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Sample records for doped ceria oxide

  1. Transition-Metal Doped Ceria Microspheres with Nanoporous Structures for CO Oxidation.

    PubMed

    Zhou, Lin; Li, Xiaoxiao; Yao, Ze; Chen, Zhuwen; Hong, Mei; Zhu, Rongshu; Liang, Yongye; Zhao, Jing

    2016-01-01

    Catalytic oxidation of carbon monoxide (CO) is of great importance in many different fields of industry. Until now it still remains challenging to use non-noble metal based catalysts to oxidize CO at low temperature. Herein, we report a new class of nanoporous, uniform, and transition metal-doped cerium (IV) oxide (ceria, CeO2) microsphere for CO oxidation catalysis. The porous and uniform microsphere is generated by sacrificed polymer template. Transition-metals, like Cu, Co, Ni, Mn and Fe, were doped into CeO2 microspheres. The combination of hierarchical structure and metal doping afford superior catalytic activities of the doped ceria microspheres, which could pave a new way to advanced non-precious metal based catalysts for CO oxidation. PMID:27030159

  2. Transition-Metal Doped Ceria Microspheres with Nanoporous Structures for CO Oxidation

    NASA Astrophysics Data System (ADS)

    Zhou, Lin; Li, Xiaoxiao; Yao, Ze; Chen, Zhuwen; Hong, Mei; Zhu, Rongshu; Liang, Yongye; Zhao, Jing

    2016-03-01

    Catalytic oxidation of carbon monoxide (CO) is of great importance in many different fields of industry. Until now it still remains challenging to use non-noble metal based catalysts to oxidize CO at low temperature. Herein, we report a new class of nanoporous, uniform, and transition metal-doped cerium (IV) oxide (ceria, CeO2) microsphere for CO oxidation catalysis. The porous and uniform microsphere is generated by sacrificed polymer template. Transition-metals, like Cu, Co, Ni, Mn and Fe, were doped into CeO2 microspheres. The combination of hierarchical structure and metal doping afford superior catalytic activities of the doped ceria microspheres, which could pave a new way to advanced non-precious metal based catalysts for CO oxidation.

  3. Transition-Metal Doped Ceria Microspheres with Nanoporous Structures for CO Oxidation

    PubMed Central

    Zhou, Lin; Li, Xiaoxiao; Yao, Ze; Chen, Zhuwen; Hong, Mei; Zhu, Rongshu; Liang, Yongye; Zhao, Jing

    2016-01-01

    Catalytic oxidation of carbon monoxide (CO) is of great importance in many different fields of industry. Until now it still remains challenging to use non-noble metal based catalysts to oxidize CO at low temperature. Herein, we report a new class of nanoporous, uniform, and transition metal-doped cerium (IV) oxide (ceria, CeO2) microsphere for CO oxidation catalysis. The porous and uniform microsphere is generated by sacrificed polymer template. Transition-metals, like Cu, Co, Ni, Mn and Fe, were doped into CeO2 microspheres. The combination of hierarchical structure and metal doping afford superior catalytic activities of the doped ceria microspheres, which could pave a new way to advanced non-precious metal based catalysts for CO oxidation. PMID:27030159

  4. Reduction Dynamics of Doped Ceria, Nickel Oxide, and Cermet Composites Probed Using In Situ Raman Spectroscopy

    PubMed Central

    Shearing, Paul R.; Brightman, Edward; Brett, Dan J. L.; Brandon, Nigel P.; Cohen, Lesley F.

    2016-01-01

    The redox properties of gadolinium doped ceria (CGO) and nickel oxide (NiO) composite cermets underpin the operation of solid oxide electrochemical cells. Although these systems have been widely studied, a full comprehension of the reaction dynamics at the interface of these materials is lacking. Here, in situ Raman spectroscopic monitoring of the redox cycle is used to investigate the interplay between the dynamic and competing processes of hydrogen spillover and water dissociation on the doped ceria surface. In order to elucidate these mechanisms, the redox process in pure CGO and NiO is studied when exposed to wet and dry hydrogen and is compared to the cermet behavior. In dry hydrogen, CGO reduces relatively rapidly via a series of intermediate phases, while NiO reduces via a single‐step process. In wet reducing atmospheres, however, the oxidation state of pure CGO is initially stabilized due to the dissociation of water by reduced Ce(III) and subsequent incorporation of oxygen into the structure. In the reduction process involving the composite cermet, the close proximity of the NiO improves the efficiency and speed of the composite reduction process. Although NiO is already incorporated into working cells, these observations suggest direct routes to further improve cell performance. PMID:27595058

  5. Energetics of Intermediate Temperature Solid Oxide Fuel Cell Electrolytes: Singly and Doubly doped Ceria Systems

    NASA Astrophysics Data System (ADS)

    Buyukkilic, Salih

    Solid oxide fuel cells (SOFCs) have potential to convert chemical energy directly to electrical energy with high efficiency, with only water vapor as a by-product. However, the requirement of extremely high operating temperatures (~1000 °C) limits the use of SOFCs to only in large scale stationary applications. In order to make SOFCs a viable energy solution, enormous effort has been focused on lowering the operating temperatures below 700 °C. A low temperature operation would reduce manufacturing costs by slowing component degradation, lessening thermal mismatch problems, and sharply reducing costs of operation. In order to optimize SOFC applications, it is critical to understand the thermodynamic stabilities of electrolytes since they directly influence device stability, sustainability and performance. Rare-earth doped ceria electrolytes have emerged as promising materials for SOFC applications due to their high ionic conductivity at the intermediate temperatures (500--700 °C). However there is a fundamental lack of understanding regarding their structure, thermodynamic stability and properties. Therefore, the enthalpies of formation from constituent oxides and ionic conductivities were determined to investigate a relationship between the stability, composition, structural defects and ionic conductivity in rare earth doped ceria systems. For singly doped ceria electrolytes, we investigated the solid solution phase of bulk Ce1-xLnxO2-0.5x where Ln = Sm and Nd (0 ≤ x ≤ 0.30) and analyzed their enthalpies of formation, mixing and association, and bulk ionic conductivities while considering cation size mismatch and defect associations. It was shown that for ambient temperatures in the dilute dopant region, the positive heat of formation reaches a maximum as the system becomes increasingly less stable due to size mismatch. In concentrated region, stabilization to a certain solubility limit was observed probably due to the defect association of trivalent cations

  6. Enhancing oxide ion incorporation kinetics by nanoscale Yttria-doped ceria interlayers.

    PubMed

    Fan, Zeng; Prinz, Fritz B

    2011-06-01

    Interlayering 17.5 nm of Yttria-doped ceria (YDC) thin films between bulk yttria-stabilized-zirconia electrolyte and a porous Pt cathode enhanced the performance of low-temperature solid oxide fuel cells. The added YDC interlayer (14.11% doped Y(2)O(3)) was fabricated by atomic layer deposition and reduced the cathode/electrolyte interfacial resistances while increasing the exchange current density j(0) by a factor of 4 at operating temperatures between 300-500 °C. Tafel plots and the fitted impedance data suggest that the charge transfer coefficient α of interlayered SOFCs was 1.25 times higher, and the electrode/interfacial activation energy was reduced from 0.85 to 0.76 eV. PMID:21563786

  7. Thickness effects of yttria-doped ceria interlayers on solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Fan, Zeng; An, Jihwan; Iancu, Andrei; Prinz, Fritz B.

    2012-11-01

    Determining the optimal thickness range of the interlayed yttria-doped ceria (YDC) films promises to further enhance the performance of solid oxide fuel cells (SOFCs) at low operating temperatures. The YDC interlayers are fabricated by the atomic layer deposition (ALD) method with one super cycle of the YDC deposition consisting of 6 ceria deposition cycles and one yttria deposition cycle. YDC films of various numbers of ALD super cycles, ranging from 2 to 35, are interlayered into bulk fuel cells with a 200 um thick yttria-stabilized zirconia (YSZ) electrolyte. Measurements and analysis of the linear sweep voltammetry of these fuel cells reveal that the performance of the given cells is maximized at 10 super cycles. Auger elemental mapping and X-ray photoelectron spectroscopy (XPS) techniques are employed to determine the film completeness, and they verify 10 super cycles of YDC to be the critical thickness point. This optimal YDC interlayer condition (6Ce1Y × 10 super cycles) is applied to the case of micro fuel cells as well, and the average performance enhancement factor is 1.4 at operating temperatures of 400 and 450 °C. A power density of 1.04 W cm-2 at 500 °C is also achieved with the optimal YDC recipe.

  8. Redox behaviour of Gd-doped ceria-nickel oxide composites

    NASA Astrophysics Data System (ADS)

    Gil, V.; Larrea, A.; Merino, R. I.; Orera, V. M.

    Reduction kinetics of NiO-gadolinium-doped ceria (GDC) composites was studied. NiO-GDC ceramic rods were fabricated by cold isostatic pressing of powders of nanometer size obtained by chemical synthesis. The rods were sintered in air at the maximum contraction temperature, 1350 °C, and treated in reducing atmosphere at different temperatures and reduction times. Progress of the reduction process was followed by the gravimetric method. By adjusting the data obtained from weight loss during the isothermal reduction at temperatures between 500 and 700 °C to standard diffusion models for a cylinder, it was possible to obtain effective diffusion coefficients for the material. The process activation energy was 0.9 ± 0.2 eV indicating that, in the whole temperature range studied, the reduction kinetics is controlled by the diffusion of O 2- throughout the ceramic matrix of GDC. SEM studies in reduced, partially reduced and completely reduced samples reveal a submicrometric microstructure with a uniform distribution of Ni phase surrounded by pores within ceramic GDC matrix. This microstructure is suitable for IT-SOFC anodes.

  9. Ceria Doped Zinc Oxide Nanoflowers Enhanced Luminol-Based Electrochemiluminescence Immunosensor for Amyloid-β Detection.

    PubMed

    Wang, Jing-Xi; Zhuo, Ying; Zhou, Ying; Wang, Hai-Jun; Yuan, Ruo; Chai, Ya-Qin

    2016-05-25

    In this work, ceria doped ZnO nanomaterials with flower-structure (Ce:ZONFs) were prepared to construct a luminol-based electrochemiluminescence (ECL) immunosensor for amyloid-β protein (Aβ) detection. Herein, carboxyl groups (-COOH) covered Ce:ZONFs were synthesized by a green method with lysine as reductant. After that, Ce:ZONFs-based ECL nanocomposite was prepared by combining the luminophore of luminol and Ce:ZONFs via amidation and physical absorption. Luminol modified on Ce:ZONFs surface could generate a strong ECL signal under the assistance of reactive oxygen species (ROSs) (such as OH(•) and O2(•-)), which were produced by a catalytic reaction between Ce:ZONFs and H2O2. It was worth noticing that a quick Ce(4+) ↔ Ce(3+) reaction in this doped material could increase the rate of electron transfer to realize the signal amplification. Subsequently, the luminol functionalized Ce:ZONFs (Ce:ZONFs-Lum) were covered by secondary antibody (Ab2) and glucose oxidase (GOD), respectively, to construct a novel Ab2 bioconjugate (Ab2-GOD@Ce:ZONFs-Lum). The wire-structured silver-cysteine complex (AgCys NWs) with a large number of -COOH, which was synthesized by AgNO3 and l-cysteine, was used as substrate of the immunosensor to capture the primary antibody (Ab1). Under the optimal conditions, this proposed ECL immunosensor had exhibited high sensitivity for Aβ detection with a wide linear range from 80 fg/mL to 100 ng/mL and an ultralow detection limit of 52 fg/mL. Meanwhile, this biosensor had good specificity for Aβ, indicating that the provided strategy had a promising potential in the detection of Aβ. PMID:27145690

  10. Solid oxide fuel cell bi-layer anode with gadolinia-doped ceria for utilization of solid carbon fuel

    NASA Astrophysics Data System (ADS)

    Kellogg, Isaiah D.; Koylu, Umit O.; Dogan, Fatih

    Pyrolytic carbon was used as fuel in a solid oxide fuel cell (SOFC) with a yttria-stabilized zirconia (YSZ) electrolyte and a bi-layer anode composed of nickel oxide gadolinia-doped ceria (NiO-GDC) and NiO-YSZ. The common problems of bulk shrinkage and emergent porosity in the YSZ layer adjacent to the GDC/YSZ interface were avoided by using an interlayer of porous NiO-YSZ as a buffer anode layer between the electrolyte and the NiO-GDC primary anode. Cells were fabricated from commercially available component powders so that unconventional production methods suggested in the literature were avoided, that is, the necessity of glycine-nitrate combustion synthesis, specialty multicomponent oxide powders, sputtering, or chemical vapor deposition. The easily-fabricated cell was successfully utilized with hydrogen and propane fuels as well as carbon deposited on the anode during the cyclic operation with the propane. A cell of similar construction could be used in the exhaust stream of a diesel engine to capture and utilize soot for secondary power generation and decreased particulate pollution without the need for filter regeneration.

  11. Ethyl Acetate Abatement on Copper Catalysts Supported on Ceria Doped with Rare Earth Oxides.

    PubMed

    Carabineiro, Sónia Alexandra Correia; Konsolakis, Michalis; Marnellos, George Emmanouil-Nontas; Asad, Muhammad Faizan; Soares, Olívia Salomé Gonçalves Pinto; Tavares, Pedro Bandeira; Pereira, Manuel Fernando Ribeiro; Órfão, José Joaquim de Melo; Figueiredo, José Luís

    2016-01-01

    Different lanthanide (Ln)-doped cerium oxides (Ce0.5Ln0.5O1.75, where Ln: Gd, La, Pr, Nd, Sm) were loaded with Cu (20 wt. %) and used as catalysts for the oxidation of ethyl acetate (EtOAc), a common volatile organic compound (VOC). For comparison, both Cu-free (Ce-Ln) and supported Cu (Cu/Ce-Ln) samples were characterized by N₂ adsorption at -196 °C, scanning/transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and temperature programmed reduction in H₂. The following activity sequence, in terms of EtOAc conversion, was found for bare supports: CeO₂ ≈ Ce0.5Pr0.5O1.75 > Ce0.5Sm0.5O1.75 > Ce0.5Gd0.5O1.75 > Ce0.5Nd0.5O1.75 > Ce0.5La0.5O1.75. Cu addition improved the catalytic performance, without affecting the activity order. The best catalytic performance was obtained for Cu/CeO₂ and Cu/Ce0.5Pr0.5O1.75 samples, both achieving complete EtOAc conversion below ca. 290 °C. A strong correlation was revealed between the catalytic performance and the redox properties of the samples, in terms of reducibility and lattice oxygen availability. Νo particular correlation between the VOC oxidation performance and textural characteristics was found. The obtained results can be explained in terms of a Mars-van Krevelen type redox mechanism involving the participation of weakly bound (easily reduced) lattice oxygen and its consequent replenishment by gas phase oxygen. PMID:27196886

  12. Coating of calcia-doped ceria with amorphous silica shell by seeded polymerization technique

    SciTech Connect

    El-Toni, Ahmed Mohamed . E-mail: el-toni@mail.tagen.tohoku.ac.jp; Yin, Shu; Yabe, Shinryo; Sato, Tsugio

    2005-07-12

    Calcia-doped ceria is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products. However, its high catalytic ability for oxidation of organic materials makes it difficult to use as a sunscreen material. Therefore, calcia-doped ceria was coated with amorphous silica by means of seeded polymerization technique in order to depress its oxidation catalytic ability. The catalytic ability as well as UV-shielding ability was investigated for coated particles.

  13. Biogas as a fuel for solid oxide fuel cells and synthesis gas production: effects of ceria-doping and hydrogen sulfide on the performance of nickel-based anode materials.

    PubMed

    Laycock, Christian J; Staniforth, John Z; Ormerod, R Mark

    2011-05-28

    Numerous investigations have been carried out into the conversion of biogas into synthesis gas (a mixture of H(2) + CO) over Ni/YSZ anode cermet catalysts. Biogas is a variable mixture of gases consisting predominantly of methane and carbon dioxide (usually in a 2 : 1 ratio, but variable with source), with other constituents including sulfur-containing gases such as hydrogen sulfide, which can cause sulfur poisoning of nickel catalysts. The effect of temperature on carbon deposition and sulfur poisoning of 90 : 10 mol% Ni/YSZ under biogas conversion conditions has been investigated by carrying out a series of catalytic reactions of methane-rich (2 : 1) CH(4)/CO(2) mixtures in the absence and presence of H(2)S over the temperature range 750-1000 °C. The effect of ceria-doping on carbon dioxide reforming, carbon deposition and sulfur tolerance has also been investigated by carrying out a similar series of reactions over ceria-doped Ni/YSZ. Ceria was doped at 5 mol% of the nickel content to give an anode catalyst composition of 85.5 : 4.5 : 10 mol% Ni/CeO(2)/YSZ. Reactions were followed using quadrupolar mass spectrometry (QMS) and the amount of carbon deposition was analysed by subjecting the reacted catalyst samples to a post-reaction temperature programmed oxidation (TPO). On undoped Ni/YSZ, carbon deposition occurred predominantly through thermal decomposition of methane. Ceria-doping significantly suppressed methane decomposition and at high temperatures simultaneously promoted the reverse Boudouard reaction, significantly lowering carbon deposition. Sulfur poisoning of Ni/YSZ occurred in two phases, the first of which caused the most activity loss and was accelerated on increasing the reaction temperature, while the second phase had greater stability and became more favourable with increasing reaction temperature. Adding H(2)S significantly inhibited methane decomposition, resulting in much less carbon deposition. Ceria-doping significantly increased the sulfur

  14. A Novel Hybrid Axial-Radial Atmospheric Plasma Spraying Technique for the Fabrication of Solid Oxide Fuel Cell Anodes Containing Cu, Co, Ni, and Samaria-Doped Ceria

    NASA Astrophysics Data System (ADS)

    Cuglietta, Mark; Kuhn, Joel; Kesler, Olivera

    2013-06-01

    Composite coatings containing Cu, Co, Ni, and samaria-doped ceria (SDC) have been fabricated using a novel hybrid atmospheric plasma spraying technique, in which a multi-component aqueous suspension of CuO, Co3O4, and NiO was injected axially simultaneously with SDC injected radially in a dry powder form. Coatings were characterized for their microstructure, permeability, porosity, and composition over a range of plasma spray conditions. Deposition efficiency of the metal oxides and SDC was also estimated. Depending on the conditions, coatings displayed either layering or high levels of mixing between the SDC and metal phases. The deposition efficiencies of both feedstock types were strongly dependent on the nozzle diameter. Plasma-sprayed metal-supported solid oxide fuel cells utilizing anodes fabricated with this technique demonstrated power densities at 0.7 V as high as 366 and 113 mW/cm2 in humidified hydrogen and methane, respectively, at 800 °C.

  15. Mesoporous NiO-samaria doped ceria for low-temperature solid oxide fuel cells.

    PubMed

    Kim, Jin-Yeop; Kim, Ji Hyeon; Choi, Hyung Wook; Kim, Kyung Hwan; Park, Sang Joon

    2014-08-01

    In order to prepare anode material for low-temperature solid oxide fuel cells (SOFCs), the mesoporous NiO-SDC was synthesized using a cationic surfactant (cetyltrimethyl-ammonium bromide; CTAB) for obtaining wide triple-phase boundary (TPB). In addition, Ni-SDC anode-supported SOFC single cells with YSZ electrolyte and LSM cathode were fabricated and the performance of single cells was evaluated at 600 °C. The microstructure of NiO-SDC was characterized by XRD, EDX, SEM, and BET, and the results showed that the mesoporous NiO-SDC with 10 nm pores could be obtained. It was found that the surface area and the electrical performance were strongly influenced by the Ni content in Ni-SDC cermets. After calcined at 600 °C, the surface area of NiO-SDC was between 90-117 m2/g at 35-45 Ni wt%, which was sufficiently high for providing large TPB in SOFC anode. The optimum Ni content for cell performance was around 45 wt% and the corresponding MPD was 0.36 W/cm2. Indeed, the mesoporous NiO-SDC cermet may be of interest for use as an anode for low-temperature SOFCs. PMID:25936125

  16. Ceria co-doping: synergistic or average effect?

    PubMed

    Burbano, Mario; Nadin, Sian; Marrocchelli, Dario; Salanne, Mathieu; Watson, Graeme W

    2014-05-14

    Ceria (CeO2) co-doping has been suggested as a means to achieve ionic conductivities that are significantly higher than those in singly doped systems. Rekindled interest in this topic over the last decade has given rise to claims of much improved performance. The present study makes use of computer simulations to investigate the bulk ionic conductivity of rare earth (RE) doped ceria, where RE = Sc, Gd, Sm, Nd and La. The results from the singly doped systems are compared to those from ceria co-doped with Nd/Sm and Sc/La. The pattern that emerges from the conductivity data is consistent with the dominance of local lattice strains from individual defects, rather than the synergistic co-doping effect reported recently, and as a result, no enhancement in the conductivity of co-doped samples is observed. PMID:24658460

  17. Synthesis and Characterization of Pure and Doped Ceria Films by Sol-gel and Sputtering

    SciTech Connect

    Koch, Kurt T.; Saraf, Laxmikant V.

    2004-12-01

    Synthesis and Characterization of Pure and Doped Ceria Films by Sol-gel and Sputtering. KURT T. KOCH (University of Missouri, Rolla, MO, 65409) LAXMIKANT SARAF (Environmental and Molecular Science Laboratory (Part of Pacific Northwest National Laboratory), Richland, Washington 99352). Pure and doped Ceria are known for their ability to gain or lose Oxygen, which is of interest to the Solid Oxide Fuel Cell (SOFC) and catalyst community. Current efforts are focused in SOFCs to reduce the operating temperature of the cell while maintaining ionic conduction. Ceria is known for its high ionic conductivity in the intermediate temperature region. (600-800 C) We have prepared pure and doped Ceria films by Sol-gel and magnetron sputtering methods. These films were characterized by X-ray diffraction (XRD), nuclear reaction analysis (NRA), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Oxygen conduction measurements. We have observed greater volume diffusion in nanocrystalline Ceria compared to bulk polycrystalline films as a result of low density. Near surface diffusion properties with increasing temperature indicate a decrease in the volume diffusion as a result of grain growth. However, a linear increase in O2 content at {approx}600nm depth was observed and can be correlated to the redistribution of O2 in the samples. Surface roughness of <111> and <200> oriented Ceria films on Al2O3 and YSZ was observed to be 0.13nm and 0.397nm, respectively. In the case of Ceria grown on YSZ, structural properties from XRD results showed a highly oriented structure with cube on cube growth. XRD results from Ceria grown on Al2O3 showed an oriented state near the surface. structure whose degree of orientation appeared to be partially dependent on substrate temperature. Preliminary XPS results indicate reduction in Ceria from the Ce4+ to Ce3+ state near the surface.

  18. Proton-conducting Micro-solid Oxide Fuel Cells with Improved Cathode Reactions by a Nanoscale Thin Film Gadolinium-doped Ceria Interlayer

    NASA Astrophysics Data System (ADS)

    Li, Yong; Wang, Shijie; Su, Pei-Chen

    2016-02-01

    An 8 nm-thick gadolinium-doped ceria (GDC) layer was inserted as a cathodic interlayer between the nanoscale proton-conducting yttrium-doped barium zirconate (BZY) electrolyte and the porous platinum cathode of a micro-solid oxide fuel cell (μ-SOFC), which has effectively improved the cathode reaction kinetics and rendered high cell power density. The addition of the GDC interlayer significantly reduced the cathodic activation loss and increased the peak power density of the μ-SOFC by 33% at 400 °C. The peak power density reached 445 mW/cm2 at 425 °C, which is the highest among the reported μ-SOFCs using proton-conducting electrolytes. The impressive performance was attributed to the mixed protonic and oxygen ionic conducting properties of the nano-granular GDC, and also to the high densities of grain boundaries and lattice defects in GDC interlayer that favored the oxygen incorporation and transportation during the oxygen reduction reaction (ORR) and the water evolution reaction at cathode.

  19. Proton-conducting Micro-solid Oxide Fuel Cells with Improved Cathode Reactions by a Nanoscale Thin Film Gadolinium-doped Ceria Interlayer

    PubMed Central

    Li, Yong; Wang, Shijie; Su, Pei-Chen

    2016-01-01

    An 8 nm-thick gadolinium-doped ceria (GDC) layer was inserted as a cathodic interlayer between the nanoscale proton-conducting yttrium-doped barium zirconate (BZY) electrolyte and the porous platinum cathode of a micro-solid oxide fuel cell (μ-SOFC), which has effectively improved the cathode reaction kinetics and rendered high cell power density. The addition of the GDC interlayer significantly reduced the cathodic activation loss and increased the peak power density of the μ-SOFC by 33% at 400 °C. The peak power density reached 445 mW/cm2 at 425 °C, which is the highest among the reported μ-SOFCs using proton-conducting electrolytes. The impressive performance was attributed to the mixed protonic and oxygen ionic conducting properties of the nano-granular GDC, and also to the high densities of grain boundaries and lattice defects in GDC interlayer that favored the oxygen incorporation and transportation during the oxygen reduction reaction (ORR) and the water evolution reaction at cathode. PMID:26928192

  20. Electrochemically Deposited Ceria Structures for Advanced Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    Brown, Evan C.

    As the pursuit towards emissions reduction intensifies with growing interest and nascent technologies, solid oxide fuel cells (SOFCs) remain an illustrious candidate for achieving our goals. Despite myriad advantages, SOFCs are still too costly for widespread deployment, even as unprecedented materials developments have recently emerged. This suggests that, in addition to informed materials selection, the necessary power output--and, thereby, cost-savings--gains must come from the fuel cell architecture. The work presented in this manuscript primarily investigates cathodic electrochemical deposition (CELD) as a scalable micro-/nanoscale fabrication tool for engineering ceria-based components in a SOFC assembly. Also, polymer sphere lithography was utilized to deposit fully connected, yet fully porous anti-dot metal films on yttira-stabilized zirconia (YSZ) with specific and knowable geometries, useful for mechanistic studies. Particular attention was given to anode structures, for which anti-dot metal films on YSZ served as composite substrates for subsequent CELD of doped ceria. By tuning the applied potential, a wide range of microstructures from high surface area coatings to planar, thin films was possible. In addition, definitive deposition was shown to occur on the electronically insulating YSZ surfaces, producing quality YSZ|ceria interfaces. These CELD ceria deposits exhibited promising electrochemical activity, as probed by A.C. Impedance Spectroscopy. In an effort to extend its usefulness as a SOFC fabrication tool, the CELD of ceria directly onto common SOFC cathode materials without a metallic phase was developed, as well as templated deposition schemes producing ceria nanowires and inverse opals.

  1. La2NiO4+δ infiltrated into gadolinium doped ceria as novel solid oxide fuel cell cathodes: Electrochemical performance and impedance modelling

    NASA Astrophysics Data System (ADS)

    Nicollet, C.; Flura, A.; Vibhu, V.; Rougier, A.; Bassat, J. M.; Grenier, J. C.

    2015-10-01

    This paper is devoted to the study of composite cathodes of La2NiO4+δ infiltrated into a Gd-doped ceria backbone. Porous Gd-doped ceria backbones are screen printed onto yttria-stabilized zirconia or Gd-doped ceria dense electrolytes, and infiltrated with a La and Ni nitrate solution (2:1 stoichiometry ratio). The influence of the preparation parameters on the polarization resistance, such as the concentration of the infiltration solution, the amount of infiltrated phase, the annealing temperature, the thickness of the electrode, and the nature of the electrolyte, is characterized by impedance spectroscopy performed on symmetrical cells. The optimization of these parameters results in a decrease of the polarization resistance down to 0.15 Ω cm2 at 600 °C. Using the Adler-Lane-Steele model, the modelling of the impedance diagrams leads to the determination of the ionic conductivity as well as the surface exchange rate of the infiltrated electrode.

  2. Synthesis and Characterization of Pure and Doped Ceria Films by Sol-Gel and Sputtering

    SciTech Connect

    Koch, K.T.; Saraf, L.

    2004-01-01

    Pure and doped Ceria are known for their ability to gain or lose Oxygen, which is of interest to the Solid Oxide Fuel Cell (SOFC) and catalyst community. Current efforts are focused in SOFCs to reduce the operating temperature of the cell while maintaining ionic conduction. Ceria is known for its high ionic conductivity in the intermediate temperature region. (600-800° C) We have prepared pure and doped Ceria films by Sol-gel and magnetron sputtering methods. Enhanced grain-boundary contribution in the conductivity can be studied in the Sol-gel process due to excellent control over the synthesis conditions, which enabled us to control the average grain size. Sputtered films were grown and investigated as a prelude to possible multi-layered CeO2 structures in the near future. These films were characterized by X-ray diffraction (XRD), nuclear reaction analysis (NRA), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Oxygen conduction measurements. We have observed greater volume diffusion in nanocrystalline Ceria compared to bulk polycrystalline films as a result of low density. Near surface diffusion properties with increasing temperature indicate a decrease in the volume diffusion as a result of grain growth. However, a linear increase in O2 content at ~600nm depth was observed and can be correlated to the redistribution of O2 in the samples. Surface roughness of <111> and <200> oriented Ceria films on Al2O3 and YSZ was observed to be 0.13nm and 0.397nm, respectively. In the case of Ceria grown on YSZ, structural properties from XRD results showed a highly oriented structure with cube on cube growth. XRD results from Ceria grown on Al2O3 showed an oriented structure whose degree of orientation appeared to be partially dependent on substrate temperature. Preliminary XPS results indicate reduction in Ceria from the Ce4+ to Ce3+ state near the surface.

  3. Electrospinning of Ceria and Nickel Oxide Nanofibers

    NASA Astrophysics Data System (ADS)

    Yerasi, Jyothi Swaroop Reddy

    Electrospinning uses an electrical charge to draw very fine fibers from a liquid. It has very high potential for industrial processing. Electrospinning is cost effective, repeatable and it can produce long, continuous nanofibers. Polymers such as polyalcohol, polyamides, and PLLA can be easily electrospun. The increase in demand for clean energy combined with the research work in progress and the potential advantages of electrospun electrodes over conventionally fabricated SOFCs makes electrospinning a strong candidate. In this thesis, ceramic nanofibers (ceria and nickel oxide) that can potentially be used in SOFCs are fabricated. A three-phase approach is implemented in the fabrication of ceria and nickel oxide nanofibers. The first phase involves the preparation of the composite ceramic-polymer solution to be electrospun. The second phase gives the processing conditions such as voltage applied, feed rate, and gauge of syringe tip used for successfully electrospinning composite ceramic-polymer fibers. The final stage demonstrates the temperature cycles used to burn out the polymer and calcine the ceramic particles in the ceramic-polymer nanofibers leaving behind ceria and nickel oxide nanofibers. Techniques such as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray Diffraction (XRD) were used to measure the average diameter of the fibers formed and to understand the chemical composition and crystallanity of the nanofibers after calcination. This thesis also discusses the advantages and possibility of fabricating side-by-side nanofibers and oriented nanofiber mats.

  4. Two-dimensional, high valence-doped ceria: Ce6WO12(100)/W(110)

    NASA Astrophysics Data System (ADS)

    Stetsovych, Vitalii; Skála, Tomáš; Beran, Jan; Dvořák, Filip; Mazur, Daniel; Tsud, Nataliya; Mašek, Karel; Mysliveček, Josef; Matolín, Vladimír

    2016-05-01

    Doping of oxides for catalytic applications represents one of the most used strategies for improving their catalytic performance. Model catalyst systems for doped oxides that would contain the dopant atoms in a well-defined geometry allowing for investigation of relationships between structure and reactivity are however rare. Here we report on preparation and structural properties of two-dimensional W-doped ceria on W(110) substrate. This model system adopts geometry of two-dimensional Ce6WO12 (100)-oriented thin film, including isolated W6+ ions that donate the charge to Ce3+ ions and act as high-valence dopants. The system represents a model catalyst for prospective use in investigating the role of W6+ active sites in CeOx-WOx catalysts and high valence dopants in ceria in general.

  5. Study on the CO Oxidation over Ceria-Based Nanocatalysts.

    PubMed

    Piumetti, Marco; Andana, Tahrizi; Bensaid, Samir; Russo, Nunzio; Fino, Debora; Pirone, Raffaele

    2016-12-01

    A series of ceria nanocatalysts have been prepared to study the structure dependency of the CO oxidation reaction. The ceria samples with well-defined nanostructures (nanocubes/Ce-NC and nanorods/Ce-NR) have been prepared using the hydrothermal method. Mesoporous ceria (Ce-MES) and ceria synthesized with solution combustion technique (Ce-SCS) have also been prepared for comparison. The lowest CO oxidation temperature has been reached by using ceria nanocubes (Ce-NC). This high activity draws immense contributions from the highly reactive (100) and (110) surfaces of the truncated nanocubes. The Ce-MES and Ce-SCS samples, despite their high surface areas, are unable to outdo the activity of Ce-NC and Ce-NR due to the abundant presence of (111) crystalline planes. This finding confirms the structure sensitivity of CO oxidation reaction catalyzed with ceria. PMID:27009532

  6. Structural and catalytic properties of lanthanide (La, Eu, Gd) doped ceria

    SciTech Connect

    Hernandez, W.Y.; Laguna, O.H.; Centeno, M.A.; Odriozola, J.A.

    2011-11-15

    Ce{sub 0.9}M{sub 0.1}O{sub 2-{delta}} mixed oxides (M=La, Eu and Gd) were synthesized by coprecipitation. Independent of the dopant cation, the obtained solids maintain the F-type crystalline structure, characteristic of CeO{sub 2} (fluorite structure) without phase segregation. The ceria lattice expands depending on the ionic radii of the dopant cation, as indicated by X-ray diffraction studies. This effect also agrees with the observed shift of the F{sub 2g} Raman vibrational mode. The presence of the dopant cations in the ceria lattice increases the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce{sup 4+}/Ce{sup 3+}. All synthesized materials show higher catalytic activity for the CO oxidation reaction than that of bare CeO{sub 2}, being Eu-doped solid the one with the best catalytic performances despite of its lower surface area. - Graphical abstract: In this work, Ce{sub 0.9}M{sub 0.1}O{sub 2-{delta}} mixed oxides (M=La, Eu and Gd) were synthesized by coprecipitation. Independent of the dopant cation, the obtained solids maintain the F-type crystalline structure, characteristic of CeO{sub 2} (fluorite structure) without phase segregation. The ceria lattice expands depending on the ionic radii of the dopant cation, as indicated by X-ray diffraction studies. This effect also agrees with the observed shift of the F{sub 2g} Raman vibrational mode. The presence of the dopant cations in the ceria lattice increases the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce{sup 4+}/Ce{sup 3+}. All synthesized materials show higher catalytic activity for the CO oxidation reaction than that of bare CeO{sub 2}, being Eu-doped solid the one with the best catalytic performances despite of its lower surface area. Highlights: > Lanthanide doped ceria as catalytic supports for CO oxidation reaction. > A higher concentration of oxygen vacancies promotes a higher catalytic activity. > Eu-doped ceria shows

  7. Effects of some rare earth and carbonate-based co-dopants on structural and electrical properties of samarium doped ceria (SDC) electrolytes for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Anwar, Mustafa; Khan, Zuhair S.; Mustafa, Kamal; Rana, Akmal

    2015-09-01

    In the present study, samarium doped ceria (SDC) and SDC-based composite with the addition of K2CO3 were prepared by co-precipitation route and effects of pH of the solution and calcination temperature on microstructure of SDC and SDC-K2CO3, respectively, were investigated. Furthermore, experimentation was performed to investigate into the ionic conductivity of pure SDC by co-doping with yttrium i.e., YSDC, XRD and SEM studies show that the crystallite size and particle size of SDC increases with the increase in pH. The SEM images of all the samples of SDC synthesized at different pH values showed the irregular shaped and dispersed particles. SDC-K2CO3 was calcined at 600∘C, 700∘C and 800∘C for 4 h and XRD results showed that crystallite size increases while lattice strain, decreases with the increase in calcination temperature and no peaks were detected for K2CO3 as it is present in an amorphous form. The ionic conductivity of the electrolytes increases with the increase in temperature and SDC-K2CO3 shows the highest value of ionic conductivity as compared to SDC and YSDC. Chemical compatibility tests were performed between the co-doped electrolyte and lithiated NiO cathode at high temperature. It revealed that the couple could be used up to the temperature of 700∘C.

  8. Special quasirandom structures for gadolinia-doped ceria and related materials.

    PubMed

    Wang, H; Chroneos, A; Jiang, C; Schwingenschlögl, U

    2012-09-01

    Gadolinia doped ceria in its doped or strained form is considered to be an electrolyte for solid oxide fuel cell applications. The simulation of the defect processes in these materials is complicated by the random distribution of the constituent atoms. We propose the use of the special quasirandom structure (SQS) approach as a computationally efficient way to describe the random nature of the local cation environment and the distribution of the oxygen vacancies. We have generated two 96-atom SQS cells describing 9% and 12% gadolinia doped ceria. These SQS cells are transferable and can be used to model related materials such as yttria stabilized zirconia. To demonstrate the applicability of the method we use density functional theory to investigate the influence of the local environment around a Y dopant in Y-codoped gadolinia doped ceria. It is energetically favourable if Y is not close to Gd or an oxygen vacancy. Moreover, Y-O bonds are found to be weaker than Gd-O bonds so that the conductivity of O ions is improved. PMID:22828722

  9. Carbon deposition behaviour in metal-infiltrated gadolinia doped ceria electrodes for simulated biogas upgrading in solid oxide electrolysis cells

    NASA Astrophysics Data System (ADS)

    Duboviks, V.; Lomberg, M.; Maher, R. C.; Cohen, L. F.; Brandon, N. P.; Offer, G. J.

    2015-10-01

    One of the attractive applications for reversible Solid Oxide Cells (SOCs) is to convert CO2 into CO via high temperature electrolysis, which is particularly important for biogas upgrading. To improve biogas utility, the CO2 component can be converted into fuel via electrolysis. A significant issue for SOC operation on biogas is carbon-induced catalyst deactivation. Nickel is widely used in SOC electrodes for reasons of cost and performance, but it has a low tolerance to carbon deposition. Two different modes of carbon formation on Ni-based electrodes are proposed in the present work based on ex-situ Raman measurements which are in agreement with previous studies. While copper is known to be resistant towards carbon formation, two significant issues have prevented its application in SOC electrodes - namely its relatively low melting temperature, inhibiting high temperature sintering, and low catalytic activity for hydrogen oxidation. In this study, the electrodes were prepared through a low temperature metal infiltration technique. Since the metal infiltration technique avoids high sintering temperatures, Cu-Ce0.9Gd0.1O2-δ (Cu-CGO) electrodes were fabricated and tested as an alternative to Ni-CGO electrodes. We demonstrate that the performance of Cu-CGO electrodes is equivalent to Ni-CGO electrodes, whilst carbon formation is fully suppressed when operated on biogas mixture.

  10. Study of gadolinia-doped ceria solid electrolyte surface by XPS

    SciTech Connect

    Datta, Pradyot Majewski, Peter; Aldinger, Fritz

    2009-02-15

    Gadolinia-doped ceria (CGO) is an important material to be used as electrolyte for solid oxide fuel cell for intermediate temperature operation. Ceria doped with 10 mol% gadolinia (Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95}) was prepared by conventional solid state synthesis and found to be single phase by room temperature X-ray diffraction (XRD). The chemical states of the surface of the prepared sample were analyzed by X-ray photoelectron spectroscopy (XPS). Though Gd was present in its characteristic chemical state, Ce was found in both Ce{sup 4+} and Ce{sup 3+} states. Presence of Ce{sup 3+} state was ascribed to the differential yield of oxygen atoms in the sputtering process.

  11. Gadolinia-Doped Ceria Cathodes for Electrolysis of CO2

    NASA Technical Reports Server (NTRS)

    Adler, Stuart B.

    2009-01-01

    Gadolinia-doped ceria, or GDC, (Gd(0.4)Ce(0.6)O(2-delta), where the value of delta in this material varies, depending on the temperature and oxygen concentration in the atmosphere in which it is being used) has shown promise as a cathode material for high-temperature electrolysis of carbon dioxide in solid oxide electrolysis cells. The polarization resistance of a GDC electrode is significantly less than that of an otherwise equivalent electrode made of any of several other materials that are now in use or under consideration for use as cathodes for reduction of carbon dioxide. In addition, GDC shows no sign of deterioration under typical temperature and gas-mixture operating conditions of a high-temperature electrolyzer. Electrolysis of CO2 is of interest to NASA as a way of generating O2 from the CO2 in the Martian atmosphere. On Earth, a combination of electrolysis of CO2 and electrolysis of H2O might prove useful as a means of generating synthesis gas (syngas) from the exhaust gas of a coal- or natural-gas-fired power plant, thereby reducing the emission of CO2 into the atmosphere. The syngas a mixture of CO and H2 could be used as a raw material in the manufacture, via the Fisher-Tropsch process, of synthetic fuels, lubrication oils, and other hydrocarbon prod

  12. Iron-ceria Aerogels Doped with Palladium as Water-gas Shift Catalysts for the Production of Hydrogen

    SciTech Connect

    Bali, S.; Huggins, F; Ernst, R; Pugmire, R; Huffman, G; Eyring, E

    2010-01-01

    Mixed 4.5% iron oxide-95.5% cerium oxide aerogels doped with 1% and 2% palladium (Pd) by weight have been synthesized, and their activities for the catalysis of water-gas shift (WGS) reaction have been determined. The aerogels were synthesized using propylene oxide as the proton scavenger for the initiation of hydrolysis and polycondensation of a homogeneous alcoholic solution of cerium(III) chloride heptahydrate and iron(III) chloride hexahydrate precursor. Palladium was doped onto some of these materials by gas-phase incorporation (GPI) using ({eta}{sup 3}-allyl)({eta}{sup 5}-cyclopentadienyl)palladium as the volatile Pd precursor. Water-gas shift catalytic activities were evaluated in a six-channel fixed-bed reactor at atmospheric pressure and reaction temperatures ranging from 150 to 350 C. Both 1% and 2% Pd-doped 4.5% iron oxide-95.5% cerium oxide aerogels showed WGS activities that increased significantly from 150 to 350 C. The activities of 1% Pd-doped 4.5% iron oxide-95.5% cerium oxide aerogels were also compared with that of the 1% Pd-doped ceria aerogel without iron. The WGS activity of 1% Pd on 4.5% iron oxide-95.5% cerium oxide aerogels is substantially higher (5 times) than the activity of 1% Pd-doped ceria aerogel without iron. The gas-phase incorporation results in a better Pd dispersion. Ceria aerogel provides a nonrigid structure wherein iron is not significantly incorporated inside the matrix, thereby resulting in better contact between the Fe and Pd and thus enhancing the WGS activity. Further, neither Fe nor Pd is reduced during the ceria-aerogel-catalyzed WGS reaction. This behavior contrasts with that noted for other Fe-based WGS catalysts, in which the original ferric oxide is typically reduced to a nonstoichiometric magnetite form.

