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Sample records for potentiostats

  1. A CMOS Potentiostat for Control of Integrated MEMS Actuators

    E-print Network

    Maryland at College Park, University of

    A CMOS Potentiostat for Control of Integrated MEMS Actuators Somashekar Bangalore Prakash, Pamela-- We describe a potentiostat designed for in situ electrochemical control of MEMS actuators. This module is tailored for integration into a hybrid CMOS-MEMS system-on- a-chip to confine cells and measure

  2. Instrumentation for potentiostatic corrosion studies with distilled water

    NASA Technical Reports Server (NTRS)

    Loess, R. E.; Youngdahl, C. A.

    1969-01-01

    Corrosion is studied potentiostatically in the corroding environment of distilled water with an instrument that measures the potential of the corroding specimen immediately after interruption of the polarizing current. No current is flowing. The process permits compensation for IR drops when potentiostatic control is used in high resistance systems.

  3. A wireless potentiostat for mobile chemical sensing and biosensing.

    PubMed

    Steinberg, Matthew D; Kassal, Petar; Kerekovi?, Irena; Steinberg, Ivana Murkovi?

    2015-10-01

    Wireless chemical sensors are used as analytical devices in homeland defence, home-based healthcare, food logistics and more generally for the Sensor Internet of Things (SIoT). Presented here is a battery-powered and highly portable credit-card size potentiostat that is suitable for performing mobile and wearable amperometric electrochemical measurements with seamless wireless data transfer to mobile computing devices. The mobile electrochemical analytical system has been evaluated in the laboratory with a model redox system - the reduction of hexacyanoferrate(III) - and also with commercially available enzymatic blood-glucose test-strips. The potentiostat communicates wirelessly with mobile devices such as tablets or Smartphones by near-field communication (NFC) or with personal computers by radio-frequency identification (RFID), and thus provides a solution to the 'missing link' in connectivity that often exists between low-cost mobile and wearable chemical sensors and ubiquitous mobile computing products. The mobile potentiostat has been evaluated in the laboratory with a set of proof-of-concept experiments, and its analytical performance compared with a commercial laboratory potentiostat (R(2)=0.9999). These first experimental results demonstrate the functionality of the wireless potentiostat and suggest that the device could be suitable for wearable and point-of-sample analytical measurements. We conclude that the wireless potentiostat could contribute significantly to the advancement of mobile chemical sensor research and adoption, in particular for wearable sensors in healthcare and sport physiology, for wound monitoring and in mobile point-of-sample diagnostics as well as more generally as a part of the Sensor Internet of Things. PMID:26078146

  4. Design of a CMOS Potentiostat Circuit for Electrochemical Detector Arrays

    PubMed Central

    Ayers, Sunitha; Gillis, Kevin D.; Lindau, Manfred; Minch, Bradley A.

    2010-01-01

    High-throughput electrode arrays are required for advancing devices for testing the effect of drugs on cellular function. In this paper, we present design criteria for a potentiostat circuit that is capable of measuring transient amperometric oxidation currents at the surface of an electrode with submillisecond time resolution and picoampere current resolution. The potentiostat is a regulated cascode stage in which a high-gain amplifier maintains the electrode voltage through a negative feedback loop. The potentiostat uses a new shared amplifier structure in which all of the amplifiers in a given row of detectors share a common half circuit permitting us to use fewer transistors per detector. We also present measurements from a test chip that was fabricated in a 0.5-?m, 5-V CMOS process through MOSIS. Each detector occupied a layout area of 35?m × 15?m and contained eight transistors and a 50-fF integrating capacitor. The rms current noise at 2kHz bandwidth is ? 110fA. The maximum charge storage capacity at 2kHz is 1.26 × 106 electrons. PMID:20514150

  5. A Current-Mode Potentiostat for Multi-Target Detection Tested with Different Lactate Biosensors

    E-print Network

    De Micheli, Giovanni

    A Current-Mode Potentiostat for Multi-Target Detection Tested with Different Lactate Biosensors S. An integrated potentiostat and readout circuit for a multi-target biosensor is presented. To realize this Hz. The circuit was fabricated in 0.18 µm technology and tested for two lactate biosensors fabricated

  6. Potentiostatic current and galvanostatic potential oscillations during electrodeposition of cadmium.

    PubMed

    López-Sauri, D A; Veleva, L; Pérez-Ángel, G

    2015-09-14

    Cathodic current and potential oscillations were observed during electrodeposition of cadmium from a cyanide electrolyte on a vertical platinum electrode, in potentiostatic and galvanostatic experiments. Electrochemical impedance spectroscopy experiments revealed a region of negative real impedance in a range of non-zero frequencies, in the second descending branch with a positive slope of the N-shape current-potential curve. This kind of dynamical behaviour is characteristic of the HN-NDR oscillators (oscillators with the N-Shape current-potential curve and hidden negative differential resistance). The oscillations could be mainly attributed to the changes in the real active cathodic area, due to the adsorption of hydrogen molecules and their detachment from the surface. The instabilities of the electrochemical processes were characterized by time series, Fast Fourier Transforms and 2-D phase portraits showing quasi-periodic oscillations. PMID:26243301

  7. An Electrochemical Potentiostat Interface for Mobile Devices: Enabling Remote Medical Diagnostics

    E-print Network

    Fu, Henry; Lew, Michael; Menon, Shruti; Scratchley, Craig; Parameswaran, M Ash

    2015-01-01

    An electrochemical potentiostat interface for mobile devices has been designed and implemented. The interface consists of a potentiostat module, a microcontroller module, and a Bluetooth module. The potentiostat module performs electrochemical measurements and detects the responses from the samples. The microcontroller module controls the test and communication processes. The Bluetooth module links the system to a mobile device, where the mobile device acts as a control-console, data storage system, communication unit, and graphical plotter for the overall diagnostic processes. This interface is suitable for point-of-care and remote diagnostics, enhancing the capabilities of mobile devices in telemedicine.

  8. Metastable pitting of carbon steel under potentiostatic control

    SciTech Connect

    Cheng, Y.F.; Luo, J.L.

    1999-03-01

    The metastable pitting of A516-70 carbon steel was studied under potentiostatic control in solutions containing chloride ions. It was shown that there were different current fluctuation patterns and spectral slopes, that is, roll-off slopes, in passivity, general corrosion, and metastable pitting. Pits were often covered by a deposit which played an important role in the current fluctuation, with a quick current rise followed by a slow drop. There was a transitional potential (about 0 mV vs Ag/AgCl electrode) below which the metastable pitting initiation rate increased with the potential, because more sites would be activated. Above the transitional potential, the decay of the pitting occurrence rate with increased potential was due to the elimination of available pit sites. When the applied potential was between {minus}50 and 100 mV, pit growth kinetics was controlled by the potential drop through the deposit over the pit mouth. The potential dependence of repassivation time was mainly due to the effect of applied potential on the deposit over the pit mouth. There seemed to be good agreement between the calculated pit size and the measured values by optical microphotography. The assumption of hemispherical pit geometry was reasonable in calculating the pit radii.

  9. DStat: A Versatile, Open-Source Potentiostat for Electroanalysis and Integration

    PubMed Central

    Dryden, Michael D. M.; Wheeler, Aaron R.

    2015-01-01

    Most electroanalytical techniques require the precise control of the potentials in an electrochemical cell using a potentiostat. Commercial potentiostats function as “black boxes,” giving limited information about their circuitry and behaviour which can make development of new measurement techniques and integration with other instruments challenging. Recently, a number of lab-built potentiostats have emerged with various design goals including low manufacturing cost and field-portability, but notably lacking is an accessible potentiostat designed for general lab use, focusing on measurement quality combined with ease of use and versatility. To fill this gap, we introduce DStat (http://microfluidics.utoronto.ca/dstat), an open-source, general-purpose potentiostat for use alone or integrated with other instruments. DStat offers picoampere current measurement capabilities, a compact USB-powered design, and user-friendly cross-platform software. DStat is easy and inexpensive to build, may be modified freely, and achieves good performance at low current levels not accessible to other lab-built instruments. In head-to-head tests, DStat’s voltammetric measurements are much more sensitive than those of “CheapStat” (a popular open-source potentiostat described previously), and are comparable to those of a compact commercial “black box” potentiostat. Likewise, in head-to-head tests, DStat’s potentiometric precision is similar to that of a commercial pH meter. Most importantly, the versatility of DStat was demonstrated through integration with the open-source DropBot digital microfluidics platform. In sum, we propose that DStat is a valuable contribution to the “open source” movement in analytical science, which is allowing users to adapt their tools to their experiments rather than alter their experiments to be compatible with their tools. PMID:26510100

  10. Synthesis of Pt nanoparticles on electrochemically reduced graphene oxide by potentiostatic and alternate current methods

    SciTech Connect

    Molina, J.; Fernández, J.; Río, A.I. del; Bonastre, J.; Cases, F.

    2014-03-01

    Reduced graphene oxide (RGO) has been synthesized on Pt wires by means of a potentiodynamic method between + 0.6 V and ? 1.4 V for 20 scans. Cyclic voltammetry characterization of the coatings showed the typical capacitative behavior of graphene. Pt nanoparticles were synthesized on Pt–RGO electrodes by means of potentiostatic methods and a comparison between different synthesis potentials (? 0.16, 0, + 0.2 and + 0.4 V) for the same synthesis charge (mC·cm{sup ?2}) was established. The electrodes obtained were characterized in 0.5 M H{sub 2}SO{sub 4} solution to observe the characteristic oxidation and reduction processes of the Pt surface. A 0.5 M H{sub 2}SO{sub 4}/0.5 M CH{sub 3}OH solution was used to measure the catalytic properties of the deposits against methanol oxidation. The most appropriate potential to perform the synthesis was 0 V followed by ? 0.16 V and + 0.2 V. The morphology of the coatings varied depending on the potential applied as observed by scanning electron microscopy. Alternate current methods were also used to synthesize Pt nanoparticles and compare the results with the traditional potentiostatic method. Different frequencies were used: 0.1, 1, 10, 100, 1000 and 10 000 Hz. Alternate current synthesis is more efficient than traditional potentiostatic methods, obtaining more electroactive coatings with less effective synthesis time. - Highlights: • Reduced graphene oxide has been obtained by electrochemical reduction on Pt wires. • Pt nanoparticles have been obtained potentiostatically at different potentials. • Pt nanoparticles have been obtained by ac methods with different frequencies. • ac synthesis is a better synthesis method than potentiostatic synthesis.

  11. A cost-effective and field-ready potentiostat that poises subsurface electrodes to monitor bacterial respiration.

    PubMed

    Friedman, Elliot S; Rosenbaum, Miriam A; Lee, Alexander W; Lipson, David A; Land, Bruce R; Angenent, Largus T

    2012-02-15

    Here, we present the proof-of-concept for a subsurface bioelectrochemical system (BES)-based biosensor capable of monitoring microbial respiration that occurs through exocellular electron transfer. This system includes our open-source design of a three-channel microcontroller-unit (MCU)-based potentiostat that is capable of chronoamperometry, which laboratory tests showed to be accurate within 0.95 ± 0.58% (95% Confidence Limit) of a commercial potentiostat. The potentiostat design is freely available online: http://angenent.bee.cornell.edu/potentiostat.html. This robust and field-ready potentiostat, which can withstand temperatures of -30°C, can be manufactured at relatively low cost ($600), thus, allowing for en-masse deployment at field sites. The MCU-based potentiostat was integrated with electrodes and a solar panel-based power system, and deployed as a biosensor to monitor microbial respiration in drained thaw lake basins outside Barrow, AK. At three different depths, the working electrode of a microbial three-electrode system (M3C) was maintained at potentials corresponding to the microbial reduction of iron(III) compounds and humic acids. Thereby, the working electrode mimics these compounds and is used by certain microbes as an electron acceptor. The sensors revealed daily cycles in microbial respiration. In the medium- and deep-depth electrodes the onset of these cycles followed a considerable increase in overall activity that corresponded to those soils reaching temperatures conducive to microbial activity as the summer thaw progressed. The BES biosensor is a valuable tool for studying microbial activity in situ in remote environments, and the cost-efficient design of the potentiostat allows for wide-scale use in remote areas. PMID:22209069

  12. Recovery of heavy metals from spent Ni-Cd batteries by a potentiostatic electrodeposition technique

    NASA Astrophysics Data System (ADS)

    Yang, Chun-Chen

    Two heavy metals, Cd and Ni, have been separately recovered from spent AA-size Ni-Cd batteries by the potentiostatic electrodeposition and chemical precipitation methods, respectively. Various types and concentrations of HCl, H 2SO 4, and HNO 3 acids had been used as leach extractants. Experimental results indicate that the acid with the best leach capability is 4 M HCl. Three complexing reagents of NH 3, sodium acetate, sodium citrate have been chosen and tested. The most effective buffer is sodium citrate. The optimum mole ratio of metallic ion to citrate ion is 1:1. The recovery process for Cd metal is conducted by the potentiostatic electrodeposition in a leach electrolyte with a sodium citrate complex. The optimum applied potential for Cd recovery is in the range -1100 to -1120 mV (versus saturated calomel electrode (SCE)). The current efficiency for the recovery process is between 70 and 90% and depends strongly on the process parameters, e.g. liquor, concentration, applied potential, temperature, type of complex reagents, mole ratio, mass-transfer rate.

  13. Distinguishing between chi and sigma phases in duplex stainless steels using potentiostatic etching

    SciTech Connect

    Jackson, E.M.L.E.M.; Visser, P.E. de . Physical Metallurgy Div.); Cornish, L.A. )

    1993-12-01

    A color interference film etching technique based on the principle of potentiostatic etching has been developed to distinguish, by optical metallography, between Cr-rich sigma and Mo-rich chi phases as well as with simultaneous identification of the ferrite and austenite phases in duplex stainless steels. The optical metallography results are confirmed by semiquantitative energy dispersive spectrometry analysis and back-scattered electron imaging. The technique is relatively simple and rapid, and makes use of low voltages and a hot etchant. Results have shown distinctively the sigma, chi, ferrite, and austenite phases, and enable observation of the microstructural development, morphology, and kinetics of formation of the phases in duplex alloys. The method, by giving excellent color contrast between sigma and chi, also facilitates quantitative image analysis of the sigma and chi volume fractions.

  14. CheapStat: An Open-Source, “Do-It-Yourself” Potentiostat for Analytical and Educational Applications

    PubMed Central

    Rowe, Aaron A.; Bonham, Andrew J.; White, Ryan J.; Zimmer, Michael P.; Yadgar, Ramsin J.; Hobza, Tony M.; Honea, Jim W.; Ben-Yaacov, Ilan; Plaxco, Kevin W.

    2011-01-01

    Although potentiostats are the foundation of modern electrochemical research, they have seen relatively little application in resource poor settings, such as undergraduate laboratory courses and the developing world. One reason for the low penetration of potentiostats is their cost, as even the least expensive commercially available laboratory potentiostats sell for more than one thousand dollars. An inexpensive electrochemical workstation could thus prove useful in educational labs, and increase access to electrochemistry-based analytical techniques for food, drug and environmental monitoring. With these motivations in mind, we describe here the CheapStat, an inexpensive (<$80), open-source (software and hardware), hand-held potentiostat that can be constructed by anyone who is proficient at assembling circuits. This device supports a number of potential waveforms necessary to perform cyclic, square wave, linear sweep and anodic stripping voltammetry. As we demonstrate, it is suitable for a wide range of applications ranging from food- and drug-quality testing to environmental monitoring, rapid DNA detection, and educational exercises. The device's schematics, parts lists, circuit board layout files, sample experiments, and detailed assembly instructions are available in the supporting information and are released under an open hardware license. PMID:21931613

  15. Fabrication of triazinedithiol functional polymeric nanofilm by potentiostatic polymerization on aluminum surface

    NASA Astrophysics Data System (ADS)

    Wang, Fang; Wang, Yabin; Li, Yanni; Wang, Qian

    2011-01-01

    The functional polymeric nanofilm of 6-(N-allyl-1,1,2,2-tetrahydroperfluorodecyl)amino-1,3,5-triazine-2,4-dithiol monosodium (AF17N) was prepared on pure aluminum surface by potentiostatic polymerization at different potentials. The thickness and weight of polymeric nanofilm increased proportionally to electro-polymerization potential following linear equation. The chemical structure of nanofilm was characterized by Fourier transform-infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Adsorption peaks in FT-IR and C1s, N1s, S2p, F1s and Al2p peaks in XPS spectra indicated that the polymeric nanofilm was poly(6-(N-allyl-1,1,2,2-tetrahydroperfluorodecyl)amino-1,3,5-triazine-2,4-disulfide) (PAF17). The morphologies of polymeric nanofilm were also observed by atomic force microscopy (AFM). All the results showed that the optimal electro-polymerization potential and time were 8 V and 20 s, respectively. Uniform and compact nanofilm of PAF17 could be obtained under these conditions. It is expected that this technique will be applied in the preparation of lubricating, dielectric and hydrophobic surface on aluminum substrate.

  16. Photoelectrochemical cell studies of Fe(2+) doped ZnSe nanorods using the potentiostatic mode of electrodeposition.

    PubMed

    Lohar, G M; Jadhav, S T; Takale, M V; Patil, R A; Ma, Y R; Rath, M C; Fulari, V J

    2015-11-15

    The Fe(2+) doped ZnSe nanorods are synthesized using simple potentiostatic mode of electrodeposition on the ITO substrate. In order to study the doping effect of Fe(2+) in ZnSe, varied the doing percent such as 0.5%, 1%, 1.5%. These films are characterized for structural, compositional, morphological, optical and electrochemical properties using the X-ray diffraction study (XRD), X-ray photoelectron spectroscopy, field emission scanning electron microscopy, UV-vis spectroscopy and electrochemical spectroscopy. Along with these Raman spectroscopy and photoluminescence spectroscopy have been studied for understanding the characteristics vibrations of ZnSe and luminescence of ZnSe nanorods. FE-SEM shows the nanorods like morphology. Photoelectrochemical cell performance studied using the J-V measurement and it shows the maximum efficiency at 1% Fe(2+) doped ZnSe nanorods. The observed maximum efficiency of Fe(2+) doped ZnSe nanorods is 0.32%. PMID:26210917

  17. IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS--I: REGULAR PAPERS, VOL. 53, NO. 11, NOVEMBER 2006 2371 16-Channel Integrated Potentiostat for Distributed

    E-print Network

    Cauwenberghs, Gert

    -domain signal processing, neurotransmitters, potentiostat. I. INTRODUCTION IMPLANTABLE integrated technologies in auditory nerve and visual cortex among others, and could lead to breakthroughs in areas such as neural prostheses, artificial tissue engineering, and automated neural disorders diagnostics and therapy. A number

  18. Re-passivation Potential of Alloy 22 in Chloride plus Nitrate Solutions using the Potentiodynamic-Galvano-static-Potentiostatic Method

    SciTech Connect

    Evans, Kenneth J.; Rebak, Raul B.

    2007-07-01

    In general, the susceptibility of Alloy 22 to suffer crevice corrosion is measured using the Cyclic Potentiodynamic Polarization (CPP) technique. This is a fast technique that gives rather accurate and reproducible values of re-passivation potential (ER1) in most cases. In the fringes of susceptibility, when the environment is not highly aggressive, the values of re-passivation potential using the CPP technique may not be highly reproducible, especially because the technique is fast. To circumvent this, the re-passivation potential of Alloy 22 was measured using a slower method that combines Potentiodynamic-Galvano-static-Potentiostatic steps (called here the Tsujikawa-Hisamatsu Electrochemical or THE method). The THE method applies the charge to the specimen in a more controlled way, which may give more reproducible re-passivation potential values, especially when the environment is not aggressive. The values of re-passivation potential of Alloy 22 in sodium chloride plus potassium nitrate solutions were measured using the THE and CPP methods. Results show that both methods yield similar values of re-passivation potential, especially under aggressive conditions. (authors)

  19. Integrated potentiostat for electrochemical sensing of urinary 3-hydroxyanthranilic acid with molecularly imprinted poly(ethylene-co-vinyl alcohol).

    PubMed

    Huang, Chun-Yueh; O'Hare, Danny; Chao, I-Jen; Wei, Hung-Wei; Liang, Yi-Fan; Liu, Bin-Da; Lee, Mei-Hwa; Lin, Hung-Yin

    2015-05-15

    Changing demographics, the rise of personalized medicine and increased identification of biomarkers for diagnosis and management of chronic disease have increased the demand for portable bioanalytical instrumentation and point-of-care. The recent development of molecularly imprinted polymers enables production of low cost and highly stable sensing chips; however, the commercially available and full functional instruments employed for electrochemical analysis have shortcomings in actual homecare applications. In this work, integrated circuits (ICs) for monolithic implementation of voltammeter potentiostat with a large dynamic current range (5 nA to 1.2 mA) and short conversion time (10 ms) were fabricated in a 0.35 ?m complementary metal-oxide-semiconductor (CMOS) process. The new instrumentation was tested with molecular imprinted sensors for 3-hydroxyanthranilic acid (3HAA) in urine. The sensor consisted of molecular imprinted of poly(ethylene-co-vinyl alcohol)s (abbreviated as EVALs) for implementation in a flow injection analysis system. The EVAL containing 32 ethylene mol% had the highest imprinting effectiveness for the target molecules. Fit-for-purpose figures of merit were achieved with a limit-of-detection (LOD) of 3.06 pg/mL. The measurements obtained in real undiluted urine samples fell within the reference concentration range of 50-550 ng/mL. PMID:25175746

  20. Finite element analysis of lithium insertion-induced expansion of a silicon thin film on a rigid substrate under potentiostatic operation

    NASA Astrophysics Data System (ADS)

    Liu, Ming

    2015-02-01

    Diffusion-induced stress and volumetric expansion under potentiostatic operation are investigated with an axisymmetric finite element model taking account of plastic yielding, coupling effects between diffusion and stress, diffusion from the edge surface, and concentration dependence of material properties. Significant differences on stresses, displacements, and fracture energies between purely elastic and elastic-plastic materials are found. Plasticity based on von-Mises criterion has no effect on concentration variation. The critical regions for fracture are the edge surface, and the regions near the edges on both the top surface and the interface.

  1. Comparison of Galvanic Currents Generated Between Different Combinations of Orthodontic Brackets and Archwires Using Potentiostat: An In Vitro Study

    PubMed Central

    Nayak, Rabindra S; Shafiuddin, Bareera; Pasha, Azam; Vinay, K; Narayan, Anjali; Shetty, Smitha V

    2015-01-01

    Background: Technological advances in wire selection and bracket design have led to improved treatment efficiency and allowed longer time intervals between appliance adjustments. The wires remain in the mouth for a longer duration and are subjected to electrochemical reactions, mechanical forces of mastication and generalized wear. These cause different types of corrosion. This study was done to compare the galvanic currents generated between different combinations of brackets and archwires commonly used in orthodontic practices. Materials and Methods: The materials used for the study included different commercially available orthodontic archwires and brackets. The galvanic current generated by individual materials and different combinations of these materials was tested and compared. The orthodontic archwires used were 0.019? × 0.025? heat-activated nickel-titanium (3M Unitek), 0.019? × 0.025? beta-titanium (3M Unitek) and 0.019? × 0.025? stainless steel (3M Unitek). The orthodontic brackets used were 0.022? MBT laser-cut (Victory Series, 3M Unitek) and metal-injection molded (Leone Company) maxillary central incisor brackets respectively. The ligature wire used for ligation was 0.009? stainless steel ligature (HP Company). The galvanic current for individual archwires, brackets, and the different bracket-archwire-ligature combinations was measured by using a Potentiostat machine. The data were generated using the Linear Sweep Voltammetry and OriginPro 8.5 Graphing and Data Analysis Softwares. The study was conducted in two phases. Phase I comprised of five groups for open circuit potential (OCP) and galvanic current (I), whereas Phase II comprised of six groups for galvanic current alone. Results: Mean, standard deviation and range were computed for the OCP and galvanic current (I) values obtained. Results were subjected to statistical analysis through ANOVA. In Phase I, higher mean OCP was recorded in stainless steel archwire, followed by beta-titanium archwire, heat-activated nickel titanium archwire, laser-cut bracket and metal-injection molded bracket, respectively. The difference in mean OCP recorded among the groups was found to be statistically significant in aerated phosphate buffered saline solution. The galvanic current (I) for metal-injection molded stainless steel brackets showed significantly higher values than all the other materials. Phase II results suggested that, in the couples formed by the archwire-bracket-ligature combinations, the bracket had more important contribution to the total galvanic current generated, since there were significant differences between galvanic current among the 2 brackets tested but not among the 3 wires. The galvanic current of the metal-injection molded bracket was significantly higher than that of laser-cut bracket. Highest mean current (I) was recorded in metal-injection molded bracket when used with heat-activated nickel titanium archwire while lowest mean current (I) was recorded in laser-cut bracket when used with beta-titanium archwire. Conclusion: The present study concluded that the bracket emerged to be the most important factor in determining the galvanic current (I). Higher mean current (I) was recorded in metal-injection molded bracket compared to laser-cut bracket. Among the three archwires, higher mean current (I) was recorded in heat-activated nickel-titanium, followed by stainless-steel and beta-titanium respectively. When coupled together; highest mean current (I) was recorded in metal-injection molded bracket when used with heat-activated nickel titanium archwire while lowest mean current (I) was recorded in laser-cut bracket when used with beta-titanium archwire. PMID:26229367

  2. Parallel Recording of Neurotransmitters Release from Chromaffin Cells Using a 10 × 10 CMOS IC Potentiostat Array with On-Chip Working Electrodes

    PubMed Central

    Kim, Brian Namghi; Herbst, Adam D.; Kim, Sung June; Minch, Bradley A.; Lindau, Manfred

    2012-01-01

    Neurotransmitter release is modulated by many drugs and molecular manipulations. We present an active CMOS-based electrochemical biosensor array with high throughput capability (100 electrodes) for on-chip amperometric measurement of neurotransmitter release. The high-throughput of the biosensor array will accelerate the data collection needed to determine statistical significance of changes produced under varying conditions, from several weeks to a few hours. The biosensor is designed and fabricated using a combination of CMOS integrated circuit (IC) technology and a photolithography process to incorporate platinum working electrodes on-chip. We demonstrate the operation of an electrode array with integrated high-gain potentiostats and output time-division multiplexing with minimum dead time for readout. The on-chip working electrodes are patterned by conformal deposition of Pt and lift-off photolithography. The conformal deposition method protects the underlying electronic circuits from contact with the electrolyte that covers the electrode array during measurement. The biosensor was validated by simultaneous measurement of amperometric currents from 100 electrodes in response to dopamine injection, which revealed the time course of dopamine diffusion along the surface of the biosensor array. The biosensor simultaneously recorded neurotransmitter release successfully from multiple individual living chromaffin cells. The biosensor was capable of resolving small and fast amperometric spikes reporting release from individual vesicle secretions. We anticipate that this device will accelerate the characterization of the modulation of neurotransmitter secretion from neuronal and endocrine cells by pharmacological and molecular manipulations of the cells. PMID:23084756

  3. Investigation of the growth and local stoichiometric point group symmetry of titania nanotubes during potentiostatic anodization of titanium in phosphate electrolytes

    NASA Astrophysics Data System (ADS)

    Cummings, F. R.; Muller, T. F. G.; Malgas, G. F.; Arendse, C. J.

    2015-10-01

    Potentiostatic anodization of commercially pure, 50 ?m-thick titanium (Ti) foil was performed in aqueous, phosphate electrolytes at increasing experimental timeframes at a fixed applied potential for the synthesis of titania nanotube arrays (TNAs). High resolution scanning electron microscopy images, combined with energy dispersive spectroscopy and x-ray diffraction spectra reveal that anodization of the Ti foil in a 1 M NaF+0.5 M H3PO4 electrolyte for 4 h yields a titanate surface with pore diameters ranging between 100 and 500 nm. The presence of rods on the Ti foil surface with lengths exceeding 20 ?m and containing high concentrations of phosphor on the exterior was also detected at these conditions, along with micro-sized coral reef-like titanate balls. We propose that the formation of these structures play a major role during the anodization process and impedes nanotube growth during the anodization process. High spatially resolved scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) performed along the length of a single anodized TiO2 nanotube reveals a gradual evolution of the nanotube crystallinity, from a rutile-rich bottom to a predominantly anatase TiO2 structure along its length.

  4. Communication: Coordination structure of bromide ions associated with hexyltrimethylammonium cations at liquid/liquid interfaces under potentiostatic control as studied by total-reflection X-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Nagatani, Hirohisa; Harada, Makoto; Tanida, Hajime; Sakae, Hiroki; Imura, Hisanori

    2014-03-01

    Total-reflection X-ray absorption fine structure (TR-XAFS) technique was applied for the first time to an interface between two immiscible electrolyte solutions under potentiostatic control. The hydration structure of bromide ions was investigated at polarized 2-octanone/water interfaces. TR-XAFS spectra at Br K-edge measured in the presence of hexyltrimethylammonium bromide (C6TAB) were slightly modified depending on the Galvani potential difference ({? }_o^w ?). The extended X-ray absorption fine structure analysis exposed hydration structure changes of bromide ions at the polarized interface. The coordination structure of bromide ions at the interface could be analyzed as compared with bromide ions dissolved in aqueous solution and Br--exchanged resin having quaternary ammonium groups. The results indicated that bromide ions were associated with C6TA+ at the polarized interface. The relative contribution of ion association form of bromide ions with quaternary ammonium groups was enhanced at a potential close to the ion transfer of C6TA+, where the interfacial concentration of C6TA+ is increased as a function of {? }_o^w ?.

  5. Potentiostatic deposition of DNA for scanning probe microscopy.

    PubMed Central

    Lindsay, S M; Tao, N J; DeRose, J A; Oden, P I; Lyubchenko YuL; Harrington, R E; Shlyakhtenko, L

    1992-01-01

    We describe a procedure for reversible adsorption of DNA onto a gold electrode maintained under potential control. The adsorbate can be imaged by scanning probe microscopy in situ. Quantitative control of a molecular adsorbate for microscopy is now possible. We found a potential window (between 0 and 180 mV versus a silver wire quasi reference) over which a gold (111) surface under phosphate buffer is positively charged, but is not covered with a dense adsorbate. When DNA is present in these conditions, molecules adsorb onto the electrode and remain stable under repeated scanning with a scanning tunneling microscope (STM). They become removed when the surface is brought to a negative charge. When operated at tunnel currents below approximately 0.4 nA, the STM yields a resolution of approximately 1 nm, which is better than can be obtained with atomic force microscopy (AFM) at present. We illustrate this procedure by imaging a series of DNA molecules made by ligating a 21 base-pair oligonucleotide. We observed the expected series of fragment lengths but small fragments are adsorbed preferentially. Images FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 8 FIGURE 9 FIGURE 10 FIGURE 11 PMID:1617139

  6. Study of Metal-NH[subscript 3] Interfaces (Metal= Cu, Ni, Ag) Using Potentiostatic Curves

    ERIC Educational Resources Information Center

    Nunes, Nelson; Martins, Angela; Leitao, Ruben Elvas

    2007-01-01

    Experiment is conducted to determine the kinetic parameters of metal-solution interfaces. During the experiment the kinetic parameters for the interfaces Cu-NH[subscript 3], Ag-NH[subscript 3] and Ni-NH[subscript 3] is easily determined.

  7. Fabrication of zero valent iron (ZVI) nanotube film via potentiostatic anodization and electroreduction.

    PubMed

    Jang, Jun-Won; Jun, Jung-Eui; Park, Jae-Woo

    2009-01-01

    Zero valent iron has been successfully used for the degradation of a wide range of contaminants. However, this reaction of using ZVI particle produces a large quantity of iron sludge. To solve the problem, we report the synthesis of self-organized nanoporous zero valent iron film treated with anodization and electro-reduction of iron foil. The iron nanotubes were fabricated in 1 M Na(2)SO(4) + 0.5 wt% NaF electrolyte by supplying constant electric currents of 50 mV/s, and holding the potential at 20, 40 and 60 V for 20 min. Nanoporous shape was produced by anodic oxidation of iron film. After anodizing process, electro-reduction of nanoporous iron film converted crystallization iron oxide to zero valent iron. Electro-reduction process was carried out by electro-reducing with powersupply to and holding the potential at 20 V for 20 min. The surface of iron nanotube film was examined by BET and the thickness of the oxidized films was evaluated by scanning electron microscope (SEM). The crystalline structures of the fabricated films were evaluated using X-ray diffraction (XRD). PMID:19542657

  8. A Novel Multi-Working Electrode Potentiostat for Electrochemical Detection of Metabolites

    E-print Network

    De Micheli, Giovanni

    . Nayak et al. [3] employed two commercially available devices for blood glucose self- monitoring (polydimethylsiloxane). So, a cell chamber is realized to perform real time and continuous monitor . The need of multi-metabolites monitoring asks for a system with multi-working electrodes. In the proposed

  9. Photoinduced Thermal Copper Reduction onto Gold Nanocrystals under Potentiostatic Peter L. Redmond,* Erich C. Walter, and Louis E. Brus

    E-print Network

    excitation can also photocatalyze small Ag colloid reformulation into large trun- cated prisms, and even fusion of such prisms into yet larger prisms.2,3 The mechanisms of these processes are not well

  10. A potentiostatic study of oxygen transport through poly(2-ethoxyethyl methacrylate-co-2,3-dihydroxypropylmethacrylate) hydrogel membranes.

    PubMed

    Compañ, Vicente; Tiemblo, Pilar; García, F; García, J M; Guzmán, Julio; Riande, Evaristo

    2005-06-01

    The oxygen permeability and diffusion coefficients of hydrogel membranes prepared with copolymers of 2-ethoxyethyl methacrylate (EEMA)/2,3-dihydroxypropylmethacrylate (MAG) with mole fraction of the second monomer in the range between 0 and 0.75 are described. Values of the permeability and diffusion coefficients of oxygen are determined by using electrochemical procedures involving the measurement of the steady-state current in membranes prepared by radical polymerization of the monomers. The results obtained for the transport properties were analyzed taking into account the fractional free volumes, the cohesive energy densities and the glass transition temperatures of the hydrogels. PMID:15626426

  11. Aerated Shewanella oneidensis in Continuously-fed Bioelectrochemical Systems for Power and Hydrogen Production

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We studied the effects of aeration of Shewanella oneidensis on potentiostatic current production, iron(III) reduction, hydrogen production in a microbial electrolysis cell, and electric power generation in a microbial fuel cell. The potentiostatic performance of aerated S. oneidensis was considerab...

  12. Electrochemical nitridation of metal surfaces

    DOEpatents

    Wang, Heli; Turner, John A.

    2015-06-30

    Electrochemical nitridation of metals and the produced metals are disclosed. An exemplary method of electrochemical nitridation of metals comprises providing an electrochemical solution at low temperature. The method also comprises providing a three-electrode potentiostat system. The method also comprises stabilizing the three-electrode potentiostat system at open circuit potential. The method also comprises applying a cathodic potential to a metal.

  13. Electrochemical Microsensors for the Detection of Cadmium(II) and Lead(II) Ions in Plants

    PubMed Central

    Krystofova, Olga; Trnkova, Libuse; Adam, Vojtech; Zehnalek, Josef; Hubalek, Jaromir; Babula, Petr; Kizek, Rene

    2010-01-01

    Routine determination of trace metals in complex media is still a difficult task for many analytical instruments. The aim of this work was to compare three electro-chemical instruments [a standard potentiostat (Autolab), a commercially available miniaturized potentiostat (PalmSens) and a homemade micropotentiostat] for easy-to-use and sensitive determination of cadmium(II) and lead(II) ions. The lowest detection limits (hundreds of pM) for both metals was achieved by using of the standard potentiostat, followed by the miniaturized potentiostat (tens of nM) and the homemade instrument (hundreds of nM). Nevertheless, all potentiostats were sensitive enough to evaluate contamination of the environment, because the environmental limits for both metals are higher than detection limits of the instruments. Further, we tested all used potentiostats and working electrodes on analysis of environmental samples (rainwater, flour and plant extract) with artificially added cadmium(II) and lead(II). Based on the similar results obtained for all potentiostats we choose a homemade instrument with a carbon tip working electrode for our subsequent environmental experiments, in which we analyzed maize and sunflower seedlings and rainwater obtained from various sites in the Czech Republic. PMID:22219663

  14. Interfacial forces in chemical-mechanical polishing 

    E-print Network

    Ng, Dedy

    2009-05-15

    ) of copper was studied. Experiments were conducted on the tribometer in combination with a potentiostat. Friction coefficient was used to monitor the polishing process and correlated with the wear behavior of post-CMP samples. Surface characterization...

  15. This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research

    E-print Network

    Angenent, Lars T.

    with electrodes and a solar panel-based power system, and deployed as a biosensor to monitor microbial respiration activity in situ in remote environments, and the cost-efficient design of the potentiostat allows for wide

  16. SWEPT-POTENTIAL ELECTROCHEMICAL DETECTOR FOR FLOW STREAMS

    EPA Science Inventory

    An instrument has been designed, constructed, and evaluated for electrochemical measurements in flow streams. The instrument is basically a computer-controlled potentiostat with features that are necessary for measurements in flow streams. These features include real-time graphic...

  17. Construction and Characterization of a Nanowell Electrode Array

    E-print Network

    Myrick, Michael Lenn

    was placed. This base was screwed into a Teflon cell, with an O-ring to ensure sealing. Au was plated an electrode, followed by the galvanostatic deposition of Ag to seal the pores and potentiostatic deposition

  18. Characterization of electrochemically deposited polypyrrole using magnetoelastic material transduction elements

    NASA Technical Reports Server (NTRS)

    Ersoz, Arzu; Ball, J. Christopher; Grimes, Craig A.; Bachas, Leonidas G.

    2002-01-01

    Magnetoelastic alloy films have been used as a working electrode in an electrochemical cell. This material allows magnetic interrogation of electrochemical deposition. This technique was used to monitor the electrochemical deposition of polypyrrole by multisweep (CV) and potentiostatic methods. Since the determination of the mass-sensitive magnetoelastic film's resonance frequency is based on magnetic transduction, an inherent advantage of this method is that it requires no electrical connections other than the working lead of the potentiostat. Increases in pyrrole deposition correlated with a decrease in the peak resonance frequency of the magnetoelastic alloy. This technique provides a novel approach by which one can monitor electrochemical processes.

  19. Apparatus for use in rapid and accurate controlled-potential coulometric analysis

    DOEpatents

    Frazzini, Thomas L. (Frankfort, IL); Holland, Michael K. (LaGrange Park, IL); Pietri, Charles E. (Downers Grove, IL); Weiss, Jon R. (Downers Grove, IL)

    1981-01-01

    An apparatus for controlled-potential coulometric analysis of a solution includes a cell to contain the solution to be analyzed and a plurality of electrodes to contact the solution in the cell. Means are provided to stir the solution and to control the atmosphere above it. A potentiostat connected to the electrodes controls potential differences among the electrodes. An electronic circuit connected to the potentiostat provides analog-to-digital conversion and displays a precise count of charge transfer during a desired chemical process. This count provides a measure of the amount of an unknown substance in the solution.

  20. Affordable Cyclic Voltammetry

    ERIC Educational Resources Information Center

    Stewart, Greg; Kuntzleman, Thomas S.; Amend, John R.; Collins, Michael J.

    2009-01-01

    Cyclic voltammetry is an important component of the undergraduate chemical curriculum. Unfortunately, undergraduate students rarely have the opportunity to conduct experiments in cyclic voltammetry owing to the high cost of potentiostats, which are required to control these experiments. By using MicroLab data acquisition interfaces in conjunction…

  1. Application of Bacterial Biocathodes in Microbial Fuel Cells Zhen He, Largus T. Angenent*

    E-print Network

    Review Application of Bacterial Biocathodes in Microbial Fuel Cells Zhen He, Largus T. Angenent breakthroughs are made. Keywords: Microbial fuel cell, Biofuel cell, Biocathode, Potentiostat-poised half cell, microbial fuel cells (MFCs) are special types of biofuel cells, producing electric power by utilizing

  2. Toward developing long-life water quality sensors for the ISS using planar REDOX and conductivity sensors

    NASA Technical Reports Server (NTRS)

    Buehler, M. G.; Kuhlman, G. M.; Keymeulen, D.; Myung, N.; Kounaves, S. P.

    2003-01-01

    REDOX and conductivity sensors are metal electrodes that are used to detect ionic species in solution by measuring the electrochemical cell current as the voltage is scanned. This paper describes the construction of the sensors, the potentiostat electronics, the measurement methodology, and applications to water quality measurements.

  3. AN ADVANCED FLUE GAS MONITOR FOR SO2 - PHASE I

    EPA Science Inventory

    The development of an instrument for continuously monitoring SO2 levels in flue gas is proposed. The SO2 will be detected by means of an electrochemical sensor cell, which operates in a three-electrode potentiostatic mode. The proposed innovation is develop-ment of an advan...

  4. Integrating Conjugated Polymer Microactuators with CMOS Sensing Circuitry

    E-print Network

    Maryland at College Park, University of

    Integrating Conjugated Polymer Microactuators with CMOS Sensing Circuitry for Studying Living Cells present the use of electroactive polymer actuators as components of a biolab-on-a-chip, which has, and packaging. Keywords: lab-on-a-chip, cells, polypyrrole, conjugated polymers, MEMS, CMOS, potentiostat

  5. In situ monitoring of the Li-O2 electrochemical reaction on nanoporous gold using electrochemical AFM.

    PubMed

    Wen, Rui; Byon, Hye Ryung

    2014-03-11

    The lithium-oxygen (Li-O2) electrochemical reaction on nanoporous gold (NPG) is observed using in situ atomic force microscopy (AFM) imaging coupled with potentiostatic measurement. Dense Li2O2 nanoparticles form a film at 2.5 V, which is decomposed at 3.8-4.0 V in an ether-based electrolyte. PMID:24469227

  6. Efficiencies of Bio-electrocatalytic Production of Hydrogen from Lactate Using Shewanella oneidensis MR-1

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Shewanella oneidensis MR-1 was grown in a chemostatic, continuously-fed bioelectrochemical cell under slightly aerated conditions. The start-up phase was controlled potentiostatically (0.4 V vs. SHE). When a stable performance was achieved, the reactor was switched to bio-electrocatalytic producti...

  7. Electrochemical approach for passivating steel and other metals and for the simultaneous production of a biocide to render water potable

    NASA Technical Reports Server (NTRS)

    1972-01-01

    Potentiostatic polarization curves indicated that the cathodic reactions in deaerated KI-I2 water solutions were due to iodine reduction and hydrogen evolution. In the presence of oxygen an additional reduction wave appeared. Anodic polarization curves revealed that iodine could be produced in the region of potential from +600 to +1000 nv vs. SCE.

  8. German Edition: DOI: 10.1002/ange.201506316Electrochemistry Very Important Paper International Edition: DOI: 10.1002/anie.201506316

    E-print Network

    in thickness). A plain carbon cloth counter electrode and an Ag/AgCl reference electrode are immersed in the reservoir of electro- lyte solution. A metal contact (not shown) rests against the platinum working electrode to complete the three-electrode system. A potentiostat (WaveNow, Pine Research Instrumen- tation

  9. Observation of electrochemically generated nitrenium ions by desorption electrospray

    E-print Network

    develops on the elec- trode surface (approximately 1 mm in thickness). A plain carbon cloth counter electrode and an Ag/AgCl reference electrode are immersed in the reservoir of electrolyte solution. A metal. A potentiostat (WaveNow, Pine Research Instrumentation, Durham, NC) is used to apply a potential across the three

  10. lution of Al. Since the electric field strength across the chan-nel bottom (i.e., the barrier layer) is much greater than that

    E-print Network

    potentiostat in an electrolyte of 0.5 M oxalic acid (Aldrich) at room temperature. Anodization was performed. The as-prepared samples appear to be dark brown, indicating the presence of stannous oxide (Sn. Jiang, P. C. Searson, C. L. Chien, Science 1993, 261, 1316. [4] P. Hoyer, N. Baba, H. Masuda, Appl. Phys

  11. MICROFABRICATED ELECTROCHEMICAL ANALYSIS SYSTEM FOR HEAVY METAL DETECTION. (R825511C047)

    EPA Science Inventory

    A low power, hand-held system has been developed for the measurement of heavy metal ions in aqueous solutions. The system consists of an electrode array sensor, a high performance single chip potentiostat and a microcontroller circuit. The sensor is a microfabricated array of ...

  12. Surface pK(sub a) of Self-Assembled Monolayers

    ERIC Educational Resources Information Center

    Hale, Penny S.; Maddox, Leone M.; Shapter, Joe G.

    2005-01-01

    The difference between solution and surface properties such as pK(sub a) is illustrated enabling students to understand the differences between nanoscale and macroscopic systems. Details regarding the usage of electrochemical instrumentation, such as a potentiostat, and of the technique such as cyclic voltammetry are given.

  13. Cybernetic Control of an Electrochemical Repertoire.

    ERIC Educational Resources Information Center

    He, Peixin; And Others

    1982-01-01

    Describes major features of a computer-operated, cybernetic potentiostat and the development, design, and operation of the software in ROM. The instrument contains control circuitry and software making it compatible with the static mercury drop electrode produced by EG&G Princeton Applied Research Corporation. Sample results using the instrument…

  14. Corrosion and creep of dental amalgam.

    PubMed

    Gjerdet, N R; Espevik, S

    1978-01-01

    The influence of stress on corrosion was investigated by a potentiostatic technique. Amalgrams with low creep, both with and without gamma2-phase, revealed small increases in current with stress application while alloys with high creep exhibited large increases in current. Rupture of protective oxide due to increased strain for high creep alloys may explain the phenomenon. PMID:277492

  15. Evaluation of Ti-6Al-4V Parts Produced with Rapid Prototyping Technology: Electron Beam Melting Machine 

    E-print Network

    Abdeen, Dana

    2014-09-29

    purposes. The results showed that EBM alloy maintained its corrosion resistance as it had the same pitting potential of wrought alloy even at higher temperatures. EBM alloy did not pit when performing potentiostatic test at 800 mV vs. Saturated Calomel...

  16. Preparation and synthesis of Ag2Se nanowires produced by template directed synthesis

    E-print Network

    consisted of an aqueous solution of 0.3 m SeO2 and 0.03 m H2SO4. The current density is understood nanowires. Silver selenide exhibits two distinct crystallographic phases separated by a transition at 406 K to be the potentiostat current divided by the effective plating area, which is defined as the number of pores

  17. A new electrochemical approach for evaluation of corrosion inhibitors in neutral aqueous solutions

    SciTech Connect

    Jovancicevic, V.; Hartwick, D.

    1997-12-01

    A new comprehensive electrochemical approach to corrosion inhibitor evaluation in neutral aqueous solutions has been developed. It consists of using concurrently three different but complementary electrochemical methods. Linear polarization resistance (LPR), concentration-step potentiostatic (CSP) and constant-concentration potentiostatic (CCP) methods are used to determine the overall corrosion rates, corrosion inhibition mechanism, and stability of the passive oxide film in the presence of corrosion inhibitors. This approach has been used successfully to evaluate corrosion inhibition of three organic inhibitor systems: a phosphonate-based corrosion inhibitor (hydroxyphosphonoacetic acid, HPA), a polymeric corrosion inhibitor (polyacrylic acid, PAA) and a non-phosphorus containing corrosion inhibitor (L-tartaric acid). Short-term CSP/CCP test results for these three inhibitors are in good agreement with long-term weight loss measurements.

  18. Salt passivation during anodic iridium dissolution in chloride melts

    SciTech Connect

    Saltykova, N.A.; Pechorskaya, L.S.; Baraboshkin, A.N.; Kotovskii, S.N.; Kosikhin, L.T.

    1986-11-01

    Anodic iridium dissolution in chloride melts at 500-700/sup 0/C was studied by potentiostatic, potentiodynamic, and galvanostatic techniques. It was found that an iridium anode is passivated by hexachloroiridates, first by the iridium (III) salt and at more positive potentials by the iridium (IV) salt. Values for anode resistance during passivation by salt films were calculated. It was shown that the morphology of the dissolving anode surface is determined by the value of polarization.

  19. Studying localized corrosion using liquid cell transmission electron microscopy

    DOE PAGESBeta

    Chee, See Wee; Pratt, Sarah H.; Hattar, Khalid; Duquette, David; Ross, Frances M.; Hull, Robert

    2014-11-07

    Using liquid cell transmission electron microscopy (LCTEM), localized corrosion of Cu and Al thin films immersed in aqueous NaCl solutions was studied. We demonstrate that potentiostatic control can be used to initiate pitting and that local compositional changes, due to focused ion beam implantation of Au+ ions, can modify the corrosion susceptibility of Al films. A discussion on strategies to control the onset of pitting is also presented.

  20. Teorell instability in concentration polarization

    NASA Astrophysics Data System (ADS)

    Abu-Rjal, Ramadan; Prigozhin, Leonid; Rubinstein, Isaak; Zaltzman, Boris

    2015-08-01

    We investigate the development of electro-osmotic (Teorell) oscillations at a weakly charged microporous membrane without a preimposed transmembrane electrolyte concentration drop. This drop, necessary for the occurrence of oscillations, develops spontaneously as a result of concentration polarization in the solution layers adjacent to the membrane. A three-layer model comprising a membrane flanked by two diffusion layers is proposed and analyzed for galvano- and potentiostatic regimes of operation.

  1. Nickel and cobalt recycling from lithium-ion batteries by electrochemical processes.

    PubMed

    Lupi, C; Pasquali, M; Dell'era, A

    2005-01-01

    The presence of LiCoO(2) and LiCo(x)Ni((1-x))O(2) in the cathodic material of Li-ion and Li-polymer batteries has stimulated the recovery of Co and Ni by hydrometallurgical processes. In particular, the two metals were separated by SX method and then recovered by electrochemical (galvanostatic and potentiostatic) processes. The metallic Ni has been electrowon at 250 A/m(2), pH 3-3.2 and 50 degrees C, with 87% current efficiency and 2.96 kWh/kg specific energy consumption. Potentiostatic electrolysis produces a very poor Ni powder in about 1 h with current efficiency changing from 70% to 45% depending on Ni concentration in the electrolyte. Current efficiency of 96% and specific energy consumption of 2.8 kWh/kg were obtained for Co at 250 A/m(2), pH 4-4.2 and 50 degrees C, by using a solution containing manganese and (NH(4))(2)SO(4). The Co powder, produced in potentiostatic conditions (-0.9 V vs. SCE, pH 4, room temperature) appears particularly suitable for Co recycling as cobaltite in new batteries. PMID:15737721

  2. A Low-Cost Smartphone-Based Electrochemical Biosensor for Point-of-Care Diagnostics

    PubMed Central

    Sun, Alexander; Wambach, Travis; Venkatesh, A. G.; Hall, Drew A.

    2015-01-01

    This paper describes the development of a smartphone-based electrochemical biosensor module. The module contains a low power potentiostat that interfaces and harvests power from a smartphone through the phone’s audio jack. A prototype with two different potentiostat designs was constructed and used to conduct proof of concept cyclic voltammetry experiments with potassium ferro-/ferricyanide (K4[Fe(CN)6] / K3[Fe(CN)6]) in a side-by-side comparison with a laboratory grade instrument. Results show that the module functions within the available power budget and that the recovered voltammogram data matches well with the data from an expensive bench top tool. Excluding the loses from supply rectification and regulation, the module consumes either 5.7 mW or 4.3 mW peak power, depending on which of the two discussed potentiostat designs is used. At single quantity pricing, the hardware for the prototype device costs less than $30. PMID:26097899

  3. Effect of chemical etching and aging in boiling water on the corrosion resistance of Nitinol wires with black oxide resulting from manufacturing process.

