol fuel cells. An atomistic modeling effort was added to this LDRD in order to establish a frame work between predicted morphology and observed PEM morphology in order to relate it to fuel cell performance. Significant progress was made in the area of PEM material design, development, and demonstration during this LDRD. A fundamental understanding involving the role of the structure of the PEM material as a function of sulfonic acid content, polymer topology, chemical composition, molecular weight, and electrode electrolyte ink development was demonstrated during this LDRD. PEM materials based upon random and block polyimides, polybenzimidazoles, and polyphenylenes were created and evaluated for improvements in proton conductivity, reduced swelling, reduced O{sub 2} and H{sub 2} permeability, and increased thermal stability. Results from this work reveal that the family of polyphenylenes potentially solves several technical challenges associated with obtaining a high temperature PEM membrane. Fuel cell relevant properties such as high proton conductivity (>120 mS/cm), good thermal stability, and mechanical robustness were demonstrated during this LDRD. This report summarizes the technical accomplishments and results of this LDRD.

  8. The tobacco Cel7 gene promoter is auxin-responsive and locally induced in nematode feeding sites of heterologous plants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Emerging evidence suggests that plant cell wall modifying enzymes induced by root-parasitic nematodes play important roles in feeding cell formation. We previously identified a tobacco endo-B-1,4-glucanase (cellulase) gene, NtCel7, that was strongly induced in both root-knot and cyst nematode feedi...

  9. Hemolytic C-type lectin CEL-III from sea cucumber expressed in transgenic mosquitoes impairs malaria parasite development.

    PubMed

    Yoshida, Shigeto; Shimada, Yohei; Kondoh, Daisuke; Kouzuma, Yoshiaki; Ghosh, Anil K; Jacobs-Lorena, Marcelo; Sinden, Robert E

    2007-12-01

    The midgut environment of anopheline mosquitoes plays an important role in the development of the malaria parasite. Using genetic manipulation of anopheline mosquitoes to change the environment in the mosquito midgut may inhibit development of the malaria parasite, thus blocking malaria transmission. Here we generate transgenic Anopheles stephensi mosquitoes that express the C-type lectin CEL-III from the sea cucumber, Cucumaria echinata, in a midgut-specific manner. CEL-III has strong and rapid hemolytic activity toward human and rat erythrocytes in the presence of serum. Importantly, CEL-III binds to ookinetes, leading to strong inhibition of ookinete formation in vitro with an IC(50) of 15 nM. Thus, CEL-III exhibits not only hemolytic activity but also cytotoxicity toward ookinetes. In these transgenic mosquitoes, sporogonic development of Plasmodium berghei is severely impaired. Moderate, but significant inhibition was found against Plasmodium falciparum. To our knowledge, this is the first demonstration of stably engineered anophelines that affect the Plasmodium transmission dynamics of human malaria. Although our laboratory-based research does not have immediate applications to block natural malaria transmission, these findings have significant implications for the generation of refractory mosquitoes to all species of human Plasmodium and elucidation of mosquito-parasite interactions. PMID:18159942

  10. Engineering Cel7A carbohydrate binding module and linker for reduced lignin inhibition.

    PubMed

    Strobel, Kathryn L; Pfeiffer, Katherine A; Blanch, Harvey W; Clark, Douglas S

    2016-06-01

    Non-productive binding of cellulases to lignin inhibits enzymatic hydrolysis of biomass, increasing enzyme requirements and the cost of biofuels. This study used site-directed mutagenesis of the Trichoderma Cel7A carbohydrate binding module (CBM) and linker to investigate the mechanisms of adsorption to lignin and engineer a cellulase with increased binding specificity for cellulose. CBM mutations that added hydrophobic or positively charged residues decreased the specificity for cellulose, while mutations that added negatively charged residues increased the specificity. Linker mutations that altered predicted glycosylation patterns selectively impacted lignin affinity. Beneficial mutations were combined to generate a mutant with 2.5-fold less lignin affinity while fully retaining cellulose affinity. This mutant was uninhibited by added lignin during hydrolysis of Avicel and generated 40% more glucose than the wild-type enzyme from dilute acid-pretreated Miscanthus. Biotechnol. Bioeng. 2016;113: 1369-1374. © 2015 Wiley Periodicals, Inc. PMID:26616493

  11. Simulation studies of substrate recognition by the exocellulase CelF from Clostridium cellulolyticum.

    PubMed

    Chen, Mo; Himmel, Michael E; Wilson, David B; Brady, John W

    2016-07-01

    Molecular dynamics (MD) simulations were used to study substrate recognition by the family 48 exocellulase CelF from Clostridium cellulolyticum. It was hypothesized that residues around the entrance of the active site tunnel of this enzyme might serve to recognize and bind the substrate through an affinity for the cellulose monomer repeat unit, β-d-glucopyranose. Simulations were conducted of the catalytic domain of this enzyme surrounded by a concentrated solution of β-d-glucopyranose, and the full three-dimensional probability distribution for finding sugar molecules adjacent to the enzyme was calculated from the trajectory. A significant probability of finding the sugar stacked against the planar faces of Trp 310 and Trp 312 at the entrance of the active site tunnel was observed. Biotechnol. Bioeng. 2016;113: 1433-1440. © 2015 Wiley Periodicals, Inc. PMID:26693961

  12. Interaction between the CBM of Cel9A from Thermobifida fusca and Cellulose Fibers

    SciTech Connect

    Oliveira, Osmair V.; Freitas, Luiz C.; Straatsma, TP; Lins, Roberto D.

    2009-01-01

    Molecular docking and molecular dynamics simulations were used to investigate the binding of a cellodextrin chain in a crystal-like conformation to the carbohydrate-binding module (CBM) of Cel9A from Thermobifida fusca. The fiber was found to bind to the CBM in a single and well-defined configuration in-line with the catalytic cleft, supporting the hypothesis that this CBM plays a role in the catalysis by feeding the catalytic domain with a polyssacharide chain. The results also expand the current known list of residues involved in the binding. The polysaccharide-protein attachment is shown to be mediated by five amine/amide-containing residues. E478 and E559 were found not to interact directly with the sugar chain; instead they seem to be responsible to stabilize the binding motif via hydrogen bonds.

  13. Processivity, substrate binding, and mechanism of cellulose hydrolysis by Thermobifida fusca Cel9A.

    PubMed

    Li, Yongchao; Irwin, Diana C; Wilson, David B

    2007-05-01

    Thermobifida fusca Cel9A-90 is a processive endoglucanase consisting of a family 9 catalytic domain (CD), a family 3c cellulose binding module (CBM3c), a fibronectin III-like domain, and a family 2 CBM. This enzyme has the highest activity of any individual T. fusca enzyme on crystalline substrates, particularly bacterial cellulose (BC). Mutations were introduced into the CD or the CBM3c of Cel9A-68 using site-directed mutagenesis. The mutant enzymes were expressed in Escherichia coli; purified; and tested for activity on four substrates, ligand binding, and processivity. The results show that H125 and Y206 play an important role in activity by forming a hydrogen bonding network with the catalytic base, D58; another important supporting residue, D55; and Glc(-1) O1. R378, a residue interacting with Glc(+1), plays an important role in processivity. Several enzymes with mutations in the subsites Glc(-2) to Glc(-4) had less than 15% activity on BC and markedly reduced processivity. Mutant enzymes with severalfold-higher activity on carboxymethyl cellulose (CMC) were found in the subsites from Glc(-2) to Glc(-4). The CBM3c mutant enzymes, Y520A, R557A/E559A, and R563A, had decreased activity on BC but had wild-type or improved processivity. Mutation of D513, a conserved residue at the end of the CBM, increased activity on crystalline cellulose. Previous work showed that deletion of the CBM3c abolished crystalline activity and processivity. This study shows that it is residues in the catalytic cleft that control processivity while the CBM3c is important for loose binding of the enzyme to the crystalline cellulose substrate. PMID:17369336

  14. Cloning, Expression, and Characterization of a Thermophilic Endoglucanase, AcCel12B from Acidothermus cellulolyticus 11B

    PubMed Central

    Wang, Junling; Gao, Gui; Li, Yuwei; Yang, Liangzhen; Liang, Yanli; Jin, Hanyong; Han, Weiwei; Feng, Yan; Zhang, Zuoming

    2015-01-01

    The gene ABK52392 from the thermophilic bacterium Acidothermus cellulolyticus 11B was predicted to be endoglucanase and classified into glycoside hydrolase family 12. ABK52392 encodes a protein containing a catalytic domain and a carbohydrate binding module. ABK52392 was cloned and functionally expressed in Escherichia coli. After purification by Ni-NTA agarose affinity chromatography and Q-Sepharose® Fast Flow chromatography, the properties of the recombinant protein (AcCel12B) were characterized. AcCel12B exhibited optimal activity at pH 4.5 and 75 °C. The half-lives of AcCel12B at 60 and 70 °C were about 90 and 2 h, respectively, under acidic conditions. The specific hydrolytic activities of AcCel12B at 70 °C and pH 4.5 for sodium carboxymethylcellulose (CMC) and regenerated amorphous cellulose (RAC) were 118.3 and 104.0 U·mg−1, respectively. The Km and Vmax of AcCel12B for CMC were 25.47 mg·mL−1 and 131.75 U·mg−1, respectively. The time course of hydrolysis for RAC was investigated by measuring reducing ends in the soluble and insoluble phases. The total hydrolysis rate rapidly decreased after the early stage of incubation and the generation of insoluble reducing ends decreased earlier than that of soluble reducing ends. High thermostability of the cellulase indicates its potential commercial significance and it could be exploited for industrial application in the future. PMID:26506341

  15. Polarity Alteration of a Calcium Site Induces a Hydrophobic Interaction Network and Enhances Cel9A Endoglucanase Thermostability.