  13. Sintering and mechanical properties of gadolinium-doped ceria ceramics

    NASA Astrophysics Data System (ADS)

    Yasuda, K.; Uemura, K.; Shiota, T.

    2012-01-01

    Gadolinium-doped ceria (GDC) ceramics were made by sintering at various temperatures from 1000°C to 1400°C in air. The true density and apparent density were measured to calculate the relative density of GDC ceramics. The change in relative density revealed that densification of GDC ceramics increased up to 1200°C, and thereafter turned downward. It was suggested that pores were formed at 1300°C and 1400°C due to non-stoichiometry of ceria. JIS-type specimens were cut from the sintered body and tested by 4-point bending. Young's modulus and bending strength decreased with increasing the sintering temperature from 1200°C to 1400°C, corresponding to the change in the relative density.

  14. Low-temperature preparation by polymeric complex solution synthesis of Cu-Gd-doped ceria cermets for solid oxide fuel cells anodes: Sinterability, microstructures and electrical properties

    NASA Astrophysics Data System (ADS)

    Tartaj, J.; Gil, V.; Moure, A.

    A homogeneous dispersion of fine CuO in a gadolinia-doped ceria (CGO) ceramic matrix by the polymeric organic complex solution method has been achieved. Highly sinterable powders were prepared by this method after calcining the precursor at 600 °C and attrition milled. The powders consist of individual particles of few tens of nanometer in size with a low agglomeration state. The isopressed compacts were sintered in air at 1000 °C and reducing in N 2 90%-H 2 10% atmosphere to form Cu-CGO cermets. The microstructures showed a uniform distribution of porous metallic Cu particles surrounded by microporous spaces. The influence of Cu content in Cu-CGO cermets on the electrode performance has been investigated in order to create the most suitable microstructure. The electrical properties of Cu-CGO cermets have been also studied using impedance spectroscopy, in the temperature range form 150 to about 700 °C in argon atmosphere. These measurements determined a high value of electrical conductivity at 700 °C, similar to that corresponded to pure metallic cupper.

  15. Disinfection effects of undoped and silver-doped ceria powders of nanometer crystallite size.

    PubMed

    Tsai, Dah-Shyang; Yang, Tzu-Sen; Huang, Yu-Sheng; Peng, Pei-Wen; Ou, Keng-Liang

    2016-01-01

    Being endowed with an ability of capturing and releasing oxygen, the ceria surface conventionally assumes the role of catalyzing redox reactions in chemistry. This catalytic effect also makes possible its cytotoxicity toward microorganisms at room temperature. To study this cytotoxicity, we synthesized the doped and undoped ceria particles of 8-9 nm in size using an inexpensive precipitation method and evaluated their disinfecting aptitudes with the turbidimetric and plate count methods. Among the samples being analyzed, the silver-doped ceria exhibits the highest sterilization ability, yet the undoped ceria is the most intriguing. The disinfection effect of undoped ceria is moderate in magnitude, demanding a physical contact between the ceria surface and bacteria cell wall, or the redox catalysis that can damage the cell wall and result in the cell killing. Evidently, this effect is short-range and depends strongly on dispersion of the nanoparticles. In contrast, the disinfection effects of silver-doped ceria reach out several millimeters since it releases silver ions to poison the surrounding microorganisms. Additionally, the aliovalent silver substitution creates more ceria defects. The synergetic combination, silver poisoning and heterogeneous redox catalysis, lifts and extends the disinfecting capability of silver-doped ceria to a superior level. PMID:27330294

  16. Disinfection effects of undoped and silver-doped ceria powders of nanometer crystallite size

    PubMed Central

    Tsai, Dah-Shyang; Yang, Tzu-Sen; Huang, Yu-Sheng; Peng, Pei-Wen; Ou, Keng-Liang

    2016-01-01

    Being endowed with an ability of capturing and releasing oxygen, the ceria surface conventionally assumes the role of catalyzing redox reactions in chemistry. This catalytic effect also makes possible its cytotoxicity toward microorganisms at room temperature. To study this cytotoxicity, we synthesized the doped and undoped ceria particles of 8–9 nm in size using an inexpensive precipitation method and evaluated their disinfecting aptitudes with the turbidimetric and plate count methods. Among the samples being analyzed, the silver-doped ceria exhibits the highest sterilization ability, yet the undoped ceria is the most intriguing. The disinfection effect of undoped ceria is moderate in magnitude, demanding a physical contact between the ceria surface and bacteria cell wall, or the redox catalysis that can damage the cell wall and result in the cell killing. Evidently, this effect is short-range and depends strongly on dispersion of the nanoparticles. In contrast, the disinfection effects of silver-doped ceria reach out several millimeters since it releases silver ions to poison the surrounding microorganisms. Additionally, the aliovalent silver substitution creates more ceria defects. The synergetic combination, silver poisoning and heterogeneous redox catalysis, lifts and extends the disinfecting capability of silver-doped ceria to a superior level. PMID:27330294

  17. Variable temperature electrochemical strain microscopy of Sm-doped ceria

    SciTech Connect

    Jesse, Stephen; Morozovska, A. N.; Kalinin, Sergei V; Eliseev, E. A.; Yang, Nan; Doria, Sandra; Tebano, Antonello

    2013-01-01

    Variable temperature electrochemical strain microscopy has been used to study the electrochemical activity of Sm-doped ceria as a function of temperature and bias. The electrochemical strain microscopy hysteresis loops have been collected across the surface at different temperatures and the relative activity at different temperatures has been compared. The relaxation behavior of the signal at different temperatures has been also evaluated to relate kinetic process during bias induced electrochemical reactions with temperature and two different kinetic regimes have been identified. The strongly non-monotonic dependence of relaxation behavior on temperature is interpreted as evidence for water-mediated mechanisms.

  18. Nickel-doped ceria nanoparticles for promoting catalytic activity of Pt/C for ethanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Tan, Qiang; Du, Chunyu; Sun, Yongrong; Du, Lei; Yin, Geping; Gao, Yunzhi

    2014-10-01

    This paper reports the facile synthesis of monodispersed nickel-doped ceria nanoparticles by a thermal decomposition method, which is used to promote catalytic properties of Pt/C. The Pt/Ni-doped CeO2/C catalyst obtained exhibits remarkably high activity and stability towards the ethanol electrooxidation in acidic media. This is attributed to higher oxygen releasing capacity and stronger interaction of Ni-doped CeO2 with Pt than pure CeO2 nanoparticles that contribute positively to the removal of poisoning intermediates. We believe that the design concept and synthetic strategy of metal doped oxides used for fuel cell catalysts can be potentially extended to other catalytic fields.

  19. Mechanical characterization of hydroxyapatite, thermoelectric materials and doped ceria

    NASA Astrophysics Data System (ADS)

    Fan, Xiaofeng

    For a variety of applications of brittle ceramic materials, porosity plays a critical role structurally and/or functionally, such as in engineered bone scaffolds, thermoelectric materials and in solid oxide fuel cells. The presence of porosity will affect the mechanical properties, which are essential to the design and application of porous brittle materials. In this study, the mechanical property versus microstructure relations for bioceramics, thermoelectric (TE) materials and solid oxide fuel cells were investigated. For the bioceramic material hydroxyapatite (HA), the Young's modulus was measured using resonant ultrasound spectroscopy (RUS) as a function of (i) porosity and (ii) microcracking damage state. The fracture strength was measured as a function of porosity using biaxial flexure testing, and the distribution of the fracture strength was studied by Weibull analysis. For the natural mineral tetrahedrite based solid solution thermoelectric material (Cu10Zn2As4S13 - Cu 12Sb4S13), the elastic moduli, hardness and fracture toughness were studied as a function of (i) composition and (ii) ball milling time. For ZiNiSn, a thermoelectric half-Heusler compound, the elastic modulus---porosity and hardness---porosity relations were examined. For the solid oxide fuel cell material, gadolina doped ceria (GDC), the elastic moduli including Young's modulus, shear modulus, bulk modulus and Poisson's ratio were measured by RUS as a function of porosity. The hardness was evaluated by Vickers indentation technique as a function of porosity. The results of the mechanical property versus microstructure relations obtained in this study are of great importance for the design and fabrication of reliable components with service life and a safety factor. The Weibull modulus, which is a measure of the scatter in fracture strength, is the gauge of the mechanical reliability. The elastic moduli and Poisson's ratio are needed in analytical or numerical models of the thermal and

  20. Calcium-doped ceria/titanate tabular functional nanocomposite by layer-by-layer coating method

    SciTech Connect

    Liu, Xiang W.; Devaraju, M.K.; Yin, Shu; Sato, Tsugio

    2010-07-15

    Ca-doped ceria (CDC)/tabular titanate (K{sub 0.8}Li{sub 0.27}Ti{sub 1.73}O{sub 4}, TT) UV-shielding functional nanocomposite with fairly uniform CDC coating layers was prepared through a polyelectrolyte-associated layer-by-layer (LbL) coating method. TT with lepidocrocite-like layered structure was used as the substrate, poly (diallyldimethylammonium chloride) (PDDA) was used as a coupling agent, CDC nanoparticles were used as the main UV-shielding component. CDC/TT nanocomposites with various coating layers of CDC were obtained through a multistep coating process. The phases were studied by X-ray diffraction. The morphology and coating quality were studied by scanning electron microscopy and element mapping of energy dispersive X-ray analysis. The oxidation catalytic activity, UV-shielding ability and using comfort were characterized by Rancimat test, UV-vis spectra and dynamic friction test, respectively. CDC/TT nanocomposites with low oxidation catalytic activity, high UV-shielding ability and good using comfort were finally obtained. - Graphical abstract: Through the control of surface charge of particles calcium-doped ceria/titanate composites with low oxidation catalytic activity, higher UV-shielding ability and excellent comfort was obtained by a facile layer-by-layer coating method.

  1. Characterization of Sm-Doped Ceria Ceramics Synthesized by Two Different Methods

    NASA Astrophysics Data System (ADS)

    Arabaci, Aliye; Serin, Özgün

    2015-07-01

    Ceria-based materials have attracted much attention as electrolyte materials for low and intermediate temperature solid oxide fuel cells (SOFCs). In this study, we examined the effect of synthesis method on the microstructure and the ionic conductivity of ceria-based electrolytes. Sm0.2Ce0.8O1.9 (SDC) electrolytes for SOFCs were prepared using the Pechini and cellulose templating (CT) methods. Microstructures of the calcined and sintered samples were characterized by XRD and SEM techniques. The XRD results indicate that a single-phase fluorite structure formed at the relatively low calcination temperature of 500 °C. The relative densities of the sintered pellets were higher than 90%, which was proved by the SEM images. Calcined powders were characterized by FTIR technique. The electrical properties of the samarium-doped ceria electrolytes were analyzed by electrochemical impedance spectroscopy. The total ionic conductivities are 3.02 × 10-2 and 3.42 × 10-2 S/cm at 750 °C for the SDC electrolytes prepared by the Pechini method and the CT method, respectively.

  2. Influence of gadolinium doping on the structure and defects of ceria under fuel cell operating temperature

    SciTech Connect

    Acharya, S. A. Gaikwad, V. M.; Sathe, V.; Kulkarni, S. K.

    2014-03-17

    Correlation between atomic positional shift, oxygen vacancy defects, and oxide ion conductivity in doped ceria system has been established in the gadolinium doped ceria system from X-ray diffraction (XRD) and Raman spectroscopy study at operating temperature (300–600 °C) of Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC). High temperature XRD data are used to quantify atomic positional shift from mean position with temperature. The Raman spectroscopy study shows additional vibration modes related to ordering of defect spaces (Gd{sub Ce}{sup ′}−V{sub o}{sup ••}){sup *} and (2Gd{sub Ce}{sup ′}−V{sub o}{sup ••}){sup x} generated due to association of oxygen vacancies and reduced cerium or dopant cations site (Gd{sup 3+}), which disappear at 450 °C; indicating oxygen vacancies dissociation from the defect complex. The experimental evidences of cation-anion positional shifting and oxygen vacancies dissociation from defect complex in the IT-SOFC operating temperature are discussed to correlate with activation energy for ionic conductivity.

  3. Kr and Xe irradiations in lanthanum (La) doped ceria: Study at the high dose regime

    NASA Astrophysics Data System (ADS)

    Yun, Di; Oaks, Aaron J.; Chen, Wei-ying; Kirk, Marquis A.; Rest, Jeffrey; Insopov, Zinetula Z.; Yacout, Abdellatif M.; Stubbins, James F.

    2011-11-01

    In order to understand cavity and bubble formation and growth in oxide nuclear fuel materials, ion beam irradiation experiments were conducted with two common fission gas species: Kr and Xe. Ceria (CeO 2) was selected as a surrogate material for uranium dioxide (UO 2) due to its many similar properties to UO 2. Ion beam energies were chosen such that both cavities and gas bubbles structures were induced by ion irradiations. The ion irradiation experiments were carried out at 600 °C, at which temperature, cavity/gas bubble structures are believed to be immobile in this material. Lanthanum (La) was chosen as a dopant in CeO 2 to investigate the effect of impurities. The presence of La in the CeO 2 lattice also introduces a predictable initial concentration of oxygen vacancies, similar to the introduction of oxygen vacancies by the existence of Pu 3+ in MOX fuel [1]. The influence of two La concentrations, 5% and 25%, were examined. The study focused on the high dose regime where cavity/gas bubble structures were clearly identifiable with their sizes and number densities readily measurable. Cavity/gas bubble coarsening by coalescence was identified with TEM (Transmission Electron Microscopy) characterizations of as-irradiated La doped CeO 2 specimens. The results revealed that lanthanum trapping has significant influence on the cavity/bubble growth in the material lattice by comparing the cavity/gas bubble size distributions between 5% La doped ceria and 25% La doped ceria. Lattice and kinetic Monte Carlo calculations described in a previous work have provided insights to the interpretations of the experimental results [2]. Solid state Xe precipitates were observed in low energy Xe implantation in 5% La doped ceria to a very high fluence of 1 × 10 17 ions/cm 2 at 600 °C. The solid state Xe precipitate structures are represented by faceted morphology. Very similar observations of solid state/near solid state Xe bubbles were made by Nogita et al. in the outer region

  4. Imaging space charge regions in Sm-doped ceria using electrochemical strain microscopy

    SciTech Connect

    Chen, Qian Nataly; Li, Jiangyu; Adler, Stuart B.

    2014-11-17

    Nanocrystalline ceria exhibits a total conductivity several orders of magnitude higher than microcrystalline ceria in air at high temperature. The most widely accepted theory for this enhancement (based on fitting of conductivity data to various transport and kinetic models) is that relatively immobile positively charged defects and/or impurities accumulate at the grain boundary core, leading to a counterbalancing increase in the number of mobile electrons (small polarons) within a diffuse space charge region adjacent to each grain boundary. In an effort to validate this model, we have applied electrochemical strain microscopy to image the location and relative population of mobile electrons near grain boundaries in polycrystalline Sm-doped ceria in air at 20–200 °C. Our results show the first direct (spatially resolved) evidence that such a diffuse space charge region does exist in ceria, and is localized to both grain boundaries and the gas-exposed surface.

  5. Nanostructured, Gd-doped ceria promoted by Pt or Pd: investigation of the electronic and surface structures and relations to chemical properties.

    PubMed

    Borchert, Holger; Borchert, Yulia; Kaichev, Vasiliy V; Prosvirin, Igor P; Alikina, Galina M; Lukashevich, Anton I; Zaikovskii, Vladimir I; Moroz, Ella M; Paukshtis, Eugenii A; Bukhtiyarov, Valerii I; Sadykov, Vladislav A

    2005-11-01

    Nanostructured ceria doped with other rare earth elements is a good oxygen ion conductor, which gives rise to various catalytic applications such as the construction of membranes for syngas production by partial oxidation of methane. This article focuses on the Gd-doped cerium dioxides, which can be modified with Pt or Pd to enhance the reactivity of the lattice oxygen in interaction with methane. The aim of the work is the elucidation of correlations between the structural, electronic, and chemical properties of these nanomaterials. Detailed studies were performed for a series of samples with and without surface modification by noble metals using a complex combination of physicochemical methods: XRD, TEM, CH(4) TPR, XPS, SIMS, and FTIR spectroscopy of adsorbed CO. XPS and TPR data revealed that surface modification with noble metals enhances the reducibility of the doped ceria support, where the effect is more pronounced for Pd than for Pt. The formation of highly cationic Pd species due to strong metal support interactions provides a possible explanation for this behavior. Furthermore, the results obtained in the present work for the Gd-doped ceria system are compared to those obtained previously for the Pr-doped ceria system. PMID:16853596

  6. Synthesis of La{sup 3+} doped nanocrystalline ceria powder by urea-formaldehyde gel combustion route

    SciTech Connect

    Biswas, M.; Bandyopadhyay, S.

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer Nano LC synthesized by gel combustion, using urea-formaldehyde fuel for first time. Black-Right-Pointing-Pointer Largely single crystals were produced in average range of 20-30 nm. Black-Right-Pointing-Pointer La{sup 3+} doping increases cell dimension linearly. Black-Right-Pointing-Pointer La{sup 3+} doping introduces ionic point defects but does not change electronic band gap. Black-Right-Pointing-Pointer Presence of Ce{sup 3+} indicates that this synthesis route produces reactive powders. -- Abstract: Nanocrystalline ceria powders doped with various concentrations of lanthanum oxide have been prepared following gel combustion route using for the first time urea-formaldehyde as fuel. The synthesized products were characterized by XRD, FESEM, TEM, PL and UV-vis spectroscopy. Peak positions of XRD were refined and the lattice parameters were obtained by applying Cohen's method. Unit cell parameter increases with concentration of La{sup 3+} ion and the variation is consistently linear. XRD calculations showed the dependence of crystallite size on dopant concentrations at lower level. TEM observation revealed unagglomerated particles to be single crystals in the average range of 20-30 nm. Band gap of the La{sup 3+} doped ceria materials does not change with doping. Spectroscopic experiments proved the existence of Ce{sup 3+} in the formed powder.

  7. Optical properties of Sm-doped ceria nanostructured films grown by electrodeposition at low temperature

    NASA Astrophysics Data System (ADS)

    Ursaki, V. V.; Lair, V.; Żivković, L.; Cassir, M.; Ringuedé, A.; Lupan, O.

    2012-09-01

    Nanostructured undoped and samarium doped ceria thin nanocolumnar films are electrodeposited onto (FTO) glass substrates at low-temperature (30 °C) with a subsequent thermal annealing at 600 °C for 1 h. Films are obtained from mixed Sm3+/Ce3+ aqueous nitrate solutions, applying a -0.8 V/(SCE) potential for 1 h. Cubic fluorite type ceria nanostructured films of high crystal quality are synthesized as confirmed by X-ray diffraction and Raman spectroscopy. SEM analysis demonstrates that doping with Sm improves the quality of the film with respect to crack formation. The incorporation and activation of the Sm3+ ions in the ceria host as well as the Stark splitting of the manifolds responsible for emission in the red-orange spectral range are investigated by means of photoluminescence spectroscopy.

  8. Effect of 1 MeV electrons on ceria-doped solar cell cover glass

    NASA Technical Reports Server (NTRS)

    Haynes, G. A.

    1973-01-01

    The effect of 1 MeV electrons on the transmission properties of 1.5-percent ceria-doped solar cell cover glass was studied. Samples of doped and undoped cover glass and synthetic fused silica were irradiated with a total integrated flux of 10 to the 15th power e/sq cm. Wideband transmission and spectral transmission measurements were made before and after irradiation. The results indicate that 1.5-percent ceria-doped cover glass is much less sensitive to radiation induced discoloration than undoped cover glass. Consequently, the glass is comparable to synthetic fused silica when used as a radiation resistant solar cell cover for many space missions.

  9. A single step solution combustion approach for preparing gadolinia doped ceria solid oxide fuel cell electrolyte material suitable for wet powder and plasma spraying processes

    NASA Astrophysics Data System (ADS)

    Shri Prakash, B.; William Grips, V. K.; Aruna, S. T.

    2012-09-01

    The present study explores the versatility of solution combustion method for preparing powders of varying characteristics suitable for intermediate temperature solid oxide fuel cell (IT-SOFC) fabrication. The promising electrolyte material for IT-SOFC, Gd0.2Ce0.8O2-δ (GDC), is considered for the present investigation. GDC powders consisting of sub-micron sized particles (<250 nm) and micron sized (>20 μm) particles are produced by varying the fuel used in the combustion reaction. Highly sinteractive nano-GDC powders prepared using oxalyl dihydrazide as a fuel results in dense pellets with high conductivity (3 × 10-4 Scm-1 at 400 °C). This powder also results in a stable suspension suitable for wet powder spraying and electrophoretic deposition. Powders with larger particle size (>20 μm) prepared by solution combustion method using mixture of fuels, exhibits necessary flowability for atmospheric plasma spraying (APS). GDC coatings fabricated by APS using flowable powders are dense with superior adhesion between the splats. Good adhesion between the splats in the APS coatings is attributed to the higher level of melting of the combustion synthesized particles in the plasma flame owing to their low specific mass.

  10. Performance Evaluation of an Oxygen Sensor as a Function of the Samaria Doped Ceria Film Thickness

    SciTech Connect

    Sanghavi, Rahul P.; Nandasiri, Manjula I.; Kuchibhatla, Satyanarayana V N T; Nachimuthu, Ponnusamy; Engelhard, Mark H.; Shutthanandan, V.; Jiang, Weilin; Thevuthasan, Suntharampillai; Kayani, Asghar N.; Prasad, Shalini

    2010-12-01

    The current demand in the automobile industry is in the control of air-fuel mixture in the combustion engine of automobiles. Oxygen partial pressure can be used as an input parameter for regulating or controlling systems in order to optimize the combustion process. Our goal is to identify and optimize the material system that would potentially function as the active sensing material for such a device that monitors oxygen partial pressure in these systems. We have used thin film samaria doped ceria (SDC) as the sensing material for the sensor operation, exploiting the fact that at high temperatures, oxygen vacancies generated due to samarium doping act as conducting medium for oxygen ions which hop through the vacancies from one side to the other contributing to an electrical signal. We have recently established that 6 atom % Sm doping in ceria films has optimum conductivity. Based on this observation, we have studied the variation in the overall conductivity of 6 atom % samaria doped ceria thin films as a function of thickness in the range of 50 nm to 300 nm at a fixed bias voltage of 2 volts. A direct proportionality in the increase in the overall conductivity is observed with the increase in sensing film thickness. For a range of oxygen pressure values from 1 mTorr to 100 Torr, a tolerable hysteresis error, good dynamic response and a response time of less than 10 seconds was observed

  11. Thickness Dependency of Thin Film Samaria Doped Ceria for Oxygen Sensing

    SciTech Connect

    Sanghavi, Rahul P.; Nandasiri, Manjula I.; Kuchibhatla, Satyanarayana V N T; Jiang, Weilin; Varga, Tamas; Nachimuthu, Ponnusamy; Engelhard, Mark H.; Shutthanandan, V.; Thevuthasan, Suntharampillai; Kayani, Asghar N.; Prasad, Shalini

    2011-01-01

    High temperature oxygen sensors are widely used for exhaust gas monitoring in automobiles. This particular study explores the use of thin film single crystalline samaria doped ceria as the oxygen sensing material. Desired signal to noise ratio can be achieved in a material system with high conductivity. From previous studies it is established that 6 atomic percent samarium doping is the optimum concentration for thin film samaria doped ceria to achieve high ionic conductivity. In this study, the conductivity of the 6 atomic percent samaria doped ceria thin film is measured as a function of the sensing film thickness. Hysteresis and dynamic response of this sensing platform is tested for a range of oxygen pressures from 0.001 Torr to 100 Torr for temperatures above 673 K. An attempt has been made to understand the physics behind the thickness dependent conductivity behavior of this sensing platform by developing a hypothetical operating model and through COMSOL simulations. This study can be used to identify the parameters required to construct a fast, reliable and compact high temperature oxygen sensor.

  12. Leaching effect in gadolinia-doped ceria aqueous suspensions for ceramic processes

    NASA Astrophysics Data System (ADS)

    Caldarelli, A.; Mercadelli, E.; Presto, S.; Viviani, M.; Sanson, A.

    2016-09-01

    Gadolinium doped ceria (CGO) is a commonly used electrolytic material for Solid Oxide Fuel Cells (SOFCs) and for this reason different shaping methods for its deposition are reported in literature. Most of these processes are based on the use of organic-based CGO suspensions, but water-based processes are acquiring increasingly interest for their economical and environmental friendly properties. In this paper we reported how the components of water-based suspension and some unexpected process parameters can deeply affect the functional properties of the final powder. In particular, we observed that CGO powders are strongly affected by ionic leaching induced by furoic acid used as dispersant: the extent of this leaching was related to the dispersant concentration and suspension's ball-milling-time; the phenomenon was confirmed by ICP-AES analyses on suspensions surnatant. Most importantly, ionic leaching affected the electrical properties of CGO: leached powder showed a higher ionic conductivity as a consequence of a partial removal of Gd ions at the grain boundaries. This work is therefore pointing out that when considering water-based suspensions, it is extremely important to carefully consider all the process parameters, including the organic components of the ceramic suspension, as these could lead to unexpected effects on the properties of the powder, affecting the performance of the final shaped material.

  13. Efficient Ceria-Platinum Inverse Catalyst for Partial Oxidation of Methanol.

    PubMed

    Ostroverkh, Anna; Johánek, Viktor; Kúš, Peter; Šedivá, Romana; Matolín, Vladimír

    2016-06-28

    Ceria-platinum-based bilayered thin films deposited by magnetron sputtering were developed and tested in regard to their catalytic activity for methanol oxidation by employing a temperature-programmed reaction (TPR) technique. The composition and structure of the samples were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Both conventional (oxide-supported metal nanoparticles [NPs]) and inverse configurations (metal with oxide overlayer) were analyzed to uncover the structural dependence of activity and selectivity of these catalysts with respect to different pathways of methanol oxidation. We clearly demonstrate that the amount of cerium oxide (ceria) loading has a profound influence on methanol oxidation reaction characteristics. Adding a noncontinuous adlayer of ceria greatly enhances the catalytic performance of platinum (Pt) in favor of partial oxidation of methanol (POM), gaining an order of magnitude in the absolute yield of hydrogen. Moreover, the undesired by-production of carbon monoxide (CO) is strongly suppressed, making the ceria-platinum inverse catalyst a great candidate for clean hydrogen production. It is suggested that the methanol oxidation process is facilitated by the synergistic effect between both components of the inverse catalyst (involving oxygen from ceria and providing a reaction site on the adjacent Pt surface) as well as by the fact that the ability of ceria to exchange oxygen (i.e., to alter the oxidation state of Ce between 3+ and 4+) during the reaction is inversely proportional to its thickness. The increased redox capability of the discontinuous ceria adlayer shifts the preferred reaction pathway from dehydrogenation of hydroxymethyl intermediate to CO in favor of its oxidation to formate. PMID:27254727

  14. A Thermodynamic Investigation of the Redox Properties of Ceria-Titania Mixed Oxides

    SciTech Connect

    Zhou,G.; Hanson, J.; Gorte, R.

    2008-01-01

    Ceria-titania solutions with compositions of Ce0.9Ti0.1O2 and Ce0.8Ti0.2O2 were prepared by the citric-acid (Pechini) method and characterized using X-ray diffraction (XRD) for structure, coulometric titration for redox thermodynamics, and water-gas-shift (WGS) reaction rates. Following calcination at 973 K, XRD suggests that the mixed oxides exist as single phase, fluorite structures, although there was no significant change in the lattice parameter compared to pure ceria. The mixed oxides are shown to be significantly more reducible than bulk ceria, with enthalpies for re-oxidation being approximately -500 kJ/mol O2, compared to -760 kJ/mol O2 for bulk ceria. However, WGS rates over 1 wt% Pd supported on ceria, Ce0.8Ti0.2O2, and Ce0.8Zr0.2O2 were nearly the same. For calcination at 1323 K, the mixed oxides separated into ceria and titania phases, as indicated by both the XRD and thermodynamic results.

  15. Methane Oxidation on Pd-Ceria. A DFT Study of the Combustion Mechanism over Pd, PdO and Pd-ceria Sites

    SciTech Connect

    Mayernick, Adam D.; Janik, Michael J.

    2010-12-24

    Palladium/ceria exhibits unique catalytic activity for hydrocarbon oxidation; however, the chemical and structural properties of active sites on the palladium–ceria surface are difficult to characterize. Strong interactions between palladium and the ceria support stabilize oxidized Pdδ+ species, which may contribute to the significant activity of Pd/ceria for methane oxidation. We present a density functional theory (DFT + U) investigation into methane oxidation over Pd/ceria and quantify the activity of the PdxCe1-xO2(1 1 1) mixed oxide surface in comparison with the PdO(1 0 0) and Pd(1 1 1) surfaces. The methane activation barrier is lowest over the PdxCe1-xO2(1 1 1) surface, even lower than over the Pd(1 1 1) surface or low coordinated stepped or kinked Pd sites. Subsequent reaction steps in complete oxidation, including product desorption and vacancy refilling, are considered to substantiate that methane activation remains the rate-limiting step despite the low barrier over PdxCe1-xO2(1 1 1). The low barrier over the PdxCe1-xO2(1 1 1) surface demonstrates that mixed ceria-noble metal oxides offer the potential for improved hydrocarbon oxidation performance with respect to dispersed noble metal particles on ceria.

  16. A palladium-doped ceria@carbon core-sheath nanowire network: a promising catalyst support for alcohol electrooxidation reactions

    NASA Astrophysics Data System (ADS)

    Tan, Qiang; Du, Chunyu; Sun, Yongrong; Du, Lei; Yin, Geping; Gao, Yunzhi

    2015-08-01

    A novel palladium-doped ceria and carbon core-sheath nanowire network (Pd-CeO2@C CSNWN) is synthesized by a template-free and surfactant-free solvothermal process, followed by high temperature carbonization. This hierarchical network serves as a new class of catalyst support to enhance the activity and durability of noble metal catalysts for alcohol oxidation reactions. Its supported Pd nanoparticles, Pd/(Pd-CeO2@C CSNWN), exhibit >9 fold increase in activity toward the ethanol oxidation over the state-of-the-art Pd/C catalyst, which is the highest among the reported Pd systems. Moreover, stability tests show a virtually unchanged activity after 1000 cycles. The high activity is mainly attributed to the superior oxygen-species releasing capability of Pd-doped CeO2 nanowires by accelerating the removal of the poisoning intermediate. The unique interconnected one-dimensional core-sheath structure is revealed to facilitate immobilization of the metal catalysts, leading to the improved durability. This core-sheath nanowire network opens up a new strategy for catalyst performance optimization for next-generation fuel cells.A novel palladium-doped ceria and carbon core-sheath nanowire network (Pd-CeO2@C CSNWN) is synthesized by a template-free and surfactant-free solvothermal process, followed by high temperature carbonization. This hierarchical network serves as a new class of catalyst support to enhance the activity and durability of noble metal catalysts for alcohol oxidation reactions. Its supported Pd nanoparticles, Pd/(Pd-CeO2@C CSNWN), exhibit >9 fold increase in activity toward the ethanol oxidation over the state-of-the-art Pd/C catalyst, which is the highest among the reported Pd systems. Moreover, stability tests show a virtually unchanged activity after 1000 cycles. The high activity is mainly attributed to the superior oxygen-species releasing capability of Pd-doped CeO2 nanowires by accelerating the removal of the poisoning intermediate. The unique

  17. Size-dependent Strain in Epitaxial (001)Gadolinium-doped Ceria Nanoislands

    SciTech Connect

    V Solovyov; M Gibert; T Puig; X Obradors

    2011-12-31

    We report size-dependent strain in epitaxial gadolinium doped ceria nanoislands, which was determined by synchrotron x-ray diffraction. Reciprocal space sections of symmetric, (004) and asymmetric, (224) reflections are approximated by a model assuming size-dependent strain of the islands using real-space size distribution obtained by atomic force microscopy. We show that the islands smaller than 40 nm are subjected to a high level of lateral tensile strain and normal compression. The lateral to normal strain ratio determined from the reciprocal map analysis suggests that lateral tension is the primary stress generator, possibly due to oxygen vacancy ordering on the island-substrate interface.

  18. Polycrystalline nanowires of gadolinium-doped ceria via random alignment mediated by supercritical carbon dioxide

    PubMed Central

    Kim, Sang Woo; Ahn, Jae-Pyoung

    2013-01-01

    This study proposes a seed/template-free method that affords high-purity semiconducting nanowires from nanoclusters, which act as basic building blocks for nanomaterials, under supercritical CO2 fluid. Polycrystalline nanowires of Gd-doped ceria (Gd-CeO2) were formed by CO2-mediated non-oriented attachment of the nanoclusters resulting from the dissociation of single-crystalline aggregates. The unique formation mechanism underlying this morphological transition may be exploited for the facile growth of high-purity polycrystalline nanowires. PMID:23572061

  19. The reduction and oxidation of ceria: A natural abundance triple oxygen isotope perspective

    NASA Astrophysics Data System (ADS)

    Hayles, Justin; Bao, Huiming

    2015-06-01

    Ceria (CeO2) is a heavily studied material in catalytic chemistry for use as an oxygen storage medium, oxygen partial pressure regulator, fuel additive, and for the production of syngas, among other applications. Ceria powders are readily reduced and lose structural oxygen when subjected to low pO2 and/or high temperature conditions. Such dis-stoichiometric ceria can then re-oxidize under higher pO2 and/or lower temperature by incorporating new oxygen into the previously formed oxygen site vacancies. Despite extensive studies on ceria, the mechanisms for oxygen adsorption-desorption, dissociation-association, and diffusion of oxygen species on ceria surface and within the crystal structure are not well known. We predict that a large kinetic oxygen isotope effect should accompany the release and incorporation of ceria oxygen. As the first attempt to determine the existence and the degree of the isotope effect, this study focuses on a set of simple room-temperature re-oxidation experiments that are also relevant to a laboratory procedure using ceria to measure the triple oxygen isotope composition of CO2. Triple-oxygen-isotope labeled ceria powders are heated at 700 °C and cooled under vacuum prior to exposure to air. By combining results from independent experimental sets with different initial oxygen isotope labels and using a combined mass-balance and triangulation approach, we have determined the isotope fractionation factors for both high temperature reduction in vacuum (⩽10-4 mbar) and room temperature re-oxidation in air. Results indicate that there is a 1.5‰ ± 0.8‰ increase in the δ18O value of ceria after being heated in vacuum at 700 °C for 1 h. When the vacuum is broken at room temperature, the previously heated ceria incorporates 3-19% of its final structural oxygen from air, with a δ18O value of 2.1-4.1+7.7 ‰ for the incorporated oxygen. The substantial incorporation of oxygen from air supports that oxygen mobility is high in vacancy

  20. Microstructure of Yttria-Doped Ceria as a Function of Oxalate Co-Precipitation Synthesis Conditions

    NASA Astrophysics Data System (ADS)

    Brissonneau, Laurent; Mathieu, Aurore; Tormos, Brigitte; Martin-Garin, Anna

    2016-06-01

    In sodium fast reactors (SFR), dissolved oxygen in sodium can be monitored via potentiometric sensors with an yttria-doped thoria electrolyte. Yttria-doped ceria (YDC) was chosen as a surrogate material to validate the process of such sensors. The material must exhibit high density and a fine grain microstructure to be resistant to the corrosion by liquid sodium and thermal shocks. Thus, the oxalic co-precipitation route was chosen to avoid milling steps that could bring impurity incorporation which is suspected to induce grain boundary corrosion in sodium. The powder and sintered pellets examination show that the synthesis conditions are of primary importance on the process yield, the oxalate powder microstructure and, eventually, on the ceramic density and microstructure. The impurity content was limited by controlling the synthesis, calcination, and sintering steps.

  1. Role of associated defects in oxygen ion conduction and surface exchange reaction for epitaxial samaria-doped ceria thin films as catalytic coatings

    DOE PAGESBeta

    Yang, Nan; Shi, Yanuo; Schweiger, Sebastian; Strelcov, Evgheni; Foglietti, Vittorio; Orgiani, Pasquale; Balestrino, Giuseppe; Kalinin, Sergei V.; Jennifer L. M. Rupp; Aruta, Carmela; et al

    2016-05-18

    Samaria-doped ceria (SDC) thin films are particularly important for energy and electronic applications such as micro-solid oxide fuel cells, electrolysers, sensors and memristors. In this paper we report a comparative study investigating ionic conductivity and surface reactions for well-grown epitaxial SDC films varying the samaria doping concentration. With increasing doping above 20 mol% of samaria, an enhancement in the defect association was observed by Raman spectroscopy. The role of such defect associates on the films` oxygen ion transport and exchange was investigated by electrochemical impedance spectroscopy and electrochemical strain microscopy (ESM). The measurements reveal that the ionic transport has amore » sharp maximum in ionic conductivity and drop in its activation energy down to 0.6 eV for 20 mol% doping. Increasing the doping concentration further up to 40 mol%, raises the activation energy substantially by a factor of two. We ascribe the sluggish transport kinetics to the "bulk" ionic-near ordering in case of the heavily doped epitaxial films. Analysis of the ESM first order reversal curve measurements indicate that these associated defects may have a beneficial role by lowering the activation of the oxygen exchange "surface" reaction for heavily doped 40 mol% of samaria. We reveal in a model experiment through a solid solution series of samaria doped ceria epitaxial films that the occurrence of associate defects in the bulk affects the surface charging state of the films to increase the exchange rates. Lastly, the implication of these findings are the design of coatings with tuned oxygen surface exchange by control of bulk associate clusters for future electro-catalytic applications.« less

  2. Role of Associated Defects in Oxygen Ion Conduction and Surface Exchange Reaction for Epitaxial Samaria-Doped Ceria Thin Films as Catalytic Coatings.

    PubMed

    Yang, Nan; Shi, Yanuo; Schweiger, Sebastian; Strelcov, Evgheni; Belianinov, Alex; Foglietti, Vittorio; Orgiani, Pasquale; Balestrino, Giuseppe; Kalinin, Sergei V; Rupp, Jennifer L M; Aruta, Carmela

    2016-06-15

    Samaria-doped ceria (SDC) thin films are particularly important for energy and electronic applications such as microsolid oxide fuel cells, electrolyzers, sensors, and memristors. In this paper, we report a comparative study investigating ionic conductivity and surface reactions for well-grown epitaxial SDC films varying the samaria doping concentration. With increasing doping above 20 mol % of samaria, an enhancement in the defect association is observed by Raman spectroscopy. The role of such associated defects on the films̀ oxygen ion transport and exchange is investigated by electrochemical impedance spectroscopy and electrochemical strain microscopy (ESM). The measurements reveal that the ionic transport has a sharp maximum in ionic conductivity and drops in its activation energy down to 0.6 eV for 20 mol % doping. Increasing the doping concentration further up to 40 mol %, it raises the activation energy substantially by a factor of 2. We ascribe the sluggish transport kinetics to the "bulk" ionic-near ordering in case of the heavily doped epitaxial films. Analysis of the ESM first-order reversal curve measurements indicates that these associated defects may have a beneficial role by lowering the activation of the oxygen exchange "surface" reaction for heavily doped 40 mol % of samaria. In a model experiment, through a solid solution series of samaria doped ceria epitaxial films, we reveal that the occurrence of associated defects in the bulk affects the surface charging state of the SDC films to increase the exchange rates. The implication of these findings is the design of coatings with tuned oxygen surface exchange by controlling the bulk associated clusters for future electrocatalytic applications. PMID:27192540

  3. Partial oxidation of methane over Rh/supported-ceria catalysts: Effect of catalyst reducibility and redox cycles

    SciTech Connect

    Salazar-Villalpando, M.D.; Berry, D.A.; Gardner, T.H.

    2008-06-01

    Partial oxidation of methane (POM) was studied over Rh/(Ce0.56Zr0.44)O2 x, Rh/(Ce0.91Gd0.09)O2 x, Rh/(Ce0.71Gd0.29)O2 x and Rh/(Ce0.88La0.12)O2 x. The effect of catalyst reducibility and redox cycles was investigated. It was found that the type of doped-ceria support and its reducibility played an important role in catalyst activity. It was also observed that redox cycles had a positive influence on H2 production, which was enhanced as the number of redox cycle increased. Results of carbon formation are discussed as a function of ionic conductivity. Temperature programmed reduction (TPR) profiles, BET surface area, ionic conductivity and XRD patterns were determined to characterize catalysts. Catalytic tests revealed that of the materials tested, Rh/(Ce0.56Zr0.44)O2 x was the most active material for the production of syngas, which correlates with its TPR profile. It was observed that doping CeO2 with Zr, rather than with La or Gd caused an enhanced reducibility of Rh/supported-ceria catalysts.

  4. Oxygen nonstoichiometry and thermodynamic characterization of Zr doped ceria in the 1573–1773 K temperature range† †Electronic supplementary information (ESI) available: XRD patterns and SEM images. See DOI: 10.1039/c4cp04916k Click here for additional data file.

    PubMed Central

    Takacs, M.; Steinfeld, A.