    PubMed

    Shabalovskaya, S; Rondelli, G; Anderegg, J; Simpson, B; Budko, S

    2003-07-15

    The effect of chemical etching in a HF/HNO(3) acid solution and aging in boiling water on the corrosion resistance of Nitinol wires with black oxide has been evaluated with the use of potentiodynamic, modified potentiostatic ASTM F746, and scratch tests. Scanning-electron microscopy, elemental XPS, and Auger analysis were employed to characterize surface alterations induced by surface treatment and corrosion testing. The effect of aging in boiling water on the temperatures of martensitic transformations and shape recovery was evaluated by means of measuring the wire electroresistance. After corrosion tests, as-received wires revealed uniformly cracked surfaces reminiscent of the stress-corrosion-cracking phenomenon. These wires exhibited negative breakdown potentials in potentiostatic tests and variable breakdown potentials in potentiodynamic tests (- 100 mV to + 400 mV versus SCE). Wires with treated surfaces did not reveal cracking or other traces of corrosion attacks in potentiodynamic tests up to + 900-1400-mV potentials and no pitting after stimulation at + 800 mV in potentiostatic tests. They exhibited corrosion behavior satisfactory for medical applications. Significant improvement of corrosion parameters was observed on the reverse scans in potentiodynamic tests after exposure of treated wires to potentials > 1000 mV. In scratch tests, the prepared surfaces repassivated only at low potentials, comparable to that of stainless steel. Tremendous improvement of the corrosion behavior of treated Nitinol wires is associated with the removal of defect surface material and the growth of stable TiO(2) oxide. The role of precipitates in the corrosion resistance of Nitinol-scratch repassivation capacity in particular-is emphasized in the discussion. PMID:12808592

  4. Template electrodeposition of ordered bismuth telluride nanowire arrays.

    PubMed

    Li, Shanghua; Liang, Yibin; Qin, Jian; Toprak, Muhammet; Muhammed, Mamoun

    2009-02-01

    Thermoelectric bismuth telluride nanowire arrays have been synthesized by direct-current electrode-position into porous anodic alumina membranes both galvanostatically and potentiostatically. The as-synthesized Bi2Te3 nanowire arrays are highly ordered in large area, stoichiometric, uniform, with high aspect ratio (above 100) and high filling ratio (>90%) of the membrane. The effects of different electrochemical deposition parameters on crystal structures, morphology and composition have been investigated. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) have been used to characterize the physical and chemical properties of the nanowires. PMID:19441566

  5. Single-crystal silver nanowires: Preparation and Surface-enhanced Raman Scattering (SERS) property

    E-print Network

    Sun, Baoliang; Dai, Shuxi; Du, Zuliang; 10.1016/j.matlet.2009.09.006

    2011-01-01

    Ordered Ag nanowire arrays with high aspect ratio and high density self-supporting Ag nanowire patterns were successfully prepared using potentiostatic electrodeposition within the confined nanochannels of a commercial porous anodic aluminium oxide (AAO) template. X-ray diffraction and selected area electron diffraction analysis show that the as-synthesized samples have preferred (220) orientation. Transmission electron microscopy and scanning electron microscopy investigation reveal that large-area and ordered Ag nanowire arrays with smooth surface and uniform diameter were synthesized. Surface-enhanced Raman Scattering (SERS) spectra show that the Ag nanowire arrays as substrates have high SERS activity.

  6. The effect of potential upon the high-temperature fatigue crack growth response of low-alloy steels. Part 1: Crack growth results

    SciTech Connect

    James, L.A.; Moshier, W.C.

    1997-04-01

    Corrosion-fatigue crack propagation experiments were conducted on several low-alloy steels in elevated temperature aqueous environments, and experimental parameters included temperature, sulfur content of the steel, applied potential level, and dissolved hydrogen (and in one case, dissolved oxygen) concentration in the water. Specimen potentials were controlled potentiostatically, and the observation (or non-observation) of accelerated fatigue crack growth rates was a complex function of the above parameters. Electrochemical results and the postulated explanation for the complex behavior are given in Part II.

  7. Corrosion resistance and electrochemical evaluation of silver mirrors

    NASA Astrophysics Data System (ADS)

    Pohlman, S. L.; Russell, P. M.

    1980-09-01

    Electrochemical methods including potentiostatic, potentiodynamic, and galvanic measurements were used to study the corrosion resistance of silver mirrors for use in solar energy concentrators. The potential driven modified scratch test appears promising as a rapid quality assurance evaluation technique. Galvanic measurements have shown that silver/copper is not an active galvanic couple and copper does provide only limited cathodic protection to the silver. Measurements have also shown that oxidation of tin or stannous ions and hydrogen formation at the silver/glass interface may occur.

  8. Over 95% of large-scale length uniformity in template-assisted electrodeposited nanowires by subzero-temperature electrodeposition

    PubMed Central

    2011-01-01

    In this work, we report highly uniform growth of template-assisted electrodeposited copper nanowires on a large area by lowering the deposition temperature down to subzero centigrade. Even with highly disordered commercial porous anodic aluminum oxide template and conventional potentiostatic electrodeposition, length uniformity over 95% can be achieved when the deposition temperature is lowered down to -2.4°C. Decreased diffusion coefficient and ion concentration gradient due to the lowered deposition temperature effectively reduces ion diffusion rate, thereby favors uniform nanowire growth. Moreover, by varying the deposition temperature, we show that also the pore nucleation and the crystallinity can be controlled. PMID:21781335

  9. Structural properties of single step electrochemically deposited ZnS nanofibers

    NASA Astrophysics Data System (ADS)

    Bhalerao, Anuradha B.; Wagh, B. G.; Lokhande, C. D.

    2013-06-01

    ZnS thin films are prepared by electro deposition technique over stainless steel substrates in potentiostatic mode from an aqueous acidic bath containing ZnSo4 and Na2S2O3. The growth kinetics of the film was studied and the deposition parameters such as electrolyte bath concentration, deposition time, deposition potential and pH of electrolyte bath are optimized. The X-ray diffraction (XRD) analysis of the deposited film showed presence of polycrystalline nature. The surface morphology studied by scanning electron microscope (SEM) shows fibrous morphology with well adherence and uniform distribution of nanosized fibers over the surface of substrate.

  10. Thin flexible intercalation anodes

    SciTech Connect

    Levy, S.C.; Cieslak, W.R.; Klassen, S.E.; Lagasse, R.R.

    1994-10-01

    Poly(acrylonitrile) fibers have been pyrolyzed under various conditions to form flexible carbon yarns capable of intercalating lithium ions. These fibers have also been formed into both woven and non woven cloths. Potentiostatic, potentiodynamic and galvanostatic tests have been conducted with these materials in several electrolytes. In some tests, a potential hold was used after each constant current charge and discharge. These tests have shown some of these flexible materials to reversibly intercalate lithium ions to levels that are suitable for use as a practical battery anode.

  11. Corrosion behavior and inhibitive effects on organotin compounds on nickel in formic acid

    SciTech Connect

    Singh, R.N.; Singh, V.B. . Dept. of Chemistry)

    1993-07-01

    Corrosion behavior of nickel (Ni) in different compositions of formic acid (HCOOH) at 30C was studied using the potentiostatic polarization method. The shape of the polarization curve was evaluated, and the corrosion current density, critical current density, and passive current density were determined. HCOOH solution of different composition were aggressive for the anodic dissolution of Ni, except for 20 and 30 mol/O HCOOH, in which feeble passitivity was observed. The organometallic compounds dibutyltin dichloride, phenyltin trichloride, diphenyltin dichloride, and triphenyltin chloride ([C[sub 6]H[sub 5

  12. Patterned electrochemical deposition of copper using an electron beam

    SciTech Connect

    Heijer, Mark den; Shao, Ingrid; Reuter, Mark C.; Ross, Frances M.; Radisic, Alex

    2014-02-01

    We describe a technique for patterning clusters of metal using electrochemical deposition. By operating an electrochemical cell in the transmission electron microscope, we deposit Cu on Au under potentiostatic conditions. For acidified copper sulphate electrolytes, nucleation occurs uniformly over the electrode. However, when chloride ions are added there is a range of applied potentials over which nucleation occurs only in areas irradiated by the electron beam. By scanning the beam we control nucleation to form patterns of deposited copper. We discuss the mechanism for this effect in terms of electron beam-induced reactions with copper chloride, and consider possible applications.

  13. Preparation and characterization of poly(5-aminoindole) by using electrochemical quartz crystal nanobalance technique.

    PubMed

    Broda, Balázs; Inzelt, György

    2014-01-01

    The electrochemical quartz crystal nanobalance (EQCN) was employed to study the electropolymerization of 5-aminoindole on platinum electrodes in acidic media. Potentiostatic or potential cycling electrooxidation of 5-aminoindole below 0.62 V vs. SCE leads to the formation of uniform, yellow, electrochemically active polymeric films. A scheme of the redox transformations of poly(5-aminoindole) which involves protonation-deprotonation steps accompanying the electron transfer is suggested. At higher positive potentials, further oxidation takes place resulting in different blue-purple, indigo-type materials which remain attached to the metal surface but show decreased or no redox activity. PMID:25125119

  14. Effects of magnetic fields from underwater electrical cutting on in vitro corrosion of dental amalgam

    SciTech Connect

    Ortendahl, T.W.; Hoegstedt, P.O.; Odelius, H.; Noren, J.G.

    1988-11-01

    Metallic taste has been reported from divers working with underwater electric welding and cutting. An in vitro model was designed to simulate the intraoral situation of the divers with respect to the magnetic field. Potentiostatic analyses were performed on amalgam samples exposed to AC and DC magnetic fields. Morphologic changes were analyzed using differential interference light microscopy and scanning electron microscopy. Chemical changes on the surface of the amalgam samples were analyzed with secondary ion mass spectrometry. Results demonstrated that dental amalgams exposed to a specific AC magnetic field underwent morphologic and chemical changes in the superficial amalgam layers.

  15. Separation of metal ions from aqueous solutions

    DOEpatents

    Almon, Amy C. (Augusta, GA)

    1994-01-01

    A process and apparatus for quantitatively and selectively separating metal ions from mixtures thereof in aqueous solution. The apparatus includes, in combination, a horizontal electrochemical flow cell containing flow bulk electrolyte solution and an aqueous, metal ion-containing solution, the cell containing a metal mesh working electrode, a counter electrode positioned downstream from the working electrode, an independent variable power supply/potentiostat positioned outside of the flow cell and connected to the electrodes, and optionally a detector such as a chromatographic detector, positioned outside the flow cell. This apparatus and its operation has significant application where trace amounts of metal ions are to be separated.

  16. Dynamics and Topography of QUASI-2D Needle-Like Silver Electrochemical Deposits Under a Quasi-Steady Regime

    NASA Astrophysics Data System (ADS)

    Pasquale, M. A.; Vicente, J. L.; Arvia, A. J.

    The electrochemical formation of single silver needles from aqueous silver sulfate was studied under both potentiostatic and galvanostatic conditions utilizing different quasi-2D cells. Under potentiostatic conditions, four (I-IV) stages of growth were distinguished. Stage III involved single needle growth under a quasi-steady-state (q-ss) regime in which, at the millimeter scale, the tip profile remained almost unchanged. Fast growing needles exhibited a truncated quasi-conical tip, and slow growing ones approached prolate hemispheroids. At stage III, the almost constant q-ss silver deposition rate was evaluated from the tip front displacement (dLz/dt) perpendicularly to the tangential plane of the tip. For the cathode to anode potential difference in the range -1.00 ? Ec-a ? -0.22 V, values of (dLz/dt) in the range 0.08-2.0 ?m s-1 were obtained. At the needle stem, the q-ss radial silver deposition rate (dLx/dt) was about two orders of magnitude lower than (dLz/dt). The transition from stage III to IV was characterized by tip thickening, i.e. a change in the tip q-conical profile to that of a prolate hemispheroid, and eventual tip splitting. Scanning electron micrographs at the micrometer scale of single silver needle tips from potentiostatic runs showed either a defined crystallography or an irregular topography covered by a large number of tiny crystals. In contrast, stems were always faceted. This difference indicated that surface relaxation processes following silver ion mass transport and discharge played a relevant role in the needle growth mode. At stage III, the growth regime is described utilizing a dual diffusion (D) and migration (M) model consisting of a DM direct contribution that becomes dominant at the needle stem, and a space charge (SC)-assisted DM contribution that operates at the tip apex. This explanation is consistent with the local cathodic current density values, the concentration ratio of silver clusters at the stem and tip apex surface, and the distinct kinetic behavior of needles produced from potentiostatic and galvanostatic runs. The complex link between mass transport phenomena of silver ions from the binary solution side, the silver ion discharge at the interface and the surface relaxation of silver adatoms and clusters at the metal lattice shed new light on the aspects of single silver needle formation.

  17. An approach to an inhibition electronic tongue to detect on-line organophosphorus insecticides using a computer controlled multi-commuted flow system.

    PubMed

    Alonso, Gustavo A; Dominguez, Rocio B; Marty, Jean-Louis; Muñoz, Roberto

    2011-01-01

    An approach to an inhibition bioelectronic tongue is presented. The work is focused on development of an automated flow system to carry out experimental assays, a custom potentiostat to measure the response from an enzymatic biosensor, and an inhibition protocol which allows on-line detections. A Multi-commuted Flow Analysis system (MCFA) was selected and developed to carry out assays with an improved inhibition method to detect the insecticides chlorpyrifos oxon (CPO), chlorfenvinfos (CFV) and azinphos methyl-oxon (AZMO). The system manifold comprised a peristaltic pump, a set of seven electronic valves controlled by a personal computer electronic interface and software based on LabView® to control the sample dilutions into the cell. The inhibition method consists in the injection of the insecticide when the enzyme activity has reached the plateau of the current; with this method the incubation time is avoided. A potentiostat was developed to measure the response from the enzymatic biosensor. Low limits of detection of 10 nM for CPO, CFV, and AZMO were achieved. PMID:22163822

  18. Electrochemical behaviour of silver in borate buffer solutions

    NASA Astrophysics Data System (ADS)

    Zaky, Ayman M.; Assaf, Fawzi H.; Abd El Rehim, Sayed S.; Mohamed, Basheer M.

    2004-01-01

    The electrochemical behaviour of Ag in aqueous 0.15 M borax and 0.15 M boric acid buffer solution was studied under various conditions using cyclic voltammetry and potentiostatic techniques. It was found that the anodic polarization curve of Ag in borate buffer solution was characterized by the appearance of two potential regions, active and passive, prior to the oxygen evolution reaction. The active potential region was characterized by the appearance of three anodic peaks, the first two peaks A 1 and A 2 correspond to the oxidation of Ag and formation of [Ag(OH) 2] - soluble compound and a passive film of Ag 2O on the electrode surface. The third anodic peak corresponds to the conversion of both [Ag(OH) 2] - and Ag 2O to Ag 2O 2. X-ray diffraction patterns confirmed the existence of Ag 2O and Ag 2O 2 passive layers on the electrode surface potentiodynamically polarized up to 800 mV. Potentiostatic current transient measurements showed that the formation of Ag 2O and Ag 2O 2 involves a nucleation and growth mechanism under diffusion control.

  19. Growth and Etch Rate Study of Low Temperature Anodic Silicon Dioxide Thin Films

    PubMed Central

    Ashok, Akarapu; Pal, Prem

    2014-01-01

    Silicon dioxide (SiO2) thin films are most commonly used insulating films in the fabrication of silicon-based integrated circuits (ICs) and microelectromechanical systems (MEMS). Several techniques with different processing environments have been investigated to deposit silicon dioxide films at temperatures down to room temperature. Anodic oxidation of silicon is one of the low temperature processes to grow oxide films even below room temperature. In the present work, uniform silicon dioxide thin films are grown at room temperature by using anodic oxidation technique. Oxide films are synthesized in potentiostatic and potentiodynamic regimes at large applied voltages in order to investigate the effect of voltage, mechanical stirring of electrolyte, current density and the water percentage on growth rate, and the different properties of as-grown oxide films. Ellipsometry, FTIR, and SEM are employed to investigate various properties of the oxide films. A 5.25?Å/V growth rate is achieved in potentiostatic mode. In the case of potentiodynamic mode, 160?nm thickness is attained at 300?V. The oxide films developed in both modes are slightly silicon rich, uniform, and less porous. The present study is intended to inspect various properties which are considered for applications in MEMS and Microelectronics. PMID:24672287

  20. Corrosion behaviour of austenitic stainless steel as a function of methanol concentration for direct methanol fuel cell bipolar plate

    NASA Astrophysics Data System (ADS)

    Wang, Lixia; Kang, Bin; Gao, Na; Du, Xiao; Jia, Linan; Sun, Juncai

    2014-05-01

    The corrosion behaviour of an AISI 304 stainless steel (304 SS) is investigated in aqueous acid methanol solutions (0.5 M H2SO4 + 2 ppm HF + x M CH3OH, x = 0, 1, 5, 10 and 20) at 50 °C to simulate the varied anodic operating conditions of direct methanol fuel cells. Electrochemical measurements including potentiodynamic polarisation, potentiostatic polarisation and electrochemical impedance spectroscopy tests, are employed to analyse the corrosion behaviour. The results reveal that the corrosion resistance of 304 SS is enhanced in solutions with higher methanol content. Scanning electron microscopy and inductively coupled plasma atomic emission spectrometry data indicate that the surface corrosion on 304 SS is alleviated when the methanol concentration is increased. According to the X-ray photoelectron spectroscopy and Mott-Schottky analyses, the passive films formed on the 304 SS after potentiostatic tests in all the test solutions are composed of a duplex electronic structure with an external n-type semiconductor layer and an internal p-type semiconductor layer. Further analyses of the surface conductivity conducted by measuring the interfacial contact resistance between the 304 SS and carbon paper reveal that the passive film formed in the solution with higher methanol content exhibits lower conductivity.

  1. Amperometric measurements of ethanol on paper with a glucometer.

    PubMed

    Wu, Grace; Zaman, Muhammad H

    2015-03-01

    Recent advances in electrochemical analysis on filter paper exemplify the versatility of this substrate for high performance testing. Its low-cost, light-weight, and environmentally friendly properties make it particularly attractive for applications in addressing health and environmental safety needs in low-resource settings and developing countries. However, the main drawback to sensitive electrochemical testing is the use of a potentiostat, a bench-top instrument that is extremely expensive, thereby negating the some of the benefits of paper-based devices. Hence there is a need to develop paper-devices for use with handheld, portable device readers that can extract quantitative readouts. In this study, we developed a method to use micro-paper electrochemical devices, or µPEDs, with a glucose meter, which are used for personal monitoring of blood glucose levels. Ethanol was chosen as a model target analyte due to its importance in the global issue of road safety. µPEDs were simple in design and could be tested with a potentiostat. We observed that inclusion of the stabilizer trehalose was critical to preparing µPEDs for later analysis. In addition, an NAD(+)-dependent enzyme was used to impart selectivity to the biosensor, which also represents a class of enzymes with targets relevant to the health and food industry. PMID:25618657

  2. Waste Water Derived Electroactive Microbial Biofilms: Growth, Maintenance, and Basic Characterization

    PubMed Central

    Gimkiewicz, Carla; Harnisch, Falk

    2013-01-01

    The growth of anodic electroactive microbial biofilms from waste water inocula in a fed-batch reactor is demonstrated using a three-electrode setup controlled by a potentiostat. Thereby the use of potentiostats allows an exact adjustment of the electrode potential and ensures reproducible microbial culturing conditions. During growth the current production is monitored using chronoamperometry (CA). Based on these data the maximum current density (jmax) and the coulombic efficiency (CE) are discussed as measures for characterization of the bioelectrocatalytic performance. Cyclic voltammetry (CV), a nondestructive, i.e. noninvasive, method, is used to study the extracellular electron transfer (EET) of electroactive bacteria. CV measurements are performed on anodic biofilm electrodes in the presence of the microbial substrate, i.e. turnover conditions, and in the absence of the substrate, i.e. nonturnover conditions, using different scan rates. Subsequently, data analysis is exemplified and fundamental thermodynamic parameters of the microbial EET are derived and explained: peak potential (Ep), peak current density (jp), formal potential (Ef) and peak separation (?Ep). Additionally the limits of the method and the state-of the art data analysis are addressed. Thereby this video-article shall provide a guide for the basic experimental steps and the fundamental data analysis. PMID:24430581

  3. Instrumental effects on in situ electrochemical STM studies: an investigation of a current surge induced Pd deposit on HOPG.

    PubMed

    Tong, X Q; Aindow, M; Farr, J P

    1996-05-01

    Knowledge of instrumental complications is vital both in interpreting experimental observations and in achieving true results. In a study of palladium electrodeposition on highly ordered pyrolytic graphite by in situ electrochemical scanning tunnelling microscopy, some unexpected experimental artefacts caused by instrumental design and tip-surface interactions have been recognised. The electrodeposition system employed in our in situ studies has been found to be very sensitive to an initial cathodic current surge when the potentiostat control was applied to the electrodes at the measured open circuit potential. As a result, palladium and/or hydrogen were immediately deposited on the graphite surface within a small radius under the imaging tip. The cause of this current surge was investigated and found to be related to the performance of the potentiostat. The deposit was removed either by anodic potential sweeps or under positive local electric fields of the imaging tip. Further cathodic deposition was possible on the surge-induced deposit. Characterisation, by ex situ x-ray diffraction, atomic force microscopy, scanning transmission electron microscopy and high resolution electron microscopy, showed that the deposits were Pd. Use of the various techniques demonstrated their complementarity in studies of the structure and dimensions of surface deposits. PMID:8859892

  4. Simplifying microbial electrosynthesis reactor design

    PubMed Central

    Giddings, Cloelle G. S.; Nevin, Kelly P.; Woodward, Trevor; Lovley, Derek R.; Butler, Caitlyn S.

    2015-01-01

    Microbial electrosynthesis, an artificial form of photosynthesis, can efficiently convert carbon dioxide into organic commodities; however, this process has only previously been demonstrated in reactors that have features likely to be a barrier to scale-up. Therefore, the possibility of simplifying reactor design by both eliminating potentiostatic control of the cathode and removing the membrane separating the anode and cathode was investigated with biofilms of Sporomusa ovata. S. ovata reduces carbon dioxide to acetate and acts as the microbial catalyst for plain graphite stick cathodes as the electron donor. In traditional ‘H-cell’ reactors, where the anode and cathode chambers were separated with a proton-selective membrane, the rates and columbic efficiencies of microbial electrosynthesis remained high when electron delivery at the cathode was powered with a direct current power source rather than with a potentiostat-poised cathode utilized in previous studies. A membrane-less reactor with a direct-current power source with the cathode and anode positioned to avoid oxygen exposure at the cathode, retained high rates of acetate production as well as high columbic and energetic efficiencies. The finding that microbial electrosynthesis is feasible without a membrane separating the anode from the cathode, coupled with a direct current power source supplying the energy for electron delivery, is expected to greatly simplify future reactor design and lower construction costs. PMID:26029199

  5. Nanopore formation on the surface oxide of commercially pure titanium grade 4 using a pulsed anodization method in sulfuric acid.

    PubMed

    Williamson, R S; Disegi, J; Griggs, J A; Roach, M D

    2013-10-01

    Titanium and its alloys form a thin amorphous protective surface oxide when exposed to an oxygen environment. The properties of this oxide layer are thought to be responsible for titanium and its alloys biocompatibility, chemical inertness, and corrosion resistance. Surface oxide crystallinity and pore size are regarded to be two of the more important properties in establishing successful osseointegration. Anodization is an electrochemical method of surface modification used for colorization marking and improved bioactivity on orthopedic and dental titanium implants. Research on titanium anodization using sulphuric acid has been reported in the literature as being primarily conducted in molarity levels 3 M and less using either galvanostatic or potentiostatic methods. A wide range of pore diameters ranging from a few nanometers up to 10 ?m have been shown to form in sulfuric acid electrolytes using the potentiostatic and galvanostatic methods. Nano sized pores have been shown to be beneficial for bone cell attachment and proliferation. The purpose of the present research was to investigate oxide crystallinity and pore formation during titanium anodization using a pulsed DC waveform in a series of sulfuric acid electrolytes ranging from 0.5 to 12 M. Anodizing titanium in increasing sulfuric acid molarities showed a trend of increasing transformations of the amorphous natural forming oxide to the crystalline phases of anatase and rutile. The pulsed DC waveform was shown to produce pores with a size range from ?0.01 to 1 ?m(2). The pore size distributions produced may be beneficial for bone cell attachment and proliferation. PMID:23807314

  6. San copolymer membranes with ion exchangers for Cu(II) removal from synthetic wastewater by electrodialysis.

    PubMed

    Caprarescu, Simona; Corobea, Mihai Cosmin; Purcar, Violeta; Spataru, Catalin Ilie; Ianchis, Raluca; Vasilievici, Gabriel; Vuluga, Zina

    2015-09-01

    Heterogeneous membranes were obtained by using styrene-acrylonitrile copolymer (SAN) blends with low content of ion-exchanger particles (5wt.%). The membranes obtained by phase inversion were used for the removal of copper ions from synthetic wastewater solutions by electrodialytic separation. The electrodialysis was conducted in a three cell unit, without electrolyte recirculation. The process, under potentiostatic or galvanostatic control, was followed by pH and conductivity measurements in the solution. The electrodialytic performance, evaluated in terms of extraction removal degree (rd) of copper ions, was better under potentiostatic control then by the galvanostatic one and the highest (over 70%) was attained at 8V. The membrane efficiency at small ion-exchanger load was explained by the migration of resin particles toward the pores surface during the phase inversion. The prepared membranes were characterized by various techniques i.e. optical microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis and differential thermal analysis and contact angle measurements. PMID:26354689

  7. Mechanism of chloride corrosion of dental amalgam.

    PubMed

    Finkelstein, G F; Greener, E H

    1979-04-01

    Polarization of conventional dental amalgam in Ringer's solution produces a dissolution of the gamma 2 phase at--250 mV (SCE) and formation of Sn-Cl and Sn-O-Cl. This study was undertaken to determine the electrochemical nature of these reactions. Potentiostatic polarization scans were run at 4, 37 and 50 degrees C in several dilutions of aerated Ringer's solution. Manipulation of reactant concentrations and electrolyte temperature produced shifts in the potentiostatic profiles. At 50 degrees C, a gamma 2 dissolution peak shift to -300 mV was observed, and at 4 degrees C the peak shifted to -200 mV. Dilution of Ringer's solution with respect to [Cl-] over three orders of magnitude produced a linear shift in the noble direction of 500 mV. Cathodic polarization appears to be limited by the oxygen half cell reaction. Changes of [Cl] affect the shape of the peak, round out its approach to the current maximum. Shifts in peak potential due to temperature and concentration changes agreed with calculations based on critical pitting potential for gamma2 dissolution due to a chloride reaction. Polarization profiles in pooled saliva agreed with calculated potentials based on known saliva [Cl-]. PMID:35596

  8. Miniaturized neural sensing and optogenetic stimulation system for behavioral studies in the rat

    NASA Astrophysics Data System (ADS)

    Kim, Min Hyuck; Nam, Ilho; Ryu, Youngki; Wellman, Laurie W.; Sanford, Larry D.; Yoon, Hargsoon

    2015-04-01

    Real time sensing of localized electrophysiological and neurochemical signals associated with spontaneous and evoked neural activity is critically important for understanding neural networks in the brain. Our goal is to enhance the functionality and flexibility of a neural sensing and stimulation system for the observation of brain activity that will enable better understanding from the level of individual cells to that of global structures. We have thus developed a miniaturized electronic system for in-vivo neurotransmitter sensing and optogenetic stimulation amenable to behavioral studies in the rat. The system contains a potentiostat, a data acquisition unit, a control unit, and a wireless data transfer unit. For the potentiostat, we applied embedded op-amps to build single potential amperometry for electrochemical sensing of dopamine. A light emitting diode is controlled by a microcontroller and pulse width modulation utilized to control optogenetic stimulation within a sub-millisecond level. In addition, this proto-typed electronic system contains a Bluetooth module for wireless data communication. In the future, an application-specific integrated circuit (ASIC) will be designed for further miniaturization of the system.

  9. TEM investigations on the local microstructure of electrodeposited galfenol nanowires.

    PubMed

    Pohl, D; Damm, C; Pohl, D; Schultz, L; Schlörb, H

    2016-01-22

    The local microstructure of Fe-Ga nanowires is investigated considering dependence on the deposition technique. Using a complexed electrolyte, smooth and homogeneous Fe80Ga20 nanowires are deposited into anodic aluminum oxide templates by either applying pulse potential or potentiostatic deposition technique. At optimized deposition conditions the wires show the desired composition of Fe80±2Ga20±2 without a gradient along the growth direction. Composition distribution, structure and microstructure are examined in detail and reveal only minor differences. Line EELS and crystal lattice measurements reveal a negligible oxygen content for both preparation routines. Neither Fe/Ga oxides nor hydroxides were found. Both potentiostatically deposited as well as pulse deposited nanowires exhibit a preferred ?110? orientation, the latter with slightly larger crystals. Different contrast patterns were found by TEM that appear more pronounced in the case of pulse deposited wires. High resolution transmission electron microscopy analysis and comparison of differently prepared focused ion beam lamellas reveal that these contrasts are caused by defects in the alternating potential deposition itself and are not induced during the TEM preparation process. The alternating potential mode causes periodic growth thereby inducing different layers with reduced wire thickness/defects at the layer interfaces. PMID:26651087

  10. Analytical modeling of dislocation effect on diffusion induced stress in a cylindrical lithium ion battery electrode

    NASA Astrophysics Data System (ADS)

    Li, Jia; Fang, Qihong; Liu, Feng; Liu, Youwen

    2014-12-01

    This paper is theoretically suggested to describe the combined effects of diffusion induced stress and dislocation induced stress in a cylinder lithium ion battery electrode on the nucleation and propagation of cracks under galvanostatic or potentiostatic solute insertion and extraction. By the conventional assumption, we develop this model accounting for dislocation mechanics in a cylindrical electrode under axisymmetric diffusion induced stress, focusing on the dislocation and size effects on the magnitude and distribution of the combined DIS during galvanostatic or potentiostatic condition. The results show that dislocation induced stress can decrease tensile stress, and converts the state of stress from tensile to compressive. The trend of the crack nucleation and propagation can be prevented as the cylindrical particle radius drops down to nanoscale range. Dislocation induced stress suppressing the crack nucleation, however, provides a novel way of mitigating internal damage in a cylindrical lithium ion battery during cycling. It may be used in conjunction with the methods of nano-engineering to create microstructures tailored to maximize suppressing the crack nucleation, yielding new strategy to improve battery life and avoid failure.

  11. Influence of dissolved hydrogen on aluminum-lithium alloy fracture behavior

    NASA Technical Reports Server (NTRS)

    Rivet, F. C.; Swanson, R. E.

    1989-01-01

    The objective of this work is to study the effects of dissolved hydrogen on the mechanical properties of 2090 and 2219 alloys. Prior to mechanical testing, potentiostatic and potentiodynamic tests were performed using NaCl/HCl solutions varying in pH from 1.5 to 7.5 (3.5 pct NaCl in deionized water). After analysis of the potentiodynamic curve for each solution, several potentiostatic experiments were conducted for various times (from 10 minutes to several hours) with a cathodic overpotential of 300 mV. These experiments were performed to select charging conditions. It is shown that the fracture of L-S and T-S orientations proceeds via slipping of layers in the S-T direction. The T-S and L-S orientations fractured with substantially higher propagation energy that the L-T and T-L orientations, due in large part to the extensive delamination propagation of the fracture.

  12. Electrochemical Behavior of Epinephrine at a Glassy Carbon Electrode Modified by Electrodeposited Films of Caffeic Acid

    PubMed Central

    Ren, Wang; Luo, Hong Qun; Li, Nian Bing

    2006-01-01

    A stable electroactive thin film of poly(caffeic acid) has been deposited on the surface of a glassy carbon electrode by potentiostatic technique in an aqueous solution containing caffeic acid. The voltammetric behavior of epinephrine (EP) at the poly(caffeic acid) modified glassy carbon electrode was studied by cyclic voltammetry. The poly(caffeic acid) modified electrode exhibited a promotion effect on the oxidation of EP. In a pH 7.4 phosphate buffer, the anodic current increased linearly with the concentration of EP in the range from 2.0 × 10?6 to 3.0 × 10?4 mol L?1 and the detection limit for EP was 6.0 × 10?7 mol L?1. The proposed method can be applied to the determination of EP in practical injection samples with simplicity, rapidness and accurate results.

  13. Integrated circuit-based electrochemical sensor for spatially resolved detection of redox-active metabolites in biofilms

    NASA Astrophysics Data System (ADS)

    Bellin, Daniel L.; Sakhtah, Hassan; Rosenstein, Jacob K.; Levine, Peter M.; Thimot, Jordan; Emmett, Kevin; Dietrich, Lars E. P.; Shepard, Kenneth L.

    2014-02-01

    Despite advances in monitoring spatiotemporal expression patterns of genes and proteins with fluorescent probes, direct detection of metabolites and small molecules remains challenging. A technique for spatially resolved detection of small molecules would benefit the study of redox-active metabolites that are produced by microbial biofilms and can affect their development. Here we present an integrated circuit-based electrochemical sensing platform featuring an array of working electrodes and parallel potentiostat channels. ‘Images’ over a 3.25 × 0.9?mm2 area can be captured with a diffusion-limited spatial resolution of 750??m. We demonstrate that square wave voltammetry can be used to detect, identify and quantify (for concentrations as low as 2.6??M) four distinct redox-active metabolites called phenazines. We characterize phenazine production in both wild-type and mutant Pseudomonas aeruginosa PA14 colony biofilms, and find correlations with fluorescent reporter imaging of phenazine biosynthetic gene expression.

  14. Enhanced removal of 8-quinolinecarboxylic acid in an activated carbon cloth by electroadsorption in aqueous solution.

    PubMed

    López-Bernabeu, S; Ruiz-Rosas, R; Quijada, C; Montilla, F; Morallón, E

    2016-02-01

    The effect of the electrochemical treatment (potentiostatic treatment in a filter-press electrochemical cell) on the adsorption capacity of an activated carbon cloth (ACC) was analyzed in relation with the removal of 8-quinolinecarboxylic acid pollutant from water. The adsorption capacity of an ACC is quantitatively improved in the presence of an electric field (electroadsorption process) reaching values of 96% in comparison to 55% in absence of applied potential. In addition, the cathodic treatment results in higher removal efficiencies than the anodic treatment. The enhanced adsorption capacity has been proved to be irreversible, since the removed compound remains adsorbed after switching the applied potential. The kinetics of the adsorption processes is also improved by the presence of an applied potential. PMID:26433936

  15. Light addressable potentiometric sensor with an array of sensing regions

    NASA Astrophysics Data System (ADS)

    Liang, Weiguo; Han, JingHong; Zhang, Hong; Chen, Deyong

    2001-09-01

    This paper describes the mechanism of light addressable poteniometric sensors (LAPS) from the viewpoints of Semiconductor Physics, and introduces the fabrication of a multi-parameter LAPS chip. The MEMS technology is applied to produce a matrix of sensing regions on the wafer. By doing that, the cross talk among these regions is reduced, and the precision of the LAPS is increased. An IR-LED matrix is used as the light source, and the flow-injection method is used to input samples. The sensor system is compact and highly integrated. The measure and control system is composed of a personal computer, a lock-in amplifier, a potentiostat, a singlechip system, and an addressing circuit. Some experiments have been done with this device. The results show that this device is very promising for practical use.

  16. Reduction mechanism of sulfur in lithium-sulfur battery: From elemental sulfur to polysulfide

    NASA Astrophysics Data System (ADS)

    Zheng, Dong; Zhang, Xuran; Wang, Jiankun; Qu, Deyu; Yang, Xiaoqing; Qu, Deyang

    2016-01-01

    The polysulfide ions formed during the first reduction wave of sulfur in Li-S battery were determined through both in-situ and ex-situ derivatization of polysulfides. By comparing the cyclic voltammetric results with and without the derivatization reagent (methyl triflate) as well as the in-situ and ex-situ derivatization results under potentiostatic condition, in-situ derivatization was found to be more appropriate than its ex-situ counterpart, since subsequent fast chemical reactions between the polysulfides and sulfur may occur during the timeframe of ex-situ procedures. It was found that the major polysulfide ions formed at the first reduction wave of elemental sulfur were the S4 2 - and S5 2 - species, while the widely accepted reduction products of S8 2 - and S6 2 - for the first reduction wave were in low abundance.

  17. Effect of annealing temperature on the pitting corrosion resistance of super duplex stainless steel UNS S32750

    SciTech Connect

    Tan Hua; Jiang Yiming; Deng Bo; Sun Tao; Xu Juliang; Li Jin

    2009-09-15

    The pitting corrosion resistance of commercial super duplex stainless steels SAF2507 (UNS S32750) annealed at seven different temperatures ranging from 1030 deg. C to 1200 deg. C for 2 h has been investigated by means of potentiostatic critical pitting temperature. The microstructural evolution and pit morphologies of the specimens were studied through optical/scanning electron microscope. Increasing annealing temperature from 1030 deg. C to 1080 deg. C elevates the critical pitting temperature, whereas continuing to increase the annealing temperature to 1200 deg. C decreases the critical pitting temperature. The specimens annealed at 1080 deg. C for 2 h exhibit the best pitting corrosion resistance with the highest critical pitting temperature. The pit morphologies show that the pit initiation sites transfer from austenite phase to ferrite phase as the annealing temperature increases. The aforementioned results can be explained by the variation of pitting resistance equivalent number of ferrite and austenite phase as the annealing temperature changes.

  18. Inhibition of mild steel corrosion by sodium dodecyl benzene sulfonate and sodium oleate in acidic solutions

    SciTech Connect

    Luo, H.; Han, K.N.; Guan, Y.C.

    1998-08-01

    Inhibition of mild steel corrosion by sodium dodecyl benzene sulfonate (C{sub 12}H{sub 25}C{sub 6}H{sub 4}SO{sub 3}Na [SDBS]) and sodium oleate (CH{sub 3}[CH{sub 2}]{sub 7}CH{double_bond}CH[CH{sub 2}]{sub 7}COONa) in acidic solutions was investigated using a potentiostat, a lock-in amplifier, a contact angle goniometer, A fourier transform infrared (FTIR) spectrometer, and an ultraviolet (UV)/visible spectrophotometer. In the presence of the organic inhibitors, the corrosion rate was reduced significantly, Anionic SDBS was adsorbed on the positively charged mild steel surface through the electrostatic attraction. However, for sodium oleate, the soluble oleic acid (CH{sub 3}[CH{sub 2}]{sub 7}CH{double_bond}CH[CH]{sub 7}COOH) chemisorbed on the steel surface at the first stage. Then, insoluble colloid adsorbed on the chemisorbed surface through van der Waals forces.

  19. Electrochemical Polishing Applications and EIS of a Novel Choline Chloride-Based Ionic Liquid

    SciTech Connect

    Wixtrom, Alex I.; Buhler, Jessica E.; Reece, Charles E.; Abdel-Fattah, Tarek M.

    2013-06-01

    Minimal surface roughness is a critical feature for high-field superconducting radio frequency (SRF) cavities used to engineer particle accelerators. Current methods for polishing Niobium cavities typically utilize solutions containing a mixture of concentrated sulfuric and hydrofluoric acid. Polishing processes such as these are effective, yet there are many hazards and costs associated with the use (and safe disposal) of the concentrated acid solutions. An alternative method for electrochemical polishing of the cavities was explored using a novel ionic liquid solution containing choline chloride. Potentiostatic electrochemical impedance spectroscopy (EIS) was used to analyze the ionic polishing solution. Final surface roughness of the Nb was found to be comparable to that of the acid-polishing method, as assessed by atomic force microscopy (AFM). This indicates that ionic liquid-based electrochemical polishing of Nb is a viable replacement for acid-based methods for preparation of SRF cavities.

  20. Electro-active sensor, method for constructing the same; apparatus and circuitry for detection of electro-active species

    NASA Technical Reports Server (NTRS)

    Buehler, Martin (Inventor)

    2009-01-01

    An electro-active sensor includes a nonconductive platform with a first electrode set attached with a first side of a nonconductive platform. The first electrode set serves as an electrochemical cell that may be utilized to detect electro-active species in solution. A plurality of electrode sets and a variety of additional electrochemical cells and sensors may be attached with the nonconductive platform. The present invention also includes a method for constructing the aforementioned electro-active sensor. Additionally, an apparatus for detection and observation is disclosed, where the apparatus includes a sealable chamber for insertion of a portion of an electro-active sensor. The apparatus allows for monitoring and detection activities. Allowing for control of attached cells and sensors, a dual-mode circuitry is also disclosed. The dual-mode circuitry includes a switch, allowing the circuitry to be switched from a potentiostat to a galvanostat mode.

  1. Self-organized highly ordered TiO{sub 2} nanotubes in organic aqueous system

    SciTech Connect

    Wan Jun; Yan Xia; Ding Junjie; Wang Meng; Hu Kongcheng

    2009-12-15

    A simple method to achieve self-organized, freestanding TiO{sub 2} nanotube array was constructed, free of corrosive etching process which was traditionally employed to separate TiO{sub 2} nanotubes from the metallic Ti substrate. The TiO{sub 2} nanotube arrays were constructed through potentiostatic anodization of Ti foil in aqueous electrolyte containing NH{sub 4}F and ethylene glycol. The nanotubes in the array were of 45 {mu}m lengths and 100 nm average pore diameters. The effect of NH{sub 4}F concentration on the length of the self-organized nanotube arrays was investigated. Electrochemical and spectroscopic measurements showed that the as-prepared nanotubes possessed large surface areas, good uniformity, and were ready for enzyme immobilization. The as-prepared nanotube arrays were amorphous, but crystallized with annealing at elevated temperatures, as demonstrated by X-ray diffraction (XRD).

  2. 3D Printed Microfluidic Device with Integrated Biosensors for Online Analysis of Subcutaneous Human Microdialysate

    PubMed Central

    2015-01-01

    This work presents the design, fabrication, and characterization of a robust 3D printed microfluidic analysis system that integrates with FDA-approved clinical microdialysis probes for continuous monitoring of human tissue metabolite levels. The microfluidic device incorporates removable needle type integrated biosensors for glucose and lactate, which are optimized for high tissue concentrations, housed in novel 3D printed electrode holders. A soft compressible 3D printed elastomer at the base of the holder ensures a good seal with the microfluidic chip. Optimization of the channel size significantly improves the response time of the sensor. As a proof-of-concept study, our microfluidic device was coupled to lab-built wireless potentiostats and used to monitor real-time subcutaneous glucose and lactate levels in cyclists undergoing a training regime. PMID:26070023

  3. Corrosion inhibition of mild steel in acidic media using newly synthesized heterocyclic organic molecules: Correlation between inhibition efficiency and chemical structure

    SciTech Connect

    Ouici, H. B. Guendouzi, A.; Benali, O.

    2015-03-30

    The corrosion inhibition of mild steel in 5% HCl solutions by some new synthesized organic compounds namely 3-(2-methoxyphenyl) 5-mercapto-1. 2. 4-triazole (2-MMT), 3-(3-methoxyphenyl) 5-mercapto-1. 2. 4-triazole (3-MMT) and 3-(2-hydroxyphenyl) 5-mercapto-1. 2. 4-triazole (2-HMT) was investigated using weight loss and potentiostatic polarization techniques. These measurements reveal that the inhibition efficiency obtained by these compounds increased by increasing their concentration. The inhibition efficiency follows the order 2-MMT >3-MMT >2-HMT. Polarization studies show that these compounds are of the mixed type but dominantly act as a cathodic inhibitors for mild steel in 5% HCl solutions. These inhibitors function through adsorption following Langmuir isotherm. Activation energy and Gibbs free energy for adsorption of inhibitors are calculated. Molecular modeling has been conducted to correlate the corrosion inhibition properties with the calculated quantum chemical parameters.

  4. Photoelectrochemical and Electrochemical Characterization of Sub-Micro-Gram Amounts of Organic Semiconductors Using Scanning Droplet Cell Microscopy

    PubMed Central

    2014-01-01

    A model organic semiconductor (MDMO-PPV) was used for testing a modified version of a photoelectrochemical scanning droplet cell microscope (PE-SDCM) adapted for use with nonaqueous electrolytes and containing an optical fiber for localized illumination. The most attractive features of the PE-SDCM are represented by the possibility of addressing small areas on the investigated substrate and the need of small amounts of electrolyte. A very small amount (ng) of the material under study is sufficient for a complete electrochemical and photoelectrochemical characterization due to the scanning capability of the cell. The electrochemical behavior of the polymer was studied in detail using potentiostatic and potentiodynamic investigations as well as electrochemical impedance spectroscopy. Additionally, the photoelectrochemical properties were investigated under illumination conditions, and the photocurrents found were at least 3 orders of magnitude higher than the dark (background) current, revealing the usefulness of this compact microcell for photovoltaic characterizations. PMID:25101149

  5. The relationship between induction time for pitting and pitting potential for high purity aluminum.

    SciTech Connect

    Wall, Frederick Douglas; Vandenavyle, Justin J.; Martinez, Michael A.

    2003-08-01

    The objective of this study was to determine if a distribution of pit induction times (from potentiostatic experiments) could be used to predict a distribution of pitting potentials (from potentiodynamic experiments) for high-purity aluminum. Pit induction times were measured for 99.99 Al in 50 mM NaCl at potentials of -0.35, -0.3, -0.25, and -0.2 V vs. saturated calomel electrode. Analysis of the data showed that the pit germination rate generally was an exponential function of the applied potential; however, a subset of the germination rate data appeared to be mostly potential insensitive. The germination rate behavior was used as an input into a mathematical relationship that provided a prediction of pitting potential distribution. Good general agreement was found between the predicted distribution and an experimentally determined pitting potential distribution, suggesting that the relationships presented here provide a suitable means for quantitatively describing pit germination rate.

  6. Integrated circuit-based electrochemical sensor for spatially resolved detection of redox-active metabolites in biofilms

    PubMed Central

    Bellin, Daniel L.; Sakhtah, Hassan; Rosenstein, Jacob K.; Levine, Peter M.; Thimot, Jordan; Emmett, Kevin; Dietrich, Lars E. P.; Shepard, Kenneth L.

    2014-01-01

    Despite advances in monitoring spatiotemporal expression patterns of genes and proteins with fluorescent probes, direct detection of metabolites and small molecules remains challenging. A technique for spatially resolved detection of small molecules would benefit the study of redox-active metabolites produced by microbial biofilms, which can drastically affect colony development. Here we present an integrated circuit-based electrochemical sensing platform featuring an array of working electrodes and parallel potentiostat channels. “Images” over a 3.25 × 0.9 mm area can be captured with a diffusion-limited spatial resolution of 750 ?m. We demonstrate that square wave voltammetry can be used to detect, identify, and quantify (for concentrations as low as 2.6 ?M) four distinct redox-active metabolites called phenazines. We characterize phenazine production in both wild-type and mutant Pseudomonas aeruginosa PA14 colony biofilms, and find correlations with fluorescent reporter imaging of phenazine biosynthetic gene expression. PMID:24510163

  7. Motion-driven electrochromic reactions for self-powered smart window system.

    PubMed

    Yeh, Min-Hsin; Lin, Long; Yang, Po-Kang; Wang, Zhong Lin

    2015-05-26

    The self-powered system is a promising concept for wireless networks due to its independent and sustainable operations without an external power source. To realize this idea, the triboelectric nanogenerator (TENG) was recently invented, which can effectively convert ambient mechanical energy into electricity to power up portable electronics. In this work, a self-powered smart window system was realized through integrating an electrochromic device (ECD) with a transparent TENG driven by blowing wind and raindrops. Driven by the sustainable output of the TENG, the optical properties, especially the transmittance of the ECD, display reversible variations due to electrochemical redox reactions. The maximum transmittance change at 695 nm can be reached up to 32.4%, which is comparable to that operated by a conventional electrochemical potentiostat (32.6%). This research is a substantial advancement toward the practical application of nanogenerators and self-powered systems. PMID:25808880

  8. Influence of surface modification of nitinol with silicon using plasma-immersion ion implantation on the alloy corrosion resistance in artificial physiological solutions

    NASA Astrophysics Data System (ADS)

    Kashin, O. A.; Borisov, D. P.; Lotkov, A. I.; Abramova, P. V.; Korshunov, A. V.

    2015-10-01

    Cyclic voltammetry and potentiostatic polarization have been applied to study electrochemical behavior and to determine corrosion resistance of nitinol, which surface was modified with silicon using plasma-immersion ion implantation, in 0.9% NaCl solution and in artificial blood plasma. It was found out that continuous, and also homogeneous in composition, thin Si-containing layers are resistant to corrosion damage at high positive potentials in artificial physiological solutions due to formation of stable passive films. Breakdown potential Eb of Si-modified NiTi depends on the character of silicon and Ni distribution at the alloy surface, Eb values amounted to 0.9-1.5 V (Ag/AgCl/KCl sat.) for the alloy samples with continuous Si-containing surface layers and with decreased Ni surface concentration.

  9. Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure

    PubMed Central

    May, Matthias M.; Lewerenz, Hans-Joachim; Lackner, David; Dimroth, Frank; Hannappel, Thomas

    2015-01-01

    Photosynthesis is nature's route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoelectrochemical water splitting utilizes customized tandem absorber structures to mimic the Z-scheme of natural photosynthesis. Here a combined chemical surface transformation of a tandem structure and catalyst deposition at ambient temperature yields photocurrents approaching the theoretical limit of the absorber and results in a solar-to-hydrogen efficiency of 14%. The potentiostatically assisted photoelectrode efficiency is 17%. Present benchmarks for integrated systems are clearly exceeded. Details of the in situ interface transformation, the electronic improvement and chemical passivation are presented. The surface functionalization procedure is widely applicable and can be precisely controlled, allowing further developments of high-efficiency robust hydrogen generators. PMID:26369620

  10. Electrochemical preparation and characterization of polypyrrole/stainless steel electrodes decorated with gold nanoparticles.

    PubMed

    Gutiérrez Pineda, Eduart; Alcaide, Francisco; Rodríguez Presa, María J; Bolzán, Agustín E; Gervasi, Claudio A

    2015-02-01

    The electrosynthesis and characterization of polypyrrole(PPy)/stainless steel electrodes decorated with gold nanoparticles and the performance of the composite electrode for sensing applications is described. PPy films were grown in potassium perchlorate and sodium salicylate solutions under comparable electropolymerization conditions. Polymer films prepared in the presence of perchlorate ions exhibited worm-like structures, whereas columnar structures were obtained in salicylate-containing solutions. Voltammetric response of PPy films prepared in salicylate solutions was more reversible. PPy films were decorated with gold nanoparticles obtained by a double step potentiostatic electrodeposition routine that allowed fine control of deposit characteristics. Analysis of deposits was performed by means of SEM and confocal Raman spectroscopy. The electrocatalytic activity of the Au/PPy electrodes was assessed for the electro-oxidation of hydrazine and hydroxylamine. Results showed a successful optimization of the route of synthesis that rendered nanocomposite electrode materials with promising applications in electrochemical sensing. PMID:25569325

  11. Structure and dye-sensitized solar cell application of TiO2 nanotube arrays fabricated by the anodic oxidation method

    NASA Astrophysics Data System (ADS)

    Ok, Seon-Yeong; Cho, Kwon-Koo; Kim, Ki-Won; Ryu, Kwang-Sun

    2010-05-01

    Well-ordered TiO2 nanotube arrays were fabricated by the potentiostatic anodic oxidation method using pure Ti foil as a working electrode and ethylene glycol solution as an electrolyte with the small addition of NH4F and H2O. The influence of anodization temperature and time on the morphology and formation of TiO2 nanotube arrays was examined. The TiO2 nanotube arrays were applied as a photoelectrode to dye-sensitized solar cells. Regardless of anodizing temperature and time, the average diameter and wall thickness of TiO2 nanotube arrays show a similar value, whereas the length increases with decreasing reaction temperature. The conversion efficiency is very low, which is due to a morphology breaking of the TiO2 nanotube arrays in the manufacturing process of a photoelectrode.