    PubMed

    Wang, Hsiu-Jung; Hsiao, Yu-Yuan; Chen, Yu-Pei; Ma, Tien-Yang; Tseng, Ching-Ping

    2016-03-01

    Structural calcium sites control protein thermostability and activity by stabilizing native folds and changing local conformations. Alicyclobacillus acidocaldarius survives in thermal-acidic conditions and produces an endoglucanase Cel9A (AaCel9A) which contains a calcium-binding site (Ser465 to Val470) near the catalytic cleft. By superimposing the Ca(2+)-free and Ca(2+)-bounded conformations of the calcium site, we found that Ca(2+) induces hydrophobic interactions between the calcium site and its nearby region by driving a conformational change. The hydrophobic interactions at the high-B-factor region could be enhanced further by replacing the surrounding polar residues with hydrophobic residues to affect enzyme thermostability and activity. Therefore, the calcium-binding residue Asp468 (whose side chain directly ligates Ca(2+)), Asp469, and Asp471 of AaCel9A were separately replaced by alanine and valine. Mutants D468A and D468V showed increased activity compared with those of the wild type with 0 mM or 10 mM Ca(2+) added, whereas the Asp469 or Asp471 substitution resulted in decreased activity. The D468A crystal structure revealed that mutation D468A triggered a conformational change similar to that induced by Ca(2+) in the wild type and developed a hydrophobic interaction network between the calcium site and the neighboring hydrophobic region (Ala113 to Ala117). Mutations D468V and D468A increased 4.5°C and 5.9°C, respectively, in melting temperature, and enzyme half-life at 75°C increased approximately 13 times. Structural comparisons between AaCel9A and other endoglucanases of the GH9 family suggested that the stability of the regions corresponding to the AaCel9A calcium site plays an important role in GH9 endoglucanase catalysis at high temperature. PMID:26729722

  16. Polarity Alteration of a Calcium Site Induces a Hydrophobic Interaction Network and Enhances Cel9A Endoglucanase Thermostability

    PubMed Central

    Wang, Hsiu-Jung; Hsiao, Yu-Yuan; Chen, Yu-Pei; Ma, Tien-Yang

    2016-01-01

    Structural calcium sites control protein thermostability and activity by stabilizing native folds and changing local conformations. Alicyclobacillus acidocaldarius survives in thermal-acidic conditions and produces an endoglucanase Cel9A (AaCel9A) which contains a calcium-binding site (Ser465 to Val470) near the catalytic cleft. By superimposing the Ca2+-free and Ca2+-bounded conformations of the calcium site, we found that Ca2+ induces hydrophobic interactions between the calcium site and its nearby region by driving a conformational change. The hydrophobic interactions at the high-B-factor region could be enhanced further by replacing the surrounding polar residues with hydrophobic residues to affect enzyme thermostability and activity. Therefore, the calcium-binding residue Asp468 (whose side chain directly ligates Ca2+), Asp469, and Asp471 of AaCel9A were separately replaced by alanine and valine. Mutants D468A and D468V showed increased activity compared with those of the wild type with 0 mM or 10 mM Ca2+ added, whereas the Asp469 or Asp471 substitution resulted in decreased activity. The D468A crystal structure revealed that mutation D468A triggered a conformational change similar to that induced by Ca2+ in the wild type and developed a hydrophobic interaction network between the calcium site and the neighboring hydrophobic region (Ala113 to Ala117). Mutations D468V and D468A increased 4.5°C and 5.9°C, respectively, in melting temperature, and enzyme half-life at 75°C increased approximately 13 times. Structural comparisons between AaCel9A and other endoglucanases of the GH9 family suggested that the stability of the regions corresponding to the AaCel9A calcium site plays an important role in GH9 endoglucanase catalysis at high temperature. PMID:26729722

  17. Site-Directed Mutagenesis of a Hyperthermophilic Endoglucanase Cel12B from Thermotoga maritima Based on Rational Design

    PubMed Central

    Zhang, Jinfeng; Shi, Hao; Xu, Linyu; Zhu, Xiaoyan; Li, Xiangqian

    2015-01-01

    To meet the demand for the application of high activity and thermostable cellulases in the production of new-generation bioethanol from nongrain-cellulose sources, a hyperthermostable β-1,4-endoglucase Cel12B from Thermotoga maritima was selected for further modification by gene site-directed mutagenesis method in the present study, based on homology modeling and rational design. As a result, two recombinant enzymes showed significant improvement in enzyme activity by 77% and 87%, respectively, higher than the parental enzyme TmCel12B. Furthermore, the two mutants could retain 80% and 90.5% of their initial activity after incubation at 80°C for 8 h, while only 45% for 5 h to TmCel12B. The Km and Vmax of the two recombinant enzymes were 1.97±0.05 mM, 4.23±0.15 μmol·mg-1·min-1 of TmCel12B-E225H-K207G-D37V, and 2.97±0.12 mM, 3.15±0.21 μmol·mg-1·min-1 of TmCel12B-E225H-K207G, respectively, when using CMC-Na as the substrate. The roles of the mutation sites were also analyzed and evaluated in terms of electron density, hydrophobicity of the modeled protein structures. The recombinant enzymes may be used in the hydrolysis of cellulose at higher temperature in the future. It was concluded that the gene mutagenesis approach of a certain active residues may effectively improve the performance of cellulases for the industrial applications and contribute to the study the thermostable mechanism of thermophilic enzymes. PMID:26218520

  18. PEM Electrolyzer Incorporating an Advanced Low-Cost Membrane

    SciTech Connect

    Hamdan, Monjid

    2013-08-29

    The Department of Energy (DOE) has identified hydrogen production by electrolysis of water at forecourt stations as a critical technology for transition to the hydrogen economy; however, the cost of hydrogen produced by present commercially available electrolysis systems is considerably higher than the DOE 2015 and 2020 cost targets. Analyses of proton-exchange membrane (PEM) electrolyzer systems indicate that reductions in electricity consumption and electrolyzer stack and system capital cost are required to meet the DOE cost targets. The primary objective is to develop and demonstrate a cost-effective energy-based system for electrolytic generation of hydrogen. The goal is to increase PEM electrolyzer efficiency and to reduce electrolyzer stack and system capital cost to meet the DOE cost targets for distributed electrolysis. To accomplish this objective, work was conducted by a team consisting of Giner, Inc. (Giner), Virginia Polytechnic Institute & University (VT), and domnick hunter group, a subsidiary of Parker Hannifin (Parker). The project focused on four (4) key areas: (1) development of a high-efficiency, high-strength membrane; (2) development of a long-life cell-separator; (3) scale-up of cell active area to 290 cm2 (from 160 cm²); and (4) development of a prototype commercial electrolyzer system. In each of the key stack development areas Giner and our team members conducted focused development in laboratory-scale hardware, with analytical support as necessary, followed by life-testing of the most promising candidate materials. Selected components were then scaled up and incorporated into low-cost scaled-up stack hardware. The project culminated in the fabrication and testing of a highly efficient electrolyzer system for production of 0.5 kg/hr hydrogen and validation of the stack and system in testing at the National Renewable Energy Laboratory (NREL).

  19. ENVIRONMENTAL TECHNOLOGY VERIFICATION REPORT ANR PIPELINE COMPANY PARAMETRIC EMISSIONS MONITORING SYSTEM (PEMS)

    EPA Science Inventory

    The Environmental Technology Verification report discusses the technology and performance of a gaseous-emissions monitoring system for large, natural-gas-fired internal combustion engines. The device tested is the Parametric Emissions Monitoring System (PEMS) manufactured by ANR ...

  20. Application of Thermo-Mechanical Measurements of Plastic Packages for Reliability Evaluation of PEMS

    NASA Technical Reports Server (NTRS)

    Sharma, Ashok K.; Teverovsky, Alexander

    2004-01-01

    Thermo-mechanical analysis (TMA) is typically employed for measurements of the glass transition temperature (Tg) and coefficients of thermal expansion (CTE) in molding compounds used in plastic encapsulated microcircuits (PEMs). Application of TMA measurements directly to PEMs allows anomalies to be revealed in deformation of packages with temperature, and thus indicates possible reliability concerns related to thermo-mechanical integrity and stability of the devices. In this work, temperature dependencies of package deformation were measured in several types of PEMs that failed environmental stress testing including temperature cycling, highly accelerated stress testing (HAST) in humid environments, and bum-in (BI) testing. Comparison of thermo-mechanical characteristics of packages and molding compounds in the failed parts allowed for explanation of the observed failures. The results indicate that TMA of plastic packages might be used for quality evaluation of PEMs intended for high-reliability applications.