    2015-01-01

    This work encompasses the thermodynamic characterization and critical evaluation of Zr4+ doped ceria, a promising redox material for the two-step solar thermochemical splitting of H2O and CO2 to H2 and CO. As a case study, we experimentally examine 5 mol% Zr4+ doped ceria and present oxygen nonstoichiometry measurements at elevated temperatures ranging from 1573 K to 1773 K and oxygen partial pressures ranging from 4.50 × 10–3 atm to 2.3 × 10–4 atm, yielding higher reduction extents compared to those of pure ceria under all conditions investigated, especially at the lower temperature range and at higher p O2. In contrast to pure ceria, a simple ideal solution model accounting for the formation of isolated oxygen vacancies and localized electrons accurately describes the defect chemistry. Thermodynamic properties are determined, namely: partial molar enthalpy, entropy, and Gibbs free energy. In general, partial molar enthalpy and entropy values of Zr4+ doped ceria are lower. The equilibrium hydrogen yields are subsequently extracted as a function of the redox conditions for dopant concentrations as high as 20%. Although reduction extents increase greatly with dopant concentration, the oxidation of Zr4+ doped ceria is thermodynamically less favorable compared to pure ceria. This leads to substantially larger temperature swings between reduction and oxidation steps, ultimately resulting in lower theoretical solar energy conversion efficiencies compared to ceria under most conditions. In effect, these results point to the importance of considering oxidation thermodynamics in addition to reduction when screening potential redox materials. PMID:25714616

  5. Adhesion and Atomic Structures of Gold on Ceria Nanostructures:The Role of Surface Structure and Oxidation State of Ceria Supports

    SciTech Connect

    Lin, Yuyuan; Wu, Zili; Wen, Jianguo; Poeppelmeier, Kenneth R; Marks, Laurence D

    2015-01-01

    Recent advances in heterogeneous catalysis have demonstrated that oxides supports with the same material but different shapes can result in metal catalysts with distinct catalytic properties. The shape-dependent catalysis was not well-understood owing to the lack of direct visualization of the atomic structures at metal-oxide interface. Herein, we utilized aberration-corrected electron microscopy and revealed the atomic structures of gold particles deposited on ceria nanocubes and nanorods with {100} or {111} facets exposed. For the ceria nanocube support, gold nanoparticles have extended atom layers at the metal-support interface. In contrast, regular gold nanoparticles and rafts are present on the ceria nanorod support. After hours of water gas shift reaction, the extended gold atom layers and rafts vanish, which is associated with the decrease of the catalytic activities. By understanding the atomic structures of the support surfaces, metal-support interfaces, and morphologies of the gold particles, a direct structure-property relationship is established.

  6. In Vivo Processing of Ceria Nanoparticles inside Liver: Impact on Free-Radical Scavenging Activity and Oxidative Stress

    PubMed Central

    Tseng, Michael T.; Jasinski, Jacek B.; Yokel, Robert A.; Unrine, Jason M.; Davis, Burtron H.; Dozier, Alan K.; Hardas, Sarita S.; Sultana, Rukhsana; Grulke, Eric A.; Allan Butterfield, D.

    2015-01-01

    The cytotoxicity of ceria ultimately lies in its electronic structure, which is defined by the crystal structure, composition, and size. Despite previous studies focused on ceria uptake, distribution, biopersistance, and cellular effects, little is known about its chemical and structural stability and solubility once sequestered inside the liver. Mechanisms will be presented that elucidate the in vivo transformation in the liver. In vivo processed ceria reveals a particle-size effect towards the formation of ultrafines, which represent a second generation of ceria. A measurable change in the valence reduction of the second-generation ceria can be linked to an increased free-radical scavenging potential. The in vivo processing of the ceria nanoparticles in the liver occurs in temporal relation to the brain cellular and protein clearance responses that stem from the ceria uptake. This information is critical to establish a possible link between cellular processes and the observed in vivo transformation of ceria. The temporal linkage between the reversal of the pro-oxidant effect (brain) and ceria transformation (liver) suggests a cause–effect relationship. PMID:26322251

  7. Investigations of oxidative stress effects and their mechanisms in rat brain after systemic administration of ceria engineered nanomaterials

    NASA Astrophysics Data System (ADS)

    Hardas, Sarita S.

    Advancing applications of engineered nanomaterials (ENM) in various fields create the opportunity for intended (e.g. drug and gene delivery) or unintended (e.g. occupational and environmental) exposure to ENM. However, the knowledge of ENM-toxicity is lagging behind their application development. Understanding the ENM hazard can help us to avoid potential human health problems associated with ENM applications as well as to increase their public acceptance. Ceria (cerium [Ce] oxide) ENM have many current and potential commercial applications. Beyond the traditional use of ceria as an abrasive, the scope of ceria ENM applications now extends into fuel cell manufacturing, diesel fuel additives and for therapeutic intervention as a putative antioxidant. However, the biological effects of ceria ENM exposure have yet to be fully defined. Both pro-and anti-oxidative effects of ceria ENM exposure are repeatedly reported in literature. EPA, NIEHS and OECD organizations have nominated ceria for its toxicological evaluation. All these together gave us the impetus to examine the oxidative stress effects of ceria ENM after systemic administration. Induction of oxidative stress is one of the primary mechanisms of ENM toxicity. Oxidative stress plays an important role in maintaining the redox homeostasis in the biological system. Increased oxidative stress, due to depletion of antioxidant enzymes or molecules and / or due to increased production of reactive oxygen (ROS) or nitrogen (RNS) species may lead to protein oxidation, lipid peroxidation and/or DNA damage. Increased protein oxidation or lipid peroxidation together with antioxidant protein levels and activity can serve as markers of oxidative stress. To investigate the oxidative stress effects and the mechanisms of ceria-ENM toxicity, fully characterized ceria ENM of different sizes (˜ 5nm, 15nm, 30nm, 55nm and nanorods) were systematically injected into rats intravenously in separate experiments. Three brain regions

  8. Enhanced hydrogen oxidation activity and H2S tolerance of Ni-infiltrated ceria solid oxide fuel cell anodes

    NASA Astrophysics Data System (ADS)

    Mirfakhraei, Behzad; Paulson, Scott; Thangadurai, Venkataraman; Birss, Viola

    2013-12-01

    The effect of Ni infiltration into porous Gd-doped ceria (GDC) anodes on their H2 oxidation performance, with and without added 10 ppm H2S, is reported here. Porous GDC anodes (ca. 10 μm thick) were deposited on yttria stabilized zirconia (YSZ) supports and then infiltrated with catalytic amounts of a Ni nitrate solution, followed by electrochemical testing in a 3-electrode half-cell setup at 500-800 °C. Infiltration of 3 wt.% Ni into the porous GDC anode lowered the polarization resistance by up to 85%, affecting mainly the low frequency impedance arc. When exposed to 10 ppm H2S, the Ni-infiltrated anodes exhibited a ca. 5 times higher tolerance toward sulfur poisoning compared to GDC anodes alone, also showing excellent long-term stability in 10 ppm H2S. In the presence of H2S, it is proposed that Ni, likely distributed as a nanophase, helps to maintain a clean GDC surface at the Ni/GDC interface at which the H2 oxidation reaction takes place. In turn, the GDC will readily supply oxygen anions to the adjacent Ni surfaces, thus helping to remove adsorbed sulfur.

  9. Catalytic ozonation of sulfosalicylic acid over manganese oxide supported on mesoporous ceria.

    PubMed

    Xing, Shengtao; Lu, Xiaoyang; Liu, Jia; Zhu, Lin; Ma, Zichuan; Wu, Yinsu

    2016-02-01

    Manganese oxide supported on mesoporous ceria was prepared and used as catalyst for catalytic ozonation of sulfosalicylic acid (SA). Characterization results indicated that the manganese oxide was mostly incorporated into the pores of ceria. The synthesized catalyst exhibited high activity and stability for the mineralization of SA in aqueous solution by ozone, and more than 95% of total organic carbon was removed in 30 min under various conditions. Mechanism studies indicated that SA was mainly degraded by ozone molecules, and hydroxyl radical reaction played an important role for the degradation of its ozonation products (small molecular organic acids). The manganese oxide in the pores of CeO2 improved the adsorption of small molecular organic acids and the generation of hydroxyl radicals from ozone decomposition, resulting in high TOC removal efficiency. PMID:26344143

  10. Anode-supported microtubular cells fabricated with gadolinia-doped ceria nanopowders

    NASA Astrophysics Data System (ADS)

    Gil, V.; Gurauskis, J.; Campana, R.; Merino, R. I.; Larrea, A.; Orera, V. M.

    Anode-supported microtubular SOFCs based on ceria 3 ± 0.2 mm diameter and about 100 mm in length have been prepared using gadolinia-doped ceria (GDC) nanopowders. Nanometric Ce 0.9Gd 0.1O 1.95 (GDC) powders were deposited on NiO-Ce 0.9Gd 0.1O 1.95 (NiO-GDC) anode supports by dip-coating technique. Fabrication conditions to obtain dense and gas tight electrolyte layers on porous microtubular supports were studied. Three different dispersing agents: commercial Beycostat C213 (CECA, France) and short chain monomer (≤4 carbon atoms) with alcohol or carboxylic acid functional groups were evaluated. By optimizing colloidal dispersion parameters and sintering process, gas tight and dense GDC layers were obtained. Significantly lower sintering temperatures than reported previously (≤1300 °C) were employed to reach ≥98% values of theoretical density within electrolyte layers of ∼10 μm in thickness. A composite cathode, LSCF-GDC 50 wt.% with about 50 μm thickness was dip coated on the co-fired half-cell and then sintered at 1050 °C for 1 h. The electrochemical performance of these cells has been tested. In spite of electronic conduction due to partial reduction of the thin-electrolyte layer, the I- V measurements show power densities of 66 mW cm -2 at 0.45 V at temperatures as low as 450 °C (using 100% H 2 as fuel in the anodic compartment and air in the cathodic chamber).

  11. A SnO2-samarium doped ceria additional anode layer in a direct carbon fuel cell

    NASA Astrophysics Data System (ADS)

    Yu, Baolong; Zhao, Yicheng; Li, Yongdan

    2016-02-01

    The role of a SnO2-samarium doped ceria (SDC) additional anode layer in a direct carbon fuel cell (DCFC) with SDC-(Li0.67Na0.33)2CO3 composite electrolyte and lithiated NiO-SDC-(Li0.67Na0.33)2CO3 composite cathode is investigated and compared with a NiO-SDC extra anode layer. Catalytic grown carbon fiber mixed with (Li0.67Na0.33)2CO3 is used as a fuel. At 750 °C, the maximum power outputs of 192 and 143 mW cm-2 are obtained by the cells with SnO2-SDC and NiO-SDC layers, respectively. In the SnO2-SDC layer, the reduction of SnO2 and the oxidation of Sn happen simultaneously during the cell operation, and the Sn/SnO2 redox cycle provides an additional route for fuel conversion. The formation of an insulating dense interlayer between the anode and electrolyte layers, which usually happens in DCFCs with metal anodes, is avoided in the cell with the SnO2-SDC layer, and the stability of the cell is improved consequently.

  12. Electrochemical performance of gadolinia-doped ceria (CGO) electrolyte thin films for ITSOFC deposited by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Reolon, Raquel Pereira; Halmenschlager, Cibele Melo; Neagu, Roberto; de Fraga Malfatti, Célia; Bergmann, Carlos Pérez

    2014-09-01

    Solid Oxide Fuel Cell is an attractive, efficient, alternative source of power generation. However several challenges remained for this technology to be viable. These challenges include high power density, degradation rate, and cost. One way to decrease the SOFC cost is to use stainless steel interconnector. To be able to use a stainless steel interconnector one of the challenges is to find a way to produce an electrolyte, which does not need sintering at high temperature. This work presents the results of the process applied to gadolinia-doped ceria thin films deposited in cycles by spray pyrolysis. The aim of this work was to obtain thin, dense, and continuous CGO coatings, which has electrochemical performance suitable to be used as electrolyte for SOFC. The results obtained show that the air flow rate influenced the droplets size and hence the film quality. X-ray diffraction analysis showed that the films were crystalline after the deposition. Electrochemical tests showed maximum power density of 510 mW cm-2 at 650 °C with a thickness average of 3.30 μm when the film was deposited in 12 cycles showing that the film has a potential to be used as an electrolyte for ITSOFC on metal support.

  13. Synthesis and properties of samaria-doped ceria electrolyte for IT-SOFCs by EDTA-citrate complexing method

    NASA Astrophysics Data System (ADS)

    Wu, Wen-Chang; Huang, Jui-Ting; Chiba, Atsushi

    An ultra-fine samaria-doped ceria (Ce 0.8Sm 0.2O 1.9, SDC) electrolyte prepared by a non-ion selective EDTA-citric complexing method is developed herein for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The rigid agglomerates due to organic compounds that exist in the SDC precursors during the EDTA-citrate complexing synthesis process inhibit crystalline growth and grain growth, leading to the generation of ultra-fine grain following the sintering procedure. Calcination is necessary above 500 °C for all precursors. The average grain size of the pellets after sintering at 1400 °C for 2 h is submicron in scale (from 200 nm to 600 nm) with various pH values, and the pellets are smaller than those obtained from other synthesis processes. Dense pellets with pH values of 10 (relative density of 99%) are obtained with precursor powder calcination at 900 °C for 3 h. Electrical conductivity is dependent on the calcination temperature and pH value of the solution, and the maximum electrical conductivity is 0.01 S cm -1 at 700 °C with a pH value of 10.

  14. Support effect in oxide catalysis: methanol oxidation on vanadia/ceria.

    PubMed

    Kropp, Thomas; Paier, Joachim; Sauer, Joachim

    2014-10-15

    Density functional theory is used for periodic models of monomeric vanadia species deposited on the CeO2(111) surface to study dissociative adsorption of methanol and its subsequent dehydrogenation to formaldehyde. Dispersion-corrected PBE+U calculations are performed and compared with HSE and B3LYP results. Dissociative adsorption of methanol at different sites on VO2·CeO2(111) is highly exothermic with adsorption energies of 1.8 to 1.9 eV (HSE+D). Two relevant pathways for desorption of formaldehyde are found with intrinsic barriers for the redox step of 1.0 and 1.4 eV (HSE+D). The calculated desorption temperatures (370 and 495 K) explain the peaks observed in temperature-programmed desorption experiments. Different sites of the supported catalyst system are involved in the two pathways: (i) methanol can chemisorb on the CeO2 surface filling a so-called pseudovacancy and the H atom is transferred to an V-O-Ce interphase bond or (ii) CH3OH may chemisorb at the V-O-Ce interphase bond and form a V-OCH3 species from which H is transferred to the ceria surface, providing evidence for true cooperativity. In both cases, ceria is directly involved in the redox process, as two electrons are accommodated in Ce f states forming two Ce(3+) ions whereas vanadium remains fully oxidized (V(5+)). PMID:25275568

  15. Kinetic lattice Monte Carlo model for oxygen vacancy diffusion in praseodymium doped ceria: Applications to materials design

    SciTech Connect

    Dholabhai, Pratik P.; Anwar, Shahriar; Adams, James B.; Crozier, Peter; Sharma, Renu

    2011-04-15

    Kinetic lattice Monte Carlo (KLMC) model is developed for investigating oxygen vacancy diffusion in praseodymium-doped ceria. The current approach uses a database of activation energies for oxygen vacancy migration, calculated using first-principles, for various migration pathways in praseodymium-doped ceria. Since the first-principles calculations revealed significant vacancy-vacancy repulsion, we investigate the importance of that effect by conducting simulations with and without a repulsive interaction. Initially, as dopant concentrations increase, vacancy concentration and thus conductivity increases. However, at higher concentrations, vacancies interfere and repel one another, and dopants trap vacancies, creating a 'traffic jam' that decreases conductivity, which is consistent with the experimental findings. The modeled effective activation energy for vacancy migration slightly increased with increasing dopant concentration in qualitative agreement with the experiment. The current methodology comprising a blend of first-principle calculations and KLMC model provides a very powerful fundamental tool for predicting the optimal dopant concentration in ceria related materials. -- graphical abstract: Ionic conductivity in praseodymium doped ceria as a function of dopant concentration calculated using the kinetic lattice Monte Carlo vacancy-repelling model, which predicts the optimal composition for achieving maximum conductivity. Display Omitted Research highlights: {yields} KLMC method calculates the accurate time-dependent diffusion of oxygen vacancies. {yields} KLMC-VR model predicts a dopant concentration of {approx}15-20% to be optimal in PDC. {yields} At higher dopant concentration, vacancies interfere and repel one another, and dopants trap vacancies. {yields} Activation energy for vacancy migration increases as a function of dopant content

  16. Electrochemical behavior of thin-film Sm-doped ceria: insights from the point-contact configuration.

    PubMed

    Oh, Tae-Sik; Haile, Sossina M

    2015-05-28

    The electrochemical behavior of chemical vapor deposition (CVD) grown porous films of Sm-doped ceria (SDC) for hydrogen oxidation has been evaluated by impedance spectroscopy using a point contact geometry at a temperature of 650 °C. Porous SDC films, 950 nm in thickness, were deposited on both sides of single-crystal YSZ(100). Pt paste was applied over the surface of one SDC layer to create a high-activity counter electrode. Ni wire was contacted to the surface of the other SDC layer to create a limited contact-area working electrode. The active area of contact at the working electrode was determined using the Newman equation and the electrolyte constriction impedance. The radius of this area varied from 5 to 18 μm, depending on gas composition and bias. The area-normalized electrode impedance (where the area was that determined as described above) varied from 0.03 to 0.17 Ω cm(2) and generally decreased with cathodic bias and decreasing oxygen partial pressure. From an analysis of the dimensions of the active area with bias, it was found that the majority of the overpotential occurred at the SDC|gas interface rather than the SDC|YSZ interface. Overall, the anode overpotential is found to be extremely small, competitive with the best oxide anodes reported in the literature. Nevertheless, the impedance falls in line with expected values based on extrapolations of the properties of dense, flat SDC model electrodes grown by pulsed laser deposition (Chueh et al., Nat. Mater., 2012). The results demonstrate that, with suitable fabrication approaches, exceptional activity can be achieved with SDC for hydrogen electrooxidation even in the absence of metal-oxide-gas triple phase boundaries. PMID:25932615

  17. Ceria-Based Anodes for Next Generation Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    Mirfakhraei, Behzad

    Mixed ionic and electronic conducting materials (MIECs) have been suggested to represent the next generation of solid oxide fuel cell (SOFC) anodes, primarily due to their significantly enhanced active surface area and their tolerance to fuel components. In this thesis, the main focus has been on determining and tuning the physicochemical and electrochemical properties of ceria-based MIECs in the versatile perovskite or fluorite crystal structures. In one direction, BaZr0.1Ce0.7Y0.1 M0.1O3-delta (M = Fe, Ni, Co and Yb) (BZCY-M) perovskites were synthesized using solid-state or wet citric acid combustion methods and the effect of various transition metal dopants on the sintering behavior, crystal structure, chemical stability under CO2 and H 2S, and electrical conductivity, was investigated. BZCY-Ni, synthesized using the wet combustion method, was the best performing anode, giving a polarization resistance (RP) of 0.4 O.cm2 at 800 °C. Scanning electron microscopy and X-ray diffraction analysis showed that this was due to the exsolution of catalytic Ni nanoparticles onto the oxide surface. Evolving from this promising result, the effect of Mo-doped CeO 2 (nCMO) or Ni nanoparticle infiltration into a porous Gd-doped CeO 2 (GDC) anode (in the fluorite structure) was studied. While 3 wt. % Ni infiltration lowered RP by up to 90 %, giving 0.09 O.cm2 at 800 °C and exhibiting a ca. 5 times higher tolerance towards 10 ppm H2, nCMO infiltration enhanced the H2 stability by ca. 3 times, but had no influence on RP. In parallel work, a first-time study of the Ce3+ and Ce 4+ redox process (pseudocapacitance) within GDC anode materials was carried out using cyclic voltammetry (CV) in wet H2 at high temperatures. It was concluded that, at 500-600 °C, the Ce3+/Ce 4+ reaction is diffusion controlled, probably due to O2- transport limitations in the outer 5-10 layers of the GDC particles, giving a very high capacitance of ca. 70 F/g. Increasing the temperature ultimately

  18. Doped zinc oxide microspheres

    DOEpatents

    Arnold, Jr., Wesley D.; Bond, Walter D.; Lauf, Robert J.

    1993-01-01

    A new composition and method of making same for a doped zinc oxide microsphere and articles made therefrom for use in an electrical surge arrestor which has increased solid content, uniform grain size and is in the form of a gel.

  19. Doped zinc oxide microspheres

    DOEpatents

    Arnold, W.D. Jr.; Bond, W.D.; Lauf, R.J.

    1993-12-14

    A new composition and method of making same for a doped zinc oxide microsphere and articles made therefrom for use in an electrical surge arrestor which has increased solid content, uniform grain size and is in the form of a gel. 4 figures.

  20. Mechanistic studies of water electrolysis and hydrogen electro-oxidation on high temperature ceria-based solid oxide electrochemical cells.

    PubMed

    Zhang, Chunjuan; Yu, Yi; Grass, Michael E; Dejoie, Catherine; Ding, Wuchen; Gaskell, Karen; Jabeen, Naila; Hong, Young Pyo; Shavorskiy, Andrey; Bluhm, Hendrik; Li, Wei-Xue; Jackson, Gregory S; Hussain, Zahid; Liu, Zhi; Eichhorn, Bryan W

    2013-08-01

    Through the use of ambient pressure X-ray photoelectron spectroscopy (APXPS) and a single-sided solid oxide electrochemical cell (SOC), we have studied the mechanism of electrocatalytic splitting of water (H2O + 2e(-) → H2 + O(2-)) and electro-oxidation of hydrogen (H2 + O(2-) → H2O + 2e(-)) at ∼700 °C in 0.5 Torr of H2/H2O on ceria (CeO2-x) electrodes. The experiments reveal a transient build-up of surface intermediates (OH(-) and Ce(3+)) and show the separation of charge at the gas-solid interface exclusively in the electrochemically active region of the SOC. During water electrolysis on ceria, the increase in surface potentials of the adsorbed OH(-) and incorporated O(2-) differ by 0.25 eV in the active regions. For hydrogen electro-oxidation on ceria, the surface concentrations of OH(-) and O(2-) shift significantly from their equilibrium values. These data suggest that the same charge transfer step (H2O + Ce(3+) <-> Ce(4+) + OH(-) + H(•)) is rate limiting in both the forward (water electrolysis) and reverse (H2 electro-oxidation) reactions. This separation of potentials reflects an induced surface dipole layer on the ceria surface and represents the effective electrochemical double layer at a gas-solid interface. The in situ XPS data and DFT calculations show that the chemical origin of the OH(-)/O(2-) potential separation resides in the reduced polarization of the Ce-OH bond due to the increase of Ce(3+) on the electrode surface. These results provide a graphical illustration of the electrochemically driven surface charge transfer processes under relevant and nonultrahigh vacuum conditions. PMID:23822749

  1. Electrical, Electrochemical, and Optical Characterization of Ceria Films

    NASA Astrophysics Data System (ADS)

    Oh, Tae-Sik

    Acceptor-doped ceria has been recognized as a promising intermediate temperature solid oxide fuel cell electrode/electrolyte material. For practical implementation of ceria as a fuel cell electrolyte and for designing model experiments for electrochemical activity, it is necessary to fabricate thin films of ceria. Here, metal-organic chemical vapor deposition was carried out in a homemade reactor to grow ceria films for further electrical, electrochemical, and optical characterization. Doped/undoped ceria films are grown on single crystalline oxide wafers with/without Pt line pattern or Pt solid layer. Deposition conditions were varied to see the effect on the resultant film property. Recently, proton conduction in nanograined polycrystalline pellets of ceria drew much interest. Thickness-mode (through-plane, z-direction) electrical measurements were made to confirm the existence of proton conductivity and investigate the nature of the conduction pathway: exposed grain surfaces and parallel grain boundaries. Columnar structure presumably favors proton conduction, and we have found measurable proton conductivity enhancement. Electrochemical property of gas-columnar ceria interface on the hydrogen electrooxidation is studied by AC impedance spectroscopy. Isothermal gas composition dependence of the electrode resistance was studied to elucidate Sm doping level effect and microstructure effect. Significantly, preferred orientation is shown to affect the gas dependence and performance of the fuel cell anode. A hypothesis is proposed to explain the origin of this behavior. Lastly, an optical transmittance based methodology was developed to obtain reference refractive index and microstructural parameters (thickness, roughness, porosity) of ceria films via subsequent fitting procedure.

  2. Structure-Activity Relationship in Nanostructured Copper-Ceria-Based Preferential CO Oxidation Catalysts

    SciTech Connect

    Gamarra,D.; Munuera, G.; Hungria, A.; Fernandez-Garcia, M.; Conesa, J.; Midgley, P.; Wang, X.; Hanson, J.; Rodriguez, J.; Martinez-Arias, A.

    2007-01-01

    Two series of nanostructured oxidized copper-cerium catalysts with varying copper loadings, and prepared, respectively, by impregnation of ceria and by coprecipitation of the two components within reverse microemulsions, have been characterized in detail at structural and electronic levels by X-ray diffraction (XRD), Raman spectroscopy, high-resolution electron microscopy (HREM), X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS) (including Ar{sup +}-sputtering), and X-ray absorption fine structure (XAFS). These results have been correlated with analysis of their catalytic properties for preferential oxidation of CO in a H{sub 2}-rich stream (CO-PROX), complemented by Operando-DRIFTS. A relevant difference between the two series of catalysts concerns the nature of the support for the surface-dispersed copper oxide entities, which is essentially ceria for the samples prepared by impregnation and a Ce-Cu mixed oxide for those prepared by microemulsion-coprecipitation. The existence of copper segregation in the form of copper oxide or copper-enriched Cu-Ce mixed oxides for the latter type of samples is uniquely revealed by nanoprobe XEDS and XPS Ar{sup +}-sputtering experiments. The CO oxidation activity under CO-PROX conditions is correlated to the degree of support-promoted reduction achieved by the dispersed copper oxide particles under reaction conditions. Nevertheless, catalysts which display higher CO oxidation activity are generally more efficient also for the undesired H{sub 2} oxidation reaction. The balance between both reactions results in differences in the CO-PROX activity between the two series of catalysts which are examined on the basis of the structural differences found.

  3. Catalytic combustion of soot over ceria-zinc mixed oxides catalysts supported onto cordierite.

    PubMed

    Nascimento, Leandro Fontanetti; Martins, Renata Figueredo; Silva, Rodrigo Ferreira; Serra, Osvaldo Antonio

    2014-03-01

    Modified substrates as outer heterogeneous catalysts was employed to reduce the soot generated from incomplete combustion of diesel or diesel/biodiesel blends, a process that harms the environment and public health. The unique storage properties of ceria (CeO2) makes it one of the most efficient catalysts available to date. Here, we proposed that ceria-based catalysts can lower the temperature at which soot combustion occurs; more specifically, from 610°C to values included in the diesel exhausts operation range (300-450°C). The sol-gel method was used to synthesize mixed oxide-based catalysts (CeO2:ZnO); the resulting catalysts were deposited onto cordierite substrates. In addition, the morphological and structural properties of the material were evaluated by XRD, BET, TPR-H2, and SEM. Thermogravimetric (TG/DTA) analysis revealed that the presence of the catalyst decreased the soot combustion temperature by 200°C on average, indicating that the oxygen species arise at low temperatures in this situation, promoting highly reactive oxidation reactions. Comparative analysis of soot emission by diffuse reflectance spectroscopy (DRS) showed that catalyst-impregnated cordierite samples efficiently oxidized soot in a diesel/biodiesel stationary motor: soot emission decreased by more than 70%. PMID:25079283

  4. Shape-Dependent Activity of Ceria for Hydrogen Electro-Oxidation in Reduced-Temperature Solid Oxide Fuel Cells.

    PubMed

    Tong, Xiaofeng; Luo, Ting; Meng, Xie; Wu, Hao; Li, Junliang; Liu, Xuejiao; Ji, Xiaona; Wang, Jianqiang; Chen, Chusheng; Zhan, Zhongliang

    2015-11-01

    Single crystalline ceria nanooctahedra, nanocubes, and nanorods are hydrothermally synthesized, colloidally impregnated into the porous La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) scaffolds, and electrochemically evaluated as the anode catalysts for reduced temperature solid oxide fuel cells (SOFCs). Well-defined surface terminations are confirmed by the high-resolution transmission electron microscopy--(111) for nanooctahedra, (100) for nanocubes, and both (110) and (100) for nanorods. Temperature-programmed reduction in H2 shows the highest reducibility for nanorods, followed sequentially by nanocubes and nanooctahedra. Measurements of the anode polarization resistances and the fuel cell power densities reveal different orders of activity of ceria nanocrystals at high and low temperatures for hydrogen electro-oxidation, i.e., nanorods > nanocubes > nanooctahedra at T ≤ 450 °C and nanooctahedra > nanorods > nanocubes at T ≥ 500 °C. Such shape-dependent activities of these ceria nanocrystals have been correlated to their difference in the local structure distortions and thus in the reducibility. These findings will open up a new strategy for design of advanced catalysts for reduced-temperature SOFCs by elaborately engineering the shape of nanocrystals and thus selectively exposing the crystal facets. PMID:26307555

  5. Arsenic doped zinc oxide

    SciTech Connect

    Volbers, N.; Lautenschlaeger, S.; Leichtweiss, T.; Laufer, A.; Graubner, S.; Meyer, B. K.; Potzger, K.; Zhou Shengqiang

    2008-06-15

    As-doping of zinc oxide has been approached by ion implantation and chemical vapor deposition. The effect of thermal annealing on the implanted samples has been investigated by using secondary ion mass spectrometry and Rutherford backscattering/channeling geometry. The crystal damage, the distribution of the arsenic, the diffusion of impurities, and the formation of secondary phases is discussed. For the thin films grown by vapor deposition, the composition has been determined with regard to the growth parameters. The bonding state of arsenic was investigated for both series of samples using x-ray photoelectron spectroscopy.

  6. Reduced-temperature firing of solid oxide fuel cells with zirconia/ceria bi-layer electrolytes

    NASA Astrophysics Data System (ADS)

    Gao, Zhan; Kennouche, David; Barnett, Scott A.

    2014-08-01

    Solid oxide fuel cells (SOFCs) with bi-layer Zirconia/Ceria electrolytes have been studied extensively because of their great potential for producing high power density at reduced operating temperature, important for reducing cost and thereby allowing broader SOFC commercialization. The bi-layer electrolytes are designed to take advantage of the high oxygen ion conductivity of Ceria, the low electronic conductivity of Zirconia, and the low reactivity of Ceria with high-performance cathodes. However, zirconia/ceria processing has proven problematic due to interdiffusion during high temperature co-firing, or ceria layer porosity after two-step firing. Here we first show a new method for bi-layer co-firing at a reduced temperature of 1250 °C, ∼150 °C lower than the usual sintering temperature, achieved using Fe2O3 as a sintering aid. This novel process enables high power density SOFCs by producing: (1) low-resistance Y0.16Zr0.92O2-δ (YSZ)/Gd0.1Ce0.9O1.95 (GDC) electrolytes that also yield high open-circuit voltage, (2) dense GDC layers that prevent reactions between highly-active La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) cathode materials and YSZ, and (3) Ni-YSZ anodes with high electrochemical activity due to fine-scale microstructure with high TPB densities.

  7. Physicochemical properties of rare earth doped ceria Ce0.9Ln0.1O1.95 (Ln = Nd, Sm, Gd) as an electrolyte material for IT-SOFC/SOEC

    NASA Astrophysics Data System (ADS)

    Chaubey, Nityanand; Wani, B. N.; Bharadwaj, S. R.; Chattopadhyaya, M. C.

    2013-06-01

    Nanosized crystallites of rare earth doped ceria Ce0.9Ln0.1O1.95 (Ln = Nd, Sm, Gd) a promising electrolyte material for Intermediate Temperature - Solid Oxide Fuel Cells/electrolysis cells have been synthesized by standard ceramic route. Detection of impurities in the samples was done by FTIR spectroscopy. X-ray diffraction studies were used for the determination of phase purity, crystal structure and average crystallite size of the samples. Kinetics involved in phase formation has been discussed. Raman study showed a major band around 465 cm-1 in all the samples, which is attributed to the cubic fluorite structure of ceria. It was also found that for samples Ce0.9Ln0.1O1.95 (Ln = Nd, Sm, Gd) the frequency of F2g shifts to lower value. Electrochemical impedance spectroscopy has been used to measure the ionic conductivity of the samples at elevated temperatures. The Gd doped sample showed the highest grain boundary and total conductivity in comparison to Sm and Nd doped sample. Bulk thermal expansion behavior, sintered densities and micro structural features of the samples have also been studied.

  8. In-situ extended X-ray absorption fine structure study of electrostriction in Gd doped ceria

    SciTech Connect

    Korobko, Roman; Wachtel, Ellen; Lubomirsky, Igor; Lerner, Alyssa; Li, Yuanyuan; Frenkel, Anatoly I.

    2015-01-26

    Studying electric field-induced structural changes in ceramics is challenging due to the very small magnitude of the atomic displacements. We used differential X-ray absorption spectroscopy, an elementally specific and spatially sensitive method, to detect such changes in Gd-doped ceria, recently shown to exhibit giant electrostriction. We found that the large electrostrictive stress generation can be associated with a few percent of unusually short Ce-O chemical bonds that change their length and degree of order under an external electric field. The remainder of the lattice is reduced to the role of passive spectator. This mechanism is fundamentally different from that in electromechanically active materials currently in use.

  9. Reduced erbium-doped ceria nanoparticles: one nano-host applicable for simultaneous optical down- and up-conversions

    PubMed Central

    2014-01-01

    This paper introduces a new synthesis procedure to form erbium-doped ceria nanoparticles (EDC NPs) that can act as an optical medium for both up-conversion and down-conversion in the same time. This synthesis process results qualitatively in a high concentration of Ce3+ ions required to obtain high fluorescence efficiency in the down-conversion process. Simultaneously, the synthesized nanoparticles contain the molecular energy levels of erbium that are required for up-conversion. Therefore, the synthesized EDC NPs can emit visible light when excited with either UV or IR photons. This opens new opportunities for applications where emission of light via both up- and down-conversions from a single nanomaterial is desired such as solar cells and bio-imaging. PMID:24940173

  10. Dopant-mediated oxygen vacancy tuning in ceria nanoparticles.

    PubMed

    Babu, Suresh; Thanneeru, Ranjith; Inerbaev, Talgat; Day, Richard; Masunov, Artëm E; Schulte, Alfons; Seal, Sudipta

    2009-02-25

    Ceria nanoparticles with 20 and 40 at.% RE (RE = Y, Sm, Gd, and Yb) dopants were synthesized through a microemulsion method. Independently of the dopant nature and concentration, nearly monodispersed nanoparticles of size 3-5 nm were observed in high resolution transmission electron microscopic analysis. The ceria lattice either expands or contracts depending on the dopant cation ionic radii, as indicated by x-ray diffraction studies. X-ray photoelectron and Raman spectroscopic studies were used to quantify the cerium oxidation state and oxygen vacancy concentration. The results show the tunability of the oxygen vacancy and Ce(3+) concentrations based on the dopant properties. First principles simulations using the free energy density functional theory method support the observed experimental trends. The reported results establish a relationship between the oxygen vacancies and oxidation states in doped ceria required for tailoring properties in catalytic and biomedical applications. PMID:19417474

  11. Active Gold-Ceria and Gold-Ceria/titania Catalysts for CO Oxidation. From Single-Crystal Model Catalysts to Powder Catalysts

    SciTech Connect

    Rodriguez, Jose A.; Si, Rui; Evans, Jaime; Xu, Wenqian; Hanson, Jonathan C.; Tao, Jing; Zhu, Yimei

    2014-07-23

    We studied CO oxidation on model and powder catalysts of Au-CeO2 and Au-CeOx/TiO2. Phenomena observed in Au-CeO2(1 1 1) and Au-CeO2/TiO2(1 1 0) provided useful concepts for designing and preparing highly active and stable Au-CeOx/TiO2 powder catalysts for CO oxidation. Small particles of Au dispersed on CeO2(1 1 1) displayed high catalytic activity, making Au-CeO2(1 1 1) a better CO oxidation catalyst than Au-TiO2(1 1 0) or Au-MgO(1 0 0). An excellent support for gold was found after depositing nanoparticles of ceria on TiO2(1 1 0). The CeOx nanoparticles act as nucleation centers for gold, improving dispersion of the supported metal and helping in the creation of reaction sites efficient for the adsorption of CO and the dissociation of the O2 molecule. High-surface area catalysts were prepared by depositing gold on ceria nanorods and CeOx/TiO2 powders. The samples were tested for the low-temperature (10–70 °C) oxygen-rich (1%CO/4%O2/He) CO oxidation reaction after pre-oxidation (20%O2/He, 300 °C) and pre-reduction (5%H2/He, 300 °C) treatments. Moreover, synchrotron-based operando X-ray diffraction (XRD) and X-ray absorption (XAS) spectroscopy were used to study the Au-CeO2 and Au-CeOx/TiO2 catalysts under reaction conditions. Our operando findings indicate that the most active phase of these catalysts for low-temperature CO oxidation consist of small particles of metallic Au dispersed on CeO2 or CeOx/TiO2.

  12. Altering properties of cerium oxide thin films by Rh doping

    SciTech Connect

    Ševčíková, Klára; Nehasil, Václav; Vorokhta, Mykhailo; Haviar, Stanislav; Matolín, Vladimír; and others

    2015-07-15

    Highlights: • Thin films of ceria doped by rhodium deposited by RF magnetron sputtering. • Concentration of rhodium has great impact on properties of Rh–CeO{sub x} thin films. • Intensive oxygen migration in films with low concentration of rhodium. • Oxygen migration suppressed in films with high amount of Rh dopants. - Abstract: Ceria containing highly dispersed ions of rhodium is a promising material for catalytic applications. The Rh–CeO{sub x} thin films with different concentrations of rhodium were deposited by RF magnetron sputtering and were studied by soft and hard X-ray photoelectron spectroscopies, Temperature programmed reaction and X-ray powder diffraction techniques. The sputtered films consist of rhodium–cerium mixed oxide where cerium exhibits a mixed valency of Ce{sup 4+} and Ce{sup 3+} and rhodium occurs in two oxidation states, Rh{sup 3+} and Rh{sup n+}. We show that the concentration of rhodium has a great influence on the chemical composition, structure and reducibility of the Rh–CeO{sub x} thin films. The films with low concentrations of rhodium are polycrystalline, while the films with higher amount of Rh dopants are amorphous. The morphology of the films strongly influences the mobility of oxygen in the material. Therefore, varying the concentration of rhodium in Rh–CeO{sub x} thin films leads to preparing materials with different properties.

  13. Aluminum-doped ceria-zirconia solid solutions with enhanced thermal stability and high oxygen storage capacity

    PubMed Central

    2012-01-01

    A facile solvothermal method to synthesize aluminum-doped ceria-zirconia (Ce0.5Zr0.5-xAlxO2-x/2, x = 0.1 to 0.4) solid solutions was carried out using Ce(NH4)2(NO3)6, Zr(NO3)3·2H2O Al(NO3)3·9H2O, and NH4OH as the starting materials at 200°C for 24 h. The obtained solid solutions from the solvothermal reaction were calcined at 1,000°C for 20 h in air atmosphere to evaluate the thermal stability. The synthesized Ce0.5Zr0.3Al0.2O1.9 particle was characterized for the oxygen storage capacity (OSC) in automotive catalysis. For the characterization, X-ray diffraction, transmission electron microscopy, and the Brunauer-Emmet-Teller (BET) technique were employed. The OSC values of all samples were measured at 600°C using thermogravimetric-differential thermal analysis. Ce0.5Zr0.3Al0.2O1.9 solid solutions calcined at 1,000°C for 20 h with a BET surface area of 18 m2 g−1 exhibited a considerably high OSC of 427 μmol-O g−1 and good OSC performance stability. The same synthesis route was employed for the preparation of the CeO2 and Ce0.5Zr0.5O2. The incorporation of aluminum ion in the lattice of ceria-based catalyst greatly enhanced the thermal stability and OSC. PMID:23025588

  14. Reduction enthalpy and charge distribution of substituted ferrites and doped ceria for thermochemical water and carbon dioxide splitting with DFT+U.

    PubMed

    Dimitrakis, D A; Tsongidis, N I; Konstandopoulos, A G

    2016-08-24

    The thermal reduction step of substituted ferrites (MFe2O4 where M = Fe, Ni, Co, Gd) and doped ceria (MxCe1-xO2, where M = Ce, Zr, Hf and x = 0.25) in two-step thermochemical cycles for H2O and CO2 splitting is investigated within the DFT+U framework. This thermal reduction step is described as the oxygen vacancy formation energy (reduction enthalpy), i.e. the energy required to create an oxygen vacancy in the crystal lattice. Oxides with a lower oxygen vacancy creation energy are easier to reduce. A Bader charge analysis of the reduction mechanism is carried out providing the charge distribution of the bulk and reduced ions, enabling interrelations of the substitute ions and the resulting reduction energies. Based on the approach presented here, interesting solar fuels producing materials are CoFe2O4, NiFe2O4 and Hf0.25Ce0.75O2. PMID:27507281

  15. Gadolinium doped cerium oxide for soot oxidation: Influence of interfacial metal-support interactions

    NASA Astrophysics Data System (ADS)

    Durgasri, D. Naga; Vinodkumar, T.; Lin, Fangjian; Alxneit, Ivo; Reddy, Benjaram M.

    2014-09-01

    The aim of the present investigation was to ascertain the role of Al2O3, SiO2, and TiO2 supports in modulating the catalytic performance of ceria-based solid solutions. In this study, we prepared nanosized Ce-Gd/Al2O3, Ce-Gd/SiO2, and Ce-Gd/TiO2 catalysts by a deposition coprecipitation method and evaluated for soot oxidation. The synthesized catalysts were calcined at two different temperatures to assess their thermal stability and extensively characterized by various techniques, namely, XRD, Raman, BET surface area, TEM, H2-TPR, and UV-vis DRS. XRD and TEM results indicate that Ce-Gd-oxide nanoparticles are in highly dispersed form on the surface of the supports. Raman results show a prominent sharp peak and a broad peak corresponding to the F2g mode of ceria and the presence of oxygen vacancies, respectively. The presence of a significant number of oxygen vacancies in all samples is also confirmed from UV-vis DRS measurements. The H2-TPR results suggest that Gd-doping facilitates the reduction of the materials and decreases the onset temperature of reduction. Among the prepared samples, Ce-Gd/TiO2 catalyst exhibited the highest activity, suggesting the existence of strong interfacial metal support interaction between the active metal oxide and the support.

  16. Unique properties of ceria nanoparticles supported on metals: novel inverse ceria/copper catalysts for CO oxidation and the water-gas shift reaction.