  12. Preparation of Nickel Oxide Embedded Self Organized Titania Nanotubes Array by New Alginate Method as a Supercapacitor Electrode

    NASA Astrophysics Data System (ADS)

    Dabaghi, Habibeh Hadad; Kazemzad, Mahmood; Ganjkhanlou, Yadolah; Eskandari, Rahmatollah

    2013-12-01

    Potentiostatic two step anodizing of titanium utilized for preparation of self organized titania nanotubes arrays with diameter of 150 nm. Then the new alginate method has been applied for incorporation of NiO into the nanotubes. The prepared hybrid materials have been characterized by various methods including field emission scanning electron microscopy, X-ray diffractometry and cyclic voltammetry analyses. The X-ray diffraction patterns of samples were also studied by Rietveld's method. Results showed that the prepared electrode containing anatase, rutile and NiO phases with fraction of 70, 8, and 22%, respectively. It was found that by application of the new method, porous NiO uniformly coated on nanotubes surface and great enhancement of specific capacitance from 0.14 to 3.8 mF cm-2 could be obtained. The prepared nanocomposites are promising materials for supercapacitance application and also for solar energy harvesting systems.

  13. Electrochemical deposition and characterization of Ni-P alloy thin films

    SciTech Connect

    Mahalingam, T. . E-mail: maha51@rediffmail.com; Raja, M.; Thanikaikarasan, S.; Sanjeeviraja, C.; Velumani, S.; Moon, Hosun; Kim, Yong Deak

    2007-08-15

    Nickel phosphorus (Ni-P) alloy thin films were prepared by electrodeposition on pre-cleaned copper substrates using a potentiostatic cathodic electrodeposition method from sulfate electrolyte baths at various sodium hypophosphite (NaH{sub 2}PO{sub 2}) concentrations. X-ray diffraction studies reveal polycrystalline cubic alloys at low concentrations of phosphorus (< 13.5 at.%) and these transformed into amorphous alloys at higher concentrations. X-ray photoelectron spectra show the presence of Ni{sub 2}p and P{sub 2}p lines corresponding to their binding energies. Scanning electron microscopic studies reveal spherical shaped grains at low phosphorus contents and modules of cauliflower type morphology at higher phosphorus concentrations. The effects of phosphorus concentration on the crystal structure, composition and morphology are studied and discussed.

  14. Improving the corrosion resistance of nitinol by plasma-immersion ion implantation with silicon for biomedical applications

    NASA Astrophysics Data System (ADS)

    Abramova, P. V.; Korshunov, A. V.; Lotkov, A. I.; Kashin, O. A.; Borisov, D. P.

    2015-11-01

    Cyclic voltammetry and potentiostatic polarization have been applied to study electrochemical behavior and to determine corrosion resistance of nitinol, which surface was modified with silicon using plasma-immersion ion implantation, in 0.9 % NaCl solution and in artificial blood plasma. It was found out that continuous, and also homogeneous in composition thin Si-containing layers are resistant to corrosion damage at high positive potentials in artificial physiological solutions due to formation of stable passive films. Breakdown potential Eb of Si-modified NiTi depends on the character of silicon and Ni distribution at the alloy surface, Eb values amounted to 0.9-1.5 V (Ag/AgCl/KCl sat.) for the alloy samples with continuous Si-containing surface layers and with decreased Ni surface concentration.

  15. Photosensitive polymer systems based on iron, ruthenium, and osmium complexes with 5-chloro-1,10-phenanthroline

    SciTech Connect

    Borisov, A.N.; Timonov, A.M.; Shagisultanova, G.A.

    1995-08-10

    The possibility of synthesis of polymers based on Fe(II), Ru(II), and Os(II) complexes with 5-chloro-1,10-phenanthroline (5Cl-phen) was demonstrated previously. It was shown that these polymeric complexes are photochemically active and possess electronic redox-conductivity and electrochromic properties. These compounds can be prepared by scanning of the platinum electrode potential from -0.7 to 1.7 V (vs. SCE) in acetonitrile solutions of corresponding monomers or with potentiostatic electrode polarization at -1.6 V. Optimal conditions of preparation of polymeric films based on the above complexes, the kinetics of their formation, data on stability, and parameters of electronic conductivity were presented previously. Here, the authors report the results of studies of the photosensitivity of electrodes modified with each component separately.

  16. Influence of sodium salts of organic acids as additives on localized corrosion of aluminum and its alloys

    SciTech Connect

    Raspini, I.A. )

    1993-10-01

    Localized pitting is best described by a characteristic parameter called the pitting potential values (E[sub p]). Although E[sub p] is governed by a number of factors, including alloy composition, metallurgical history, and the corrosive environment, the strongest effect on E[sub p] is produced by certain additives that differ from the aggressive anion and exert a beneficial effect. These are referred to as inhibitors. Potentiokinetic and potentiostatic anodic polarization curves were obtained on aluminum (Al) and Al alloys in mixed solutions containing sodium chloride with sodium benzoate, sodium acetate, or thioglycolic acid as inhibitors. Immersion time at the rest potential and corrosion products accumulated in the pits influenced the inhibition efficiency. Reliability of the polarization method was discussed.

  17. High frequency reference electrode

    DOEpatents

    Kronberg, J.W.

    1994-05-31

    A high frequency reference electrode for electrochemical experiments comprises a mercury-calomel or silver-silver chloride reference electrode with a layer of platinum around it and a layer of a chemically and electrically resistant material such as TEFLON around the platinum covering all but a small ring or halo' at the tip of the reference electrode, adjacent to the active portion of the reference electrode. The voltage output of the platinum layer, which serves as a redox electrode, and that of the reference electrode are coupled by a capacitor or a set of capacitors and the coupled output transmitted to a standard laboratory potentiostat. The platinum may be applied by thermal decomposition to the surface of the reference electrode. The electrode provides superior high-frequency response over conventional electrodes. 4 figs.

  18. Use of array of conducting polymers for differentiation of coconut oil products.

    PubMed

    Rañola, Rey Alfred G; Santiago, Karen S; Sevilla, Fortunato B

    2016-01-01

    An array of chemiresistors based on conducting polymers was assembled for the differentiation of coconut oil products. The chemiresistor sensors were fabricated through the potentiostatic electrodeposition of polyaniline (PANi), polypyrrole (PPy) and poly(3-methylthiophene) (P-3MTp) on the gap separating two planar gold electrodes set on a Teflon substrate. The change in electrical resistance of the sensors was measured and observed after exposing the array to the headspace of oil samples. The sensor response was found rapid, reversible and reproducible. Different signals were obtained for each coconut oil sample and pattern recognition techniques were employed for the analysis of the data. The developed system was able to distinguish virgin coconut oil (VCO) from refined, bleached & deodorised coconut oil (RBDCO), flavoured VCO, homemade VCO, and rancid VCO. PMID:26695237

  19. High-throughput screening of thin-film semiconductor material libraries I: system development and case study for Ti-W-O.

    PubMed

    Sliozberg, Kirill; Schäfer, Dominik; Erichsen, Thomas; Meyer, Robert; Khare, Chinmay; Ludwig, Alfred; Schuhmann, Wolfgang

    2015-04-13

    An automated optical scanning droplet cell (OSDC) enables high-throughput quantitative characterization of thin-film semiconductor material libraries. Photoelectrochemical data on small selected measurement areas are recorded including intensity-dependent photopotentials and -currents, potentiodynamic and potentiostatic photocurrents, as well as photocurrent (action) spectra. The OSDC contains integrated counter and double-junction reference electrodes and is fixed on a precise positioning system. A Xe lamp with a monochromator is coupled to the cell through a thin poly(methyl methacrylate) (PMMA) optical fiber. A specifically designed polytetrafluoroethylene (PTFE) capillary tip is pressed on the sample surface and defines through its diameter the homogeneously illuminated measurement area. The overall and wavelength-resolved irradiation intensities and the cell surface area are precisely determined and calibrated. System development and its performance are demonstrated by means of screening of a Ti?W?O thin film. PMID:25727402

  20. Structural and compositional characterization of Bi1-xSbx nanowire arrays grown by pulsed deposition to improve growth uniformity

    NASA Astrophysics Data System (ADS)

    Cassinelli, M.; Müller, S.; Aabdin, Z.; Peranio, N.; Eibl, O.; Trautmann, C.; Toimil-Molares, M. E.

    2015-12-01

    Arrays of Bi1-xSbx nanowire with various compositions (0 ? x ? 1) are grown in etched ion-track membranes by pulsed electrochemical deposition. Nanowires of diameter from 130 nm down to 18 nm are characterized by means of X-ray diffraction and high-resolution electron microscopy combined with electron diffraction and energy dispersive X-ray analysis. Compared to potentiostatic deposition, the pulsed synthesis method leads to a more uniform growth and higher filling rate of the wires across the entire template. By tuning the deposition parameters, we demonstrate excellent control over the wire composition and crystallographic orientation. The deposition process presented facilitates the development of future nanowire-based thermoelectric sensors, which are expected to exhibit a higher sensitivity and a faster response compared to thin film sensors.

  1. A model for pore growth in anodically etched gallium phosphide

    NASA Astrophysics Data System (ADS)

    Ricci, P. C.; Salis, M.; Anedda, A.

    2005-06-01

    The electrochemical etching process of porous gallium phosphide was studied by means of the characteristic current-potential (I-V) curves. Measurements were performed in H2SO4 0.5-M aqueous solution both in the dark and by illuminating the samples with the 351-nm line of an argon laser. Raman spectroscopy was applied to investigate the surface morphology of the samples prepared under different anodizing conditions within the potentiostatic regime. Based on a few reasonable assumptions, a simple model of pore growth is proposed. The enhancing effect in current intensity due to the branching of pores and the opposite effect due to a concomitant decrease in the effective cross area available for carrier transport are accounted for to explain the main features of the recorded I -V curves.

  2. Crevice corrosion products of dental amalgam

    SciTech Connect

    Sutow, E.J.; Jones, D.W.; Hall, G.C.; Owen, C.G. )

    1991-07-01

    The objective of this study was to determine the in vitro corrosion products that resulted from crevice corrosion of low- and high-copper dental amalgams. Specimens were potentiostatically polarized in a chloride-containing electrolyte while set against a PTFE surface to form a crevice. After 16 h, corrosion products were examined by light microscopy, SEM, EDS, and XRD. Analysis showed the presence of three previously reported products (Sn4(OH)6Cl2, SnO, and Cu2O) and a new product, CuCl, which formed on high-copper, {gamma} 2-free amalgams. Thermodynamic considerations show that CuCl is stable for the reported in vivo potentials of amalgam restorations and the high acidity and high chloride ion concentration associated with crevice corrosion.

  3. Relaxation phenomena in lithium ion insertion cells and simulation of the Sony cell

    SciTech Connect

    Fuller, T.F.; Doyle, M.; Newman, J.

    1994-12-31

    Relaxation phenomena in lithium-ion-insertion cells are modeled. Simulation results are presented for a dual lithium-ion-insertion cell and for a cell using a lithium-foil negative electrode. A period of relaxation after a charge or discharge can cause appreciable changes in the distribution of material in the insertion electrodes. Local concentration cells in the solution phase and an open-circuit potential that depends on state of charge for the solid phase drive the redistribution of material. Concentration profiles in solid and solution phases during relaxation are analyzed, and the consequences for cell performance are discussed. The model predicts the effects of relaxation time on multiple charge-discharge cycles and on peak power. Galvanostatic and potentiostatic charging are simulated; the results are compared to experimental data for a commercial battery.

  4. Use of cyclic current reversal polarization voltammetry for investigating the relationship between corrosion resistance and heat-treatment induced variations in microstructures of 400 C martensitic stainless steels

    NASA Technical Reports Server (NTRS)

    Ambrose, John R.

    1992-01-01

    Software for running a cyclic current reversal polarization voltammagram has been developed for use with a EG&G Princeton Applied Research Model 273 potentiostat/galvanostat system. The program, which controls the magnitude, direction and duration of an impressed galvanostatic current, will produce data in ASCII spreadsheets (Lotus, Quattro) for graphical representation of CCRPV voltammograms. The program was used to determine differences in corrosion resistance of 440 C martenstic stainless steel produced as a result of changes in microstructure effected by tempering. It was determined that tempering at all temperatures above 400 F resulted in increased polarizability of the material, with the increased likelihood that pitting would be initiated upon exposure to marine environments. These results will be used in development of remedial procedures for lowering the susceptibility of these alloys toward the stress corrosion cracking experienced in bearings used in high pressure oxygen turbopumps used in the main engines of space shuttle orbiters.

  5. Electrochemical flowcell for in-situ investigations by soft x-ray absorption and emission spectroscopy

    SciTech Connect

    Schwanke, C.; Lange, K. M.; Golnak, R.; Xiao, J.

    2014-10-15

    A new liquid flow-cell designed for electronic structure investigations at the liquid-solid interface by soft X-ray absorption and emission spectroscopy is presented. A thin membrane serves simultaneously as a substrate for the working electrode and solid state samples as well as for separating the liquid from the surrounding vacuum conditions. In combination with counter and reference electrodes this approach allows in-situ studies of electrochemical deposition processes and catalytic reactions at the liquid-solid interface in combination with potentiostatic measurements. As model system in-situ monitoring of the deposition process of Co metal from a 10 mM CoCl{sub 2} aqueous solution by X-ray absorption and emission spectroscopy is presented.

  6. Corrosion inhibition of mild steel in acidic media using newly synthesized heterocyclic organic molecules: Correlation between inhibition efficiency and chemical structure

    NASA Astrophysics Data System (ADS)

    Ouici, H. B.; Benali, O.; Guendouzi, A.

    2015-03-01

    The corrosion inhibition of mild steel in 5% HCl solutions by some new synthesized organic compounds namely 3-(2-methoxyphenyl) 5-mercapto-1. 2. 4-triazole (2-MMT), 3-(3-methoxyphenyl) 5-mercapto-1. 2. 4-triazole (3-MMT) and 3-(2-hydroxyphenyl) 5-mercapto-1. 2. 4-triazole (2-HMT) was investigated using weight loss and potentiostatic polarization techniques. These measurements reveal that the inhibition efficiency obtained by these compounds increased by increasing their concentration. The inhibition efficiency follows the order 2-MMT >3-MMT >2-HMT. Polarization studies show that these compounds are of the mixed type but dominantly act as a cathodic inhibitors for mild steel in 5% HCl solutions. These inhibitors function through adsorption following Langmuir isotherm. Activation energy and Gibbs free energy for adsorption of inhibitors are calculated. Molecular modeling has been conducted to correlate the corrosion inhibition properties with the calculated quantum chemical parameters.

  7. The alkaline zinc electrode as a mixed potential system

    NASA Technical Reports Server (NTRS)

    Fielder, W. L.

    1979-01-01

    Cathodic and anodic processes for the alkaline zinc electrode in 0.01 molar zincate electrolyte (9 molar hydroxide) were investigated. Cyclic voltammograms and current-voltage curves were obtained by supplying pulses through a potentiostat to a zinc rotating disk electrode. The data are interpreted by treating the system as one with a mixed potential; the processes are termed The zincate and corrosion reactions. The relative proportions of the two processes vary with the supplied potential. For the cathodic region, the cathodic corrosion process predominates at higher potentials while both processes occur simultaneously at a lower potential (i.e., 50 mV). For the anodic region, the anodic zincate process predominates at higher potentials while the anodic corrosion process is dominant at lower potential (i.e., 50 mV) if H2 is present.

  8. Synthesis of nano-structured polypyrrole/copper electrodes for nitrate and nitrite electroreduction

    NASA Astrophysics Data System (ADS)

    Phuong Thoa Nguyen, Thi; Thinh Nguyen, Viet; Nguyen Bui, Nhat; Do, Duong Kim Bao; Pham, Anh Minh

    2010-09-01

    Nanostructured polypyrrole film was synthesized onto a copper electrode in solutions of oxalic and salicylic acids and their buffers. The electrooxidation of pyrrole to form polypyrrole film and the electroreduction of nitrate and nitrite ions at synthesized Ppy modified copper electrodes (Ppy/Cu) in potassium chloride aqueous solutions were studied using chronoamperometry. The nanoporous structure of the synthesized Ppy films was characterized by scanning electron microscopy (SEM). Nitrate and nitrite reduction were performed by an electrochemical method under potentiostatic conditions. The Ppy/Cu electrodes prepared in the oxalate buffer and salicylic acid solutions perform more stable catalytic activity for nitrate reduction; their service life is about ten times longer than that for the electrodes prepared in oxalic acid solution. After 20?h of electrolysis, the nitrite was reduced completely with 100% efficiency and the nitrate was reduced with 35% efficiency. Report submitted to the 5th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN, Hanoi, 9-12 November 2010.

  9. 3D Printed Microfluidic Device with Integrated Biosensors for Online Analysis of Subcutaneous Human Microdialysate.

    PubMed

    Gowers, Sally A N; Curto, Vincenzo F; Seneci, Carlo A; Wang, Chu; Anastasova, Salzitsa; Vadgama, Pankaj; Yang, Guang-Zhong; Boutelle, Martyn G

    2015-08-01

    This work presents the design, fabrication, and characterization of a robust 3D printed microfluidic analysis system that integrates with FDA-approved clinical microdialysis probes for continuous monitoring of human tissue metabolite levels. The microfluidic device incorporates removable needle type integrated biosensors for glucose and lactate, which are optimized for high tissue concentrations, housed in novel 3D printed electrode holders. A soft compressible 3D printed elastomer at the base of the holder ensures a good seal with the microfluidic chip. Optimization of the channel size significantly improves the response time of the sensor. As a proof-of-concept study, our microfluidic device was coupled to lab-built wireless potentiostats and used to monitor real-time subcutaneous glucose and lactate levels in cyclists undergoing a training regime. PMID:26070023

  10. Electrocatalytic activities of cathode electrodes for water electrolysis using tetra-alkyl-ammonium-sulfonic acid ionic liquid as electrolyte

    NASA Astrophysics Data System (ADS)

    Fiegenbaum, Fernanda; de Souza, Michèle O.; Becker, Márcia R.; Martini, Emilse M. A.; de Souza, Roberto F.

    2015-04-01

    The hydrogen evolution reaction (HER) performed with platinum (Pt), nickel (Ni), stainless steel 304 (SS) or glassy carbon (GC) cathodes in 0.1 M 3-triethylammonium-propanesulfonic acid tetrafluoroborate (TEA-PS.BF4) solution is studied using quasi-potentiostatic and impedance spectroscopy techniques. The objective is to compare the catalytic effect on the cathode using different materials to obtain hydrogen by water electrolysis. Furthermore, the catalytic effect of the ionic liquid (IL) on the cathode compared with that of a hydrochloric acid (HCl) solution with same pH value (0.8) is reported. A low activation energy (Ea) of 8.7 kJ mol-1 is found for the glassy carbon cathode. Tafel plots obtained with TEA-PS.BF4 IL suggest the formation of an electroactive layer of IL on the cathode, which may be responsible for the catalytically enhanced performance observed.

  11. Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure.

    PubMed

    May, Matthias M; Lewerenz, Hans-Joachim; Lackner, David; Dimroth, Frank; Hannappel, Thomas

    2015-01-01

    Photosynthesis is nature's route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoelectrochemical water splitting utilizes customized tandem absorber structures to mimic the Z-scheme of natural photosynthesis. Here a combined chemical surface transformation of a tandem structure and catalyst deposition at ambient temperature yields photocurrents approaching the theoretical limit of the absorber and results in a solar-to-hydrogen efficiency of 14%. The potentiostatically assisted photoelectrode efficiency is 17%. Present benchmarks for integrated systems are clearly exceeded. Details of the in situ interface transformation, the electronic improvement and chemical passivation are presented. The surface functionalization procedure is widely applicable and can be precisely controlled, allowing further developments of high-efficiency robust hydrogen generators. PMID:26369620

  12. Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure

    NASA Astrophysics Data System (ADS)

    May, Matthias M.; Lewerenz, Hans-Joachim; Lackner, David; Dimroth, Frank; Hannappel, Thomas

    2015-09-01

    Photosynthesis is nature's route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoelectrochemical water splitting utilizes customized tandem absorber structures to mimic the Z-scheme of natural photosynthesis. Here a combined chemical surface transformation of a tandem structure and catalyst deposition at ambient temperature yields photocurrents approaching the theoretical limit of the absorber and results in a solar-to-hydrogen efficiency of 14%. The potentiostatically assisted photoelectrode efficiency is 17%. Present benchmarks for integrated systems are clearly exceeded. Details of the in situ interface transformation, the electronic improvement and chemical passivation are presented. The surface functionalization procedure is widely applicable and can be precisely controlled, allowing further developments of high-efficiency robust hydrogen generators.

  13. Template-assisted electrochemical growth of polypyrrole nanotubes for development of high sensitivity glucose biosensor.

    PubMed

    Palod, Pragya Agar; Pandey, Shyam S; Hayase, Shuji; Singh, Vipul

    2014-10-01

    In this paper, we report the growth of polypyrrole (PPy) nanotube arrays using template-assisted electrochemical polymerization to fabricate enzymatic glucose biosensors. The PPy nanotubes were grown on platinum-coated alumina membranes (Anodisc™s). By varying the polymerization time during the potentiostatic electropolymerization, the size/diameter of the PPy nanotubes were controlled, leading to changes in the subsequent enzyme immobilization (via physical adsorption). Enzyme electrode thus fabricated resulted in to the optimum sensitivity of 18.6 mA cm(-2) M(-1), a wide range of linear operation (0.25-20 mM) and the lowest detection limit of 0.25 mM glucose concentration for the biosensor with the polymerization time of 40 s. The effect of polymerization duration on the sensitivity has been explained on the basis of porosity and enzyme-loading capacity of polymerized electrodes. PMID:24912977

  14. Electro-Mechanical Actuation of Carbon Nanotube Yarns, Sheets, Composites

    NASA Astrophysics Data System (ADS)

    Oh, Jiyoung; Kozlov, Mikhail; Zhang, Mei; Fang, Shaoli; Baughman, Ray

    2011-03-01

    We report preparation of highly conductive carbon nanotube yarns and sheets. The materials aim at such applications as electronic textiles, electro-mechanical actuators, and conductive coatings. The electro-mechanical response of the specimens was measured using custom made force transducer operating in an isometric mode. The measurements were carried out at room temperature in aqueous and organic electrolytes; square-wave potential of variable amplitude was applied with a potentiostat. It was found that the maximum isometric stress generated by nanotube actuators could be as large as 12 MPa. This approaches the stress generation capability of commercial ferroelectrics and is significantly larger than that of natural muscles. A variety of applications of the materials is discussed.

  15. High frequency reference electrode

    DOEpatents

    Kronberg, James W. (Aiken, SC)

    1994-01-01

    A high frequency reference electrode for electrochemical experiments comprises a mercury-calomel or silver-silver chloride reference electrode with a layer of platinum around it and a layer of a chemically and electrically resistant material such as TEFLON around the platinum covering all but a small ring or "halo" at the tip of the reference electrode, adjacent to the active portion of the reference electrode. The voltage output of the platinum layer, which serves as a redox electrode, and that of the reference electrode are coupled by a capacitor or a set of capacitors and the coupled output transmitted to a standard laboratory potentiostat. The platinum may be applied by thermal decomposition to the surface of the reference electrode. The electrode provides superior high-frequency response over conventional electrodes.

  16. Adhesion and proliferation of osteoblast-like cells on anodic porous alumina substrates with different morphology.

    PubMed

    Salerno, Marco; Caneva-Soumetz, Federico; Pastorino, Laura; Patra, Niranjan; Diaspro, Alberto; Ruggiero, Carmelina

    2013-06-01

    We have fabricated nanoporous alumina surfaces by means of anodization in oxalic acid in different conditions and used them as the substrates for the growth of cells from a human osteoblast-like cell line. The rough nanoporous alumina substrates have been compared both with smooth standard Petri dishes used as the control and with commercial substrates of similar material. The viability of the cells has been assessed at different culture times of 4, 11, 18, and 25 days in vitro. It turned out that the porous side of the galvanostatically fabricated alumina performed similar to the control and better than the commercial porous alumina, whereas the potentiostatically fabricated porous alumina performed better than all the other substrates at all times, and in particular at the two shortest time periods of 4 and 11 days in vitro. The best performance of the substrates is associated with intermediate surface roughness and feature spacing. PMID:23722279

  17. Microbial characterization of anode-respiring bacteria within biofilms developed from cultures previously enriched in dissimilatory metal-reducing bacteria.

    PubMed

    Pierra, Mélanie; Carmona-Martínez, Alessandro A; Trably, Eric; Godon, Jean-Jacques; Bernet, Nicolas

    2015-11-01

    This work evaluated the use of a culture enriched in DMRB as a strategy to enrich ARB on anodes. DMRB were enriched with Fe(III) as final electron acceptor and then transferred to a potentiostatically-controlled system with an anode as sole final electron acceptor. Three successive iron-enrichment cultures were carried out. The first step of enrichment revealed a successful selection of the high current-producing ARB Geoalkalibacter subterraneus. After few successive enrichment steps, the microbial community analysis in electroactive biofilms showed a significant divergence with an impact on the biofilm electroactivity. Enrichment of ARB in electroactive biofilms through the pre-selection of DMRB should therefore be carefully considered. PMID:26182995

  18. Effect of microstructure and strain on the degradation behavior of novel bioresorbable iron-manganese alloy implants.

    PubMed

    Heiden, Michael; Kustas, Andrew; Chaput, Kevin; Nauman, Eric; Johnson, David; Stanciu, Lia

    2015-02-01

    Advancing the understanding of microstructural effects and deformation on the degradability of Fe-Mn bioresorbable alloys (specifically, Fe-33%Mn) will help address the current problems associated with designing degradable fracture fixation implants for hard tissues. Potentiostatic polarization tests were conducted on a wide variety of metal samples to examine how different deformation processes affect the instantaneous rate of degradation of Fe-Mn alloys. Large-strain machining (LSM), a novel severe plastic deformation (SPD) technique was utilized during these experiments to modify the degradation properties of the proposed Fe-Mn alloy. It was discovered that Fe-33%Mn after LSM with a rake angle of 0° (effective strain?=?2.85) showed the most promising increase in degradation rate compared to as-cast, annealed, and additional deformation conditions (rolled and other LSM parameters) for the same alloy. The mechanisms for enhancement of the corrosion rate are discussed. PMID:24825402

  19. Synthesis of mesoporous nanocomposites for their application in solid oxide electrolysers cells: microstructural and electrochemical characterization.

    PubMed

    Torrell, M; Almar, L; Morata, A; Tarancón, A

    2015-10-10

    Fabrication routes for new SOEC mesoporous nanocomposite materials as electrodes are presented in this paper. NiO-CGO and SDC-SSC are described as possible new materials and their synthesis and the cell fabrication are discussed. The obtained materials are microstructurally characterised by SEM, TEM and XRD, where the mesoporous structures are observed and analysed. The obtained samples are electrochemically analysed by I-V polarisation curves and EIS analysis, showing a maximum current density of 330 mA cm(-2) at 1.7 V. A degradation of the cell performance is evidenced after a potentiostatic test at 1.4 V after more than 40 hours. Oxygen electrode delaminating is detected, which is most probably the main cause of ageing. Even taking into account the lack of durability of the fabricated cells, the mesoporous electrodes do not seem to be altered, opening the possibility for further studies devoted to this high stability material for SOEC electrodes. PMID:26212761

  20. Effects of TiN coating on the corrosion of nanostructured Ti-30Ta-xZr alloys for dental implants

    NASA Astrophysics Data System (ADS)

    Kim, Won-Gi; Choe, Han-Cheol

    2012-01-01

    Electrochemical characteristics of a titanium nitride (TiN)-coated/nanotube-formed Ti-Ta-Zr alloy for biomaterials have been researched by using the magnetic sputter and electrochemical methods. Ti-30Ta-xZr (x = 3, 7 and 15 wt%) alloys were prepared by arc melting and heat treated for 24 h at 1000 °C in an argon atmosphere and then water quenching. The formation of oxide nanotubes was achieved by anodizing a Ti-30Ta-xZr alloy in H3PO4 electrolytes containing small amounts of fluoride ions at room temperature. Anodization was carried out using a scanning potentiostat, and all experiments were conducted at room temperature. The microstructure and morphology of nanotube arrays were characterized by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The TiN coatings were obtained by the radio-frequency (RF) magnetron sputtering technique. The depositions were performed from pure Ti targets on Ti-30Ta-xZr alloys substrates. The corrosion properties of the specimens were examined using potentiodynamic test in a 0.9% NaCl solution by using potentiostat. The microstructures of Ti-30Ta-xZr alloys were changed from an equiaxed to a needle-like structure with increasing Zr content. The interspace between the nanotubes was approximately 20, 80 and 200 nm for Zr contents of 3, 7 and 15 wt%, respectively. The corrosion resistance of the TiN-coated on the anodized Ti-30Ta-xZr alloys was higher than that of the untreated Ti alloys, indicating a better protective effect.

  1. Real-Time Telemetry System for Amperometric and Potentiometric Electrochemical Sensors

    PubMed Central

    Wang, Wei-Song; Huang, Hong-Yi; Chen, Shu-Chun; Ho, Kuo-Chuan; Lin, Chia-Yu; Chou, Tse-Chuan; Hu, Chih-Hsien; Wang, Wen-Fong; Wu, Cheng-Feng; Luo, Ching-Hsing

    2011-01-01

    A real-time telemetry system, which consists of readout circuits, an analog-to-digital converter (ADC), a microcontroller unit (MCU), a graphical user interface (GUI), and a radio frequency (RF) transceiver, is proposed for amperometric and potentiometric electrochemical sensors. By integrating the proposed system with the electrochemical sensors, analyte detection can be conveniently performed. The data is displayed in real-time on a GUI and optionally uploaded to a database via the Internet, allowing it to be accessed remotely. An MCU was implemented using a field programmable gate array (FPGA) to filter noise, transmit data, and provide control over peripheral devices to reduce power consumption, which in sleep mode is 70 mW lower than in operating mode. The readout circuits, which were implemented in the TSMC 0.18-?m CMOS process, include a potentiostat and an instrumentation amplifier (IA). The measurement results show that the proposed potentiostat has a detectable current range of 1 nA to 100 ?A, and linearity with an R2 value of 0.99998 in each measured current range. The proposed IA has a common-mode rejection ratio (CMRR) greater than 90 dB. The proposed system was integrated with a potentiometric pH sensor and an amperometric nitrite sensor for in vitro experiments. The proposed system has high linearity (an R2 value greater than 0.99 was obtained in each experiment), a small size of 5.6 cm × 8.7 cm, high portability, and high integration. PMID:22164093

  2. 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 effects by ice formation in the porous structures which lead to significant performance loss.

  3. Effects of Crystallographic Orientation on Corrosion Behavior of Magnesium Single Crystals

    NASA Astrophysics Data System (ADS)

    Shin, Kwang Seon; Bian, Ming Zhe; Nam, Nguyen Dang

    2012-06-01

    The corrosion behavior of magnesium single crystals with various crystallographic orientations was examined in this study. To identify the effects of surface orientation on the corrosion behavior in a systematic manner, single-crystal specimens with ten different rotation angles of the plane normal from the [0001] direction to the [ 10overline{1} 0] direction at intervals of 10° were prepared and subjected to potentiodynamic polarization and potentiostatic tests as well as electrochemical impedance spectroscopy (EIS) measurements in 3.5 wt.% NaCl solution. Potentiodynamic polarization results showed that the pitting potential ( E pit) first decreased from -1.57 V SCE to -1.64 V SCE with an increase in the rotation angle from 0° to 40°, and then increased to -1.60 V SCE with a further increase in the rotation angle to 90°. The results obtained from potentiostatic tests are also in agreement with the trend in potentiodynamic polarization tests as a function of rotation angle. A similar trend was also observed for the depressed semicircle and the total resistances in the EIS measurements due to the facile formation of MgO and Mg(OH)2 passive films on the magnesium surface. In addition, the amount of chloride in the passive film was found first to increase with an increase in rotation angle from 0° to 40°, then decrease with a further increase in rotation angle, indicating that the tendency to form a more protective passive film increased for rotation angle near 0° [the (0001) plane] or 90° [the ( 10overline{1} 0) plane].

  4. A combined electrochemical and optical trapping platform for measuring single cell respiration rates at electrode interfaces.

    PubMed

    Gross, Benjamin J; El-Naggar, Mohamed Y

    2015-06-01

    Metal-reducing bacteria gain energy by extracellular electron transfer to external solids, such as naturally abundant minerals, which substitute for oxygen or the other common soluble electron acceptors of respiration. This process is one of the earliest forms of respiration on earth and has significant environmental and technological implications. By performing electron transfer to electrodes instead of minerals, these microbes can be used as biocatalysts for conversion of diverse chemical fuels to electricity. Understanding such a complex biotic-abiotic interaction necessitates the development of tools capable of probing extracellular electron transfer down to the level of single cells. Here, we describe an experimental platform for single cell respiration measurements. The design integrates an infrared optical trap, perfusion chamber, and lithographically fabricated electrochemical chips containing potentiostatically controlled transparent indium tin oxide microelectrodes. Individual bacteria are manipulated using the optical trap and placed on the microelectrodes, which are biased at a suitable oxidizing potential in the absence of any chemical electron acceptor. The potentiostat is used to detect the respiration current correlated with cell-electrode contact. We demonstrate the system with single cell measurements of the dissimilatory-metal reducing bacterium Shewanella oneidensis MR-1, which resulted in respiration currents ranging from 15 fA to 100 fA per cell under our measurement conditions. Mutants lacking the outer-membrane cytochromes necessary for extracellular respiration did not result in any measurable current output upon contact. In addition to the application for extracellular electron transfer studies, the ability to electronically measure cell-specific respiration rates may provide answers for a variety of fundamental microbial physiology questions. PMID:26133851

  5. Silver(I) Ions Ultrasensitive Detection at Carbon Electrodes—Analysis of Waters, Tobacco Cells and Fish Tissues

    PubMed Central

    Krizkova, Sona; Krystofova, Olga; Trnkova, Libuse; Hubalek, Jaromir; Adam, Vojtech; Beklova, Miroslava; Horna, Ales; Havel, Ladislav; Kizek, Rene

    2009-01-01

    We used carbon paste electrodes and a standard potentiostat to detect silver ions. The detection limit (3 Signal/Noise ratio) was estimated as 0.5 ?M. A standard electrochemical instrument microanalysis of silver(I) ions was suggested. As a working electrode a carbon tip (1 mL) or carbon pencil was used. Limits of detection estimated by dilution of a standard were 1 (carbon tip) or 10 nM (carbon pencil). Further we employed flow injection analysis coupled with carbon tip to detect silver(I) ions released in various beverages and mineral waters. During first, second and third week the amount of silver(I) ions releasing into water samples was under the detection limit of the technique used for their quantification. At the end of a thirteen weeks long experiment the content of silver(I) ions was several times higher compared to the beginning of release detected in the third week and was on the order of tens of nanomoles. In subsequent experiments the influence of silver(I) ions (0, 5 and 10 ?M) on a plant model system (tobacco BY-2 cells) during a four-day exposition was investigated. Silver(I) ions were highly toxic to the cells, which was revealed by a double staining viability assay. Moreover we investigated the effect of silver(I) ions (0, 0.3, 0.6, 1.2 and 2.5 ?M) on guppies (Poecilia reticulata). Content of Ag(I) increased with increasing time of the treatment and applied concentrations in fish tissues. It can be concluded that a carbon tip or carbon pencil coupled with a miniaturized potentiostat can be used for detection of silver(I) ions in environmental samples and thus represents a small, portable, low cost and easy-to-use instrument for such purposes. PMID:22399980

  6. A combined electrochemical and optical trapping platform for measuring single cell respiration rates at electrode interfaces

    NASA Astrophysics Data System (ADS)

    Gross, Benjamin J.; El-Naggar, Mohamed Y.

    2015-06-01

    Metal-reducing bacteria gain energy by extracellular electron transfer to external solids, such as naturally abundant minerals, which substitute for oxygen or the other common soluble electron acceptors of respiration. This process is one of the earliest forms of respiration on earth and has significant environmental and technological implications. By performing electron transfer to electrodes instead of minerals, these microbes can be used as biocatalysts for conversion of diverse chemical fuels to electricity. Understanding such a complex biotic-abiotic interaction necessitates the development of tools capable of probing extracellular electron transfer down to the level of single cells. Here, we describe an experimental platform for single cell respiration measurements. The design integrates an infrared optical trap, perfusion chamber, and lithographically fabricated electrochemical chips containing potentiostatically controlled transparent indium tin oxide microelectrodes. Individual bacteria are manipulated using the optical trap and placed on the microelectrodes, which are biased at a suitable oxidizing potential in the absence of any chemical electron acceptor. The potentiostat is used to detect the respiration current correlated with cell-electrode contact. We demonstrate the system with single cell measurements of the dissimilatory-metal reducing bacterium Shewanella oneidensis MR-1, which resulted in respiration currents ranging from 15 fA to 100 fA per cell under our measurement conditions. Mutants lacking the outer-membrane cytochromes necessary for extracellular respiration did not result in any measurable current output upon contact. In addition to the application for extracellular electron transfer studies, the ability to electronically measure cell-specific respiration rates may provide answers for a variety of fundamental microbial physiology questions.

  7. Utilization of subsurface microbial electrochemical systems to elucidate the mechanisms of competition between methanogenesis and microbial iron(III)/humic acid reduction in Arctic peat soils

    NASA Astrophysics Data System (ADS)

    Friedman, E. S.; Miller, K.; Lipson, D.; Angenent, L. T.

    2012-12-01

    High-latitude peat soils are a major carbon reservoir, and there is growing concern that previously dormant carbon from this reservoir could be released to the atmosphere as a result of continued climate change. Microbial processes, such as methanogenesis and carbon dioxide production via iron(III) or humic acid reduction, are at the heart of the carbon cycle in Arctic peat soils [1]. A deeper understanding of the factors governing microbial dominance in these soils is crucial for predicting the effects of continued climate change. In previous years, we have demonstrated the viability of a potentiostatically-controlled subsurface microbial electrochemical system-based biosensor that measures microbial respiration via exocellular electron transfer [2]. This system utilizes a graphite working electrode poised at 0.1 V NHE to mimic ferric iron and humic acid compounds. Microbes that would normally utilize these compounds as electron acceptors donate electrons to the electrode instead. The resulting current is a measure of microbial respiration with the electrode and is recorded with respect to time. Here, we examine the mechanistic relationship between methanogenesis and iron(III)- or humic acid-reduction by using these same microbial-three electrode systems to provide an inexhaustible source of alternate electron acceptor to microbes in these soils. Chamber-based carbon dioxide and methane fluxes were measured from soil collars with and without microbial three-electrode systems over a period of four weeks. In addition, in some collars we simulated increased fermentation by applying acetate treatments to understand possible effects of continued climate change on microbial processes in these carbon-rich soils. The results from this work aim to increase our fundamental understanding of competition between electron acceptors, and will provide valuable data for climate modeling scenarios. 1. Lipson, D.A., et al., Reduction of iron (III) and humic substances plays a major role in anaerobic respiration in an Arctic peat soil. Journal of Geophysical Research-Biogeosciences, 2010. 115. 2. Friedman, E.S., et al., A cost-effective and field-ready potentiostat that poises subsurface electrodes to monitor bacterial respiration. Biosensors and Bioelectronics, 2012. 32(1): p. 309-313.

  8. A XPS Study of the Passivity of Stainless Steels Influenced by Sulfate-Reducing Bacteria.

    NASA Astrophysics Data System (ADS)

    Chen, Guocun

    The influence of sulfate-reducing bacteria (SRB) on the passivity of type 304 and 317L stainless steels (SS) was investigated by x-ray photoelectron spectroscopy (XPS), microbiological and electrochemical techniques. Samples were exposed to SRB, and then the resultant surfaces were analyzed by XPS, and the corrosion resistance by potentiodynamic polarization in deaerated 0.1 M HCl. To further understand their passivity, the SRB-exposed samples were analyzed by XPS after potentiostatic polarization at a passive potential in the hydrochloric solution. The characterization was performed under two surface conditions: unrinsed and rinsed by deaerated alcohol and deionized water. Comparisons were made with control samples immersed in uninoculated medium. SRB caused a severe loss of the passivity of 304 SS through sulfide formation and possible additional activation to form hexavalent chromium. The sulfides included FeS, FeS_2, Cr_2S _3, NiS and possibly Fe_ {rm 1-x}S. The interaction took place nonuniformly, resulting in undercutting of the passive film and preferential hydration of inner surface layers. The bacterial activation of the Cr^{6+ }^ecies was magnified by subsequent potentiostatic polarization. In contrast, 317L SS exhibited a limited passivity. The sulfides were formed mainly in the outer layers. Although Cr^{6+}^ecies were observed after the exposure, they were dissolved upon polarization. Since 317L SS has a higher Mo content, its higher passivity was ascribed to Mo existing as molybdate on the surface and Mo^{5+} species in the biofilm. Consequently, the interaction of SRB with Mo was studied. It was observed that molybdate could be retained on the surfaces of Mo coupons by corrosion products. In the presence of SRB, however, a considerable portion of the molybdate interacted with intermediate sulfur -containing proteins, forming Mo(V)-S complexes and reducing bacterial growth and sulfate reduction. The limited insolubility of the Mo(V)-S complexes in 0.1 M HCl provided a certain protection so that the pitting potential of the SRB-exposed Mo coupons was not considerably decreased. The interaction of the sulfur-containing proteins with Mo also provided mechanistic information about the adhesion of biofilm to Mo-bearing steels. Additionally, the interactions of SRB with other alloying elements, Cr and Ni, were investigated.

  9. Polyphenol biosensor based on laccase immobilized onto silver nanoparticles/multiwalled carbon nanotube/polyaniline gold electrode.

    PubMed

    Rawal, Rachna; Chawla, Sheetal; Pundir, C S

    2011-12-15

    Laccase purified from Ganoderma sp. was immobilized covalently onto electrochemically deposited silver nanoparticles (AgNPs)/carboxylated multiwalled carbon nanotubes (cMWCNT)/polyaniline (PANI) layer on the surface of gold (Au) electrode. A polyphenol biosensor was fabricated using this enzyme electrode (laccase/AgNPs/cMWCNT/PANI/Au electrode) as the working electrode, Ag/AgCl as the reference electrode, and platinum (Pt) wire as the auxiliary electrode connected through a potentiostat. The biosensor showed optimal response at pH 5.5 (0.1 M acetate buffer) and 35°C when operated at a scan rate of 50 mV s(-1). Linear range, response time, and detection limit were 0.1-500 ?M, 6 s, and 0.1 ?M, respectively. The sensor was employed for the determination of total phenolic content in tea, alcoholic beverages, and pharmaceutical formulations. The enzyme electrode was used 200 times over a period of 4 months when stored at 4°C. The biosensor has an advantage over earlier enzyme sensors in that it has no leakage of enzyme during reuse and is unaffected by the external environment due to the protective PANI microenvironment. PMID:21855525

  10. Effects of concentration-dependent elastic modulus on Li-ions diffusion and diffusion-induced stresses in spherical composition-gradient electrodes

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Li, Yong; Zheng, Bailin

    2015-09-01

    The composition-gradient electrode material is considered as one of the most promising materials for lithium-ion batteries because of its excellent electrochemical performance and thermal stability. In this work, the effects of concentration-dependent elastic modulus on Li-ions diffusion and diffusion-induce stress in the composition-gradient electrodes were studied. The coupling equations of elasticity and diffusion under both potentiostatic charging and galvanostatic charging were developed to obtain the distributions of both the Li-ions concentration and the stress. The results indicated that the effects of the concentration-dependent elastic modulus on the Li-ions diffusion and the diffusion-induce stresses are controlled by the lithiation induced stiffening factor in the composition-gradient electrodes: a low stiffening factor at the center and a high stiffening factor at the surface lead to a significant effect, whereas a high stiffening factor at the center and a low stiffening factor at the surface result in a minimal effect. The results in this work provide guidance for the selection of electrode materials.

  11. Effects of concentration-dependent elastic modulus on the diffusion of lithium ions and diffusion induced stress in layered battery electrodes

    NASA Astrophysics Data System (ADS)

    He, Y.-L.; Hu, H. J.; Song, Y.-C.; Guo, Z.-S.; Liu, C.; Zhang, J.-Q.

    2014-02-01

    A stress assisted diffusion model considering concentration-dependent elastic modulus of active material has been established for the multi-layered electrodes of lithium batteries. The physical mechanism for the effect of modulus variation on the Li-ion diffusion and corresponding biaxial stress is well elucidated. Moreover, the analytic solutions of maximum stress in both active layer and collector are respectively derived. It has been found that the modulus stiffening gives rise to the additional stress gradient and enhances Li-ion diffusion, therefore to increase the biaxial stress in the plate electrode. In contrast, modulus softening makes the stress assisted diffusion less significant and the corresponding stresses are reduced. These coupled effects are more significant during potentiostatic charging and galvanostatic charging with high charging rates. Moreover, the maximum stress in the active layer is independent of charging process, but depends upon the elastic modulus variation due to Li-ion insertion. Finally, with increasing thickness ratio between collector and active material, the impacts of concentration dependent modulus on the Li-ion diffusion in active layer decreases, whereas this effect on maximum stress in the current collector increases.

  12. Dithionite/air direct ion liquid fuel cell

    NASA Astrophysics Data System (ADS)

    Noack, Jens; Tübke, Jens; Pinkwart, Karsten

    2015-07-01

    The feasibility of an alkaline S2O42-/air-fuel cell was evaluated at room temperature, using a cell with an anion exchange membrane and a platinum oxygen reduction reaction catalyst. The tests performed were open circuit voltage analysis, linear sweep voltammetry, discharge analysis and electrochemical impedance spectroscopy (EIS) with registration of anode half-cell potential. With 0.85 M Na2S2O4 in 2 M KOH, the cell achieved a maximum power density of 2 mW cm-2, and the open circuit cell voltage was about 0.9 V. In a potentiostatic discharging at 0.2 V cell voltage, an energy efficiency of 12.3% was achieved at an energy density of 8.6 Wh L-1. The low power density was mainly due to the low reaction kinetics of dithionite oxidation at graphite electrodes. The low energy efficiency was mainly caused by a low cathode potential, which probably resulted from mixed potential formation and the low anode kinetics.

  13. Effect of gelling on the impedance parameters of Pb/PbSO 4 electrode in maintenance-free lead-acid batteries

    NASA Astrophysics Data System (ADS)

    Vinod, M. P.; Vijayamohanan, K.

    The impedance parameters of Pb/PbSO 4 electrode in 4.8 M sulfuric acid have been measured potentiostatically under open-circuit conditions over a wide range of frequencies (10 -2 to 10 4 Hz) under both deep-discharged (state-of-charge, SoC=0) and fully charged (SoC=1) conditions. Immobilization of the electrolyte by adding sodium silicate (5 g/l) on the impedance of Pb/PbSO 4 electrode shows significant difference in comparison with the flooded system. Four equivalent circuits have been formulated for overcharged and deep-discharged electrodes in gelled and flooded electrolytes, respectively. Impedance parameters are calculated using a phenomenological model, which indicates that in the case of gelled electrolytes, the electrochemical reactions are mass-transfer controlled, in contrast to the flooded electrolyte cells, where the process is known to be charge-transfer controlled. The study provides a non-destructive investigation of the effect of gelling on the electrical performance of sealed maintenance-free lead-acid batteries.

  14. Synthesis of dendritic silver nanostructures supported by graphene nanosheets and its application for highly sensitive detection of diazepam.

    PubMed

    Majidi, Mir Reza; Ghaderi, Seyran; Asadpour-Zeynali, Karim; Dastangoo, Hossein

    2015-12-01

    In this paper, preparation, characterization and application of a new sensor for fast and simple determination of trace amount of diazepam were described. This sensor is based on Ag nanodendrimers (AgNDs) supported by graphene nanosheets modified glassy carbon electrode (GNs/GCE). The AgNDs were directly electrodeposited on the surface of electrode via potentiostatic method without using any templates, surfactants, or stabilizers. The structure of the synthesized AgNDs/GNs was characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) techniques. The nanodendrimers with tree-like and hierarchical structures have a fascinating structure for fabrication of effective electrocatalysts. The experimental results confirmed that AgNDs/GNs/GC electrode has good electrocatalytic activity toward the reduction of diazepam. A low detection limit of 8.56×10(-8)M and a wide linear detection range of 1.0×10(-7) to 1.0×10(-6)M and 1.0×10(-6) to 20×10(-6)M were achieved via differential pulse voltammetry (DPV). The proposed electrode displayed excellent repeatability and long-term stability and it was satisfactorily used for determination of diazepam in real samples (commercially tablet, injection and human blood plasma) with high recovery. PMID:26354262

  15. Time-domain fitting of battery electrochemical impedance models

    NASA Astrophysics Data System (ADS)

    Alavi, S. M. M.; Birkl, C. R.; Howey, D. A.

    2015-08-01

    Electrochemical impedance spectroscopy (EIS) is an effective technique for diagnosing the behaviour of electrochemical devices such as batteries and fuel cells, usually by fitting data to an equivalent circuit model (ECM). The common approach in the laboratory is to measure the impedance spectrum of a cell in the frequency domain using a single sine sweep signal, then fit the ECM parameters in the frequency domain. This paper focuses instead on estimation of the ECM parameters directly from time-domain data. This may be advantageous for parameter estimation in practical applications such as automotive systems including battery-powered vehicles, where the data may be heavily corrupted by noise. The proposed methodology is based on the simplified refined instrumental variable for continuous-time fractional systems method ('srivcf'), provided by the Crone toolbox [1,2], combined with gradient-based optimisation to estimate the order of the fractional term in the ECM. The approach was tested first on synthetic data and then on real data measured from a 26650 lithium-ion iron phosphate cell with low-cost equipment. The resulting Nyquist plots from the time-domain fitted models match the impedance spectrum closely (much more accurately than when a Randles model is assumed), and the fitted parameters as separately determined through a laboratory potentiostat with frequency domain fitting match to within 13%.

  16. A comparison of the corrosion behaviour and surface characteristics of vacuum-brazed and heat-treated Ti6Al4V alloy.

    PubMed

    Lee, T M; Chang, E; Yang, C Y

    1998-08-01

    The corrosion characteristics of the brazed Ti6Al4V specimens were analysed and compared with respect to the conventionally heat-treated specimens by an electrochemical corrosion test. The object of this research was to explore the potentiality of the brazed titanium for biomaterials. The characteristics of the 1300 degrees C heat-treated and the 970 degrees C brazed specimens, with passivation and sterilization treatment, were evaluated by measurement of corrosion potential, Ecorr, corrosion current densities, Icorr, polarization resistance of the reacted surface films, Rp, in a potentiodynamic test. The experimental results show that the corrosion rates of the heat-treated and the brazed samples are similar at Ecorr, and the value of Ecorr for the brazed sample is noble to the heat-treated samples. The passive current density of the brazed specimen is either lower or higher than the heat-treated specimen, depending on the polarization potential. By Auger electron spectroscopic and high-resolution X-ray photoelectron spectroscopic analysis on specimens from the potentiostatic test, the elements of copper and nickel in the brazing filler were not detected while less alumina was found in the reacted film of the brazed specimens when compared with the heat-treated specimens. The implication of the results is discussed. PMID:15348855

  17. Lab-on-a-Bird: Biophysical Monitoring of Flying Birds

    PubMed Central

    Gumus, Abdurrahman; Lee, Seoho; Ahsan, Syed S.; Karlsson, Kolbeinn; Gabrielson, Richard; Guglielmo, Christopher G.; Winkler, David W.; Erickson, David

    2015-01-01

    The metabolism of birds is finely tuned to their activities and environments, and thus research on avian systems can play an important role in understanding organismal responses to environmental changes. At present, however, the physiological monitoring of bird metabolism is limited by the inability to take real-time measurements of key metabolites during flight. In this study, we present an implantable biosensor system that can be used for continuous monitoring of uric acid levels of birds during various activities including flight. The system consists of a needle-type enzymatic biosensor for the amperometric detection of uric acid in interstitial fluids. A lightweight two-electrode potentiostat system drives the biosensor, reads the corresponding output current and wirelessly transfers the data or records to flash memory. We show how the device can be used to monitor, in real time, the effects of short-term flight and rest cycles on the uric acid levels of pigeons. In addition, we demonstrate that our device has the ability to measure uric acid level increase in homing pigeons while they fly freely. Successful application of the sensor in migratory birds could open up a new way of studying birds in flight which would lead to a better understanding of the ecology and biology of avian movements. PMID:25880904

  18. Microbial Biofilm Voltammetry: Direct Electrochemical Characterization of Catalytic Electrode-Attached Biofilms? †

    PubMed Central

    Marsili, Enrico; Rollefson, Janet B.; Baron, Daniel B.; Hozalski, Raymond M.; Bond, Daniel R.