  1. Amino acid sequence and carbohydrate-binding analysis of the N-acetyl-D-galactosamine-specific C-type lectin, CEL-I, from the Holothuroidea, Cucumaria echinata.

    PubMed

    Hatakeyama, Tomomitsu; Matsuo, Noriaki; Shiba, Kouhei; Nishinohara, Shoichi; Yamasaki, Nobuyuki; Sugawara, Hajime; Aoyagi, Haruhiko

    2002-01-01

    CEL-I is one of the Ca2+-dependent lectins that has been isolated from the sea cucumber, Cucumaria echinata. This protein is composed of two identical subunits held by a single disulfide bond. The complete amino acid sequence of CEL-I was determined by sequencing the peptides produced by proteolytic fragmentation of S-pyridylethylated CEL-I. A subunit of CEL-I is composed of 140 amino acid residues. Two intrachain (Cys3-Cys14 and Cys31-Cys135) and one interchain (Cys36) disulfide bonds were also identified from an analysis of the cystine-containing peptides obtained from the intact protein. The similarity between the sequence of CEL-I and that of other C-type lectins was low, while the C-terminal region, including the putative Ca2+ and carbohydrate-binding sites, was relatively well conserved. When the carbohydrate-binding activity was examined by a solid-phase microplate assay, CEL-I showed much higher affinity for N-acetyl-D-galactosamine than for other galactose-related carbohydrates. The association constant of CEL-I for p-nitrophenyl N-acetyl-beta-D-galactosaminide (NP-GalNAc) was determined to be 2.3 x 10(4) M(-1), and the maximum number of bound NP-GalNAc was estimated to be 1.6 by an equilibrium dialysis experiment. PMID:11866098

  2. 21st Century Renewable Fuels, Energy, and Materials

    SciTech Connect

    Berry, K. Joel; Das, Susanta K.

    2012-11-29

    The objectives of this project were multi-fold: (i) conduct fundamental studies to develop a new class of high temperature PEM fuel cell material capable of conducting protons at elevated temperature (180°C), (ii) develop and fabricate a 5k We novel catalytic flat plate steam reforming process for extracting hydrogen from multi-fuels and integrate with high-temperature PEM fuel cell systems, (iii) research and develop improved oxygen permeable membranes for high power density lithium air battery with simple control systems and reduced cost, (iv) research on high energy yield agriculture bio-crop (Miscanthus) suitable for reformate fuel/alternative fuel with minimum impact on human food chain and develop a cost analysis and production model, and (v) develop math and science alternative energy educator program to include bio-energy and power.

  3. CAPSTONE SENIOR DESIGN - SUPRAMOLECULAR PROTON EXCHANGE MEMBRANES FOR FUEL CELLS

    EPA Science Inventory

    In order to assume a leading role in the burgeoning hydrogen economy, new infrastructure will be required for fuel cell manufacturing and R&D capabilities. The objective of this proposal is the development of a new generation of advanced proton exchange membrane (PEM) technol...

  4. Optimal design of a hybridization scheme with a fuel cell using genetic optimization

    NASA Astrophysics Data System (ADS)

    Rodriguez, Marco A.

    Fuel cell is one of the most dependable "green power" technologies, readily available for immediate application. It enables direct conversion of hydrogen and other gases into electric energy without any pollution of the environment. However, the efficient power generation is strictly stationary process that cannot operate under dynamic environment. Consequently, fuel cell becomes practical only within a specially designed hybridization scheme, capable of power storage and power management functions. The resultant technology could be utilized to its full potential only when both the fuel cell element and the entire hybridization scheme are optimally designed. The design optimization in engineering is among the most complex computational tasks due to its multidimensionality, nonlinearity, discontinuity and presence of constraints in the underlying optimization problem. this research aims at the optimal utilization of the fuel cell technology through the use of genetic optimization, and advance computing. This study implements genetic optimization in the definition of optimum hybridization rules for a PEM fuel cell/supercapacitor power system. PEM fuel cells exhibit high energy density but they are not intended for pulsating power draw applications. They work better in steady state operation and thus, are often hybridized. In a hybrid system, the fuel cell provides power during steady state operation while capacitors or batteries augment the power of the fuel cell during power surges. Capacitors and batteries can also be recharged when the motor is acting as a generator. Making analogies to driving cycles, three hybrid system operating modes are investigated: 'Flat' mode, 'Uphill' mode, and 'Downhill' mode. In the process of discovering the switching rules for these three modes, we also generate a model of a 30W PEM fuel cell. This study also proposes the optimum design of a 30W PEM fuel cell. The PEM fuel cell model and hybridization's switching rules are postulated

  5. A performance study of PEMS applied to the Hsinta power station of Taipower

    NASA Astrophysics Data System (ADS)

    Chien, T. W.; Chu, H.; Hsu, W. C.; Tu, Y. Y.; Tsai, H. S.; Chen, K. Y.

    2005-01-01

    Predictive emission monitoring systems (PEMS) have been shown to be a promising technology for calculating the emissions from gas-fired stationary sources. One of the first demonstration PEMS in Taiwan was installed and operated successfully at the Hsinta power plant of the Taiwan Power Company (Taipower) in 2000. To improve the accuracy of this PEMS model, further studies were conducted at the same combined cycle gas turbine (CCGT) unit #1 of the Hsinta power plant. To optimize the NOX PEMS model, several functions were progressively developed including a log model, a one-level linear model, a three-level linear model, a 15-variable linear model, and a 15-variable with start-up mode model. The latter gave the relative accuracies (RA) and correlation coefficients between PEMS and a continuous emission monitoring system (CEMS) in the range of 3.38-14.77% and 0.955-0.989, respectively, which fulfill the criteria of the USEPA draft on PEMS performance specifications. Similarly, this model demonstrated RAs for low, medium, high level, and a three-level average less than 20% which meet CEMS requirements set out by Taiwan EPA.

  6. HOGEN{trademark} proton exchange membrane hydrogen generators: Commercialization of PEM electrolyzers

    SciTech Connect

    Smith, W.F.; Molter, T.M.

    1997-12-31

    PROTON Energy Systems` new HOGEN series hydrogen generators are Proton Exchange Membrane (PEM) based water electrolyzers designed to generate 300 to 1000 Standard Cubic Feet Per Hour (SCFH) of high purity hydrogen at pressures up to 400 psi without the use of mechanical compressors. This paper will describe technology evolution leading to the HOGEN, identify system design performance parameters and describe the physical packaging and interfaces of HOGEN systems. PEM electrolyzers have served US and UK Navy and NASA needs for many years in a variety of diverse programs including oxygen generators for life support applications. In the late 1970`s these systems were advocated for bulk hydrogen generation through a series of DOE sponsored program activities. During the military buildup of the 1980`s commercial deployment of PEM hydrogen generators was de-emphasized as priority was given to new Navy and NASA PEM electrolysis systems. PROTON Energy Systems was founded in 1996 with the primary corporate mission of commercializing PEM hydrogen generators. These systems are specifically designed and priced to meet the needs of commercial markets and produced through manufacturing processes tailored to these applications. The HOGEN series generators are the first step along the path to full commercial deployment of PEM electrolyzer products for both industrial and consumer uses. The 300/1000 series are sized to meet the needs of the industrial gases market today and provide a design base that can transition to serve the needs of a decentralized hydrogen infrastructure tomorrow.

  7. Proton exchange membrane fuel cell degradation: A parametric analysis using Computational Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Ozden, Ender; Tari, Ilker

    2016-02-01

    A Polymer Electrolyte Membrane (PEM) fuel cell is numerically investigated both as fresh and as degraded with the help of observed degradation patterns reported in the literature. The fresh fuel cell model is validated and verified with the data from the literature. Modifying the model by varying the parameters affected by degradation, a degraded PEM fuel cell model is created. The degraded fuel cell is parametrically analyzed by using a commercial Computational Fluid Dynamics (CFD) software. The investigated parameters are the membrane equivalent weight, the Catalyst Layer (CL) porosity and viscous resistance, the Gas Diffusion Layer (GDL) porosity and viscous resistance, and the bipolar plate contact resistance. It is shown for the first time that PEM fuel cell overall degradation can be numerically estimated by combining experimental data from degraded individual components. By comparing the simulation results for the fresh and the degraded PEM fuel cells for two years of operation, it is concluded that the effects of overall degradation on cell potential is significant - estimated to be 17% around the operating point of the fuel cell at 0.95 V open circuit voltage and 70 °C operating temperature.