    PubMed

    Senanayake, Sanjaya D; Stacchiola, Dario; Rodriguez, Jose A

    2013-08-20

    Oxides play a central role in important industrial processes, including applications such as the production of renewable energy, remediation of environmental pollutants, and the synthesis of fine chemicals. They were originally used as catalyst supports and were thought to be chemically inert, but now they are used to build catalysts tailored toward improved selectivity and activity in chemical reactions. Many studies have compared the morphological, electronic, and chemical properties of oxide materials with those of unoxidized metals. Researchers know much less about the properties of oxides at the nanoscale, which display distinct behavior from their bulk counterparts. More is known about metal nanoparticles. Inverse-model catalysts, composed of oxide nanoparticles supported on metal or oxide substrates instead of the reverse (oxides supporting metal nanoparticles), are excellent tools for systematically testing the properties of novel catalytic oxide materials. Inverse models are prepared in situ and can be studied with a variety of surface science tools (e.g. scanning tunneling microscopy, X-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, low-energy electron microscopy) and theoretical tools (e.g. density functional theory). Meanwhile, their catalytic activity can be tested simultaneously in a reactor. This approach makes it possible to identify specific functions or structures that affect catalyst performance or reaction selectivity. Insights gained from these tests help to tailor powder systems, with the primary objective of rational design (experimental and theoretical) of catalysts for specific chemical reactions. This Account describes the properties of inverse catalysts composed of CeOx nanoparticles supported on Cu(111) or CuOx/Cu(111) as determined through the methods described above. Ceria is an important material for redox chemistry because of its interchangeable oxidation states (Ce⁴⁺ and Ce³⁺). Cu(111), meanwhile, is

  17. Electrochemical characteristics of samaria-doped ceria infiltrated strontium-doped LaMnO3 cathodes with varied thickness for yttria-stabilized zirconia electrolytes

    SciTech Connect

    Dong Ding; Mingyang Gonga; Chunchuan Xu; Nicholas Baxter; Yihong Li; John Zondlo; Kirk Gerdes; Xingbo Liu

    2010-11-09

    Samaria-doped ceria (SDC) infiltrated into strontium-doped LaMnO3 (LSM) cathodes with varied cathode thickness on yttria-stabilized zirconia (YSZ) were investigated via symmetrical cell, half cell, and full cell configurations. The results of the symmetrical cells showed that the interfacial polarization resistance (RP) decreased with increasing electrode thickness up to∼30#2;m, and further increases in the thickness of the cathode did not cause significant variation of electrode performance. At 800 ◦C, the minimum RP was around 0.05#2;cm2. The impedance spectra indicated that three main electrochemical processes existed, possibly corresponding to the oxygen ion incorporation, surface diffusion of oxygen species and oxygen adsorption and dissociation. The DC polarization on the half cells and characterization of the full cells also demonstrated a similar correlation between the electrode performance and the electrode thickness. The peak power densities of the single cells with the 10, 30, and 50-#2;m thick electrodes were 0.63, 1.16 and 1.11Wcm−2, respectively. The exchange current densities under moderate polarization are calculated and possible rate-determining steps are discussed.

  18. Activating Nonreducible Oxides via Doping.

    PubMed

    Nilius, Niklas; Freund, Hans-Joachim

    2015-05-19

    Nonreducible oxides are characterized by large band gaps and are therefore unable to exchange electrons or to form bonds with surface species, explaining their chemical inertness. The insertion of aliovalent dopants alters this situation, as new electronic states become available in the gap that may be involved in charge-transfer processes. Consequently, the adsorption and reactivity pattern of doped oxides changes with respect to their nondoped counterparts. This Account describes scanning tunneling microscopy (STM) and photoelectron spectroscopy (XPS) experiments that demonstrate the impact of dopants on the physical and chemical properties of well-defined crystalline oxide films. For this purpose, MgO and CaO as archetypical rocksalt oxides have been loaded either with high-valence (Mo, Cr) or low-valence dopants (Li). While the former generate filled states in the oxide band gap and serve as electron donors, the latter produce valence-band holes and give rise to an acceptor response. The dopant-related electronic states and their polarization effect on the surrounding host material are explored with XPS and STM spectroscopy on nonlocal and local scales. Moreover, charge-compensating defects were found to develop in the oxide lattice, such as Ca and O vacancies in Mo- and Li-doped CaO films, respectively. These native defects are able to trap the excess charges of the impurities and therefore diminish the desired doping effect. If noncompensated dopants reside in the host lattice, electron exchange with surface species is observed. Mo ions in CaO, for example, were found to donate electrons to surface Au atoms. The anionic Au strongly binds to the CaO surface and nucleates in the form of monolayer islands, in contrast to the 3D growth prevailing on pristine oxides. Charge transfer is also revealed for surface O2 that traps one Mo electron by forming a superoxo-species. The activated oxygen is characterized by a reinforced binding to the surface, an elongated O

  19. CO Oxidation on Inverse CeOx/Cu(111) Catalysts: High Catalytic Activity and Ceria-Promoted Dissociation of O2

    SciTech Connect

    F Yang; J Graciani; J Evans; P Liu; J Hrbek; J Fdez. Sanz; J Rodriguez

    2011-12-31

    A Cu(111) surface displays a low activity for the oxidation of carbon monoxide (2CO + O{sub 2} {yields} 2CO{sub 2}). Depending on the temperature, background pressure of O{sub 2}, and the exposure time, one can get chemisorbed O on Cu(111) or a layer of Cu{sub 2}O that may be deficient in oxygen. The addition of ceria nanoparticles (NPs) to Cu(111) substantially enhances interactions with the O{sub 2} molecule and facilitates the oxidation of the copper substrate. In images of scanning tunneling microscopy, ceria NPs exhibit two overlapping honeycomb-type moire structures, with the larger ones (H{sub 1}) having a periodicity of 4.2 nm and the smaller ones (H{sub 2}) having a periodicity of 1.20 nm. After annealing CeO{sub 2}/Cu(111) in O{sub 2} at elevated temperatures (600-700 K), a new phase of a Cu{sub 2}O{sub 1+x} surface oxide appears and propagates from the ceria NPs. The ceria is not only active for O{sub 2} dissociation, but provides a much faster channel for oxidation than the step edges of Cu(111). Exposure to CO at 550-750 K led to a partial reduction of the ceria NPs and the removal of the copper oxide layer. The CeO{sub x}/Cu(111) systems have activities for the 2CO + O{sub 2} {yields} 2CO{sub 2} reaction that are comparable or larger than those reported for surfaces of expensive noble metals such as Rh(111), Pd(110), and Pt(100). Density-functional calculations show that the supported ceria NPs are able to catalyze the oxidation of CO due to their special electronic and chemical properties. The configuration of the inverse oxide/metal catalyst opens new interesting routes for applications in catalysis.

  20. Dimethyl methylphosphonate decomposition on fully oxidized and partially reduced ceria thin films

    NASA Astrophysics Data System (ADS)

    Chen, Donna A.; Ratliff, Jay S.; Hu, Xiaofeng; Gordon, Wesley O.; Senanayake, Sanjaya D.; Mullins, David R.

    2010-03-01

    The thermal decomposition of dimethyl methylphosphonate (DMMP) on crystalline ceria thin films grown on Ru(0 0 0 1) was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and infrared absorption reflection spectroscopy (IRAS). TPD experiments show that methanol and formaldehyde desorb as the two main products at 575 K, while water, formaldehyde and CO are produced above 800 K. IRAS studies demonstrate that DMMP adsorbs via the phosphoryl oxygen at 200 K, but the P dbnd O bond converts to a bridging O sbnd P sbnd O species at 300 K. DMMP decomposition initially occurs via P sbnd OCH 3 bond scission to form methyl methylphosphonate (MMP) and methyl phosphonate (MP) between 300 and 500 K; XPS and IRAS data are consistent with a methoxy intermediate on the surface at these temperatures. The more stable P sbnd CH 3 bonds remain intact up to 700 K, and the only surface intermediate at higher temperatures is believed to be PO x. Although the presence of PO x decreases activity for DMMP decomposition, some activity on the ceria surface remains even after 7 cycles of adsorption and reaction. The ceria films become reduced by multiple DMMP adsorption-reaction cycles, with the Ce +4 content dropping to 30% after seven cycles. Investigations of DMMP reaction on reduced ceria surfaces show that CO and H 2 are produced in addition to methanol and formaldehyde. Furthermore, DMMP decomposition activity on the reduced ceria films is almost completely inhibited after only 3 adsorption-reaction cycles. Similarities between DMMP and methanol chemistry on the ceria films suggest that methoxy is a key surface intermediate in both reactions.

  1. Dimethyl methylphosphonate Decomposition on fully Oxidized and Partially Reduced ceria Thin Films

    SciTech Connect

    Chen, D.; Ratliff, J; Hu, X; Gordon, W; Senanayake, S; Mullins, D

    2010-01-01

    The thermal decomposition of dimethyl methylphosphonate (DMMP) on crystalline ceria thin films grown on Ru(0 0 0 1) was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and infrared absorption reflection spectroscopy (IRAS). TPD experiments show that methanol and formaldehyde desorb as the two main products at 575 K, while water, formaldehyde and CO are produced above 800 K. IRAS studies demonstrate that DMMP adsorbs via the phosphoryl oxygen at 200 K, but the P{double_bond}O bond converts to a bridging O{single_bond}P{single_bond}O species at 300 K. DMMP decomposition initially occurs via P{_}OCH{sub 3} bond scission to form methyl methylphosphonate (MMP) and methyl phosphonate (MP) between 300 and 500 K; XPS and IRAS data are consistent with a methoxy intermediate on the surface at these temperatures. The more stable P{_}CH{sub 3} bonds remain intact up to 700 K, and the only surface intermediate at higher temperatures is believed to be PO{sub x}. Although the presence of PO{sub x} decreases activity for DMMP decomposition, some activity on the ceria surface remains even after 7 cycles of adsorption and reaction. The ceria films become reduced by multiple DMMP adsorption-reaction cycles, with the Ce{sup +4} content dropping to 30% after seven cycles. Investigations of DMMP reaction on reduced ceria surfaces show that CO and H{sub 2} are produced in addition to methanol and formaldehyde. Furthermore, DMMP decomposition activity on the reduced ceria films is almost completely inhibited after only 3 adsorption-reaction cycles. Similarities between DMMP and methanol chemistry on the ceria films suggest that methoxy is a key surface intermediate in both reactions.

  2. Shape-controlled ceria-reduced graphene oxide nanocomposites toward high-sensitive in situ detection of nitric oxide.

    PubMed

    Hu, Fang Xin; Xie, Jia Le; Bao, Shu Juan; Yu, Ling; Li, Chang Ming

    2015-08-15

    Nitric oxide (NO) is an important signal molecule released by most cancer cells under drug stimulation or/and disease development but it is extremely challenging to in situ while real-time sensitively detect NO due to its large diffusivity, low concentration and fast decay. Herein, shape-controlled reduced graphene oxide nanocomposing with ceria (rGO-CeO2) was synthesized via hydrothermal reaction to construct a highly sensitive real-time sensing platform for NO detection. The crystal shape of CeO2 nanoparticles in rGO-CeO2 composites significantly affects the sensing performance of rGO-CeO2, of which the regular hexagonal nanocrystal CeO2 achieves the highest sensitivity (1676.06 mA cm(-2) M(-1)), a wide dynamic range (18.0 nM to 5.6 µM) and a low detection limit (9.6 nM). This attributes to a synergical effect from high catalytic activity of the specifically shaped CeO2 nanocrystal and good conductivity/high surface area of rGO. This work demonstrates a way by rationally compose individual merit components while well control the nanostructure for a superior synergistic effect to build a smart sensing platform, while offering a great application potential to sensitively real-time detect NO released from living cells for diagnosis or/and studies of complicated biological processes. PMID:25840016

  3. Composite solid oxide fuel cell anode based on ceria and strontium titanate

    DOEpatents

    Marina, Olga A.; Pederson, Larry R.

    2008-12-23

    An anode and method of making the same wherein the anode consists of two separate phases, one consisting of a doped strontium titanate phase and one consisting of a doped cerium oxide phase. The strontium titanate phase consists of Sr.sub.1-xM.sub.xTiO.sub.3-.delta., where M is either yttrium (Y), scandium (Sc), or lanthanum (La), where "x" may vary typically from about 0.01 to about 0.5, and where .delta. is indicative of some degree of oxygen non-stoichiometry. A small quantity of cerium may also substitute for titanium in the strontium titanate lattice. The cerium oxide consists of N.sub.yCe.sub.1-yO.sub.2-.delta., where N is either niobium (Nb), vanadium (V), antimony (Sb) or tantalum (Ta) and where "y" may vary typically from about 0.001 to about 0.1 and wherein the ratio of Ti in said first phase to the sum of Ce and N in the second phase is between about 0.2 to about 0.75. Small quantities of strontium, yttrium, and/or lanthanum may additionally substitute into the cerium oxide lattice. The combination of these two phases results in better performance than either phase used separately as an anode for solid oxide fuel cell or other electrochemical device.

  4. Ceria catalyst for inert-substrate-supported tubular solid oxide fuel cells running on methane fuel

    NASA Astrophysics Data System (ADS)

    Zhao, Kai; Kim, Bok-Hee; Du, Yanhai; Xu, Qing; Ahn, Byung-Guk

    2016-05-01

    A ceria catalyst is applied to an inert-substrate supported tubular single cell for direct operation on methane fuel. The tubular single cell comprises a porous yttria-stabilized zirconia (YSZ) supporter, a Ni-Ce0.8Sm0.2O1.9 anode, a YSZ/Ce0.8Sm0.2O1.9 bi-layer electrolyte, and a La0.6Sr0.4Co0.2Fe0.8O3-δ cathode. The ceria catalyst is incorporated into the porous YSZ supporter layer by a cerium nitrate impregnation. The effects of ceria on the microstructure and electrochemical performance of the tubular single cell are investigated with respect to the number of impregnations. The optimum number of impregnations is determined to be four based on the maximum power density and polarization property of the tubular single cell in hydrogen and methane fuels. At 700 °C, the tubular single cell shows similar maximum power densities of ∼260 mW cm-2 in hydrogen and methane fuels, respectively. Moreover, the ceria catalyst significantly improves the performance stability of the cell running on methane fuel. At a current density of 350 mA cm-2, the single cell shows a low degradation rate of 2.5 mV h-1 during the 13 h test in methane fuel. These results suggest the feasibility of applying the ceria catalyst to the inert-substrate supported tubular single cell for direct operation on methane fuel.

  5. A spray drying system for synthesis of rare-earth doped cerium oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Sharma, Vaneet; Eberhardt, Kathryn M.; Sharma, Renu; Adams, James B.; Crozier, Peter A.

    2010-08-01

    We have constructed a spray dryer to synthesize doped ceria nanoparticles. The system was employed to synthesize mixed oxide nanoparticles of praseodymium doped CeO 2 (Ce 0.97Pr 0.03O 2, Ce 0.90Pr 0.10O 2, and Ce 0.80Pr 0.20O 2). X-ray diffraction confirmed the fluorite-like cubic crystal structure of the synthesized materials after heat treatment at 700 °C for 2 h. As-dried CeO 2 samples were found to have an average particle size of (6.0 ± 0.2) nm which increased to (17.0 ± 0.4) nm after heat treatment with an improvement in crystallinity. The particle size increased steadily with Pr content. The lattice parameter of Pr-doped CeO 2 was found to increase or decrease with Pr content depending on the heat treatment process.

  6. Nanocrystalline ceria coatings on solid oxide fuel cell anodes: the role of organic surfactant pretreatments on coating microstructures and sulfur tolerance

    PubMed Central

    Wu, Chieh-Chun; Tang, Ling

    2014-01-01

    Summary Treatments with organic surfactants, followed by the deposition of nanocrystalline ceria coatings from aqueous solution, were applied to anodes of solid oxide fuel cells. The cells were then operated in hydrogen/nitrogen fuel streams with H2S contents ranging from 0 to 500 ppm. Two surfactant treatments were studied: immersion in dodecanethiol, and a multi-step conversion of a siloxy-anchored alkyl bromide to a sulfonate functionality. The ceria coatings deposited after the thiol pretreatment, and on anodes with no pretreatment, were continuous and uniform, with thicknesses of 60–170 nm and 100–140 nm, respectively, and those cells exhibited better lifetime performance and sulfur tolerance compared to cells with untreated anodes and anodes with ceria coatings deposited after the sulfonate pretreatment. Possible explanations for the effects of the treatments on the structure of the coatings, and for the effects of the coatings on the performance of the cells, are discussed. PMID:25383282

  7. The role of CO2 as a soft oxidant for dehydrogenation of ethylbenzene to styrene over a high-surface-area ceria catalyst

    SciTech Connect

    Zhang, Li; Wu, Zili; Nelson, Nicholas; Sadow, Aaron D.; Slowing, Igor I.; Overbury, Steven H.

    2015-09-22

    Catalytic performance and the nature of surface adsorbates were investigated for high-surface-area ceria during ethylbenzene oxidative dehydrogenation (ODH) reaction using CO2 as a soft oxidant. A template assisted method was used to synthesize the high-surface-area ceria. The interactions between ethylbenzene, styrene and CO2 on the surface of ceria and the role of CO2 for the ethylbenzene ODH reaction have been investigated in detail by using activity test, in situ Diffuse Reflectance Infrared and Raman spectroscopy. Not only did CO2 as an oxidant favor the higher yield of styrene, but it also inhibited the deposition of coke during the ethylbenzene ODH reaction. Ethylbenzene ODH reaction over ceria followed a two-step pathway: Ethylbenzene is first dehydrogenated to styrene with H2 formed simultaneously, and then CO2 reacts with H2 via the reverse water gas shift. The styrene produced can easily polymerize to form polystyrene, a key intermediate for coke formation. In the absence of CO2, the polystyrene transforms into graphite-like coke at temperatures above 500 °C, which leads to catalyst deactivation. While in the presence of CO2, the coke deposition can be effectively removed via oxidation with CO2.

  8. The role of CO2 as a soft oxidant for dehydrogenation of ethylbenzene to styrene over a high-surface-area ceria catalyst

    DOE PAGESBeta

    Zhang, Li; Wu, Zili; Nelson, Nicholas; Sadow, Aaron D.; Slowing, Igor I.; Overbury, Steven H.

    2015-09-22

    Catalytic performance and the nature of surface adsorbates were investigated for high-surface-area ceria during ethylbenzene oxidative dehydrogenation (ODH) reaction using CO2 as a soft oxidant. A template assisted method was used to synthesize the high-surface-area ceria. The interactions between ethylbenzene, styrene and CO2 on the surface of ceria and the role of CO2 for the ethylbenzene ODH reaction have been investigated in detail by using activity test, in situ Diffuse Reflectance Infrared and Raman spectroscopy. Not only did CO2 as an oxidant favor the higher yield of styrene, but it also inhibited the deposition of coke during the ethylbenzene ODHmore » reaction. Ethylbenzene ODH reaction over ceria followed a two-step pathway: Ethylbenzene is first dehydrogenated to styrene with H2 formed simultaneously, and then CO2 reacts with H2 via the reverse water gas shift. The styrene produced can easily polymerize to form polystyrene, a key intermediate for coke formation. In the absence of CO2, the polystyrene transforms into graphite-like coke at temperatures above 500 °C, which leads to catalyst deactivation. While in the presence of CO2, the coke deposition can be effectively removed via oxidation with CO2.« less

  9. Influence of the process parameters on the spray pyrolysis technique, on the synthesis of gadolinium doped-ceria thin film

    SciTech Connect

    Halmenschlager, C.M.; Neagu, R.; Rose, L.; Malfatti, C.F.

    2013-02-15

    Graphical abstract: Gas-tight CGO made by spray pyrolysis suitable to be used as SOFC electrolyte. Display Omitted Highlights: ► Dense and crystalline CGO films deposited by spray pyrolysis on various substrates. ► Solvent did not have a strong influence on the film microstructure, defect concentration or thickness. ► The substrate did not have a strong influence on the film microstructure, defect concentration or thickness. ► Films with at least 2.5 μm of thickness presented high impermeability. ► The films obtained are suitable to use as a SOFC electrolyte. -- Abstract: This work presents the results of a process of optimization applied to gadolinia-doped ceria (Ce{sub 0.8}Gd{sub 0.2}O{sub 1.9−x}, or CGO) thin films, deposited by spray pyrolysis (SP). Spray pyrolysis is a high thermal deposition method that combines material deposition and heat treatment. This combination is advantageous since the post-deposition heat treatment step is not necessary. However, stresses are solidified in the coating during the deposition, which may lead to the initiation of a crack in the coating. The aim of this work was to achieve thin, dense, and continuous CGO coatings, which may be used as gas separation membranes and as a solid state electrochemical interfaces. Dense, flat, low-defect substrates such as silica slides, silicon mono crystal wafers, and porous substrates were used as substrates in this work. Cerium ammonium nitrate and gadolinium acetylacetonate were dissolved in ethanol and butyl carbitol to form a precursor solution that was sprayed on the heated substrates. Process parameters such as solvent composition, deposition rate and different heating regimes were analyzed. The microstructure was analyzed by secondary electron microscopy (SEM) and was found that thin, dense, and defect-free films could be produced on dense and porous substrates. The results obtained show that it is possible to obtain a CGO dense film deposited by spray pyrolysis. X

  10. Effect of Nickel Contents on the Microstructure of Mesoporous Nickel Gadolinium-Doped Ceria

    NASA Astrophysics Data System (ADS)

    Ahn, Seunghyun; Koo, Hyun; Bae, Sung-Hwan; Park, Chan; Cho, Guyoung; Chang, Ikwhang; Cha, Suk-Won; Yoo, Young-Sung

    2013-12-01

    The effect of NiO contents on the microstructure of mesoporous NiO-Gd0.25Ce0.75O2-x (NiO-GDC) composite for intermediate temperature solid oxide fuel cells (IT-SOFC) was investigated. Mesoporous NiO-GDC powders with different NiO contents were synthesized by self-assembly hydrothermal method using tri-block copolymer, Pluronic F127, as a structure directing agent. Grain growth/agglomeration behaviors of NiO particles and changes of mesoporous structure of GDC particles were characterized by microstructural analyses. NiO-GDC powders were composed of GDC nano particles with ordered mesopore inside the particles and octahedral NiO grains with truncated-edges. As the amount of NiO increases, specific area value of mesoporous NiO-GDC was decreased, and the agglomeration/growth behavior of NiO grains was accelerated.

  11. Nanofabrication of Doped, Complex Oxides

    SciTech Connect

    Stein, A.; Waller, G.H.; Abiade, J.T.

    2012-01-01

    Complex oxides have many promising attributes, including wide band gaps for high temperature semiconductors, ion conducting electrolytes in fuel cells, ferroelectricity and ferromagnetism. Bulk and thin film oxides can be readily manufactured and tested however these physically hard and chemically inert materials cannot be nanofabricated by direct application of conventional methods. In order to study these materials at the nanoscale there must first be a simple and effective means to achieve the desired structures. Here we discuss the use of pulsed laser deposition at room temperature onto electron beam lithography defined templates of poly methyl methacrylate photoresist. Following a resist liftoff in organic solvents, a heat treatment was used to crystallize the nanostructures. The morphology of these structures was studied using scanning electron microscopy and atomic force microscopy. Crystallinity and composition as determined by x ray diffraction and photo-electron spectroscopy respectively is reported for thin film analogues of the nanostructured oxide. The oxide studied in this report is Nb doped SrTiO{sub 3}, which has been investigated for use as a high temperature thermoelectric material; however the approach used is not materials-dependent.

  12. Engineering the defect state and reducibility of ceria based nanoparticles for improved anti-oxidation performance

    NASA Astrophysics Data System (ADS)

    Wang, Yan-Jie; Dong, Hao; Lyu, Guang-Ming; Zhang, Huai-Yuan; Ke, Jun; Kang, Li-Qun; Teng, Jia-Li; Sun, Ling-Dong; Si, Rui; Zhang, Jing; Liu, Yan-Jun; Zhang, Ya-Wen; Huang, Yun-Hui; Yan, Chun-Hua

    2015-08-01

    Due to their excellent anti-oxidation performance, CeO2 nanoparticles receive wide attention in pharmacological application. Deep understanding of the anti-oxidation mechanism of CeO2 nanoparticles is extremely important to develop potent CeO2 nanomaterials for anti-oxidation application. Here, we report a detailed study on the anti-oxidation process of CeO2 nanoparticles. The valence state and coordination structure of Ce are characterized before and after the addition of H2O2 to understand the anti-oxidation mechanism of CeO2 nanoparticles. Adsorbed peroxide species are detected during the anti-oxidation process, which are responsible for the red-shifted UV-vis absorption spectra of CeO2 nanoparticles. Furthermore, the coordination number of Ce in the first coordination shell slightly increased after the addition of H2O2. On the basis of these experimental results, the reactivity of coordination sites for peroxide species is considered to play a key role in the anti-oxidation performance of CeO2 nanoparticles. Furthermore, we present a robust method to engineer the anti-oxidation performance of CeO2 nanoparticles through the modification of the defect state and reducibility by doping with Gd3+. Improved anti-oxidation performance is also observed in cell culture, where the biocompatible CeO2-based nanoparticles can protect INS-1 cells from oxidative stress induced by H2O2, suggesting the potential application of CeO2 nanoparticles in the treatment of diabetes.Due to their excellent anti-oxidation performance, CeO2 nanoparticles receive wide attention in pharmacological application. Deep understanding of the anti-oxidation mechanism of CeO2 nanoparticles is extremely important to develop potent CeO2 nanomaterials for anti-oxidation application. Here, we report a detailed study on the anti-oxidation process of CeO2 nanoparticles. The valence state and coordination structure of Ce are characterized before and after the addition of H2O2 to understand the anti-oxidation

  13. Synthesis and atomic level in situ redox characterization in ceria and ceria zirconia

    NASA Astrophysics Data System (ADS)

    Wang, Ruigang

    2007-12-01

    Nanocrystalline ceria-based oxides are widely used in automotive three-way catalytic converters to reduce the emissions of carbon monoxide, nitrogen oxides, and unburned hydrocarbons. The primary function of ceria-based oxides in the catalytic process is to adjust the local oxygen partial pressure and maintain an air-to-fuel ratio near the stoichiometric value (˜14.5) required for the optimal catalyst performance for carbon monoxide, hydrocarbon oxidation, and nitrogen oxides reduction. In this dissertation, a study of the relationship between the nanoscale structure, chemistry, and the redox behavior on high surface area ceria and ceria zirconia is presented. Precipitation and spray freezing methods were used to synthesize nanocrystalline ceria and ceria zirconia solid solution powders respectively. The effect of thermal treatments in oxidizing and reducing atmospheres on the reducibility of the materials has been systematically investigated. X-ray diffraction and thermogravimetric analysis were used to characterize the average structure and reducibility. In situ environmental transmission electron microscope was exploited to visualize the dynamic changes during redox processes at the atomic level. This resulted in the identification of the nanoscale structure and chemistry for the most active nanoparticles in these oxides. The correlation between ex situ macroscopic redox properties and in situ redox behavior of individual nanoparticles is demonstrated. The addition of zirconia to ceria clearly enhances the reducibility and thermal stability of ceria. A fundamental difference between ceria and ceria zirconia during in situ redox processes is related to oxygen vacancy ordering. Ceria showed oxygen vacancy ordering during reduction, whereas ceria zirconia did not. It is suggested that the absence of oxygen vacancy ordering might be a fundamental factor for improved redox properties of ceria zirconia compared with pure ceria. The 50% ceria-50% zirconia solid

  14. Catalytic processes during preferential oxidation of CO in H 2-rich streams over catalysts based on copper-ceria

    NASA Astrophysics Data System (ADS)

    Gamarra, D.; Hornés, A.; Koppány, Zs.; Schay, Z.; Munuera, G.; Soria, J.; Martínez-Arias, A.

    Nanostructured catalysts based on combinations between oxidised copper and cerium entities prepared by two different methods (impregnation of ceria and coprecipitation of the two components within reverse microemulsions) have been examined with respect to their catalytic performance for preferential oxidation of CO in a H 2-rich stream (CO-PROX). Correlations between their catalytic and redox properties are established on the basis of parallel analyses of temperature programmed reduction results employing both H 2 and CO as reactants as well as by XPS. Although general catalytic trends can be directly correlated with the redox properties observed upon separate interactions with each of the two reductants (CO and H 2), the existence of interferences between both reductants must be considered to complete details for such activity/redox correlation. Differences in the nature of the active oxidised copper-cerium contacts present in each case determine the catalytic properties of these systems for the CO-PROX process.

  15. Characterization of ceria-based SOFCs

    SciTech Connect

    Doshi, R.; Routbort, J.; Krumpelt, M.

    1996-12-31

    Solid Oxide Fuel Cells (SOFCs) operating at low temperatures (500-700{degrees}C) offer many advantages over the conventional zirconia-based fuel cells operating at higher temperatures. Reduced operating temperatures result in: (1) Application of metallic interconnects with reduced oxidation problems (2) Reduced time for start-up and lower energy consumption to reach operating temperatures (3) Increased thermal cycle ability for the cell structure due to lower thermal stresses of expansion mismatches. While this type of fuel cell may be applied to stationary applications, mobile applications require the ability for rapid start-up and frequent thermal cycling. Ceria-based fuel cells are currently being developed in the U.K. at Imperial College, Netherlands at ECN, and U.S.A. at Ceramatec. The cells in each case are made from a doped ceria electrolyte and a La{sub 1-x}Sr{sub x}Co{sub 1-y}Fe{sub y}O{sub 3} cathode.

  16. Kinetics of CO2 Reduction over Nonstoichiometric Ceria

    PubMed Central

    2015-01-01

    The kinetics of CO2 reduction over nonstoichimetric ceria, CeO2−δ, a material of high potential for thermochemical conversion of sunlight to fuel, has been investigated for a wide range of nonstoichiometries (0.02 ≤ δ ≤ 0.25), temperatures (693 ≤ T ≤ 1273 K), and CO2 concentrations (0.005 ≤ pCO2 ≤ 0.4 atm). Samples were reduced thermally at 1773 K to probe low nonstoichiometries (δ < 0.05) and chemically at lower temperatures in a H2 atmosphere to prevent particle sintering and probe the effect of higher nonstoichiometries (δ < 0.25). For extents greater than δ = 0.2, oxidation rates at a given nonstoichiometry are hindered for the duration of the reaction, presumably because of near-order changes, such as lattice compression, as confirmed via Raman Spectroscopy. Importantly, this behavior is reversible and oxidation rates are not affected at lower δ. Following thermal reduction at very low δ, however, oxidation rates are an order of magnitude slower than those of chemically reduced samples, and rates monotonically increase with the initial nonstoichiometry (up to δ = 0.05). This dependence may be attributed to the formation of stable defect complexes formed between oxygen vacancies and polarons. When the same experiments are performed with 10 mol % Gd3+ doped ceria, in which defect complexes are less prevalent than in pure ceria, this dependence is not observed. PMID:26693270

  17. Lattice Strain Defects in a Ceria Nanolayer

    PubMed Central

    2016-01-01

    An ultrathin two-dimensional CeO2 (ceria) phase on a Cu(110) surface has been fabricated and fully characterized by high-resolution scanning tunneling microscopy, photoelectron spectroscopy, and density functional theory. The atomic lattice structure of the ceria/Cu(110) system is revealed as a hexagonal CeO2(111)-type monolayer separated from the Cu(110) surface by a partly disordered Cu–O intercalated buffer layer. The epitaxial coupling of the two-dimensional ceria overlayer to the Cu(110)-O surface leads to a nanoscopic stripe pattern, which creates defect regions of quasi-periodic lattice distortions. The symmetry and lattice mismatch at the interface is clarified to be responsible for the topographic stripe geometry and the related anisotropic strain defect regions at the ceria surface. This ceria monolayer is in a fully oxidized and thermodynamically stable state. PMID:26988695

  18. Energetics of Rare Earth Doped Uranium Oxide Solid Solutions

    NASA Astrophysics Data System (ADS)

    Zhang, Lei

    J/mol. Since all the other doped fluorite oxides based on zirconia, hafnia, ceria, and thoria are in the oxygen deficit (oxygen vacancy formation) regime, a systematic study of these rare earth doped fluorite oxides (LnxA 1-xO2-0.5x) was made comparing experimental and computational results. A consistent trend suggested by both calorimetry and computation, was found for all oxygen vacancy containing systems (actinide and non-actinide oxide systems). Larger size mismatch between the smaller host cation (A 4+) and the larger rare earth dopant cation (Ln3+) generally produces more stable solid solutions. The energetics of these systems is the result of competition between strain energy arising from size mismatch (endothermic) and defect association (exothermic). The formation enthalpies of LnxU1-xO2-0.5x obtained from calculation are slightly positive.

  19. Tuning the Thickness of Ba-Containing "Functional" Layer toward High-Performance Ceria-Based Solid Oxide Fuel Cells.

    PubMed

    Gong, Zheng; Sun, Wenping; Shan, Duo; Wu, Yusen; Liu, Wei

    2016-05-01

    Developing highly efficient ceria-based solid oxide fuel cells with high power density is still a big concern for commercial applications. In this work, a novel structured Ce0.8Sm0.2O2-δ (SDC)-based fuel cell with a bilayered anode consisting of Ni-SDC and Ni-BaZr0.1Ce0.7Y0.2O3-δ (Ni-BZCY) was designed. In addition to the catalysis function, the Ni-BZCY anode "functional" layer also provides Ba source for generating an electron-blocking layer in situ at the anode/electrolyte interface during sintering. The Ni-BZCY thickness significantly influences the quality of the electron-blocking layer and electrochemical performances of the cell. The cell with a 50 μm thick Ni-BZCY layer exhibits the best performance in terms of open circuit voltage (OCV) and peak power density (1068 mW cm(-2) at 650 °C). The results demonstrate that this cell with an optimal structure has a distinct advantage of delivering high power performance with a high efficiency at reduced temperatures. PMID:27078722

  20. IR-doped ruthenium oxide catalyst for oxygen evolution

    NASA Technical Reports Server (NTRS)

    Valdez, Thomas I. (Inventor); Narayanan, Sekharipuram R. (Inventor)

    2012-01-01

    A method for preparing a metal-doped ruthenium oxide material by heating a mixture of a doping metal and a source of ruthenium under an inert atmosphere. In some embodiments, the doping metal is in the form of iridium black or lead powder, and the source of ruthenium is a powdered ruthenium oxide. An iridium-doped or lead-doped ruthenium oxide material can perform as an oxygen evolution catalyst and can be fabricated into electrodes for electrolysis cells.

  1. Preperation and electrochemical characterization of Sm and Gd co-doped ceria/carbonate composite electrolytes for IT-SOFC applications

    NASA Astrophysics Data System (ADS)

    Dikmen, Sibel; Ozsakarya, Rabia; Dikmen, Erdal

    2014-03-01

    Sm and Gd co-doped ceria based composite electrolytes were prepared by mixing nanosized powders of Ce0.8Sm0.1Gd0.1O2-δ (SGDC) and alkaline carbonates (Na-Li)2CO3, (Li-K)2CO3,and(Na-K)2CO3 at a weight ratio of 4:1. Structure of the samples was characterized by powder X-ray diffraction. The microstructure and morphology were examined by SEM. Impedance spectroscopy was used to perform electrochemical characterization. The conductivities of the samples increase as the temperature increases and for the composite electrolytes SGDC(Na-Li)2CO3,andSGDC(Li-K)2CO3, there is a sharp increase in conductivity at around 475 and 450oC, respectively. This sudden change in the conductivity refers to superionic phase transition in the interfaces between SGDC phase and salt phase. The single cell power density reached a maximum of 1056, 826, and 565 mWcm-2 for SGDC/ (Na-Li)2CO3, SGDC/(Li-K)2CO3,andSGDC/(Na-K)2CO3 as the electrolytes, respectively. This work was funded by TUB?TAK 106T536, SDU-BAP 3231-YL1-12.

  2. Structural Analysis of the Combustion Synthesized Y3+ Doped Ceria (Ce0.9Y0.1O1.95)

    NASA Astrophysics Data System (ADS)

    Jeyanthi, C. Esther; Siddheswaran, R.; Kumar, Pushpendra; Mangalaraja, R. V.; Siva Shankar, V.; Rajarajan, K.

    2013-08-01

    Y3+ doped CeO2 nanopowders (Ce0.9Y0.1O1.95, abbreviated as YDC) were synthesized by citrate-nitrate-auto combustion process using cerium nitrate hexahydrate, yttrium nitrate hexahydrate and citric acid. The as-synthesized powders were calcined at 700°C and converted into dense bodies followed by sintering at 1200°C. The microstructure of the synthesized powders and sintered bodies were examined by scanning electron microscopy (SEM). The surface morphology of the nanoparticles and clusters were also analysed by transmission electron microscopy (TEM). The particles size of the YDC was found to be in the range from 10 to 30 nm, which is in good agreement with the crystallite size calculated from X-ray peak broadening method. Also, the X-ray diffraction confirmed that the Ce0.9Y0.1O1.95 crystallizes as the cubic fluorite structure of pure ceria. The optical absorption by functional molecules, impurities and oxygen vacancies were analysed by FTIR and Raman spectroscopic studies. From the FTIR spectrum, the absorption peak found at 530 cm-1 is attributed to the vibrations of metal-oxygen bonds. The characteristic Raman peak was found to be 468 cm-1, and the minute absorption of oxygen vacancies were observed in the region 500-640 cm-1.

  3. Doped palladium containing oxidation catalysts

    DOEpatents

    Mohajeri, Nahid

    2014-02-18

    A supported oxidation catalyst includes a support having a metal oxide or metal salt, and mixed metal particles thereon. The mixed metal particles include first particles including a palladium compound, and second particles including a precious metal group (PMG) metal or PMG metal compound, wherein the PMG metal is not palladium. The oxidation catalyst may also be used as a gas sensor.

  4. Impact of dynamic specimen shape evolution on the atom probe tomography results of doped epitaxial oxide multilayers: Comparison of experiment and simulation

    SciTech Connect

    Madaan, Nitesh; Nandasiri, Manjula; Devaraj, Arun; Bao, Jie; Xu, Zhijie; Thevuthasan, Suntharampillai

    2015-08-31

    The experimental atom probe tomography (APT) results from two different specimen orientations (top-down and sideways) of a high oxygen ion conducting Samaria-doped-ceria/Scandia-stabilized-zirconia multilayer thin film solid oxide fuel cell electrolyte was compared with level-set method based field evaporation simulations for the same specimen orientations. This experiment-simulation comparison explains the dynamic specimen shape evolution and ion trajectory aberrations that can induce density artifacts in final reconstruction, leading to inaccurate estimation of interfacial intermixing. This study highlights the importance of comparing experimental results with field evaporation simulations when using APT to study oxide heterostructure interfaces.

  5. Impact of Dynamic Specimen Shape Evolution on the Atom Probe Tomography Results of Doped Epitaxial Oxide Multilayers: Comparison of Experiment and Simulation

    SciTech Connect

    Madaan, Nitesh; Bao, Jie; Nandasiri, Manjula I.; Xu, Zhijie; Thevuthasan, Suntharampillai; Devaraj, Arun

    2015-08-31

    The experimental atom probe tomography results from two different specimen orientations (top-down and side-ways) of a high oxygen ion conducting Samaria-doped-ceria/Scandia-stabilized-zirconia multilayer thin film solid oxide fuel cell electrolyte was correlated with level-set method based field evaporation simulations for the same specimen orientations. This experiment-theory correlation explains the dynamic specimen shape evolution and ion trajectory aberrations that can induce density artifacts in final reconstruction leading to inaccurate estimation of interfacial intermixing. This study highlights the need and importance of correlating experimental results with field evaporation simulations when using atom probe tomography for studying oxide heterostructure interfaces.

  6. Aluminum doped zinc oxide for organic photovoltaics

    SciTech Connect

    Murdoch, G. B.; Hinds, S.; Sargent, E. H.; Tsang, S. W.; Mordoukhovski, L.; Lu, Z. H.

    2009-05-25

    Aluminum doped zinc oxide (AZO) was grown via magnetron sputtering as a low-cost alternative to indium tin oxide (ITO) for organic photovoltaics (OPVs). Postdeposition ozone treatment resulted in devices with lower series resistance, increased open-circuit voltage, and power conversion efficiency double that of devices fabricated on untreated AZO. Furthermore, cells fabricated using ozone treated AZO and standard ITO displayed comparable performance.

  7. The growth and structure of thin oxide films on nickel superficially modified with ceria and cerium

    NASA Astrophysics Data System (ADS)

    Czerwinski, Franciszek

    A small addition of elements with a high affinity to oxygen can have a profound effect on the high temperature oxidation behaviour of many metals and alloys. In order to explain the improvement in oxidation resistance, the research was conducted using Ni-NiO as a model system of cation-diffusing oxides, and Ce as a typical reactive element. Three essential techniques were employed to modify the surface of Ni with Ce and CeO2: ion implantation, sol-gel technology, and reactive sputtering. The improvement of Ni oxidation resistance was assessed by oxygen uptake measurements mainly during the early stages but also for long-term exposures at temperatures between 873 and 1073 K in pure oxygen, both at low and atmospheric pressures. The variety of oxides produced were examined in detail by several advanced techniques including Rutherford backscattering spectrometry, Auger electron spectroscopy, secondary ion-mass spectrometry, transmission- and scanning-transmission electron microscopy equipped with electron and x-ray analyzers, atomic force microscopy, infrared spectroscopy, and x-ray diffraction techniques. In order to provide direct evidence regarding the mechanism of oxide growth, a sequential oxidation using oxygen isotopes 16O2/18O2 was conducted. After conversion to the form of ceramic coating, superficially applied CeO2 sol-gel significantly reduced the Ni oxidation rate as well as changing the NiO morphology and internal microstructure. The extent of the effect depended on coating thickness, size of CeO2 particles, substrate surface finishing and preoxidation before coating. Under optimum conditions, the reduction in the Ni oxidation rate achieved by sol-gel, reactive sputtering, and ion implantation, was similar. It was found that Ni oxidation resistance is controlled by a well-defined NiO sublayer that is composed of randomly-oriented NiO grains and CeO2 particles. Moreover, in this sublayer, the Ce4+ ions segregate to the NiO grain boundaries. At high

  8. Electroconductive properties in doped spinel oxides

    NASA Astrophysics Data System (ADS)

    Dwivedi, Shalini; Sharma, Ramesh; Sharma, Yamini

    2014-11-01

    The application of spinel oxides as transparent conducting oxides (TCOs) in optoelectronic devices as a substitute for ZnO is attracting attention in the recent years. Despite attractive photo-luminescence properties of zinc aluminate and zinc gallate, relatively little work has been done to interpret the optical response of spinel oxides on the basis of energy band structures. We present the electronic properties of ZnX2O4 (X = Al, Ga, In) calculated by the full potential linearized augmented plane wave method. Optical properties such as absorption coefficient and reflectivity are calculated and interpreted in terms of energy bands and density of states. Enhancement in optical properties was studied for Li and Mn ions doped in the ZnGa2O4 matrix. The main features in the experimentally observed photoluminescence spectra for doped and undoped ZnGa2O4 have been verified through the optical parameters. The transparence of spinel oxides to UV radiations is also clearly illustrated in the reflectivity vs. energy curves. At very small wavelengths the oxides may be used as reflective coating materials. Transport properties of the zinc spinel oxides have been investigated for the first time, and are found to have high Seebeck coefficients, high electrical conductivity and low thermal conductivity, with high value of figure of merit ZT ∼ 0.8. The study of vibrational and thermodynamic properties by the projector augmented wave method confirms the dynamic stability of the doped and undoped spinel oxides. Zinc spinel oxides are found to be p-type semiconductors with an optimum value of band gap ∼2-3 eV and appear to meet the conditions of low resistivity and high transparency (>80%) for state-of-art TCOs.