    2008-01-01

    While electrochemical characterization of enzymes immobilized on electrodes has become common, there is still a need for reliable quantitative methods for study of electron transfer between living cells and conductive surfaces. This work describes growth of thin (<20 ?m) Geobacter sulfurreducens biofilms on polished glassy carbon electrodes, using stirred three-electrode anaerobic bioreactors controlled by potentiostats and nondestructive voltammetry techniques for characterization of viable biofilms. Routine in vivo analysis of electron transfer between bacterial cells and electrodes was performed, providing insight into the main redox-active species participating in electron transfer to electrodes. At low scan rates, cyclic voltammetry revealed catalytic electron transfer between cells and the electrode, similar to what has been observed for pure enzymes attached to electrodes under continuous turnover conditions. Differential pulse voltammetry and electrochemical impedance spectroscopy also revealed features that were consistent with electron transfer being mediated by an adsorbed catalyst. Multiple redox-active species were detected, revealing complexity at the outer surfaces of this bacterium. These techniques provide the basis for cataloging quantifiable, defined electron transfer phenotypes as a function of potential, electrode material, growth phase, and culture conditions and provide a framework for comparisons with other species or communities. PMID:18849456

  19. Comparison of Pt and Pd catalysts for hydrogen pump separation from reformate

    NASA Astrophysics Data System (ADS)

    Wu, Xuemei; Benziger, Jay; He, Gaohong

    2012-11-01

    Hydrogen recovery from CO2/H2 reformate mixtures by selective electrochemical pumping was compared from carbon supported Pt and Pd catalysts. Catalyst coated membranes were prepared by air-brushing a suspension of commercially available 20 wt% Pt/C or 20 wt% Pd/C catalysts and solubilized Nafion in methanol onto Nafion 115 membranes. Electrochemical activity and separation efficiency for the different catalyst layer formulations were evaluated by cyclic voltammetry, polarization and potentiostatic hydrogen pumping. The effective membrane-electrode-assembly (MEA) resistance increased due to dilution of H2 by CO2; the effective MEA resistance was greater for Pd/C catalysts than for Pt/C catalysts. CO2 adsorbed more strongly to Pd catalysts than Pt catalysts reducing the electrochemical active surface area available for hydrogen oxidation/reduction. Pd/C catalysts had an energy efficiency for hydrogen recovery from reformate mixtures approximately 80% that of Pt catalysts. Because Pd is ten times less costly than Pt the results presented here suggest that Pd/C catalysts would be a promising candidate for hydrogen pumps to recover H2 from reformate mixtures.

  20. Corrosion and Fretting Corrosion Studies of Medical Grade CoCrMo Alloy in a Clinically Relevant Simulated Body Fluid Environment

    NASA Astrophysics Data System (ADS)

    Ocran, Emmanuel K.; Guenther, Leah E.; Brandt, Jan-M.; Wyss, Urs; Ojo, Olanrewaju A.

    2015-06-01

    In modular hip implants, fretting corrosion at the head/neck and neck/stem interfaces has been identified as a major cause of early revision in hip implants, particularly those with heads larger than 32 mm. It has been found that the type of fluid used to simulate the fretting corrosion of biomedical materials is crucial for the reliability of laboratory tests. Therefore, to properly understand and effectively design against fretting corrosion damage in modular hips, there is the need to replicate the human body environment as closely as possible during in vitro testing. In this work, corrosion and fretting corrosion behavior of CoCrMo in 0.14 M NaCl, phosphate buffered saline, and in a clinically relevant novel simulated body fluid was studied using a variety of electrochemical characterization techniques and tribological experiments. Electrochemical, spectroscopy and tribo-electrochemical techniques employed include Potentiodynamic polarization, Potentiostatic polarization, Electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, augur electron spectroscopy, inductively coupled plasma mass spectroscopy, and pin-on-disk wear simulation. The presence of phosphate ions in PBS accounted for the higher corrosion rate when compared with 0.14 M NaCl and the clinically relevant novel simulated body fluid. The low corrosion rates and the nature of the protective passive film formed in the clinically relevant simulated body fluid make it suitable for future corrosion and fretting corrosion studies.

  1. Square wave anodic stripping voltammetric determination of Cd²? and Pb²? at bismuth-film electrode modified with electroreduced graphene oxide-supported thiolated thionine.

    PubMed

    Li, Zou; Chen, Li; He, Fang; Bu, Lijuan; Qin, Xiaoli; Xie, Qingji; Yao, Shouzhuo; Tu, Xinman; Luo, Xubiao; Luo, Shenglian

    2014-05-01

    Graphene oxide (GO)-thionine (TH) nanocomposite was prepared by ?-? stacking. The nanocomposite was cast-coated on a glassy carbon electrode (GCE) to prepare an electroreduced GO (ERGO)-TH/GCE, then 2-mercaptoethanesulfonate (MES) was covalently tethered to ERGO-TH by potentiostatic anodization to form an ERGO-TH-MES/GCE. The thiolation reaction was monitored by electrochemical quartz crystal microbalance (EQCM). Square wave anodic stripping voltammetry (SWASV) was used to determine Cd(2+) and Pb(2+) at the ERGO-TH-MES/GCE further modified with Nafion and Bi. Under the optimal conditions, the linear calibration curves for Cd(2+) and Pb(2+) are from 1 to 40 ?g L(-1), with limits of detection (S/N=3) of 0.1 ?g L(-1) for Cd(2+) and 0.05 ?g L(-1) for Pb(2+), respectively. The electrode was used for the simultaneous analysis of Cd(2+) and Pb(2+) in water samples with satisfactory recovery. PMID:24720997

  2. Corrosion inhibitor storage and release property of TiO{sub 2} nanotube powder synthesized by rapid breakdown anodization method

    SciTech Connect

    Arunchandran, C.; Ramya, S.; George, R.P.; Kamachi Mudali, U.

    2013-02-15

    Graphical abstract: Display Omitted Highlights: ? TiO{sub 2} nanotube powders were synthesized by rapid breakdown anodization method. ? Benzotriazole was loaded into the TiO{sub 2} nanotube powders. ? Low pH induced release of benzotriazole from TiO{sub 2} nanotube powders was proved. -- Abstract: Titanium dioxide (TiO{sub 2}) is one of the most studied substances in material science due to its versatile properties and diverse applications. In this study titanium dioxide nanotube powder were synthesized by rapid breakdown anodization (RBA) method. The synthesis involved potentiostatic anodization of titanium foil in 0.1 M HClO{sub 4} electrolyte under an applied voltage of 20 V and rapid stirring. The morphology and the phase of titanium dioxide nanotube powder were studied using field emission scanning electron microscopy, laser Raman spectroscopy and high resolution transmission electron microscopy. Benzotriazole was chosen as model inhibitor to evaluate TiO{sub 2} nanotube powder's corrosion inhibitor loading and releasing properties. The storage and release properties of TiO{sub 2} nanotube powder were studied using UV–visible spectroscopy and thermogravimetric analysis.

  3. Electrochemical Fractionation of Molybdenum Stable Isotopes

    NASA Astrophysics Data System (ADS)

    Crawford, J.; Black, J.; Wasylenki, L.; Gordon, G.; Anbar, A.; Kavner, A.

    2008-12-01

    Stable isotope signatures were measured from Molybdenum (Mo) electrodeposited from aqueous solution. As potential varied from -1.35 V to -2.00 V (relative to Ag/AgCl), fractionation decreases from ?97/95Mo = -1.3 ‰ to -0.9 ‰ (?97/95Mo defined as the difference in the 97Mo/95Mo ratio of deposited Mo relative to aqueous Mo). Natural variations of ?97/95Mo span a range of ~ 3 ‰ [Barling, J. and Anbar, A. D., EPSL. 2004, 217: 315], therefore, charge transfer driven fractionation may be responsible for some of the observed variation in Mo stable isotope geochemistry. Following previous approaches with Fe and Zn [Kavner, A. et al. Geochim. Cosmochim. Acta. 2005, 69: 2971; 2008, 72: 1731], Mo was plated in a three-electrode cell from a neutral to slightly alkaline solution (pH ~ 8.7). Voltage was held constant during electrodeposition using an Autolab Potentiostat. In all experiments, less than 0.5 % of the Mo was deposited, which insures that the plating reservoir remains at an approximately constant isotopic composition. Plated Mo was then recovered in acid, and the isotopic composition of samples and stock solutions were measured using a Thermo Scientific Neptune MC-ICP-MS. These experiments show that the redox process induces an isotopic signature with respect to the starting material, with a trend showing that fractionation decreases as a function of applied voltage.

  4. The Prediction of Long-Term Coating Performance from Short-Term Electrochemical Data. Part 2; Comparison of Electrochemical Data to Field Exposure Results for Coatings on Steel

    NASA Technical Reports Server (NTRS)

    Contu, F.; Taylor, S. R.; Calle, L. M.; Hintze, P. E.; Curran, J. P.; Li, W.

    2009-01-01

    The pace of coatings development is limited by the time required to assess their corrosion protection properties. This study takes a step f orward from Part I in that it correlates the corrosion performance of organic coatings assessed by a series of short-term electrochemical measurement with 18-month beachside exposure results of duplicate pan els. A series of 19 coating systems on A36 steel substrates were test ed in a completely blind study using the damage tolerance test (DTT). In the DTT, a through-film pinhole defect is created, and the electro chemical characteristics of the defect are then monitored over the ne xt 4 to 7 days while immersed in 0.SM NaCl. The open circuit potentia l, anodic potentiostatic polarization tests and electrochemical imped ance spectroscopy were used to study the corrosion behavior of the co ating systems. The beachside exposure tests were conducted at the Ken nedy Space Center according to ASTM D610-01. It was found that for 79 % of the coatings systems examined, the 18 month beachside exposure r esults could be predicted by two independent laboratory tests obtained within 7 days.

  5. An Implantable RFID Sensor Tag toward Continuous Glucose Monitoring.

    PubMed

    Xiao, Zhibin; Tan, Xi; Chen, Xianliang; Chen, Sizheng; Zhang, Zijian; Zhang, Hualei; Wang, Junyu; Huang, Yue; Zhang, Peng; Zheng, Lirong; Min, Hao

    2015-05-01

    This paper presents a wirelessly powered implantable electrochemical sensor tag for continuous blood glucose monitoring. The system is remotely powered by a 13.56-MHz inductive link and utilizes an ISO 15693 radio frequency identification (RFID) standard for communication. This paper provides reliable and accurate measurement for changing glucose level. The sensor tag employs a long-term glucose sensor, a winding ferrite antenna, an RFID front-end, a potentiostat, a 10-bit sigma-delta analog to digital converter, an on-chip temperature sensor, and a digital baseband for protocol processing and control. A high-frequency external reader is used to power, command, and configure the sensor tag. The only off-chip support circuitry required is a tuned antenna and a glucose microsensor. The integrated chip fabricated in SMIC 0.13-?m CMOS process occupies an area of 1.2 mm ×2 mm and consumes 50 ?W. The power sensitivity of the whole system is -4 dBm. The sensor tag achieves a measured glucose range of 0-30 mM with a sensitivity of 0.75 nA/mM. PMID:25823049

  6. Submicron patterned metal hole etching

    DOEpatents

    McCarthy, Anthony M. (Menlo Park, CA); Contolini, Robert J. (Lake Oswego, OR); Liberman, Vladimir (Needham, MA); Morse, Jeffrey (Martinez, CA)

    2000-01-01

    A wet chemical process for etching submicron patterned holes in thin metal layers using electrochemical etching with the aid of a wetting agent. In this process, the processed wafer to be etched is immersed in a wetting agent, such as methanol, for a few seconds prior to inserting the processed wafer into an electrochemical etching setup, with the wafer maintained horizontal during transfer to maintain a film of methanol covering the patterned areas. The electrochemical etching setup includes a tube which seals the edges of the wafer preventing loss of the methanol. An electrolyte composed of 4:1 water: sulfuric is poured into the tube and the electrolyte replaces the wetting agent in the patterned holes. A working electrode is attached to a metal layer of the wafer, with reference and counter electrodes inserted in the electrolyte with all electrodes connected to a potentiostat. A single pulse on the counter electrode, such as a 100 ms pulse at +10.2 volts, is used to excite the electrochemical circuit and perform the etch. The process produces uniform etching of the patterned holes in the metal layers, such as chromium and molybdenum of the wafer without adversely effecting the patterned mask.

  7. Understanding the fundamentals of redox mediators in Li-O2 batteries: a case study on nitroxides.

    PubMed

    Bergner, Benjamin J; Hofmann, Christine; Schürmann, Adrian; Schröder, Daniel; Peppler, Klaus; Schreiner, Peter R; Janek, Jürgen

    2015-11-25

    The development of aprotic lithium-oxygen (Li-O2) batteries suffers from high charging overvoltages. Dissolved redox mediators, like nitroxides, providing increased energy efficiency and longer lifetime are promising tools to overcome this challenge. Since this auspicious concept is still in its infancy, the underlying chemical reactions as well as the impact of the different (electro)chemical parameters are poorly understood. Herein, we derive an electrochemical model for the charging reactions, which is validated by potentiostatic measurements. The model elucidates the impact of the major factors including basic cell parameters and the chemical properties of the redox mediator. The model is applied to the promising class of nitroxides, which is systematically investigated by using derivatives of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), AZADO (2-azaadamantane-N-oxyl), and an azaphenalene based nitroxide. The nitroxides are electrochemically characterized by cyclic voltammetry and their performance as redox mediators is studied in Li-O2 batteries with an ether-based electrolyte. Based on the presented model, the charging profiles of the different nitroxide redox mediators are correlated with their molecular structures. PMID:26563563

  8. Zinc oxide nanostructures for electrochemical cortisol biosensing

    NASA Astrophysics Data System (ADS)

    Vabbina, Phani Kiran; Kaushik, Ajeet; Tracy, Kathryn; Bhansali, Shekhar; Pala, Nezih

    2014-05-01

    In this paper, we report on fabrication of a label free, highly sensitive and selective electrochemical cortisol immunosensors using one dimensional (1D) ZnO nanorods (ZnO-NRs) and two dimensional nanoflakes (ZnO-NFs) as immobilizing matrix. The synthesized ZnO nanostructures (NSs) were characterized using scanning electron microscopy (SEM), selective area diffraction (SAED) and photoluminescence spectra (PL) which showed that both ZnO-NRs and ZnO-NFs are single crystalline and oriented in [0001] direction. Anti-cortisol antibody (Anti-Cab) are used as primary capture antibodies to detect cortisol using electrochemical impedance spectroscopy (EIS). The charge transfer resistance increases linearly with increase in cortisol concentration and exhibits a sensitivity of 3.078 K?. M-1 for ZnO-NRs and 540 ?. M -1 for ZnO-NFs. The developed ZnO-NSs based immunosensor is capable of detecting cortisol at 1 pM. The observed sensing parameters are in physiological range. The developed sensors can be integrated with microfluidic system and miniaturized potentiostat to detect cortisol at point-of-care.

  9. Delayed feedback induced multirhythmicity in the oscillatory electrodissolution of copper.

    PubMed

    Nagy, Timea; Verner, Erika; Gáspár, Vilmos; Kori, Hiroshi; Kiss, István Z

    2015-06-01

    Occurrence of bi- and trirhythmicities (coexistence of two or three stable limit cycles, respectively, with distinctly different periods) has been studied experimentally by applying delayed feedback control to the copper-phosphoric acid electrochemical system oscillating close to a Hopf bifurcation point under potentiostatic condition. The oscillating electrode potential is delayed by ? and the difference between the present and delayed values is fed back to the circuit potential with a feedback gain K. The experiments were performed by determining the period of current oscillations T as a function of (both increasing and decreasing) ? at several fixed values of K. With small delay times, the period exhibits a sinusoidal type dependence on ?. However, with relatively large delays (typically ? ? T) for each feedback gain K, there exists a critical delay ?crit above which birhythmicity emerges. The experiments show that for weak feedback, K?crit is approximately constant. At very large delays, the dynamics becomes even more complex, and trirhythmicity could be observed. Results of numerical simulations based on a general kinetic model for metal electrodissolution were consistent with the experimental observations. The experimental and numerical results are also interpreted by using a phase model; the model parameters can be obtained from experimental data measured at small delay times. Analytical solutions to the phase model quantitatively predict the parameter regions for the appearance of birhythmicity in the experiments, and explain the almost constant value of K?crit for weak feedback. PMID:26117133

  10. Delayed feedback induced multirhythmicity in the oscillatory electrodissolution of copper

    NASA Astrophysics Data System (ADS)

    Nagy, Timea; Verner, Erika; Gáspár, Vilmos; Kori, Hiroshi; Kiss, István Z.

    2015-06-01

    Occurrence of bi- and trirhythmicities (coexistence of two or three stable limit cycles, respectively, with distinctly different periods) has been studied experimentally by applying delayed feedback control to the copper-phosphoric acid electrochemical system oscillating close to a Hopf bifurcation point under potentiostatic condition. The oscillating electrode potential is delayed by ? and the difference between the present and delayed values is fed back to the circuit potential with a feedback gain K. The experiments were performed by determining the period of current oscillations T as a function of (both increasing and decreasing) ? at several fixed values of K. With small delay times, the period exhibits a sinusoidal type dependence on ?. However, with relatively large delays (typically ? ? T) for each feedback gain K, there exists a critical delay ?crit above which birhythmicity emerges. The experiments show that for weak feedback, K?crit is approximately constant. At very large delays, the dynamics becomes even more complex, and trirhythmicity could be observed. Results of numerical simulations based on a general kinetic model for metal electrodissolution were consistent with the experimental observations. The experimental and numerical results are also interpreted by using a phase model; the model parameters can be obtained from experimental data measured at small delay times. Analytical solutions to the phase model quantitatively predict the parameter regions for the appearance of birhythmicity in the experiments, and explain the almost constant value of K?crit for weak feedback.

  11. Electrodeposition of PVA-protected PtCo electrocatalysts for the oxygen reduction reaction in H2SO4

    NASA Astrophysics Data System (ADS)

    Gasparotto, Luiz H. S.; Ciapina, Eduardo G.; Ticianelli, Edson A.; Tremiliosi-Filho, Germano

    2012-01-01

    In this paper we report the electrosynthesis of PVA-protected PtCo films (PVA = poly(vinylalcohol)) and their activities towards the oxygen reduction reaction (ORR). PtCo electrodeposits were potentiostatically obtained in the presence and absence of PVA at distinct potentials. The film morphology and composition were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), which revealed that the use of PVA in the electrodeposition of PtCo films was decisive to achieve better film composition control. Cyclic voltammetry for PVA-protected PtCo films showed that the electrochemical surface area is dependent on the electrodeposition potentials and suggested different adsorption strengths of oxygen-containing species. Films produced in the presence of PVA presented the following activity order towards ORR as a function of the electrodeposition potential (vs. Ag/AgCl): -0.9 V > -0.8 V > -1.0 V > -0.7 V. In contrast, PtCo films electrodeposited in the absence of PVA displayed very similar activities regardless of the electrodeposition potential. The simplicity of the electrodeposition method combined with its effectiveness enabled the production of “model electrodes” for investigating the fundamental aspects of the reactions taking place in the fuel cell cathodes.

  12. Pulse-reverse treatment of carbon nanomaterials for the electrochemical storage of energy

    NASA Astrophysics Data System (ADS)

    Zhylinski, V. V.; Drozdovich, V. B.; Krauklis, A. V.; Zhdanok, S. A.; Zharski, I. M.

    2011-04-01

    The paper dwells upon the investigation of carbon nanomaterials synthesized by an electric arc-method from methane-air mixture under atmospheric pressure in presence of Ni catalyst. These materials may be used for the electrochemical storage of energy. According to the data of transmission electron microscopy the carbon nanomaterials are generally represented by carbon nanotubes with the diameter of 20-80 nm. The pulse-reverse treatment of carbon nanomaterials in concentrated sulphuric electrolytes with addition of fluoride and lithium ions is carried out to increase their discharge capacity in 1 M H2SO4 and 1 M KOH. The properties of carbon nanomaterials are studied using the Brunauer-Emmett-Teller method, chemical energy-dispersive X-ray analysis, potentiostatic charge method of electrochemical saturation of hydrogen and potentiodynamic discharge method. The maximum discharge capacity of 940 C g-1 in 1 M H2SO4 is revealed for CNMs subjected to pulse-reverse treatment in concentrated sulphuric electrolyte containing fluoride and lithium ions.

  13. TiO2 membranes for concurrent photocatalytic organic degradation and corrosion protection

    NASA Astrophysics Data System (ADS)

    Liang, Robert; Hatat-Fraile, Melisa; He, Horatio; Arlos, Maricor; Servos, Mark R.; Zhou, Y. Norman

    2015-10-01

    Organic contaminants and corrosion in water treatment effluents are a current global problem and the development of effective methods to facilitate the removal of organic contaminants and corrosion control strategies are required to mitigate this problem. TiO2 nanomaterials that are exposed to UV light can generate electron-hole pairs, which undergo redox reactions to produce hydroxyl radicals from adsorbed molecular oxygen. They hydroxyl radicals are able to oxidize organic contaminants in water. This same process can be used in conjunction to protect metals from corrosion via cathodic polarization. In this work, TiO2 nanomaterials were synthesized and electrophoretically deposited on conductive substrates to serve as films or membranes. An illuminated TiO2 film on a conductive surface served as the photoanode and assisted in the cathodic protection of stainless steel (SS304) and the degradation of organic pollutants, in this case glucose. This proof-of-concept relied on photoelectrochemical experiments conducted using a potentiostat and a xenon lamp illumination source. The open-circuit potential changes that determine whether a metal is protected from corrosion under illumination was observed; and the electrical characteristics of the TiO2 film or membrane under dark and arc lamp illumination conditions were also analyzed. Furthermore, the effect of organic contaminants on the photocathodic protection mechanism and the oxidation of glucose during this process were explored.

  14. Fatigue crack growth rates in a pressure vessel steel under various conditions of loading and the environment

    NASA Astrophysics Data System (ADS)

    Hicks, P. D.; Robinson, F. P. A.

    1986-10-01

    Corrosion fatigue (CF) tests have been carried out on SA508 Cl 3 pressure vessel steel, in simulated P.W.R. environments. The test variables investigated included air and P.W.R. water environments, frequency variation over the range 1 Hz to 10 Hz, transverse and longitudinal crack growth directions, temperatures of 20 °C and 50 °C, and R-ratios of 0.2 and 0.7. It was found that decreasing the test frequency increased fatigue crack growth rates (FCGR) in P.W.R. environments, P.W.R. environment testing gave enhanced crack growth (vs air tests), FCGRs were greater for cracks growing in the longitudinal direction, slight increases in temperature gave noticeable accelerations in FCGR, and several air tests gave FCGR greater than those predicted by the existing ASME codes. Fractographic evidence indicates that FCGRs were accelerated by a hydrogen embrittlement mechanism. The presence of elongated MnS inclusions aided both mechanical fatigue and hydrogen embrittlement processes, thus producing synergistically fast FCGRs. Both anodic dissolution and hydrogen embrittlement mechanisms have been proposed for the environmental enhancement of crack growth rates. Electrochemical potential measurements and potentiostatic tests have shown that sample isolation of the test specimens from the clevises in the apparatus is not essential during low temperature corrosion fatigue testing.

  15. Quantifying capacity loss due to solid-electrolyte-interphase layer formation on silicon negative electrodes in lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Nadimpalli, Siva P. V.; Sethuraman, Vijay A.; Dalavi, Swapnil; Lucht, Brett; Chon, Michael J.; Shenoy, Vivek B.; Guduru, Pradeep R.

    2012-10-01

    Charge lost per unit surface area of a silicon electrode due to the formation of solid-electrolyte-interphase (SEI) layer during initial lithiation was quantified, and the species that constitute this layer were identified. Coin cells made with Si thin-film electrodes were subjected to a combination of galvanostatic and potentiostatic lithiation and delithiation cycles to accurately measure the capacity lost to SEI layer formation. While the planar geometry of amorphous thin films allows accurate calculation of surface area, creation of additional surface by cracking was prevented by minimizing the thickness of the Si film. The cycled electrodes were analyzed with X-ray photoelectron spectroscopy to characterize the composition of the SEI layer. The charge lost due to SEI formation measured from coin cell experiments was found to be in good agreement with the first-cycle capacity loss during the initial lithiation of a Si(100) crystal with planar geometry. The methodology presented in this work is expected to provide a useful practical tool for battery-material developers in estimating the expected capacity loss due to first cycle SEI layer formation and in choosing an appropriate particle size distribution that balances mechanical integrity and the first cycle capacity loss in large volume expansion electrodes for lithium-ion batteries.

  16. Analysis of gas products from direct utilization of carbon in a solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Siengchum, Tritti; Guzman, Felipe; Chuang, Steven S. C.

    2012-09-01

    The evolution of gases from direct utilization of carbon in a solid oxide fuel cell (C-SOFC) was studied by potentiostatic/galvanostatic discharge of a fuel cell with coconut carbon, a carbonaceous material with low ash and sulfur content. Operation of C-SOFC at 750 °C produced less CO and more CO2 than those predicted by thermodynamic calculation using total Gibbs free energy minimization method. The addition of CO2 to the anode chamber increased CO formation and maximum power density from 0.09 W cm-2 to 0.13 W cm-2, indicating the occurrence of Boudouard reaction (CO2 + C ? 2CO) coupling with CO electrochemical oxidation on the C-SOFC. Analysis of CO and CO2 concentration as a function of current and voltage revealed that electricity was mainly produced from the electrochemical oxidation of carbon at low current density and produced from the electrochemical oxidation of CO at high current density. The results suggest the electrochemical oxidation of solid carbon is more mass transfer limited than electrochemical oxidation of CO.

  17. Lithographically Patterned PEDOT Nanowires for the Detection of Iron(III) with Nanomolar Sensitivity.

    PubMed

    Kindra, Lindsay R; Eggers, Crystin J; Liu, Andrew T; Mendoza, Kelly; Mendoza, Jennifer; Klein Myers, Aviva R; Penner, Reginald M

    2015-11-17

    Arrays of nanowires of an electronically conductive polymeric affinity medium tailored to the detection of Fe(III) are prepared, and their properties for detecting Fe(III) are evaluated. This polymeric affinity medium consists of poly(3,4-ethylenedioxythiophene) (PEDOT) into which an iron chelator, deferoxamine (DFA), has been doped during the polymerization process. PEDOT-DFA nanowires are potentiostatically deposited from a solution containing both EDOT and DFA using lithographically patterned nanowire electrodeposition (LPNE). The through-nanowire electrical resistance of PEDOT-DFA nanowires is measured as a function of the Fe(III) concentration. In parallel with measurements on PEDOT-DFA nanowire arrays, the electrochemical impedance of PEDOT-DFA films is characterized as a function of the Fe(III) concentration and the frequency of the impedance measurement in order to better understand the mechanism of transduction. PEDOT-DFA nanowires detect Fe(III) from 10(-4) to 10(-8) M with a limit of detection of 300 pM (calculated) and 10 nM (measured). PMID:26499338

  18. Electrodeposited ZnO films with high UV emission properties

    SciTech Connect

    Matei, Elena; Enculescu, Ionut

    2011-11-15

    Highlights: {yields} Electrodeposition of ZnO from nitrate baths is investigated. {yields} The influence of process parameters on morphological and optical properties is studied. {yields} Experimental conditions to fabricate ZnO films with high UV emission were found. -- Abstract: We report here our results in the preparation of ZnO films with high UV band to band characteristic luminescence emission by potentiostatic electrodeposition. Zinc nitrate aqueous baths with different concentration and additives were employed for the preparation of the films on platinum substrates. We focused our research in determining how the electrodeposition bath composition, i.e. zinc nitrate concentration and addition of KCl or polyvinyl pyrolidone and applied overpotential influence the morphological and optical properties of the oxide films. Scanning electron microscopy was employed for characterizing the films in terms of morphology. Optical reflection, photoluminescence spectroscopy and cathodoluminescence were used for determining the optical characteristics of the samples. The morphology of the deposit varies from hexagonal prisms to platelets as a function of the deposition rate. This experimental parameter also influences the luminescence properties. We found that at low deposition rates high UV luminescent material is obtained.

  19. Optical properties of electrochemically synthesized polypyrrole thin films: the electrolyte effect

    NASA Astrophysics Data System (ADS)

    Thombare, J. V.; Shinde, S. K.; Lohar, G. M.; Chougale, U. M.; Dhasade, S. S.; Dhaygude, H. D.; Relekar, B. P.; Fulari, V. J.

    2014-06-01

    Polypyrrole thin films are prepared by the potentiostatic mode of electrodeposition at +0:7 V versus a saturated calomel electrode (SCE). The polypyrrole films are prepared in the presence of different electrolytes such as: p-toluene sulphonic acid (PTS), oxalic acid and H2SO4. The prepared films are characterized by UV—vis absorption spectroscopy and normal reflectance measurements. The electrochemically synthesized films are semiconductor in nature. The band gap energy of polypyrrole thin films is found to be 1.95, 1.92 and 1.79 eV for H2SO4, oxalic acid and p-toluene sulphonic acid, respectively. The normal reflectance spectroscopy of polypyrrole films shows that the maximum reflectance is in the presence of p-toluene sulphonic acid; this is may be due to a more distinct microstructure than the others. The optical constants such as the extinction coefficient, refractive index, optical conductivity, etc. are calculated and studied with various electrolytes.

  20. Photoelectrocatalytic oxidation of glucose at a ruthenium complex modified titanium dioxide electrode promoted by uric acid and ascorbic acid for photoelectrochemical fuel cells

    NASA Astrophysics Data System (ADS)

    Lu, Shuo-Jian; Ji, Shi-Bo; Liu, Jun-Chen; Li, Hong; Li, Wei-Shan

    2015-01-01

    The simultaneous presence of uric acid (UA) and ascorbic acid (AA) is first found to largely promote the photoelectrocatalytic oxidation of glucose (GLU) at an indium-tin oxide (ITO) or TiO2 nanoparticles/ITO electrode modified with [Ru(tatp)3]2+ (tatp = 1,4,8,9-tetra-aza-triphenylene) possessing good redox activity and nanoparticle size distribution. A well-defined electrocatalytic peak for GLU oxidation is shown at 0.265 V (vs. SCE) under approximate physiological conditions upon incorporation of UA and AA. The [Ru(tatp)3]2+/ITO electrode exhibits attractive amperometric oxidation responses towards GLU, UA and AA, while controlled potentiostatically at 0.3 V, 0.7 V and 1.0 V, respectively, indicating high sensitivity and excellent reproducibility. On basis of the photoelectrocatalysis of [Ru(tatp)3]2+/TiO2/ITO anode, a GLU concentration-dependent photoelectrochemical fuel cell vs. SCE is elaborately assembled. The proposed free-enzyme photoelectrochemical fuel cell employing 0.1 M GLU associated with 0.01 M UA and 0.01 M AA as fuel shows open-circuit photovoltage of 0.608 V, short-circuit photocurrent density of 124.5 ?A cm-2 and maximum power density of 21.75 ?W cm-2 at 0.455 V, fill factor of 0.32 and photoenergy conversion efficiency of 36.65%, respectively.

  1. Synthesis of dendritic silver nanostructures supported by graphene nanosheets and its application for highly sensitive detection of diazepam

    PubMed Central

    Majidi, Mir Reza; Ghaderi, Seyran; Asadpour-Zeynali, Karim; Dastangoo, Hossein

    2015-01-01

    In this paper, preparation, characterization and application of a new sensor for fast and simple determination of trace amount of diazepam were described. This sensor is based on Ag nanodendrimers (AgNDs) supported by graphene nanosheets modified glassy carbon electrode (GNs/GCE). The AgNDs were directly electrodeposited on the surface of electrode via potentiostatic method without using any templates, surfactants, or stabilizers. The structure of the synthesized AgNDs/GNs was characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) techniques. The nanodendrimers with tree-like and hierarchical structures have a fascinating structure for fabrication of effective electrocatalysts. The experimental results confirmed that AgNDs/GNs/GC electrode has good electrocatalytic activity toward the reduction of diazepam. A low detection limit of 8.56 × 10? 8 M and a wide linear detection range of 1.0 × 10? 7 to 1.0 × 10? 6 M and 1.0 × 10? 6 to 20 × 10? 6 M were achieved via differential pulse voltammetry (DPV). The proposed electrode displayed excellent repeatability and long-term stability and it was satisfactorily used for determination of diazepam in real samples (commercially tablet, injection and human blood plasma) with high recovery. PMID:26354262

  2. Bioelectrocatalytic application of titania nanotube array for molecule detection.

    PubMed

    Xie, Yibing; Zhou, Limin; Huang, Haitao

    2007-06-15

    A bioelectrocatalysis system based on titania nanotube electrode has been developed for the quantitative detection application. Highly ordered titania nanotube array with inner diameter of 60 nm and total length of 540 nm was formed by anodizing titanium foils. The functionalization modification was achieved by embedding glucose oxidases inside tubule channels and electropolymerizing pyrrole for interfacial immobilization. Morphology and microstructure characterization, electrochemical properties and bioelectrocatalytic reactivities of this composite were fully investigated. The direct detection of hydrogen peroxide by electrocatalytic reduction reaction was fulfilled on pure titania nanotube array with a detection limit up to 2.0 x 10(-4)mM. A biosensor based on the glucose oxidase-titania/titanium electrode was constructed for amperometric detection and quantitative determination of glucose in a phosphate buffer solution (pH 6.8) under a potentiostatic condition (-0.4V versus SCE). The resulting glucose biosensor showed an excellent performance with a response time below 5.6s and a detection limit of 2.0 x 10(-3)mM. The corresponding detection sensitivity was 45.5 microA mM(-1)cm(-2). A good operational reliability was also achieved with relative standard deviations below 3.0%. This novel biosensor exhibited quite high response sensitivity and low detection limit for potential applications. PMID:17188856

  3. Rapid, Single-Cell Electrochemical Detection of Mycobacterium tuberculosis Using Colloidal Gold Nanoparticles.

    PubMed

    Ng, Benjamin Y C; Xiao, Wei; West, Nicholas P; Wee, Eugene J H; Wang, Yuling; Trau, Matt

    2015-10-20

    Tuberculosis (TB) remains a global health threat, with over a third of the world population suffering from the disease, and 1.5 million deaths due to the disease in 2013 alone. Despite significant advances in TB detection strategies in recent years, a bigger push toward detecting TB in the shortest and easiest way possible at the point-of-care (POC) is still in demand. To this end, we have designed a simple yet rapid and sensitive bioassay that detects Mtb DNA electrochemically using colloidal gold nanoparticles. This assay couples rapid isothermal amplification of target DNA that is specific to Mtb with gold nanoparticle electrochemistry on disposable screen printed carbon electrodes. The assay is capable of detecting a positive differential pulse voltammetry (DPV) response from as low as 1 CFU of Mtb bacilli DNA input material, having shown its exquisite sensitivity over a conventional gel based readout. The translation of our assay onto a portable potentiostat was also demonstrated, with promising results. We believe that our assay has significant potential for translation into broader bioassay applications or development as a POC diagnostic tool. PMID:26382883

  4. Stress corrosion cracking of alpha-beta brass in distilled water and sodium sulfate solutions

    NASA Astrophysics Data System (ADS)

    Hintz, M. B.; Nettleton, L. J.; Heldt, L. A.

    1985-05-01

    Specimens of a Cu-42 wt pct Zn alpha-beta alloy have been tested to failure in uniaxial tension at constant extension rates in a variety of environments. Testing in distilled H25O and 1 N Na2SO4 solutions over a range of potential-pH conditions results in large ductility losses and an interfacial + transgranular cleavage-like fracture mode. The electrochemical potentials of the specimens have been monitored and/or controlled during testing, and a shift to significantly more active open circuit potentials on straining is observed in environments which cause large ductility losses. The appearance of the transgranular beta fracture surfaces and the effects of potentiostatic polarization on the observed SCC behavior are similar to those seen for alpha phase Cu-Zn, which suggests that SCC of alpha and beta phase Cu-Zn are mechanistically similar. It is concluded that the observed behavior is most consistent with an SCC mechanism based upon the adsorption of a damaging species from the environment.

  5. Tribocorrosion mechanisms of Ti6Al4V biomedical alloys in artificial saliva with different pHs

    NASA Astrophysics Data System (ADS)

    Licausi, M. P.; Igual Muñoz, A.; Amigó Borrás, V.

    2013-10-01

    Titanium and its alloys has been widely used for the design of dental implants because of its biocompatibility, mechanical properties and corrosion resistance. The powder-metallurgy process is a promising alternative to the casting fabrication process of titanium alloys for bone implants design as the porous structure mimics the natural bone structures, allowing the bone to grow into the pores which results in a better fixation of the artificial implant. However, under in vivo conditions the implants are subjected to tribocorrosion phenomenon, which consists in the degradation mechanisms due to the combined effect of wear and corrosion. The aim of this study is to evaluate the tribocorrosion behaviour of cast and sintered Ti6Al4V biomedical alloy for dental applications using the cast material as reference. Titanium samples were tested in artificial human saliva solution with three different pHs (3, 6, 9) and in an acidic saliva with 1000 ppm fluorides (AS-3-1000F-) by different electrochemical techniques (potentiodynamic curves, potentiostatic tests and tribo-electrochemical tests). Cast and sintered titanium alloys exhibit the same tribocorrosion mechanisms in AS independently of the pH which consists in plastic deformation with passive dissolution, but the addition of fluorides to the acidified solution changes the degradation mechanism towards active dissolution of the titanium alloys.

  6. Facile synthesis of polypyrrole functionalized nickel foam with catalytic activity comparable to Pt for the poly-generation of hydrogen and electricity

    NASA Astrophysics Data System (ADS)

    Tang, Tiantian; Li, Kan; Shen, Zhemin; Sun, Tonghua; Wang, Yalin; Jia, Jinping

    2016-01-01

    Polypyrrole functionalized nickel foam is facilely prepared through the potentiostatic electrodeposition. The PPy-functionalized Ni foam functions as a hydrogen-evolution cathode in a rotating disk photocatalytic fuel cell, in which hydrogen energy and electric power are generated by consuming organic wastes. The PPy-functionalized Ni foam cathode exhibits stable catalytic activities after thirteen continuous runs. Compared with net or plate structure, the Ni foam with a unique three-dimensional reticulate structure is conducive to the electrodeposition of PPy. Compared with Pt-group electrode, PPy-coated Ni foam shows a satisfactory catalytic performance for the H2 evolution. The combination of PPy and Ni forms a synergistic effect for the rapid trapping and removal of proton from solution and the catalytic reduction of proton to hydrogen. The PPy-functionalized Ni foam could be applied in photocatalytic and photoelectrochemical generation of H2. In all, we report a low cost, high efficient and earth abundant PPy-functionalized Ni foam with a satisfactory catalytic activities comparable to Pt for the practical application of poly-generation of hydrogen and electricity.

  7. Electrochemical behavior of silver sulfide

    SciTech Connect

    Drouven, B.U.E.

    1982-01-01

    The electrochemical behavior of silver sulfide in sulfuric acid as well as in nitric acid was studied using electrodes made from synthetic silver sulfide. The primary techniques used were potentiostatic, potentiodynamic, galvanostatic and corrosion cell experiments. The cathodic reaction of silver sulfide produces silver and hydrogen sulfide. This reaction mechanism is a sequential two step charge transfer involving a single electron in each step. Silver ions are produced from silver sulfide upon applying an anodic potential. The dissolution rate of silver sulfide can be so high that the formation of silver sulfate occurs which partially covers the silver sulfide surface and inhibits a further rate increase. The sulfur from the silver sulfide will be oxidized at low overpotentials to elemental sulfur; at high overpotentials, the oxidation to sulfate or bisulfate is observed. The results suggest that the catalysis of chalcopyrite by the addition of silver ions is caused by the formation and subsequent dissolution of silver sulfide leaving a porous layer behind. The understanding of the reaction mechanism of silver sulfide dissolution and its optimization will significantly improve the economic evaluation of industrial processes using the catalyzed leaching of chalcopyrite. The present knowledge of the catalysis indicates that other ions may be substituted for silver ions which would increase the feasibility of hydrometallurgical processes.

  8. Synthesis of single-walled carbon nanotubes and graphene composite in arc for ultracapacitors

    NASA Astrophysics Data System (ADS)

    Li, Jian; Cheng, Xiaoqian; Shashurin, Alexey; Keidar, Michael

    2012-10-01

    Arc discharge supported by the erosion of graphite anode is considered as one of the most practical and efficient methods to synthesize various carbon nanostructures such as single-walled carbon nanotubes (SWCNT) and graphene with minimal defects and large yield due to the relatively high synthesis temperature and eco-friendly growth mechanism. By introducing a non-uniform magnetic field during synthesis process, large-scale graphene and high-purity SWCNT can be obtained in one step. In addition, the yield of graphene can be controlled by external parameters, such as the type and pressure of buffer gas, the temperature of substrate, and so on. Possessing the properties of highly accessible surface area and good electrical conductivity, the composite of graphene and SWCNT are promising nanomaterials for the electrodes of ultracapacitor, which can store electric energy with high level of capacitance. In this work, we fabricated electrodes of ultracapacitor based on nanostructures composite by wire-wound rod coating method, characterized them by SEM, EDX and Raman spectroscopy, and tested the performance by a potentiostat/galvanostat.

  9. Polyion selective polymeric membrane-based pulstrode as a detector in flow-injection analysis.

    PubMed

    Bell-Vlasov, Andrea K; Zajda, Joanna; Eldourghamy, Ayman; Malinowska, Elzbieta; Meyerhoff, Mark E

    2014-04-15

    A method for the detection of polyions using fully reversible polyion selective polymeric membrane type pulstrodes as detectors in a flow-injection analysis (FIA) system is examined. The detection electrode consists of a plasticized polymeric membrane doped with 10 wt % of tridodecylmethylammonium-dinonylnaphthalene sulfonate (TDMA/DNNS) ion-exchanger salt. The pulse sequence used involves a short (1 s) galvanostatic pulse, an open-circuit pulse (0.5 s) during which the EMF of the cell is measured, and a longer (15 s) potentiostatic pulse to return the membrane to its original chemical composition. It is shown that total pulse sequence times can be optimized to yield reproducible real-time detection of injected samples of protamine and heparin at up to 20 samples/h. Further, it is shown that the same membrane detector can be employed for FIA detection of both polycations at levels ?10 ?g/mL and polyanions at levels of ?40 ?g/mL by changing the direction of the galvanostatic pulse. The methodology described may also be applicable in the detection of polyionic species at low levels in other flowing configurations, such as in liquid chromatography and capillary electrophoresis. PMID:24650129

  10. Polyion Selective Polymeric Membrane-Based Pulstrode as a Detector in Flow-Injection Analysis

    PubMed Central

    2015-01-01

    A method for the detection of polyions using fully reversible polyion selective polymeric membrane type pulstrodes as detectors in a flow-injection analysis (FIA) system is examined. The detection electrode consists of a plasticized polymeric membrane doped with 10 wt % of tridodecylmethylammonium-dinonylnaphthalene sulfonate (TDMA/DNNS) ion-exchanger salt. The pulse sequence used involves a short (1 s) galvanostatic pulse, an open-circuit pulse (0.5 s) during which the EMF of the cell is measured, and a longer (15 s) potentiostatic pulse to return the membrane to its original chemical composition. It is shown that total pulse sequence times can be optimized to yield reproducible real-time detection of injected samples of protamine and heparin at up to 20 samples/h. Further, it is shown that the same membrane detector can be employed for FIA detection of both polycations at levels ?10 ?g/mL and polyanions at levels of ?40 ?g/mL by changing the direction of the galvanostatic pulse. The methodology described may also be applicable in the detection of polyionic species at low levels in other flowing configurations, such as in liquid chromatography and capillary electrophoresis. PMID:24650129

  11. Electrochemical Polishing Applications and EIS of a Vitamin B{sub 4}-Based Ionic Liquid

    SciTech Connect

    Wixtrom, Alex I.; Buhler, Jessica E.; Reece, Charles E.; Abdel-Fattah, Tarek M.

    2013-01-01

    Modern particle accelerators require minimal interior surface roughness for Niobium superconducting radio frequency (SRF) cavities. Polishing of the Nb is currently achieved via electrochemical polishing with concentrated mixtures of sulfuric and hydrofluoric acids. This acid-based approach is effective at reducing the surface roughness to acceptable levels for SRF use, but due to acid-related hazards and extra costs (including safe disposal of used polishing solutions), an acid-free method would be preferable. This study focuses on an alternative electrochemical polishing method for Nb, using a novel ionic liquid solution containing choline chloride, also known as Vitamin B{sub 4} (VB{sub 4}). Potentiostatic electrochemical impedance spectroscopy (EIS) was also performed on the VB4-based system. Nb polished using the VB4-based method was found to have a final surface roughness comparable to that achieved via the acid-based method, as assessed by atomic force microscopy (AFM). These findings indicate that acid-free VB{sub 4}-based electrochemical polishing of Nb represents a promising replacement for acid-based methods of SRF cavity preparation.

  12. Study on Electro-polymerization Nano-micro Wiring System Imitating Axonal Growth of Artificial Neurons towards Machine Learning

    NASA Astrophysics Data System (ADS)

    Dang, Nguyen Tuan; Akai-Kasada, Megumi; Asai, Tetsuya; Saito, Akira; Kuwahara, Yuji; Hokkaido University Collaboration

    2015-03-01

    Machine learning using the artificial neuron network research is supposed to be the best way to understand how the human brain trains itself to process information. In this study, we have successfully developed the programs using supervised machine learning algorithm. However, these supervised learning processes for the neuron network required the very strong computing configuration. Derivation from the necessity of increasing in computing ability and in reduction of power consumption, accelerator circuits become critical. To develop such accelerator circuits using supervised machine learning algorithm, conducting polymer micro/nanowires growing process was realized and applied as a synaptic weigh controller. In this work, high conductivity Polypyrrole (PPy) and Poly (3, 4 - ethylenedioxythiophene) PEDOT wires were potentiostatically grown crosslinking the designated electrodes, which were prefabricated by lithography, when appropriate square wave AC voltage and appropriate frequency were applied. Micro/nanowire growing process emulated the neurotransmitter release process of synapses inside a biological neuron and wire's resistance variation during the growing process was preferred to as the variation of synaptic weigh in machine learning algorithm. In a cooperation with Graduate School of Information Science and Technology, Hokkaido University.

  13. Ultrathin, Stretchable, Multiplexing pH Sensor Arrays on Biomedical Devices With Demonstrations on Rabbit and Human Hearts Undergoing Ischemia

    PubMed Central

    Chung, Hyun-Joong; Sulkin, Matthew S.; Kim, Jong-Seon; Goudeseune, Camille; Chao, Hsin-Yun; Song, Joseph W.; Yang, Sang Yoon; Hsu, Yung-Yu; Ghaffari, Roozbeh

    2014-01-01

    Stable pH is an established biomarker of health, relevant to all tissues of the body, including the heart. Clinical monitoring of pH in a practical manner, with high spatiotemporal resolution, is particularly difficult in organs such as the heart due to its soft mechanics, curvilinear geometry, heterogeneous surfaces and continuous, complex rhythmic motion. The results presented here illustrate that advanced strategies in materials assembly and electrochemical growth can yield interconnected arrays of miniaturized IrOx pH sensors encapsulated in thin, low-modulus elastomers to yield conformal monitoring systems capable of non-invasive measurements on the surface of the beating heart. A thirty channel custom data acquisition system enables spatiotemporal pH mapping with a single potentiostat. In-vitro testing reveals super-Nernstian sensitivity with excellent uniformity (69.9 ± 2.2 mV/pH), linear response to temperature (?1.6 mV/°C), and minimal influence of extracellular ions (< 3.5 mV). Device examples include sensor arrays on balloon catheters and on skin-like stretchable membranes. Real-time measurement of pH on the surfaces of explanted rabbit hearts and a donated human heart during protocols of ischemia-reperfusion illustrate some of the capabilities. Envisioned applications range from devices for biological research, to surgical tools and long-term implants. PMID:23868871

  14. Enhanced durability of a proton conducting oxide fuel cell with a purified yttrium-doped barium zirconate-cerate electrolyte

    NASA Astrophysics Data System (ADS)

    Hakim, Muhammad; Yoo, Chung-Yul; Joo, Jong Hoon; Yu, Ji Haeng

    2015-03-01

    The aim of this study is to investigate the effect of yttrium-doped barium zirconate-cerate (BaZr0.3Ce0.5Y0.2O3-?, BZCY) refinement on cell stability under operational fuel cell conditions. For this purpose, anode-supported cells, comprised of a nickel oxide (NiO)-BZCY anode, a BZCY electrolyte, and a BZCY-La0.6Sr0.4Co0.2Fe0.8O3-? composite cathode are successfully prepared with refined or as-calcined BZCY powder. The long-term fuel cell performance is evaluated under a potentiostatic measurement at 600 °C. The cell with the refined BZCY electrolyte shows a modest power density of 47 mW cm-2 at a 600 °C operating temperature over 480 h without any significant performance loss, whereas the cell with the as-calcined BZCY electrolyte displays a rapid degradation of cell performance over 110 h. A post-testing analysis of the cell with the refined BZCY does not reveal any evidence of delamination resulting from electrolyte surface decomposition. These results demonstrate that the refinement process significantly enhances the chemical stability of BZCY-based proton conducting fuel cells, which produce a high content of water vapor on the cathode side.

  15. Discrete electrochemical transients of aluminium alloys generated by slurry jet impingement

    NASA Astrophysics Data System (ADS)

    Akiyama, Eiji; Stratmann, Martin; Hassel, Achim Walter

    2006-08-01

    Slurry impingement is a type of tribocorrosion resulting from simultaneous mechanical and electrochemical surface degradation. In order to understand the elementary process of slurry impingement and the effect of mechanical damage on passive films, electrochemical responses associated with passive film breakdown by particle impacts and following repassivation were measured during slurry impingement on Al and Al-1wt%Si alloy microelectrodes. Measurements were made using a slurry jet system which consists of a pump, a microelectrode, a potentiostat suited for measurements of fast transients of small currents and a high frequency data acquisition system. Current transients corresponding to separated single particle impacts have been successfully measured. The current transient sharply rises and gradually decays following a high field model of oxide growth. It is shown that pure Al repassivates faster after particle impact than the Al-1 wt% Si alloy. This type of erodent particle had an influence on the apparent repassivation rate of these electrodes, and both Al and Al-1 wt% Si alloy showed slower current decay after the impact of angular SiC particle than after the impact of spheroidal zirconia particle. The SiC particles made deep scars and scratches, and the zirconia particles made shallow depressions.

  16. Stress-corrosion behavior of aluminum-lithium alloys in aqueous salt environments

    NASA Technical Reports Server (NTRS)

    Pizzo, P. P.; Galvin, R. P.; Nelson, H. G.

    1984-01-01

    The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg; two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

  17. Phosphate Detection through a Cost-Effective Carbon Black Nanoparticle-Modified Screen-Printed Electrode Embedded in a Continuous Flow System.