  8. System level modeling and component level control of fuel cells

    NASA Astrophysics Data System (ADS)

    Xue, Xingjian

    This dissertation investigates the fuel cell systems and the related technologies in three aspects: (1) system-level dynamic modeling of both PEM fuel cell (PEMFC) and solid oxide fuel cell (SOFC); (2) condition monitoring scheme development of PEM fuel cell system using model-based statistical method; and (3) strategy and algorithm development of precision control with potential application in energy systems. The dissertation first presents a system level dynamic modeling strategy for PEM fuel cells. It is well known that water plays a critical role in PEM fuel cell operations. It makes the membrane function appropriately and improves the durability. The low temperature operating conditions, however, impose modeling difficulties in characterizing the liquid-vapor two phase change phenomenon, which becomes even more complex under dynamic operating conditions. This dissertation proposes an innovative method to characterize this phenomenon, and builds a comprehensive model for PEM fuel cell at the system level. The model features the complete characterization of multi-physics dynamic coupling effects with the inclusion of dynamic phase change. The model is validated using Ballard stack experimental result from open literature. The system behavior and the internal coupling effects are also investigated using this model under various operating conditions. Anode-supported tubular SOFC is also investigated in the dissertation. While the Nernst potential plays a central role in characterizing the electrochemical performance, the traditional Nernst equation may lead to incorrect analysis results under dynamic operating conditions due to the current reverse flow phenomenon. This dissertation presents a systematic study in this regard to incorporate a modified Nernst potential expression and the heat/mass transfer into the analysis. The model is used to investigate the limitations and optimal results of various operating conditions; it can also be utilized to perform the

  9. Crystallization and preliminary crystallographic study of an invertebrate C-type lectin, CEL-I, from the marine invertebrate Cucumaria echinata.

    PubMed

    Hatakeyama, Tomomitsu; Matsuo, Noriaki; Aoyagi, Haruhiko; Sugawara, Hajime; Uchida, Tatsuya; Kurisu, Genji; Kusunoki, Masami

    2002-01-01

    CEL-I is a GalNAc-specific carbohydrate-binding protein (lectin) isolated from the sea cucumber Cucumaria echinata. This protein belongs to the widely distributed C-type lectin family of animal lectins, which require Ca(2+) for their carbohydrate-binding ability and play important roles in various molecular-recognition processes in organisms. CEL-I was crystallized with 2-methyl-2,4-pentanediol using the hanging-drop vapour-diffusion technique. The CEL-I crystals belong to the monoclinic space group C2, with unit-cell parameters a = 92.38 (3), b = 69.94 (3), c = 76.69 (3) A, beta = 136.46 (2) degrees. Diffraction data were collected to 2.0 A resolution using synchrotron radiation. The asymmetric unit contains one CEL-I molecule. PMID:11752793

  10. Proton exchange membrane fuel cells for electrical power generation on-board commercial airplanes.

    SciTech Connect

    Curgus, Dita Brigitte; Munoz-Ramos, Karina; Pratt, Joseph William; Akhil, Abbas Ali; Klebanoff, Leonard E.; Schenkman, Benjamin L.

    2011-05-01

    Deployed on a commercial airplane, proton exchange membrane fuel cells may offer emissions reductions, thermal efficiency gains, and enable locating the power near the point of use. This work seeks to understand whether on-board fuel cell systems are technically feasible, and, if so, if they offer a performance advantage for the airplane as a whole. Through hardware analysis and thermodynamic and electrical simulation, we found that while adding a fuel cell system using today's technology for the PEM fuel cell and hydrogen storage is technically feasible, it will not likely give the airplane a performance benefit. However, when we re-did the analysis using DOE-target technology for the PEM fuel cell and hydrogen storage, we found that the fuel cell system would provide a performance benefit to the airplane (i.e., it can save the airplane some fuel), depending on the way it is configured.

  11. Proton Exchange Membrane Fuel Cells for Electrical Power Generation On-Board Commercial Airplanes

    SciTech Connect

    Pratt, Joesph W.; Klebanoff, Leonard E.; Munoz-Ramos, Karina; Akhil, Abbas A.; Curgus, Dita B.; Schenkman, Benjamin L.

    2011-05-01

    Deployed on a commercial airplane, proton exchange membrane fuel cells may offer emissions reductions, thermal efficiency gains, and enable locating the power near the point of use. This work seeks to understand whether on-board fuel cell systems are technically feasible, and, if so, if they offer a performance advantage for the airplane as a whole. Through hardware analysis and thermodynamic and electrical simulation, we found that while adding a fuel cell system using today’s technology for the PEM fuel cell and hydrogen storage is technically feasible, it will not likely give the airplane a performance benefit. However, when we re-did the analysis using DOE-target technology for the PEM fuel cell and hydrogen storage, we found that the fuel cell system would provide a performance benefit to the airplane (i.e., it can save the airplane some fuel), depending on the way it is configured.

  12. Protein energy malnutrition (PEM), brain and various facets of child development.

    PubMed

    Udani, P M

    1992-01-01

    Protein energy malnutrition (PEM) is a global problem. Nearly 150 million children under 5 years in the world and 70-80 million in India suffer from PEM, nearly 20 million in the world and 4 million in India suffer from severe forms of PEM, viz., marasmus, kwashiorkor and marasmic kwashiorkor. The studies in experimental animals in the west and children in developing countries have revealed the adverse effects of PEM on the biochemistry of developing brain which leads to tissue damage and tissue contents, growth arrest, developmental differentiation, myelination, reduction of synapses, synaptic transmitters and overall development of dendritic activity. Many of these adverse effects have been described in children in clinical data, biochemical studies, reduction in brain size, histology of the spinal cord, quantitative studies and electron microscopy of sural nerve, neuro -CT scan, magnetic resonance imaging (MRI) and morphological changes in the cerebellar cells. Longer the PEM, younger the child, poorer the maternal health and literacy, more adverse are the effects of PEM on the nervous system. Just like the importance of nutrients on the developing brain, so are the adverse effects on the child development of lack of environmental stimulation, emotional support and love and affection to the child. When both the adverse factors are combined, the impact is severe. Hence prevention of PEM in pregnant and lactating mothers, breast feeding, adequate home based supplements, family support and love will improve the physical growth, mental development, social competence and academic performance of the child. Hence nutritional rehabilitation, psychosocial and psychomotor development of the child should begin in infancy and continue throughout. It should be at all levels, most important being in family, school, community and various intervention programmes, local, regional and national. Moreover medical students, health personnel, all medical disciplines concerned with

  13. Recombinant Trichoderma harzianum endoglucanase I (Cel7B) is a highly acidic and promiscuous carbohydrate-active enzyme.

    PubMed

    Pellegrini, Vanessa O A; Serpa, Viviane Isabel; Godoy, Andre S; Camilo, Cesar M; Bernardes, Amanda; Rezende, Camila A; Junior, Nei Pereira; Franco Cairo, João Paulo L; Squina, Fabio M; Polikarpov, Igor

    2015-11-01

    Trichoderma filamentous fungi have been investigated due to their ability to secrete cellulases which find various biotechnological applications such as biomass hydrolysis and cellulosic ethanol production. Previous studies demonstrated that Trichoderma harzianum IOC-3844 has a high degree of cellulolytic activity and potential for biomass hydrolysis. However, enzymatic, biochemical, and structural studies of cellulases from T. harzianum are scarce. This work reports biochemical characterization of the recombinant endoglucanase I from T. harzianum, ThCel7B, and its catalytic core domain. The constructs display optimum activity at 55 °C and a surprisingly acidic pH optimum of 3.0. The full-length enzyme is able to hydrolyze a variety of substrates, with high specific activity: 75 U/mg for β-glucan, 46 U/mg toward xyloglucan, 39 U/mg for lichenan, 26 U/mg for carboxymethyl cellulose, 18 U/mg for 4-nitrophenyl β-D-cellobioside, 16 U/mg for rye arabinoxylan, and 12 U/mg toward xylan. The enzyme also hydrolyzed filter paper, phosphoric acid swollen cellulose, Sigmacell 20, Avicel PH-101, and cellulose, albeit with lower efficiency. The ThCel7B catalytic domain displays similar substrate diversity. Fluorescence-based thermal shift assays showed that thermal stability is highest at pH 5.0. We determined kinetic parameters and analyzed a pattern of oligosaccharide substrates hydrolysis, revealing cellobiose as a final product of C6 degradation. Finally, we visualized effects of ThCel7B on oat spelt using scanning electron microscopy, demonstrating the morphological changes of the substrate during the hydrolysis. The acidic behavior of ThCel7B and its considerable thermostability hold a promise of its industrial applications and other biotechnological uses under extremely acidic conditions. PMID:26156238

  14. Enhancement of Expression and Apparent Secretion of Erwinia chrysanthemi Endoglucanase (Encoded by celZ) in Escherichia coli B†

    PubMed Central

    Zhou, Shengde; Yomano, Lorraine P.; Saleh, Alif Z.; Davis, Francis C.; Aldrich, Henry C.; Ingram, Lonnie O.