  9. The characterization of CrCe-doped on TiO2-pillared clay nanocomposites for NO oxidation and the promotion effect of CeOx

    NASA Astrophysics Data System (ADS)

    Zhang, Jingxin; Zhang, Shule; Cai, Wei; Zhong, Qin

    2013-03-01

    A series of chromium-ceria doped on TiO2-pillared clay nanocomposites catalysts with various Cr/Ce ratios were investigated in the oxidation of NO. This study aimed to not only synthesize the CrCe/TiO2-PILC nanocomposites, but also figure out the promotion effect of Ce in the oxidation process and the interaction between chromium and ceria on the surface of TiO2-PILC. The samples were characterized by XRD, SEM, TEM, XPS and H2-TPR methods. The best catalyst Cr(1)Ce(0.25)/TiO2-pillared clay yielded 69% NO to NO2 conversion at 350 °C (in the condition of GHSV = 35,400 h-1). With the content of ceria increasing, the NO conversion increased significantly while when the Cr/Ce equaled 1:1, the activity decreased. The chromium oxides were well dispersed on the surface of the support. Analysis of XPS indicated that the addition of ceria oxides could promote the formation of chemisorbed oxygen and raise the quantivalency of Cr. The powerful electron withdrawing ability of Ce made the electron density around Ti atoms decrease. The result showed that CeOx enhanced the metal-support interaction. H2-TPR indicated that the proper addition of CeOx increased the reducible phase that was beneficial to the reaction. Moreover, the catalysts showed a good resistance to SO2 and H2O. When SO2 and H2O were added in the feed gas, the catalytic activity decreased but when removed, the activity recovered. The deactivation was not totally irreversible.

  10. Solvothermal synthesis and characterization of ceria-zirconia mixed oxides for catalytic applications.

    PubMed

    Devaraju, M K; Liu, Xiangwen; Yusuke, Kikuchi; Yin, S; Sato, T

    2009-10-01

    Solvothermal synthesis under supercritical conditions (400 degrees C) and high autogenous pressure (about 40 MPa), has been carried out for the direct preparation of nanocrystalline powders of CeO2, Ce(0.85)Zr(0.15)O2, Ce(0.75)Zr(0.25)O2, Ce(0.65)Zr(0.35)O2 and Ce(0.5)Zr(0.5)O2 which are characterized for applications as catalysts for oxygen storage in automotive catalysis. The synthesis was carried out in the presence of polyethylene glycol and water. For the characterization, x-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS) and the Brunauer-Emmet-Teller (BET) technique were employed. The oxygen storage capacity (OSC) of as-prepared and calcined samples without loading of noble metals was measured using thermogravimetric-differential thermal analysis (TG-DTA) at 600 degrees C with a continuous flow of CO-N2 gas and air alternately. Ce(0.5)Zr(0.5)O2 nanoparticles with a BET surface area of 102 m(2) g(-1) exhibited the highest OSC of 0.073 50 mol-O2/mol-CeO2. The OSC values obtained increased with increasing the amount of ZrO2 doping in the samples. PMID:19738312

  11. Real-Time Observation of Platinum Redispersion on Ceria-Based Oxide by In-situ Turbo-XAS in Fluorescence Mode

    SciTech Connect

    Nagai, Yasutaka; Dohmae, Kazuhiko; Tanabe, Toshitaka; Shinjoh, Hirofumi; Takagi, Nobuyuki; Ikeda, Yasuo; Guilera, Gemma; Pascarelli, Sakura; Newton, Mark; Matsumoto, Shin'ichi

    2007-02-02

    A real-time observation of the redispersion behavior of sintered Pt on ceria-based oxide was made possible by in-situ time-resolved Turbo-XAS in fluorescence mode. 2 wt% Pt/Ce-Zr-Y mixed oxide samples were prepared, and then treated under an aging condition. The average Pt particle size measured by CO absorption method after aging was 7 nm. Redispersion treatments of the previously aged catalyst were carried out at 600 deg. C within an in-situ XAS cell in a cyclical flow of reducing/oxidizing gases. Pt L3-edge XANES spectra were collected every 1.1 second under in-situ conditions. From a change in the XANES spectra, we observed that the Pt particle size of the aged catalyst decreased from 7 to 5 nm after 60 seconds and then to 3 nm after 1000 seconds.

  12. Monte Carlo simulations in the preferential oxidation of carbon monoxide on a copper-ceria catalyst

    NASA Astrophysics Data System (ADS)

    Cortés, Joaquín; Valencia, Eliana; Araya, Paulo

    2014-09-01

    A kinetic Monte Carlo simulation algorithm has been developed for the preferential oxidation of CO over the nanostructured catalyst Cu0.1Ce0.9O2- based on a recent mechanism from the literature. Among other results, the simulations reproduce qualitatively recently published experimental information, showing, for example, a maximum of CO2 production versus temperature at T = Tmax, a continuous increase of H2O production for T > Tmax, and a decrease of the selectivity from a value approximately equal to 1.0 at T = Tmax. Production of CO2 also shows a maximum with CO concentration in the gas phase, corresponding to a minimum of H2O production.

  13. Electrochemical & Thermochemical Behavior of Cerium(IV) Oxide delta

    NASA Astrophysics Data System (ADS)

    Chueh, William C.

    The mixed-valent nature of nonstoichiometric ceria (CeO2-delta ) gives rise to a wide range of intriguing properties, such as mixed ionic and electronic conduction and oxygen storage. Surface and transport behavior in rare-earth (samaria) doped and undoped ceria were investigated, with particular emphasis on applications in electrochemical and thermochemical energy conversion processes such as fuel cells and solar fuel production. The electrochemical responses of bulk-processed ceria with porous Pt and Au electrodes were analyzed using 1-D and 2-D transport models to decouple surface reactions, near-surface transport and bulk transport. Combined experimental and numerical results indicate that hydrogen electro-oxidation and hydrolysis near open-circuit conditions occur preferentially over the ceria | gas interface rather than over the ceria | gas | metal interface, with the rate-limiting step likely to be either surface reaction or transport through the surface oxygen vacancy depletion layer. In addition, epitaxial thin films of ceria were grown on zirconia substrates using pulsed-laser deposition to examine electrocatalysis over well-defined microstructures. Physical models were derived to analyze the electrochemical impedance response. By varying the film thickness, interfacial and chemical capacitance were decoupled, with the latter shown to be proportional to the small polaron densities. The geometry of microfabricated metal current collectors (metal = Pt, Ni) was also systematically varied to investigate the relative activity of the ceria | gas and the ceria | metal | gas interfaces. The data suggests that the electrochemical activity of the metal-ceria composite is only weakly dependent on the metal due to the relatively high activity of the ceria | gas interface. In addition to electrochemical experiments, thermochemical reduction-oxidation studies were performed on ceria. It was shown that thermally-reduced ceria, upon exposure to H 2O and/or CO2, can be

  14. Transparent conducting oxides: A -doped superlattice approach

    SciTech Connect

    Cooper, Valentino R; Seo, Sung Seok A.; Lee, Suyoun; Kim, Jun Sung; Choi, Woo Seok; Okamoto, Satoshi; Lee, Ho Nyung

    2014-01-01

    Two-dimensional electron gases (2DEGs) at the interface of oxide heterostructures have been the subject of recent experiment and theory, due to the intriguing phenomena that occur in confined electronic states. However, while much has been done to understand the origin of 2DEGs and related phenomena, very little has been explored with regards to the control of conduction pathways and the distribution of charge carriers. Using first principles simulations and experimental thin film synthesis methods, we examine the effect of dimensionality on carrier transport in La delta-doped SrTiO3 (STO) superlattices, as a function of the thickness of the insulating STO spacer. Our computed Fermi surfaces and layer-resolved carrier density proles demonstrate that there is a critical thickness of the STO spacer, below which carrier transport is dominated by three-dimensional conduction of interface charges arising from appreciable overlap of the quantum mechanical wavefunctions between neighboring delta-doped layers. We observe that, experimentally, these superlattices remain highly transparent to visible light. Band structure calculations indicate that this is a result of the appropriately large gap between the O 2p and Ti d states. The tunability of the quantum mechanical wavefunctions and the optical transparency highlight the potential for using oxide heterostructures in novel opto-electronic devices; thus providing a route to the creation of novel transparent conducting oxides.

  15. Silica Supported Ceria Nanoparticles: A Hybrid Nanostructure To Increase Stability And Surface Reactivity Of Nano-crystalline Ceria

    SciTech Connect

    Munusamy, Prabhakaran; Sanghavi, Shail P.; Varga, Tamas; Thevuthasan, Suntharampillai

    2014-01-21

    The mixed oxidation state (3+/4+) of ceria nanoparticles of smaller sizes make them attractive materials for their catalytic antioxidant biological properties. However the unmodified smaller ceria nanoparticles are limited in their use due to particles agglomeration and reduced surface chemical reactivity in the solutions used to disperse the nanoparticles. This work describes an effort to stabilize small ceria nanoparticles, retaining their desired activity, on a larger stable silica support. The ceria nanoparticles attached to silica was synthesized by a solution synthesis technique in which the surface functional groups of silica nanoparticles were found to be essential for the formation of smaller ceria nanoparticles. The surface chemical and vibrational spectroscopy analysis revealed cerium–silicate (Ce-O-Si) covalent bond linkage between silica and cerium oxide nanoparticles. The colloidal properties (agglomerate particle size and suspension stability) of ceria attached to silica was significantly improved due to inherent physico-chemical characteristics of silica against random collision and gravitation settling as opposed to unmodified ceria nanoparticles in solution. The bio-catalytic activity of ceria nanoparticles in the 3+ oxidation state was not found to be limited by attachment to the silica support as measured by free radical scavenging activity in different biological media conditions.

  16. Cathodes for ceria-based fuel cells

    SciTech Connect

    Doshi, R.; Krumpelt, M.; Ricvhards, V.L.

    1997-08-01

    Work is underway to develop a solid oxide fuel cell that has a ceria-based electrolyte and operates at lower temperatures (500-600{degrees}C) than conventional zirconia-based cells. At present the performance of this ceria-based solid oxide fuel cell is limited by the polarization of conventional cathode materials. The performance of alternative cathodes was measured by impedance spectroscopy and dc polarization. The performance was found to improve by using a thin dense interface layer and by using two-phase cathodes with an electrolyte and an electronic phase. The cathode performance was also found to increase with increasing ionic conductivity for single phase cathodes.

  17. Alleviating coking in ethanol steam reforming by co-loading binary oxides Ni-M (M=Ag, Cu, Mn) on peony-like ceria

    NASA Astrophysics Data System (ADS)

    Xian, C. N.; Li, J. G.; Li, H.; Chen, L. Q.; Sun, J.; Lee, J. S.

    2011-06-01

    Previously, hydrothermally prepared mesoporous peony-like ceria (PCO) material was shown to exhibit superior catalytic properties for CO oxidation and ethanol reforming. Ni supported PCO had been shown to have high activity for ethanol steam reforming at low temperature. In this work, Ag, Cu and Mn is co-loaded with Ni on PCO catalysts by impregnation method. The catalysts were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and a combined thermogravimetry, differential scanning calorimetry, and mass spectrometry (TG-DSC-MS). It was found that all the catalysts gave 100% ethanol conversion above ca. 300°C and exhibited similar H2 yield. It is found that the severe coking problem for the Ni-loaded PCO catalyst was alleviated significantly if Ag, Cu or Mn is co-loaded. Among them, the addition of Mn is the most effective in reducing carbon formation.

  18. Statistical thermodynamics of non-stoichiometric ceria and ceria zirconia solid solutions.

    PubMed

    Bulfin, B; Hoffmann, L; de Oliveira, L; Knoblauch, N; Call, F; Roeb, M; Sattler, C; Schmücker, M

    2016-08-17

    The thermodynamic redox properties of ceria and ceria zirconia solid solutions are analysed with a new methodology for modelling such systems based on the statistical mechanics of lattice configurations. Experimental thermogravimetric equilibrium data obtained for small non-stoichiometry measurements are combined with literature data to cover a large range of non-stoichiometry (CeO2-δ, δ = 0.001-0.32), temperature (1073-1773 K) and oxygen partial pressure (1-10(-13) bar). A dilute species model of defect clusters , obeying the law of mass action, was sufficient to describe the system over the whole range of conditions, leading to a simple analytical equation of state for the system. This offers new physical insight into the redox properties of ceria based materials, and the theoretical methods developed should also be of great interest for other materials which exhibit continuous oxygen non-stoichiometry similar to ceria, such as perovskite oxides. PMID:27494765

  19. Controlled Variable Oxidative Doping of Individual Organometallic Nanoparticles.

    PubMed

    Feng, Ann; Cheng, Wei; Holter, Jennifer; Young, Neil; Compton, Richard G

    2016-05-10

    The charging and controlled oxidative doping of single organometallic ferrocene nanoparticles is reported in aqueous sodium tetrafluoroborate using the nano-impacts method. It is shown that ferrocene nanoparticles of approximately 105 nm diameter are essentially quantitatively oxidatively doped with the uptake of one tetrafluoroborate anion per ferrocene molecule at suitably high overpotentials. By using lower potentials, it is possible to achieve low doping levels of single nanoparticles in a controlled manner. PMID:27038252

  20. Growth and characterization of ceria thin films and Ce-doped γ-Al2O3 nanowires using sol-gel techniques.

    PubMed

    Gravani, S; Polychronopoulou, K; Stolojan, V; Cui, Q; Gibson, P N; Hinder, S J; Gu, Z; Doumanidis, C C; Baker, M A; Rebholz, C

    2010-11-19

    γ-Al(2)O(3) is a well known catalyst support. The addition of Ce to γ-Al(2)O(3) is known to beneficially retard the phase transformation of γ-Al(2)O(3) to α-Al(2)O(3) and stabilize the γ-pore structure. In this work, Ce-doped γ-Al(2)O(3) nanowires have been prepared by a novel method employing an anodic aluminium oxide (AAO) template in a 0.01 M cerium nitrate solution, assisted by urea hydrolysis. Calcination at 500 °C for 6 h resulted in the crystallization of the Ce-doped AlOOH gel to form Ce-doped γ-Al(2)O(3) nanowires. Ce(3+) ions within the nanowires were present at a concentration of < 1 at.%. On the template surface, a nanocrystalline CeO(2) thin film was deposited with a cubic fluorite structure and a crystallite size of 6-7 nm. Characterization of the nanowires and thin films was performed using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. The nanowire formation mechanism and urea hydrolysis kinetics are discussed in terms of the pH evolution during the reaction. The Ce-doped γ-Al(2)O(3) nanowires are likely to find useful applications in catalysis and this novel method can be exploited further for doping alumina nanowires with other rare earth elements. PMID:20975211

  1. Cerium oxide for sunscreen cosmetics

    NASA Astrophysics Data System (ADS)

    Yabe, Shinryo; Sato, Tsugio

    2003-02-01

    Ultrafine particles of Mn+ -doped ceria ( Mn+ =Mg 2+, Ca 2+, Sr 2+, Ba 2+, Y 3+, La 3+, Nd 3+, Sm 3+, Eu 3+, Tb 3+) for UV filter were prepared via soft solution chemical routes at 40°C. X-ray diffraction revealed that the prepared doped particles had the cubic fluorite structures although peak positions changed depending on the kind and amount of doped metal ion. Doping with 20 mol% Ca 2+ and 20 mol% Zn 2+ resulted in extremely decreasing the particle size (2-4 nm) and the catalytic activity of ceria for oxidation of castor oil. Ca 2+-doped cerium dioxide showed excellent UV absorbing effect and transparency in the visible ray region compared with undoped cerium dioxide.

  2. Influence of doping with third group oxides on properties of zinc oxide thin films

    SciTech Connect

    Palimar, Sowmya Bangera, Kasturi V.; Shivakumar, G. K.

    2013-03-15

    The study of modifications in structural, optical and electrical properties of vacuum evaporated zinc oxide thin films on doping with III group oxides namely aluminum oxide, gallium oxide and indium oxide are reported. It was observed that all the films have transmittance ranging from 85 to 95%. The variation in optical properties with dopants is discussed. On doping the film with III group oxides, the conductivity of the films showed an excellent improvement of the order of 10{sup 3} {Omega}{sup -1} cm{sup -1}. The measurements of activation energy showed that all three oxide doped films have 2 donor levels below the conduction band.

  3. Surface morphology, optical and electrochemical properties of undoped and Ni-doped CeO2 thin films prepared by polymeric precursor method

    NASA Astrophysics Data System (ADS)

    Khosousi Sani, Zara; Esmaeli Ghodsi, Farhad; Mazloom, Jamal

    2016-04-01

    In this study, undoped and Ni-doped CeO2 thin films were deposited onto glass and ITO substrates by polymeric precursor (Pechini) method. Grazing incidence X-ray diffraction analysis revealed that the ceria thin film has a cerianite structure with the average crystallite size of 14 nm while the doped samples are amorphous. X-ray photoelectron spectroscopy (XPS) confirmed the presence of predominant Ce4+ oxidation state of ceria and Ni2+ in the films. Scanning electron microscopy (SEM) micrographs showed that the surface texture is crack free and the CeO2 grains regularly distributed on the surface. Optical constant (refractive index and extinction coefficient) and thickness of films were calculated using pointwise unconstraint minimization approach. The optical transmittance increases and the absorption edge has a blue shift by Ni incorporation. The highest band gap value (i.e., 3.43 eV) was obtained for 2.5 mol.% Ni doping sample. The refractive index and extinction coefficient of ceria films were decreased by Ni doping. The evaluated thicknesses are in the range of 150-170 nm. The strength of interband transition was appraised as a function of nickel content by using dielectric function. Luminescent emission intensity of the ceria film was enhanced by Ni doping. Cyclic voltammetry (CV) measurement revealed that the total charge density and ion storage capacitance of ceria thin film were increased by Ni doping.

  4. Zinc oxide doped graphene oxide films for gas sensing applications

    NASA Astrophysics Data System (ADS)

    Chetna, Kumar, Shani; Garg, A.; Chowdhuri, A.; Dhingra, V.; Chaudhary, S.; Kapoor, A.

    2016-05-01

    Graphene Oxide (GO) is analogous to graphene, but presence of many functional groups makes its physical and chemical properties essentially different from those of graphene. GO is found to be a promising material for low cost fabrication of highly versatile and environment friendly gas sensors. Selectivity, reversibility and sensitivity of GO based gas sensor have been improved by hybridization with Zinc Oxide nanoparticles. The device is fabricated by spin coating of deionized water dispersed GO flakes (synthesized using traditional hummer's method) doped with Zinc Oxide on standard glass substrate. Since GO is an insulator and functional groups on GO nanosheets play vital role in adsorbing gas molecules, it is being used as an adsorber. Additionally, on being exposed to certain gases the electric and optical characteristics of GO material exhibit an alteration in behavior. For the conductivity, we use Zinc Oxide, as it displays a high sensitivity towards conduction. The effects of the compositions, structural defects and morphologies of graphene based sensing layers and the configurations of sensing devices on the performances of gas sensors were investigated by Raman Spectroscopy, X-ray diffraction(XRD) and Keithley Sourcemeter.

  5. Fluorine compounds for doping conductive oxide thin films

    SciTech Connect

    Gessert, Tim; Li, Xiaonan; Barnes, Teresa M; Torres, Jr., Robert; Wyse, Carrie L

    2013-04-23

    Methods of forming a conductive fluorine-doped metal oxide layer on a substrate by chemical vapor deposition are described. The methods may include heating the substrate in a processing chamber, and introducing a metal-containing precursor and a fluorine-containing precursor to the processing chamber. The methods may also include adding an oxygen-containing precursor to the processing chamber. The precursors are reacted to deposit the fluorine-doped metal oxide layer on the substrate. Methods may also include forming the conductive fluorine-doped metal oxide layer by plasma-assisted chemical vapor deposition. These methods may include providing the substrate in a processing chamber, and introducing a metal-containing precursor, and a fluorine-containing precursor to the processing chamber. A plasma may be formed that includes species from the metal-containing precursor and the fluorine-containing precursor. The species may react to deposit the fluorine-doped metal oxide layer on the substrate.

  6. Influence of the activation conditions on the elimination of residual impurities on ceria-zirconia mixed oxides

    NASA Astrophysics Data System (ADS)

    Daturi, M.; Binet, C.; Lavalley, J. C.; Vidal, H.; Kaspar, J.; Graziani, M.; Blanchard, G.

    1998-10-01

    A series of samples belonging to the ceria-zirconia solid solution has been investigated from the point of view of surface impurities, via TPO/TPD and FTIR spectroscopy. Species likely due either to the precursors or to atmospheric contamination have been taken into account and their stability has been studied following two different thermal treatments. A complete cleaning treatment is proposed in order to obtain powders of satisfactory quality for catalytic purposes. Les impuretés superficielles contenues dans une série d'oxydes mixtes cérine- zircone ont été étudiées par TPO/TPD et spectroscopie infrarouge. Les impuretés provenant soit des précurseurs soit de la contamination atmosphérique (carbonates) ont été identifiées et leur stabilité thermique a été étudiée en fonction de différents traitements thermiques. Une méthode thermique de purification est proposée afin d'obtenir des poudres de qualité suffisante pour les applications catalytiques.

  7. Comparative Pulmonary Toxicity of Two Ceria Nanoparticles with the Same Primary Size

    PubMed Central

    Peng, Lu; He, Xiao; Zhang, Peng; Zhang, Jing; Li, Yuanyuan; Zhang, Junzhe; Ma, Yuhui; Ding, Yayun; Wu, Zhenqiang; Chai, Zhifang; Zhang, Zhiyong

    2014-01-01

    Ceria nanoparticles (nano-ceria) have recently gained a wide range of applications, which might pose unwanted risks to both the environment and human health. The greatest potential for the environmental discharge of nano-ceria appears to be in their use as a diesel fuel additive. The present study was designed to explore the pulmonary toxicity of nano-ceria in mice after a single exposure via intratracheal instillation. Two types of nano-ceria with the same distribution of a primary size (3–5 nm), but different redox activity, were used: Ceria-p, synthesized by a precipitation route, and Ceria-h, synthesized by a hydrothermal route. Both Ceria-p and Ceria-h induced oxidative stress, inflammatory responses and cytotoxicity in mice, but their toxicological profiles were quite different. The mean size of Ceria-p agglomerates was much smaller compared to Ceria-h, thereby causing a more potent acute inflammation, due to their higher number concentration of agglomerates and higher deposition rate in the deep lung. Ceria-h had a higher reactivity to catalyzing the generation of reactive oxygen species (ROS), and caused two waves of lung injury: bronchoalveolar lavage (BAL) inflammation and cytotoxicity in the early stage and redox-activity-evoked lipid peroxidation and pro-inflammation in the latter stage. Therefore, the size distribution of ceria-containing agglomerates in the exhaust, as well as their surface chemistry are essential characteristics to assess the potential risks of using nano-ceria as a fuel additive. PMID:24727375

  8. Oxygen transport in ceria: a first-principles study

    NASA Astrophysics Data System (ADS)

    Sergei, Simak

    2012-02-01

    Ceria (CeO2) is an important material for environmentally benign applications, ranging from solid-oxide fuel cells (SOFC) to oxygen storage [1-2]. The key characteristic needed to be improved is the mobility of oxygen ions. Optimization of ionic transport in ceria has been the topic of many studies. In particular, it has been discovered how the ionic conductivity in ceria might be improved by choosing the proper kind and concentration of dopants [3]. In this presentation we will approach the problem from a different direction by adjusting structural parameters of ceria via the change of external conditions. A systematic first-principles study of the energy landscape and kinetics of reduced ceria as a function of external parameters reveals a physically transparent way to improve oxygen transport in ceria. [4pt] [1] N. Skorodumova, S. Simak, B. Lundqvist, I. Abrikosov, and B. Johansson, Physical Review Letters 89, 14 (2002). [0pt] [2] A. Trovarelli, in Catalysis by Ceria and related materials (Imperial College Press, London, 2002). [0pt] [3] D. A. Andersson, S. I. Simak, N. V. Skorodumova, I. A.Abrikosov, and B. Johansson, Proceedings of the National Academy of Sciences of the United States of America 103, 3518 (2006).

  9. Surface and catalytic properties of doped tin oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Wang, Chien-Tsung; Lai, De-Lun; Chen, Miao-Ting

    2010-10-01

    Mixed oxides composed of Zn-Sn, Ti-Sn and V-Sn were prepared by a co-precipitation method and evaluated as catalysts for methanol oxidation in an ambient fixed-bed reactor. Surface analysis by X-ray photoelectron spectroscopy (XPS) revealed an electronic interaction between dopant and Sn atoms in the oxide structure and showed the formation of surface states associated with the dopants. Oxygen vacancies were present on the Zn-doped oxide, and the oxidation of methanol to carbon oxides was favored. The Ti-doped oxide exhibited a favorable selectivity to dimethyl ether, related to the oxygen anions near Ti centers. Vanadium dopants not only dramatically increased the catalytic activity but also promoted the partial oxidation of methanol to formaldehyde. Results demonstrate that the bridging dopant-O-Sn bond acts as active sites and influences product distribution.

  10. Nanocrystalline ceria powders through citrate-nitrate combustion.

    PubMed

    Purohit, R D; Saha, S; Tyagi, A K

    2006-01-01

    Nanocrystalline ceria powders have been synthesized by combustion technique using citric acid as a fuel and nitrate as an oxidizer. The auto-ignition of the gels containing cerium nitrate and citric acid resulted in ceria powders. A theory based on adiabatic flame temperature for different citric acid-to-cerium nitrate molar ratios has been proposed to explain the nature of combustion reaction and its correlation with the powder characteristics. Specific surface area and primary particle size of the ceria powder obtained through fuel-deficient precursor was found to be approximately = 127 m2/g and 2.5-10 nm, respectively. The combustion synthesized ceria powder when cold pressed and sintered in air at 1250 degrees C for 1 hour resulted in approximately = 96% of its theoretical density with sub-micron grains. PMID:16573097

  11. Preparation and Evaluation of Nitrogen Doped Tungsten Oxide Thin Films

    NASA Astrophysics Data System (ADS)

    Nakagawa, Koichi; Miura, Noboru; Matsumoto, Setsuko; Nakano, Ryotaro; Matsumoto, Hironaga

    Nitrogen doped tungsten oxide thin films were prepared by RF reactive sputtering in a gas mixture of argon, oxygen and nitrogen at room temperature. As a result of X-ray photoelectron spectroscopy, it was thought that the doped nitrogen in the films is bonding to tungsten of WO3 bonding states as anion and exits in substitution sites in WO3. The optical absorption edge was shifted to lower energy region with nitrogen doping. The nitrogen doped thin films exhibit a coloration to black from transparent yellow by electrochromism. Additionally, a new peak at 2.3 eV related to nitrogen doping is observed in the spectra of color center at bleaching process.

  12. Non-Prestonian behavior of rectangular shaped ceria slurry in shallow trench isolation chemical mechanical planarization.

    PubMed

    Kim, Ye-Hwan; Jung, Yeon-Gil; Yoon, Gwang Seob; Moon, Jinok; Watanabe, Akira; Naito, Makio; Paik, Ungyu

    2012-03-01

    Rectangular ceria particles were synthesized using the flash creation method. The influence of the morphology of ceria particles and the surfactant concentration on the removal rate was systematically investigated. These ceria slurries with polymeric surfactant molecules as the passivation agents of Si3N4 film, shows an exceptional non-Prestonian behaviors. The non-Prestonian behavior can be attributed to the increase in the contact area of the ceria particles with the SiO2 film, which is dominated by the morphology of the ceria particles. Force measurements using an atomic force microscope (AFM) at different concentrations of polymeric surfactant molecules was used to identify the interactions between the polymeric molecules and the oxide film and analyze the non-Prestonian behavior of ceria slurry having rectangular abrasives. PMID:22755127

  13. Doping-Promoted Solar Water Oxidation on Hematite Photoanodes.

    PubMed

    Zhang, Yuchao; Ji, Hongwei; Ma, Wanhong; Chen, Chuncheng; Song, Wenjing; Zhao, Jincai

    2016-01-01

    As one of the most promising materials for solar water oxidation, hematite has attracted intense research interest for four decades. Despite their desirable optical band gap, stability and other attractive features, there are great challenges for the implementation of hematite-based photoelectrochemical cells. In particular, the extremely low electron mobility leads to severe energy loss by electron hole recombination. Elemental doping, i.e., replacing lattice iron with foreign atoms, has been shown to be a practical solution. Here we review the significant progresses in metal and non-metal element doping-promoted hematite solar water oxidation, focusing on the role of dopants in adjusting carrier density, charge collection efficiency and surface water oxidation kinetics. The advantages and salient features of the different doping categories are compared and discussed. PMID:27376262

  14. Plasma sprayed ceria-containing interlayer

    DOEpatents

    Schmidt, Douglas S.; Folser, George R.

    2006-01-10

    A plasma sprayed ceria-containing interlayer is provided. The interlayer has particular application in connection with a solid oxide fuel cell used within a power generation system. The fuel cell advantageously comprises an air electrode, a plasma sprayed interlayer disposed on at least a portion of the air electrode, a plasma sprayed electrolyte disposed on at least a portion of the interlayer, and a fuel electrode applied on at least a portion of the electrolyte.

  15. Tuning the surface oxygen concentration of {111} surrounded ceria nanocrystals for enhanced photocatalytic activities

    NASA Astrophysics Data System (ADS)

    Younis, Adnan; Chu, Dewei; Kaneti, Yusuf Valentino; Li, Sean

    2015-12-01

    For oxide semiconductors, the morphology, particle size and oxygen vacancies are usually considered as key influential parameters for photocatalytic degradation of organic pollutants/dyes. It is widely accepted that cation doping not only modifies their phase and microstructures but also introduces variations in oxygen vacancy concentration. Herein, we report the fabrication of sub-10 nm sized pure and indium doped CeO2 nanocrystals (NCs) via a facile, green hydrothermal method for the investigation of photocatalytic activities. X-ray diffraction and transmission electron microscopy were employed to examine the crystal phase and morphology of the as-prepared nanocrystals. Raman and X-ray photoelectron spectroscopy techniques were implemented to investigate the presence and variations in oxygen vacancy concentration in un-doped and indium doped CeO2 nanocrystals. The photocatalytic activity results revealed that 10 at% doping is the optimal indium doping level to demonstrate superior dye removal efficiency (~40%) over un-doped and doped CeO2 NCs. Moreover, the 10% In-doped CeO2 nanocrystals expressed excellent cycling stability and superior photocatalytic performance toward other dye pollutants. Finally, on the basis of our findings, a possible photocatalytic mechanism in which indium doping can generate more surface oxygen vacancies in the ceria lattice which delay the electron-hole recombination rates, thus increasing the lifetime of electron-hole separation for enhanced photocatalytic performances was proposed.For oxide semiconductors, the morphology, particle size and oxygen vacancies are usually considered as key influential parameters for photocatalytic degradation of organic pollutants/dyes. It is widely accepted that cation doping not only modifies their phase and microstructures but also introduces variations in oxygen vacancy concentration. Herein, we report the fabrication of sub-10 nm sized pure and indium doped CeO2 nanocrystals (NCs) via a facile

  16. Dysprosium oxide and dysprosium-oxide-doped titanium oxide thin films grown by atomic layer deposition

    SciTech Connect

    Tamm, Aile Kozlova, Jekaterina; Aarik, Lauri; Aarik, Jaan; Kukli, Kaupo; Link, Joosep; Stern, Raivo

    2015-01-15

    Dysprosium oxide and dysprosium-oxide-doped titanium oxide thin films were grown by atomic layer deposition on silicon substrates. For depositing dysprosium and titanium oxides Dy(thd){sub 3}-O{sub 3} and TiCl{sub 4}-O{sub 3} were used as precursors combinations. Appropriate parameters for Dy(thd){sub 3}-O{sub 3} growth process were obtained by using a quartz crystal microbalance system. The Dy{sub 2}O{sub 3} films were deposited on planar substrates and on three-dimensional substrates with aspect ratio 1:20. The Dy/Ti ratio of Dy{sub 2}O{sub 3}-doped TiO{sub 2} films deposited on a planar silicon substrate ranged from 0.04 to 0.06. Magnetometry studies revealed that saturation of magnetization could not be observed in planar Dy{sub 2}O{sub 3} films, but it was observable in Dy{sub 2}O{sub 3} films on 3D substrates and in doped TiO{sub 2} films with a Dy/Ti atomic ratio of 0.06. The latter films exhibited saturation magnetization 10{sup −6} A cm{sup 2} and coercivity 11 kA/m at room temperature.

  17. Hydrothermal preparation and electrochemical properties of Gd 3+ and Bi 3+, Sm 3+, La 3+, and Nd 3+ codoped ceria-based electrolytes for intermediate temperature-solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Dikmen, Sibel; Aslanbay, Hasan; Dikmen, Erdal; Şahin, Osman

    The structure, the thermal expansion coefficient, electrical conductivities of Ce 0.8Gd 0.2- xM xO 2- δ (for M: Bi, x = 0-0.1, and for M: Sm, La, and Nd, x = 0.02) solid solutions, prepared for the first time hydrothermally, are investigated. The uniformly small particle size (28-59 nm) of the materials allows sintering of the samples into highly dense ceramic pellets at 1300-1400 °C. The maximum conductivity, σ 700 °C around 4.46 × 10 -2 S cm -1 with E a = 0.52 eV, is found at x = 0.1 for Bi-co-doping. Among various metal-co-dopings, for x = 0.02, the maximum conductivity, σ 700 °C around 2.88 × 10 -2 S cm -1 with E a = 0.67 eV, is found for Sm-co-doping. The electrolytic domain boundary (EDB) of Ce 0.8Gd 0.1Bi 0.1O 2- δ is found to be 1.2 × 10 -19 atm, which is relatively lower than that of the singly doped samples. The thermal expansion coefficients, determined from high-temperature X-ray data are 11.6 × 10 -6 K -1 for the CeO 2, 12.1 × 10 -6 K -1 for Ce 0.8Gd 0.2O 2- δ, and increase with co-doping to 14.2 × 10 -6 K -1 for Ce 0.8Gd 0.18Bi 0.02O 2- δ. The maximum power densities for the single cell based on the codoped samples are higher than that of the singly doped sample. These results suggest that co-doping can further improve the electrical performance of ceria-based electrolytes.

  18. Rationalization of interactions in precious metal/ceria catalysts using the d-band center model.

    PubMed

    Acerbi, N; Tsang, S C Edman; Jones, G; Golunski, S; Collier, P

    2013-07-22

    A correlation between ceria reducibility and the precious-metal d-band center is reported for ceria-supported precious-metal catalysts. The results could provide the missing link to fully explain the occurrence of strong metal-support interaction (SMSI) and hydrogen spillover in catalysts that consist of dispersed metals in contact with reducible metal oxides. PMID:23780919

  19. CSA doped polypyrrole-zinc oxide thin film sensor

    NASA Astrophysics Data System (ADS)

    Chougule, M. A.; Jundale, D. M.; Raut, B. T.; Sen, Shashwati; Patil, V. B.

    2013-02-01

    The polypyrrole-zinc oxide (PPy-ZnO) hybrid sensor doped with different weight ratios of camphor sulphonic acid (CSA) were prepared by spin coating technique. These CSA doped PPy-ZnO hybrids were characterized by field emission scanning electron microscope (FESEM) and fourier transform infrared (FTIR) which proved the formation of polypyrrole, PPy-ZnO and the interaction between polypyrrole - ZnO (PPy-ZnO) hybrid with CSA doping. The gas sensing properties of the PPy-ZnO hybrid films doped with CSA have been studied for oxidizing (NO2) as well as reducing (H2S, NH3, CH4OH and CH3OH) gases at room temperature. We demonstrate that CSA doped PPy-ZnO hybrid films are highly selective to NO2 along with high-sensitivity at low concentration (80% to 100 ppm) and better stability, which suggested that the CSA doped PPy-ZnO hybrid films are potential candidate for NO2 detection at room temperature.

  20. Molten carbonate fuel cell cathode with mixed oxide coating

    DOEpatents

    Hilmi, Abdelkader; Yuh, Chao-Yi

    2013-05-07

    A molten carbonate fuel cell cathode having a cathode body and a coating of a mixed oxygen ion conductor materials. The mixed oxygen ion conductor materials are formed from ceria or doped ceria, such as gadolinium doped ceria or yttrium doped ceria. The coating is deposited on the cathode body using a sol-gel process, which utilizes as precursors organometallic compounds, organic and inorganic salts, hydroxides or alkoxides and which uses as the solvent water, organic solvent or a mixture of same.

  1. Self-limited kinetics of electron doping in correlated oxides

    SciTech Connect

    Chen, Jikun Zhou, You; Jiang, Jun; Shi, Jian; Ramanathan, Shriram; Middey, Srimanta; Chakhalian, Jak; Chen, Nuofu; Chen, Lidong; Shi, Xun; Döbeli, Max

    2015-07-20

    Electron doping by hydrogenation can reversibly modify the electrical properties of complex oxides. We show that in order to realize large, fast, and reversible response to hydrogen, it is important to consider both the electron configuration on the transition metal 3d orbitals, as well as the thermodynamic stability in nickelates. Specifically, large doping-induced resistivity modulations ranging several orders of magnitude change are only observed for rare earth nickelates with small ionic radii on the A-site, in which case both electron correlation effects and the meta-stability of Ni{sup 3+} are important considerations. Charge doping via metastable incorporation of ionic dopants is of relevance to correlated oxide-based devices where advancing approaches to modify the ground state electronic properties is an important problem.

  2. Investigation of tungsten doped tin oxide thin film transistors

    NASA Astrophysics Data System (ADS)

    Yang, Jianwen; Meng, Ting; Yang, Zhao; Cui, Can; Zhang, Qun

    2015-11-01

    Tungsten doped tin oxide thin film transistors (TWO-TFTs) were fabricated by radio frequency magnetron sputtering. With TWO thin films as the channel layers, the TFTs show lower off-current and positive shift turn-on voltage than the intrinsic tin oxide TFTs, which can be explained by the reason that W doping is conducive to suppress the carrier concentration of the TWO channel layer. It is important to elect an appropriate channel thickness for improving the TFT performance. The optimum TFT performance in enhancement mode is achieved at W doping content of 2.7 at% and channel thickness of 12 nm, with the saturation mobility, turn-on voltage, subthreshold swing value and on-off current ratio of 5 cm2 V-1 s-1, 0.4 V, 0.4 V/decade and 2.4  ×  106, respectively.

  3. Chemical vapor deposition of fluorine-doped zinc oxide

    DOEpatents

    Gordon, Roy G.; Kramer, Keith; Liang, Haifan

    2000-06-06

    Fims of fluorine-doped zinc oxide are deposited from vaporized precursor compounds comprising a chelate of a dialkylzinc, such as an amine chelate, an oxygen source, and a fluorine source. The coatings are highly electrically conductive, transparent to visible light, reflective to infrared radiation, absorbing to ultraviolet light, and free of carbon impurity.

  4. Process for fabricating doped zinc oxide microsphere gel

    DOEpatents

    Arnold, Jr., Wesley D.; Bond, Walter D.; Lauf, Robert J.

    1991-01-01

    A new composition and method of making same for a doped zinc oxide microsphere and articles made therefrom for use in an electrical surge arrestor which has increased solid content, uniform grain size and is in the form of a gel.

  5. Process for fabricating doped zinc oxide microsphere gel

    DOEpatents

    Arnold, W.D. Jr.; Bond, W.D.; Lauf, R.J.

    1991-11-05

    Disclosed are a new composition and method of making same for a doped zinc oxide microsphere and articles made therefrom for use in an electrical surge arrestor which has increased solid content, uniform grain size and is in the form of a gel. 4 figures.

  6. Metal oxide charge transport material doped with organic molecules

    DOEpatents

    Forrest, Stephen R.; Lassiter, Brian E.

    2016-08-30

    Doping metal oxide charge transport material with an organic molecule lowers electrical resistance while maintaining transparency and thus is optimal for use as charge transport materials in various organic optoelectronic devices such as organic photovoltaic devices and organic light emitting devices.