    PubMed

    Talarico, Daria; Cinti, Stefano; Arduini, Fabiana; Amine, Aziz; Moscone, Danila; Palleschi, Giuseppe

    2015-07-01

    An automatable flow system for the continuous and long-term monitoring of the phosphate level has been developed using an amperometric detection method based on the use of a miniaturized sensor. This method is based on the monitoring of an electroactive complex obtained by the reaction between phosphate and molybdate that is consequently reduced at the electrode surface. The use of a screen-printed electrode modified with carbon black nanoparticles (CBNPs) leads to the quantification of the complex at low potential, because CBNPs are capable of electrocatalitically enhancing the phosphomolybdate complex reduction at +125 mV versus Ag/AgCl without fouling problems. The developed system also incorporates reagents and waste storage and is connected to a portable potentiostat for rapid detection and quantification of phosphate. Main analytical parameters, such as working potential, reagent concentration, type of cell, and flow rate, were evaluated and optimized. This system was characterized by a low detection limit (6 ?M). Interference studies were carried out. Good recovery percentages comprised between 89 and 131.5% were achieved in different water sources, highlighting its suitability for field measurements. PMID:26066782

  18. Fabrication of CIGS Films by Electrodeposition Method for Photovoltaic Cells

    NASA Astrophysics Data System (ADS)

    Lee, Hyunju; Yoon, Hyukjoo; Ji, Changwook; Lee, Dongyun; Lee, Jae-Ho; Yun, Jae-Ho; Kim, Yangdo

    2012-12-01

    Cu(InGa)Se2 (CIGS) thin films were fabricated by electrochemical deposition in a single bath containing Cu, In, Ga, and Se ions. The electrolyte was prepared by dissolving CuCl2, InCl3, GaCl3, H2SeO3, and LiCl in deionized water. The potentiostatic deposition process was achieved by applying a voltage ranging from -0.5 V to -0.8 V versus Ag/AgCl. The effects of different chemical bath concentrations on the film composition and morphology were investigated. Stoichiometric CIGS film composition could be achieved by controlling the chemical compositions of the bath and the voltage. Gelatin was added to the solution to improve the surface and microstructures of the CIGS film. The as-deposited films were annealed at 500°C in Ar atmosphere for crystallization. The structural, morphological, and compositional properties of the CIGS thin films before and after annealing were examined by x-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. This study showed that the composition of the CIGS films is dependent on the bath concentration, whereas the applied potential had relatively less effect on the CIGS film composition. In addition, the use of gelatin helped in the fabrication of crack-free CIGS thin films with greatly improved surface morphology.

  19. Batch-injection analysis with amperometric detection of the DPPH radical for evaluation of antioxidant capacity.

    PubMed

    Oliveira, Gracy K F; Tormin, Thiago F; Sousa, Raquel M F; de Oliveira, Alberto; de Morais, Sérgio A L; Richter, Eduardo M; Munoz, Rodrigo A A

    2016-02-01

    This work proposes the application of batch-injection analysis with amperometric detection to determine the antioxidant capacity of real samples based on the measurement of DPPH radical consumption. The efficient concentration or EC50 value corresponds to the concentration of sample or standard required to scavenge 50% DPPH radicals. For the accurate determination of EC50, samples were incubated with DPPH radical for 1h because many polyphenolic compounds typically found in plants and responsible for the antioxidant activity exhibit slow kinetics. The BIA system with amperometric detection using a glassy-carbon electrode presented high precision (RSD = 0.7%, n = 12), low detection limit (1 ?mol L(-1)) and selective detection of DPPH (free of interferences from antioxidants). These contributed to low detection limits for the antioxidant (0.015 and 0.19 ?mol L(-1) for gallic acid and butylated hydroxytoluene, respectively). Moreover, BIA methods show great promise for portable analysis because battery-powered instrumentation (electronic micropipette and potentiostats) is commercially available. PMID:26304399

  20. Using anodic aluminum oxide templates and electrochemical method to deposit BiSbTe-based thermoelectric nanowires

    NASA Astrophysics Data System (ADS)

    Kuo, Hsin-Hui; Kuo, Chin-Guo; Yen, Chia-Ying; Yang, Cheng-Fu

    2014-02-01

    In this study, the cyclic voltammetry method was first used to find the reduced voltages and anodic peaks of Bi3+, Sb3+, and Te4+ ions as the judgments for the growth of the (Bi,Sb)2 - x Te3 + x -based materials. Ethylene glycol (C2H6O2) was used as a solvent, and 0.3 M potassium iodide (KI) was used to improve the conductivity of the solution. Two different electrolyte formulas were first used: (a) 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 and (b) 0.015 M Bi(NO3)3-5H2O, 0.005 M SbCl3, and 0.0075 M TeCl4. The potentiostatic deposition process was first used to find the effect of reduced voltage on the variation of compositions of the (Bi,Sb)2 - x Te3 + x -based materials. After finding the better reduced voltage, 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 were used as the electrolyte formula. The pulse deposition process was successfully used to control the composition of the (Bi,Sb)2 - x Te3 + x -based materials and grow the nanowires in anodic aluminum oxide (AAO) templates.

  1. Lab-on-a-bird: biophysical monitoring of flying birds.

    PubMed

    Gumus, Abdurrahman; Lee, Seoho; Ahsan, Syed S; Karlsson, Kolbeinn; Gabrielson, Richard; Guglielmo, Christopher G; Winkler, David W; Erickson, David

    2015-01-01

    The metabolism of birds is finely tuned to their activities and environments, and thus research on avian systems can play an important role in understanding organismal responses to environmental changes. At present, however, the physiological monitoring of bird metabolism is limited by the inability to take real-time measurements of key metabolites during flight. In this study, we present an implantable biosensor system that can be used for continuous monitoring of uric acid levels of birds during various activities including flight. The system consists of a needle-type enzymatic biosensor for the amperometric detection of uric acid in interstitial fluids. A lightweight two-electrode potentiostat system drives the biosensor, reads the corresponding output current and wirelessly transfers the data or records to flash memory. We show how the device can be used to monitor, in real time, the effects of short-term flight and rest cycles on the uric acid levels of pigeons. In addition, we demonstrate that our device has the ability to measure uric acid level increase in homing pigeons while they fly freely. Successful application of the sensor in migratory birds could open up a new way of studying birds in flight which would lead to a better understanding of the ecology and biology of avian movements. PMID:25880904

  2. Electrochemical nucleophilic synthesis of di-tert-butyl-(4-[18F]fluoro-1,2-phenylene)-dicarbonate.

    PubMed

    He, Qinggang; Wang, Ying; Alfeazi, Ines; Sadeghi, Saman

    2014-09-01

    An electrochemical method with the ability to conduct (18)F-fluorination of aromatic molecules through direct nucleophilic fluorination of cationic intermediates is presented in this paper. The reaction was performed on a remote-controlled automatic platform. Nucleophilic electrochemical fluorination of tert-butyloxycarbonyl (Boc) protected catechol, an intermediate model molecule for the positron emission tomography (PET) probe (3,4-dihydroxy-6-[(18)F]fluoro-L-phenylalanine), was performed. Fluorination was achieved under potentiostatic anodic oxidation in acetonitrile containing Et3N·3HF and other supporting electrolytes. Radiofluorination efficiency was influenced by a number of variables, including the concentration of the precursor, concentration of Et3N·3HF, type of supporting electrolyte, temperature and time, as well as applied potentials. Radio-fluorination efficiency of 10.4±0.6% (n=4) and specific activity of up to 43GBq/mmol was obtained after 1h electrolysis of 0.1M of 4-tert-butyl-diboc-catechol in the acetonitrile solution of Et3N·3HF (0.033M) and NBu4PF6 (0.05M). Density functional theory (DFT) was employed to explain the tert-butyl functional group facilitation of electrochemical oxidation and subsequent fluorination. PMID:25000498

  3. Amperometric determination of acetylcholine-A neurotransmitter, by chitosan/gold-coated ferric oxide nanoparticles modified gold electrode.

    PubMed

    Chauhan, Nidhi; Pundir, C S

    2014-11-15

    An amperometric acetylcholine biosensor was constructed by co-immobilizing covalently, a mixture of acetylcholinesterase (AChE) and choline oxidase (ChO) onto nanocomposite of chitosan (CHIT)/gold-coated ferric oxide nanoparticles (Fe@AuNPs) electrodeposited onto surface of a Au electrode and using it as a working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode connected through potentiostat. The biosensor is based on electrochemical measurement of H2O2 generated from oxidation of choline by immobilized ChO, which in turn is produced from hydrolysis of acetylcholine by immobilized AChE. The biosensor exhibited optimum response within 3s at +0.2V, pH 7.0 and 30°C. The enzyme electrode had a linear working range of 0.005-400 µM, with a detection limit of 0.005 µM for acetylcholine. The biosensor measured plasma acetylcholine in apparently healthy and persons suffering from Alzheimer's disease. The enzyme electrode was unaffected by a number of serum substances but lost 50% of its initial activity after its 100 uses over a period of 3 months, when stored at 4°C. PMID:24836212

  4. A 1000-cell SOFC reactor for domestic cogeneration

    NASA Astrophysics Data System (ADS)

    Alston, T.; Kendall, K.; Palin, M.; Prica, M.; Windibank, P.

    A cogeneration system was built using 1000 cells with the intention of supplying 30 kW of hot water and 500 W of power. The basis of the cogenerator was the small tubular SOFC design. 8Y zirconia was mixed into a plastic paste and extruded to form thin-walled tubes. The process produced a zirconia material with high strength and good electrical properties. After drying and firing to full density, electrodes were coated onto the inner and outer surfaces of the electrolyte, then sintered. Current collecting wires were wound around the tubular cells and the tubes were assembled into a reactor. Either hydrogen or a premix of natural gas and air was fed through the tubes and ignited by a hot wire. The ignition shock did not damage the cells in any way. Cycling was achieved within minutes. A steel heat exchanger/recuperator was used to feed hot air to the cell stack. The electrical output was measured via a potentiostat.

  5. The influence of Cu2O crystal structure on the Cu2O/ZnO heterojunction photovoltaic performance

    NASA Astrophysics Data System (ADS)

    Elfadill, Nezar G.; Hashim, M. R.; Chahrour, Khaled M.; Qaeed, M. A.; Bououdina, M.

    2015-09-01

    Cuprous oxide (Cu2O) films were potentiostatically electrodeposited onto platinum (Pt) film coated onto silicon (Si) wafer from lactic solution at pH 9. The influence of applied potential on Cu2O crystal structure was carefully examined. At higher electrochemical applied potential, a polycrystalline structure was observed, and then as the applied potential decreased, a single crystalline structure oriented along (1 1 1) was obtained. Further decrease in the applied potential leads to the formation of a polycrystalline structure and finally at much lower applied potential, a single crystalline structure growing along (2 0 0) orientation (equivalent to (1 0 0) orientation) was revealed. Cu2O/ZnO heterojunction photodiodes based on these three crystal structures were fabricated and studied under dark and illuminated conditions. The best performance of the solar cell efficiency was achieved by the heterojunction based on (1 1 1) oriented Cu2O film (?1.45%) compared to other structures (0.34% and 0.25%), which may be attributed to the formation of high quality heterojunction interface due to the heteroepitaxial-like growth of (0 0 2) oriented ZnO.

  6. Morphological Evolution of Nanocluster Aggregates and Single Crystals in Alkaline Zinc Electrodeposition

    SciTech Connect

    Desai, D; Turney, DE; Anantharaman, B; Steingart, DA; Banerjee, S

    2014-04-24

    The morphology of Zn electrodeposits is studied on carbon-coated transmission electron microscopy grids. At low over-potentials (eta = -50 mV), the morphology develops by aggregation at two distinct length scales: similar to 5 nm diameter monocrystalline nanoclusters form similar to 50 nm diameter polycrystalline aggregates, and the aggregates form a branched network. Epitaxial (00 (0) over bar2) growth above an overpotential of vertical bar eta(c)vertical bar > 125 mV leads to the formation of hexagonal single crystals up to 2 mu m in diameter. Potentiostatic current transients were used to calculate the nucleation rate from Scharifker et al.'s model. The exp(eta) dependence of the nucleation rates indicates that atomistic nucleation theory explains the nucleation process better than Volmer-Weber theory. A kinetic model is provided using the rate equations of vapor solidification to simulate the evolution of the different morphologies. On solving these equations, we show that aggregation is attributed to cluster impingement and cluster diffusion while single-crystal formation is attributed to direct attachment.

  7. Stress-corrosion behavior of aluminum-lithium alloys in aqueous environments

    NASA Technical Reports Server (NTRS)

    Pizzo, P. P.; Galvin, R. P.; Nelson, H. G.

    1983-01-01

    The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

  8. Corrosion behaviour of magnesium alloys coated with TiN by cathodic arc deposition in NaCl and Na{sub 2}SO{sub 4} solutions

    SciTech Connect

    Altun, Hikmet Sinici, Hakan

    2008-03-15

    Magnesium-based light-metal alloys belong to a class of structural materials with increasing industrial attention. Magnesium alloys show the lowest density among the engineering metallic materials, low cost and large availability. However, the limitations according to mechanical strength and the low corrosion resistance restrict their practical application. In this study, TiN was coated on magnesium-based AZ91 magnesium-aluminium-zinc alloy using cathodic arc PVD process. The corrosion behaviours of uncoated and coated magnesium alloys in 1% NaCl, 3% NaCl and 3% Na{sub 2}SO{sub 4} solutions and the influence of the coatings on the corrosion behaviour of the substrate were investigated utilizing potentiodynamic polarization tests. A potentiostat for electrochemical corrosion tests, a cathodic arc physical vapour deposition coating system for coating processes, a scanning electron microscopy for surface examination and elemental analysis of the coatings were used in this study. It was determined that corrosion resistance of magnesium alloys can be increased with TiN coating on the alloys using cathodic arc PVD process.

  9. Preparation of Supercapacitors on Flexible Substrates with Electrodeposited PEDOT/Graphene Composites.

    PubMed

    Lehtimäki, Suvi; Suominen, Milla; Damlin, Pia; Tuukkanen, Sampo; Kvarnström, Carita; Lupo, Donald

    2015-10-14

    Composite films consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) and graphene oxide (GO) were electrochemically polymerized by electrooxidation of EDOT in ionic liquid (BMIMBF4) onto flexible electrode substrates. Two polymerization approaches were compared, and the cyclic voltammetry (CV) method was found to be superior to potentiostatic polymerization for the growth of PEDOT/GO films. After deposition, incorporated GO was reduced to rGO by a rapid electrochemical method of repetitive cathodic potential cycling, without using any reducing reagents. The films were characterized in 3-electrode configuration in BMIMBF4. Symmetric supercapacitors with aqueous electrolyte were assembled from the composite films and characterized through cyclic voltammetry and galvanostatic discharge tests. It was shown that PEDOT/rGO composites have better capacitive properties than pure PEDOT or the unreduced composite film. The cycling stability of the supercapacitors was also tested, and the results indicate that the specific capacitance still retains well over 90% of the initial value after 2000 consecutive charging/discharging cycles. The supercapacitors were demonstrated as energy storages in a room light energy harvester with a printed organic solar cell and printed electrochromic display. The results are promising for the development of energy-autonomous, low-power, and disposable electronics. PMID:26381462

  10. Effect of Acidified Feronia elephantum Leaf Extract on the Corrosion Behavior of Mild Steel

    NASA Astrophysics Data System (ADS)

    Muthukrishnan, Pitchaipillai; Prakash, Periakaruppan; Ilayaraja, Murugan; Jeyaprabha, Balasubramanian; Shankar, Karikalan

    2015-03-01

    Mild steel is used as a structural material for pipes, tank, reaction vessels, etc. which are known to corrode invariably in contact with various solvents. From the view point of a nation's economy and financial implications of corrosion hazard, it is necessary to adopt appropriate means and ways to reduce the losses due to corrosion. The use of eco-friendly corrosion inhibitors are increasing day by day. Feronia elephantum leaf extract (FELE) has been tested as eco-friendly corrosion inhibitor for A262 mild steel in 1 M H2SO4 and 1 M HCl solutions using non-electrochemical (Gravimetric, X-ray diffraction analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy) and electrochemical techniques (open circuit potential, potentiostatic polarization, and electrochemical impedance measurements). The protection efficiency is found to increase with increase in FELE concentration but decrease with temperature, which is suggestive of physical adsorption mechanism. The adsorption of FELE on mild steel surface obeys the Langmuir adsorption isotherm. SEM results confirm the formation of a protective layer by FELE over mild steel surface.

  11. Electrochemical generation of oxygen. 1: The effects of anions and cations on hydrogen chemisorption and anodic oxide film formation on platinum electrode. 2: The effects of anions and cations on oxygen generation on platinum electrode

    NASA Technical Reports Server (NTRS)

    Huang, C. J.; Yeager, E.; Ogrady, W. E.

    1975-01-01

    The effects were studied of anions and cations on hydrogen chemisorption and anodic oxide film formation on Pt by linear sweep voltammetry, and on oxygen generation on Pt by potentiostatic overpotential measurement. The hydrogen chemisorption and anodic oxide film formation regions are greatly influenced by anion adsorption. In acids, the strongly bound hydrogen occurs at more cathodic potential when chloride and sulfate are present. Sulfate affects the initial phase of oxide film formation by produced fine structure while chloride retards the oxide-film formation. In alkaline solutions, both strongly and weakly bound hydrogen are influenced by iodide, cyanide, and barium and calcium cations. These ions also influence the oxide film formation. Factors considered to explain these effects are discussed. The Tafel slope for oxygen generation was found to be independent on the oxide thickness and the presence of cations or anions. The catalytic activity indicated by the exchange current density was observed decreasing with increasing oxide layer thickness, only a minor dependence on the addition of certain cations and anions was found.

  12. Unveiling the Hard Anodization Regime of Aluminum: Insight into Nanopores Self-Organization and Growth Mechanism.

    PubMed

    Vega, Víctor; García, Javier; Montero-Moreno, Josep M; Hernando, Blanca; Bachmann, Julien; Prida, Víctor M; Nielsch, Kornelius

    2015-12-30

    Pores growth mechanism and their self-ordering conditions are investigated for nanoporous alumina membranes synthesized by hard anodization (HA) of Al in a broad range of anodic conditions, covering oxalic acid electrolytes with concentrations from 0.300 M down to 0.075 M and potentiostatic anodization voltages between 120 and 225 V. The use of linear sweep voltammetry (LSV) and scanning and transmission electron microscopy, together with image analysis techniques allow one to characterize the intrinsic nature of the HA regime. HA of aluminum is explained on the basis of a phenomenological model taking into account the role of oxalate ions and their limited diffusion through alumina nanochannels from a bulk electrolyte. The depletion of oxalate ions at the bottom of the pores causes an increased growth of the alumina barrier layer at the oxide/electrolyte interface. Furthermore, an innovative method has been developed for the determination of the HA conditions leading to self-ordered pore growth in any given electrolyte, thus allowing one to extend the available range of interpore distances of the highly ordered hexagonal pore arrangement in a wide range of 240-507 nm, while keeping small pore diameters of 50-60 nm. PMID:26646814

  13. Electrochemical nucleophilic synthesis of di-tert-butyl-(4-[18F]fluoro-1,2-phenylene)-dicarbonate

    PubMed Central

    He, Qinggang; Wang, Ying; Alfeazi, Ines; Sadeghi, Saman

    2015-01-01

    An electrochemical method with the ability to conduct 18F-fluorination of aromatic molecules through direct nucleophilic fluorination of cationic intermediates is presented in this paper. The reaction was performed on a remote-controlled automatic platform. Nucleophilic electrochemical fluorination of tert-butyloxycarbonyl (Boc) protected catechol, an intermediate model molecule for the positron emission tomography (PET) probe (3,4-dihydroxy-6-[18F]fluoro-l-phenylalanine), was performed. Fluorination was achieved under potentiostatic anodic oxidation in acetonitrile containing Et3N · 3HF and other supporting electrolytes. Radiofluorination efficiency was influenced by a number of variables, including the concentration of the precursor, concentration of Et3N · 3HF, type of supporting electrolyte, temperature and time, as well as applied potentials. Radiofluorination efficiency of 10.4 ± 0.6% (n = 4) and specific activity of up to 43 GBq/mmol was obtained after 1 h electrolysis of 0.1 M of 4-tert-butyl-diboc-catechol in the acetonitrile solution of Et3N · 3HF (0.033 M) and NBu4PF6 (0.05 M). Density functional theory (DFT) was employed to explain the tert-butyl functional group facilitation of electrochemical oxidation and subsequent fluorination. PMID:25000498

  14. Assessment of corrosion rate in prestressed concrete with acoustic emission

    NASA Astrophysics Data System (ADS)

    Mangual, Jesé; ElBatanouny, Mohamed K.; Vélez, William; Ziehl, Paul; Matta, Fabio; González, Miguel

    2011-04-01

    Acoustic Emission (AE) sensing was employed to assess the rate of corrosion of steel strands in small scale concrete block specimens. The corrosion process was accelerated in a laboratory environment using a potentiostat to supply a constant potential difference with a 3% NaCl solution as the electrolyte. The embedded prestressing steel strand served as the anode, and a copper plate served as the cathode. Corrosion rate, half-cell potential measurements, and AE activity were recorded continuously throughout each test and examined to assess the development of corrosion and its rate. At the end of each test the steel strands were cleaned and re-weighed to determine the mass loss and evaluate it vis-á-vis the AE data. The initiation and propagation phases of corrosion were correlated with the percentage mass loss of steel and the acquired AE signals. Results indicate that AE monitoring may be a useful aid in the detection and differentiation of the steel deterioration phases, and estimation of the locations of corroded areas.

  15. New Secondary Batteries Utilizing Electronically Conductive Polypyrrole Cathode. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Yeu, Taewhan

    1991-01-01

    To gain a better understanding of the dynamic behavior in electronically conducting polypyrroles and to provide guidance toward designs of new secondary batteries based on these polymers, two mathematical models are developed; one for the potentiostatically controlled switching behavior of polypyrrole film, and one for the galvanostatically controlled charge/discharge behavior of lithium/polypyrrole secondary battery cell. The first model is used to predict the profiles of electrolyte concentrations, charge states, and electrochemical potentials within the thin polypyrrole film during switching process as functions of applied potential and position. Thus, the detailed mechanisms of charge transport and electrochemical reaction can be understood. Sensitivity analysis is performed for independent parameters, describing the physical and electrochemical characteristic of polypyrrole film, to verify their influences on the model performance. The values of independent parameters are estimated by comparing model predictions with experimental data obtained from identical conditions. The second model is used to predict the profiles of electrolyte concentrations, charge state, and electrochemical potentials within the battery system during charge and discharge processes as functions of time and position. Energy and power densities are estimated from model predictions and compared with existing battery systems. The independent design criteria on the charge and discharge performance of the cell are provided by studying the effects of design parameters.

  16. Nucleation and growth in electrodeposition of thin copper films on pyrolytic graphite

    SciTech Connect

    Kinaci, F.S.; Muller, R.H.

    1992-05-01

    Electrodeposition of Cu on graphite electrodes was studied, with emphasis on nucleation. Various ex-situ and in-situ methods were investigated for determining the number density of nuclei. Two direct methods were studied (scanning electron microscopy and scanning tunneling microscopy); indirect determinations included Raman spectroscopy and analysis of potentiostatic current transients. Though some of the techniques correctly predicted the nucleation densities under special conditions, SEM was the most reliable tool. The large scatter in the data necessitated steps to minimize this effect. To electrodeposit Cu on graphite, a nucleation overpotential of 250 mV was measured with cyclic voltammetry; such a large overpotential does not occur on a Pt or on a Cu-covered graphite electrode. The deposition potential is the dominant parameter governing nucleation density. There is a sharp increase in the nucleation density with applied potential. Cu can be deposited on highly oriented pyrolytic graphite only between the nucleation overpotential and the hydrogen evolution potential. To increase the Cu nucleation density, while avoiding excessive H evolution, a double pulse potential technique was used; nucleation densities on the order of 10{sup 10} nuclei/cm{sup 2} were achieved. The use of inhibitors (PVA, benzotriazole) was also investigated. Deposition on conducting polymer electrodes was also studied; initial results with polyaniline show promise. 57 figs, 6 tabs, refs. (DLC)

  17. Development of Amperometric Biosensors Based on Nanostructured Tyrosinase-Conducting Polymer Composite Electrodes

    PubMed Central

    Lupu, Stelian; Lete, Cecilia; Balaure, Paul C?t?lin; Caval, Dan Ion; Mihailciuc, Constantin; Lakard, Boris; Hihn, Jean-Yves; del Campo, Francisco Javier

    2013-01-01

    Bio-composite coatings consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) and tyrosinase (Ty) were successfully electrodeposited on conventional size gold (Au) disk electrodes and microelectrode arrays using sinusoidal voltages. Electrochemical polymerization of the corresponding monomer was carried out in the presence of various Ty amounts in aqueous buffered solutions. The bio-composite coatings prepared using sinusoidal voltages and potentiostatic electrodeposition methods were compared in terms of morphology, electrochemical properties, and biocatalytic activity towards various analytes. The amperometric biosensors were tested in dopamine (DA) and catechol (CT) electroanalysis in aqueous buffered solutions. The analytical performance of the developed biosensors was investigated in terms of linear response range, detection limit, sensitivity, and repeatability. A semi-quantitative multi-analyte procedure for simultaneous determination of DA and CT was developed. The amperometric biosensor prepared using sinusoidal voltages showed much better analytical performance. The Au disk biosensor obtained by 50 mV alternating voltage amplitude displayed a linear response for DA concentrations ranging from 10 to 300 ?M, with a detection limit of 4.18 ?M. PMID:23698270

  18. Comparison of Electrochemical Methods to Determine Crevice Corrosion Repassivation Potential of Alloy 22 in Chloride Solutions

    SciTech Connect

    K. Evans; A. Yilmaz; S. Day; L. Wong; J. Estill

    2004-08-23

    Alloy 22 (N06022) is a nickel-based alloy highly resistant to corrosion. In some aggressive conditions of high chloride concentration, temperature and applied potential, Alloy 22 may suffer crevice corrosion, a form of localized corrosion. There are several electrochemical methods that can be used to determine localized corrosion in metallic alloys. One of the most popular for rapid screening is the cyclic potentiodynamic polarization (CPP). This work compares the repassivation potentials obtained using CPP to related repassivation potential values obtained using the Tsujikawa-Hisamatsu Electrochemical (THE) method and the potentiostatic (POT) method. Studied variables included temperature and chloride concentration. The temperature was varied from 30 C and 120 C and the chloride concentration was varied between 0.0005 M to 4 M. Results show that similar repassivation potentials were obtained for Alloy 22 using CPP and THE methods. Generally, under more aggressive conditions, the repassivation potentials were more conservative using the CPP method. POT tests confirmed the validity of the repassivation potential as a threshold below which localized corrosion does not nucleate. The mode of attack in the tested specimens varied depending if the test method was CPP or THE; however, the repassivation potential remained the same.

  19. Wearable salivary uric acid mouthguard biosensor with integrated wireless electronics.

    PubMed

    Kim, Jayoung; Imani, Somayeh; de Araujo, William R; Warchall, Julian; Valdés-Ramírez, Gabriela; Paixão, Thiago R L C; Mercier, Patrick P; Wang, Joseph

    2015-12-15

    This article demonstrates an instrumented mouthguard capable of non-invasively monitoring salivary uric acid (SUA) levels. The enzyme (uricase)-modified screen printed electrode system has been integrated onto a mouthguard platform along with anatomically-miniaturized instrumentation electronics featuring a potentiostat, microcontroller, and a Bluetooth Low Energy (BLE) transceiver. Unlike RFID-based biosensing systems, which require large proximal power sources, the developed platform enables real-time wireless transmission of the sensed information to standard smartphones, laptops, and other consumer electronics for on-demand processing, diagnostics, or storage. The mouthguard biosensor system offers high sensitivity, selectivity, and stability towards uric acid detection in human saliva, covering the concentration ranges for both healthy people and hyperuricemia patients. The new wireless mouthguard biosensor system is able to monitor SUA level in real-time and continuous fashion, and can be readily expanded to an array of sensors for different analytes to enable an attractive wearable monitoring system for diverse health and fitness applications. PMID:26276541

  20. Tyrosinase conjugated reduced graphene oxide based biointerface for bisphenol A sensor.

    PubMed

    Reza, K Kamil; Ali, Md Azahar; Srivastava, Saurabh; Agrawal, Ved Varun; Biradar, A M

    2015-12-15

    We have fabricated a nanocomposite of reduced graphene oxide (rGO) sheets and chitosan (Cn) polymer based highly sensitive electrochemical biosensor for detection of bisphenol A (BPA). The two-dimensional structure and chemical functionality of rGO and Cn provide an excellent electrode surface for loading of tyrosinase enzyme molecules. This rGO-Cn nanocomposite is capable of effectively utilizing their superior conductivity, larger effective surface area and superior electrochemical performance due to its synergistic effect between rGO and Cn. The structural, morphological and electrochemical characterizations of nanocomposite sheets have been performed by electron microscopy, X-ray diffraction, FTIR and Potentiostat/Galvanostat techniques. This fabricated biosensor is sensitive to nanomolar (0.74 nM) concentration of BPA and detection time is 10s compared to conventional BPA ELISA kit (0.3 µg/L and 2.5h). The rGO-Cn based biosensor exhibits a higher sensitivity (83.3 µA nM(-1) cm(-2)), wider linearity (0.01-50 µM) with good selectivity towards BPA. This biosensor is capable to quantify real sample of BPA using packaged drinking water bottles. This rGO-Cn nanocomposite sheets emerges as a potential electrode material for detection of other estrogenic substrate. PMID:26201981

  1. Effects of Zn amount on the properties of Zn-Zu2O composite films grown for PEC photoelectrodes by using electrochemical deposition

    NASA Astrophysics Data System (ADS)

    Kim, Tae Gyoum; Lee, Hu Joong; Ryu, Hyukhyun; Lee, Won-Jae

    2015-10-01

    In this study, Zn-Cu2O composite films were grown on fluorine-doped tin-oxide (FTO) substrates by using the electrochemical deposition method. Various amounts of Zinc (Zn) were added to grow the Zn-Cu2O composite films. We analyzed the morphological, structural, optical energy band gap and photocurrent density properties of the Zn-Cu2O composite films by using various measurements such as field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), UV-visible spectrophotometry and potentiostat/galvanostat measurements, respectively. As a result, the highest photocurrent density value of -4.04 mA/cm2 was obtained for the 30-wt% sample, which had the lowest Cu2O (111)/ ZnO (101) XRD peak intensity ratio. The highest photocurrent density value from the 30-wt% sample was approximately 2.35 times higher than that from the non-composite Cu2O film (0-wt% sample). From this study, we found that adding Zn could improve the photocurrent values of Zn-Cu2O composite films.

  2. Electrochemical sensing method for point-of-care cortisol detection in human immunodeficiency virus-infected patients

    PubMed Central

    Kaushik, Ajeet; Yndart, Adriana; Jayant, Rahul Dev; Sagar, Vidya; Atluri, Venkata; Bhansali, Shekhar; Nair, Madhavan

    2015-01-01

    A novel electrochemical sensing method was devised for the first time to detect plasma cortisol, a potential psychological stress biomarker, in human immunodeficiency virus (HIV)-positive subjects. A miniaturized potentiostat (reconfigured LMP91000 chip) interfaced with a microfluidic manifold containing a cortisol immunosensor was employed to demonstrate electrochemical cortisol sensing. This fully integrated and optimized electrochemical sensing device exhibited a wide cortisol-detection range from 10 pg/mL to 500 ng/mL, a low detection limit of 10 pg/mL, and sensitivity of 5.8 ?A (pg mL)?1, with a regression coefficient of 0.995. This cortisol-selective sensing system was employed to estimate plasma cortisol in ten samples from HIV patients. The electrochemical cortisol-sensing performance was validated using an enzyme-linked immunosorbent assay technique. The results obtained using both methodologies were comparable within 2%–5% variation. The information related to psychological stress of HIV patients can be correlated with disease-progression parameters to optimize diagnosis, therapeutic, and personalized health monitoring. PMID:25632229

  3. Wafer Scale Integration of CMOS Chips for Biomedical Applications via Self-Aligned Masking

    PubMed Central

    Uddin, Ashfaque; Milaninia, Kaveh; Chen, Chin-Hsuan; Theogarajan, Luke

    2011-01-01

    This paper presents a novel technique for the integration of small CMOS chips into a large area substrate. A key component of the technique is the CMOS chip based self-aligned masking. This allows for the fabrication of sockets in wafers that are at most 5 µm larger than the chip on each side. The chip and the large area substrate are bonded onto a carrier such that the top surfaces of the two components are flush. The unique features of this technique enable the integration of macroscale components, such as leads and microfluidics. Furthermore, the integration process allows for MEMS micromachining after CMOS die-wafer integration. To demonstrate the capabilities of the proposed technology, a low-power integrated potentiostat chip for biosensing implemented in the AMI 0.5 µm CMOS technology is integrated in a silicon substrate. The horizontal gap and the vertical displacement between the chip and the large area substrate measured after the integration were 4 µm and 0.5 µm, respectively. A number of 104 interconnects are patterned with high-precision alignment. Electrical measurements have shown that the functionality of the chip is not affected by the integration process. PMID:22400126

  4. Amperometric determination of xanthine in fish meat by zinc oxide nanoparticle/chitosan/multiwalled carbon nanotube/polyaniline composite film bound xanthine oxidase.

    PubMed

    Devi, Rooma; Yadav, Sandeep; Pundir, C S

    2012-02-01

    Xanthine oxidase (XOD) was immobilized on a composite film of zinc oxide nanoparticle/chitosan/carboxylated multiwalled carbon nanotube/polyaniline (ZnO-NP/CHIT/c-MWCNT/PANI) electrodeposited over the surface of a platinum (Pt) electrode. A xanthine biosensor was fabricated using XOD/ZnO-NP/CHIT/c-MWCNT/PANI/Pt as working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode connected through a potentiostat. The ZnO-NPs were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the enzyme electrode was characterized by cyclic voltammetry, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). The biosensor showed optimum response within 4 s at 0.5 V potential, pH 7.0, 35 °C and linear range 0.1-100 ?M with a detection limit of 0.1 ?M. The enzyme electrode was employed for determination of xanthine in fish meat during storage. The electrode lost 30% of its initial activity after 80 uses over one month, when stored at 4 °C. PMID:22135777

  5. Immobilization of rat brain acetylcholinesterase on porous gold-nanoparticle-CaCO? hybrid material modified Au electrode for detection of organophosphorous insecticides.

    PubMed

    Chauhan, Nidhi; Narang, Jagriti; Pundir, C S

    2011-12-01

    An acetylcholinesterase (AChE) purified from rat brain was immobilized onto gold nanoparticles (AuNPs) assembled on the surface of porous calcium carbonate (CaCO(3)) microsphere. The resulting AChE-AuNPs-CaCO(3) bioconjugate was mounted on the surface of Au electrode with the help of silica sol-gel matrix to prepare the working electrode. This electrode was connected to Ag/AgCl (3M/saturated KCl) as standard and Pt wire as an auxiliary electrode through a potentiostat to construct an organophosphorus (OP) biosensor. The biosensor was based on inhibition of AChE by OP compounds/insecticides. The biosensor showed optimum response at pH 7.0, 30°C, when polarized at +0.2V. Two OP compounds, malathion and chlorpyrifos could be detected in the range of 0.1-100 nM and 0.1-70 nM, respectively at 2.0-3.0% inhibition level of AChE. The sensor was reactivated by immersing it in 0.1 mM 2-pyridine aldoxime for 10 min. The detection limit of the sensor was 0.1 nM for both malathion and chlorpyrifos. The biosensor exhibited good reusability (50 times without considerable loss) and storage stability (50% within 60 days, when stored at 4°C). PMID:21856330

  6. Electrochemical oxidation of tramadol in low-salinity reverse osmosis concentrates using boron-doped diamond anodes.

    PubMed

    Lütke Eversloh, Christian; Schulz, Manoj; Wagner, Manfred; Ternes, Thomas A

    2015-04-01

    The electrochemical treatment of low-salinity reverse osmosis (RO) concentrates was investigated using tramadol (100 ?M) as a model substance for persistent organic contaminants. Galvanostatic degradation experiments using boron-doped diamond electrodes at different applied currents were conducted in RO concentrates as well as in ultra-pure water containing either sodium chloride or sodium sulfate. Kinetic investigations revealed a significant influence of in-situ generated active chlorine besides direct anodic oxidation. Therefore, tramadol concentrations decreased more rapidly at elevated chloride content. Nevertheless, reduction of total organic carbon (TOC) was found to be comparatively low, demonstrating that transformation rather than mineralization was taking place. Early stage product formation could be attributed to both direct and indirect processes, including demethylation, hydroxylation, dehydration, oxidative aromatic ring cleavage and halogenation reactions. The latter led to various halogenated derivatives and resulted in AOX (adsorbable organic halogens) formation in the lower mg/L-range depending on the treatment conditions. Characterisation of transformation products (TPs) was achieved via MS(n) experiments and additional NMR measurements. Based on identification and quantification of the main TPs in different matrices and on additional potentiostatic electrolysis, a transformation pathway was proposed. PMID:25660808

  7. Effect of Fluid Flow on Zinc Electrodeposits from Acid Chloride Electrolytes. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Abdelmassir, A. A.

    1982-01-01

    Zinc was deposited potentiostatically from acid chloride baths. Once bath chemistry and electrochemistry were controlled, the study was focused on convective mass transfer at horizontal electrodes and its effect on cell performance. A laser schlieren imaging technique allowed in situ observations of flow patterns and their correlation with current transients. Convection was turbulent and mass transfer as a function of Rayleigh number was well correlated by: Sh = 0.14 R to the 1/3 power. Similarly, convection initiation time was correlated by DT/d squared = 38 Ra to the -2/3 power. Time scale of fluctuations was about half the initiation time. Taking the boundary layer thickness as a characteristic length, a critical Rayleigh number for the onset of convection was deduced: Ra sub CR = 5000. Placing the anode on the top of the cathode completely changed the flow pattern but kept the I-t curves identical whereas the use of a cathode grid doubled the limiting current. A well defined plateau in the current voltage curves suggested that hydrogen evolution has been successfully inhibited. Finally, long time deposition showed that convection at horizontal electrodes increased the induction time for dentrite growth by at least a factor of 2 with respect to a vertical wire.

  8. Seed layer-free electrodeposition of well-aligned ZnO submicron rod arrays via a simple aqueous electrolyte

    SciTech Connect

    Xu Feng; Lu Yinong; Xia Lili; Xie Yan; Dai Min; Liu Yunfei

    2009-08-05

    A potentiostatic electrodeposition technique was used to directly fabricate large-scale, well-aligned, and single-crystalline submicron ZnO rod arrays on tin doped indium oxide glass substrate without a pre-prepared seed layer of ZnO from an aqueous solution only containing zinc nitrate. The effects of electrochemical parameters, such as electrodeposition potential, electrodeposition duration, solution temperature, and precursor concentration, on the orientation, morphology, aspect ratio, and growth rate of ZnO rod arrays were systematically investigated. Results show that submicron ZnO rod arrays with (0 0 0 2) preferred orientation and perfect crystallization were obtained when electrodeposition potential was in the range from -0.6 to -1.1 V and solution temperature was controlled above 60 deg. C. Both high solution temperature and low precursor concentration resulted in the decrease in rod diameters. Photoluminescence measures showed that small diameter and nanotips of ZnO rod arrays should be responsible for strong and sharp ultraviolet emission in the room temperature photoluminescence spectra.

  9. Microelectrospotting as a new method for electrosynthesis of surface-imprinted polymer microarrays for protein recognition.

    PubMed

    Bosserdt, Maria; Erd?ssy, Júlia; Lautner, Gergely; Witt, Julia; Köhler, Katja; Gajovic-Eichelmann, Nenad; Yarman, Aysu; Wittstock, Gunther; Scheller, Frieder W; Gyurcsányi, Róbert E

    2015-11-15

    Here we introduce microelectrospotting as a new approach for preparation of protein-selective molecularly imprinted polymer microarrays on bare gold SPR imaging chips. During electrospotting both the gold chip and the spotting tip are electrically connected to a potentiostat as working and counter electrodes, respectively. The spotting pin encloses the monomer-template protein cocktail that upon contacting the gold surface is in-situ electropolymerized resulting in surface confined polymer spots of ca. 500 µm diameter. By repeating this procedure at preprogrammed locations for various composition monomer-template mixtures microarrays of nanometer-thin surface-imprinted films are generated in a controlled manner. We show that the removal and rebinding kinetics of the template and various potential interferents to such microarrays can be monitored in real-time and multiplexed manner by SPR imaging. The proof of principle for microelectrospotting of electrically insulating surface-imprinted films is made by using scopoletin as monomer and ferritin as protein template. It is shown that microelectrospotting in combination with SPR imaging can offer a versatile platform for label-free and enhanced throughput optimization of the molecularly imprinted polymers for protein recognition and for their analytical application. PMID:26056955

  10. Specific and efficient electrochemical selection of Geoalkalibacter subterraneus and Desulfuromonas acetoxidans in high current-producing biofilms.

    PubMed

    Pierra, Mélanie; Carmona-Martínez, Alessandro A; Trably, Eric; Godon, Jean-Jacques; Bernet, Nicolas

    2015-12-01

    Two different saline sediments were used to inoculate potentiostatically controlled reactors (a type of microbial bioelectrochemical system, BES) operated in saline conditions (35 gNaCl l(-1)). Reactors were fed with acetate or a mixture of acetate and butyrate at two pH values: 7.0 or 5.5. Electroactive biofilm formation lag-phase, maximum current density production and coulombic efficiency were used to evaluate the overall performance of reactors. High current densities up to 8.5 A m(-2) were obtained using well-defined planar graphite electrodes. Additionally, biofilm microbial communities were characterized by CE-SSCP and 454 pyrosequencing. As a result of this procedure, two anode-respiring bacteria (ARB) always dominated the anodic biofilms: Geoalkalibacter subterraneus and/or Desulfuromonas acetoxidans. This suggests that a strong electrochemically driven selection process imposed by the applied potential occurs in the BES system. Moreover, the emergence of Glk. subterraneus in anodic biofilms significantly contributes to broaden the spectrum of high current producing microorganisms electrochemically isolated from environmental samples. PMID:25717030

  11. Effect of Fluoride on Nickel-Titanium and Stainless Steel Orthodontic Archwires: An In-Vitro Study

    PubMed Central

    Heravi, Farzin; Moayed, Mohamad Hadi; Mokhber, Nima

    2015-01-01

    Objectives: The commonly used Nickel-Titanium (NiTi) archwires in orthodontic treatment are often exposed to fluoride-containing mouthwashes. The aim of this in-vitro study was to evaluate and compare the corrosion resistance of three commercially available NiTi archwires exposed to 0.05 wt% and 0.2 wt% fluoride mouthwashes. Materials and Methods: Three different types of NiTi archwires, 0.016? in diameter, from Dentaurum, Global, and GAC, and a stainless steel archwire from Dentaurum were examined to assess their corrosion resistance in Fusayama-Meyer artificial saliva and in two other artificial saliva containing 0.05 wt% and 0.2 wt% sodium fluoride (NaF). After the primary setup of wires, they were tested by potentiodynamic and potentiostatic polarization and corrosion potential/time analyses. Their surfaces were evaluated using a scanning electronic microscope (SEM). Results: The results showed that all the wires were passive in artificial saliva. In contrast, by adding fluoride ions to the solution, the decrease in the archwires’ corrosion resistance was in direct proportion to the increase in fluoride concentration. Conclusion: The NiTi wires experienced deterioration of their corrosion properties under the effect of fluoride but not as much as the stainless steel archwires. PMID:26005454

  12. Deformation and fracture of aluminum-lithium alloys: The effect of dissolved hydrogen

    NASA Technical Reports Server (NTRS)

    Rivet, F. C.; Swanson, R. E.

    1990-01-01

    The effects of dissolved hydrogen on the mechanical properties of 2090 and 2219 alloys are studied. The work done during this semi-annual period consists of the hydrogen charging study and some preliminary mechanical tests. Prior to SIMS analysis, several potentiostatic and galvanostatic experiments were performed for various times (going from 10 minutes to several hours) in the cathodic zone, and for the two aqueous solutions: 0.04N of HCl and 0.1N NaOH both combined with a small amount of As2O3. A study of the surface damage was conducted in parallel with the charging experiments. Those tests were performed to choose the best charging conditions without surface damage. Disk rupture tests and tensile tests are part of the study designed to investigate the effect of temperature, surface roughness, strain rate, and environment on the fracture behavior. The importance of the roughness and environment were shown using the disk rupture test as well as the importance of the strain rate under hydrogen environment. The tensile tests, without hydrogen effects, have not shown significant differences between low and room temperature.

  13. Reduction of CO2 to low carbon alcohols on CuO FCs/Fe2O3 NTs catalyst with photoelectric dual catalytic interfaces

    NASA Astrophysics Data System (ADS)

    Li, Peiqiang; Wang, Huying; Xu, Jinfeng; Jing, Hua; Zhang, Jun; Han, Haixiang; Lu, Fusui

    2013-11-01

    In this paper, the CuO FCs/Fe2O3 NTs catalyst was obtained after Fe2O3 nanotubes (Fe2O3 NTs) were decorated with CuO flower clusters (CuO FCs) by the pulse electrochemical deposition method. The in situ vertically aligned Fe2O3 NTs were prepared on the ferrous substrate by a potentiostatic anodization method. The SEM result showed the volcano-like Fe2O3 NTs were arranged in order and the CuO FCs constituted of flaky CuO distributed on the Fe2O3 NTs surface uniformly. After CuO FCs were loaded on Fe2O3 NTs, the absorption of visible light was enhanced noticeably, and its band gap narrowed to 1.78 eV from 2.03 eV. The conduction band and valence band locating at -0.73 eV and 1.05 eV, respectively were further obtained. In the PEC reduction of CO2 process, methanol and ethanol were two major products identified by chromatography. Their contents reached 1.00 mmol L-1 cm-2 and 107.38 ?mol L-1 cm-2 after 6 h, respectively. This high-efficiency catalyst with photoelectric dual catalytic interfaces has a great guidance and reference significance for CO2 reduction to liquid carbon fuels.In this paper, the CuO FCs/Fe2O3 NTs catalyst was obtained after Fe2O3 nanotubes (Fe2O3 NTs) were decorated with CuO flower clusters (CuO FCs) by the pulse electrochemical deposition method. The in situ vertically aligned Fe2O3 NTs were prepared on the ferrous substrate by a potentiostatic anodization method. The SEM result showed the volcano-like Fe2O3 NTs were arranged in order and the CuO FCs constituted of flaky CuO distributed on the Fe2O3 NTs surface uniformly. After CuO FCs were loaded on Fe2O3 NTs, the absorption of visible light was enhanced noticeably, and its band gap narrowed to 1.78 eV from 2.03 eV. The conduction band and valence band locating at -0.73 eV and 1.05 eV, respectively were further obtained. In the PEC reduction of CO2 process, methanol and ethanol were two major products identified by chromatography. Their contents reached 1.00 mmol L-1 cm-2 and 107.38 ?mol L-1 cm-2 after 6 h, respectively. This high-efficiency catalyst with photoelectric dual catalytic interfaces has a great guidance and reference significance for CO2 reduction to liquid carbon fuels. Electronic supplementary information (ESI) available: Reduction of CO2 to low carbon alcohols on CuO FCs/Fe2O3 NTs catalyst with photoelectric dual catalytic interfaces. See DOI: 10.1039/c3nr03352j

  14. Experimental Study on the pH of Pore water in Compacted Bentonite under Reducing Conditions with Electromigration

    SciTech Connect

    Nessa, S.A.; Idemitsu, K.; Yamazaki, S.; Ikeuchi, H.; Inagaki, Y.; Arima, T.

    2008-07-01

    Compacted bentonite and carbon steel are considered a good buffer and over-pack materials in the repositories of high-level radioactive waste disposal. Sodium bentonite, Kunipia-F contains approximately 95 wt% of montmorillonite. Bentonites prominent properties of high swelling, sealing ability and cation exchange capacity provide retardation against the transport of radionuclides from the waste into the surrounding rocks in the repository and its properties determine the behavior of bentonite. In this regards, the pH of pore water in compacted bentonite is measured with pH test paper wrapped with semi-permeable membrane of collodion sheet under reducing conditions. On 30 days, the pH test paper in the experimental apparatus indicated that the pH of pore water in compacted bentonite is around 8.0 at saturated state. The carbon steel coupon is connected as the working electrode to the potentiostat and is held at a constant supplied potential between +300 and -300 mV vs. Ag/AgCl electrode for up to 7 days. During applying electromigration the pH of pore water in bentonite decreased and it reached 6.0{approx}6.0 on 7 days. The concentration of iron and sodium showed nearly complementary distribution in the bentonite specimen after electromigration. It is expected that iron could migrate as ferrous ion through the interlayer of montmorillonite replacing exchangeable sodium ions in the interlayer. Semi-permeable membrane of collodion sheet does not affect the color change of pH test paper during the experiment. (authors)

  15. The effect of dopant concentration on properties of transparent conducting Al-doped ZnO thin films for efficient Cu2ZnSnS4 thin-film solar cells prepared by electrodeposition method

    NASA Astrophysics Data System (ADS)

    Mkawi, E. M.; Ibrahim, K.; Ali, M. K. M.; Farrukh, M. A.; Mohamed, A. S.

    2015-11-01

    Al-doped ZnO (AZO) thin films were potentiostatically deposited on indium tin oxide substrates. The influence of the doping level of the ZnO:Al films was investigated. The results of the X-ray diffraction and scanning electron microscopy analysis revealed that the structural properties of the AZO films were found polycrystalline with a hexagonal wurtzite-type structure along the (002) plane. The grain size of the AZO films was observed as approximately 3 ?m in the film doping with 4 mol% ZnO:Al concentration. The thin films also exhibited an optical transmittance as high as 90 % in the wavelength range of 100-1,000 nm. The optical band gap increased from 3.33 to 3.45 eV. Based on the Hall studies, the lowest resistivity (4.78 × 10-3 ? cm) was observed in the film doping with 3 mol% ZnO:Al concentration. The sheet resistant, carrier concentration and Hall mobility values were found as 10.78 ?/ square, 9.03 × 1018 cm-3 and 22.01 cm2/v s, respectively, which showed improvements in the properties of AZO thin films. The ZnO:Al thin films were used as a buffer layer in thin-film solar cells with the structure of soda-lime glass/Mo/Cu2ZnSnS4/ZnS/ZnO/Al grid. The best solar cell efficiency was 2.3 % with V OC of 0.430 V, J SC of 8.24 mA cm-2 and FF of 68.1 %.

  16. Part I. Carbon and mercury-carbon optically transparent electrodes. Part II. Investigation of redox properties of technetium by cyclic voltammetry and thin layer spectroelectrochemistry

    SciTech Connect

    Hurst, R.W.

    1980-01-01

    A carbon optically transparent electrode (C OTE) has been prepared by vapor-deposithing a thin carbon film (150 to 310 A thick) on glass and quartz. Optical transparency is good throughout the ultraviolet-visible region. Electrochemical and spectroelectrochemical measurements were made with ferricyanide and o-tolidine respectively. The C OTE serves as a good substrate for deposition of a thin mercury film to form a mercury film transparent electrode (Hg-C OTE). The Hg-C OTE exhibits electrochemical properties of conventional mercury film electrodes as evidenced by Pb/sup 2 +/ cyclic voltammograms. The Hg-C OTE exhibits electrochemical properties of conventional mercury film electrodes as evidenced by Pb/sup 2 -/ cyclic VOHammograms. The Hg-C OTE enabled the spectrochemical characterization of cysteine oxidation, which was shown to involve the oxidation of mercury to form mercurous cysteinate. An 8080 based microcomputer has been interfaced with a Harrick oscillating mirror rapid scanning uv-visible spectrophotometer. Two different approaches are compared for controlling the galvanometer. The first utilizes the digital hardware on the Harrick processing module to derive the mirror drive waveform, while the second creates the waveform under direct software control. A potentiostat is also interfaced and the system is demonstrated by the spectroelectrochemical determination of the redox potential of o-tolidine. Redox potentials are also determined for a series of technetium complexes by the spectropotentiostatic technique. These include hexahalogens, ditertiary arsine, and 1,2-bis(diphenylphosphino) ethane complexes of technetium. Transient hexavalent technetium is produced, detected, and characterized in aqueous alkaline media by pulse radiolysis and very fast scan cyclic voltammetry. The lifetime is of the order of milliseconds. This species is potentially useful in the preparation of technetium radiopharmaceuticals.