    1999-01-01

    Escherichia coli B has been engineered as a biocatalyst for the conversion of lignocellulose into ethanol. Previous research has demonstrated that derivatives of E. coli B can produce high levels of Erwinia chrysanthemi endoglucanase (encoded by celZ) as a periplasmic product and that this enzyme can function with commercial fungal cellulase to increase ethanol production. In this study, we have demonstrated two methods that improve celZ expression in E. coli B. Initially, with a low-copy-number vector, two E. coli glycolytic gene promoters (gap and eno) were tested and found to be less effective than the original celZ promoter. By screening 18,000 random fragments of Zymomonas mobilis DNA, a surrogate promoter was identified which increased celZ expression up to sixfold. With this promoter, large polar inclusion bodies were clearly evident in the periplasmic space. Sequencing revealed that the most active surrogate promoter is derived from five Sau3A1 fragments, one of which was previously sequenced in Z. mobilis. Visual inspection indicated that this DNA fragment contains at least five putative promoter regions, two of which were confirmed by primer extension analysis. Addition of the out genes from E. chrysanthemi EC16 caused a further increase in the production of active enzyme and facilitated secretion or release of over half of the activity into the extracellular environment. With the most active construct, of a total of 13,000 IU of active enzyme per liter of culture, 7,800 IU was in the supernatant. The total active endoglucanase was estimated to represent 4 to 6% of cellular protein. PMID:10347024

  15. A comparative study of the unfolding of the endoglucanase Cel45 from Humicola insolens in denaturant and surfactant.

    PubMed Central

    Otzen, D. E.; Christiansen, L.; Schülein, M.

    1999-01-01

    Cellulases are increasingly being used for industrial purposes, particularly in washing powders, yet little is known of the factors governing the stability of proteins in detergent solutions. We present a comparative analysis of the behavior of the cellulase Cel45 from Humicola insolens in the presence of the denaturant guanidinium chloride and the anionic detergent C12-LAS. Although Cel45 unfolds in GdmCl according to a simple two-state model under equilibrium conditions, it accumulates a transient intermediate during refolding. The four disulfide bonds do not contribute detectably to the stability of the native state. Cel45 is unfolded by very low concentrations of C12-LAS (1-4 mM). An analysis of 16 mutants of Cel45 shows a very weak correlation between unfolding rates in denaturant and detergent; mutants that have the same unfolding rate in GdmCl (within a factor of 1.5) vary 1,000-fold in their unfolding rates in C12-LAS. The data support a simple model for unfolding by detergent, in which the introduction of positive charges or removal of negative charges greatly increases detergent sensitivity, while interactions with the hydrophobic detergent tail contribute to a smaller extent. This implies that different detergent-mediated unfolding pathways exist, whose accessibilities depend on individual residues. Double-mutant cycles reveal that mutations in two proximal residues lead to repulsion and a destabilization greater than the sum of the individual mutations as measured by GdmCl denaturation, but they also reduce the affinity for LAS and therefore actually stabilize the protein relative to wild-type. Ligands that interact strongly with the denatured state may therefore alter the unfolding process. PMID:10493589

  16. Thermostability Mechanism for the Hyperthermophilicity of Extremophile Cellulase TmCel12A: Implied from Molecular Dynamics Simulation.

    PubMed

    Lian, Peng; Yuan, Congmin; Xu, Qin; Fu, Wei

    2016-08-01

    Thermostability is of considerable importance for the application of cellulase in cellulosic ethanol production. The cellulase 12A from the hyperthermophile Thermotoga maritima (TmCel12A) is an ideal candidate to study thermostability of cellulases. Optimal temperature of the wild-type enzyme is 85 °C. Recently, it has been observed that surface loop mutation Y61G not only accelerates the hydrolysis rate but also extends the half-life of the enzyme at high temperature. However, the mechanism of how Y61G enhances thermostability of TmCel12A has not been revealed. Here, molecular dynamics simulation together with dynamic correlation network analysis was used to explore thermostability mechanism of TmCel12A. A hydrophobic cluster constructed by Y61, W176, V62, and L144 in the binding pocket was found to play a pivotal role in modulating thermostability as well as catalytic capability of TmCel12A. It stabilizes the apoenzyme at high temperature; however, it impedes the substrate binding. Y61G mutation disturbs the hydrophobic cluster as the counterpart amino acid W176 forms a cation-π interaction with R60 instead of the π-π interaction with Y61 in WT. Moreover, Y61G mutation makes the enzyme more rigid and more extended via altering the amino acid communities at the hinge part of the enzyme. An earlier hypothesis proposed from crystallographic observation that Y61G may accelerate the products releasing has been also confirmed by our simulations. These findings may provide a new direction for both theoretical and experimental scientists to improve the thermostability of other cellulases that can be potentially applied in biofuel industry. PMID:27384708

  17. N-linked glycosylation of recombinant cellobiohydrolase I (Cel7A) from Penicillium verruculosum and its effect on the enzyme activity.

    PubMed

    Dotsenko, Anna S; Gusakov, Alexander V; Volkov, Pavel V; Rozhkova, Aleksandra M; Sinitsyn, Arkady P

    2016-02-01

    Cellobiohydrolase I from Penicillium verruculosum (PvCel7A) has four potential N-glycosylation sites at its catalytic module: Asn45, Asn194, Asn388, and Asn430. In order to investigate how the N-glycosylation influences the activity and other properties of the enzyme, the wild type (wt) PvCel7A and its mutant forms, carrying Asn to Ala substitutions, were cloned into Penicillium canescens PCA10 (niaD-) strain, a fungal host for production of heterologous proteins. The rPvCel7A-wt and N45A, N194A, N388A mutants were successfully expressed and purified for characterization, whereas the expression of N430A mutant was not achieved. The MALDI-TOF mass spectrometry fingerprinting of peptides, obtained as a result of digestion of rPvCel7A forms with specific proteases, showed that the N-linked glycans represent variable high-mannose oligosaccharides and the products of their sequential enzymatic trimming, according to the formula (Man)0-13 (GlcNAc)2 , or a single GlcNAc residue. Mutations had no notable effect on pH-optimum of PvCel7A activity and enzyme thermostability. However, the mutations influenced both the enzyme adsorption ability on Avicel and its activity against natural and synthetic substrates. In particular, the N45A mutation led to a significant increase in the rate of Avicel and milled aspen wood hydrolysis, while the substrate digestion rates in the case of N194A and N388A mutants were notably lower relative to rPvCel7A-wt. These data, together with data of 3D structural modeling of the PvCel7A catalytic module, indicate that the N-linked glycans are an important part of the processive catalytic machinery of PvCel7A. PMID:26301455

  18. Single-molecule imaging analysis of elementary reaction steps of Trichoderma reesei cellobiohydrolase I (Cel7A) hydrolyzing crystalline cellulose Iα and IIII.

    PubMed

    Shibafuji, Yusuke; Nakamura, Akihiko; Uchihashi, Takayuki; Sugimoto, Naohisa; Fukuda, Shingo; Watanabe, Hiroki; Samejima, Masahiro; Ando, Toshio; Noji, Hiroyuki; Koivula, Anu; Igarashi, Kiyohiko; Iino, Ryota

    2014-05-16

    Trichoderma reesei cellobiohydrolase I (TrCel7A) is a molecular motor that directly hydrolyzes crystalline celluloses into water-soluble cellobioses. It has recently drawn attention as a tool that could be used to convert cellulosic materials into biofuel. However, detailed mechanisms of action, including elementary reaction steps such as binding, processive hydrolysis, and dissociation, have not been thoroughly explored because of the inherent challenges associated with monitoring reactions occurring at the solid/liquid interface. The crystalline cellulose Iα and IIII were previously reported as substrates with different crystalline forms and different susceptibilities to hydrolysis by TrCel7A. In this study, we observed that different susceptibilities of cellulose Iα and IIII are highly dependent on enzyme concentration, and at nanomolar enzyme concentration, TrCel7A shows similar rates of hydrolysis against cellulose Iα and IIII. Using single-molecule fluorescence microscopy and high speed atomic force microscopy, we also determined kinetic constants of the elementary reaction steps for TrCel7A against cellulose Iα and IIII. These measurements were performed at picomolar enzyme concentration in which density of TrCel7A on crystalline cellulose was very low. Under this condition, TrCel7A displayed similar binding and dissociation rate constants for cellulose Iα and IIII and similar fractions of productive binding on cellulose Iα and IIII. Furthermore, once productively bound, TrCel7A processively hydrolyzes and moves along cellulose Iα and IIII with similar translational rates. With structural models of cellulose Iα and IIII, we propose that different susceptibilities at high TrCel7A concentration arise from surface properties of substrate, including ratio of hydrophobic surface and number of available lanes. PMID:24692563

  19. Biomass Burning Influences on the Composition of the Remote South Pacific Troposphere: Analysis Based on Observations from PEM Tropics-A

    NASA Technical Reports Server (NTRS)

    Singh, H. B.; Viezee, W.; Chen, Y.; Bradshaw, J.; Sandholm, S.; Blake, D.; Blake, N.; Heikes, B.; Snow, J.; Talbot, R.; Sachse, G.; Vay, S.