  7. Reversibility of hydrogen chemisorption on a ceria-supported rhodium catalyst

    SciTech Connect

    Bernal, S.; Calvino, J.J.; Cifredo, G.A.; Izquierdo, J.M. Rodriguez ); Perrichon, V.; Laachir, A. )

    1992-09-01

    Cerium dioxide is an important component of the so-called three-way catalysts. This work reports on some new aspects of the chemistry of hydrogen-ceria systems. It is shown that, at room temperature, in the presence of highly dispersed rhodium, ceria chemisorbs large amounts of hydrogen. As deduced from magnetic measurements carried out in situ, this spillover process leads to the reduction of ceria to an extent of 21% of the total amount of cerium ions present in the sample, which is roughly equivalent to the complete surface reduction of the oxide. It is found that over a highly hydroxylated sample the reduction of ceria induced by the spillover process is partly reversible even at 295 K. If the sample is pumped off at 773 K, the initial oxidation state of ceria is almost completely recovered. Both the rate and extent of hydrogen chemisorption on ceria were found to be sensitive to the specific pretreatment applied to the catalyst. Over bare ceria, hydrogen chemisorption at 298 K was negligible, temperatures as high as 473 K being necessary to activate the process. In contrast to the rhodium-containing catalyst, over pure ceria the desorption of hydrogen leads to a much larger extent to water formation, thus revealing a deeper irreversible reduction of the oxide.

  8. Combustion Synthesis of Doped Thermoelectric Oxides

    SciTech Connect

    Selig, Jiri; Lin, Sidney; Lin, Hua-Tay; Johnson, D Ray

    2012-01-01

    Self-propagating high-temperature synthesis (SHS) was used to prepare silver doped calcium cobaltates (Ca1.24- xAgxCo1.62O3.86, x = 0.03 - 0.12) powders. SHS is a simple and economic process to synthesize ceramic materials with minimum energy requirements. The heat generated by the SHS reaction can sustain the propagation of the reaction front and convert reactants to desired products. The effect of doping level on thermoelectric properties was investigated in this study. Results show the substitution of calcium by silver decreases the thermal conductivity significantly. XRD and surface area measurements show synthesized powders are phase pure and have large specific surface areas.

  9. Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films.

    PubMed

    Figueroa, A I; van der Laan, G; Harrison, S E; Cibin, G; Hesjedal, T

    2016-01-01

    The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi(3+) in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state. PMID:26956771

  10. Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films

    PubMed Central

    Figueroa, A. I.; van der Laan, G.; Harrison, S. E.; Cibin, G.; Hesjedal, T.

    2016-01-01

    The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi3+ in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state. PMID:26956771

  11. Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films

    NASA Astrophysics Data System (ADS)

    Figueroa, A. I.; van der Laan, G.; Harrison, S. E.; Cibin, G.; Hesjedal, T.

    2016-03-01

    The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi3+ in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state.

  12. Measuring bandgap states in individual non-stoichiometric oxide nanoparticles using monochromated STEM EELS: The Praseodymium-ceria case.

    PubMed

    Bowman, W J; March, K; Hernandez, C A; Crozier, P A

    2016-08-01

    We describe a method to perform high spatial resolution measurement of the position and density of inter-band impurity states in non-stoichiometric oxides using ultra-high energy resolution electron energy-loss spectroscopy (EELS). This can be employed to study optical and electronic properties of atomic and nanoscale defects in electrically-conducting and optically-active oxides. We employ a monochromated scanning transmission electron microscope with subnanometer diameter electron probe, making this technique suitable for correlating spectroscopic information with high spatial resolution images from small objects such as nanoparticles, surfaces or interfaces. The specific experimental approach outlined here provides direct measurement of the Pr inter-band impurity states in Pr0.1Ce0.9O2-δ via valence-loss EELS, which is interpreted with valence-loss spectral simulation based on density of states data to determine the energy level and character of the inter-band state. Additionally, observation of optical color change upon chemically-induced oxygen non-stoichiometry indicates that the population of the inter-band state is accompanied by an energy level shift within the bandgap. PMID:27152715

  13. Sulphur mustard degradation on zirconium doped Ti-Fe oxides.

    PubMed

    Štengla, Václav; Grygar, Tomáš Matys; Opluštil, František; Němec, Tomáš

    2011-09-15

    Zirconium doped mixed nanodispersive oxides of Ti and Fe were prepared by homogeneous hydrolysis of sulphate salts with urea in aqueous solutions. Synthesized nanodispersive metal oxide hydroxides were characterised as the Brunauer-Emmett-Teller (BET) surface area and Barrett-Joiner-Halenda porosity (BJH), X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) microanalysis, and acid-base titration. These oxides were taken for an experimental evaluation of their reactivity with sulphur mustard (chemical warfare agent HD or bis(2-chloroethyl)sulphide). The presence of Zr(4+) dopant tends to increase both the surface area and the surface hydroxylation of the resulting doped oxides in such a manner that it can contribute to enabling the substrate adsorption at the oxide surface and thus accelerate the rate of degradation of warfare agents. The addition of Zr(4+) to the hydrolysis of ferric sulphate with urea shifts the reaction route and promotes formation of goethite at the expense of ferrihydrite. We discovered that Zr(4+) doped oxo-hydroxides of Ti and Fe exhibit a higher degradation activity towards sulphur mustard than any other yet reported reactive sorbents. The reaction rate constant of the slower parallel reaction of the most efficient reactive sorbents is increased with the increasing amount of surface base sites. PMID:21775058

  14. Nitrogen doped zinc oxide thin film

    SciTech Connect

    Li, Sonny X.

    2003-12-15

    To summarize, polycrystalline ZnO thin films were grown by reactive sputtering. Nitrogen was introduced into the films by reactive sputtering in an NO{sub 2} plasma or by N{sup +} implantation. All ZnO films grown show n-type conductivity. In unintentionally doped ZnO films, the n-type conductivities are attributed to Zn{sub i}, a native shallow donor. In NO{sub 2}-grown ZnO films, the n-type conductivity is attributed to (N{sub 2}){sub O}, a shallow double donor. In NO{sub 2}-grown ZnO films, 0.3 atomic % nitrogen was found to exist in the form of N{sub 2}O and N{sub 2}. Upon annealing, N{sub 2}O decomposes into N{sub 2} and O{sub 2}. In furnace-annealed samples N{sub 2} redistributes diffusively and forms gaseous N{sub 2} bubbles in the films. Unintentionally doped ZnO films were grown at different oxygen partial pressures. Zni was found to form even at oxygen-rich condition and led to n-type conductivity. N{sup +} implantation into unintentionally doped ZnO film deteriorates the crystallinity and optical properties and leads to higher electron concentration. The free electrons in the implanted films are attributed to the defects introduced by implantation and formation of (N{sub 2}){sub O} and Zni. Although today there is still no reliable means to produce good quality, stable p-type ZnO material, ZnO remains an attractive material with potential for high performance short wavelength optoelectronic devices. One may argue that gallium nitride was in a similar situation a decade ago. Although we did not obtain any p-type conductivity, we hope our research will provide a valuable reference to the literature.

  15. Theoretical Study of Sulphur Interaction with Ceria

    SciTech Connect

    Baranek, Ph.; Gauthier, L.; Marrony, M.

    2007-12-26

    Sulphur-containing molecules are responsible for the poisoning of catalysts used in many chemical processes such as fuel processing for hydrogen production and for fuel cells. An option which would constitute a breakthrough in this field would be to develop sulphur tolerant catalysts. Ceria (CeO{sub 2}) is an important ceramic material exploited in a wide range of applications such as solid oxide fuel cells. Then it is important to understand its surface catalytic properties. The adsorption of S, H{sub 2}S and other S-containing compounds on different surfaces of ceria are investigated at the ab initio quantum mechanical level, by using the periodic CRYSTAL06 code. In this extended abstract, we focus on the S adsorption on the stoichiometric (111), (110) and (100) surfaces of ceria. The equilibrium lattice parameters of CeO{sub 2}, surface stabilities, and S adsorption energies have been evaluated. The calculations have been performed at the Hartree-Fock (HF), density functional theory (DFT) and hybrid levels. A good agreement between calculated, and, other theoretical and experimental various properties has been found with hybrid approximations. The role of f orbitals of Ce is commented.

  16. Theoretical Study of Sulphur Interaction with Ceria

    NASA Astrophysics Data System (ADS)

    Baranek, Ph.; Gauthier, L.; Marrony, M.

    2007-12-01

    Sulphur-containing molecules are responsible for the poisoning of catalysts used in many chemical processes such as fuel processing for hydrogen production and for fuel cells. An option which would constitute a breakthrough in this field would be to develop sulphur tolerant catalysts. Ceria (CeO2) is an important ceramic material exploited in a wide range of applications such as solid oxide fuel cells. Then it is important to understand its surface catalytic properties. The adsorption of S, H2S and other S-containing compounds on different surfaces of ceria are investigated at the ab initio quantum mechanical level, by using the periodic CRYSTAL06 code. In this extended abstract, we focus on the S adsorption on the stoichiometric (111), (110) and (100) surfaces of ceria. The equilibrium lattice parameters of CeO2, surface stabilities, and S adsorption energies have been evaluated. The calculations have been performed at the Hartree-Fock (HF), density functional theory (DFT) and hybrid levels. A good agreement between calculated, and, other theoretical and experimental various properties has been found with hybrid approximations. The role of f orbitals of Ce is commented.

  17. Study of the doping of thermally evaporated zinc oxide thin films with indium and indium oxide

    NASA Astrophysics Data System (ADS)

    Palimar, Sowmya; Bangera, Kasturi V.; Shivakumar, G. K.

    2013-12-01

    The present paper reports observations made on investigations carried out to study structural, optical and electrical properties of thermally evaporated ZnO thin films and their modulations on doping with metallic indium and indium oxide separately. ZnO thin film in the undoped state is found to have a very good conductivity of 90 Ω-1 cm-1 with an excellent transmittance of up to 90 % in the visible region. After doping with metallic indium, the conductivity of the film is found to be 580 Ω-1 cm-1, whereas the conductivity of indium oxide-doped films is increased up to 3.5 × 103 Ω-1 cm-1. Further, the optical band gap of the ZnO thin film is widened from 3.26 to 3.3 eV when doped with indium oxide and with metallic indium it decreases to 3.2 eV. There is no considerable change in the transmittance of the films after doping. All undoped and doped films were amorphous in nature with smooth and flat surface without significant modifications due to doping.

  18. Pt/Ceria-based Catalysts for Small Alcohol Electrooxidation

    NASA Astrophysics Data System (ADS)

    Menendez-Mora, Christian L.

    High emissions of fossil-based energy sources have led to scientists around the world to develop new alternatives for the future. In this sense, fuel cells are a remarkable and promising energy option with less environmental impact. The most used fuels for this technology are hydrogen and small chain alcohols, which can be oxidized to transform their chemical energy into electrical power. To do this, fuel cells need catalysts that will act as an active surface where the oxidation can take place. The problem with platinum catalysts is its possible CO poisoning with intermediates that are produced before the complete oxidation of alcohol to CO2. Different approaches have been taken to try to resolve this issue. In this case, cerium oxide (ceria) was selected as a co-catalyst to mitigate the effect of CO poisoning of platinum. Ceria is a compound that has the ability to work as an "oxygen tank" and can donate oxygen to carbon monoxide that is strongly adsorbed at platinum surface to produce CO2 (carbon dioxide), regenerating the Pt surface for further alcohol oxidation. Therefore, enhancing the current density as well as the power output of a fuel cell. First, an occlusion deposition technique was used to prepare platinum/ceria composite electrodes and tested them towards small chain alcohol oxidation such as methanol oxidation reaction in acidic and alkaline media. The preliminary results demonstrated that the Pt/ceria electrodes were more efficient towards methanol electrooxidation when compared to Pt electrodes. This enhancement was attributed to the presence of ceria. A second preparation method was selected for the synthesis of ceria/Pt catalysts. In this case, a hydrothermal method was used and the catalysis were studied for the effect of MeOH, EtOH and n-BuOH oxidation. The observed effect was that electrodes made of Pt/Pt:CeO2-x showed better catalytic effect than Pt/ceria and platinum electrodes. Moreover, a comparison between ceria nanorods versus

  19. Organic solar cells on indium tin oxide and aluminum doped zinc oxide anodes

    NASA Astrophysics Data System (ADS)

    Schulze, Kerstin; Maennig, Bert; Leo, Karl; Tomita, Yuto; May, Christian; Hüpkes, Jürgen; Brier, Eduard; Reinold, Egon; Bäuerle, Peter

    2007-08-01

    The authors compare organic solar cells using two different transparent conductive oxides as anode: indium tin oxide (ITO) and three kinds of aluminum doped zinc oxide (ZAO). These anodes with different work functions are used for small molecule photovoltaic devices based on an oligothiophene derivative as donor and fullerene C60 as acceptor molecule. It turns out that cells on ITO and ZAO have virtually identical properties. In particular, the authors demonstrate that the work function of the anode does not influence the Voc of the photovoltaic device due to the use of doped transport layers.

  20. Periodic macroporous nanocrystalline antimony-doped tin oxide electrode.

    PubMed

    Arsenault, Eric; Soheilnia, Navid; Ozin, Geoffrey A

    2011-04-26

    Optically transparent and electrically conductive electrodes are ubiquitous in the myriad world of devices. They are an indispensable component of solar and photoelectrochemical cells, organic and polymer light emitting diodes, lasers, displays, electrochromic windows, photodetectors, and chemical sensors. The majority of the electrodes in such devices are made of large electronic band-gap doped metal oxides fashioned as a dense low-surface-area film deposited on a glass substrate. Typical transparent conducting oxide materials include indium-, fluorine-, or antimony-doped tin oxides. Herein we introduce for the first time a transparent conductive periodic macroporous electrode that has been self-assembled from 6 nm nanocrystalline antimony-doped tin oxide with high thermal stability, optimized electrical conductivity, and high quality photonic crystal properties, and present an electrochemically actuated optical light switch built from this electrode, whose operation is predicated on its unique combination of electrical, optical, and photonic properties. The ability of this macroporous electrode to host active functional materials like dyes, polymers, nanocrystals, and nanowires provides new opportunities to create devices with improved performance enabled by the large area, spatially accessible and electroactive internal surface. PMID:21391718

  1. Selection Rule of Preferred Doping Site for n-Type Oxides

    SciTech Connect

    Li, C.; Li, J.; Li, S. S.; Xia, J. B.; Wei, S. H.

    2012-06-25

    Using first-principles calculations and analysis, we show that to create shallow n-type dopants in oxides, anion site doping is preferred for more covalent oxides such as SnO{sub 2} and cation site doping is preferred for more ionic oxides such as ZnO. This is because for more ionic oxides, the conduction band minimum (CBM) state actually contains a considerable amount of O 3s orbitals, thus anion site doping can cause large perturbation on the CBM and consequently produces deeper donor levels. We also show that whether it is cation site doping or anion site doping, the oxygen-poor condition should always be used.

  2. Cerium(IV) Hexanuclear Clusters from Cerium(III) Precursors: Molecular Models for Oxidative Growth of Ceria Nanoparticles.

    PubMed

    Mathey, Laurent; Paul, Mitali; Copéret, Christophe; Tsurugi, Hayato; Mashima, Kazushi

    2015-09-14

    Reactions of cerium(III) nitrate, Ce(NO3 )3 ⋅6 H2 O, with different carboxylic acids, such as pivalic acid, benzoic acid, and 4-methoxybenzoic acid, in the presence of a tridentate N,N,N-donor ligand, diethylenetriamine (L(1) ), under aerobic conditions yielded the corresponding cerium hexamers Ce6 O8 (O2 CtBu)8 (L(1) )4 (1), Ce6 O8 (O2 CC6 H5 )8 (L(1) )4 (2), and Ce6 O8 (O2 CC6 H4 -4-OCH3 )8 (L(1) )4 (3). Hexamers 1, 2, and 3 contain the same octahedral Ce(IV) 6 O8 core, in which all interstitial oxygen atoms are connected by μ3 -oxo bridging ligands. In contrast, treatment of the Ce(IV) precursor (NH4 )2 Ce(NO3 )6 (CAN) with pivalic acid and the ligand L(1) under the same conditions afforded Ce6 O4 (OH)4 (O2 CtBu)12 (L(1) )2 (4), exhibiting a deformed octahedral Ce(IV) 6 O4 (OH)4 core containing μ3 -oxo and μ3 -hydroxo moieties in defined positions. In contrast to the formation of 1-3, the use of N-methyldiethanolamine (L) in the reaction with Ce(NO3 )3 ⋅6 H2 O and pivalic acid afforded a previously reported Ce(III) dinuclear cluster, Ce2 (O2 CtBu)6 L2 , even in the presence of dioxygen. ESI-MS analysis of the reaction mixture clearly indicated the importance of the ligand L(1) in promoting oxidation of the Ce(III) aggregates, [Cen (O2 CtBu)3n (L(1) )2 ], which is necessary for the formation of Ce(IV) hexamers. PMID:26236034

  3. Silica-Ceria Hybrid Nanostructures

    SciTech Connect

    Munusamy, Prabhakaran; Sanghavi, Shail P.; Nachimuthu, Ponnusamy; Baer, Donald R.; Thevuthasan, Suntharampillai

    2012-04-25

    A new hybrid material system that consists of ceria attached silica nanoparticles has been developed. Because of the versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and antioxidant properties of ceria nanoparticles, this material system is ideally suited for biomedical applications. The silica particles of size ~50nm were synthesized by the Stöber synthesis method and ceria nanoparticles of size ~2-3nm was attached to the silica surface using a hetrocoagulation method. The presence of silanol groups on the surface of silica particles mediated homogenous nucleation of ceria which were attached to silica surface by Si-O-Ce bonding. The formations of silica-ceria hybrid nanostructures were characterized by X-photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The HRTEM image confirms the formation of individual crystallites of ceria nanoparticles attached to the silica surface. The XPS analysis indicates that ceria nanoparticles are chemically bonded to surface of silica and possess mixture of +3 and +4 chemical states.

  4. Electronic doping of transition metal oxide perovskites

    NASA Astrophysics Data System (ADS)

    Cammarata, Antonio; Rondinelli, James M.

    2016-05-01

    CaFeO3 is a prototypical negative charge transfer oxide that undergoes electronic metal-insulator transition concomitant with a dilation and contraction of nearly rigid octahedra. Altering the charge neutrality of the bulk system destroys the electronic transition, while the structure is significantly modified at high charge content. Using density functional theory simulations, we predict an alternative avenue to modulate the structure and the electronic transition in CaFeO3. Charge distribution can be modulated using strain-rotation coupling and thin film engineering strategies, proposing themselves as a promising avenue for fine tuning electronic features in transition metal-oxide perovskites.

  5. Enhanced electrochromism in cerium doped molybdenum oxide thin films

    SciTech Connect

    Dhanasankar, M.; Purushothaman, K.K.; Muralidharan, G.

    2010-12-15

    Cerium (5-15% by weight) doped molybdenum oxide thin films have been prepared on FTO coated glass substrate at 250 {sup o}C using sol-gel dip coating method. The structural and morphological changes were observed with the help of XRD, SEM and EDS analysis. The amorphous structure of the Ce doped samples, favours easy intercalation and deintercalation processes. Mo oxide films with 10 wt.% of Ce exhibit maximum anodic diffusion coefficient of 24.99 x 10{sup -11} cm{sup 2}/s and the change in optical transmittance of ({Delta}T at 550 nm) of 79.28% between coloured and bleached state with the optical density of ({Delta}OD) 1.15.

  6. Nitrogen-doped reduced graphene oxide electrodes for electrochemical supercapacitors.

    PubMed

    Nolan, Hugo; Mendoza-Sanchez, Beatriz; Ashok Kumar, Nanjundan; McEvoy, Niall; O'Brien, Sean; Nicolosi, Valeria; Duesberg, Georg S

    2014-02-14

    Herein we use Nitrogen-doped reduced Graphene Oxide (N-rGO) as the active material in supercapacitor electrodes. Building on a previous work detailing the synthesis of this material, electrodes were fabricated via spray-deposition of aqueous dispersions and the electrochemical charge storage mechanism was investigated. Results indicate that the functionalised graphene displays improved performance compared to non-functionalised graphene. The simplicity of fabrication suggests ease of up-scaling of such electrodes for commercial applications. PMID:24418938

  7. Electrical Properties of Electrospun Sb-Doped Tin Oxide Nanofibers

    NASA Astrophysics Data System (ADS)

    León-Brito, Neliza; Melendez, Anamaris; Ramos, Idalia; Pinto, Nicholas J.; Santiago-Aviles, Jorge J.

    2007-03-01

    Transparent and conducting tin oxide fibers are of considerable interest for solar energy conversion, sensors and in various electrode applications. Appropriate doping can further enhance the conductivity of the fibers without loosing optical transparency. Undoped and antimony-doped tin oxide fibers have been synthesized by our group in previous work using electrospinning and metallorganic decomposition techniques. The undoped tin oxide fibers were obtained using a mixture of pure tin oxide sol made from tin (IV) chloride : water : propanol : isopropanol at a molar ratio of 1:9:9:6, and a viscous solution made from poly(ethylene oxide) (PEO) and chloroform at a ratio of 200 mg PEO/10 mL chloroform. In this work, antimony doped fibers were obtained by adding a dopant solution of antimony trichloride and isopropanol at a ratio of 2.2812 g antimony trichloride/10 ml isopropanol to the original tin oxide precursor solution. The Sb concentration in the precursor solution is 1.5%. After deposition, the fibers were sintered 600°C in air for two hours. The electrical conductivity of single fibers measured at room temperature increases by up to three orders of magnitude when compared to undoped fibers prepared using the same method. The resistivity change as a function of the annealing temperature can be attributed to the thermally activated formation of a nearly stoichoimetric solid. The resistivity of the fibers changes monotonically with temperature from 714Ω-cm at 2 K to 0.1Ω-cm at 300 K. In the temperature range from 2 to 8 K the fibers have a positive magnetoresistance (MR) with the highest value of 155 % at 2 K and ±9 T. At temperatures of 10 and 12 K the sign of MR changes to negative values for low magnetic fields and positive for high magnetic fields. For higher temperatures (15 K and above) the MR becomes negative and its magnitude decreases with temperature.

  8. The effect of Nd on the properties of ceria-zirconia solid solution and the catalytic performance of its supported Pd-only three-way catalyst for gasoline engine exhaust reduction.

    PubMed

    Wang, Qiuyan; Li, Guangfeng; Zhao, Bo; Zhou, Renxian

    2011-05-15

    A series of ceria-zirconia-neodymia mixed oxides with different contents of neodymia and the supported Pd-only three-way catalysts before and after aging have been prepared and characterized. The influence of Nd doping on the structural/textural properties of ceria-zirconia (CZ) and the effect on the three-way catalytic performance are also investigated. The results demonstrate that the addition of neodymia results in the formation of ceria-zirconia-neodymia ternary solid solution (CZN) with better textural and structural properties as well as improved reducibility and redox behavior, leading to the promoted three-way catalytic activity and enlarged air/fuel operation window. The modified solid solution with 5 wt.% neodymia shows the preferable textural/structural properties considering that the capacity of foreign cation is limited in the crystal lattice of ceria-zirconia solid solution, and Pd/CZN5 shows the optimum three-way catalytic performance and wider air/fuel operation window, especially for the corresponding aged one. PMID:21371821

  9. Photochemical doping of graphene oxide with nitrogen for photoluminescence enhancement

    NASA Astrophysics Data System (ADS)

    Liu, Fuchi; Tang, Nujiang; Tang, Tao; Liu, Yuan; Feng, Qian; Zhong, Wei; Du, Youwei

    2013-09-01

    Nitrogen-doped graphene oxide (NGO) was synthesized by irradiation of graphene oxide (GO) in NH3 atmosphere. NGO obtained by irradiation of GO for 10 min has high N content of 13.62 at. %. The photoluminescence (PL) properties of NGO were investigated. The results showed that compared with GO, NGO exhibits significant PL enhancement with a high enhancement ratio of approximately 1501.57%. It may attribute to the high content of amino-like N, which can effectively enhance PL of GO because of the amino conjugation effect.

  10. Photochemical doping of graphene oxide with nitrogen for photoluminescence enhancement

    SciTech Connect

    Liu, Fuchi; Tang, Nujiang; Tang, Tao; Liu, Yuan; Feng, Qian; Zhong, Wei; Du, Youwei

    2013-09-16

    Nitrogen-doped graphene oxide (NGO) was synthesized by irradiation of graphene oxide (GO) in NH{sub 3} atmosphere. NGO obtained by irradiation of GO for 10 min has high N content of 13.62 at. %. The photoluminescence (PL) properties of NGO were investigated. The results showed that compared with GO, NGO exhibits significant PL enhancement with a high enhancement ratio of approximately 1501.57%. It may attribute to the high content of amino-like N, which can effectively enhance PL of GO because of the amino conjugation effect.

  11. Probing adsorption sites for CO on ceria.

    PubMed

    Mudiyanselage, Kumudu; Kim, Hyun You; Senanayake, Sanjaya D; Baber, Ashleigh E; Liu, Ping; Stacchiola, Dario

    2013-10-14

    Ceria based catalysts show remarkable activity for CO conversion reactions such as CO oxidation and the water-gas shift reaction. The identification of adsorption sites on the catalyst surfaces is essential to understand the reaction mechanisms of these reactions, but the complexity of heterogeneous powder catalysts and the propensity of ceria to easily change oxidation states in the presence of small concentrations of either oxidizing or reducing agents make the process difficult. In this study, the adsorption of CO on CuOx/Cu(111) and CeOx/Cu(111) systems has been studied using infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. IR peaks for the adsorbed CO on O/Cu(111) with only chemisorbed oxygen, well-ordered Cu2O/Cu(111) and disordered copper oxide [CuOx/Cu(111)] were observed at 2070-2072, 2097-2098 and 2101-2111 cm(-1), respectively. On CeOx/Cu(111) systems CO chemisorbs at 90 K only on Cu sites under ultra-high vacuum (UHV) conditions, whereas at elevated CO pressures and low temperatures adsorption of CO on Ce(3+) is observed, with a corresponding IR peak at 2162 cm(-1). These experimental results are further supported by DFT calculations, and help to unequivocally distinguish the presence of Ce(3+) cations on catalyst samples by using CO as a probe molecule. PMID:23942870

  12. Macro- and microscopic properties of strontium doped indium oxide

    SciTech Connect

    Nikolaenko, Y. M.; Kuzovlev, Y. E.; Medvedev, Y. V.; Mezin, N. I.; Fasel, C.; Gurlo, A.; Schlicker, L.; Bayer, T. J. M.; Genenko, Y. A.

    2014-07-28

    Solid state synthesis and physical mechanisms of electrical conductivity variation in polycrystalline, strontium doped indium oxide In{sub 2}O{sub 3}:(SrO){sub x} were investigated for materials with different doping levels at different temperatures (T = 20–300 °C) and ambient atmosphere content including humidity and low pressure. Gas sensing ability of these compounds as well as the sample resistance appeared to increase by 4 and 8 orders of the magnitude, respectively, with the doping level increase from zero up to x = 10%. The conductance variation due to doping is explained by two mechanisms: acceptor-like electrical activity of Sr as a point defect and appearance of an additional phase of SrIn{sub 2}O{sub 4}. An unusual property of high level (x = 10%) doped samples is a possibility of extraordinarily large and fast oxygen exchange with ambient atmosphere at not very high temperatures (100–200 °C). This peculiarity is explained by friable structure of crystallite surface. Friable structure provides relatively fast transition of samples from high to low resistive state at the expense of high conductance of the near surface layer of the grains. Microscopic study of the electro-diffusion process at the surface of oxygen deficient samples allowed estimation of the diffusion coefficient of oxygen vacancies in the friable surface layer at room temperature as 3 × 10{sup −13} cm{sup 2}/s, which is by one order of the magnitude smaller than that known for amorphous indium oxide films.

  13. Ozonation of bezafibrate over ceria and ceria supported on carbon materials.

    PubMed

    Gonçalves, Alexandra G; Órfão, José J M; Pereira, Manuel Fernando R

    2015-01-01

    Two catalysts containing ceria dispersed on the surface of multi-walled carbon nanotubes and activated carbon were investigated as ozonation catalysts for the mineralization of bezafibrate (BZF). The results were compared with those obtained in the absence of the catalyst and in the presence of the parent carbon materials, as well as in the presence of ceria (CeO2). Carbon materials containing ceria showed an interesting catalytic effect. Both materials enhanced the mineralization of BZF relatively to single ozonation and ozonation catalysed by the corresponding carbon materials. In the catalytic ozonation with these materials, both surface and bulk reactions are supposed to occur. The BZF ozonation catalysed by CeO2 leaded to the highest mineralization degrees, indicating that the reaction mechanism followed in the presence of CeO2 (free radical oxidation in solution) leads to the formation of intermediates more easily degradable, mainly after 120 min of reaction. Some primary products and refractory final oxidation compounds in single and catalytic ozonation of BZF were followed. The original chlorine present on the BZF molecule is completely converted to chloride anion and part of the nitrogen is mainly converted to NO3- along with smaller amounts of NO2- and NH4+. Microtox tests revealed that simultaneous use of ozone and CeO2 originated lower acute toxicity. PMID:25189707

  14. A new symmetric solid oxide fuel cell with a samaria-doped ceria framework and a silver-infiltrated electrocatalyst

    NASA Astrophysics Data System (ADS)

    Lin, Ye; Su, Chao; Huang, Cheng; Kim, Ju Sik; Kwak, Chan; Shao, Zongping

    2012-01-01

    A new symmetric SOFC with an SDC framework and a silver-infiltrated electrocatalyst is presented for the first time in this paper. A three-electrode polarization test shows that the Ag-SDC has a low area specific resistance of 1.07 Ω cm2 at 600 °C, a low activation energy of 85 kJ mol-1 and high exchange current densities of 428.2 and 129.0 mA cm-2 at 750 and 650 °C, respectively, when it is used as an oxygen reduction electrode. It also exhibits low polarization resistance in a humidified hydrogen atmosphere. A symmetric single cell is used in real fuel cell conditions to deliver peak power densities of 200 and 84 mW cm-2 at 750 and 650 °C, respectively, when humidified hydrogen is used as a fuel and ambient air is used as the cathode atmosphere. The cell still reaches a peak power density of 81 mW cm-2 at 750 °C when operating on CO. O2-TPO analysis demonstrates that the Ag-SDC electrode has even better coking resistance than the pure SDC scaffold. The results indicate that Ag-SDC|SDC|Ag-SDC symmetric cells with an infiltrated silver electrocatalyst are a promising new type of fuel cell for use with both hydrogen fuel and carbon-containing fuels.

  15. Highly Conducting Transparent Indium-Doped Zinc Oxide Thin Films

    NASA Astrophysics Data System (ADS)

    Singh, Budhi; Ghosh, Subhasis

    2014-09-01

    Highly conducting transparent indium-doped zinc oxide (IZO) thin films have been achieved by controlling different growth parameters using radio frequency magnetron sputtering. The structural, electrical, and optical properties of the IZO thin films have been investigated for varied indium content and growth temperature ( T G) in order to find out the optimum level of doping to achieve the highest conducting transparent IZO thin films. The highest mobility and carrier concentration of 11.5 cm2/V-s and 3.26 × 1020 cm-3, respectively, have been achieved in IZO doped with 2% indium. It has been shown that as T G of the 2% IZO thin films increase, more and more indium atoms are substituted into Zn sites leading to shift in (002) peaks towards higher angles which correspond to releasing the stress within the IZO thin film. The minimum resistivity of 5.3 × 10-4 Ω-cm has been achieved in 2% indium-doped IZO grown at 700°C.

  16. Rare earth doped zinc oxide varistors

    DOEpatents

    McMillan, April D.; Modine, Frank A.; Lauf, Robert J.; Alim, Mohammad A.; Mahan, Gerald D.; Bartkowiak, Miroslaw

    1998-01-01

    A varistor includes a Bi-free, essentially homogeneous sintered body of a ceramic composition including, expressed as nominal weight %, 0.2-4.0% oxide of at least one rare earth element, 0.5-4.0% Co.sub.3 O.sub.4, 0.05-0.4% K.sub.2 O, 0.05-0.2% Cr.sub.2 O.sub.3, 0-0.2% CaO, 0.00005-0.01% Al.sub.2 O.sub.3, 0-2% MnO, 0-0.05% MgO, 0-0.5% TiO.sub.3, 0-0.2% SnO.sub.2, 0-0.02% B.sub.2 O.sub.3, balance ZnO.

  17. Rare earth doped zinc oxide varistors

    DOEpatents

    McMillan, A.D.; Modine, F.A.; Lauf, R.J.; Alim, M.A.; Mahan, G.D.; Bartkowiak, M.

    1998-12-29

    A varistor includes a Bi-free, essentially homogeneous sintered body of a ceramic composition including, expressed as nominal weight %, 0.2--4.0% oxide of at least one rare earth element, 0.5--4.0% Co{sub 3}O{sub 4}, 0.05--0.4% K{sub 2}O, 0.05--0.2% Cr{sub 2}O{sub 3}, 0--0.2% CaO, 0.00005--0.01% Al{sub 2}O{sub 3}, 0--2% MnO, 0--0.05% MgO, 0--0.5% TiO{sub 3}, 0--0.2% SnO{sub 2}, 0--0.02% B{sub 2}O{sub 3}, balance ZnO. 4 figs.

  18. Electrochromism Properties of Palladium Doped Tungsten-Oxide Thin Films Prepared with RF Reactive Sputtering

    NASA Astrophysics Data System (ADS)

    Yabumoto, Taihei; Iwai, Yuki; Miura, Noboru; Matsumoto, Setsuko; Nakano, Ryotaro; Matsumoto, Hironaga

    Palladium doped tungsten oxide thin films were prepared by RF reactive sputtering in a mixture of argon and oxygen at room temperature. XRD patterns indicated that these films were amorphous. SEM imaging indicated a smaller grain size of palladium doped thin film compared with that of undoped tungsten oxide thin film. With electrochromism, palladium doped tungsten oxide exhibited a reverse optical modulation with respect to the applied potential.

  19. Electrical properties of tin-doped zinc oxide nanostructures doped at different dopant concentrations

    NASA Astrophysics Data System (ADS)

    Nasir, M. F.; Zainol, M. N.; Hannas, M.; Mamat, M. H.; Rahman, S. A.; Rusop, Mohamad

    2016-07-01

    This project has been focused on the electrical and optical properties respectively on the effect of Tin doped zinc oxide (ZnO) thin films at different dopant concentrations. These thin films were doped with different Sn dopant concentrations at 1 at%, 2 at%, 3 at%, 4 at% and 5 at% was selected as the parameter to optimize the thin films quality while the annealing temperature is fixed 500 °C. Sn doped ZnO solutions were deposited onto the glass substrates using sol-gel spin coating method. This project was involved with three phases, which are thin films preparation, deposition and characterization. The thin films were characterized using Current Voltage (I-V) measurement and ultraviolet-visible-near-infrared (UV-vis-NIR) spectrophotometer (Perkin Elmer Lambda 750) for electrical properties and optical properties. The electrical properties show that the resistivity is the lowest at 4 at% Sn doping concentration with the value 3.08 × 103 Ωcm-1. The absorption coefficient spectrum obtained shows all films exhibit very low absorption in the visible (400-800nm) and near infrared (NIR) (>800nm) range but exhibit high absorption in the UV range.

  20. The properties of Co- and Fe-doped GDC for low-temperature processing of solid oxide fuel cell by electron-beam evaporation.

    PubMed

    Yang, Seon-Ho; Kim, Kyung-Hwan; Choi, Hyung-Wook

    2013-08-01

    This study is transition metal oxides (FeO and CoO) were added to Gd-doped ceria (Gd0.1Ce0.9O1.95, GDC) powder for preparing the thin-film electrolyte used in the Ni-GDC anode-supported intermediate temperature solid oxide fuel cell (SOFC). Recently much attention was aimed at successful powder preparation with high sinter activity and conductivity. However, one of the challenges in preparing the GDC electrolytes is the densification issue. It is difficult to achieve the densification of GDC below 1600 degrees C. To overcome this drawback, attentions of the research on the densification of the GDC electrolyte is paid more on changing of the fabrication technology, the powder properties, and the sintering mechanism. Among them, Fe3+ and Co2+ showed the significant beneficial effect on the grain boundary conductivity. So, electrolyte powder made of Co- and Fe-doped GDC by solid-state reaction method. And thin-film electrolyte was fabricated on the presintered Ni-GDC cermet anode substrate by E-beam evaporating method and then co-sintered to form the electrolyte/anode bilayer. We realized crystal structure of Co and Fe doped Gd0.1Ce0.9O1.95 (GDC) electrolyte by X-ray diffraction (XRD). The morphology was measured by scanning electron microscopy (SEM) for the sintered samples were performed. The performance of the cells was evaluated over 500-800 degrees C using humidified hydrogen as fuel and air as oxidant. PMID:23882837

  1. Synthesis and characterization of magnesium doped cerium oxide for the fuel cell application

    NASA Astrophysics Data System (ADS)

    Kumar, Amit; Kumari, Monika; Kumar, Mintu; Kumar, Sacheen; Kumar, Dinesh

    2016-05-01

    Cerium oxide has attained much attentions in global nanotechnology market due to valuable application for catalytic, fuel additive, and widely as electrolyte in solid oxide fuel cell. Doped cerium oxide has large oxygen vacancies that allow for greater reactivity and faster ion transport. These properties make cerium oxide suitable material for SOFCs application. Cerium oxide electrolyte requires lower operation temperature which shows improvement in processing and the fabrication technique. In our work, we synthesized magnesium doped cerium oxide by the co-precipitation method. With the magnesium doping catalytic reactivity of CeO2 was increased. Synthesized nanoparticle were characterized by the XRD and UV absorption techniques.

  2. Morphological Control of Metal Oxide-Doped Zinc Oxide and Application to Cosmetics

    NASA Astrophysics Data System (ADS)

    Goto, Takehiro; Yin, Shu; Sato, Tsugio; Tanaka, Takumi

    2012-06-01

    Zinc oxide shows excellent transparency and ultraviolet radiation shielding ability, and is used for various cosmetics.1-3 However, it possesses high catalytic activity and lower dispersibility. Therefore, spherical particles of zinc oxide have been synthesized by soft solution reaction using zinc nitrate, ethylene glycol, sodium hydroxide and triethanolamine as starting materials. After dissolving these compounds in water, the solution was heated at 90°C for 1 h to form almost mono-dispersed spherical zinc oxide particles. The particle size changed depending on zinc ion concentration, ethylene glycol concentration and so on. Furthermore, with doping some metal ions, the phtocatalytic activity could be decreased. The obtained monodispersed metal ion-doped spherical zinc oxides showed excellent UV shielding ability and low photocatalytic activity. Therefore, they are expected to be used as cosmetics ingredients.

  3. Ce K edge XAS of ceria-based redox materials under realistic conditions for the two-step solar thermochemical dissociation of water and/or CO2.

    PubMed

    Rothensteiner, Matthäus; Sala, Simone; Bonk, Alexander; Vogt, Ulrich; Emerich, Hermann; van Bokhoven, Jeroen A

    2015-10-28

    X-ray absorption spectroscopy was used to characterise ceria-based materials under realistic conditions present in a reactor for solar thermochemical two-step water and carbon dioxide splitting. A setup suitable for in situ measurements in transmission mode at the cerium K edge from room temperature up to 1773 K is presented. Time-resolved X-ray absorption near-edge structure (XANES) data, collected for a 10 mol% hafnium-doped ceria sample (Ce0.9Hf0.1O2-δ) during reduction at 1773 K in a flow of inert gas and during re-oxidation by CO2 at 1073 K, enables the quantitative determination of the non-stoichiometry δ of the fluorite-type structure. XANES analysis suggests the formation of the hexagonal Ce2O3 phase upon reduction in 2% hydrogen/helium at 1773 K. We discuss the experimental limitations and possibilities of high-temperature in situ XAS at edges of lower energy as well as the importance of the technique for understanding and improving the properties of ceria-based oxygen storage materials for thermochemical solar energy conversion. PMID:26412705

  4. FETs Based on Doped Polyaniline/Polyethylene Oxide Fibers

    NASA Technical Reports Server (NTRS)

    Theofylaktos, Noulie; Robinson, Daryl; Miranda, Felix; Pinto, Nicholas; Johnson, Alan, Jr.; MacDiarmid, Alan; Mueller, Carl

    2006-01-01

    A family of experimental highly miniaturized field-effect transistors (FETs) is based on exploitation of the electrical properties of nanofibers of polyaniline/ polyethylene oxide (PANi/PEO) doped with camphorsulfonic acid. These polymer-based FETs have the potential for becoming building blocks of relatively inexpensive, low-voltage, highspeed logic circuits that could supplant complementary metal oxide/semiconductor (CMOS) logic circuits. The development of these polymerbased FETs offers advantages over the competing development of FETs based on carbon nanotubes. Whereas it is difficult to control the molecular structures and, hence, the electrical properties of carbon nanotubes, it is easy to tailor the electrical properties of these polymerbased FETs, throughout the range from insulating through semiconducting to metallic, through choices of doping levels and chemical manipulation of polymer side chains. A further advantage of doped PANi/PEO nanofibers is that they can be made to draw very small currents and operate at low voltage levels, and thus are promising for applications in which there are requirements to use many FETs to obtain large computational capabilities while minimizing power demands. Fabrication of an experimental FET in this family begins with the preparation of a substrate as follows: A layer of silicon dioxide between 50 and 200 nm thick is deposited on a highly doped (resistivity 0.01 W.cm) silicon substrate, then gold electrodes/contact stripes are deposited on the oxide. Next, one or more fibers of camphorsulphonic acid-doped PANi/PEO having diameters of the order of 100 nm are electrospun onto the substrate so as to span the gap between the gold electrodes (see Figure 1). Figure 2 depicts measured current-versus-voltage characteristics of the device of Figure 1, showing that saturation channel currents occur at source-todrain potentials that are surprisingly low, relative to those of CMOS FETs. The hole mobility in the depletion regime in

  5. Transparent conducting oxides: A δ-doped superlattice approach

    NASA Astrophysics Data System (ADS)

    Cooper, Valentino; Lee, Suyoun; Seo, Sung Seok; Kim, Jun Sung; Choi, Woo Seok; Okamoto, Satoshi; Lee, Ho Nyung

    2014-03-01

    Interfaces between dissimilar insulating oxides have been shown to exhibit intriguing phenomena such as metallic states, superconductivity and magnetism. Despite tremendous progress in understanding their origins, very little is known about how to control the conduction pathways and the distribution of charge carriers. Using first principles simulations we examine the effect of SrTiO3 (STO) spacer layer thickness on the physical and chemical properties of La δ-doped STO superlattices. In superlattices with relatively thin STO layers, we predict that three-dimensional conduction would occur due to appreciable overlap of the quantum mechanical wavefunctions between neighboring δ-doped layers. Experimentally these superlattices remain highly transparent to visible light; a direct consequence of the appropriately large gap between the O 2 p and Ti d states. These results highlight the potential for using superlattice thickness as a means for tuning the properties of oxide heterostructures with demonstrated importance for optoelectronic devices; providing a unique route for creating transparent conducting oxides. Supported by: U.S. D.O.E, Basic Energy Sciences, Materials Sciences and Engineering Division (V.R.C., W.S.C., H.N.L., S.O., S.S.A.S), the Office of Science Early Career Research Program (V.R.C) and the Korea Insitute of Technology (SL).