  17. Tuning the crystallinity of thermoelectric Bi(2)Te(3) nanowire arrays grown by pulsed electrodeposition.

    PubMed

    Lee, Jongmin; Farhangfar, Shadyar; Lee, Jaeyoung; Cagnon, Laurent; Scholz, Roland; Gösele, Ulrich; Nielsch, Kornelius

    2008-09-10

    Arrays of thermoelectric bismuth telluride (Bi(2)Te(3)) nanowires were grown into porous anodic alumina (PAA) membranes prepared by a two-step anodization. Bi(2)Te(3) nanowire arrays were deposited by galvanostatic, potentiostatic and pulsed electrodeposition from aqueous solution at room temperature. Depending on the electrodeposition method and as a consequence of different growth mechanisms, Bi(2)Te(3) nanowires exhibit different types of crystalline microstructure. Bi(2)Te(3) nanowire arrays, especially those grown by pulsed electrodeposition, have a highly oriented crystalline structure and were grown uniformly as compared to those grown by other electrodeposition techniques used. X-ray diffraction (XRD) analyses are indicative of the existence of a preferred growth orientation. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) confirm the formation of a preferred orientation and highly crystalline structure of the grown nanowires. The nanowires were further analyzed by scanning electron microscopy (SEM). Energy dispersive x-ray spectrometry (EDX) indicates that the composition of Bi-Te nanowires can be controlled by the electrodeposition method and the relaxation time in the pulsed electrodeposition approach. The samples fabricated by pulsed electrodeposition were electrically characterized within the temperature range 240 K?T?470 K. Below T?440 K, the nanowire arrays exhibited a semiconducting behavior. Depending on the relaxation time in the pulsed electrodeposition, the semiconductor energy gaps were estimated to be 210-290 meV. At higher temperatures, as a consequence of the enhanced carrier-phonon scattering, the measured electrical resistances increased slightly. The Seebeck coefficient was measured for every Bi(2)Te(3) sample at room temperature by a very simple method. All samples showed a positive value (12-33 µV K(-1)), indicating a p-type semiconductor behavior. PMID:21828882

  18. A Miniaturized Transcutaneous System for Continuous Glucose Monitoring

    PubMed Central

    Croce, Robert A.; Vaddiraju, SanthiSagar; Kondo, Jun; Wang, Yan; Zuo, Liang; Zhu, Kai; Islam, Syed K.; Burgess, Diane; Papadimitrakopoulos, Fotios; Jain, Faquir C.

    2012-01-01

    Implantable sensors for continuous glucose monitoring hold great potential for optimal diabetes management. This is often undermined by a variety of issues associated with: (1) negative tissue response; (2) poor sensor performance; and (3) lack of device miniaturization needed to reduce implantation trauma. Herein, we report our initial results towards constructing an implantable device that simultaneously address all three aforementioned issues. In terms of device miniaturization, a highly miniaturized CMOS (complementary metal-oxide-semiconductor) potentiostat and signal processing unit was employed (with a combined area of 0.665 mm2). The signal processing unit converts the current generated by a transcutaneous, Clark-type amperometric sensor to output frequency in a linear fashion. The Clark-type amperometric sensor employs stratification of five functional layers to attain a well-balanced mass transfer which in turn yields a linear sensor response from 0 to 25 mM of glucose concentration, well beyond the physiologically observed (2 to 22 mM) range. In addition, it is coated with a thick polyvinyl alcohol (PVA) hydrogel with embedded poly(lactic-co-glycolic acid) (PLGA) microspheres intended to provide continuous, localized delivery of dexamethasone to suppress inflammation and fibrosis. In vivo evaluation in rat model has shown that the transcutaneous sensor system reproducibly tracks repeated glycemic events. Clarke’s error grid analysis on the as –obtained glycemic data has indicated that all of the measured glucose readings fell in the desired Zones A & B and none fell in the erroneous Zones C, D and E. Such reproducible operation of the transcutaneous sensor system, together with low power (140 ?W) consumption and capability for current-to-frequency conversion renders this a versatile platform for continuous glucose monitoring and other biomedical sensing devices. PMID:22992979

  19. Electrochemical incineration of wastes

    NASA Technical Reports Server (NTRS)

    Bhardwaj, R. C.; Sharma, D. K.; Bockris, J. OM.

    1990-01-01

    The novel technology of waste removal in space vehicles by electrochemical methods is presented to convert wastes into chemicals that can be eventually recycled. The important consideration for waste oxidation is to select a right kind of electrode (anode) material that should be stable under anodic conditions and also a poor electrocatalyst for oxygen and chlorine evolution. On the basis of long term electrolysis experiments on seven different electrodes and on the basis of total organic carbon reduced, two best electrodes were identified. The effect of redox ions on the electrolyte was studied. Though most of the experiments were done in mixtures of urine and waste, the experiments with redox couples involved 2.5 M sulfuric acid in order to avoid the precipitation of redox ions by urea. Two methods for long term electrolysis of waste were investigated: (1) the oxidation on Pt and lead dioxide electrodes using the galvanostatic methods; and (2) potentiostatic method on other electrodes. The advantage of the first method is the faster rate of oxidation. The chlorine evolution in the second method is ten times less then in the first. The accomplished research has shown that urine/feces mixtures can be oxidized to carbon dioxide and water, but current densities are low and must be improved. The perovskite and Ti4O7 coated with RuO2 are the best electrode materials found. Recent experiment with the redox agent improves the current density, however, sulphuric acid is required to keep the redox agent in solution to enhance oxidation effectively. It is desirable to reduce the use of acid and/or find substitutes.

  20. Lipopolysaccharide inhibits or accelerates biomedical titanium corrosion depending on environmental acidity.

    PubMed

    Yu, Fei; Addison, Owen; Baker, Stephen J; Davenport, Alison J

    2015-01-01

    Titanium and its alloys are routinely used as biomedical implants and are usually considered to be corrosion resistant under physiological conditions. However, during inflammation, chemical modifications of the peri-implant environment including acidification occur. In addition certain biomolecules including lipopolysaccharide (LPS), a component of Gram-negative bacterial cell walls and driver of inflammation have been shown to interact strongly with Ti and modify its corrosion resistance. Gram-negative microbes are abundant in biofilms which form on dental implants. The objective was to investigate the influence of LPS on the corrosion properties of relevant biomedical Ti substrates as a function of environmental acidity. Inductively coupled plasma mass spectrometry was used to quantify Ti dissolution following immersion testing in physiological saline for three common biomedical grades of Ti (ASTM Grade 2, Grade 4 and Grade 5). Complementary electrochemical tests including anodic and cathodic polarisation experiments and potentiostatic measurements were also conducted. All three Ti alloys were observed to behave similarly and ion release was sensitive to pH of the immersion solution. However, LPS significantly inhibited Ti release under the most acidic conditions (pH 2), which may develop in localized corrosion sites, but promoted dissolution at pH 4-7, which would be more commonly encountered physiologically. The observed pattern of sensitivity to environmental acidity of the effect of LPS on Ti corrosion has not previously been reported. LPS is found extensively on the surfaces of skin and mucosal penetrating Ti implants and the findings are therefore relevant when considering the chemical stability of Ti implant surfaces in vivo.International Journal of Oral Science advance online publication, 30 January 2015; doi:10.1038/ijos.2014.76. PMID:25634122

  1. Advanced carbon manufacturing for energy and biological applications

    NASA Astrophysics Data System (ADS)

    Turon Teixidor, Genis

    The science of miniaturization has experienced revolutionary advances during the last decades, witnessing the development of the Integrated Circuit and the emergence of MEMS and Nanotechnology. Particularly, MEMS technology has pioneered the use of non-traditional materials in microfabrication by including polymers, ceramics and composites to the well known list of metals and semiconductors. One of the latest additions to this set of materials is carbon, which represents a very important inclusion given its significance in electrochemical energy conversion systems and in applications where it is used as sensor probe material. For these applications, carbon is optimal in several counts: It has a wide electrochemical stability window, good electrical and thermal conductivity, high corrosion resistance and mechanical stability, and is available in high purity at a low cost. Furthermore carbon is biocompatible. This thesis presents several microfabricated devices that take advantage of these properties. The thesis has two clearly differentiated parts. In the first one, applications of micromachined carbon in the field of energy conversion and energy storage are presented. These applications include lithium ion micro batteries and the development of new carbon electrodes with fractal geometries. In the second part, the focus shifts to biological applications. First, the study of the interaction of living cells with micromachined carbon is presented, followed by the description of a sensor based on interdigitated nano-electrode arrays, and finally the development of the new instrumentation needed to address arrays of carbon electrodes, a multiplexed potentiostat. The underlying theme that connects all these seemingly different topics is the use of carbon microfabrication techniques in electrochemical systems.

  2. Self-Assembled Monolayers of n-Alkanethiols Suppress Hydrogen Evolution and Increase the Efficiency of Rechargeable Iron Battery Electrodes

    SciTech Connect

    Malkhandi, S; Yang, B; Manohar, AK; Prakash, GKS; Narayanan, SR

    2013-01-09

    Iron-based rechargeable batteries, because of their low cost, eco-friendliness, and durability, are extremely attractive for large-scale energy storage. A principal challenge in the deployment of these batteries is their relatively low electrical efficiency. The low efficiency is due to parasitic hydrogen evolution that occurs on the iron electrode during charging and idle stand. In this study, we demonstrate for the first time that linear alkanethiols are very effective in suppressing hydrogen evolution on alkaline iron battery electrodes. The alkanethiols form self-assembled monolayers on the iron electrodes. The degree of suppression of hydrogen evolution by the alkanethiols was found to be greater than 90%, and the effectiveness of the alkanethiol increased with the chain length. Through steady-state potentiostatic polarization studies and impedance measurements on high-purity iron disk electrodes, we show that the self-assembly of alkanethiols suppressed the parasitic reaction by reducing the interfacial area available for the electrochemical reaction. We have modeled the effect of chain length of the alkanethiol on the surface coverage, charge-transfer resistance, and double-layer capacitance of the interface using a simple model that also yields a value for the interchain interaction energy. We have verified the improvement in charging efficiency resulting from the use of the alkanethiols in practical rechargeable iron battery electrodes. The results of battery tests indicate that alkanethiols yield among the highest faradaic efficiencies reported for the rechargeable iron electrodes, enabling the prospect of a large-scale energy storage solution based on low-cost iron-based rechargeable batteries.

  3. Mechanical characterization of conducting polymer actuated neural probes under physiological settings

    NASA Astrophysics Data System (ADS)

    Daneshvar, Eugene D.; Smela, Elisabeth; Kipke, Daryl R.

    2010-04-01

    Most implantable chronic neural probes have fixed electrode sites on the shank of the probe. Neural probe shapes and insertion methods have been shown to have considerable effects on the resulting chronic reactive tissue response that encapsulates probes. We are developing probes with controllable articulated electrode projections, which are expected to provoke less reactive tissue response due to the projections being minimally sized, as well as to permit a degree of independence from the probe shank allowing the recording sites to "float" within the brain. The objective of this study was to predict and analyze the force-generating capability of conducting polymer bilayer actuators under physiological settings. Custom parylene beams 21 ?m thick, 1 cm long, and of varying widths (200 - 1000 ?m) were coated with Cr/Au. Electroplated weights were fabricated at the ends of the beams to apply known forces. Polypyrrole was potentiostatically polymerized to varying thicknesses onto the Au at 0.5 V in a solution of 0.1 M pyrrole and 0.1 M dodecylbenzenesulfonate (DBS). Using cyclic voltammetry, the bilayer beams were cycled in artificial cerebrospinal fluid (aCSF) at 37 °C, as well as in aqueous NaDBS as a control. Digital images and video were analyzed to quantify the deflections. The images and the cyclic voltammograms showed that divalent cations in the aCSF interfered with polymer reduction. By integrating polypyrrole-based conducting polymer actuators, we present a type novel neural probe. We demonstrate that actuating PPy(DBS) under physiological settings is possible, and that the technique of microfabricating weights onto the actuators is a useful tool for studying actuation forces.

  4. Automated Controlled-Potential Coulometer for the IAEA

    SciTech Connect

    Cordaro, J.V.; Holland, M.K.; Fields, T.

    1998-01-29

    An automated controlled-potential coulometer has been developed at the Savannah River Site (SRS) for the determination of plutonium for use at the International Atomic Energy Agency`s (IAEA) Safeguards Analytical Laboratory in Siebersdorf, Austria. The system is functionally the same as earlier systems built for use at the Savannah River Site`s Analytical Laboratory. All electronic circuits and printed circuits boards have been upgraded with state-of-the-art components. A higher amperage potentiostat with improved control stability has been developed. The system achieves electronic calibration accuracy and linearity of better than 0.01 percent, with a precision and accuracy better than 0.1 percent has been demonstrated. This coulometer features electrical calibration of the integration system, electrolysis current background corrections, and control-potential adjustment capabilities. These capabilities allow application of the system to plutonium measurements without chemical standards, achieving traceability to the international measurement system through electrical standards and Faraday`s constant. the chemist is provided with the capability to perform measurements without depending upon chemical standards, which is a significant advantage for applications such as characterization of primary and secondary standards. Additional benefits include reducing operating cost to procure, prepare and measure calibration standards and the corresponding decrease in radioactive waste generation. The design and documentation of the automated instrument are provided herein. Each individual module`s operation, wiring, layout, and alignment are described. Interconnection of the modules and system calibration are discussed. A complete set of prints and a list of associated parts are included.

  5. Microstructure and corrosion behavior of porous coatings on titanium alloy by vacuum-brazed method.

    PubMed

    Lee, T M; Chang, E; Yen, C H

    2006-05-01

    The microstructural evolution and electrochemical characteristics of brazed porous-coated Ti-6Al-4V alloy were analyzed and compared with respect to the conventionally 1300 degrees C sintering method. The titanium filler metal of low-melting-point (934 degrees C) Ti-15Cu-15Ni was used to braze commercially pure (CP) titanium beads onto the substrate of Ti-6Al-4V alloy at 970 degrees C for 2 and 8 h. Optical microscopy, scanning and transmission electron microscopy, and X-ray diffractometry (XRD) were used to characterize the microstructure and phase of the brazed metal; also, the potentiostat was used for corrosion study. Experimental results indicate that the bead/substrate contact interface of the 970 degrees C brazed specimens show larger contact area and higher radius curvature in comparison with 1300 degrees C sintering method. The microstructure of brazed specimens shows the Widmanstätten structure in the brazed zone and equiaxed alpha plus intergranular beta in the Ti-6Al-4V substrate. The intermetallic Ti2Ni phase existing in the prior filler metal diminishes, while the Ti2Cu phase can be identified for the substrate at 970 for 2 h, but the latter phase decrease with time. In Hank's solution at 37 degrees C, the corrosion rates of the 1300 degrees C sintering and the 970 degrees C brazed samples are similar at corrosion potential (E(corr)) in potentiodynamic test, and the value of E(corr) for the brazed sample is noble to the sintering samples. The current densities of the brazed specimens do not exceed 100 microA/cm2 at 3.5 V (SCE). These results suggest that the vacuum-brazed method exhibits the potentiality to manufacture the porous-coated specimens for biomedical application. PMID:16278850

  6. Enhanced electrocatalytic activity of the Au-electrodeposited Pt nanoparticles-coated conducting oxide for the quantum dot-sensitized solar cells

    SciTech Connect

    Yoon, Yeung-Pil; Kim, Jae-Hong; Ahn, Kwang-Soon; Kang, Soon-Hyung; Kim, Hyunsoo; Choi, Chel-Jong; Kim, Kyong-Kook

    2014-08-25

    Au was electrodeposited potentiostatically at 0.3?V for 5?min on nanoporous Pt nanoparticle-coated F-doped SnO{sub 2} (FTO/Pt) substrates. For comparison, Au-electrodeposited FTO (FTO/Au) and Au-uncoated FTO/Pt were prepared. FTO/Au showed large-sized Au clusters dispersed sparsely over FTO, which resulted in lower electrocatalytic activity than FTO/Pt. In contrast, FTO/Pt exhibited poor stability unlike FTO/Au due to poisoning by the adsorption of sulfur species. The Au-electrodeposited FTO/Pt (FTO/Pt/Au) consisted of small Au clusters deposited over the entire area of Pt due to the effective Au nucleation provided by nanoporous metallic Pt. FTO/Pt/Au exhibited enhanced electrocatalytic activity and excellent stability because the small Au particles well-dispersed over the nanoporous metallic Pt network provided numerous electrochemical reaction sites, and the Pt surface was not exposed to the electrolyte. When FTO/Pt/Au was used as the counter electrode (CE) of a quantum dot-sensitized solar cell, the significantly enhanced electrocatalytic activity of the FTO/Pt/Au CE facilitated the reduction reaction of S{sub n}{sup 2??}+?2e{sup ?} (CE) ? S{sub n?1}{sup 2?} +?S{sup 2?} at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, S{sub n}{sup 2??}+?2e{sup ?} (TiO{sub 2} in the photoanode) ? S{sub n-1}{sup 2?} +?S{sup 2?}, and significantly improved overall energy conversion efficiency.

  7. Integration of solid-state nanopores in a 0.5 ?m CMOS foundry process

    NASA Astrophysics Data System (ADS)

    Uddin, A.; Yemenicioglu, S.; Chen, C.-H.; Corigliano, E.; Milaninia, K.; Theogarajan, L.

    2013-04-01

    High-bandwidth and low-noise nanopore sensor and detection electronics are crucial in achieving single-DNA-base resolution. A potential way to accomplish this goal is to integrate solid-state nanopores within a CMOS platform, in close proximity to the biasing electrodes and custom-designed amplifier electronics. Here we report the integration of solid-state nanopore devices in a commercial complementary metal-oxide-semiconductor (CMOS) potentiostat chip implemented in On-Semiconductor’s 0.5 ?m technology. Nanopore membranes incorporating electrodes are fabricated by post-CMOS micromachining utilizing the n+ polysilicon/SiO2/n+ polysilicon capacitor structure available in the aforementioned process. Nanopores are created in the CMOS process by drilling in a transmission electron microscope and shrinking by atomic layer deposition. We also describe a batch fabrication method to process a large of number of electrode-embedded nanopores with sub-10 nm diameter across CMOS-compatible wafers by electron beam lithography and atomic layer deposition. The CMOS-compatibility of our fabrication process is verified by testing the electrical functionality of on-chip circuitry. We observe high current leakage with the CMOS nanopore devices due to the ionic diffusion through the SiO2 membrane. To prevent this leakage, we coat the membrane with Al2O3, which acts as an efficient diffusion barrier against alkali ions. The resulting nanopore devices also exhibit higher robustness and lower 1/f noise as compared to SiO2 and SiNx. Furthermore, we propose a theoretical model for our low-capacitance CMOS nanopore devices, showing good agreement with the experimental value. In addition, experiments and theoretical models of translocation studies are presented using 48.5 kbp ?-DNA in order to prove the functionality of on-chip pores coated with Al2O3.

  8. Nanostructuring effect of multi-walled carbon nanotubes on electrochemical properties of carbon foam as constructive electrode for lead acid battery

    NASA Astrophysics Data System (ADS)

    Kumar, Rajeev; Kumari, Saroj; Mathur, Rakesh B.; Dhakate, Sanjay R.

    2015-01-01

    In the present study, nanostructuring effect of multi-walled carbon nanotubes (MWCNTs) on electrochemical properties of coal tar pitch (CTP) based carbon foam (CFoam) was investigated. The different weight fractions of MWCNTs were mixed with CTP and foam was developed from the mixture of CTP and MWCNTs by sacrificial template technique and heat treated at 1,400 and 2,500 °C in inert atmosphere. These foams were characterized by scanning electron microscopy, X-ray diffraction, and potentiostat PARSTAT for cyclic voltammetry. It was observed that, bulk density of CFoam increases with increasing MWCNTs content and decreases after certain amount. The MWCNTs influence the morphology of CFoam and increase the width of ligaments as well as surface area. During the heat treatment, stresses exerting at MWCNTs/carbon interface accelerate ordering of the graphene layer which have positive effect on the electrochemical properties of CFoam. The current density increases from 475 to 675 mA/cm2 of 1,400 °C heat treated and 95 to 210 mA/cm2 of 2,500 °C heat-treated CFoam with 1 wt% MWCNTs. The specific capacitance was decreases with increasing the scan rate from 100 to 1,000 mV/s. In case of 1 % MWCNTs content CFoam the specific capacitance at the scan rate 100 mV/s was increased from 850 to 1,250 ?F/cm2 and 48 to 340 ?F/cm2 of CFoam heat treated at 1,400 °C and 2,500 °C respectively. Thus, the higher value surface area and current density of MWCNTs-incorporated CFoam heat treated to 1,400 °C can be suitable for lead acid battery electrode with improved charging capability.

  9. Lipopolysaccharide inhibits or accelerates biomedical titanium corrosion depending on environmental acidity

    PubMed Central

    Yu, Fei; Addison, Owen; Baker, Stephen J; Davenport, Alison J

    2015-01-01

    Titanium and its alloys are routinely used as biomedical implants and are usually considered to be corrosion resistant under physiological conditions. However, during inflammation, chemical modifications of the peri-implant environment including acidification occur. In addition certain biomolecules including lipopolysaccharide (LPS), a component of Gram-negative bacterial cell walls and driver of inflammation have been shown to interact strongly with Ti and modify its corrosion resistance. Gram-negative microbes are abundant in biofilms which form on dental implants. The objective was to investigate the influence of LPS on the corrosion properties of relevant biomedical Ti substrates as a function of environmental acidity. Inductively coupled plasma mass spectrometry was used to quantify Ti dissolution following immersion testing in physiological saline for three common biomedical grades of Ti (ASTM Grade 2, Grade 4 and Grade 5). Complementary electrochemical tests including anodic and cathodic polarisation experiments and potentiostatic measurements were also conducted. All three Ti alloys were observed to behave similarly and ion release was sensitive to pH of the immersion solution. However, LPS significantly inhibited Ti release under the most acidic conditions (pH 2), which may develop in localized corrosion sites, but promoted dissolution at pH 4–7, which would be more commonly encountered physiologically. The observed pattern of sensitivity to environmental acidity of the effect of LPS on Ti corrosion has not previously been reported. LPS is found extensively on the surfaces of skin and mucosal penetrating Ti implants and the findings are therefore relevant when considering the chemical stability of Ti implant surfaces in vivo. PMID:25634122

  10. A new look at oxide formation at the copper/electrolyte interface by in situ spectroscopies.

    PubMed

    Toparli, Cigdem; Sarfraz, Adnan; Erbe, Andreas

    2015-11-25

    The widely used engineering material copper is a prototype of an electrochemically passive metal. In this work, the passive films on evaporated copper in 0.1 M NaOH are investigated in situ and operando by spectroscopic ellipsometry and Raman spectroscopy, both conducted during oxidation in potentiostatic step experiments. Oxide growth is initiated by jumping from a potential at which the surface is oxide-free to -0.1 V vs. Ag|AgCl|3 M KCl (+0.11 V vs. standard hydrogen electrode, SHE). At subsequent electrode potential jumps, no corresponding jumps in the thickness are observed; instead, oxide growth proceeds steadily. Above +0.3 V vs. Ag|AgCl|3 M KCl (+0.51 V vs. SHE), the oxide layer thickness remains constant at ?7 nm. Raman spectra show a peak at 530 cm(-1), which agrees with the dominant peak in spectra of copper mixed oxide, Cu4O3 (Cu2(I)Cu2(II)O3). Crystalline Cu4O3 nucleates from a precursor state showing strong photoluminescence (PL), which hints at the involvement of Cu2O. Overall, the PL spectra of the growing oxide and absorption spectra indicate the presence of Cu2O in the thin films. Absorption spectra cannot be understood as a superposition of the spectra from different well-described copper oxides, which points to defect-rich oxides that show rather different spectra. Raman spectra also point to an involvement of both crystalline and amorphous oxides that coexist. The results show that the passive layers on copper are more complex than the duplex layers described in the literature; they do contain an oxide with a mixed valency of copper. PMID:26555893

  11. Electrochemical behavior of polypyrrol/AuNP composites deposited by different electrochemical methods: sensing properties towards catechol

    PubMed Central

    García-Hernández, Celia; Medina-Plaza, Cristina; Martín-Pedrosa, Fernando; Blanco, Yolanda; de Saja, José Antonio

    2015-01-01

    Summary Two different methods were used to obtain polypyrrole/AuNP (Ppy/AuNP) composites. One through the electrooxidation of the pyrrole monomer in the presence of colloidal gold nanoparticles, referred to as trapping method (T), and the second one by electrodeposition of both components from one solution containing the monomer and a gold salt, referred to as cogeneration method (C). In both cases, electrodeposition was carried out through galvanostatic and potentiostatic methods and using platinum (Pt) or stainless steel (SS) as substrates. Scanning electron microscopy (SEM) demonstrated that in all cases gold nanoparticles of similar size were uniformly dispersed in the Ppy matrix. The amount of AuNPs incorporated in the Ppy films was higher when electropolymerization was carried out by chronopotentiometry (CP). Besides, cogeneration method allowed for the incorporation of a higher number of AuNPs than trapping. Impedance experiments demonstrated that the insertion of AuNPs increased the conductivity. As an electrochemical sensor, the Ppy/AuNp deposited on platinum exhibited a strong electrocatalytic activity towards the oxidation of catechol. The effect was higher in films obtained by CP than in films obtained by chronoamperometry (CA). The influence of the method used to introduce the AuNPs (trapping or cogeneration) was not so important. The limits of detection (LOD) were in the range from 10?5 to 10?6 mol/L. LODs attained using films deposited on platinum were lower due to a synergy between AuNPs and platinum that facilitates the electron transfer, improving the electrocatalytic properties. Such synergistic effects are not so pronounced on stainless steel, but acceptable LOD are attained with lower price sensors. PMID:26665076

  12. Attenuated total reflection surface-enhanced infrared absorption spectroscopy at a cobalt electrode.

    PubMed

    Huo, Sheng-Juan; Wang, Jin-Yi; Sun, Da-Lin; Cai, Wen-Bin

    2009-10-01

    In situ surface-enhanced infrared absorption spectroscopy (SEIRAS) in attenuated total reflection (ATR) configuration has been extended to a Co electrode fabricated by potentiostatic deposition of a 50-nm-thick Co overlayer onto a Au underlayer chemically preformed on the reflecting plane of an ATR Si hemi-cylindrical prism. The as-prepared Co-on-Au film was characterized with atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The AFM images of the films before and after Co coating revealed island structures facilitating the SEIRA effect with Co nanoparticles much smaller than the underlying Au ones. The XPS spectrum did not contain any characteristic peaks related to Au, suggestive of a virtually pinhole-free nature of the Co overlayer. The voltammetric response of the as-prepared films in phosphate buffer solution (PBS, pH 6.9) was characteristic of a polycrystalline bulk Co electrode. Normally directed unipolar bands were found for surface probe CO molecules on Co surfaces in the PBS with their major band (CO(L)) intensity being one order of magnitude higher than that obtained with conventional IR reflection-absorption spectroscopy (IRRAS). By taking advantage of the higher detection sensitivity, the bands for linearly bonded CO (CO(L)) at 1965-2005 cm(-1) and the multi-bonded (CO(M)) band at 1845-1875 cm(-1) were clearly detected with their Stark tuning rates being 59 and 63 cm(-1) x V(-1), respectively, which would be otherwise unobtainable with the conventional IRRAS in the neutral solution. PMID:19843367

  13. Nanotubular oxide surface and layer formed on the Ti-35Ta-xZr alloys for biomaterials.

    PubMed

    Kim, Eun-Ju; Kim, Won-Gi; Jeong, Yong-Hoon; Choe, Han-Cheol

    2011-08-01

    Titanium and its alloys are widely used as a dental implant material in clinical dentistry and as an orthopedic implant materials due to their good mechanical properties, corrosion resistance, and biocompatibility. In this study, nanotubular oxide surface and layer formed on the Ti-35Ta-xZr alloys for biomaterials have been investigated by using electrochemical methods. Ti-35Ta-xZr alloys were prepared by arc melting and heat treated for 24 hr at 1000 degrees C in argon atmosphere, and then water quenching. Ti oxide nanotubes were formed on the Ti-35Ta-xZr alloys by anodizing in H3PO4 containing 0.8 wt% NaF solution at 25 degrees C. Anodization was carried out using a scanning potentiostat. Microstructures of the alloys and nanotube surface were examined by FE-SEM, EDX, and XRD. Crystallization treatment of nanotube surface was carried out for 3 hr at 450 degrees C. Microstructures of the Ti-35Ta-xZr alloys were changed from beta phase to alpha'' phase, and changed from an equiaxed to a needle-like structure with increasing Zr content. Nanotubular oxide surface and layers consisting of highly ordered nanotubes with a wide range of diameters (approximately 150-200 nm) and lengths (approximately 4-10 microm) can be formed on alloys in the Ti-35Ta-xZr alloys with Zr content. As the Zr content increased from 3% to 15%, length of step between the bamboo knob-like had increasing values of approximately 50 nm, 80 nm, and 140 nm, respectively. The nanotubes formed on the Ti-35Ta-xZr alloy surface were amorphous structure before heat treatment, but oxide surface had mainly an anatase structure by heat treatment. PMID:22103213

  14. Characterization of anodized titanium for hydrometallurgical applications—Evidence for the reduction of cupric on titanium dioxide

    NASA Astrophysics Data System (ADS)

    Liu, Jing; Alfantazi, Akram; Asselin, Edouard

    2013-10-01

    Anodic oxide films (AOFs) were potentiostatically formed on commercially pure titanium in 0.5 M sulfuric acid solutions at various anodizing voltages (up to 80 V) at room temperature. The subject of this study was the corrosion resistance of the AOFs in synthetic copper sulfide leaching solutions containing 30 g L-1 sulfuric acid as well as 12 g L-1 Cl-, 15 g L-1 Cu2+ and 1 g L-1 Fe3+. Open circuit potential (OCP) measurement, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) were used to study the corrosion response of the AOFs in copper sulfide leaching solutions up to 85 °C. Scanning electron microscopy (SEM) was used to investigate the morphology of the AOFs before and after 12 h of immersion at 85 °C. X-ray photoelectron spectroscopy (XPS) was used to examine the surface chemistry of the AOFs after immersion. OCP measurements showed that the final failure of the AOFs occurred in 2 h in de-aerated 30 g L-1 H2SO4 and 12 g L-1 Cl- solutions at 85 °C. Both LPR and EIS results showed a significant increase in the corrosion resistance of the anodized titanium versus that of freshly polished titanium. Electrochemical results were confirmed by SEM analysis, where the AOF formed at 80 V lead to the best improvement in corrosion resistance. XPS measurements revealed that Cu2+ was reduced to Cu or Cu+ within the titanium oxide film. It was further confirmed that the presence of leaching oxidants would inhibit the reduction of Cu2+ on titanium dioxide in chloride containing copper sulfide leaching solutions.

  15. Reversible detection of heparin and other polyanions by pulsed chronopotentiometric polymer membrane electrode.

    PubMed

    Gemene, Kebede L; Meyerhoff, Mark E

    2010-03-01

    The first fully reversible polymeric membrane-based sensor for the anticoagulant heparin and other polyanions using a pulsed chronopotentiometry (pulstrode) measurement mode is reported. Polymeric membranes containing a lipophilic inert salt of the form R(+)R(-) (where R(+) and R(-) are tridodecylmethylammonium (TDMA(+)) and dinonylnaphthalene sulfonate (DNNS(-)), respectively) are used to suppress unwanted spontaneous ion extractions under zero-current equilibrium conditions. An anodic galvanostatic current pulse applied across the membrane perturbs the equilibrium lipophilic ion distribution within the membrane phase in such a way that anions/polyanions are extracted into the membrane from the sample. The membrane is then subjected to an open-circuit zero current state for a short period, and finally a 0 V vs reference electrode potentiostatic pulse is applied to restore the membrane to its initial full equilibrium condition. Potentials are sampled as average values during the last 10% of the 0.5 s open circuit phase of the measurement cycle. Fully reversible and reproducible electromotive force (emf) responses are observed for heparin, pentosan polysulfate (PPS), chondroitin sulfate (CS), and oversulfated chondroitin sulfate (OSCS), with the magnitude of the potentiometric response proportional to charge density of the polyanions. The sensor provides an emf response related to heparin concentrations in the range of 1-20 U/mL. The responses to variations in heparin levels and toward other polyanions of the pulstrode configuration are analogous to the already established single-use, nonreversible potentiometric polyion sensors based on membranes doped only with the lipophilic anion exchanger TDMA(+). PMID:20121058

  16. Low temperature operation and influence parameters on the cold start ability of portable PEMFCs

    NASA Astrophysics Data System (ADS)

    Oszcipok, M.; Zedda, M.; Riemann, D.; Geckeler, D.

    The start up behaviour of PEM fuel cells below 0 °C is one of the most challenging tasks to be solved before commercialisation. The automotive industry started to develop solutions to reduce the start up time of fuel cell systems in the middle of the nineties. The strategies varied from catalytic combustion of hydrogen on the electrode catalyst to fuel starvation or external stack heating via cooling loops to increase the stack temperature. Beside the automotive sector the cold start ability is as well important for portable PEMFC applications for outdoor use. But here the cold start issue is even more complicated, as the fuel cell system should be operated as passive as possible. Below 0 °C freezing of water inside the PEMFC could form ice layers in the electrode and in the gas diffusion layer. Therefore the cell reaction is limited or even inhibited. Product water during the start up builds additional barriers and leads to a strong decay of the output power at isothermal operating conditions. In order to find out which operational and hardware parameters affect this decay, potentiostatic experiments on single cells were performed at isothermal conditions. These experiments comprise investigations of the influence of membrane thickness and different GDL types as well as the effect of gas flow rates and humidification levels of the membrane. As pre stage to physical based models, empirical based prediction models are used to gain a better understanding of the main influence parameters during cold start. The results are analysed using the statistical software Cornerstone 4.0. The experience of single cell investigations are compared to start up behaviour of portable fuel cell stacks which are operated in a climate chamber at different ambient temperatures below 0 °C. Additional flow sharing problems in the fuel cell stack could be seen during cold start up experiments.

  17. Measurements and mechanisms of localized aqueous corrosion in aluminum-lithium-copper alloys

    NASA Technical Reports Server (NTRS)

    Wall, Douglas; Stoner, Glenn E.

    1991-01-01

    Summary information is included for electrochemical aspects of stress corrosion cracking in alloy 2090 and an introduction to the work to be initiated on the new X2095 (Weldalite) alloy system. Stress corrosion cracking (SCC) was studied in both S-T and L-T orientations in alloy 2090. A constant load TTF test was performed in several environments with a potentiostatically applied potential. In the same environments the electrochemical behavior of phases found along subgrain boundaries was assessed. It was found that rapid failure due to SCC occurred when the following criteria was met: E(sub BR,T1) is less than E(sub applied) is less than E(sub Br, matrix phase). Although the L-T orientation is usually considered more resistant to SCC, failures in this orientation occurred when the stated criteria was met. This may be due to the relatively isotropic geometry of the subgrains which measure approximately 12 to 25 microns in diameters. Initial studies of alloy X2095 includes electrochemical characterization of three compositional variations each at three temperatures. The role of T(sub 1) dissolution in SCC behavior is addressed using techniques similar to those used in the research of 2090 described. SCC susceptibility is also studied using alternate immersion facilities at Reynolds Metals Corporation. Pitting is investigated in terms of stability, role of precipitate phases and constituent particles, and as initiation sites for SCC. In all research endeavors, attempts are made to link electrochemistry to microstructure. Previous work on 2090 provides a convenient basis for comparison since both alloys contain T(sub 1) precipitates but with different distributions. In 2090 T(sub 1) forms preferentially on subgrain boundaries whereas in X2095 the microstructure appears to be more homogeneous with finer T(sub 1) particles. Another point for comparison is the delta prime strengthening phase found in 2090 but absent in X2095.

  18. Microscopy of hierarchically organized TiO2 photoelectrode for dye solar cells

    NASA Astrophysics Data System (ADS)

    Eskandar, A.; Mohamed, N. M.

    2015-07-01

    Research on improving the performance of dye solar cells has various aspects of the device being investigated. This paper analyzes the deliberately hierarchized photoelectrode configuration for DSC applications to improve the performance of DSCs. Multiple layers of differently composed TiO2 particle types namely aggregates and nanoparticles were deposited to form a photoelectrode with thickness of about 12 µm. The photoelectrodes were assembled into working DSCs with an active area of 1 cm2. Measurement for solar power conversion performance was measured under 1 sun at AM1.5 spectrum simulated sunlight. Electron microscopy for photoelectrode analysis was conducted using Field Emission Scattering Electron Microscopy with enhanced resolution. External Quantum Efficiency was measured using a purpose built instrument. Kinetics were investigated using the Electrochemical Impedance Spectroscopy (EIS) measurement with a potentiostat. The best performing DSC is of the hierarchically organized photoelectrode with a photoconversion efficiency of 4.58%, an increase of 14% in comparison to the reference samples with fully aggregates configuration. Short circuit current density, Jsc increases by about 2.223 mA cm-2 relative to the blanks. The electron microscopy confirmed expected thickness at around 10 µm and layers forming the photoelectrode being hierarchically deposited with ˜20 nm TiO2 nanoparticles and 450 nm TiO2 aggregates mixture composition. EQE improved especially for visible region of 500-550 nm light wavelengths with 12 % increase in the response of in that region. Improvement to the diffusion coefficient as measured by the EIS contributed to the performance increase of the photoelectrode configuration under investigation.

  19. Using anodic aluminum oxide templates and electrochemical method to deposit BiSbTe-based thermoelectric nanowires

    PubMed Central

    2014-01-01

    In this study, the cyclic voltammetry method was first used to find the reduced voltages and anodic peaks of Bi3+, Sb3+, and Te4+ ions as the judgments for the growth of the (Bi,Sb)2 - x Te3 + x-based materials. Ethylene glycol (C2H6O2) was used as a solvent, and 0.3 M potassium iodide (KI) was used to improve the conductivity of the solution. Two different electrolyte formulas were first used: (a) 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 and (b) 0.015 M Bi(NO3)3-5H2O, 0.005 M SbCl3, and 0.0075 M TeCl4. The potentiostatic deposition process was first used to find the effect of reduced voltage on the variation of compositions of the (Bi,Sb)2 - xTe3 + x-based materials. After finding the better reduced voltage, 0.01 M Bi(NO3)3-5H2O, 0.01 M SbCl3, and 0.01 M TeCl4 were used as the electrolyte formula. The pulse deposition process was successfully used to control the composition of the (Bi,Sb)2 - xTe3 + x-based materials and grow the nanowires in anodic aluminum oxide (AAO) templates. PMID:24502697

  20. Determination of the critical potentials for pitting, protection, and stress corrosion cracking of 67-33 brass in fluoride solutions

    SciTech Connect

    Lee, C.K.; Shih, H.C.

    1995-03-01

    Pitting potentials and protection potentials have been determined for {alpha}-brass (33% Zn) using a cyclic polarization method. Increasing the F{sup {minus}} concentration shifts the critical potential to more active values. The pitting potentials, E{sub p}, and protection potentials, E{sub pp}, depend on the logarithmic concentration of F{sup {minus}} ions according to the equations: E{sub p} = a + b log [F{sup {minus}}] and E{sub pp} = a + b log [F{sup {minus}}]. Slow strain rate tests (SSRT), at a strain rate of 5 {times} 10{sup {minus}5} s{sup {minus}1}, were performed under open-circuit and potentiostatic conditions to study the stress corrosion cracking (SCC) characteristics of the {alpha}-brass in NaF solutions of various concentrations (pH 6.8) at 25 C. The minimum concentration of NaF that caused intergranular stress corrosion cracking (IGSCC) was 1 {times} 10{sup {minus}4} M. This concentration, was also the critical level for repassivation, observed in cyclic polarization tests. These results demonstrate a good correlation between the electrical and the mechanical breakdown of the passive film. In the presence of 10{sup {minus}1}M NaF the potential range for IGSCC was {minus}150 to {minus}50 mV (SCE). These critical potentials were restricted to the stable passive potential range and also fell within the potential-pH region where Cu{sub 2}O was stable. The formation of a Cu{sub 2}O film on the brass after polarization in the passive region was confirmed by X-ray diffraction (XRD). At more noble potentials and at cathodic potentials below the Cu{sub 2}O domain, the failure mode was ductile fracture. These observations of IGSCC of the brass in fluoride solutions support a film rupture-dissolution mechanism.

  1. Structure and corrosive wear resistance of plasma-nitrided alloy steels in 3% sodium chloride solutions

    SciTech Connect

    Lee, C.K.; Shih, H.C. . Dept. of Materials Science and Engineering)

    1994-11-01

    Type 304 stainless steel (SS), type 410 SS, and type 4140 low-alloy steel were plasma nitrided in a commercial furnace at 560 C for 50 h. Microstructure and the composition of the nitrided layer were analyzed. The resistance to corrosive wear was evaluated by a tribotest in which the specimen was held under potentiostatic control at anodic and cathodic potentials in 3% sodium chloride solution (pH 6.8). Electrochemical polarization measurements were made, and the surface morphology and composition after corrosive wear were examined. Wear rates at cathodic potentials were very low, but significant weight losses were observed as the applied potentials were increased anodically. The coefficient of friction varied in a fashion similar to the wear rate. For the untreated alloys, the magnitude of the wear rate and coefficient of friction decreased as follows: type 4140 alloy > type 41 SS > type 304 SS. For the plasma-nitrided alloys, the ranking was: type 304 SS > type 410 SS. type 4140 alloy. Plasma nitriding was shown to be beneficial to the corrosive wear resistance of type 4140 alloy, but an adverse effect was obtained for types 304 and 410 SS. These findings could be interpreted in terms of the electrochemical polarization characteristics of a static specimen and were strongly related to the subtleties of the nitrided microstructures. The stable chromium nitride (CrN) segregated in the [gamma]-iron (type 304 SS) and [alpha]-Fe (type 41 SS) matrices and resulted in a pitting and spalling type of corrosive wear mechanism. The phases [epsilon]-(Fe, Cr)[sub 2-3]N and [gamma]-(Fe, Cr)[sub 4]N enriched in the surface layer of nitrided type 4140 alloy provided excellent corrosive wear resistance.

  2. Corrosion probes for fireside monitoring in coal-fired boilers

    SciTech Connect

    Covino, Bernard S., Jr.; Bullard, Sophie J.; Ziomek-Moroz, M.; Holcomb, Gordon R.

    2005-01-01

    Corrosion probes are being developed and combined with an existing measurement technology to provide a tool for assessing the extent of corrosion of metallic materials on the fireside in coal-fired boilers. The successful development of this technology will provide power plant operators the ability to (1) accurately monitor metal loss in critical regions of the boiler, such as waterwalls, superheaters, and reheaters; and (2) use corrosion rates as process variables. In the former, corrosion data could be used to schedule maintenance periods and in the later, processes can be altered to decrease corrosion rates. The research approach involves laboratory research in simulated environments that will lead to field tests of corrosion probes in coal-fired boilers. Laboratory research has already shown that electrochemically-measured corrosion rates for ash-covered metals are similar to actual mass loss corrosion rates. Electrochemical tests conducted using a potentiostat show the corrosion reaction of ash-covered probes at 500?C to be electrochemical in nature. Corrosion rates measured are similar to those from an automated corrosion monitoring system. Tests of corrosion probes made with mild steel, 304L stainless steel (SS), and 316L SS sensors showed that corrosion of the sensors in a very aggressive incinerator ash was controlled by the ash and not by the alloy content. Corrosion rates in nitrogen atmospheres tended to decrease slowly with time. The addition of oxygen-containing gases, oxygen and carbon dioxide to nitrogen caused a more rapid decrease in corrosion rate, while the addition of water vapor increased the corrosion rate.

  3. Multiple redox states of multiheme cytochromes may enable bacterial response to changing redox environments

    NASA Astrophysics Data System (ADS)

    Arbour, T.; Wrighton, K. C.; Mullin, S. W.; Castelle, C.; Luef, B.; Gilbert, B.; Banfield, J. F.

    2013-12-01

    Multiheme c-type cytochromes (MHCs) are key components in electron-transport pathways that enable some microorganisms to transfer electron byproducts of metabolism to a variety of minerals. As a response to changes in mineral redox potential, microbial communities may shift their membership, or individual organisms may adjust protein expression. Alternatively, the ability to respond may be conferred by the innate characteristics of certain electron-transport-chain components. Here, we used potentiostat-controlled microbial fuel cells (MFCs) to measure the timescale of response to imposed changes in redox conditions, thus placing constraints on the importance of these different mechanisms. In the experiments, a solid electrode acts as an electron-accepting mineral whose redox potential can be precisely controlled. We inoculated duplicate MFCs with a sediment/groundwater mixture from an aquifer at Rifle, Colorado, supplied acetate as an electron donor, and obtained stable, mixed-species biofilms dominated by Geobacter and a novel Geobacter-related family. We poised the anode at potentials spanning the range of natural Fe(III)-reduction, then performed cyclic voltammetry (CV) to characterize the overall biofilm redox signature. The apparent biofilm midpoint potential shifted directly with anode set potential when the latter was changed within the range from about -250 to -50 mV vs. SHE. Following a jump in set potential by 200 mV, the CV-midpoint shift by ~100 mV over a timescale of ~30 minutes to a few hours, depending on the direction of the potential change. The extracellular electron transfer molecules, whose overall CV signature is very similar to those of purified MHCs, appear to span a broad redox range (~200 mV), supporting the hypothesis that MHCs confer substantial redox flexibility. This flexibility may be a principle reason for the abundance of MHCs expressed by microorganisms capable of extracellular electron transfer to minerals.

  4. A High-Throughput Study of PtNiZr Catalysts for Application in PEM Fuel Cells

    SciTech Connect

    Whitacre, J.F.; Valdez, T.I.; Narayanan, S.R.

    2009-05-26

    The effects of adding Zr to PtNi oxygen reduction reaction (ORR) electrocatalyst alloys were examined in a study aimed at probing the possibility of creating catalysts with enhanced resistance to corrosion in a PEM fuel cell environment. Samples consisting of pure Pt or PtNiZr alloys with a range of compositions (not exceeding 11 at.% Zr) were fabricated using co-sputter deposition. A high-throughput fabrication approach was used wherein 18 distinct thin film catalyst alloy samples with varying compositions were deposited onto a large-area substrate with individual Au current collector structures. A multi-channel pseudo-potentiostat allowed for the simultaneous quantitative study of catalytic activity for all 18 electrodes in a single test bath, a first for the study of ORR electrocatalysts. A properly stirred oxygenated 1 M H{sub 2}SO{sub 4} electrolyte solution was used to provide each electrode with a steady-state flow of reactants during electrochemical evaluation. The onset potentials, absolute current density values, and Tafel analysis data obtained using this technique were compared with literature reports. The analyses showed that most PtNiZr alloys tested offered improvements over pure Pt, however those surfaces with a high mole fraction (>4 at.%) of Zr exhibited reduced activity that was roughly inversely correlated to the amount of Zr present. Film composition, morphology, and crystallographic properties were examined using X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), SEM, and synchrotron X-ray diffraction. These data were then correlated with electrochemical data to elucidate the relationships between composition, structure, and relative performance for this ternary system.

  5. Surface Analysis by Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Coury, Louis A., Jr.; Johnson, Mario; Murphy, Tammy J.

    1995-12-01

    In both student projects a Burleigh Instruments ARIS-2200E STM was employed to image polycrystalline gold electrodes before and after deposition of a second metal onto the surface. Students prepared their own tungsten STM tips using an A.C.-etching procedure in 5% NaNO2. The electrodes used were available commercailly (AAI-AbTech, Yardley, PA) and consisted of 1000 of Au over a 100 adhesion layer of Ti on electronics-grade borosilicate glass. Electrodes were affixed to the STM sample holder using conductive carbon tape (SPI, West Chester, PA) and imaged in air. Modified electrodes were prepared by sonochemical deposition of 300 nm-Cu particles onto the Au surface in a procedure described elsewhere (2) or by the electrolytic deposition of various metals used in dental amalgams from acidic media using a Cypress Systems CS-1087 potentiostat. ResultsIn a typical image obtained for an unmodified Au surface (see image below), small crystallites (~500 to 1000 in diameter) of Au formed during the sputtering process during electrode fabrication are clearly visible. Images of modified electrodes (not shown) always show a markedly different morphology, with visible characteristic surface features ranging in size from hundreds of nanometers to several microns. The concepts students learn in these studies include electron tunneling, electroplating, nucleation phenomena, and amalgam chemistry. Although primarily touted as a method for atomic resolution imaging, STM clearly has utility for examining surfaces with features in the 100-nm to 1-micrometer size regime. Because of the recent availability of inexpensive instruments with user-friendly software, we encourage others to consider incorporating STM into the undergraduate curriculum. AcknowledgmentThis project was supported partially by a grant, DUE-9351426, from the National Science Foundation Division of Undergraduate Education Instrumentation and Laboratory Improvement Program. Literature Cited Lederman, L. Science 1991, 251, 1S--20S. Madigan, N. A.; Murphy, T. J.; Fortune, J. M.; Hagan, C. R. S.; Coury, L. A. submitted.

  6. Nuclear magnetic resonance spectroscopic study of the electrochemical oxidation product of methanol on platinum black

    SciTech Connect

    Day, J.B.; Oldfield, E.; Wieckowski, A.; Vuissoz, P.A.; Ansermet, J.P.

    1996-12-25

    The absorbate resulting from the potentiostatic, catalytic decomposition of methanol (0.1 M CH{sub 3}OH in 0.5 M H{sub 2}SO{sub 4}) on a platinum black electrode has been studied via {sup 13}C nuclear magnetic resonance spectroscopy, at open cell potential. Cyclic voltammetry results indicate that coverage is a function of electrodecomposition time and potential. The spin-spin relaxation time T{sub 2} is dependent on surface coverage and ranges from {approx}3 to {approx}1.8 ms at coverages ranging from 0.3 to 0.75 ML, due to the increased effectiveness of {sup 13}C-{sup 13}C dipolar interactions at high coverage. At 0.5 ML, the temperature dependence of the {sup 13}CO T{sub 2} (in a {sup 2}H{sub 2}O-exchanged electrolyte system) has been determined from 80 to 250 K. There is a well-defined peak in relaxation rate at {approx}170 K which can be modeled using a simple diffusional model having an activation energy of 7.9 {+-} 2.0 kcal/ mol. Spin-lattice relaxation results from 10 to 250 K reveal Korringa behavior, with a T{sub 1}T product (and Knight shift) that is independent of surface coverage, and has the same value for the electrochemical adsorbate as gas phase CO adsorbed on Pt. The similarity in T{sub 1}T, T{sub 2}, Knight shift, and activation energy for surface diffusion are in general accord with values previously measured in gas phase heterogeneous catalyst systems and strongly support the idea of primarily on top CO with C-down, on one major type of surface site. 18 refs., 8 figs., 2 tabs.