    1999-01-01

    Airborne, in-situ measurements from PEM-Tropics-A (September/October 1996) are analyzed to show the presence of distinct pollution plumes in the middle-tropical troposphere of the remote South Pacific (10-30degS). These elevated plumes cause a relative maximum at about 5-7km attitude in the vertical distribution of primary and secondary species characteristic of fuel combustion and biomass burning (CO, C2H2, C2H6, CH3Cl, PAN, O3). Similar plumes were also observed at mid-latitudes in the middle troposphere during three flights east of New Zealand (40-45degS). In all, pollution plumes with CO larger than 100 ppb were observed 24 times on 7 separate flight days south of the equator. The observed plumes were generally embedded in very dry air. Ten-day back trajectory analysis supports the view that these originated from the biomass burning regions of South Africa (and South America) and were transported to the South Pacific along long-distance subsiding trajectories. The chemical composition of the southern Pacific troposphere analyzed from the PEM-Tropics-A data is compared with data from the tropical regions of the northern Pacific (PEM-West-A) and southern Atlantic (TRACE-A) during the same Sept/Oct time period. Sizable perturbations in the abundance of ozone and its key precursors, resulting from the transport of pollution originating from biomass burning sources, are observed in much of the Southern Hemispheric troposphere.

  20. Self-humidified proton exchange membrane fuel cells: Operation of larger cells and fuel cell stacks

    SciTech Connect

    Dhar, H.P.; Lee, J.H.; Lewinski, K.A.

    1996-12-31

    The PEM fuel cell is promising as the power source for use in mobile and stationary applications primarily because of its high power density, all solid components, and simplicity of operation. For wide acceptability of this power source, its cost has to be competitive with the presently available energy sources. The fuel cell requires continuous humidification during operation as a power source. The humidification unit however, increases fuel cell volume, weight, and therefore decreases its overall power density. Great advantages in terms of further fuel cell simplification can be achieved if the humidification process can be eliminated or minimized. In addition, cost reductions are associated with the case of manufacturing and operation. At BCS Technology we have developed a technology of self-humidified operation of PEM fuel cells based on the mass balance of the reactants and products and the ability of membrane electrode assembly (MEA) to retain water necessary for humidification under the cell operating conditions. The reactants enter the fuel cell chambers without carrying any form of water, whether in liquid or vapor form. Basic principles of self-humidified operation of fuel cells as practiced by BCS Technology, Inc. have been presented previously in literature. Here, we report the operation of larger self-humidified single cells and fuel cell stacks. Fuel cells of areas Up to 100 cm{sup 2} have been operated. We also show the self-humidified operation of fuel cell stacks of 50 and 100 cm{sup 2} electrode areas.

  1. Recombinant Expression of Trichoderma reesei Cel61A in Pichia pastoris: Optimizing Yield and N-terminal Processing.

    PubMed

    Tanghe, Magali; Danneels, Barbara; Camattari, Andrea; Glieder, Anton; Vandenberghe, Isabel; Devreese, Bart; Stals, Ingeborg; Desmet, Tom

    2015-12-01

    The auxiliary activity family 9 (AA9, formerly GH61) harbors a recently discovered group of oxidative enzymes that boost cellulose degradation. Indeed, these lytic polysaccharide monooxygenases (LPMOs) are able to disrupt the crystalline structure of cellulose, thereby facilitating the work of hydrolytic enzymes involved in biomass degradation. Since these enzymes require an N-terminal histidine residue for activity, their recombinant production as secreted protein is not straightforward. We here report the expression optimization of Trichoderma reesei Cel61A (TrCel61A) in the host Pichia pastoris. The use of the native TrCel61A secretion signal instead of the alpha-mating factor from Saccharomyces cerevisiae was found to be crucial, not only to obtain high protein yields (>400 mg/L during fermentation) but also to enable the correct processing of the N-terminus. Furthermore, the LPMO activity of the enzyme is demonstrated here for the first time, based on its degradation profile of a cellulosic substrate. PMID:26285758

  2. Evaluating endoglucanase Cel7B-lignin interaction mechanisms and kinetics using quartz crystal microgravimetry.

    PubMed

    Pfeiffer, Katherine A; Sorek, Hagit; Roche, Christine M; Strobel, Kathryn L; Blanch, Harvey W; Clark, Douglas S

    2015-11-01

    The kinetics and mechanisms of protein interactions with solid surfaces are important to fields as diverse as industrial biocatalysis, biomedical engineering, food science, and cell biology. The nonproductive adsorption of cellulase enzymes to lignin, a plant cell wall polymer, reduces their effectiveness in saccharifying biomass. Cellulase has been shown to interact with lignin, but the heterogeneity of lignin surfaces, challenges in measuring irreversible components of these interactions, and fast adsorption rates make quantifying the reaction kinetics difficult. This work employs quartz crystal microgravimetry with dissipation monitoring (QCM-D) for real-time measurement of adsorbed mass on a flat lignin surface. We have developed a method for casting homogeneous lignin films that are chemically similar to lignin found in pretreated biomass, and used QCM-D to compare three models of reversible-irreversible binding behavior: a single-site transition model, a transition model with changing adsorbate footprint, and a two-site transition model. Of the three models tested, the two-site transition model provides the only kinetic mechanism able to describe the behavior of Cel7B binding to lignin. While the direct implications of lignin-cellulase interactions may be limited to biomass deconstruction for renewable energy and green chemistry, the analytical and experimental methods demonstrated in this work are relevant to any system in which the kinetics and reaction mechanism of reversible and irreversible protein adsorption at a solid-liquid interface are important. PMID:25994114

  3. Characterization of the Dielectric Constant in the Trichoderma reesei Cel7B Active Site.

    PubMed

    Song, Xiangfei; Wang, Yefei; Zhang, Shujun; Yan, Shihai; Li, Tong; Yao, Lishan

    2015-07-27

    An attempt is made to evaluate the dielectric constant of the Trichoderma reesei Cel7B active site. Through kinetic measurements, the pKa value of the catalytic acid E201 is determined. Mutations (away from E201) with net charge changes are introduced to perturb the E201 pKa. It is shown that the mutation with a +1 charge change (including G225R, G230R, and A335R) decreases the pKa of E201, whereas the mutation with a -1 charge change (including Q149E, A222D, G225D, and G230D) increases the pKa. This effect is consistent with the electrostatic interaction between the changed charge and the E201 side chain. The fitting of the experimental data yields an apparent dielectric constant of 25-80. Molecular dynamics simulations with explicit water molecules indicate that the high solvent accessibility of the active site contributes largely to the high dielectric constant. ONIOM calculations show that high dielectric constant benefits the catalysis through decreasing the energy of the transition state relative to that of the enzyme substrate complex. PMID:26114648

  4. A mechanistic study of Trichoderma reesei Cel7B catalyzed glycosidic bond cleavage.

    PubMed

    Zhang, Yu; Yan, Shihai; Yao, Lishan

    2013-07-25

    An ONIOM study is performed to illustrate the mechanism of Trichoderma reesei Cel7B catalyzed p-nitrophenyl lactoside hydrolysis. In both the glycosylation and deglycosylation steps, the reaction proceeds in a concerted way, meaning the nucleophilic attack and the glycosidic bond cleavage occur simultaneously. The glycosylation step is rate limiting with a barrier of 18.9 kcal/mol, comparable to the experimental value derived from the kcat measured in this work. The function of four residues R108, Y146, Y170, and D172, which form a hydrogen-bond network involving the substrate, is studied by conservative mutations. The mutants, including R108K, Y146F, Y170F, and D172N, decrease the enzyme activity by about 150-8000-fold. Molecular dynamics simulations show that the mutations disrupt the hydrogen-bond network, cause the substrate to deviate from active binding and hinder either the proton transfer from E201 to O4(+1) or the nucleophilic attack from E196 to C1(-1). PMID:23822607

  5. Alteration of the carbohydrate-binding specificity of a C-type lectin CEL-I mutant with an EPN carbohydrate-binding motif.