  6. Significant improvement in electronic properties of transparent amorphous indium zinc oxide through yttrium doping

    NASA Astrophysics Data System (ADS)

    Sun, Jian; Yu, Zhigen; Huang, Yanhua; Xia, Yijie; Lai, Weng Soon; Gong, Hao

    2014-04-01

    One big challenge in transparent conducting oxides (TCOs) is to achieve high conductivity and mobility at a low processing temperature. Although optimized conductivity has been achieved in indium zinc oxide (IZO) without doping, it is still interesting to find whether doping can improve conductivity of IZO further. In this paper, we report a low processing temperature achievement of high conductivity and mobility of IZO through yttrium (Y) doping. We found that with different Y doping levels, room temperature fabricated amorphous IZO (a-IZO) samples can be controlled to exhibit either metallic or semiconductor characteristics. Y2O3 is demonstrated to be an effective doping source to achieve conductivity 300% higher than the non-doped IZO sample. Anomalously improved mobility of certain Y2O3-doped IZO samples compared with the non-doped IZO sample is found and analyzed. Besides, a low-temperature resistivity anomaly (semiconductor metal transition) phenomenon is observed and discussed.

  7. Nanostructured gadolinium-doped ceria microsphere synthesis from ion exchange resin: Multi-scale in-situ studies of solid solution formation

    SciTech Connect

    Caisso, Marie; Lebreton, Florent; Horlait, Denis; Neuville, Daniel R.; Dardenne, Kathy; Rothe, Jörg; Delahaye, Thibaud

    2014-10-15

    In the current nano-sized material revolution, the main limitations to a large-scale deployment of nanomaterials involve health concerns related to nano-dissemination via air. Developing new chemical routes benefiting from nano-size advantages while avoiding their hazards could overcome these limitations. Addressing this need, a chemical route leading to soft nano-particle agglomerates, i.e., macroscopic precursors presenting the ability to be decomposed into nano-sized materials, was developed and applied to Ce{sub 0.8}Gd{sub 0.2}O{sub 2−δ}. Using cerium/gadolinium-loaded ion exchange resin, the Ce{sub 0.8}Gd{sub 0.2}O{sub 2−δ} solid solution formation as a function of temperature was studied in-situ through X-ray diffraction, X-ray absorption spectroscopy and Raman spectroscopy. Temperatures corresponding to the organic skeleton decomposition and to the mixed oxide crystallization were identified. An optimal heat treatment, leading to nanostructured soft agglomerates, was established. Microsphere processing capabilities were evaluated and particle size distribution measurements were recorded. A very low fracture strength was calculated, and a nanometric particle size distribution (170 nm) was determined. - Graphical abstract: The elaboration of micro-spherical precursors leading to the formation of nano-oxide soft agglomerates was studied and approved through the use of ion exchange resin loaded with cerium and gadolinium. The formation of the solid solution was followed through in-situ measurements such as XAS, XRD, Raman, TGA and DSC. Key temperatures were identified for the formation of the mixed-oxide. Following this study, the microstructure and particle size of oxide microspheres formed highlight the formation of soft nano-arrangments. - Highlights: • Soft microspherical agglomerates able to be decomposed into nano-sized materials. • In situ study of cerium/gadolinium-loaded ion exchange resin conversion in oxide. • In situ multi-scale study

  8. Iridium-Doped Ruthenium Oxide Catalyst for Oxygen Evolution

    NASA Technical Reports Server (NTRS)

    Valdez, Thomas I.; Narayan, Sri R.; Billings, Keith J.

    2011-01-01

    NASA requires a durable and efficient catalyst for the electrolysis of water in a polymer-electrolyte-membrane (PEM) cell. Ruthenium oxide in a slightly reduced form is known to be a very efficient catalyst for the anodic oxidation of water to oxygen, but it degrades rapidly, reducing efficiency. To combat this tendency of ruthenium oxide to change oxidation states, it is combined with iridium, which has a tendency to stabilize ruthenium oxide at oxygen evolution potentials. The novel oxygen evolution catalyst was fabricated under flowing argon in order to allow the iridium to preferentially react with oxygen from the ruthenium oxide, and not oxygen from the environment. Nanoparticulate iridium black and anhydrous ruthenium oxide are weighed out and mixed to 5 18 atomic percent. They are then heat treated at 300 C under flowing argon (in order to create an inert environment) for a minimum of 14 hours. This temperature was chosen because it is approximately the creep temperature of ruthenium oxide, and is below the sintering temperature of both materials. In general, the temperature should always be below the sintering temperature of both materials. The iridium- doped ruthenium oxide catalyst is then fabricated into a PEM-based membrane- electrode assembly (MEA), and then mounted into test cells. The result is an electrolyzer system that can sustain electrolysis at twice the current density, and at the same efficiency as commercial catalysts in the range of 100-200 mA/sq cm. At 200 mA/sq cm, this new system operates at an efficiency of 85 percent, which is 2 percent greater than commercially available catalysts. Testing has shown that this material is as stable as commercially available oxygen evolution catalysts. This means that this new catalyst can be used to regenerate fuel cell systems in space, and as a hydrogen generator on Earth.

  9. Modifying ceria (111) with a TiO2 nanocluster for enhanced reactivity.

    PubMed

    Nolan, Michael

    2013-11-14

    Modification of ceria catalysts is of great interest for oxidation reactions such as oxidative dehydrogenation of alcohols. Improving the reactivity of ceria based catalysts for these reactions means that they can be run at lower temperatures and density functional theory (DFT) simulations of new structures and compositions are proving valuable in the development of these catalysts. In this paper, we have used DFT+U (DFT corrected for on-site Coulomb interactions) to examine the reactivity of a novel modification of ceria, namely, modifying with TiO2, using the example of a Ti2O4 species adsorbed on the ceria (111) surface. The oxygen vacancy formation energy in the Ti2O4-CeO2 system is significantly reduced over the bare ceria surfaces, which together with previous work on ceria-titania indicates that the presence of the interface favours oxygen vacancy formation. The energy gain upon hydrogenation of the catalyst, which is the rate determining step in oxidative dehydrogenation, further points to the improved oxidation power of this catalyst structure. PMID:24320294

  10. Modifying ceria (111) with a TiO2 nanocluster for enhanced reactivity

    NASA Astrophysics Data System (ADS)

    Nolan, Michael

    2013-11-01

    Modification of ceria catalysts is of great interest for oxidation reactions such as oxidative dehydrogenation of alcohols. Improving the reactivity of ceria based catalysts for these reactions means that they can be run at lower temperatures and density functional theory (DFT) simulations of new structures and compositions are proving valuable in the development of these catalysts. In this paper, we have used DFT+U (DFT corrected for on-site Coulomb interactions) to examine the reactivity of a novel modification of ceria, namely, modifying with TiO2, using the example of a Ti2O4 species adsorbed on the ceria (111) surface. The oxygen vacancy formation energy in the Ti2O4-CeO2 system is significantly reduced over the bare ceria surfaces, which together with previous work on ceria-titania indicates that the presence of the interface favours oxygen vacancy formation. The energy gain upon hydrogenation of the catalyst, which is the rate determining step in oxidative dehydrogenation, further points to the improved oxidation power of this catalyst structure.

  11. Synthesis and tribology of doped carbon films and oxide multilayers

    NASA Astrophysics Data System (ADS)

    Freyman, Christina A.

    The focus of this research is to synthesize thin films coatings by reactive magnetron sputtering with properties that will result in energy savings. Tailoring of hydrogenated carbon film properties to minimize environment effects on friction is accomplished by sulfur doping. Synthesis results in smooth surfaces and mid-range hardness. The stabilization of ultra-low friction in humid air can be attributed to the reduction of water adsorption on the surface, which is verified by results of quartz crystal microbalance and temperature-programmed desorption experiments. Even at 90% relative humidity, sulfur-doped films have less than one monolayer of water adsorbed on the surface. This reduction in water coverage is due to the decrease in residence time of water on the surface, which is related to the strength of the bonding between water molecules and the sulfur-doped surface. These results indicate that sulfur doping results in weaker bonding between water and the film surface due to a reduction in the polar nature of the surface. Metal nitrides, carbides, and borides are widely used as protective coatings due to their high hardness, but are not stable above 600°C due to coating oxidation. Hardness enhancement techniques have been applied to thermally stable oxide multilayers for use at high temperatures. Amorphous Al2 O3 and crystalline TiO2 nanoscale layers have been deposited using reactive d.c. magnetron sputtering at different partial pressures of oxygen. Hardness enhancement of twice the rule of mixtures has been observed in oxide multilayers for the first time due to clear interfaces and large difference in modulus between amorphous Al2O3 and crystalline TiO2 layers. Multilayer films with majority bilayer component of Al2O3 showed greater resistance to wear due to increased elastic recovery and H/E ratio over monolithic films and TiO2 majority phase multilayers. Multilayer films retain their high hardness up to ˜800°C in air; some hardness enhancement in the

  12. Ab initio analysis of the defect structure of ceria

    NASA Astrophysics Data System (ADS)

    Zacherle, T.; Schriever, A.; De Souza, R. A.; Martin, M.

    2013-04-01

    We calculated the formation energies of all simple point defects in cubic fluorite structured CeO2 using density functional theory within the GGA+U approximation. All possible defect charge states were considered, and also polarons CeCe' and associates of polarons with oxygen vacancies: (VO··-CeCe')· and (CeCe'-VO··-CeCe')×. From the individual defect energies, we extracted Schottky, Frenkel, and anti-Frenkel energies: we find that anti-Frenkel disorder has the lowest energy in ceria. Energies for the reduction and the hydration of ceria are also computed, and the results are in good agreement with experiment. Finally, point-defect concentrations and conductivities are predicted for undoped and donor-doped systems as a function of oxygen partial pressure and temperature. The characteristic slopes found in experiment are reproduced.

  13. Simple cerium-triethanolamine complex: Synthesis, characterization, thermal decomposition and its application to prepare ceria support for platinum catalysts used in methane steam reforming

    NASA Astrophysics Data System (ADS)

    Wattanathana, Worawat; Nootsuwan, Nollapan; Veranitisagul, Chatchai; Koonsaeng, Nattamon; Laosiripojana, Navadol; Laobuthee, Apirat

    2015-06-01

    Cerium-triethanolamine complex was synthesized by simple complexation method in 1-propanol solvent using cerium(III) chloride as a metal source and triethanolamine as a ligand. The structures of the prepared complex were proposed based on FT-IR, FT-Raman and ESI-MS results as equimolar of triethanolamine and cerium chelated complex having monomeric tricyclic structure with and without chloride anion as another coordinating group known as ceratrane. The complex was used as a precursor for ceria material done by thermal decomposition. XRD result revealed that when calcined at 600 °C for 2 h, the cerium complex was totally turned into pure ceria with cubic fluorite structure. The obtained ceria was then employed to synthesize platinum doped ceria catalysts for methane steam reforming. Various amounts of platinum i.e. 1, 3, 5 and 10 mol percents were introduced on the ceria support by microwave-assisted wetness impregnation using ammonium tetrachloroplatinate(II). The platinum-impregnated ceria powders were subjected to calcination in 10% hydrogen/helium atmosphere at 500 °C for 3 h to reduce platinum(II) to platinum(0). XRD patterns of the catalysts confirmed that the platinum particles doped on the ceria support were in the form of platinum(0). Catalytic activity test showed that the catalytic activities got higher as the amounts of platinum doped increased. Besides, the portions of coke formation on the surface of catalysts were reduced as the amounts of platinum doped increased.

  14. Effect of doping of tin on optoelectronic properties of indium oxide: DFT study

    SciTech Connect

    Tripathi, Madhvendra Nath

    2015-06-24

    Indium tin oxide is widely used transparent conductor. Experimentally observed that 6% tin doping in indium oxide is suitable for optoelectronic applications and more doping beyond this limit degrades the optoelectronic property. The stoichiometry (In{sub 32-x}Sn{sub x}O{sub 48+x/2}; x=0-6) is taken to understand the change in lattice parameter, electronic structure, and optical property of ITO. It is observed that lattice parameter increases and becomes constant after 6% tin doping that is in good agreement of the experimental observation. The electronic structure calculation shows that the high tin doping in indium oxide adversely affects the dispersive nature of the bottom of conduction band of pure indium oxide and decreases the carrier mobility. Optical calculations show that transmittance goes down upto 60% for the tin concentration more than 6%. The present paper shows that how more than 6% tin doping in indium oxide adversely affects the optoelectronic property of ITO.

  15. Nanostructured gadolinium-doped ceria microsphere synthesis from ion exchange resin: Multi-scale in-situ studies of solid solution formation

    NASA Astrophysics Data System (ADS)

    Caisso, Marie; Lebreton, Florent; Horlait, Denis; Picart, Sébastien; Martin, Philippe M.; Bès, René; Renard, Catherine; Roussel, Pascal; Neuville, Daniel R.; Dardenne, Kathy; Rothe, Jörg; Delahaye, Thibaud; Ayral, André

    2014-10-01

    In the current nano-sized material revolution, the main limitations to a large-scale deployment of nanomaterials involve health concerns related to nano-dissemination via air. Developing new chemical routes benefiting from nano-size advantages while avoiding their hazards could overcome these limitations. Addressing this need, a chemical route leading to soft nano-particle agglomerates, i.e., macroscopic precursors presenting the ability to be decomposed into nano-sized materials, was developed and applied to Ce0.8Gd0.2O2-δ. Using cerium/gadolinium-loaded ion exchange resin, the Ce0.8Gd0.2O2-δ solid solution formation as a function of temperature was studied in-situ through X-ray diffraction, X-ray absorption spectroscopy and Raman spectroscopy. Temperatures corresponding to the organic skeleton decomposition and to the mixed oxide crystallization were identified. An optimal heat treatment, leading to nanostructured soft agglomerates, was established. Microsphere processing capabilities were evaluated and particle size distribution measurements were recorded. A very low fracture strength was calculated, and a nanometric particle size distribution (170 nm) was determined.

  16. High power density solid oxide fuel cells

    DOEpatents

    Pham, Ai Quoc; Glass, Robert S.

    2004-10-12

    A method for producing ultra-high power density solid oxide fuel cells (SOFCs). The method involves the formation of a multilayer structure cells wherein a buffer layer of doped-ceria is deposited intermediate a zirconia electrolyte and a cobalt iron based electrode using a colloidal spray deposition (CSD) technique. For example, a cobalt iron based cathode composed of (La,Sr)(Co,Fe)O (LSCF) may be deposited on a zirconia electrolyte via a buffer layer of doped-ceria deposited by the CSD technique. The thus formed SOFC have a power density of 1400 mW/cm.sup.2 at 600.degree. C. and 900 mW/cm.sup.2 at 700.degree. C. which constitutes a 2-3 times increased in power density over conventionally produced SOFCs.

  17. Charge Compensated (Al, N) Co-Doped Zinc Oxide (ZnO) Films for Photlelectrochemical Application

    SciTech Connect

    Shet, S.

    2012-01-01

    ZnO thin films with significantly reduced bandgaps were synthesized by doping N and co-doping Al and N at 100oC. All the films were synthesized by radio-frequency magnetron sputtering on F-doped tin-oxide-coated glass. We found that co-doped ZnO:(Al,N) thin films exhibited significantly enhanced crystallinity as compared to ZnO doped solely with N, ZnO:N, at the same growth conditions. Furthermore, annealed ZnO:(Al,N) thin films exhibited enhanced N incorporation over ZnO:N films. As a result, ZnO:(Al,N) films exhibited improved photocurrents than ZnO:N films grown with pure N doping, suggesting that charge-compensated donor-acceptor co-doping could be a potential method for bandgap reduction of wide-bandgap oxide materials to improve their photoelectrochemical performance.

  18. Method of preparing doped oxide catalysts for lean NOx exhaust

    DOEpatents

    Park, Paul W.

    2004-03-09

    The lean NOx catalyst includes a substrate, an oxide support material, preferably .gamma.-alumina deposited on the substrate and a metal or metal oxide promoter or dopant introduced into the oxide support material. The metal promoters or dopants are selected from the group consisting of indium, gallium, tin, silver, germanium, gold, nickel, cobalt, copper, iron, manganese, molybdenum, chromium cerium, and vanadium, and oxides thereof, and any combinations thereof. The .gamma.-alumina preferably has a pore volume of from about 0.5 to about 2.0 cc/g; a surface area of between 80 and 350 m.sup.2 /g; an average pore size diameter of between about 3 to 30 nm; and an impurity level of less than or equal to about 0.2 weight percent. In a preferred embodiment the .gamma.-alumina is prepared by a sol-gel method, with the metal doping of the .gamma.-alumina preferably accomplished using an incipient wetness impregnation technique.

  19. Performance studies of copper-iron/ceria-yttria stabilized zirconia anode for electro-oxidation of butane in solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Kaur, Gurpreet; Basu, Suddhasatwa

    2013-11-01

    Addition of second metal to Cu is useful for electro-oxidation of hydrocarbons in solid oxide fuel cells (SOFC). In this work, electro-catalysts based on Cu-Fe bimetallic anode for use of both H2 and n-C4H10 in SOFC is prepared by wet impregnation method into a porous CeO2-YSZ matrix. The prepared Cu-Fe/CeO2-YSZ anodes are then characterized by thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), elemental dispersive X-ray (EDX) and scanning electron microscopy (SEM). Carbonaceous deposits formed on Cu-Fe/CeO2-YSZ anodes after exposure to n-C4H10 are studied using a combination of i-V characteristics and TGA measurements. It is observed that the addition of Fe to Cu in CeO2-YSZ cermet anode enhance the performance in H2 and n-C4H10 fuels. The performance of cell having molar ratio of Cu-Fe of 1:1 in Cu-Fe/CeO2-YSZ anode shows power density of 240 mW cm-2 and 260 mW cm-2 in n-C4H10 and in H2 after n-C4H10 flow at 800 °C. The i-V curve shows that the conductivity of the anode improves after exposure to n-C4H10. No apparent degradation in performance is observed after n-C4H10 flow except for carbon fibre formation indicating Cu-Fe bimetallic is worth considering as an anode for direct butane SOFC.

  20. Paper bioassay based on ceria nanoparticles as colorimetric probes.

    PubMed

    Ornatska, Maryna; Sharpe, Erica; Andreescu, Daniel; Andreescu, Silvana

    2011-06-01

    We report the first use of redox nanoparticles of cerium oxide as colorimetric probes in bioanalysis. The method is based on changes in the physicochemical properties of ceria nanoparticles, used here as chromogenic indicators, in response to the analyte. We show that these particles can be fully integrated in a paper-based bioassay. To construct the sensor, ceria nanoparticles and glucose oxidase were coimmobilized onto filter paper using a silanization procedure. In the presence of glucose, the enzymatically generated hydrogen peroxide induces a visual color change of the ceria nanoparticles immobilized onto the bioactive sensing paper, from white-yellowish to dark orange, in a concentration-dependent manner. A detection limit of 0.5 mM glucose with a linear range up to 100 mM and a reproducibility of 4.3% for n = 11 ceria paper strips were obtained. The assay is fully reversible and can be reused for at least 10 consecutive measurement cycles, without significant loss of activity. Another unique feature is that it does not require external reagents, as all the sensing components are fixed onto the paper platform. The bioassay can be stored for at least 79 days at room temperature while maintaining the same analytical performance. An example of analytical application was demonstrated for the detection of glucose in human serum. The results demonstrate the potential of this type of nanoparticles as novel components in the development of robust colorimetric bioassays. PMID:21524141

  1. Synthesis and characterization of ceria nanomaterials

    NASA Astrophysics Data System (ADS)

    Cheong Ng, Nitzia

    Cerium dioxide or ceria, CeO2, has been widely used in industry as catalyst for automotive exhaust controls, chemical mechanical polishing (CMP) slurries, and high temperature fuel cells because of its unique metal oxide properties. This well-known rare metal oxide has high thermal stability, electrical conductivity and chemical diffusivity. Proper synthesis method requires knowledge of reaction temperature, concentration, and time effects on the synthesis. In this work, ceria nanomaterials were prepared via the hydrothermal method using a Teflon autoclave. Cerium nitrate solution was used as the source and three different precursors: NaOH, H2O 2, and NH4OH were used as the oxidizing agents. CeO 2 nanoplates, nanocubes and nanorods were produced and studied using transmission electron microscopy (TEM), BET specific surface area, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Through characterization, CeO2 nanomaterials showed the presence of mixed valence states (Ce3+ and Ce4+) through XPS spectra. Deconvolution was performed to investigate the ratio of Ce 3+/Ce4+ concentration in the synthesized CeO2 nanostructures. Nanocubes showed a higher Ce3+ concentration. CeO2 nanomaterials were found to be mesoporous. Nanoplates synthesized with H2O2, and NH4OH were found with surface areas of 95.11 m2/g and 62.07 m2/g, respectively. Nanorods and nanocubes showed surface areas of 16.77 m2/g and 16.55 m2/g, respectively. The prepared ceria nanoplates, nanocubes and nanorods had crystallite size in the range of 5--25 nm and pore size range of 7--15 nm. XRD spectra confirmed that the peaks were indexed to the cubic phase of CeO2 with fluorite structure and with an average lattice parameter, 5.407 A. Higher Ce3+ concentration and exposed surface of crystalline planes suggest that nanorods are better catalyst for CO oxidation and oxygen storage capacity (OSC).

  2. Rice husk ash/calcium oxide/ceria sorbent for simultaneous removal of sulfur dioxide and nitric oxide from flue gas at low temperature

    SciTech Connect

    Dahlan, I.; Lee, K.T.; Kamaruddin, A.H.; Mohamed, A.R.

    2009-06-15

    The reduction of sulfur dioxide (SO{sub 2}) and nitric oxide (NO) emissions has become an isssue of great importance to government regulatory agencies and general public due to their negative effect towards the environment and human health. In this work, the simultaneous removal of sulfur dioxide (SO{sub 2}) and nitric oxide (NO) from simulated flue gas was investigated in a fixed-bed reactor using rice husk ash (RHA)/CaO/CeO{sub 2} sorbent. Attention was focused on the major reactor operation parameters affecting sorption capacity of RHA/CaO/CeO{sub 2} sorbent, which include feed concentration of SO{sub 2} and NO, relative humidity (RH), operating temperature and space velocity (GHSV). This is because such information is unavailable for RHA-based sorbent and the effects of these parameters reported in the literature are also not reliable. Enhancement effect of NO on removal of SO{sub 2} was observed and the presence of SO{sub 2} was essential to the removal of NO. However, at a high level of SO{sub 2}/NO concentration, competition in the sorption of NO and SO{sub 2} on the sorbent active sites might have occurred. RH was found to significantly enhance the SO{sub 2} sorption of the RHA/CaO/CeO{sub 2} sorbent. By contrast, NO sorption capacity decreases when RH was further introduced, as it was not easy to sorb NO in the presence of water. Apart from that, the results also shows that there was a threshold value for the RH to ensure higher SO{sub 2} and NO removal and this value was observed at 50% RH. Higher operating temperatures were favored for SO{sub 2} and NO removal. Nevertheless, beyond 150 degrees C the SO{sub 2} removal was found to decrease. On the other hand, a lower space velocity resulted in a higher SO{sub 2} and NO removal.

  3. Control of metal nanocrystal size reveals metal-support interface role for ceria catalysts.

    PubMed

    Cargnello, Matteo; Doan-Nguyen, Vicky V T; Gordon, Thomas R; Diaz, Rosa E; Stach, Eric A; Gorte, Raymond J; Fornasiero, Paolo; Murray, Christopher B

    2013-08-16

    Interactions between ceria (CeO2) and supported metals greatly enhance rates for a number of important reactions. However, direct relationships between structure and function in these catalysts have been difficult to extract because the samples studied either were heterogeneous or were model systems dissimilar to working catalysts. We report rate measurements on samples in which the length of the ceria-metal interface was tailored by the use of monodisperse nickel, palladium, and platinum nanocrystals. We found that carbon monoxide oxidation in ceria-based catalysts is greatly enhanced at the ceria-metal interface sites for a range of group VIII metal catalysts, clarifying the pivotal role played by the support. PMID:23868919

  4. Thermally stable single-atom platinum-on-ceria catalysts via atom trapping.

    PubMed

    Jones, John; Xiong, Haifeng; DeLaRiva, Andrew T; Peterson, Eric J; Pham, Hien; Challa, Sivakumar R; Qi, Gongshin; Oh, Se; Wiebenga, Michelle H; Pereira Hernández, Xavier Isidro; Wang, Yong; Datye, Abhaya K

    2016-07-01

    Catalysts based on single atoms of scarce precious metals can lead to more efficient use through enhanced reactivity and selectivity. However, single atoms on catalyst supports can be mobile and aggregate into nanoparticles when heated at elevated temperatures. High temperatures are detrimental to catalyst performance unless these mobile atoms can be trapped. We used ceria powders having similar surface areas but different exposed surface facets. When mixed with a platinum/aluminum oxide catalyst and aged in air at 800°C, the platinum transferred to the ceria and was trapped. Polyhedral ceria and nanorods were more effective than ceria cubes at anchoring the platinum. Performing synthesis at high temperatures ensures that only the most stable binding sites are occupied, yielding a sinter-resistant, atomically dispersed catalyst. PMID:27387946

  5. Control of Metal Nanocrystal Size Reveals Metal-Support Interface Role for Ceria Catalysts

    SciTech Connect

    Cargnello, M; Doan-Nguyen, VVT; Gordon, TR; Diaz, RE; Stach, EA; Gorte, RJ; Fornasiero, P; Murray, CB

    2013-08-15

    Interactions between ceria (CeO2) and supported metals greatly enhance rates for a number of important reactions. However, direct relationships between structure and function in these catalysts have been difficult to extract because the samples studied either were heterogeneous or were model systems dissimilar to working catalysts. We report rate measurements on samples in which the length of the ceria-metal interface was tailored by the use of monodisperse nickel, palladium, and platinum nanocrystals. We found that carbon monoxide oxidation in ceria-based catalysts is greatly enhanced at the ceria-metal interface sites for a range of group VIII metal catalysts, clarifying the pivotal role played by the support.

  6. Electrochromism and Electronic Structures of Nitrogen Doped Tungsten Oxide Thin Films Prepared by RF Reactive Sputtering

    NASA Astrophysics Data System (ADS)

    Nakagawa, Koichi; Miura, Noboru; Matsumoto, Setsuko; Nakano, Ryotaro; Matsumoto, Hironaga

    2008-09-01

    The doping effect of nitrogen on amorphous tungsten trioxide (a-WO3) thin films was investigated with regard to electrochromism and electronic structures. The N-doped thin films exhibit a change in electrochromic coloration from transparent yellow to black, whereas the un-doped thin films exhibit blue coloration. In addition, a new absorption peak related to nitrogen doping is observed at 2.3 eV in photoabsorption spectra during the electrochemical coloration/bleaching process. To explain these experimental results, the electronic structures of N-doped tungsten oxide were calculated by the DV-Xα molecular orbital method.

  7. Development of transition-metal doped copper oxide and zinc oxide dilute magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Ivill, Mathew P.

    The field of spintronics has recently attracted much attention because of its potential to provide new functionalities and enhanced performance in conventional electronic devices. Oxide materials provide a convenient platform to study the spin-based functionality in host semiconducting material. Recent theoretical treatments predict that wide band-gap semiconductors, including ZnO, can exhibit high temperature ferromagnetic ordering when doped with transition metals. This work focused on the possibility of using wide band-gap oxide semiconductors as potential spintronic materials. The structure, magnetic, and electronic transport properties of transition-metal doped ZnO and Cu 2O were investigated. Mn and Co were used as transition metal dopants. Thin films of these materials were fabricated using pulsed laser deposition (PLD). The Mn solubility in Cu2O was found to be small and the precipitation of Mn-oxides was favored at high growth temperatures. Phase pure Mn-doped Cu2O samples were found to be non-magnetic. Samples were p-type with carrier concentrations on the order of 1014-10 16 cm-3. The effects of carrier concentration on the magnetic properties of Mn-doped ZnO were studied using Sn and P as electronic codopants. Sn acts as an n-type dopant providing extra electrons to the ZnO. P acts as a p-type dopant that supplies excess holes to compensate the native electron concentration in ZnO. The electron concentration was decreased using P, but the films remained n-type. An inverse correlation was found between the ferromagnetism and the electron concentration; the ferromagnetic coupling between Mn spins increased with decreasing electron concentration. The nature of ferromagnetism in Co-doped ZnO was also investigated. Ferromagnetism was found in films deposited at 400°C in vacuum, while films deposited in oxygen or at higher temperatures were non-magnetic. Films deposited under vacuum had rather high electron concentrations and were presumably doped with

  8. Oxidative unzipping of stacked nitrogen-doped carbon nanotube cups.

    PubMed

    Dong, Haifeng; Zhao, Yong; Tang, Yifan; Burkert, Seth C; Star, Alexander

    2015-05-27

    We demonstrate a facile synthesis of different nanostructures by oxidative unzipping of stacked nitrogen-doped carbon nanotube cups (NCNCs). Depending on the initial number of stacked-cup segments, this method can yield graphene nanosheets (GNSs) or hybrid nanostructures comprised of graphene nanoribbons partially unzipped from a central nanotube core. Due to the stacked-cup structure of as-synthesized NCNCs, preventing complete exposure of graphitic planes, the unzipping mechanism is hindered, resulting in incomplete unzipping; however, individual, separated NCNCs are completely unzipped, yielding individual nitrogen-doped GNSs. Graphene-based materials have been employed as electrocatalysts for many important chemical reactions, and it has been proposed that increasing the reactive edges results in more efficient electrocatalysis. In this paper, we apply these graphene conjugates as electrocatalysts for the oxygen reduction reaction (ORR) to determine how the increase in reactive edges affects the electrocatalytic activity. This investigation introduces a new method for the improvement of ORR electrocatalysts by using nitrogen dopants more effectively, allowing for enhanced ORR performance with lower overall nitrogen content. Additionally, the GNSs were functionalized with gold nanoparticles (GNPs), resulting in a GNS/GNP hybrid, which shows efficient surface-enhanced Raman scattering and expands the scope of its application in advanced device fabrication and biosensing. PMID:25946723

  9. Stabilizing the ferroelectric phase in doped hafnium oxide

    SciTech Connect

    Hoffmann, M.; Schroeder, U.; Schenk, T.; Shimizu, T.; Funakubo, H.; Sakata, O.; Pohl, D.; Drescher, M.; Adelmann, C.; Materlik, R.; Kersch, A.; Mikolajick, T.

    2015-08-21

    The ferroelectric properties and crystal structure of doped HfO{sub 2} thin films were investigated for different thicknesses, electrode materials, and annealing conditions. Metal-ferroelectric-metal capacitors containing Gd:HfO{sub 2} showed no reduction of the polarization within the studied thickness range, in contrast to hafnia films with other dopants. A qualitative model describing the influence of basic process parameters on the crystal structure of HfO{sub 2} was proposed. The influence of different structural parameters on the field cycling behavior was examined. This revealed the wake-up effect in doped HfO{sub 2} to be dominated by interface induced effects, rather than a field induced phase transition. TaN electrodes were shown to considerably enhance the stabilization of the ferroelectric phase in HfO{sub 2} compared to TiN electrodes, yielding a P{sub r} of up to 35 μC/cm{sup 2}. This effect was attributed to the interface oxidation of the electrodes during annealing, resulting in a different density of oxygen vacancies in the Gd:HfO{sub 2} films. Ab initio simulations confirmed the influence of oxygen vacancies on the phase stability of ferroelectric HfO{sub 2}.

  10. High dielectric constant nickel-doped titanium oxide films prepared by liquid-phase deposition

    NASA Astrophysics Data System (ADS)

    Lee, Ming-Kwei; Yen, Chih-Feng; Fan, Cho-Han

    2014-09-01

    The electrical characteristics of nickel-doped titanium oxide films prepared by liquid-phase deposition on p-type (100) silicon substrate were investigated. The aqueous solutions of ammonium hexafluorotitanate and boric acid were used as precursors for the growth of titanium oxide films and the dielectric constant is 29. The dielectric constant can be improved to 94 by nickel doping at the thermal annealing at 700 °C in nitrous oxide.

  11. Effects of different precursors on size and optical properties of ceria nanoparticles prepared by microwave-assisted method

    SciTech Connect

    Samiee, Sara; Goharshadi, Elaheh K.

    2012-04-15

    Highlights: Black-Right-Pointing-Pointer A rapid and efficient microwave method was applied for synthesis of nano ceria. Black-Right-Pointing-Pointer Changing precursor has great effects on optical properties and size of nano ceria. Black-Right-Pointing-Pointer Fabrication of ceria nanoparticles using Ce{sup 4+} salts leads to better results. Black-Right-Pointing-Pointer Band gap energies of ceria nanoparticles were evaluated by UV-vis spectroscopy. -- Abstract: Cerium oxide, ceria (CeO{sub 2}), is one of the favourable nanoparticles (NPs) that possesses many remarkable properties so that it can be used in medicine, chemistry, environment, energy, information, industry, and so on. In this study, the crystalline ceria NPs were successfully prepared by an efficient microwave-assisted heating technique from an aqueous solution using different cerium salts (Ce(IV) and Ce(III) salts). The products were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), FTIR spectroscopy, Raman spectroscopy, and UV-vis absorption spectroscopy. The results revealed that changing the precursor led to great effects on size, band gap energy, and the reaction time of preparing the ceria NPs. The significant feature of this manuscript is that the effects of different precursors on the structural and optical properties of ceria NPs were investigated for the first time. The average particle size of different samples was below 8 nm.

  12. Conductivity study of nitrogen-doped calcium zinc oxide prepared by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Hsu, Yu-Ting; Lan, Wen-How; Huang, Kai-Feng; Lin, Jia-Ching; Chang, Kuo-Jen

    2016-01-01

    In this study, the spray pyrolysis method was used to prepare unintentionally doped and nitrogen-doped calcium zinc oxide films by using zinc acetate, calcium nitrate precursor, and ammonium acetate precursor. Morphological and structural analyses were conducted using scanning electron microscopy and X-ray diffraction. The results indicated that film grain size decreased as the nitrogen doping was increased. Both calcium oxide and zinc oxide structures were identified in the unintentionally doped calcium zinc oxide. When nitrogen doping was introduced, the film mainly exhibited a zinc oxide structure with preferred (002) and (101) orientations. The concentration and mobility were investigated using a Hall measurement system. P-type films with a mobility and concentration of 10.6 cm2 V-1 s-1 and 2.8×1017 cm-3, respectively, were obtained. Moreover, according to a temperature-dependent conductivity analysis, an acceptor state with activation energy 0.266 eV dominated the p-type conduction for the unintentionally doped calcium zinc oxide. By contrast, a grain boundary with a barrier height of 0.274-0.292 eV dominated the hole conduction for the nitrogen-doped calcium zinc oxide films.

  13. The role of strain and structure on oxygen ion conduction in nanoscale zirconia and ceria thin films

    NASA Astrophysics Data System (ADS)

    Jiang, Jun

    Solid oxide fuel cells (SOFCs), an all solid-state energy conversion device, are promising for their high efficiency and materials stability. The solid oxide electrolytes are a key component that must provide high ionic conductivity, which is especially challenging for intermediate temperature SOFCs operating between 500 °C - 700 °C. Doped zirconia and ceria are the most common solid electrolyte materials. Recent reports have suggested that nanoscale ytrria stabilized zirconia (YSZ) thin films may provide better performance in this regard. However, the mechanism behind the increased conductivity of nanoscale thin films is still unclear and the reported experimental results are controversial. In the thesis presented here, the effects of mechanical strain and microstructure on the ionic conductivity have been investigated in ultrathin zirconia- and ceria-based thin films. Reactive RF co-sputtering with metal targets was used to prepare zirconia and ceria based thin films for high purity, modulated composition and thickness. The films were as thin as 10-20 atomic layers thick. X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy were the main tools to investigate the composition, crystal orientation and microstructure of these sputtered thin films. Microscale interdigitated Pt electrodes were prepared through a lift-off process using photolithography. The electrochemical properties of these sputtered doped zirconia and ceria thin films were investigated using impedance spectroscopy. YSZ thin films deposited on MgO (111) and, especially, MgO (100) showed highly variable crystal orientations, while MgO (110) offered much more stable growth. Regardless of whether the growth was epitaxial or highly disordered polycrystalline, 50 nm thick YSZ thin films on MgO (100), (110), and (111) substrates exhibited similar conductivity with YSZ single crystal. While decreasing the thickness further to 12 nm, the conductivities of YSZ thin films

  14. Doped titanium oxide photcatalysts: Preparation, structure and interaction with viruses

    NASA Astrophysics Data System (ADS)

    Li, Qi

    Since the discovery of photoelectrochemical splitting of water on n-titanium oxide (n-TiO2) electrodes by Fujishima and Honda in 1972, there has been much interest in semiconductor-based materials as photocatalysts for both solar energy conversion and environmental applications in the past several decades. Among various semiconductor-based photocatalysts, TiO2 is the only candidate suitable for industrial use because of its high chemical stability, good photoactivity, relatively low cost, and nontoxicity. However, the photocatalytic capability of TiO 2 is limited to only ultraviolet (UV) light (wavelength, lambda, < 400 nm), seriously limiting its solar efficiency. In this study, both chemical and physical modification approaches were developed to extend the absorption band-edge of TiO2 into the visible light region with improved stability, photocatalytic efficiency and ease of the doping process. Two major approaches were used in the material synthesis and processing, including the ion-beam-assisted-deposition (IBAD) technique and sol-gel based processes. Both nitrogen-doped TiO2 (TiON) and nitrogen/palladium co-doped TiO2 (TiON/PdO) photocatalysts were created and their photocatalytic activity was investigated by the degradation of methylene blue (MB) and disinfection of bacteria and viruses under visible light illumination. The sol-gel process was optimized to produce high quality TiON-based photocatalysts by carefully modulating the precursor ratio and calcination temperature. A TiON inverse opal structure was created, which demonstrated enhanced visible light absorption and subsequently improved photocatalytic efficiency by the combination of chemical and physical modifications on n-TiO2. The effect of palladium dopant on the optical and photocatalytic properties of TiON/PdO photocatalyst was examined, which suggests that a careful optimization of the transition metal ion dopant concentration is needed to achieve high photocatalytic efficiency in these anion

  15. Highly sensitive nonenzymatic glucose sensor based on electrospun copper oxide-doped nickel oxide composite microfibers.

    PubMed

    Cao, Fei; Guo, Shu; Ma, Huiyan; Yang, Guocheng; Yang, Shengxue; Gong, Jian

    2011-10-30

    An improved nonenzymatic glucose sensor based on copper oxide-doped nickel oxide composite microfibers (CuO-NiO-MFs) modified fluorine tin oxide (FTO) electrode was prepared by electrospinning and calcination technologies without using any immobilization. The results of cyclic voltammetry (CV) and chronoamperometry demonstrated that the CuO-NiO-MFs modified electrode displayed much higher electrocatalytic activity than the nickel oxide microfibers (NiO-MFs) modified electrode toward glucose. The nonenzymatic glucose sensor based on CuO-NiO-MFs showed the highest sensitivity of 3165.53 μA mM(-1)cm(-2) with the lowest detection limit of 1 × 10(-9)M (signal/noise ratio (S/N)=3) in the nonenzymatic glucose sensors that have been reported in the literature. Additionally, its application for detecting glucose concentration of human serum sample showed good agreement with the results obtained from automatic biochemical analyzer. PMID:22063533

  16. Corrosion evaluation of zirconium doped oxide coatings on aluminum formed by plasma electrolytic oxidation.

    PubMed

    Bajat, Jelena; Mišković-Stanković, Vesna; Vasilić, Rastko; Stojadinović, Stevan

    2014-01-01

    The plasma electrolytic oxidation (PEO) of aluminum in sodium tungstate (Na(2)WO(4) · (2)H(2)O) and Na(2)WO(4) · (2)H(2)O doped with Zr was analyzed in order to obtain oxide coatings with improved corrosion resistance. The influence of current density in PEO process and anodization time was investigated, as well as the influence of Zr, with the aim to find out how they affect the chemical content, morphology, surface roughness, and corrosion stability of oxide coatings. It was shown that the presence of Zr increases the corrosion stability of oxide coatings for all investigated PEO times. Evolution of EIS spectra during the exposure to 3% NaCl, as a strong corrosive agent, indicated the highest corrosion stability for PEO coating formed on aluminum at 70 mA/cm(2) for 2 min in a zirconium containing electrolyte. PMID:25125114

  17. Structure and photocatalysis activity of silver doped titanium oxide nanotubes array for degradation of pollutants

    NASA Astrophysics Data System (ADS)

    Al-Arfaj, E. A.

    2013-10-01

    Semiconductor titanium oxide showed a wonderful performance as a photocatalysis for environmental remediation. Owing to high stability and promising physicochemical properties, titanium oxide nanostructures are used in various applications such as wastewater treatment, antimicrobial and air purification. In the present study, titanium oxide nanotubes and silver doped titanium oxide nanotubes were synthesized via anodic oxidation method. The morphology and composition structure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results depicted that nanotubes possess anatase phase with average tube diameter of 65 nm and 230 ± 12 nm in length. The band gap of the un-doped and silver doped titanium dioxide nanotubes was determined using UV-Vis. spectrophotometer. The results showed that the band gap of titanium dioxide nanotubes is decreased when doped with silver ions. The photocatalysis activity of un-doped and silver doped TiO2 nanotubes were evaluated in terms of degradation of phenol in the presence of ultra violet irradiation. It was found that silver doped TiO2 nanotubes exhibited much higher photocatalysis activity than un-doped TiO2 nanotubes.