  7. Integration of solid-state nanopores in a 0.5 ?m cmos foundry process

    PubMed Central

    Uddin, A; Yemenicioglu, S; Chen, C-H; Corigliano, E; Milaninia, K; Theogarajan, L

    2013-01-01

    High-bandwidth and low-noise nanopore sensor and detection electronics are crucial in achieving single-DNA base resolution. A potential way to accomplish this goal is to integrate solid-state nanopores within a CMOS platform, in close proximity to the biasing electrodes and custom-designed amplifier electronics. Here we report the integration of solid-state nanopore devices in a commercial complementary metal-oxide semiconductor (CMOS) potentiostat chip implemented in On-Semiconductor’s 0.5 ?m technology. Nanopore membranes incorporating electrodes are fabricated by post-CMOS micromachining utilizing the N+ polysilicon/SiO2/N+ polysilicon capacitor structure available in the aforementioned process. Nanopores are created in the CMOS process by drilling in a transmission electron microscope and shrinking by atomic layer deposition. We also describe a batch fabrication method to process a large of number of electrode-embedded nanopores with sub-10 nm diameter across CMOS-compatible wafers by electron beam lithography and atomic layer deposition. The CMOS-compatibility of our fabrication process is verified by testing the electrical functionality of on-chip circuitry. We observe high current leakage with the CMOS nanopore devices due to the ionic diffusion through the SiO2 membrane. To prevent this leakage, we coat the membrane with Al2O3 which acts as an efficient diffusion barrier against alkali ions. The resulting nanopore devices also exhibit higher robustness and lower 1/f noise as compared to SiO2 and SiNx. Furthermore, we propose a theoretical model for our low-capacitance CMOS nanopore devices, showing good agreement with the experimental value. In addition, experiments and theoretical models of translocation studies are presented using 48.5 kbp ?-DNA in order to prove the functionality of on-chip pores coated with Al2O3. PMID:23519330

  8. VOLTINT: A Matlab ®-based program for semi-automated processing of geochemical data acquired by voltammetry

    NASA Astrophysics Data System (ADS)

    Bristow, Gwendolyn; Taillefert, Martial

    2008-02-01

    Recent progress has resulted in the development of advanced techniques to acquire geochemical information in situ in aquatic systems. Among these techniques, voltammetry has generated significant interest for its ability to detect several important redox-sensitive chemical species in a fast, reliable, and automated manner. Many research groups worldwide have now adopted these techniques for geochemical measurements in various marine and freshwater systems, including water column, sediment, microbial mat, and groundwater, with a high spatial and temporal resolution. Unfortunately, the ability to conduct multiple measurements with great spatial and temporal resolutions generates large data sets that are difficult to integrate manually. We report a new computer program, voltammetric integration software (VOLTINT), that can integrate large voltammetric data sets semi-automatically. This program implemented in Matlab ® is based on a graphical user interface to visualize and identify voltammetric signals. The program differentiates between voltammetric techniques and derives or integrates voltammetric signals to produce output data files containing the redox potentials, current intensities, and, when appropriate, peak surface areas of each electrochemical species that can be detected. VOLTINT was developed with the intention of integrating voltammetric data obtained with potentiostats from a specific company Analytical Instrument Systems, Inc. (AIS). However, the scripts can be easily altered to process any ASCII file containing voltammetric data. The details of the program are presented, and examples provided along with recommendations regarding the analysis of voltammetric data in the context of this program. VOLTINT is available free of charge to anyone who is interested in integrating multiple voltammetric data files in a fast and reliable manner.

  9. Effect of bicarbonate ion additives on pitting corrosion of type 316L stainless steel in aqueous 0.5 M sodium chloride solution

    SciTech Connect

    Park, J.J.; Pyun, S.I.; Lee, W.J.; Kim, H.P.

    1999-04-01

    The effect of bicarbonate ions (HCO{sub 3}{sup {minus}}) on pitting corrosion of type 316L stainless steel (SS, UNS S3 1603) was investigated in aqueous 0.5 M sodium chloride (NaCl) solution using potentiodynamic polarization, the abrading electrode technique, alternating current (AC) impedance spectroscopy combined with x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Addition of HCO{sub 3}{sup {minus}} ions to NaCl solutions extended the passive potential region in width and, at the same time, raised the pitting potential in value on the potentiodynamic polarization curve. Potentiostatic current transients obtained from the moment just after interrupting the abrading action showed the repassivation rate of propagating pits increased and that the pit growth rate decreased with increasing HCO{sub 3}{sup {minus}} ion concentration. Over the whole applied potential, the oxide film resistance was higher in the presence of HCO{sub 3}{sup {minus}} ions. The pit number density decreased with increasing HCO{sub 3}{sup {minus}} ion concentration. Moreover, addition of HCO{sub 3}{sup {minus}} ions to NaCl solutions retarded lateral pit growth, while promoting downward pit growth from the surface. The bare surface of the specimen repassivated preferentially along the pit mouth and walls, compared to the pit bottom, as a result of formation of a surface film with a high content of protective mixed ferrous-chromous carbonate ([Fe,Cr]CO{sub 3}) that formed from preferential adsorption of HCO{sub 3}{sup {minus}} ions.

  10. Comparing atrazine and cyanuric acid electro-oxidation on mixed oxide and boron-doped diamond electrodes.

    PubMed

    Malpass, Geoffroy R P; Salazar-Banda, Giancarlo R; Miwa, Douglas W; Machado, Sérgio A S; Motheo, Artur J

    2013-01-01

    The breakdown of pesticides has been promoted by many methods for clean up of contaminated soil and wastewaters. The main goal is to decrease the toxicity of the parent compound to achieve non-toxic compounds or even, when complete mineralization occurs, carbon dioxide and water. Therefore, electrochemical degradation (potentiostatic and galvanostatic) of both the pesticide atrazine and cyanuric acid (CA) at boron-doped diamond (BDD) and Ti/Ru0.3Ti0.7O2 dimensionally stable anode (DSA) electrodes, in different supporting electrolytes (NaCl and Na2SO4), is presented with the aim of establishing the influence of the operational parameters on the process efficiency. The results demonstrate that both the electrode material and the supporting electrolyte have a strong influence on the rate of atrazine removal. In the chloride medium, the rate of atrazine removal is always greater than in sulfate under all conditions employed. Furthermore, in the sulfate medium, atrazine degradation was significant only at the BDD electrode. The total organic carbon (TOC) load decreased by 79% and 56% at the BDD and DSA electrodes, respectively, in the chloride medium. This trend was maintained in the sulfate medium but the TOC removal was lower (i.e. 33% and 13% at BDD and DSA electrodes, respectively). CA, a stable atrazine degradation intermediate, was also studied and it is efficiently removed using the BDD electrode in both media, mainly when high current densities are employed. The use of the BDD electrode in the chloride medium not only degrades atrazine but also mineralized cyanuric acid leading to the higher TOC removal. PMID:23837356

  11. Liquid infused porous surfaces for mineral fouling mitigation.

    PubMed

    Charpentier, Thibaut V J; Neville, Anne; Baudin, Sophie; Smith, Margaret J; Euvrard, Myriam; Bell, Ashley; Wang, Chun; Barker, Richard

    2015-04-15

    Prevention of mineral fouling, known as scale, is a long-standing problem in a wide variety of industrial applications, such as oil production, water treatment, and many others. The build-up of inorganic scale such as calcium carbonate on surfaces and facilities is undesirable as it can result in safety risks and associated flow assurance issues. To date the overwhelming amount of research has mainly focused on chemical inhibition of scale bulk precipitation and little attention has been paid to deposition onto surfaces. The development of novel more environmentally-friendly strategies to control mineral fouling will most probably necessitate a multifunctional approach including surface engineering. In this study, we demonstrate that liquid infused porous surfaces provide an appealing strategy for surface modification to reduce mineral scale deposition. Microporous polypyrrole (PPy) coatings were fabricated onto stainless steel substrates by electrodeposition in potentiostatic mode. Subsequent infusion of low surface energy lubricants (fluorinated oil Fluorinert FC-70 and ionic liquid 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIm)) into the porous coatings results in liquid-repellent slippery surfaces. To assess their ability to reduce surface scaling the coatings were subjected to a calcium carbonate scaling environment and the scale on the surface was quantified using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). PPy surfaces infused with BMIm (and Fluorinert to a lesser extent) exhibit remarkable antifouling properties with the calcium carbonate deposition reduced by 18 times in comparison to untreated stainless steel. These scaling tests suggest a correlation between the stability of the liquid infused surfaces in artificial brines and fouling reduction efficiency. The current work shows the great potential of such novel coatings for the management of mineral scale fouling. PMID:25585291

  12. Oxygen reduction at the platinum/Nafion{reg_sign} interface: Electrode kinetics and mass transport

    SciTech Connect

    Parthasarathy, A.

    1992-12-31

    Research in solid polymer electrolyte fuel cells is gaining momentum because of the prospects of attaining high energy efficiencies and power densities, essential for transportation and space applications. The most advanced solid polymer electrolytes for these fuel cells are the perfluorosulfonate ionomers (PFSIs) such as duPont`s Naflon and the Dow PFSIs. The high oxygen solubility, chemical stability, proton conductivity and permselectivity exhibited by Naflon and the Dow PFSI`s make them ideal candidates as electrolytes for fuel cells. Furthermore, the minimal anion adsorption on electrodes from fluorinated acids enhances oxygen reduction kinetics. The primary objectives of this work were to determine the concentration and diffusion coefficient of oxygen in Naflon, and the electrode kinetic parameters for the reduction of oxygen at the Pt/Nafion interface under totally solid-state conditions. Cyclic voltammetric and potentiostatic transient measurements were made at the Pt/Nafion interface. Slow sweep voltammograms yielded Tafel parameters for oxygen reduction. From the two-section Tafel, plot, the calculated exchange current densities were found to be higher than those obtained at any other Pt/acid interface. From an analysis of the transients, the values of oxygen solubility and diffusion coefficient in Naflon were determined. Electrochemical impedance spectroscopic (EIS) investigations were then used to study oxygen reduction under lower humidfication conditions. EIS clearly permits the discrimination of electrode kinetics, mass transport of O{sub 2} and the electrical characteristics of the membrane. A temperature-dependence study in the range of 30{degrees}C to 80{degrees}C yielded the activation energy for oxygen reduction at the Pt/Naflon interface. The diffusion coefficient of oxygen in Nafion increases with temperature while its solubility decreases. the pressure-dependence of oxygen reduction kinetics shows that the reaction order of oxygen is unity.

  13. Electrochemical and Structural Study of the Layered, 'Li-Excess' Lithium-Ion Battery Electrode Material Li[Li[subscript 1/9]Ni[subscript 1/3]Mn[subscript 5/9

    SciTech Connect

    Jiang, Meng; Key, Baris; Meng, Ying S.; Grey, Clare P.

    2009-09-15

    The overcapacity mechanism and high voltage process of the Li-excess electrode material Li[Li{sub 1/9}Ni{sub 1/3}Mn{sub 5/9}]O{sub 2} are studied by solid-state NMR, X-ray diffraction, X-ray absorption spectroscopy, transmission electron microscopy, combined with galvanostatic and potentiostatic intermittent titration electrochemical measurements. The cycling performance is improved noticeably when the material is cycled between potential windows of 5.3-2.5 V compared to 4.6-2.5 V. Diffraction data show that structural changes occur at high voltages, the solid-state NMR data of the same samples indicating that the high voltage processes above 4.4 V are associated with Li removal from the structure, in addition to electrolyte decomposition. The NMR spectra of the discharged samples show that cation rearrangements in the transition metal layers have occurred. The XAS spectra confirm that the Mn oxidation state remains unchanged at 4+, whereas Ni{sup 2+} is oxidized to Ni{sup 4+} on charging to 4.4 V, returning to Ni{sup 2+} on discharge, independent of the final charge voltage. A significant change of the shape of the Ni edge is observed in the 4.6-5.3 V potential range on charge, which is ascribed to a change in the Ni local environment. No O{sub 2} evolution was detected based on ex situ analysis of the gases evolved in the batteries, the TEM data showing that thick passivating films form on the electrodes. The results suggest that at least some of the oxygen loss from these lithium-excess materials occurs via a mechanism involving electrolyte decomposition.

  14. A Versatile Coating Strategy to Highly Improve the Electrochemical Properties of Layered Oxide LiMO2 (M = Ni0.5Mn0.5 and Ni1/3Mn1/3Co1/3).

    PubMed

    Zhao, Enyue; Chen, Minmin; Chen, Dongfeng; Xiao, Xiaoling; Hu, Zhongbo

    2015-12-16

    This work provides a convenient, effective and highly versatile coating strategy for the layered oxide LiMO2 (M = Ni0.5Mn0.5 and Ni1/3Mn1/3Co1/3). Here, layered oxide LiMO2 (M = Ni0.5Mn0.5 and Ni1/3Mn1/3Co1/3) has been successfully coated with ion conductor of Li2SiO3 by in situ hydrolysis of tetraethyl orthosilicate (TEOS) followed by the lithiation process. The discharge capacity, cycle stability, rate capability, and some other electrochemical performances of layered cathode materials LiMO2 can be highly enhanced through surface-modification by coating appropriate content of Li2SiO3. Particularly, the 3 mol % Li2SiO3 coated LiNi1/3Mn1/3Co1/3O2 exhibits approximately a discharge capacity of 111 mAh/g after 300 cycles at the current density of 800 mA/g (5 C). Potentiostatic intermittent titration technique (PITT) test was carried out to investigate the mechanism of the improvement in the electrochemical properties. The diffusion coefficient of Li(+)-ion (DLi) of Li2SiO3 coated layered oxide materials has been greatly increased. We believe our methodology provides a convenient, effective and highly versatile coating strategy, which can be expected to open the way to ameliorate the electrochemical properties of electrode materials for lithium ion batteries. PMID:26599838

  15. Synthesis Structure Property Relations in Layered, Li-excess Oxides Electrode Materials Li[Li1/3-2x/3NixMn2/3-x/3]O2 (x=1/3, 1/4 and 1/5)

    SciTech Connect

    Fell, Christopher; Carroll, Kyler; Chi, Miaofang; Meng, Ying Shirley

    2010-01-01

    Relations between synthesis conditions, detailed crystal structures, and electrochemical properties of the Li-excess layered oxides Li[Ni{sub x}Li{sub 1/3-2x/3}Mn{sub 2/3-x/3}]O{sub 2}(0 < x < 1/2) are studied by X-ray diffraction, scanning electron microscopy (EELS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron energy-loss spectrometry, combined with electrochemical property measurements including potentiostatic intermittent titration technique (PITT). Optimal synthesis conditions are obtained for stoichiometric samples sintered at 1000 C in air followed by furnace cooling. The materials exhibit capacities of {approx}250, 230, and 200 mAh/g within a voltage range of 2-4.8 V on discharge for x = 1/5, 1/4 and 1/3, respectively. Diffraction data of electrochemically cycled electrode materials show an expanded c/a lattice ratio and changing Li/Ni interlayer mixing indicating peculiar cation migration in the structures. High resolution TEM images and XPS spectra show obvious differences in the surface characteristics of the samples synthesized with stoichiometric and excess amount of LiOH, suggesting that surface characteristics is one of the contributing factors to the difference in electrochemical properties. Our results suggest that the first cycle irreversible capacity is affected by both the bulk and surface characteristics of pristine materials, which is strongly influenced by precursor chemistry. The PITT results suggest that cation rearrangement during the charge/discharge has a significant impact on the lithium chemical diffusivity.

  16. Electronic, Structural, and Electrochemical Properties of LiNi[subscript x]Cu[subscript y]Mn[subscript 2?x?y]O[subscript 4] (0 ; x ; 0.5, 0 ; y ; 0.5) High-Voltage Spinel Materials

    SciTech Connect

    Yang, Ming-Che; Xu, Bo; Cheng, Ju-Hsiang; Pan, Chun-Jern; Hwang, Bing-Joe; Meng, Ying S.

    2011-09-06

    First principles computation is carried out for investigating the electronic, structural, and electrochemical properties of LiM{sub 1/2}Mn{sub 3/2}O{sub 4} (M = Ti, V, Cr, Fe, Co, Ni, and Cu). The computation results suggest that doping with Co or Cu can potentially lower Li diffusion barrier as compared to Ni doping. Our experimental research has focused on LiNi{sub x}Cu{sub y}Mn{sub 2-x-y}O{sub 4} (0 < x < 0.5, 0 < y < 0.5), and we found that the amount of Cu will affect the lattice parameters, the cation disorder in the spinel lattice, the particle morphology, as well as the electrochemical properties. Crystal structures, electronic structures, and electrochemical properties of LiNi{sub x}Cu{sub y}Mn{sub 2-x-6}O{sub 4} (0 < x < 0.5, 0 < y < 0.5) are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray absorption spectroscopy (XAS), and electrochemical measurements including potentiostatic intermittent titration technique (PITT). With detailed electrochemical measurements and in situ XAS experiments of LiNi{sub 0.25}Cu{sub 0.25}Mn{sub 1.50}O{sub 4}, the proposed explanation of the voltage profile by the first principles computation was proven, a second plateau at 4.2 V originates from the oxidation of Cu{sup 2+} to Cu{sup 3+}, and the plateau at 4.95 V may originate from extra electrons provided by oxygen ions. Although the reversible discharge capacity decreases with increasing Cu amount, optimized composition such as LiCu{sub 0.25}Ni{sub 0.25}Mn{sub 1.5}O{sub 4} exhibits high capacities at high rates.

  17. High-Performance and Stable Gel-State Dye-Sensitized Solar Cells Using Anodic TiO2 Nanotube Arrays and Polymer-Based Gel Electrolytes.

    PubMed

    Seidalilir, Zahra; Malekfar, Rasoul; Wu, Hui-Ping; Shiu, Jia-Wei; Diau, Eric Wei-Guang

    2015-06-17

    Highly ordered and vertically oriented TiO2 nanotube (NT) arrays were synthesized with potentiostatic anodization of Ti foil and applied to fabricate gel-state dye-sensitized solar cells (DSSCs). The open structure of the TiO2 NT facilitates the infiltration of the gel-state electrolyte; their one-dimensional structural feature provides effective charge transport. TiO2 NTs of length L=15-35 ?m were produced on anodization for periods of t=5-15 h at a constant voltage of 60 V, and sensitized with N719 for photovoltaic characterization. A commercially available copolymer, poly(methyl methacrylate-co-ethyl acrylate) (PMMA-EA), served as a gelling agent to prepare a polymer-gel electrolyte (PGE) for DSSC applications. The PGE as prepared exhibited a maximum conductivity of 4.58 mS cm(-1) with PMMA-EA (7 wt %). The phase transition temperature (Tp) of the PGE containing PMMA-EA at varied concentrations was determined on the basis of the viscosities measured at varied temperatures. Tp increased with increasing concentration of PMMA-EA. An NT-DSSC with L=30 ?m assembled using a PGE containing PMMA-EA (7 wt %) exhibited an overall power conversion efficiency (PCE) of 6.9%, which is comparable with that of a corresponding liquid-type device, PCE=7.1%. Moreover, the gel-state NT-DSSC exhibited excellent thermal and light-soaking enduring stability: the best device retained ?90% of its initial efficiency after 1000 h under 1 sun of illumination at 50 °C, whereas its liquid-state counterpart decayed appreciably after light soaking for 500 h. PMID:25984747

  18. Impedance study of tea with added taste compounds using conducting polymer and metal electrodes.

    PubMed

    Dhiman, Mopsy; Kapur, Pawan; Ganguli, Abhijit; Singla, Madan Lal

    2012-09-01

    In this study the sensing capabilities of a combination of metals and conducting polymer sensing/working electrodes for tea liquor prepared by addition of different compounds using an impedance mode in frequency range 1 Hz-100 KHz at 0.1 V potential has been carried out. Classification of six different tea liquor samples made by dissolving various compounds (black tea liquor + raw milk from milkman), (black tea liquor + sweetened clove syrup), (black tea liquor + sweetened ginger syrup), (black tea liquor + sweetened cardamom syrup), (black tea liquor + sweet chocolate syrup) and (black tea liquor + vanilla flavoured milk without sugar) using six different working electrodes in a multi electrode setup has been studied using impedance and further its PCA has been carried out. Working electrodes of Platinum (Pt), Gold (Au), Silver (Ag), Glassy Carbon (GC) and conducting polymer electrodes of Polyaniline (PANI) and Polypyrrole (PPY) grown on an ITO surface potentiostatically have been deployed in a three electrode set up. The impedance response of these tea liquor samples using number of working electrodes shows a decrease in the real and imaginary impedance values presented on nyquist plots depending upon the nature of the electrode and amount of dissolved salts present in compounds added to tea liquor/solution. The different sensing surfaces allowed a high cross-selectivity in response to the same analyte. From Principal Component Analysis (PCA) plots it was possible to classify tea liquor in 3-4 classes using conducting polymer electrodes; however tea liquors were well separated from the PCA plots employing the impedance data of both conducting polymer and metal electrodes. PMID:23035436

  19. Electrochemical behavior of polypyrrol/AuNP composites deposited by different electrochemical methods: sensing properties towards catechol.

    PubMed

    García-Hernández, Celia; García-Cabezón, Cristina; Medina-Plaza, Cristina; Martín-Pedrosa, Fernando; Blanco, Yolanda; de Saja, José Antonio; Rodríguez-Méndez, María Luz

    2015-01-01

    Two different methods were used to obtain polypyrrole/AuNP (Ppy/AuNP) composites. One through the electrooxidation of the pyrrole monomer in the presence of colloidal gold nanoparticles, referred to as trapping method (T), and the second one by electrodeposition of both components from one solution containing the monomer and a gold salt, referred to as cogeneration method (C). In both cases, electrodeposition was carried out through galvanostatic and potentiostatic methods and using platinum (Pt) or stainless steel (SS) as substrates. Scanning electron microscopy (SEM) demonstrated that in all cases gold nanoparticles of similar size were uniformly dispersed in the Ppy matrix. The amount of AuNPs incorporated in the Ppy films was higher when electropolymerization was carried out by chronopotentiometry (CP). Besides, cogeneration method allowed for the incorporation of a higher number of AuNPs than trapping. Impedance experiments demonstrated that the insertion of AuNPs increased the conductivity. As an electrochemical sensor, the Ppy/AuNp deposited on platinum exhibited a strong electrocatalytic activity towards the oxidation of catechol. The effect was higher in films obtained by CP than in films obtained by chronoamperometry (CA). The influence of the method used to introduce the AuNPs (trapping or cogeneration) was not so important. The limits of detection (LOD) were in the range from 10(-5) to 10(-6) mol/L. LODs attained using films deposited on platinum were lower due to a synergy between AuNPs and platinum that facilitates the electron transfer, improving the electrocatalytic properties. Such synergistic effects are not so pronounced on stainless steel, but acceptable LOD are attained with lower price sensors. PMID:26665076

  20. Quantification of carbon dioxide poisoning in air breathing alkaline fuel cells

    NASA Astrophysics Data System (ADS)

    Tewari, A.; Sambhy, V.; Urquidi Macdonald, M.; Sen, A.

    Carbon dioxide intolerance has impeded the development of alkaline fuel cells as an alternate source of power supply. The CO 2, in a fuel cell system, could come from the anode side (if "dirty" H 2 is used as fuel), from the cathode side (if air instead of pure O 2 is used as an oxidant) or from inside the electrolyte (if methanol is used as a fuel). In this work, an novel analytical approach is proposed to study and quantify the carbon dioxide poisoning problem. Accelerated tests were carried out in an alkaline fuel cell using methanol as a fuel with different electrical loads and varying the concentration of carbon dioxide in a mixture CO 2/O 2 used as oxidant. Two characteristic quantities, tmax and Rmax, were specified which were shown to comprehensively define the nature and extent of carbon dioxide poisoning in alkaline fuel cells. The poisoning phenomenon was successfully quantified by determining the dependence of these characteristic quantities on the operating parameters, viz. atmospheric carbon dioxide concentration and applied electrical load. Such quantification enabled the prediction of the output of a fuel cell operating in a carbon dioxide enriched atmosphere. In addition, static and dynamic analyses of electrolytes were carried out to determine the dependence of cell current on the electrolyte composition in a fuel cell undergoing poisoning. It was observed that there is a critical concentration of KOH in the electrolyte only below which the effect of carbon dioxide poisoning is reflected on the cell performance. Potentiostatic polarization tests confirmed that the underlying reason for the decreased cell performance because of carbon dioxide poisoning is the sluggish kinetics of methanol oxidation in the presence of potassium carbonate in the electrolyte. Moreover, the decreased conductivity of the electrolyte resulting from hydroxide to carbonate conversion was also shown to increase the ohmic loses in an alkaline fuel cell leading to lower efficiencies.

  1. Angstrom-resolved real-time dissection of electrochemically active noble metal interfaces.

    PubMed

    Shrestha, Buddha R; Baimpos, Theodoros; Raman, Sangeetha; Valtiner, Markus

    2014-06-24

    Electrochemical solid|liquid interfaces are critically important for technological applications and materials for energy storage, harvesting, and conversion. Yet, a real-time Angstrom-resolved visualization of dynamic processes at electrified solid|liquid interfaces has not been feasible. Here we report a unique real-time atomistic view into dynamic processes at electrochemically active metal interfaces using white light interferometry in an electrochemical surface forces apparatus. This method allows simultaneous deciphering of both sides of an electrochemical interface-the solution and the metal side-with microsecond resolution under dynamically evolving reactive conditions that are inherent to technological systems in operando. Quantitative in situ analysis of the potentiodynamic electrochemical oxidation/reduction of noble metal surfaces shows that Angstrom thick oxides formed on Au and Pt are high-ik materials; that is, they are metallic or highly defect-rich semiconductors, while Pd forms a low-ik oxide. In contrast, under potentiostatic growth conditions, all noble metal oxides exhibit a low-ik behavior. On the solution side, we reveal hitherto unknown strong electrochemical reaction forces, which are due to temporary charge imbalance in the electric double layer caused by depletion/generation of charged species. The real-time capability of our approach reveals significant time lags between electron transfer, oxide reduction/oxidation, and solution side reaction during a progressing electrode process. Comparing the kinetics of solution and metal side responses provides evidence that noble metal oxide reduction proceeds via a hydrogen adsorption and subsequent dissolution/redeposition mechanism. The presented approach may have important implications for designing emerging materials utilizing electrified interfaces and may apply to bioelectrochemical processes and signal transmission. PMID:24826945

  2. Electrochemical photovoltaic cells. Project 65021 quarterly technical progress report, October 15, 1979-January 15, 1980

    SciTech Connect

    Ang, P.G.P.; Remick, R.J.; Sammells, A.F.

    1980-03-01

    During the third quarter of this program, liquid junction devices based upon the semiconductors MoSe/sub 2/, MoS/sub 2/, GaAs, and CdSe have been evaluated. Lifetime testing of MoSe/sub 2/ and MoS/sub 2/ materials in acidic halogen electrolytes at constant current densities of 5 mA/cm/sup 2/ have shown excellent stability to date. For MoSe/sub 2/ single crystals in the electrolyte 1M HBr + 1M Br/sub 2/, short-circuit currents of 63 mA/cm/sup 2/ were achieved with a power conversion efficiency of 6.7% for 200 mW/cm/sup 2/ xenon light illumination. Transient potentiostatic measurements made on MoSe/sub 2/ in this electrolyte indicated little diffusion control, with exchange currents being of the order of 1 to 10 mA/cm/sup 2/. Good photoresponse of MoS/sub 2/ has been observed in 1M HBr + 1M Br/sub 2/. The performance of the natural crystal is comparable to the performance of a single-crystal MoS/sub 2/ in this electrolyte. CdSe thermally evaporated onto porous titanium gave efficiencies of about 4% with 100 mW/cm/sup 2/ xenon illumination. Experimental work was initiated on the dye sensitization of Fe/sub 2/O/sub 3/ and TiO/sub 2/ materials. Of the twelve dyes evaluated, little enhancement of the photoresponse of these materials was noted. Solid-state photoelectrochemical cells have been fabricated, based upon LiI. Cells of the configuration - cond. glass CdSe/LiI + PbI/sub 2//LiI/LiI + C + PbI/sub 2//cond. glass - were fabricated. Photoresponses up to 150 mV were observed.

  3. Localized surface plasmon mediated photochemistry and charge transfer in noble metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Wu, Xiaomu

    This thesis addresses the fundamental physical and chemical processes of localized surface plasmon mediated photochemistry and charge transfer in noble metal nanoparticles. The first chapter introduces the theory and application of surface plasmons. It includes a discussion of propagating and localized surface plasmons, plasmon decay dynamics, factors governing plasmon excitation of metal nanoparticles, near-field enhanced photochemistry and plasmon mediated charge transfer. The second chapter presents a photovoltage mechanism for room light conversion of citrate stabilized silver nanocrystal seeds to large nanoprisms. The process relies on the excitation of silver surface plasmons and requires citrate and oxygen. The transformation rate is first-order in seed concentration. The mechanism involves oxidative etching of seeds and subsequent photoreduction of aqueous silver ions preferentially onto silver prisms that have a cathodic photovoltage resulting from plasmon hot hole citrate photo- oxidation. This idea also explains several previously reported experiments including single and dual wavelength irradiation and the core/shell synthesis of silver layers on gold seeds. The third chapter explores the photo-driven growth of citrate stabilized silver nanoparticles. Under plasmon excitation, particles that absorb/scatter light weakly reduce dioxygen and lose silver ions, whereas particles with resonant plasmons build up a high photovoltage due to citrate photo-oxidation and reduce silver ions. Overall, growth is favored for on-resonant particles. Compared to the borohydride reduction method, more monodisperse, round 10-20 nm diameter silver nanoparticles are obtained by plasmon mediated approaches. Adding a trace amount of potassium chloride can speed up the growth and inhibit the formation of Ag aggregates. The fourth chapter investigates the plasmon induced photochemical charge separation in gold nanoparticles on a transparent indium tin oxide (ITO) substrate. Photocurrent and photovoltage are directly measured under potentiostatic control in air. It is proposed that gold plasmon excitation causes hot electrons to inject into the ITO conduction band, while hot holes are scavenged by citrate and other solution redox species. A resonant increase in the photocurrent generated at more oxidizing potentials is observed.

  4. Growth mechanism of surface roughed platinum nanowires through electrodeposition current control and their electrochemical applications

    NASA Astrophysics Data System (ADS)

    Ruan, Dajiang

    The aim of this work is to investigate the effect of current density on the grain size and surface morphology of electrodeposited platinum nanowires and their applications. Platinum (Pt) nanowires were fabricated by a galvanostatic electrodeposition method in a porous anodic alumina oxide (AAO) template with different current densities. Both direct current and pulse current electrodeposition were used to synthesize the Pt nanowires. The grain size and surface morphology of the Pt nanowires were studied by field emission scanning electron microscopy (FE-SEM), transmission electron microcopy (TEM) and X-ray diffraction (XRD). The experimental results showed that the current density was the key factor to control the surface roughness. The surface of the Pt nanowires became rougher and the grain sizes were increased by increasing the current densities. From the experimental results, a growth mechanism of Pt nanowires based on progressive nucleation and crystallization was proposed in order to find out the relationship between the surface morphology and current density. The electrochemical properties and catalytic activities of these surface roughed Pt nanowires were investigated in the detection of H20 2 and for the methanol oxidation. Cyclic voltammograms of Pt nanowire modified electrodes were obtained using a potentiostat, which showed that rougher Pt nanowires have higher response and better activity than that of smooth nanowires. For H202 detection, the effect of scan rate and H202 concentration were studied and it was found that the peak current for hydrogen peroxide reduction became larger with the increasing of either scan rate or H202 concentration. It can be inferred that the process of electrocatalytic hydrogen peroxide reduction may be controlled by diffusion of hydrogen peroxide and the Pt nanowire modified glassy carbon electrode (GCE) is well suited for the detection of H202. From the relationship between the peak current and square root of scan rates for methanol oxidation, it can be inferred that the process of electrocatalytic methanol oxidation was controlled by diffusion of methanol. To understand the effect of the morphological feature on the electrocatalytic activity of the Pt nanowire catalysts, the electrochemically active surface area (ECSA) as a function of deposited current density was investigated, which suggests that Pt nanowire catalysts deposited at highest current density had the most ECSA surface morphology of the Pt nanowires. The chronoamperometric curves and electrochemical impedance spectroscopy (EIS) results confirmed that the Pt nanowire catalyst synthesized at higher current density possessed longer durability and gave more efficient electrochemical performance.

  5. Mechanistic, kinetic, and processing aspects of tungsten chemical mechanical polishing

    NASA Astrophysics Data System (ADS)

    Stein, David

    This dissertation presents an investigation into tungsten chemical mechanical polishing (CMP). CMP is the industrially predominant unit operation that removes excess tungsten after non-selective chemical vapor deposition (CVD) during sub-micron integrated circuit (IC) manufacture. This work explores the CMP process from process engineering and fundamental mechanistic perspectives. The process engineering study optimized an existing CMP process to address issues of polish pad and wafer carrier life. Polish rates, post-CMP metrology of patterned wafers, electrical test data, and synergy with a thermal endpoint technique were used to determine the optimal process. The oxidation rate of tungsten during CMP is significantly lower than the removal rate under identical conditions. Tungsten polished without inhibition during cathodic potentiostatic control. Hertzian indenter model calculations preclude colloids of the size used in tungsten CMP slurries from indenting the tungsten surface. AFM surface topography maps and TEM images of post-CMP tungsten do not show evidence of plow marks or intergranular fracture. Polish rate is dependent on potassium iodate concentration; process temperature is not. The colloid species significantly affects the polish rate and process temperature. Process temperature is not a predictor of polish rate. A process energy balance indicates that the process temperature is predominantly due to shaft work, and that any heat of reaction evolved during the CMP process is negligible. Friction and adhesion between alumina and tungsten were studied using modified AFM techniques. Friction was constant with potassium iodate concentration, but varied with applied pressure. This corroborates the results from the energy balance. Adhesion between the alumina and the tungsten was proportional to the potassium iodate concentration. A heuristic mechanism, which captures the relationship between polish rate, pressure, velocity, and slurry chemistry, is presented. In this mechanism, the colloid reacts with the chemistry of the slurry to produce active sites. These active sites become inactive by removing tungsten from the film. The process repeats when then inactive sites are reconverted to active sites. It is shown that the empirical form of the heuristic mechanism fits all of the data obtained. The mechanism also agrees with the limiting cases that were investigated.

  6. COUPLED MULTI-ELECTRODE INVESTIGATION OF CREVICE CORROSION OF 316 STAINLESS STEEL

    SciTech Connect

    F. Bocher and J. R. Scully

    2006-01-30

    Crevice corrosion is currently studied using either one of two techniques depending on the data needed. The first method is a multi-crevice former over a metallic sample; this provides information on the severity of crevice corrosion (depth, position, frequency) but delivers little to no electrochemical information [1]. The second method involves the potentiodynamic or potentiostatic study of an uncreviced sample in model crevice solution or under a crevice former in aggressive solution [2]. Crevice corrosion is highly dependent on the position in the crevice. The distance from the crevice mouth will affect the depth of attack, the solution composition and pH, and the ohmic drop and the true potential in the crevice [3-6]. These in turn affect the current density as a function of potential and position. A Multi-Channel Micro-Electrode Analyzer (MMA) has been recently used to demonstrate the interaction between localized corrosion sites (pitting corrosion and intergranular corrosion) [7]. MMA can provide spatial resolution of electrochemical properties in the crevice. By coupling such a tool with scaling laws derived from experimental data (a simple equation linking the depth of crevice corrosion initiation to the crevice gap), it is possible to produce highly instrumented crevices, rescaled to enable spatial resolution of local corrosion processes. In this study, the use of multi-wires arrays (up to 100 closed packed wires simulating a planar electrode, divided in 10 distinctively controllable groups) electrically coupled through zero resistance ammeters enables the observation of the current evolution as a function of position inside and outside the crevice. For instance, the location of crevice initiation sites and propagation behavior can be studied under various conditions. Experiments can be conducted with various realistic variables. These can either be electrochemical (such as proximate cathode) or physical (crevice former material or position). Using new impedance-capable MMA, it is also possible to monitor the film breakdown and the early stages of crevice corrosion as a function of the wires position. In this talk, the use of multi-electrode array to study crevice corrosion of 316 stainless steel and a Ni-Cr-Mo alloy is reviewed.

  7. COUPLED MULTI-ELECTRODE INVESTIGATION OF CREVICE CORROSION OF 316 STAINLESS STEEL

    SciTech Connect

    F. Bocher, J. R. Scully

    2006-01-30

    Crevice corrosion is currently studied using either one of two techniques depending on the data needed. The first method is a multi-crevice former over a metallic sample; this provides information on the severity of crevice corrosion (depth, position, frequency) but delivers little to no electrochemical information [1]. The second method involves the potentiodynamic or potentiostatic study of an uncreviced sample in model crevice solution or under a crevice former in aggressive solution [2]. Crevice corrosion is highly dependent on the position in the crevice. The distance from the crevice mouth will affect the depth of attack, the solution composition and pH, and the ohmic drop and the true potential in the crevice [3-6]. These in turn affect the current density as a function of potential and position. An Multi-Channel Micro-Electrode Analyzer' (MMA) has been recently used to demonstrate the interaction between localized corrosion sites (pitting corrosion and intergranular corrosion) [7]. MMA can provide spatial resolution of electrochemical properties in the crevice. By coupling such a tool with scaling laws derived from experimental data (a simple equation linking the depth of crevice corrosion initiation to the crevice gap), it is possible to produce highly instrumented crevices, rescaled to enable spatial resolution of local corrosion processes. In this study, the use of multi-wires arrays (up to 100 closed packed wires simulating a planar electrode, divided in 10 distinctively controllable groups) electrically coupled through zero resistance ammeters enables the observation of the current evolution as a function of position inside and outside the crevice. For instance, the location of crevice initiation sites and propagation behavior can be studied under various conditions. Experiments can be conducted with various realistic variables. These can either be electrochemical (such as proximate cathode) or physical (crevice former material or position). Using new impedance-capable MMA, it is also possible to monitor the film breakdown and the early stages of crevice corrosion as a function of the wires position. In this talk, the use of multi-electrode array to study crevice corrosion of 316 stainless steel and a Ni-Cr-Mo alloy is reviewed.

  8. Investigation of stress and morphology in electrodeposited copper nanofilms by cantilever beam method and in situ electrochemical atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Ahmed, S.; Ahmed, T. T.; O'Grady, M.; Nakahara, S.; Buckley, D. N.

    2008-04-01

    Both stress and atomic force microscopy (AFM) measurements were carried out in situ during potentiostatic electrodeposition of copper on gold in 0.05moldm-3 CuSO4 in 0.1moldm-3 H2SO4 with and without additives. With no additives, compressive stress generally developed initially and films subsequently underwent a compressive-to-tensile (C-T ) transition. With increasing negative potential, the time for the C-T transition decreased rapidly as the rate of coalescence of nuclei (measured by AFM) increased rapidly. This is consistent with models that attribute the C-T transition to increasing tensile stress due to coalescence of nuclei. Furthermore, at a potential of -75mV (Cu /Cu2+), where AFM showed very little coalescence of nuclei, no C-T transition was observed, again consistent with these models. The nucleation density measured by AFM increased from 2.7×107cm-2 at -75mVto2.5×109cm-2 at -300mV. Stress measurements with a combination of three additives [1×10-3moldm-3 Cl-, 8.82×10-5moldm-3 polyethylene glycol, and 1×10-5moldm-3 3-mercapto-1-propanesulfonic acid sodium salt (MPSA)] also showed that compressive stress generally developed initially and its magnitude was greater than in additive-free electrolyte. At less negative potentials, even though the rate of coalescence of nuclei was rapid, as observed by AFM, the stress continued to evolve in the compressive direction. At intermediate potentials (-90to-150mV), classical compressive-tensile-compressive (C-T-C) behavior was observed, while at more negative potentials the stress continued to evolve in the tensile direction. Similar results were obtained with a combination of two additives (1×10-3moldm-3 Cl- and 1×10-5mol dm-3 MPSA), but in that case the compressive stress appeared to be greater, and consequently the T-C transition was observed even at -500mV. The results are consistent with enhancement of a compressive component of stress in the presence of additives.

  9. Dynamics of Li4Ti5O12/sulfone-based electrolyte interfaces in lithium-ion batteries.

    PubMed

    Demeaux, Julien; De Vito, Eric; Le Digabel, Matthieu; Galiano, Hervé; Claude-Montigny, Bénédicte; Lemordant, Daniel

    2014-03-21

    Binary mixtures of cyclic (TMS) or acyclic sulfones (MIS, EIS and EMS) with EMC or DMC have been used in electrolytes containing LiPF6 (1 M) in both Li4Ti5O12/Li half-cells and Li4+xTi5O12/Li4Ti5O12 symmetric cells and compared with standard EC/EMC or EC/DMC mixtures. In half-cells, sulfone-based electrolytes cannot be satisfactorily cycled owing to the formation of a resistive layer at the lithium interface, which is not stable and generates species (RSO2(-) and RSO3(-)) able to migrate toward the titanate electrode interface. Potentiostatic and galvanostatic tests of Li4Ti5O12/Li half-cells show that charge transfer resistance increases drastically when sulfones are used in the electrolyte composition. Moreover, cyclability and coulombic efficiency are low. Conversely, when symmetric Li4+xTi5O12/Li4Ti5O12 cells are used, it is demonstrated that MIS-(methyl isopropyl sulfone) and TMS-(tetra methyl sulfone) based electrolytes exhibit reasonable electrochemical performances as compared to the EC/DMC or EC/EMC standard mixtures. Surface analysis by XPS of both the Li4+xTi5O12 (partially oxidized) and Li7Ti5O12 (reduced) electrodes taken from symmetric cells reveals that sulfones do not participate in the formation of surface layers. Alkylcarbonates (EMC or DMC), used as co-solvents in sulfone-based binary electrolytes, ensure the formation of surface layers at the titanate interfaces. Therefore, EMC reduction at the two Li4+xTi5O12/electrolyte interfaces in symmetric cells leads to the formation of carbonates, ethers and mineral compounds such as ROCO2Li and Li2CO3. Finally, huge amounts of LiF are detected at the titanate electrode surface, resulting in an increase in the resistivity of symmetric cells and capacity losses. PMID:24487415

  10. Seedless electrochemical deposition of copper on air-exposed tantalum nitride barriers with ultra-thin adhesion layers

    NASA Astrophysics Data System (ADS)

    Lay, Nicole Elizabeth

    Copper has replaced aluminum for microelectronic applications, bringing the challenges of adapting to a new material with new processing systems. One impetus of changing from aluminum to copper for electronic applications is the lower resistivity which results in higher device speed. It is of the utmost importance to produce electrochemical deposition (ECD) copper with a resistivity as near to the bulk value of 1.7 muOcm as possible to assure maximum device performance [1]. Current technology requires ever decreasing feature geometries and increasing aspect ratios to improve device speed. The challenge in designing smaller devices is in achieving a uniformly continuous, adherent seed layer. As geometry size is reduced and aspect ratios increase, the ability to achieve coverage with physical vapor deposition (PVD) for a copper seed layer becomes impossible. It is projected that PVD seed layers will no longer be viable below the 90 nm node [2]. The development of plating baths for direct electrodeposition of copper onto metal and metal nitride barrier layers for interconnect technology is a primary concern. Basic electrochemical principles as well as specific reasons for the choice of copper bath base and additives are discussed. This work presented here includes electrochemical data consisting of potentiodynamic experiments, cyclic polarization data, and current density analysis for potentiostatic experiments as well as galvanostatic deposition. Samples were analyzed with electrochemical techniques, field emission scanning electron microscopy (FESEM), Scotch tape adhesion tests, and mass transport experiments utilizing a rotating disk electrode. Atomic Force Microscopy (AFM) has been employed to determine surface roughness changes indicative of the grain structure and surface condition of samples. An initial examination of copper plate has been conducted using transmission electron microscopy. Other experimental work includes a four point probe resistivity study with annealing to optimize copper conditions, XPS to quantify the impurity concentration of copper plate as well as possibility of impurity concentration in Cu deposits. The parameters of bath additive concentration and deposition potentials, that promote good adhesion of copper on barrier layers are one of the most important aspects of this study. This is quantified using four point bend testing to determine adhesion values. Superfilling using ultra thin adhesion promoting layers both an electrochemically deposited, ECD, copper seed and atomic layer deposition (ALD) deposited palladium and ruthenium will be quantified. (Abstract shortened by UMI.)

  11. Hydrogen Induced Stress Cracking of Materials Under Cathodic Protection

    NASA Astrophysics Data System (ADS)

    LaCoursiere, Marissa P.

    Hydrogen embrittlement of AISI 4340, InconelRTM 718, Alloy 686 and Alloy 59 was studied using slow strain rate tests of both smooth and notched cylindrical specimens. Two heat treatments of the AISI 4340 material were used as a standard for two levels of yield strength: 1479 MPa, and 1140 MPa. A subset of the 1140 MPa AISI 4340 material also underwent plasma nitriding. The InconelRTM 718 material was hardened following AMS 5663M to obtain a yield strength of 1091 MPa. The Alloy 686 material was obtained in the Grade 3 condition with a minimum yield strength of 1034 MPa. The Alloy 59 material was obtained with a cold worked condition similar to the Alloy 686 and with a minimum yield strength of 1034 MPa. Ninety-nine specimens were tested, including smooth cylindrical tensile test specimens and smooth and notched cylindrical slow strain rate tensile tests specimens. Testing included specimens that had been precharged with hydrogen in 3.5% NaCl at 50°C for 2 weeks (AISI 4340), 4 weeks (InconelRTM 718, Alloy 686, Alloy 59) and 16 weeks (InconelRTM 718, Alloy 686, Alloy 59) using a potentiostat to deliver a cathodic potential of -1100 mV vs. SCE. The strain rate over the gauge section for the smooth specimens and in the notch root for the notched specimens was 1 x 10-6 /s. It was found that the AISI 4340 was highly embrittled in simulated ocean water when compared to the nickel based superalloys. The higher strength AISI 4340 showed much more embrittlement, as expected. Testing of the AISI 4340 at both 20°C and 4°C showed that the temperature had no effect on the hydrogen embrittlement response. The InconelRTM 718 was highly embrittled when precharged, although it only showed low levels of embrittlement when unprecharged. Both the Alloy 686 and Alloy 59 showed minimal embrittlement in all conditions. Therefore, for the materials examined, the use of Alloy 686 and Alloy 59 for components in salt water environments when under a cathodic potential of -1100 mV vs. SCE is recommended.

  12. Compact autonomous voltammetric sensor for sulfide monitoring in deep sea vent habitats

    NASA Astrophysics Data System (ADS)

    Contreira-Pereira, Leonardo; Yücel, Mustafa; Omanovic, Dario; Brulport, Jean-Pierre; Le Bris, Nadine

    2013-10-01

    In situ chemical monitoring at deep-sea hydrothermal vents remains a challenge. Particularly, tools are still scarce for assessing the ranges and temporal variability of sulfide in these harsh environmental conditions. There is a particular need for compact and relatively simple devices to enlarge the capacity of in situ measurements of this major energy source in chemosynthetic ecosystems. With this objective, a voltammetric sensor based on a bare-silver working electrode was developed and tested in real conditions. In the laboratory, the sensor presented a linear response from 10 to 1000 ?M sulfide, together with a low pH sensitivity and moderate temperature dependence. The device was operated at 850 and 2500 m depth during 3 cruises over two different vent fields. The autonomous potentiostat (290 mm length, ? 35 mm) equipped with laboratory-made electrodes was mounted on a wand, for manipulation from a submersible, or on a holder for unattended deployments. The system was applied in mussel, tubeworm and annelid worm habitats, characterized by different ranges of sulfide concentration, pH and temperature. Calibrations performed before and after each deployment confirmed the stability of the sensor response over a few hours to 11 days, with a maximum drift of 11.4% during this period. Short-term measurements in the vicinity of Riftia pachyptila and Alvinella pompejana were consistent with previous results on these habitats, with concentrations ranging from 20 to 140 ?M and 100 to 450 ?M and sulfide versus temperature ratio of 14 ?M °C-1 and 20 ?M °C-1, respectively. A continuous 4-day record on a bed of Bathymodiolus Thermophilus mussels furthermore illustrated the capacity of the sensor to capture fluctuating sulfide concentration between 0 and 70 ?M, in combination to temperature, and to investigate the changes in the sulfide versus temperature ratio over time. The method has a higher detection limit (<10 ?M) than previous in situ sulfide measurement methods, but has the advantage of selectivity to free sulfide (compared to colorimetry), low pH sensitivity (compared to amperometry) and lower reconditioning requirement for electrode surface (with respect to gold-amalgam voltammetry). This sensor is therefore a valuable complementary tool for discrete and continuous measurements within the moderate temperature environment of fauna at deep-sea vents.

  13. Electrochemical growth behavior, surface properties, and enhanced in vivo bone response of TiO2 nanotubes on microstructured surfaces of blasted, screw-shaped titanium implants

    PubMed Central

    Sul, Young-Taeg

    2010-01-01

    TiO2 nanotubes are fabricated on TiO2 grit-blasted, screw-shaped rough titanium (ASTM grade 4) implants (3.75 × 7 mm) using potentiostatic anodization at 20 V in 1 M H3PO4 + 0.4 wt.% HF. The growth behavior and surface properties of the nanotubes are investigated as a function of the reaction time. The results show that vertically aligned nanotubes of ?700 nm in length, with highly ordered structures of ?40 nm spacing and ?15 nm wall thickness may be grown independent of reaction time. The geometrical properties of nanotubes increase with reaction time (mean pore size, pore size distribution [PSD], and porosity ?90 nm, ?40–127 nm and 45%, respectively for 30 minutes; ?107 nm, ?63–140 nm and 56% for one hour; ?108 nm, ?58–150 nm and 60% for three hours). It is found that the fluorinated chemistry of the nanotubes of F-TiO2, TiOF2, and F-Ti-O with F ion incorporation of ?5 at.%, and their amorphous structure is the same regardless of the reaction time, while the average roughness (Sa) gradually decreases and the developed surface area (Sdr) slightly increases with reaction time. The results of studies on animals show that, despite their low roughness values, after six weeks the fluorinated TiO2 nanotube implants in rabbit femurs demonstrate significantly increased osseointegration strengths (41 vs 29 Ncm; P = 0.008) and new bone formation (57.5% vs 65.5%; P = 0.008) (n = 8), and reveal more frequently direct bone/cell contact at the bone–implant interface by high-resolution scanning electron microscope observations as compared with the blasted, moderately rough implants that have hitherto been widely used for clinically favorable performance. The results of the animal studies constitute significant evidence that the presence of the nanotubes and the resulting fluorinated surface chemistry determine the nature of the bone responses to the implants. The present in vivo results point to potential applications of the TiO2 nanotubes in the field of bone implants and bone tissue engineering. PMID:20463928

  14. Sodium molybdate - an additive of choice for enhancing the performance of AC/AC electrochemical capacitors in a salt aqueous electrolyte.

    PubMed

    Abbas, Q; Ratajczak, P; Béguin, F

    2014-01-01

    Sodium molybdate (Na2MoO4) has been used as an additive to 1 mol L(-1) lithium sulfate electrolyte for electrochemical capacitors based on activated carbon (AC) electrodes, in order to reduce the corrosion of stainless steel current collectors. We demonstrate that the MoO4(2-) anions improve the overall capacitance owing to pseudofaradaic processes. In a two-electrode cell, capacitance values of 121 F g(-1) have been achieved up to 1.6 V using 1 mol L(-1) Li2SO4 + 0.1 mol L(-1) Na2MoO4, as compared to 103 F g(-1) when 1 mol L(-1) Li2SO4 is used. Further, by using a two-electrode setup equipped with a reference electrode, we could demonstrate that, at 1.6 V, the positive electrode potential reaches a value of 0.96 V vs. NHE in 1 mol L(-1) Li2SO4, crossing the thermodynamic potential limit of oxygen evolution (Eox = 0.846 V vs. NHE), and the pitting potential, Epit = 0.95 V vs. NHE. By contrast, in 1 mol L(-1) Li2SO4 + 0.1 mol L(-1) Na2MoO4, the pseudofaradaic contribution occurring at -0.05 V vs. NHE due to MoO4(2-) anions drives the positive electrode to reach only 0.798 V vs. NHE. Hence, the oxidation of the AC and corrosion of the stainless steel current collector at the positive electrode are unlikely in Li2SO4 + Na2MoO4 when the capacitor operates at 1.6 V. During potentiostatic floating of the capacitor at 1.6 V for 120 hours in Li2SO4 + Na2MoO4, the capacitance and resistance remain constant at 125 F g(-1) and ~1.0 ?, respectively, while the resistance increases from 1.4 ? to 3.1 ? in Li2SO4. Overall, the addition of MoO4(2-) anions to Li2SO4 aqueous electrolyte allows the capacitance to be enhanced, corrosion of the positive stainless steel current collector to be inhibited and the AC/AC electrochemical capacitor to demonstrate stable performance up to 1.6 V. PMID:25427248

  15. Characteristic corrosion resistance of nanocrystalline TiN films prepared by high density plasma reactive magnetron sputtering.