    PubMed

    Hatakeyama, Tomomitsu; Ishimine, Tomohiro; Baba, Tomohiro; Kimura, Masanari; Unno, Hideaki; Goda, Shuichiro

    2013-07-01

    CEL-I is a Gal/GalNAc-specific C-type lectin isolated from the sea cucumber Cucumaria echinata. This lectin is composed of two carbohydrate-recognition domains (CRDs) with the carbohydrate-recognition motif QPD (Gln-Pro- Asp), which is generally known to exist in galactose-specific C-type CRDs. In the present study, a mutant CEL-I with EPN (Glu-Pro-Asn) motif, which is thought to be responsible for the carbohydrate-recognition of mannose-specific Ctype CRDs, was produced in Escherichia coli, and its effects on the carbohydrate-binding specificity were examined using polyamidoamine dendrimer (PD) conjugated with carbohydrates. Although wild-type CEL-I effectively formed complexes with N-acetylgalactosamine (GalNAc)-PD but not with mannose-PD, the mutant CEL-I showed relatively weak but definite affinity for mannose-PD. These results indicated that the QPD and EPN motifs play a significant role in the carbohydrate-recognition mechanism of CEL-I, especially in the discrimination of galactose and mannose. Additional mutations in the recombinant CEL-I binding site may further increase its specificity for mannose, and should provide insights into designing novel carbohydrate-recognition proteins. PMID:23157284

  6. Calibration of a PEM detector with depth of interactionmeasurement

    SciTech Connect

    Wang, G.-C.; Huber, J.S.; Moses, W.W.; Choong, W.-S.; Maltz, J.S.

    2004-06-03

    We present an in situ calibration technique for the LBNL positron emission mammography (PEM) detector module that is capable of measuring depth of interaction (DOI). The detector module consists of 64LSO crystals coupled on one end to a single photomultiplier tube (PMT) and on the opposite end to a 64 pixel array of silicon photodiodes (PD). The PMT provides an accurate timing pulse, the PDs identify the crystal of interaction, the sum provides a total energy signal and the /splGamma/=PD/(PD+PMT) ratio determines the depth of interaction. We calibrate using the /sup 176/Lu natural background radiation of the LSO crystals. We determine the relative gain (K) of the PMT and PD by minimizing the asymmetry of the /spl Gamma/ distribution. We determine the depth dependence from the width of the /spl Gamma/ distribution with optimal K. The performance of calibrated detector modules is evaluated by averaging results from 12 modules. The energy resolution is a function of depth ranging from 24 percent FWHM at the PD end to 51 percent FWHM at the PMT end, and the DOI resolution ranges from 6 mm FWHM at the PD end to 11 mm FWHM at the PMT end.

  7. Chrysler Pentastar direct hydrogen fuel cell program

    SciTech Connect

    Kimble, M.; Deloney, D.

    1995-08-01

    The Chrysler Pentastar Electronics, Inc. Direct Hydrogen Fueled PEM Fuel Cell Hybrid Vehicle Program (DPHV) was initiated 1 July, 1994 with the following mission, {open_quotes}Design, fabricate, and test a Direct Hydrogen Fueled Proton Exchange Membrane (PEM) Fuel Cell System including onboard hydrogen storage, an efficient lightweight fuel cell, a gas management system, peak power augmentation and a complete system controls that can be economically mass produced and comply with all safety environmental and consumer requirements for vehicle applications for the 21st century.{close_quotes} The Conceptual Design for the entire system based upon the selection of an applicable vehicle and performance requirements that are consistent with the PNGV goals will be discussed. A Hydrogen Storage system that has been selected, packaged, and partially tested in accordance with perceived Hydrogen Safety and Infrastructure requirements will be discussed in addition to our Fuel Cell approach along with design of the {open_quotes}real{close_quotes} module. The Gas Management System and the Load Leveling System have been designed and the software programs have been developed and will be discussed along with a complete fuel cell test station that has the capability to test up to a 60 kW fuel cell system.

  8. Regenerative fuel cell engineering - FY99

    SciTech Connect

    Michael A. Inbody; Rodney L. Borup; James C. Hedstrom; Jose Tafoya; Byron Morton; Lois Zook; Nicholas E. Vanderborgh

    2000-01-01

    The authors report the work conducted by the ESA-EPE Fuel Cell Engineering Team at Los Alamos National Laboratory during FY99 on regenerative fuel cell system engineering. The work was focused on the evaluation of regenerative fuel cell system components obtained through the RAFCO program. These components included a 5 kW PEM electrolyzer, a two-cell regenerative fuel cell stack, and samples of the electrolyzer membrane, anode, and cathode. The samples of the electrolyzer membrane, anode, and cathode were analyzed to determine their structure and operating characteristics. Tests were conducted on the two-cell regenerative fuel cell stack to characterize its operation as an electrolyzer and as a fuel cell. The 5 kW PEM electrolyzer was tested in the Regenerative Fuel Cell System Test Facility. These tests served to characterize the operation of the electrolyzer and, also, to verify the operation of the newly completed test facility. Future directions for this work in regenerative fuel cell systems are discussed.

  9. Instructions for Plastic Encapsulated Microcircuit(PEM) Selection, Screening and Qualification.

    NASA Technical Reports Server (NTRS)

    King, Terry; Teverovsky, Alexander; Leidecker, Henning

    2002-01-01

    The use of Plastic Encapsulated Microcircuits (PEMs) is permitted on NASA Goddard Space Flight Center (GSFC) spaceflight applications, provided each use is thoroughly evaluated for thermal, mechanical, and radiation implications of the specific application and found to meet mission requirements. PEMs shall be selected for their functional advantage and availability, not for cost saving; the steps necessary to ensure reliability usually negate any initial apparent cost advantage. A PEM shall not be substituted for a form, fit and functional equivalent, high reliability, hermetic device in spaceflight applications. Due to the rapid change in wafer-level designs typical of commercial parts and the unknown traceability between packaging lots and wafer lots, lot specific testing is required for PEMs, unless specifically excepted by the Mission Assurance Requirements (MAR) for the project. Lot specific qualification, screening, radiation hardness assurance analysis and/or testing, shall be consistent with the required reliability level as defined in the MAR. Developers proposing to use PEMs shall address the following items in their Performance Assurance Implementation Plan: source selection (manufacturers and distributors), storage conditions for all stages of use, packing, shipping and handling, electrostatic discharge (ESD), screening and qualification testing, derating, radiation hardness assurance, test house selection and control, data collection and retention.

  10. Compendium of NASA data base for the global tropospheric experiment's Pacific Exploratory Mission West-B (PEM West-B)

    NASA Technical Reports Server (NTRS)

    Gregory, Gerald L.; Scott, A. Donald, Jr.

    1995-01-01

    This compendium describes aircraft data that are available from NASA's Pacific Exploratory Mission West-B (PEM West-B). PEM West is a component of the International Global Atmospheric Chemistry's (IGAC) East Asia/North Pacific Regional Study (APARE) project. Objectives of PEM West are to investigate the atmospheric chemistry of ozone over the northwest Pacific -- natural budgets and the impact of anthropogenic/continental sources; and to investigate sulfur chemistry -- continental and marine sulfur sources. The PEM West program encompassed two expeditions. PEM West-A was conducted in September 1991 during which the predominance of tropospheric air was from mid-Pacific (marine) regions, but (at times) was modified by Asian outflow. PEM West-B was conducted during February 1994, a period characterized by maximum Asian outflow. Results from PEM West-A and B are public domain. PEM West-A data are summarized in NASA TM 109177 (published February 1995). Flight experiments were based at Guam, Hong Kong, and Japan. This document provides a representation of NASA DC-8 aircraft data that are available from NASA Langley's Distributed Active Archive Center (DAAC). The DAAC includes numerous other data such as meteorological and modeling products, results from surface studies, satellite observations, and sonde releases.

  11. Compendium of NASA data base for the Global Tropospheric Experiment's Pacific Exploratory Mission West-A (PEM West-A)

    NASA Technical Reports Server (NTRS)

    Gregory, G. L.; Scott, A. D., Jr.

    1995-01-01

    This compendium describes aircraft data that are available from NASA's Pacific Exploratory Mission West-A (PEM West-A). PEM West is a component of the International Global Atmospheric Chemistry's (IGAC) East Asia/North Pacific Regional Study (APARE) project. The PEM- West program encompassed two expeditions to study contrasting meteorological regimes in the Pacific. Objectives of PEM West are to investigate the atmospheric chemistry of ozone over the northwest Pacific -- natural budgets and the impact of anthropogenic sources; and to investigate sulfur chemistry -- continental versus marine sulfur sources. PEM West-A was conducted in September 1991 during which the predominance of tropospheric air is from the mid-Pacific (marine) regions, but (at times) is modified/mixed with Asian continental outflow. PEM West-B was conducted during February 1994, a period characterized by maximum continental outflow. PEM-B data (not included) will become public domain during the Summer of 1995. PEM West-A flight experiments were based at Japan, Hong Kong, and Guam. This document provides a representation of NASA DC-8 aircraft data that are available from NASA Langley's Distributed Active Archive Center (DAAC), which include numerous data such as meteorological observations, modeling products, results from surface studies, satellite observations, and sonde releases.

  12. Effects of Treatment on Disruptive Behaviors: A Quantitative Synthesis of Single-Subject Researches Using the PEM Approach

    ERIC Educational Resources Information Center

    Chen, Chiu-Wen; Ma, Hsen-Hsing

    2007-01-01

    The present study uses the PEM approach to synthesize the effectiveness of treatment on disruptive behaviors and simultaneously tests whether the higher validity of the PEM approach than that of the PND approach is repeatable. A hand search of the "Journal of Applied Behavior Analysis" was conducted, and reference lists from reviewed articles were…

  13. Chip integrated fuel cell accumulator

    NASA Astrophysics Data System (ADS)

    Frank, M.; Erdler, G.; Frerichs, H.-P.; Müller, C.; Reinecke, H.

    A unique new design of a chip integrated fuel cell accumulator is presented. The system combines an electrolyser and a self-breathing polymer electrolyte membrane (PEM) fuel cell with integrated palladium hydrogen storage on a silicon substrate. Outstanding advantages of this assembly are the fuel cell with integrated hydrogen storage, the possibility of refuelling it by electrolysis and the opportunity of simply refilling the electrolyte by adding water. By applying an electrical current, wiring the palladium hydrogen storage as cathode and the counter-electrode as anode, the electrolyser produces hydrogen at the palladium surface and oxygen at the electrolyser cell anode. The generated hydrogen is absorbed by the palladium electrode and the hydrogen storage is refilled consequently enabling the fuel cell to function.

  14. Metrology for Fuel Cell Manufacturing

    SciTech Connect

    Stocker, Michael; Stanfield, Eric

    2015-02-04

    The project was divided into three subprojects. The first subproject is Fuel Cell Manufacturing Variability and Its Impact on Performance. The objective was to determine if flow field channel dimensional variability has an impact on fuel cell performance. The second subproject is Non-contact Sensor Evaluation for Bipolar Plate Manufacturing Process Control and Smart Assembly of Fuel Cell Stacks. The objective was to enable cost reduction in the manufacture of fuel cell plates by providing a rapid non-contact measurement system for in-line process control. The third subproject is Optical Scatterfield Metrology for Online Catalyst Coating Inspection of PEM Soft Goods. The objective was to evaluate the suitability of Optical Scatterfield Microscopy as a viable measurement tool for in situ process control of catalyst coatings.

  15. Dynamic behavior of gasoline fuel cell electric vehicles

    NASA Astrophysics Data System (ADS)

    Mitchell, William; Bowers, Brian J.; Garnier, Christophe; Boudjemaa, Fabien

    As we begin the 21st century, society is continuing efforts towards finding clean power sources and alternative forms of energy. In the automotive sector, reduction of pollutants and greenhouse gas emissions from the power plant is one of the main objectives of car manufacturers and innovative technologies are under active consideration to achieve this goal. One technology that has been proposed and vigorously pursued in the past decade is the proton exchange membrane (PEM) fuel cell, an electrochemical device that reacts hydrogen with oxygen to produce water, electricity and heat. Since today there is no existing extensive hydrogen infrastructure and no commercially viable hydrogen storage technology for vehicles, there is a continuing debate as to how the hydrogen for these advanced vehicles will be supplied. In order to circumvent the above issues, power systems based on PEM fuel cells can employ an on-board fuel processor that has the ability to convert conventional fuels such as gasoline into hydrogen for the fuel cell. This option could thereby remove the fuel infrastructure and storage issues. However, for these fuel processor/fuel cell vehicles to be commercially successful, issues such as start time and transient response must be addressed. This paper discusses the role of transient response of the fuel processor power plant and how it relates to the battery sizing for a gasoline fuel cell vehicle. In addition, results of fuel processor testing from a current Renault/Nuvera Fuel Cells project are presented to show the progress in transient performance.

  16. Optimum hydrogen generation capacity and current density of the PEM-type water electrolyzer operated only during the off-peak period of electricity demand

    NASA Astrophysics Data System (ADS)

    Oi, Tsutomu; Sakaki, Yoshinori

    A requirement for widespread adoption of fuel cell vehicles in the transportation sector will be ready availability of pure hydrogen at prices that result in operating costs comparable to, or less than, that of gasoline internal combustion engine vehicles. The existing electrical power grid could be used as the backbone of the hydrogen infrastructure system in combination with water electrolyzers. A water electrolyzer can contribute to the load leveling by changing operational current density in accordance with the change of electricity demand. The optimum hydrogen generation capacity and current density of the polymer electrolyte membrane (PEM)-type water electrolyzer operated only during the off-peak period of electricity demand in respect of both the shortest time required for start and the higher efficiency of water electrolysis are obtained as 500 Nm 3 h -1 and 30 kA m -2, respectively. This PEM-type water electrolyzer could be used in the hydrogen refueling stations and energy storage systems constructed around hydrogen.

  17. Development and testing of a PEM SO2-depolarized electrolyzer and an operating method that prevents sulfur accumulation

    SciTech Connect

    Steimke, John L.; Steeper, Timothy J.; Colon-Mercado, Hector R.; Gorensek, Maximilian B.

    2015-09-02

    The hybrid sulfur (HyS) cycle is being developed as a technology to generate hydrogen by splitting water, using heat and electrical power from a nuclear or solar power plant. A key component is the SO2-depolarized electrolysis (SDE) cell, which reacts SO2 and water to form hydrogen and sulfuric acid. SDE could also be used in once-through operation to consume SO2 and generate hydrogen and sulfuric acid for sale. A proton exchange membrane (PEM) SDE cell based on a PEM fuel cell design was fabricated and tested. Measured cell potential as a function of anolyte pressure and flow rate, sulfuric acid concentration, and cell temperature are presented for this cell. Sulfur accumulation was observed inside the cell, which could have been a serious impediment to further development. A method to prevent sulfur formation was subsequently developed. As a result, this was made possible by a testing facility that allowed unattended operation for extended periods.

  18. Corrections for the effects of accidental coincidences, Compton scatter, and object size in positron emission mammography (PEM) imaging

    SciTech Connect

    Raymond Raylman; Stanislaw Majewski; Randolph Wojcik; Andrew Weisenberger; Brian Kross; Vladimir Popov

    2001-06-01

    Positron emission mammography (PEM) has begun to show promise as an effective method for the detection of breast lesions. Due to its utilization of tumor-avid radiopharmaceuticals labeled with positron-emitting radionuclides, this technique may be especially useful in imaging of women with radiodense or fibrocystic breasts. While the use of these radiotracers affords PEM unique capabilities, it also introduces some limitations. Specifically, acceptance of accidental and Compton-scattered coincidence events can decrease lesion detectability. The authors studied the effect of accidental coincidence events on PEM images produced by the presence of 18F-Fluorodeoxyglucose in the organs of a subject using an anthropomorphic phantom. A delayed-coincidence technique was tested as a method for correcting PEM images for the occurrence of accidental events. Also, a Compton scatter correction algorithm designed specifically for PEM was developed and tested using a compressed breast phantom.

  19. Oxygen supply for CHO cells immobilized on a packed-bed of Fibra-Cel disks.

    PubMed

    Meuwly, F; Loviat, F; Ruffieux, P-A; Bernard, A R; Kadouri, A; von Stockar, U

    2006-03-01

    Packed-bed bioreactors (PBR) have proven to be efficient systems to culture mammalian cells at very high cell density in perfusion mode, thus leading to very high volumetric productivity. However, the immobilized cells must be continuously supplied with all nutrients in sufficient quantities to remain viable and productive over the full duration of the perfusion culture. Among all nutrients, oxygen is the most critical since it is present at very low concentration due to its low solubility in cell culture medium. This work presents the development of a model for oxygenation in a packed-bed bioreactor system. The experimental system used to develop the model was a packed-bed of Fibra-Cel disk carriers used to cultivate Chinese Hamster Ovary cells at high density ( approximately 6.1 x 10(7) cell/mL) in perfusion mode. With the help of this model, it was possible to identify if a PBR system is operated in optimal or sub-optimal conditions. Using the model, two options were proposed, which could improve the performance of the basal system by about twofold, that is, by increasing the density of immobilized cells per carrier volume from 6.1 x 10(7) to 1.2 x 10(8) cell/mL, or by increasing the packed-bed height from 0.2 to 0.4 m. Both strategies would be rather simple to test and implement in the packed-bed bioreactor system used for this study. As a result, it would be possible to achieve a substantial improvement of about twofold higher productivity as compared with the basal conditions. PMID:16358288

  20. Fast measurement of proton exchange membrane fuel cell impedance based on pseudo-random binary sequence perturbation signals and continuous wavelet transform

    NASA Astrophysics Data System (ADS)

    Debenjak, Andrej; Boškoski, Pavle; Musizza, Bojan; Petrovčič, Janko; Juričić, Đani

    2014-05-01

    This paper proposes an approach to the estimation of PEM fuel cell impedance by utilizing pseudo-random binary sequence as a perturbation signal and continuous wavelet transform with Morlet mother wavelet. With the approach, the impedance characteristic in the frequency band from 0.1 Hz to 500 Hz is identified in 60 seconds, approximately five times faster compared to the conventional single-sine approach. The proposed approach was experimentally evaluated on a single PEM fuel cell of a larger fuel cell stack. The quality of the results remains at the same level compared to the single-sine approach.