    PubMed

    Kim, J H; Kang, C G; Kim, Y T; Cheong, W S; Song, P K

    2013-07-01

    Nanocytalline TiN films were deposited on non-alkali glass and Al substrates by reactive DC magnetron sputtering (DCMS) with an electromagnetic field system (EMF). The microstructure and corrosion resistance of the TiN-coated Al substrates were estimated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical methods. All the TiN films shows that they have a (111) preferred orientation at room temperature. TiN films deposited on Al substrate using only DCMS 400 W showed a sheet resistance of 3.22 x 10-1 omega/symbol see texts (resistivity, 3.22 x 10-5 omegacm). On the other hand, a relatively low sheet resistance of 1.91 x 10-1 omega/symbol see text (1.91 x 10-5 omegacm) was obtained for the dense nanocrystalline TiN film deposited on Al substrate using DCMS 375 W+ EMF 25 W, indicating that the introduction of an EMF system enhanced the electrical properties of the TiN film. TiN films deposited on Al substrate at 400 degreesC had a (200) preferred orientation with the lowest sheet resistance of 1.28x10-1 omega/symbol see texts (1.28 x 10-5 omegacm) which was attributed to reduced nano size defects and an improvement of the crystallinity. Potentiostatic and Potentiodynamic tests with a TiN-coated Al showed good corrosion resistance (l/corr, = 2.03 microA/cm2, Ecorr = -348 mV) compared to the uncoated Al substrate (/corr = 4.45 microA/cm2, Ecorr = -650 mV). Furthermore, EMF system showed that corrosion resistance of the TiN film also was enhanced compared to DCMS only. For the TiN film deposited on Al substrate at 400 degreesC, corrosion current and potential was 0.63 micro/cm2 and -1.5 mV, respectively. This improved corrosion resistance of the TiN film could be attributed to the densification of the film caused by enhancement of nitrification with increasing high reactive nitrogen radicals. PMID:23901480

  16. Direct Electrolytic Deposition of Mats of Mn(x)O(y) Nanowires

    NASA Technical Reports Server (NTRS)

    Myung, Nosang; West, William; Whitacre, Jay; Bugga, Ratnakumar

    2004-01-01

    Mats of free-standing manganese oxide (MnxOy) nanowires have been fabricated as experimental electrode materials for rechargeable electrochemical power cells and capacitors. Because they are free-standing, the wires in these mats are electrochemically accessible. The advantage of the mat-of-nanowires configuration, relative to other configurations of electrode materials, arises from the combination of narrowness and high areal number density of the wires. This combination offers both high surface areas for contact with electrolytes and short paths for diffusion of ions into and out of the electrodes, thereby making it possible to charge and discharge at rates higher than would otherwise be possible and, consequently, to achieve greater power densities. The nanowires are fabricated in an electrolytic process in which there is no need for an electrode binder material. Moreover, there is no need to incorporate an electrically conductive additive into the electrode material; the only electrically conductive material that must be added is a thin substrate contact film at the anchored ends of the nanowires. Hence, the mass fraction of active electrode material is close to 100 percent, as compared with about 85 percent in conventional electrodes made from a slurry of active electrode material, binder, and conductive additive pressed onto a metal foil. The locations and sizes of the nanowires are defined by holes in templates in the form of commercially available porous alumina membranes. In experiments to demonstrate the present process, alumina membranes of various pore sizes and degrees of porosity were used. First, a film of Au was sputtered onto one side of each membrane. The membranes were then attached, variously, to carbon tape or a gold substrate by use of silver or carbon paste. Once thus attached, the membranes were immersed in a plating solution comprising 0.01 M MnSO4 + 0.03 M (NH4)2SO4. The pH of the solution was kept constant at 8 by addition of H2SO4 or NH4OH as needed. Mn(x)O(y) nanowires were potentiostatically electrodeposited in the pores in the alumina templates. Depending on the anodic deposition potentials, Mn(x)O(y) was deposited in various oxidation states [divalent (Mn3O4), trivalent (Mn2O3), or tetravalent (MnO2)]. The Mn(x)O(y) wires were made free-standing (see figure) by dissolving the alumina templates, variously, in KOH or NaOH at a concentration of 20 volume percent.

  17. Well-defined ultrathin palladium films on platinum(111): Electrochemical preparation and interfacial chemistry

    NASA Astrophysics Data System (ADS)

    Park, Yeon Su

    Well-defined ultrathin films of palladium, with coverages ranging from submonolayer, thetaPd = 0.5 monolayer (ML), to multilayer, theta Pd = 8 ML, were electrochemically deposited on Pt(111) using potentiostatic and potentiodynamic methods. In both methods, between the coverage regimes studied, the growth of the Pd films follows the Stranski-Krastanov mechanism. The interfacial electrochemical properties associated with the film-to-bulk transition were characterized by conventional voltammetric techniques in combination with low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The voltammetric peaks associated with H-atom adsorption and desorption on terrace sites indicate that the Pd electrodeposit starts to exhibit bulk-like properties at a coverage of 3 ML. Voltammetric cycling, in sulfuric acid solution, between the hydrogen evolution and the double-layer regions, was found to exert minimal influence on the annealing (smoothening) of the electrodeposited Pd films. However, cycling within the same potential region in the presence of bromide anions (at which Br- adsorption/Br desorption takes place) smoothens the initially rough Pd films essentially as well as high-temperature annealing. The influence of chemisorbed bromine on the anodic dissolution of Pd was also studied; this was for comparison with previous work on the anodic dissolution of Pd, in inert electrolyte, catalyzed by chemisorbed iodine. The present studies indicated that a small but measurable amount of bromine was desorbed along with dissolution of the Pd step atoms; bromine at the Pd terrace behaved identically to iodine in that the coverage of iodine is maintained regardless of the amount or origin of the anodically stripped Pd. Atomically smooth, well-defined ultrathin Pd films were prepared by a constant potential deposition (CPD) method followed by multiple potential cycles, in dilute Br- solution, within the double-layer region and reductive removal of Brads, by simple emersion at a potential just before the hydrogen evolution reaction potential (EHER ). A previously adapted method for the same purpose involved the chemisorption of iodine onto ultrathin PdCPD films, from dilute I- solution, followed by reductive desorption of Iads in iodide-free solution at pH 10 and at a potential just before EHER.

  18. Institute for Advanced Materials at University of Louisville

    SciTech Connect

    Sunkara, Mahendra; Sumaneskara, Gamini; Starr, Thomas L; Willing, G A; Robert W, Cohn

    2009-10-29

    In this project, a university-wide, academic center has been established entitled ?Institute for Advanced Materials and Renewable Energy?. In this institute, a comprehensive materials characterization facility has been established by co-locating several existing characterization equipment and acquiring several state of the art instrumentation such as field emission transmission electron microscope, scanning electron microscope, high resolution X-ray diffractometer, Particle Size Distribution/Zeta Potential measurement system, and Ultra-microtome for TEM specimen. In addition, a renewable energy conversion and storage research facility was also established by acquiring instrumentation such as UV-Vis absorption spectroscopy, Atomic Layer Deposition reactor, Solar light simulator, oxygen-free glove box, potentiostat/galvanostats and other miscellaneous items. The institute is staffed with three full-time staff members (one senior research technologist, a senior PhD level research scientist and a junior research scientist) to enable proper use of the techniques. About thirty faculty, fifty graduate students and several researchers access the facilities on a routine basis. Several industry R&D organizations (SudChemie, Optical Dynamics and Hexion) utilize the facility. The established ?Institute for Advanced Materials? at UofL has three main objectives: (a) enable a focused research effort leading to the rapid discovery of new materials and processes for advancing alternate energy conversion and storage technologies; (b) enable offering of several laboratory courses on advanced materials science and engineering; and (c) develop university-industry partnerships based on the advanced materials research. The Institute?s efforts were guided by an advisory board comprising eminent researchers from outside KY. Initial research efforts were focused on the discovery of new materials and processes for solar cells and Li ion battery electrodes. Initial sets of results helped PIs to secure a successful EPSCoR cluster implementation grant by teaming with additional researchers from UK. In addition to research efforts, the project enabled several other outcomes: (a) helped recruit a junior faculty member (Dr. Moises Carreon) and establish a lab focused on meso-porous materials toward separation and catalysis; (b) enabled offering of three new, graduate level courses (Materials characterization using spectroscopy and microscopy; Electron and x-ray diffraction; and renewable energy systems); and (c) mentoring of a junior faculty members (Dr. Gerold Willing).

  19. A study of photocatalytic graphene–TiO{sub 2} synthesis via peroxo titanic acid refluxed sol

    SciTech Connect

    Low, Wasu; Boonamnuayvitaya, Virote

    2013-08-01

    Graphical abstract: - Highlights: • TiO{sub 2} synthesized via PTA as a precursor demonstrates exclusively anatase phase. • The TEM image of GR–TiO{sub 2} (PTA) demonstrates that TiO{sub 2} nanoparticles are successfully loaded onto graphene sheet. • The specific surface area seems to increase with increasing weight ratio of graphene oxide. It was observed that GR–TiO{sub 2} showed higher adsorption compared to bare TiO{sub 2} (PTA). • The GR–TiO{sub 2} (PTA, 1:50) catalyst showed higher photocatalytic activity than any other catalyst. - Abstract: In the present work, graphene–TiO{sub 2} (GR–TiO{sub 2}) photocatalyst with various weight ratios of graphene was synthesized using peroxo titanic acid solution (PTA) as a precursor for TiO{sub 2}. Graphene oxide prepared by Hummer's method was converted to graphene under ultraviolet (UV) irradiation in ethanol–water solvent for 48 h. The as-prepared GR–TiO{sub 2} composites were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV–vis spectrophotometry, and transmission electron microscopy (TEM). The automated potentiostat was applied to measure the photocurrent generations of prepared catalysts. The photocatalytic activities of GR–TiO{sub 2} (PTA) catalysts were determined by measuring the percentage methylene blue (MB) degradation. The results showed that TiO{sub 2} nanoparticles were successfully loaded onto graphene sheet and the surface area of catalysts increased with increasing weight ratio of graphene. In addition, GR–TiO{sub 2} (PTA, 1:50) exhibited the highest photocatalytic activity among the catalysts under UV and visible light irradiation. The adsorption edge of GR–TiO{sub 2} was shifted to a longer wavelength of 400 nm in comparison with that of pure TiO{sub 2} (PTA). The increase in the photocatalytic performance of GR–TiO{sub 2} (PTA) catalyst may be attributed to the increase in surface area, the extension of light absorption in the visible light region, and prevention of charge recombination.

  20. Direct electrochemical oxidation of ammonia on graphite as a treatment option for stored source-separated urine.

    PubMed

    Zöllig, Hanspeter; Fritzsche, Cristina; Morgenroth, Eberhard; Udert, Kai M

    2015-02-01

    Electrolysis can be a viable technology for ammonia removal from source-separated urine. Compared to biological nitrogen removal, electrolysis is more robust and is highly amenable to automation, which makes it especially attractive for on-site reactors. In electrolytic wastewater treatment, ammonia is usually removed by indirect oxidation through active chlorine which is produced in-situ at elevated anode potentials. However, the evolution of chlorine can lead to the formation of chlorate, perchlorate, chlorinated organic by-products and chloramines that are toxic. This study focuses on using direct ammonia oxidation on graphite at low anode potentials in order to overcome the formation of toxic by-products. With the aid of cyclic voltammetry, we demonstrated that graphite is active for direct ammonia oxidation without concomitant chlorine formation if the anode potential is between 1.1 and 1.6 V vs. SHE (standard hydrogen electrode). A comparison of potentiostatic bulk electrolysis experiments in synthetic stored urine with and without chloride confirmed that ammonia was removed exclusively by continuous direct oxidation. Direct oxidation required high pH values (pH > 9) because free ammonia was the actual reactant. In real stored urine (pH = 9.0), an ammonia removal rate of 2.9 ± 0.3 gN·m(-2)·d(-1) was achieved and the specific energy demand was 42 Wh·gN(-1) at an anode potential of 1.31 V vs. SHE. The measurements of chlorate and perchlorate as well as selected chlorinated organic by-products confirmed that no chlorinated by-products were formed in real urine. Electrode corrosion through graphite exfoliation was prevented and the surface was not poisoned by intermediate oxidation products. We conclude that direct ammonia oxidation on graphite electrodes is a treatment option for source-separated urine with three major advantages: The formation of chlorinated by-products is prevented, less energy is consumed than in indirect ammonia oxidation and readily available and cheap graphite can be used as the electrode material. PMID:25497427

  1. Predictive Framework and Experimental Tests of the Kinetic Isotope Effect at Redox-Active Interfaces

    NASA Astrophysics Data System (ADS)

    Kavner, A.; John, S.; Black, J. R.

    2013-12-01

    Electrochemical reactions provide a compelling framework to study kinetic isotope effects because redox-related processes are important for a wide variety of geological and environmental processes. In the laboratory, electrochemical reaction rates can be electronically controlled and measured in the laboratory using a potentiostat. This enables variation of redox reactions rates independent of changes in chemistry and, and the resulting isotope compositions of reactants and products can be separated and analyzed. In the past years, a series of experimental studies have demonstrated a large, light, and tunable kinetic isotope effect during electrodeposition of metal Fe, Zn, Li, Cu, and Mo from a variety of solutions (e.g. Black et al., 2009, 2010, 2011). A theoretical framework based on Marcus kinetic theory predicts a voltage-dependent kinetic isotope effect (Kavner et al., 2005, 2008), however while this framework was able to predict the tunable nature of the effect, it was not able to simultaneously predict absolute reaction rates and relative isotope rates. Here we present a more complete development of a statistical mechanical framework for simple interfacial redox reactions, which includes isotopic behavior. The framework is able to predict a kinetic isotope effect as a function of temperature and reaction rate, starting with three input parameters: a single reorganization energy which describes the overall kinetics of the electron transfer reaction, and the equilibrium reduced partition function ratios for heavy and light isotopes in the product and reactant phases. We show the framework, elucidate some of the predictions, and show direct comparisons against isotope fractionation data obtained during laboratory and natural environment redox processes. A. Kavner, A. Shahar, F. Bonet, J. Simon and E. Young (2005) Geochim. Cosmochim. Acta, 69(12), 2971-2979. A. Kavner, S. G. John, S. Sass, and E. A. Boyle (2008), Geochim. Cosmochim. Acta, vol 72, pp. 1731-1741. J. R. Black, Umeda, G., Dunn, B., McDonough, W. F. and A. Kavner. (2009), J. Amer. Chem. Soc., vol. 131, No.29 2009 pp. 9904-9905 DOI: 10.1021/ja903926x. J. R. Black, S. John, E.D. Young, and A. Kavner, (2010), Geochim. Cosmochim. Acta, vol 74 (18) pp. 5187-5201. J. R. Black, J. Crawford, S. John, and A. Kavner, (2011) Redox-driven stable isotope fractionation, in Aquatic Redox Chemistry ACS Symposium Series, Vol. 1071. Tratnyek, P.G., T. J. Grundl, and S. B. Haderlein, eds. Chapter 16, pp 345-359

  2. Electrochemical Detection of Multiple Bioprocess Analytes

    NASA Technical Reports Server (NTRS)

    Rauh, R. David

    2010-01-01

    An apparatus that includes highly miniaturized thin-film electrochemical sensor array has been demonstrated as a prototype of instruments for simultaneous detection of multiple substances of interest (analytes) and measurement of acidity or alkalinity in bioprocess streams. Measurements of pH and of concentrations of nutrients and wastes in cell-culture media, made by use of these instruments, are to be used as feedback for optimizing the growth of cells or the production of desired substances by the cultured cells. The apparatus is designed to utilize samples of minimal volume so as to minimize any perturbation of monitored processes. The apparatus can function in a potentiometric mode (for measuring pH), an amperometric mode (detecting analytes via oxidation/reduction reactions), or both. The sensor array is planar and includes multiple thin-film microelectrodes covered with hydrous iridium oxide. The oxide layer on each electrode serves as both a protective and electrochemical transducing layer. In its transducing role, the oxide provides electrical conductivity for amperometric measurement or pH response for potentiometric measurement. The oxide on an electrode can also serve as a matrix for one or more enzymes that render the electrode sensitive to a specific analyte. In addition to transducing electrodes, the array includes electrodes for potential control. The array can be fabricated by techniques familiar to the microelectronics industry. The sensor array is housed in a thin-film liquid-flow cell that has a total volume of about 100 mL. The flow cell is connected to a computer-controlled subsystem that periodically draws samples from the bioprocess stream to be monitored. Before entering the cell, each 100-mL sample is subjected to tangential-flow filtration to remove particles. In the present version of the apparatus, the electrodes are operated under control by a potentiostat and are used to simultaneously measure the pH and the concentration of glucose. It is anticipated that development of procedures for trapping more enzymes into hydrous iridium oxide (and possibly into other electroactive metal oxides) and of means for imparting long-term stability to the transducer layers should make it possible to monitor concentrations of products of many enzyme reactions for example, such key bioprocess analytes as amino acids, vitamins, lactose, and acetate.

  3. Reduction of Metal Oxide to Metal using Ionic Liquids

    SciTech Connect

    Dr. Ramana Reddy

    2012-04-12

    A novel pathway for the high efficiency production of metal from metal oxide means of electrolysis in ionic liquids at low temperature was investigated. The main emphasis was to eliminate the use of carbon and high temperature application in the reduction of metal oxides to metals. The emphasis of this research was to produce metals such as Zn, and Pb that are normally produced by the application of very high temperatures. The reduction of zinc oxide to zinc and lead oxide to lead were investigated. This study involved three steps in accomplishing the final goal of reduction of metal oxide to metal using ionic liquids: 1) Dissolution of metal oxide in an ionic liquid, 2) Determination of reduction potential using cyclic voltammetry (CV) and 3) Reduction of the dissolved metal oxide. Ionic liquids provide additional advantage by offering a wide potential range for the deposition. In each and every step of the process, more than one process variable has been examined. Experimental results for electrochemical extraction of Zn from ZnO and Pb from PbO using eutectic mixtures of Urea ((NH2)2CO) and Choline chloride (HOC2H4N(CH3)3+Cl-) or (ChCl) in a molar ratio 2:1, varying voltage and temperatures were carried out. Fourier Transform Infra-Red (FTIR) spectroscopy studies of ionic liquids with and without metal oxide additions were conducted. FTIR and induction coupled plasma spectroscopy (ICPS) was used in the characterization of the metal oxide dissolved ionic liquid. Electrochemical experiments were conducted using EG&G potentiostat/galvanostat with three electrode cell systems. Cyclic voltammetry was used in the determination of reduction potentials for the deposition of metals. Chronoamperometric experiments were carried out in the potential range of -0.6V to -1.9V for lead and -1.4V to -1.9V for zinc. The deposits were characterized using XRD and SEM-EDS for phase, morphological and elemental analysis. The results showed that pure metal was deposited on the cathode. Successful extraction of metal from metal oxide dissolved in Urea/ChCl (2:1) was accomplished. The current efficiencies were relatively high in both the metal deposition processes with current efficiency greater than 86% for lead and 95% for zinc. This technology will advance the metal oxide reduction process by increasing the process efficiency and also eliminate the production of CO2 which makes this an environmentally benign technology for metal extraction.

  4. Electrodeposition and device incorporation of bismuth antimony nanowire arrays

    NASA Astrophysics Data System (ADS)

    Keyani, Jennifer

    Thermoelectric materials have the unique property where the application of a potential difference across the material results in the formation of a temperature gradient, and vice versa. There is continued interest in bulk thermoelectric materials for power generation and refrigeration applications, however these materials are not currently in widespread use due to their low conversion efficiency. It has been predicted that nanostructured thermoelectric materials will show enhanced performance over their bulk counterparts. In this study, bismuth antimony (Bi1-xSbx) nanowire arrays have been synthesized and assembled into devices in order to demonstrate an enhanced performance in nanostructured thermoelectric materials. Bi1-xSbx nanowire arrays were fabricated by potentiostatic electrodeposition into porous alumina templates from a dimethyl sulfoxide (DMSO) solution. The nanowire composition and texture were studied as a function of the electrodeposition conditions in order to maximize their thermoelectric performance. Energy dispersive spectrometry and electron microprobe analysis were used to study the nanowire composition as a function of the electroactive and non-electroactive species in solution. Texturing in the nanowire arrays was observed by X-ray diffraction and controlled by the applied voltage and presence of supporting electrolyte. The nanowire arrays were also optimized for device incorporation by maximizing the number of nanowires and minimizing their length distribution. The areal density of nanowire arrays was on the order of 1010 wires/cm2 due to the high density of pores in the alumina and the high degree to which those pores were filled with electrodeposited material. A narrow distribution of nanowire lengths was observed by scanning electron microscopy across millimeter-length portions of the arrays. A hybrid nanowire-bulk thermoelectric device was assembled after electrical contacts were electrodeposited over Bi1-xSbx nanowire arrays. Nickel was used as the contact material and its electrodeposition was studied with respect to the applied potential (direct and pulsed) and the deposition bath contents. The thermoelectric performance of hybrid devices assembled from these nanowire composites was determined by the Harman method. An unoptimized Bi1-xSbx nanowire array produced a temperature difference of 7°C and the hybrid device had a ZT of 0.12, which is on par with an equivalent bulk couple. The results of this work illustrate the proof of concept where a thermoelectric nanowire array was taken from fabrication to device to measurement.

  5. HYBRID SULFUR ELECTROLYZER DEVELOPMENT, NHI WORK PACKAGE N-SR07TC0301, FY07 FIRST QUARTER REPORT

    SciTech Connect

    Summers, W

    2006-12-20

    The proof of concept of SO2 electrolysis for the hybrid sulfur (HyS) process is the second priority research target of the DOE Nuclear Hydrogen Initiative's thermochemical program for FY07. The proof of concept of the liquid-phase option must be demonstrated at the single cell level for an extended run times (>100 hours). The rate of development of HyS will depend on the identification of a promising membrane or an alternative means for controlling sulfur formation. Once successful long-duration operation has been demonstrated, SRNL will develop a multi-cell stack that can be connected to the H2SO4 decomposer being developed by SNL for the S-I ILS for a Hybrid Sulfur Integrated Laboratory-Scale Experiment during FY 2008. During the first quarter of FY07, SRNL continued the component development and membrane development activities with the goal of identifying and characterizing improved electrodes, electrocatalysts, membranes and MEA configurations which could then be tested at larger scale in the SDE test facility. A modified glass cell was fabricated to allow measurements of sulfur dioxide (SO2) transport across membrane samples at elevated temperatures (up to 70 C). This testing also includes evaluating SO2 transport in different sulfuric acid concentrations (30-70 wt%). A new potentiostat/frequency analyzer was installed for determining ionic conductivity of membranes. This instrument enhances our capabilities to characterize membrane, electrocatalyst and MEA properties and performance. Continuing work from FY06, evaluations were preformed on various commercial and experimental membranes and electrocatalyst materials for the SDE. Several different types of commercially-available membranes were analyzed for sulfur dioxide transport as a function of acid strength including perfluorinated sulfonic acid (PFSA), sulfonated polyetherketone-ketone, and poly-benzimidazole (PBI) membranes. Experimental membranes from the sulfonated diels-alder polyphenylenes (SDAPP) and modified Nafion{reg_sign} 117 were evaluated for SO{sub 2} transport as well. These membranes exhibited reduced transport coefficient for SO{sub 2} transport without the loss in ionic conductivity.

  6. Long-term pressure and thermal cycling studies on lithium imide-lithium amide complex hydrides and vanadium-carbon hydrides, and electrochemical hydrogen permeation studies

    NASA Astrophysics Data System (ADS)

    Lamb, Joshua H.

    Solid-state hydrogen storage is becoming increasingly important for future development of non-polluting vehicular fuels and nuclear technology. Understanding the nature of classical and complex hydrides is of great importance in developing new high gravimetric or volumetric capacity hydrides. Towards the nuclear technology, we have studied vanadium hydrides with lattice impurities for high volumetric capacities and very low pressures. For the vehicular technology, we have studied complex hydrides with emphasis on gaseous impurity effects upon pressure cycling. Another aspect of this work is to understand fundamental hydrogen permeation in materials, for example permeations in steel. In nuclear applications, vanadium hydride has been generally studied at high pressures, but very little work has been done on low pressure hydriding and the effect of impurities. Thermodynamic pressure composition-isotherms and structural studies were performed on V-0.5 at.%C. The addition of carbon did not change the thermodynamics significantly but it had an impact on the decrepitation effects usually observed in metal hydrides. In vehicular applications, high gravimetric capacities are desirable. This study was focused on modern complex hydrides especially Li based imide-amide and binary amide-alanate systems. In this case, the emphasis was on effect of gaseous impurities upon pressure cycling, and other related. These contamination studies are important as candidate materials must have long-term stability under repeated loading of the hydride beds with fresh hydrogen charges. The starting material was Li3N and during hydriding Li2NH (imide) and subsequently, LiNH 2 (amide) phases were formed with a full capacity of ˜10 wt.% hydrogen. The pressure cycling occurred between the imide and amide phases, yielding ˜5.6 wt.% reversible hydrogen. The gaseous contamination effects on the amide-imide system were studied using 100 ppm levels of impurity gases such as O 2, H2O, CH4, CO and NH3 mixed with UHP hydrogen. In addition, commercial-grade industrial hydrogen was also used to simulate the hydrogen purchased from a commercial "Hydrogen gas" station. In the case of industrial hydrogen we found a ˜50% loss (˜2.6 wt% out of ˜5.6 wt% H2) after 1100 pressure cycles. Using the more oxygenated 100ppm O2-UHP H2 mixtures we found a capacity loss of ˜75% (1.4 wt% out of 5.6 wt%) after 560 pressure cycles. Ex-situ x-ray diffraction studies after cycling revealed formation of predominant new Li2O phase along with Li2NH-LiH phases. The addition of H2O, CH4, NH3, and CO showed varying degrees capacity loss. The alanate-imide binary mixed hydridese were also tested for resistance to impurity gases in hydrogen. These samples were obtained from DoE's Metal Hydride Center of Excellence (MHCoE) partner from University of Utah. Thermodynamic measurements were performed by pressure cycling with O2, and thermal aging with CO on the alanate-imide binary mixtures The initial desorption of the material showed ˜7 wt% hydrogen storage, and subsequent hydriding/dehydriding showed 3 wt.% capacity when using a maximum rehydriding pressure of ˜10 bar. The final portion of this work focuses on electrochemical hydrogen permeation experiments performed on steels for nuclear repository service at Yucca Mountain, Nevada. Hydrogen embrittlement and hydrogen induced cracking are common modes of failure when steel is exposed to hydrogen. In this, we studied the diffusion properties of hydrogen in both low and medium carbon steel using the electrochemical Devanathan-Stachurski method. The diffusivities and total hydrogen flux created by galvanostatic charging were measured in both standard 0.1 N NaOH electrolyte and in electrolyte simulating well water taken near Yucca Mountain. Potentiodynamic, potentiostatic permeation electrochemical tests, along with structural and elemental characterization was performed.

  7. Portable Hand-Held Electrochemical Sensor for the Transuranics

    SciTech Connect

    Dale D. Russell, William B. Knowlton, Ph.D.; Russel Hertzog, Ph.D

    2005-11-25

    During the four-year period of the grant all of the goals of the originally proposed work were achieved, and some additional accomplishments are here reported. Two types of sensors were designed and built in the lab, capable of detecting uranium, plutonium and thorium at the 10 part-per-trillion level. The basis of both sensor types is a specially designed polymer having selective binding sites for actinyl ions of the form MO{sub 2}{sup 2+}(aq), where M is any actinide in the +6 oxidation state. This binding site also traps ions of the form MO{sub 2}{sup +}(aq), where M is any actinide in the +4 oxidation state. In this way, the polymer is responsive to the two most common water-soluble ions of the actinide series. The chelating ring responsible for binding the actinyl ions was identified from the literature, calix[n]arene where n = 6. Several versions of this sensing polymer were coated on conductive substrates and demonstrated for actinide sensing. An optimized sensor was developed and is fully described in this report. It has a polymer bilayer, fabricated under the particular conditions given below. Two different operating modes were demonstrated having different capabilities. One is the chemFET mode (a FET is a field effect transistor) and the other is the voltammetric mode. These two sensors give complementary information regarding the actinide species in a sample. Therefore our recommendation is that both be used together in a probe. A detailed design for such a probe has been filed as a patent application with the United States Patent Office, and is patent pending. The sensing polymer incorporating this actinyl-chelating ring was tested under a variety of conditions and the operating limits were determined. A full factorial experiment testing the polymerization method was conducted to optimize performance and characteristics of this polymer. The actinyl-sensing polymer was also deposited on the gate of a field effect transistor (FET) and demonstrated as a sensitive detector for uranium. Millimeter scale electrodes, operated by a hand-held instrument assembled in this lab and operated in the voltammetric mode, were transported to the DOE-Nevada test site (Las Vegas, NV) where field detection and quantitation of plutonium, uranium, and a mixture of these two elements was also demonstrated. Several probe designs were prepared, built and tested including probes with movable protective windows. A miniature, battery powered potentiostat was designed, built and demonstrated for use in a hand-held field portable instrument. This work was performed largely by undergraduates who gained valuable research experience, and many of them have continued on to graduate schools. In addition, they all gained exposure to and appreciation for national security research, in particular non-proliferation research. Four graduate students participated and one earned the MS degree on this project.

  8. In situ solid-state NMR spectroscopy of electrochemical cells: batteries, supercapacitors, and fuel cells.

    PubMed

    Blanc, Frédéric; Leskes, Michal; Grey, Clare P

    2013-09-17

    Electrochemical cells, in the form of batteries (or supercapacitors) and fuel cells, are efficient devices for energy storage and conversion. These devices show considerable promise for use in portable and static devices to power electronics and various modes of transport and to produce and store electricity both locally and on the grid. For example, high power and energy density lithium-ion batteries are being developed for use in hybrid electric vehicles where they improve the efficiency of fuel use and help to reduce greenhouse gas emissions. To gain insight into the chemical reactions involving the multiple components (electrodes, electrolytes, interfaces) in the electrochemical cells and to determine how cells operate and how they fail, researchers ideally should employ techniques that allow real-time characterization of the behavior of the cells under operating conditions. This Account reviews the recent use of in situ solid-state NMR spectroscopy, a technique that probes local structure and dynamics, to study these devices. In situ NMR studies of lithium-ion batteries are performed on the entire battery, by using a coin cell design, a flat sealed plastic bag, or a cylindrical cell. The battery is placed inside the NMR coil, leads are connected to a potentiostat, and the NMR spectra are recorded as a function of state of charge. (7)Li is used for many of these experiments because of its high sensitivity, straightforward spectral interpretation, and relevance to these devices. For example, (7)Li spectroscopy was used to detect intermediates formed during electrochemical cycling such as LixC and LiySiz species in batteries with carbon and silicon anodes, respectively. It was also used to observe and quantify the formation and growth of metallic lithium microstructures, which can cause short circuits and battery failure. This approach can be utilized to identify conditions that promote dendrite formation and whether different electrolytes and additives can help prevent dendrite formation. The in situ method was also applied to monitor (by (11)B NMR) electrochemical double-layer formation in supercapacitors in real time. Though this method is useful, it comes with challenges. The separation of the contributions from the different cell components in the NMR spectra is not trivial because of overlapping resonances. In addition, orientation-dependent NMR interactions, including the spatial- and orientation-dependent bulk magnetic susceptibility (BMS) effects, can lead to resonance broadening. Efforts to understand and mitigate these BMS effects are discussed in this Account. The in situ NMR investigation of fuel cells initially focused on the surface electrochemistry at the electrodes and the electrochemical oxidation of methanol and CO to CO2 on the Pt cathode. On the basis of the (13)C and (195)Pt NMR spectra of the adsorbates and electrodes, CO adsorbed on Pt and other reaction intermediates and complete oxidation products were detected and their mode of binding to the electrodes investigated. Appropriate design and engineering of the NMR hardware has allowed researchers to integrate intact direct methanol fuel cells into NMR probes. Chemical transformations of the circulating methanol could be followed and reaction intermediates could be detected in real time by either (2)H or (13)C NMR spectroscopy. By use of the in situ NMR approach, factors that control fuel cell performance, such as methanol cross over and catalyst performance, were identified. PMID:24041242

  9. Coupled Multi-Electrode Investigation of Crevice Corrosion of 316 Stainless Steel and NiCrMo Alloy 625

    SciTech Connect

    F. Bocher; F.J. Presuel-Moreno; J.R. Scully

    2006-06-08

    Crevice corrosion is currently mostly studied using either one of two techniques depending on the information desired. The first method involves two multicrevice formers or washers fastened on both sides of a sample plate. This technique provides exposure information regarding the severity of crevice corrosion (depth, position, frequency of attack) but delivers little or no electrochemical information. The second method involves the potentiodynamic or potentiostatic study of an uncreviced sample in a model crevice solution or under a crevice former in aggressive solution where crevice corrosion may initiate and propagate and global current is recorded. However, crevice corrosion initiation and propagation behavior is highly dependent on exact position in the crevice over time. The distance from the crevice mouth will affect the solution composition, the pH, the ohmic potential drop and the true potential in the crevice. Coupled multi-electrode arrays (MEA) were used to study crevice corrosion in order to take in account spatial and temporal evolution of electrochemistry simultaneously. Scaling laws were used to rescale the crevice geometry while keeping the corrosion electrochemical properties equivalent to that of a natural crevice at a smaller length scale. one of the advantages was to be able to use commercial alloys available as wires electrode and, in the case of MEA, to spread the crevice corrosion over many individual electrodes so each one of them will have a near homogeneous electrochemical behavior. The initial step was to obtain anodic polarization curves for the relevant material in acid chloride solution which simulated the crevice electrolyte. using the software Crevicer{trademark}, the potential distribution inside the crevice as a function of the distance from the crevice mouth was determined for various crevice gaps and applied potentials, assuming constant chemistry throughout the crevice. The crevice corrosion initiation location x{sub crit} is the position where the potential drops to E{sub Flade}. Figure 1 illustrates the resulting x{sub crit} vs. G scaling laws for 316 Stainless Steel in 1 M HCl at 50 C. The coupled multi-wire array is composed of one hundred identical 316 Stainless Steel wires in a five by twenty formation inserted in a groove of a 316 Stainless Steel rod such that the ends of the wires are flush mounted with the rod. The 100 wires are coupled electrically through in-line zero resistance ammeters. The diameter of the wires (250 {micro}m) was chosen so that x{sub crit} (critical initiation distance from the crevice mouth) and the expected zone of crevice corrosion (predicted from the scaling law) would be larger than the radius of a single wire. The array created a flush mounted planar electrode with the surface/volume ratio obtained in planar crevices. The observation of the current evolution as a function of position inside and outside the crevice as function of time was made possible as illustrated in Figure 2 in 0.6 M NaCl at 50 C.

  10. Effect of slurry chemicals on chemical-mechanical planarization of copper

    NASA Astrophysics Data System (ADS)

    Hong, Youngki

    An important component of the slurries used in chemical mechanical planarization (CMP) is an appropriately chosen corrosion/dissolution inhibitor, which facilitates selective material removal from protrusions while protecting recessed regions of the surface. The present work demonstrates the utility of two environmentally benign anionic surfactants, sodium dodecyl sulfate (SDS) and ammonium dodecyl sulfate (ADS) as dissolution inhibitors. Using these surfactants in a standard slurry (1 wt% glycine with 5 wt% H2O 2 at pH = 4.0) typically used for Cu CMP, and combining measurements of open circuit potentials and contact angles with those of Cu removal rates, we show that both SDS and ADS suppress chemical dissolution and polish rates of Cu. The dissolution inhibition efficiencies of ADS and SDS measured in these experiments are found to be superior to those of benzotriazole (BTA), a traditional inhibiting agent used for copper CMP. It has been demonstrated that ADS can also be utilized as an inhibiting agent for the application in electrochemical-mechanical planarization (ECMP) of copper. Using an acidic electrolyte of glycine and H2O 2, and small Cu discs, we show that the corrosion inhibition efficiency of ADS is superior to that of benzotriazole even in ECMP application. The relation between PE of Cu patterns and complexing agents has been investigated by measuring removal rates and surface topographies from patterns created on blanket Cu films. It has been observed that PE is dependent on the step height and drops significantly beyond a threshold step height that is in the range of 1000 A. Since the same type of polishing pad (IC 1400) was used in all the experiments, it might be the complexing agent that determines this characteristic PE threshold. Also, the huge increase in Cu dissolution rate for the citric acid system with increasing temperature appears to be responsible for the low PE values measured for this system. The synergetic effect of mixtures of ADS and BTA on Cu planarization has also been demonstrated. A model slurry containing a mixture of 3 mM ADS and 0.5 mM BTA shows much lower dissolution rate of Cu than that containing 10 mM BTA while sustaining similar polish rates of Cu at 2 psi. The planarization efficiency evaluated using the topographies created on Cu film surface (width: ˜ 15mum, depth: ˜ 5000 A) also shows better results while using the mixture of 3mM ADS and 0.5 mM BTA compared to 10 mM BTA. The relation between the copper dissolution rate and planarization efficiency is shown to be inversely logarithmically proportional to each other. The information from potentiostatic polarization, contact angle, UV/VIS spectroscopy and FTIR spectroscopy suggests that the synergetic effect of the mixture of BTA and ADS is due to electrostatic attraction between Cu/Cu-BTA complex and dodecyl sulfate as well as the complexation of Cu-BTA-dodecyl sulfate.

  11. Carbon nanotube macrofilm-based nanocomposite electrodes for energy applications

    NASA Astrophysics Data System (ADS)

    Cao, Zeyuan

    Finding new electrode materials for energy conversion and storage devices have been the focus of recent research in the fields of science and engineering. Suffering from poor electronic conductivity, chemical and mechanical stability, active electrode materials are usually coupled with different carbon nanostructured materials to form nanocomposite electrodes, showing promising electrochemical performance. Among the carbon nanostructured materials, carbon nanotube (CNT) macrofilms draw great attention owing to their extraordinary properties, such as a large specific surface area, exceptionally high conductivity, porous structure, flexibility, mechanical robustness, and adhesion. They could effectively enhance the electrochemical performance of the incorporated active materials in the nanocomposites. In this dissertation, CNT macrofilm-based nanocomposites are investigated for rechargeable lithium-ion batteries, supercapacitors, and electrocatalysts of fuel cells. The progressive research developed various nanocomposites from cathode materials to anode materials followed by a general nanocomposite solution due to the unique adhesive property of the fragmented CNT macrofilms. The in-situ synthesis strategy are explored to in-situ deposit unlithiated cathode materials V2O5 and lithiated cathode materials LiMn2O4 nanocrystals in the matrix of the CNT macrofilms as nanocomposites to be paired with metallic lithium in half cells. The presence of oxygen-containing functional groups on the surface of the CNT macrofilms after purification can enhance the association with the active materials to enable the facilitated transport of solvated ions to the electrolyte/electrode interfaces and increase the diffusion kinetics, consequently enhancing the battery performance in terms of high specific capacity, rate capability, and cycling stability. It is also significant to demonstrate a reliable, low-cost, and effective route to synthesize the family of metal oxides (MxOy (M=Fe, Co, Ni)) with CNT macofilms as high performance anodes for rechargeable lithium-ion batteries and as catalysts for oxygen reduction/evolution (ORR/OER). All MxOy-CNT macrofilm nanocomposites inherit the high specific capacity and cycling stability for lithium-ion batteries. NiO/SWNT and Co3O4/SWNT (200 °C) have their specialized high catalytic activities for ORR and OER in alkaline solutions, respectively. NiO/SWNT also exhibits an excellent electrochemical performance in asymmetric supercapacitors with a high power and energy density. Experimental measurements on electrochemical kinetics such as potentiostatic/galvanostatic intermittent titration techniques (PITT/GITT) are depended to understand the underlying improved Li+ diffusion behavior of nanocomposites. Critical effects of the film thickness have been identified. The CNT macrofilm with a thickness that is comparable to the characteristic diffusion length of 300~500 nm enables the nanocomposite with the highest Li+ chemical diffusion coefficient and thus an optimal electrochemical performance. The adhesive characteristic of CNT macrofilms is noticed for the first time after fragmentation by ultrasound that origins from irregular structures of laterally 2-D distributed CNT segments. The fragmented CNT macrofilms (FCNT) as "bifunctional" adhesive conductors promote a general approach to construct nanocomposite electrodes with both cathode and anode materials for lithium-ion batteries. An in-situ tribology method combining the wear track imaging and force measurement is employed to evaluate the adhesion strength of the adhesive FCNT conductors. The results show that the FCNT macrofilms have a higher adhesion strength than the conventional polymer binder polyvinylidene fluoride (PVDF). It is confirmed that the fabricated nanocomposite electrodes exhibit high rate and retention capabilities, superior to the electrodes using PVDF and carbon black. Thus, FCNT is recognized to be a competent substitute for polymer binders to maintain mechanical integrity and meanwhile to improve electrical connectivity

  12. Technological aspects of corrosion control in metallic systems

    NASA Astrophysics Data System (ADS)

    Taylor, Matthew Logan

    Three corrosion control technologies were investigated, including the effect of nitrogen on the passivity of chromium in sulfate solutions, possible issues associated with the use of amines in steam turbine environments and the microstructure of naval advanced amorphous coatings. Nitrogen (N) is a minor alloying element commonly used to increase the strength of steels by stabilizing the austenite phase. Physical vapor deposited chromium + nitrogen (0, 6.8 and 8.9 at.%N) coatings were investigated as a model system, to test the model. Because Cr passive films have been observed to be generally n-type semiconductors, an impedance function containing a n-type Faradaic impedance was constructed and optimized to electrochemical impedance spectra for the model system at pH 4,7 and 10 1M sulfate solution at 30°C. An apparent deviation from theory was observed, however. The n-type model predicted steady state currents which were independent of potential, while the observed current densities had a positive correlation with potential. Mott-Schottky analysis revealed that the test potentials were within the n-p transition and p-type potential range, which resolves the apparent deviation. Despite this difficulty, however, the impedance model produced reasonably accurate results, calculating current densities to within one order of magnitude of the measured steady state currents where anodic currents were available and passive film thicknesses on the order of 1-2 nm. Various amines are commonly used to inhibit corrosion in thermal power generation systems, including steam turbines, by increasing the pH. However, during the shutdown phase of the power plant, it is possible for these inhibitors to concentrate and cause corrosion of the turbine rotor. The effect of two ammine inhibitors (monoethanolamine and dimethylamine) on the passivity of ASTM A470/471 steel is investigated in a simulated turbine environment at pH 7, and temperatures of 95°C and at 175°C. Potentiodynamic scans and potentiostatic measurements revealed that the steel depassivated with high (0.1M) concentrations of monoethanolamine, in combination with acetate. Because the steel depassivated at low potentials and at neutral pH, it is unlikely to be acid or transpassive depassivation. The proposed mechanism for this depassivation is resistive depassivation, whereby the potential drop incurred by the precipitated outer-layer robs the barrier layer of the passive film of the potential required to maintain a finite film thickness. High velocity oxy-fuel (HFOV) coatings are employed in maritime environments to protect against corrosion and wear. The performance of such coatings is dominated by flaws in the microstructure, such as porosity, delamination and secondary phases. A nondestructive evaluation technique that is capable of determining the quality of a HVOF coating was developed, based on electrochemical impedance spectroscopy (EIS). The EIS measurement was correlated to the microstructure observed via scanning electron microscopy (SEM). Because a transmission line model was unable to provide discriminatory information, a convenient mathematical impedance function was constructed, with two separated time constants defined by constant phase elements, with time constants for a "fast" and a "slow" process. Enabling the impedance studies above is a new software package for fitting complicated impedance functions of up to 50 parameters to complex impedance data, developed specifically for this work. The curve-fitting software utilizes differential evolution, an evolutionary algorithm which is relatively new to the field of impedance modeling, enabling the operator to obtain high quality fits without the need for excellent starting guesses, taking trial and error out of the curve-fitting process and vastly improving the man-hour efficiency involved in optimizing complicated impedance functions such as the Faradaic impedance of the Point Defect Model. (Abstract shortened by UMI.)

  13. Voltage effects on cells cultured on metallic biomedical implants

    NASA Astrophysics Data System (ADS)

    Haerihosseini, Seyed Morteza

    Electrochemical voltage shifts in metallic biomedical implants occur in-vivo due to a number of processes including mechanically assisted corrosion. Surface potential of biomedical implants and excursions from resting open circuit potential (OCP), which is the voltage they attain while in contact with an electrolyte, can significantly change the interfacial properties of the metallic surfaces and alter the behavior of the surrounding cells, compromising the biocompatibility of metallic implants. Voltages can also be controlled to modulate cell function and fate. To date, the details of the physico-chemical phenomena and the role of different biomaterial parameters involved in the interaction between cells and metallic surfaces under cathodic bias have not been fully elucidated. In this work, changes in the interfacial properties of a CoCrMo biomedical alloy (ASTM F-1537) in phosphate-buffered saline (PBS) (pH 7.4) at different voltages was studied. Step polarization impedance spectroscopy technique was used to apply 50 mV voltage steps to samples, and the time-based current transients were recorded. A new equation was derived based on capacitive discharge through a Tafel element and generalized to deal with non-ideal impedance behavior. The new function compared to the KWW-Randles function, better matched the time-transient response. The results also showed a voltage dependent oxide resistance and capacitance behavior. Additionally, the in-vitro effect of static voltages on the behavior of MC3T3-E1 pre-osteoblasts cultured on CoCrMo alloy (ASTM-1537) was studied to determine the range of cell viability and mode of cell death beyond the viable range. Cell viability and morphology, changes in actin cytoskeleton, adhesion complexes and nucleus, and mode of cell death (necrosis, or intrinsic or extrinsic apoptosis) were characterized at different voltages ranging from -1000 to +500 mV (Ag/AgCl). Moreover, electrochemical currents and metal ion concentrations at each voltage were measured and related to the observed responses. Results show that cathodic and anodic voltages outside the voltage viability range (-400 < V < +500) lead to primarily intrinsic apoptotic and necrotic cell death, respectively. Cell death is associated with cathodic current densities of 0.1 uAcm-2 and anodic current densities of 10 uAcm-2. Significant increase in metallic ions (Co, Cr, Ni, Mo) was seen at +500 mV, and -1000 mV (Cr only) compared to open circuit potential. The number and total projected area of adhesion complexes was also lower on the polarized alloy (p < 0.05). These results show that reduction reactions on CoCrMo alloys leads to apoptosis of cells on the surface and may be a relevant mode of cell death for metallic implants in-vivo. . On the other hand, we studied how surface oxide thickness of Ti affects its voltage viability range and cellular response and whether anodic oxidation can serve as a means to extend this range. Cellular behavior (cell viability, cytoskeletal organization, and cellular adhesion) on bare and anodized Ti samples, potentiostatically held at voltages at the cathodic edge of the viability range, were assessed. Surfaces were characterized using contact angle (CA) measurement technique and atomic force microscopy (AFM), and the observed cellular response was related to the changes in the electrochemical properties (electrochemical currents, open circuit potential, and impedance spectra) of the samples. Results show that anodization at a low voltage (9 V) in phosphate buffer saline (PBS) generates a compact surface oxide with comparable surface roughness and energy to the starting native oxide on the bare surface. The anodized surface extends the viability range at 24 hours by about a 100 mV in the cathodic region, and preserved the cytoskeletal integrity and cell adhesion. Broadening of the viability range corresponds to an increase in impedance of the anodized surface at -400 mV(Ag/AgCl) and the resulting low average currents (below 0.1 uAcm-2) at the interface, which diminish the harmful cathodic r

  14. An investigation into the doping and crystallinity of anodically fabricated titania nanotube arrays: Towards an efficient material for solar energy applications

    NASA Astrophysics Data System (ADS)

    Allam Abdel-Motalib, Nageh Khalaf

    The primary focus of this dissertation was to improve the properties of the anodically fabricated TiO2 nanotube arrays; notably its band gap and crystallinity while retaining its tubular structure unaffected. The underlying hypothesis was that controlling the crystallinity and band gap while retaining the tubular structure will result in an enormous enhancement of the photoconversion capability of the material. To this end, a direct one-step facile approach for the in-situ doping of TiO2 nanotube arrays during their electrochemical fabrication in both aqueous and non-aqueous electrolytes has been investigated. The effect of doping on the morphology, optical and photoelectrochemical properties of the fabricated nanotube arrays is discussed. In an effort to improve the crystallinity of the anodically fabricated TiO2 nanotube arrays while retaining the tubular morphology, novel processing routes have been investigated to fabricate crystalline TiO 2 nanotube array electrodes. For the sake of comparison, the nanotubes were annealed at high temperature using the conventionally used procedure. The samples were found to be stable up to temperatures around 580°C, however, higher temperatures resulted in crystallization of the titanium support which disturbed the nanotube architecture, causing it to partially and gradually collapse and densify. The maximum photoconversion efficiency for water splitting using 7 mum-TiO2 nanotube arrays electrodes annealed at 580°C was measured to be about 10% under UV illumination. We investigated the effect of subsequent low temperature crystallization step. Rapid infrared (IR) annealing was found to be an efficient technique for crystallizing the nanotube array films within a few minutes. The IR-annealed 7mum-nanotube array films showed significant photoconversion efficiencies (eta=13.13%) upon their use as photoanodes to photoelectrochemically split water under UV illumination. This was related, in part, to the reduction in the barrier layer thickness from 1100 nm for the thermally annealed sample down to 200 nm for the IR-annealed sample under same conditions. These results support the hypothesis that reducing the barrier layer thickness would result in better performance of the material. Regarding the possibility of low temperature crystallization, this dissertation encompasses the first report on low-temperature synthesis of crystalline TiO 2 nanotube arrays. Nanotube arrays of up to 1.4 mum length using a two-step process have been demonstrated. The two-step process consists of initial treatment of the Ti foil in an oxidizing agent (H2O 2 or (NH4)2S2O8)-containing electrolytes, followed by potentiostatic anodization of the resulting foil in NH4F-containing electrolytes. The as-synthesized crystalline nanotube arrays were successfully tested as anode electrodes for water photoelectrolysis, with performances comparable to samples annealed at high temperatures, and for liquid junction dye (N 719 dye)-sensitized solar cells. With the motivation of finding an electrolyte composition that might yield better crystalline nanotubes than that obtained in the HCl-containing electrolytes, the effect of using some polyol electrolytes (diethylene, triethylene, tetraethylene and polyethylene glycols) on the crystallinity and morphology of the fabricated TiO2 nanotube arrays was investigated. The study showed that the use of these electrolytes helped to induce partial crystallinity in the formed nanotube arrays with the intensity of anatase (101) peak was found to increase with increasing the molecular weight of the polyol electrolyte. This thesis reports, for the first time, synthesis of high-aspect-ratio tantalum oxide nanotube arrays via one-step anodization of Ta foil. The use of aqueous electrolytes containing HF:H2SO4 in the volumetric ratios 1:9 and 2:8 results in formation of ordered nanodimpled surfaces with 40-55 nm pore diameters over the potential range 10-20 V. The addition of 5-10% of either ethylene glycol (EG) or dimethyl sulfoxide (DMSO) to the HF and H2SO4 aqueous electrolytes resulted i