  18. Vibration DOS of 57Fe and Zn doped rutile Sn(Sb) oxides

    NASA Astrophysics Data System (ADS)

    Nomura, Kiyoshi; Rykov, Alexandre; Németh, Zoltán; Yoda, Yoshitaka

    2012-03-01

    Sn oxides co-doped with Zn, Sb and 57Fe were prepared by sol-gel method, and especially the doping effect of non-magnetic Zn ions was studied. The bulk saturation magnetization is in accordance with the intensity of the magnetic component in Mössbauer spectra. The nuclear inelastic scattering (NIS) spectra of these compounds were measured in SPring 8. The vibration density of states (VDOS) of 57Fe doped Sn(Sb) oxides showed that the softening peaks around 15-20 meV appeared by doping less than 10% Zn ions. The clusters of non-magnetic ZnFe2O4 may be most probably formed under the limit of XRD detections. The results suggest that the strengthening of ferromagnetism, which appears in the dilute Zn doping, may occur due to the spin arrangement of dilute Fe3 + through magnetic defects rather than the formation of magnetic iron oxides.

  19. Doping Rules in A2 BO 4 Spinel Oxides

    NASA Astrophysics Data System (ADS)

    Zunger, Alex; Paudel, T.; Stevanovic, V.; Lany, S.

    2011-03-01

    Many of the physical phenomena surrounding Complex Oxide involve the creation and annihilation of charge carriers by cross --substitution of atoms or by the formation of vacancies and interstitials. We have used the machinery of First-Principles defect calculation, developed and tested over the years on semiconductors (where experimental data needed to test DFT corrections is rather clear), applying it to a large number of oxides, initially from the Spinel family. We calculate defect formation energies as a function of temperature and oxygen partial pressure, as well as the concentration of donors and acceptors and the ensuing free carriers. A number of regularities emerge. (i) Oxygen vacancies are not a viable source of electrons and cation vacancies are (usually) not a viable source of holes. (ii) Instead, cation-anti-sites (A-on-B donor and B-on-A acceptors) tend to form in significant numbers and release carriers. (iii) For the group of A3+ and B2+ spinels we find four ``doping classes'' (a) both donor and acceptor are in the gap (Al 2 Mg O4) (b) Only acceptor is in the gap (Co 2 Zn O4) (c) only donor in the gap and (d) none in the gap. Simple regularities can be used as first-order rules to guess electrical behavior from composition. This work was supported through the Center for Inverse Design, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

  20. Nitrogen-doped carbon nanotube as a potential metal-free catalyst for CO oxidation.

    PubMed

    Lin, I-Hsiang; Lu, Yu-Huan; Chen, Hsin-Tsung

    2016-04-28

    We elucidate the possibility of nitrogen-doped carbon nanotube as a robust catalyst for CO oxidation. We have performed first-principles calculations considering the spin-polarization effect to demonstrate the reaction of CO oxidation catalyzed by the nitrogen-doped carbon nanotube. The calculations show that O2 species can be partially reduced with charge transfer from the nitrogen-doped carbon nanotube and directly chemisorbed on the C-N sites of the nitrogen-doped carbon nanotube. The partially reduced O2 species at the C-N sites can further directly react with a CO molecule via the Eley-Rideal mechanism with the barriers of 0.45-0.58 eV for the different diameter of nanotube. Ab initio molecular dynamics (AIMD) simulations were performed and showed that the oxidation of CO occurs by the Eley-Rideal mechanism. The relationship between the curvature and reactivity of the nitrogen doped carbon nanotube was also unraveled. It appears that the barrier height of the rate-limiting step depends on the curvature of the nitrogen-doped carbon nanotube in the trend of (3,3)-NCNT < (4,4)-NCNT < (5,5)-NCNT (decreases with increased curvature). Using this relationship, we can predict the barriers for other N-doped carbon nanotubes with different tube diameters. Our results reveal that the nitrogen doped carbon nanomaterials can be a good, low-cost, and metal-free catalyst for CO oxidation. PMID:27074831

  1. Magnesium oxide doping reduces acoustic wave attenuation in lithium metatantalate and lithium metaniobate crystals

    NASA Technical Reports Server (NTRS)

    Croft, W.; Damon, R.; Kedzie, R.; Kestigian, M.; Smith, A.; Worley, J.

    1970-01-01

    Single crystals of lithium metatantalate and lithium metaniobate, grown from melts having different stoichiometries and different amounts of magnesium oxide, show that doping lowers temperature-independent portion of attenuation of acoustic waves. Doped crystals possess optical properties well suited for electro-optical and photoelastic applications.

  2. Water Oxidation and Oxygen Monitoring by Cobalt-Modified Fluorine-Doped Tin Oxide Electrodes

    SciTech Connect

    Kent, CA; Concepcion, JJ; Dares, CJ; Torelli, DA; Rieth, AJ; Miller, AS; Hoertz, PG; Meyer, TJ

    2013-06-12

    Electrocatalytic water oxidation occurs at fluoride-doped tin oxide (FTO) electrodes that have been surface-modified by addition of Co(II). On the basis of X-ray photoelectron spectroscopy and transmission electron microscopy measurements, the active surface site appears to be a single site or small-molecule assembly bound as Co(II), with no evidence for cobalt oxide film or cluster formation. On the basis of cyclic voltammetry measurements, surface-bound Co(II) undergoes a pH-dependent 1e(-)/1H(+) oxidation to Co(III), which is followed by pH-dependent catalytic water oxidation. O-2 reduction at FTO occurs at -0.33 V vs NHE, allowing for in situ detection of oxygen as it is formed by water oxidation on the surface. Controlled-potential electrolysis at 1.61 V vs NHE at pH 7.2 resulted in sustained water oxidation catalysis at a current density of 0.16 mA/cm(2) with 29 000 turnovers per site over an electrolysis period of 2 h. The turnover frequency for oxygen production per Co site was 4 s(-1) at an overpotential of 800 mV at pH 7.2. Initial experiments with Co(II) on a mesoporous, high-surface-area nanoFTO electrode increased the current density by a factor of similar to 5

  3. Enhancing Sulfur Tolerance of Ni-Based Cermet Anodes of Solid Oxide Fuel Cells by Ytterbium-Doped Barium Cerate Infiltration.

    PubMed

    Li, Meng; Hua, Bin; Luo, Jing-Li; Jiang, San Ping; Pu, Jian; Chi, Bo; Li, Jian

    2016-04-27

    Conventional anode materials for solid oxide fuel cells (SOFCs) are Ni-based cermets, which are highly susceptible to deactivation by contaminants in hydrocarbon fuels. Hydrogen sulfide is one of the commonly existed contaminants in readily available natural gas and gasification product gases of pyrolysis of biomasses. Development of sulfur tolerant anode materials is thus one of the critical challenges for commercial viability and practical application of SOFC technologies. Here we report a viable approach to enhance substantially the sulfur poisoning resistance of a Ni-gadolinia-doped ceria (Ni-GDC) anode through impregnation of proton conducting perovskite BaCe0.9Yb0.1O3-δ (BCYb). The impregnation of BCYb nanoparticles improves the electrochemical performance of the Ni-GDC anode in both H2 and H2S containing fuels. Moreover, more importantly, the enhanced stability is observed in 500 ppm of H2S/H2. The SEM and XPS analysis indicate that the infiltrated BCYb fine particles inhibit the adsorption of sulfur and facilitate sulfur removal from active sites, thus preventing the detrimental interaction between sulfur and Ni-GDC and the formation of cerium sulfide. The preliminary results of the cell with the BCYb+Ni-GDC anode in methane fuel containing 5000 ppm of H2S show the promising potential of the BCYb infiltration approach in the development of highly active and stable Ni-GDC-based anodes fed with hydrocarbon fuels containing a high concentration of sulfur compounds. PMID:27052726

  4. Preparation of spherical ceria coated silica nanoparticle abrasives for CMP application

    NASA Astrophysics Data System (ADS)

    Peedikakkandy, Lekha; Kalita, Laksheswar; Kavle, Pravin; Kadam, Ankur; Gujar, Vikas; Arcot, Mahesh; Bhargava, Parag

    2015-12-01

    This paper describes synthesis of spherical and highly mono-dispersed ceria coated silica nanoparticles of size ∼70-80 nm for application as abrasive particles in Chemical Mechanical Planarization (CMP) process. Core silica nanoparticles were initially synthesized using micro-emulsion method. Ceria coating on these ultrafine and spherical silica nanoparticles was achieved using controlled chemical precipitation method. Study of various parameters influencing the formation of ceria coated silica nanoparticles of size less than 100 nm has been undertaken and reported. Ceria coating over silica nanoparticles was varied by controlling the reaction temperature, pH and precursor concentrations. Characterization studies using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Energy Dispersive X-ray analysis show formation of crystalline CeO2 coating of ∼10 nm thickness over silica with spherical morphology and particle size <100 nm. Aqueous slurry of ceria coated silica abrasive was prepared and employed for polishing of oxide and nitride films on silicon substrates. Polished films were studied using ellipsometry and an improvement in SiO2:SiN selective removal rates up to 12 was observed using 1 wt% ceria coated silica nanoparticles slurry.

  5. Carbon dioxide activation and dissociation on ceria (110): A density functional theory study

    NASA Astrophysics Data System (ADS)

    Cheng, Zhuo; Sherman, Brent J.; Lo, Cynthia S.

    2013-01-01

    Ceria (CeO2) is a promising catalyst for the reduction of carbon dioxide (CO2) to liquid fuels and commodity chemicals, in part because of its high oxygen storage capacity, yet the fundamentals of CO2 adsorption, activation, and reduction on ceria surfaces remain largely unknown. We use density functional theory, corrected for onsite Coulombic interactions (GGA+U), to explore various adsorption sites and configurations for CO2 on stoichiometric and reduced ceria (110), the latter with either an in-plane oxygen vacancy or a split oxygen vacancy. We find that CO2 adsorption on both reduced ceria (110) surfaces is thermodynamically favored over the corresponding adsorption on stoichiometric ceria (110), but the most stable adsorption configuration consists of CO2 adsorbed parallel to the reduced ceria (110) surface at a split oxygen vacancy. Structural changes in the CO2 molecule are also observed upon adsorption. At the split vacancy, the molecule bends out of plane to form a unidentate carbonate with the remaining oxygen anion at the surface; this is in stark contrast to the bridged carbonate observed for CO2 adsorption at the in-plane vacancy. Also, we analyze the pathways for CO2 conversion to CO on reduced ceria (110). The subtle difference in the energies of activation for the elementary steps suggest that CO2 dissociation is favored on the split vacancy, while the reverse process of CO oxidation may favor the formation of the in-plane vacancy. We thus show how the structure and properties of the ceria catalyst govern the mechanism of CO2 activation and reduction.

  6. Synthesis of ethylene and ethane by partial oxidation of methane over lithium-doped magnesium oxide

    NASA Astrophysics Data System (ADS)

    Ito, Tomoyasu; Lunsford, Jack H.

    1985-04-01

    The partial oxidation of methane into more useful chemicals such as methanol, ethylene and benzene has been investigated extensively, although yields for these products have been poor1-4. Moreover, in several of these processes the required oxidant is N2O rather than O2. Recent work5 in our laboratory has demonstrated that lithium-doped magnesium oxide (Li/MgO) in the presence of O2 has high activity for abstracting H from CH4 to form .CH3 radicals. This suggests that C2H6 and C2H4 (C2 compounds) are produced by a coupling between two gaseous .CH3 radicals formed on this catalyst. We report here our success in converting CH4 to C2 compounds in high yields in conventional catalytic conditions.

  7. Oxidation Induced Doping of Nanoparticles Revealed by in Situ X-ray Absorption Studies.

    PubMed

    Kwon, Soon Gu; Chattopadhyay, Soma; Koo, Bonil; Dos Santos Claro, Paula Cecilia; Shibata, Tomohiro; Requejo, Félix G; Giovanetti, Lisandro J; Liu, Yuzi; Johnson, Christopher; Prakapenka, Vitali; Lee, Byeongdu; Shevchenko, Elena V

    2016-06-01

    Doping is a well-known approach to modulate the electronic and optical properties of nanoparticles (NPs). However, doping at nanoscale is still very challenging, and the reasons for that are not well understood. We studied the formation and doping process of iron and iron oxide NPs in real time by in situ synchrotron X-ray absorption spectroscopy. Our study revealed that the mass flow of the iron triggered by oxidation is responsible for the internalization of the dopant (molybdenum) adsorbed at the surface of the host iron NPs. The oxidation induced doping allows controlling the doping levels by varying the amount of dopant precursor. Our in situ studies also revealed that the dopant precursor substantially changes the reaction kinetics of formation of iron and iron oxide NPs. Thus, in the presence of dopant precursor we observed significantly faster decomposition rate of iron precursors and substantially higher stability of iron NPs against oxidation. The same doping mechanism and higher stability of host metal NPs against oxidation was observed for cobalt-based systems. Since the internalization of the adsorbed dopant at the surface of the host NPs is driven by the mass transport of the host, this mechanism can be potentially applied to introduce dopants into different oxidized forms of metal and metal alloy NPs providing the extra degree of compositional control in material design. PMID:27152970

  8. Novel Carbon Dioxide Microsensor Based on Tin Oxide Nanomaterial Doped With Copper Oxide

    NASA Technical Reports Server (NTRS)

    Xu, Jennifer C.; Hunter, Gary W.; Lukco, Dorothy; Liu, Chung-Chiun; Ward, Benjamin J.

    2008-01-01

    Carbon dioxide (CO2) is one of the major indicators of fire and therefore its measurement is very important for low-false-alarm fire detection and emissions monitoring. However, only a limited number of CO2 sensing materials exist due to the high chemical stability of CO2. In this work, a novel CO2 microsensor based on nanocrystalline tin oxide (SnO2) doped with copper oxide (CuO) has been successfully demonstrated. The CuO-SnO2 based CO2 microsensors are fabricated by means of microelectromechanical systems (MEMS) technology and sol-gel nanomaterial-synthesis processes. At a doping level of CuO: SnO2 = 1:8 (molar ratio), the resistance of the sensor has a linear response to CO2 concentrations for the range of 1 to 4 percent CO2 in air at 450 C. This approach has demonstrated the use of SnO2, typically used for the detection of reducing gases, in the detection of an oxidizing gas.

  9. Catalytic propane reforming mechanism over Mn-Doped CeO2 (111)

    NASA Astrophysics Data System (ADS)

    Krcha, Matthew D.; Janik, Michael J.

    2015-10-01

    MnOx/CeOx mixed oxide systems exhibit encouraging hydrocarbon oxidation activity, without the inclusion of a noble metal. Using density functional theory (DFT) methods, we examined the oxidative reforming path of propane over the Mn-doped CeO2 (1 1 1) surface. A plausible set of elementary reaction steps are identified for conversion of propane to CO/CO2 and H2/H2O over the oxide surface. The rate-limiting reaction process may vary with redox conditions, with C-H dissociation limiting under more oxidizing conditions and more complex reaction sequences, including surface re-oxidation, limiting under highly reducing conditions. The possibility of intermediate desorption from the surface during the reforming process is low, with desorption energies of the intermediates being much less favorable than further surface reactions until CO/CO2 products are formed. The reforming paths over Mn-doped ceria are similar to those previously identified over Zr-doped ceria. The extent of surface reduction and the electronic structure of the surface intermediates are examined.

  10. Catalytic soot oxidation over Ce- and Cu-doped hydrotalcites-derived mesoporous mixed oxides.

    PubMed

    Wang, Zhongpeng; Wang, Liguo; He, Fang; Jiang, Zheng; Xiao, Tiancun; Zhang, Zhaoliang

    2014-09-01

    Ce- and Cu-doped hydrotalcites derived mixed oxides were prepared through co-precipitation and calcination method, and their catalytic activities for soot oxidation with O2 and O2/NO were investigated. The solids were characterized by XRD, TG-DTG, BET, H2-TPR, in situ FTIR and TPO techniques. All the catalysts precursors showed the typical diffraction patterns of hydrotalcite-like materials having layered structure. The derived mixed oxides exhibited mesoporous properties with specific surface area of 45-160 m2/g. After both Ce and Cu incorporated, mixed crystalline phases of CuO (tenorite), CeO2 (fluorite) and MgAl2O4 (spinel) were formed. As a result, the NO(x) adsorption capacity of this catalyst was largely increased to 201 μmol/g, meanwhile, it was also the most effective to convert NO into NO2 in the sorption process due to the enhanced reducibility. The in situ FTIR spectra revealed that NO(x) were stored mainly as chelating bidentate and monodentate nitrate. The interaction effect between Cu and Ce in the mixed oxide resulted in different NO(x) adsorption behavior. Compared with the non-catalyzed soot oxidation, soot conversion curves over the mixed oxides catalysts shift to low temperature in O2. The presence of NO in the gas phase significantly enhanced the soot oxidation activity with ignition temperature decreased to about 320 degrees C, which is due to NO conversion to NO2 over the catalyst followed by the reaction of NO2 with soot. This explains the cooperative effect of Ce and Cu in the mixed oxide on soot oxidation with high activity and 100% selectivity to CO2 formation. PMID:25924375

  11. Crystalline structure of ceria particles controlled by the oxygen partial pressure and STI CMP performances.

    PubMed

    Kim, Ye-Hwan; Kim, Sang-Kyun; Kim, Namsoo; Park, Jea-Gun; Paik, Ungyu

    2008-09-01

    The effect of the crystalline structures of nano-sized ceria particles on shallow trench isolation (STI) chemical mechanical planarization (CMP) performance was investigated. The ceria particles were synthesized via a solid-state displacement reaction method, and their crystalline structure was controlled by regulating the oxygen partial pressure at the reaction site on the precursor. The crystalline structures of ceria particles were analyzed by the high-resolution TEM nano-beam diffraction pattern. In a calcination process with a high oxygen concentration, the synthesized ceria particles had a cubic fluorite structure (CeO(2)), because of the decarbonation of the cerium precursor. However, a low oxygen concentration results in a hexagonal phase cerium oxide (Ce(2)O(3)) rather than the cubic phase due to the insufficient oxidation of Ce(3+) to Ce(4+). In the STI CMP evaluation, the ceria slurry prepared with the cubic CeO(2) shows enhanced performances of the oxide-to-nitride removal selectivity. PMID:18562111

  12. Different properties of aluminum doped zinc oxide nanostructured thin films prepared by radio frequency magnetron sputtering

    SciTech Connect

    Bidmeshkipour, Samina Shahtahmasebi, Nasser

    2013-06-15

    Aluminium doped zinc oxide (AZO) nanostructured thin films are prepared by radio frequency magnetron sputtering on glass substrate using specifically designed ZnO target containing different amount of Al{sub 2}O{sub 3} powder as the Al doping source. The optical properties of the aluminium doped zinc oxide films are investigated. The topography of the deposited films were investigated by Atomic Force Microscopy. Variation of the refractive index by annealing temperature are considered and it is seen that the refractive index increases by increasing the annealing temperature.

  13. Impact of thin metal layer on the optical and electrical properties of indium-doped-tin oxide and aluminum-doped-zinc oxide layers

    NASA Astrophysics Data System (ADS)

    Kumar, Melvin David; Park, Yun Chang; Kim, Joondong

    2015-06-01

    The distinguished transparent conductive oxide (TCO) layers like indium-doped-tin oxide (ITO) and aluminum-doped-zinc oxide (AZO) layers were prepared in different combinations with and without thin Ni metal layer. The optical and electrical properties of prepared samples were analyzed and compared with the objective to understand the role and influence of the Ni layer in each TCO combination. The highest transmittance value of 91.49% was exhibited by prepared AZO layers. Even though if the transmittance of Ni inserting TCO layers was marginally reduced than that of the ordinary TCO samples, they exhibited balanced optical properties with enhanced electrical properties. Carrier concentration of indium doped tin-oxide and aluminum doped zinc oxide (ITO/AZO) bilayer sample is increased more than double the times when the Ni layer was inserted between ITO and AZO. Thin layer of Ni in between TCO layers reduced sheet resistance and offered substantial transmittance, so that the figure of merit (FOM) value of Ni embedding TCOs was greater than that of TCOs without Ni layer. The ITO/Ni/AZO combination provided optimum results in all the electrical properties. As compared to other TCO/metal combinations, the overall performance of ITO/Ni/AZO tri-layer combination was appreciable. These results show that the optical and electrical properties of TCO layers could be enhanced by inserting a Ni layer with optimum thickness in between them.

  14. Electrochromic characteristics of niobium-doped titanium oxide film on indium tin oxide/glass by liquid phase deposition

    NASA Astrophysics Data System (ADS)

    Lee, Ming-Kwei; Lee, Chia-Jung

    2015-10-01

    Ammonium hexafluorotitanate and boric acid aqueous solutions were used as precursors for the growth of titanium oxide films on indium tin oxide (ITO)/glass substrate. For as-grown titanium oxide film used in an electrochromic device, Li+ ions from electrolyte will be trapped to hydroxyl groups and degrade the electrochromic durability during the cyclic voltammogram characterization. For niobium doped titanium oxide film, lower growth rate from more HF incorporation from the niobium doped solution and rougher surface morphology from the formation of nanocrystals were obtained. However, niobium doping reduces hydroxyl groups and the electrochromic durability is enhanced from 5 × 103 to 1 × 104 times. The transmittance is enhanced from 37 to 51% at the wavelength of 550 nm.

  15. Fabrication of iron (III) oxide doped polystyrene shells

    NASA Astrophysics Data System (ADS)

    Cai, Pei-Jun; Tang, Yong-Jian; Zhang, Lin; Du, Kai; Feng, Chang-Gen

    2004-03-01

    A type of iron (III) oxide doped plastic shell used for inertial confinement fusion experiments has been fabricated by emulsion techniques. Three different phases of solution (W1, O, and W2) are used for the fabrication process. The W1 phase is a 1 wt % of sodium lauryl sulfate in water. This W1 phase solution is mixed with a 3 wt % Fe2O3-polystyrene (PS) solution in benzene-dichloroethane (O phase) while stirring. The resulting emulsion (W1/O) is poured into a 3 wt % aqueous polyvinyl alcohol solution (W2 phase) while stirring. The resulting emulsion (W1/O/W2) is then heated to evaporate benzene and dichloroethane, and thus a solid Fe2O3-PS shell is formed. The diameter and wall thickness of the shells range from 150 to 500 μm and 5 to 15 μm, respectively. The average surface roughness of the shells is 40 nm, similar to that of the usual PS shells. .

  16. A perfectly stoichiometric and flat CeO2(111) surface on a bulk-like ceria film

    PubMed Central

    Barth, C.; Laffon, C.; Olbrich, R.; Ranguis, A.; Parent, Ph.; Reichling, M.

    2016-01-01

    In surface science and model catalysis, cerium oxide (ceria) is mostly grown as an ultra-thin film on a metal substrate in the ultra-high vacuum to understand fundamental mechanisms involved in diverse surface chemistry processes. However, such ultra-thin films do not have the contribution of a bulk ceria underneath, which is currently discussed to have a high impact on in particular surface redox processes. Here, we present a fully oxidized ceria thick film (180 nm) with a perfectly stoichiometric CeO2(111) surface exhibiting exceptionally large, atomically flat terraces. The film is well-suited for ceria model studies as well as a perfect substitute for CeO2 bulk material. PMID:26879800

  17. A perfectly stoichiometric and flat CeO2(111) surface on a bulk-like ceria film

    NASA Astrophysics Data System (ADS)

    Barth, C.; Laffon, C.; Olbrich, R.; Ranguis, A.; Parent, Ph.; Reichling, M.

    2016-02-01

    In surface science and model catalysis, cerium oxide (ceria) is mostly grown as an ultra-thin film on a metal substrate in the ultra-high vacuum to understand fundamental mechanisms involved in diverse surface chemistry processes. However, such ultra-thin films do not have the contribution of a bulk ceria underneath, which is currently discussed to have a high impact on in particular surface redox processes. Here, we present a fully oxidized ceria thick film (180 nm) with a perfectly stoichiometric CeO2(111) surface exhibiting exceptionally large, atomically flat terraces. The film is well-suited for ceria model studies as well as a perfect substitute for CeO2 bulk material.

  18. Improving the oxidation potential of Sb-doped SnO2 electrode by Zn/Sb co-doping

    NASA Astrophysics Data System (ADS)

    Chen, Aqing; Bin Li, Bin; Miljkovic, Bojan; Souza, Christina; Zhu, Kaigui; Ruda, Harry E.

    2014-07-01

    Inorganic oxides are recognized as attractive materials for developing anodes for wastewater treatment, potentially offering a cost effective solution for electro-oxidation. A key parameter in measuring the effectiveness of different anode materials is the oxygen over potential. In this paper, we study the role of Zn and Sb co-doping of SnO2 thin films to achieve enhanced oxidation potentials, suitable for use in wastewater treatment. The morphology, chemical, and electrochemical properties of the films were characterized, and as a result of an optimization study, suitable anode materials for wastewater treatment are identified.

  19. Synthesis and characterization of N-doped zinc oxide nanotetrapods

    NASA Astrophysics Data System (ADS)

    Al Rifai, S. A.; Kulnitskiy, B. A.

    2016-05-01

    Nitrogen-doped (N-doped) self-assembled nanotetrapods ZnO were synthesized via chemical vapor deposition process using N2O as a dopant source via vapor-solid (VS) growth. The decomposition of N2O gas giving NO and NO2 during the synthesis provided successful N-doping of the sample. All samples (N-doped and undoped) were characterized by XRD, SEM, TEM, EDX, photoluminescence (PL), Fourier transform infrared (FT-IR), and diffuse reflection spectra. After nitrogen-doping process, N-doped ZnO samples show the change in structural and optical properties. The detailed structure and the growth mechanism of individual ZnO tetrapod is characterized by TEM and SEM investigations. The TEM study gives the direct assumption about the formation of zincblende (sphalerite) structure on the initial stage of growth of N-doped tetrapods. Besides, SEM observation indicated that tetrapods have perfect tetrahedral symmetry. N-Doped ZnO samples exhibit a broad orange-red PL emission band, peaking near 2.1 eV, in good agreement with the deep-acceptor model for the nitrogen impurity. An IR absorption peak at 3146 cm-1 at room temperature was observed for N-doped sample. This peak has been unambiguously assigned to N-H complex.

  20. Determination of optical and microstructural parameters of ceria films

    NASA Astrophysics Data System (ADS)

    Oh, Tae-Sik; Tokpanov, Yury S.; Hao, Yong; Jung, WooChul; Haile, Sossina M.

    2012-11-01

    Light-matter interactions are of tremendous importance in a wide range of fields from solar energy conversion to photonics. Here the optical dispersion behavior of undoped and 20 mol. % Sm doped ceria thin films, both dense and porous, were evaluated by UV-Vis optical transmission measurements, with the objective of determining both intrinsic and microstructural properties of the films. Films, ranging from 14 to 2300 nm in thickness, were grown on single crystal YSZ(100) and MgO(100) using pulsed laser deposition (both dense and porous films) and chemical vapor deposition (porous films only). The transmittance spectra were analyzed using an in-house developed methodology combining full spectrum fitting and envelope treatment. The index of refraction of ceria was found to fall between 2.65 at a wavelength of 400 nm and 2.25 at 800 nm, typical of literature values, and was relatively unchanged by doping. Reliable determination of film thickness, porosity, and roughness was possible for films with thickness ranging from 500 to 2500 nm. Physically meaningful microstructural parameters were extracted even for films so thin as to show no interference fringes at all.

  1. Unique Electronic and Structural Effects in Vanadia/Ceria-Catalyzed Reactions.

    PubMed

    Wu, Xin-Ping; Gong, Xue-Qing

    2015-10-21

    Vanadia/ceria supported catalysts exhibit ultrahigh catalytic activities in oxidative dehydrogenation (ODH) reactions. Here, we performed systematic density functional theory calculations to illustrate the underlying mechanisms. It is found that unique electronic and structural effects are both crucial in the catalytic processes. Calculations of the catalytic performance of different oxygen species in oxidation of methanol to formaldehyde suggested that the oxygen of the interface V-O-Ce group is catalytically more active, especially when H adsorption energy is small, indicating the strong structural effect in the vanadia/ceria supported catalyst. In addition, new empty localized states of O 2p generated in a ceria-supported system through depositing VO3- and VO4-type monomeric vanadia species are determined to participate in the whole ODH reaction processes and help to reduce the barriers at various steps. PMID:26440141

  2. Soot Combustion over Nanostructured Ceria with Different Morphologies.

    PubMed

    Zhang, Wen; Niu, Xiaoyu; Chen, Liqiang; Yuan, Fulong; Zhu, Yujun

    2016-01-01

    In this study, nano-structure ceria with three different morphologies (nanorod, nanoparticle and flake) have been prepared by hydrothermal and solvothermal methods. The ceria samples were deeply characterized by XRD, SEM, TEM, H2-TPR, XPS and in-situ DRIFTS, and tested for soot combustion in absence/presence NO atmospheres under loose and tight contact conditions. The prepared ceria samples exhibit excellent catalytic activities, especially, the CeO2 with nanorod (Ce-R) shows the best catalytic activity, for which the peak temperature of soot combustion (Tm) is about 500 and 368 °C in loose and tight contact conditions, respectively. The catalytic activity for Ce-R is higher than that of the reported CeO2 catalysts and reaches a level that of precious metals. The characterization results reveal that the maximal amounts of adsorbed oxygen species on the surface of the nanostructure Ce-R catalyst should be the crucial role to decide the catalytic soot performance. High BET surface area may also be a positive effect on soot oxidation activity under loose contact conditions. PMID:27353143

  3. Soot Combustion over Nanostructured Ceria with Different Morphologies

    NASA Astrophysics Data System (ADS)

    Zhang, Wen; Niu, Xiaoyu; Chen, Liqiang; Yuan, Fulong; Zhu, Yujun

    2016-06-01

    In this study, nano-structure ceria with three different morphologies (nanorod, nanoparticle and flake) have been prepared by hydrothermal and solvothermal methods. The ceria samples were deeply characterized by XRD, SEM, TEM, H2-TPR, XPS and in-situ DRIFTS, and tested for soot combustion in absence/presence NO atmospheres under loose and tight contact conditions. The prepared ceria samples exhibit excellent catalytic activities, especially, the CeO2 with nanorod (Ce-R) shows the best catalytic activity, for which the peak temperature of soot combustion (Tm) is about 500 and 368 °C in loose and tight contact conditions, respectively. The catalytic activity for Ce-R is higher than that of the reported CeO2 catalysts and reaches a level that of precious metals. The characterization results reveal that the maximal amounts of adsorbed oxygen species on the surface of the nanostructure Ce-R catalyst should be the crucial role to decide the catalytic soot performance. High BET surface area may also be a positive effect on soot oxidation activity under loose contact conditions.

  4. Soot Combustion over Nanostructured Ceria with Different Morphologies

    PubMed Central

    Zhang, Wen; Niu, Xiaoyu; Chen, Liqiang; Yuan, Fulong; Zhu, Yujun

    2016-01-01

    In this study, nano-structure ceria with three different morphologies (nanorod, nanoparticle and flake) have been prepared by hydrothermal and solvothermal methods. The ceria samples were deeply characterized by XRD, SEM, TEM, H2-TPR, XPS and in-situ DRIFTS, and tested for soot combustion in absence/presence NO atmospheres under loose and tight contact conditions. The prepared ceria samples exhibit excellent catalytic activities, especially, the CeO2 with nanorod (Ce-R) shows the best catalytic activity, for which the peak temperature of soot combustion (Tm) is about 500 and 368 °C in loose and tight contact conditions, respectively. The catalytic activity for Ce-R is higher than that of the reported CeO2 catalysts and reaches a level that of precious metals. The characterization results reveal that the maximal amounts of adsorbed oxygen species on the surface of the nanostructure Ce-R catalyst should be the crucial role to decide the catalytic soot performance. High BET surface area may also be a positive effect on soot oxidation activity under loose contact conditions. PMID:27353143

  5. Nanocrystals of Uranium Oxide: Controlled Synthesis and Enhanced Electrochemical Performance of Hydrogen Evolution by Ce Doping.

    PubMed

    Hu, Shi; Li, Haoyi; Liu, Huiling; He, Peilei; Wang, Xun

    2015-06-10

    A preliminary study of the growth of 0D, 1D, and 2D nanostructures of uranium oxides with feature sizes from several nanometers down to 1 nm are presented. Cerium is successfully doped into these oxides and its influence on the growth dynamics and electrochemical performance investigated. PMID:25627103

  6. Sulfur and Nitrogen Co-Doped Graphene for Metal-Free Catalytic Oxidation Reactions.

    PubMed

    Duan, Xiaoguang; O'Donnell, Kane; Sun, Hongqi; Wang, Yuxian; Wang, Shaobin

    2015-07-01

    Sulfur and nitrogen co-doped reduced graphene oxide (rGO) is synthesized by a facile method and demonstrated remarkably enhanced activities in metal-free activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol. Based on first-order kinetic model, S-N co-doped rGO (SNG) presents an apparent reaction rate constant of 0.043 ± 0.002 min(-1) , which is 86.6, 22.8, 19.7, and 4.5-fold as high as that over graphene oxide (GO), rGO, S-doped rGO (S-rGO), and N-doped rGO (N-rGO), respectively. A variety of characterization techniques and density functional theory calculations are employed to investigate the synergistic effect of sulfur and nitrogen co-doping. Co-doping of rGO at an optimal sulfur loading can effectively break the inertness of carbon systems, activate the sp(2) -hybridized carbon lattice and facilitate the electron transfer from covalent graphene sheets for PMS activation. Moreover, both electron paramagnetic resonance (EPR) spectroscopy and classical quenching tests are employed to investigate the generation and evolution of reactive radicals on the SNG sample for phenol catalytic oxidation. This study presents a novel metal-free catalyst for green remediation of organic pollutants in water. PMID:25786381

  7. Preparation and characterization of solid electrolytes for solid oxide fuel cells. Quarterly report, July 1--September 30, 1996

    SciTech Connect

    1996-12-31

    During this quarter, the authors have analyzed EXAFS spectra of rare earth doped ceria and identified Gd and Sm doped ceria electrolytes for further investigations in this project. Although electrical properties of the material have been examined in detail, very little work has considered the microstructural/property relationships, particularly in relationship to atomic and geometric structures of these ceria based oxides. The authors have observed an ionic conductivity of 8.3 {times} 10{sup {minus}2} S/Cm in the (CeO{sub 2}){sub 0.8}(GdO{sub 1.5}){sub 0.2} at 800 C which is approximately four times that of Y{sub 2}O{sub 3} doped ZrO{sub 3} doped ZrO{sub 2} at the same temperature. The fraction of Ce{sup +4} ions reduced to Ce{sup +3} as a function of temperature and oxygen partial pressure. The partial reduction of cerium oxide generates mobile electrons and causes electronic conductivity in the electrolyte at temperatures above 500 C. In this quarter, the authors have attempted to measure the microstructural properties using SEM, TEM and HVC STM techniques. Other parts of this investigation are also discussed.

  8. Structural study of VO {sub x} doped aluminium fluoride and aluminium oxide catalysts

    SciTech Connect

    Scheurell, Kerstin; Scholz, Gudrun; Kemnitz, Erhard

    2007-02-15

    The structural properties of vanadium doped aluminium oxyfluorides and aluminium oxides, prepared by a modified sol-gel synthesis route, were thoroughly investigated. The influence of the preparation technique and the calcination temperature on the coordination of vanadium, aluminium and fluorine was analysed by different spectroscopic methods such as Raman, MAS NMR and ESR spectroscopy. In all samples calcined at low temperatures (350 deg. C), vanadium coexists in two oxidation states V{sup IV} and V{sup V}, with V{sup IV} as dominating species in the vanadium doped aluminium oxyfluorides. In the fluoride containing solids aluminium as well as vanadium are coordinated by fluorine and oxygen. Thermal annealing of 800 deg. C leads to an extensive reorganisation of the original matrices and to the oxidation of V{sup IV} to V{sup V} in both systems. - Graphical abstract: Structure model for VO {sub x} doped aluminium oxide.

  9. Exploring routes to tailor the physical and chemical properties of oxides via doping: an STM study.

    PubMed

    Nilius, Niklas

    2015-08-01

    Doping opens fascinating possibilities for tailoring the electronic, optical, magnetic, and chemical properties of oxides. The dopants perturb the intrinsic behavior of the material by generating charge centers for electron transfer into adsorbates, by inducing new energy levels for electronic and optical excitations, and by altering the surface morphology and hence the adsorption and reactivity pattern. Despite a vivid scientific interest, knowledge on doped oxides is limited when compared to semiconductors, which reflects the higher complexity and the insulating nature of many oxides. In fact, atomic-scale studies, aiming at a mechanistic understanding of dopant-related processes, are still scarce.In this article, we review our scanning tunneling microscopy (STM) experiments on thin, crystalline oxide films with a defined doping level. We demonstrate how the impurities alter the surface morphology and produce cationic/anionic vacancies in order to keep the system charge neutral. We discuss how individual dopants can be visualized in the lattice, even if they reside in subsurface layers. By means of STM-conductance and x-ray photoelectron spectroscopy, we determine the electronic impact of dopants, including the energies of their eigen states and local band-bending effects in the host oxide. Electronic transitions between dopant-induced gap states give rise to new optical modes, as detected with STM luminescence spectroscopy. From a chemical perspective, dopants are introduced to improve the redox potential of oxide materials. Electron transfer from Mo-donors, for example, alters the growth behavior of gold and activates O2 molecules on a wide-gap CaO surface. Such results demonstrate the enormous potential of doped oxides in heterogeneous catalysis. Our experiments address the issue of doping from a fundamental viewpoint, posing questions on the lattice position, charge state, and electron-transfer potential of the impurity ions. Whether doped oxides are suitable

  10. Iodine doping effects on the lattice thermal conductivity of oxidized polyacetylene nanofibers

    SciTech Connect

    Bi, Kedong E-mail: kedongbi@seu.edu.cn; Weathers, Annie; Pettes, Michael T.; Shi, Li E-mail: kedongbi@seu.edu.cn; Matsushita, Satoshi; Akagi, Kazuo; Goh, Munju

    2013-11-21

    Thermal transport in oxidized polyacetylene (PA) nanofibers with diameters in the range between 74 and 126 nm is measured with the use of a suspended micro heater device. With the error due to both radiation and contact thermal resistance corrected via a differential measurement procedure, the obtained thermal conductivity of oxidized PA nanofibers varies in the range between 0.84 and 1.24 W m{sup −1} K{sup −1} near room temperature, and decreases by 40%–70% after iodine doping. It is also found that the thermal conductivity of oxidized PA nanofibers increases with temperature between 100 and 350 K. Because of exposure to oxygen during sample preparation, the PA nanofibers are oxidized to be electrically insulating before and after iodine doping. The measurement results reveal that iodine doping can result in enhanced lattice disorder and reduced lattice thermal conductivity of PA nanofibers. If the oxidation issue can be addressed via further research to increase the electrical conductivity via doping, the observed suppressed lattice thermal conductivity in doped polymer nanofibers can be useful for the development of such conducting polymer nanostructures for thermoelectric energy conversion.

  11. Effects of Calcination and Milling Process Conditions for Ceria Slurry on Shallow-Trench-Isolation Chemical-Mechanical Polishing Performance

    NASA Astrophysics Data System (ADS)

    Kim, Jun-Seok; Kang, Hyun-Goo; Kanemoto, Manabu; Paik, Ungyu; Park, Jea-Gun

    2007-12-01

    To improve the performance of shallow trench isolation chemical-mechanical polishing (STI-CMP) in terms of the removal selectivity of oxide and nitride films and the formation of surface defects, we investigated the effects of the calcination and milling process conditions during ceria slurry synthesis. We have focused on the effects of particle size distribution, the large-particle size, and the dispersion stability in a ceria slurry. We determined the optimum bead size for milling and appropriate calcination temperatures in order to obtain a reasonable particle distribution, with lower numbers of fine primary particles and large, agglomerated particles, in ceria slurry. This was achieved by reducing the quantity of aggregated particles during milling and two-step calcination process generating higher-density particles. These results can be qualitatively explained by abrasive collisions occurring between the milling beads and the decarbonation of cerium carbonate through diffusion during the manufacturing process used for the ceria slurry.

  12. Plasma-induced highly efficient synthesis of boron doped reduced graphene oxide for supercapacitors.

    PubMed

    Li, Shaobo; Wang, Zhaofeng; Jiang, Hanmei; Zhang, Limei; Ren, Jingzheng; Zheng, Mingtao; Dong, Lichun; Sun, Luyi

    2016-09-21

    In this work, we presented a novel route to synthesize boron doped reduced graphene oxide (rGO) by using the dielectric barrier discharge (DBD) plasma technology under ambient conditions. The doping of boron (1.4 at%) led to a significant improvement in the capacitance of rGO and supercapacitors based on the as-synthesized B-rGO exhibited an outstanding specific capacitance. PMID:27534806

  13. Gas-generated thermal oxidation of a coordination cluster for an anion-doped mesoporous metal oxide

    PubMed Central

    Hirai, Kenji; Isobe, Shigehito; Sada, Kazuki

    2015-01-01

    Central in material design of metal oxides is the increase of surface area and control of intrinsic electronic and optical properties, because of potential applications for energy storage, photocatalysis and photovoltaics. Here, we disclose a facile method, inspired by geochemical process, which gives rise to mesoporous anion-doped metal oxides. As a model system, we demonstrate that simple calcination of a multinuclear coordination cluster results in synchronic chemical reactions: thermal oxidation of Ti8O10(4-aminobenzoate)12 and generation of gases including amino-group fragments. The gas generation during the thermal oxidation of Ti8O10(4-aminobenzoate)12 creates mesoporosity in TiO2. Concurrently, nitrogen atoms contained in the gases are doped into TiO2, thus leading to the formation of mesoporous N-doped TiO2. The mesoporous N-doped TiO2 can be easily synthesized by calcination of the multinuclear coordination cluster, but shows better photocatalytic activity than the one prepared by a conventional sol-gel method. Owing to an intrinsic designability of coordination compounds, this facile synthetic will be applicable to a wide range of metal oxides and anion dopants. PMID:26681104

  14. Gas-generated thermal oxidation of a coordination cluster for an anion-doped mesoporous metal oxide.

    PubMed

    Hirai, Kenji; Isobe, Shigehito; Sada, Kazuki

    2015-01-01

    Central in material design of metal oxides is the increase of surface area and control of intrinsic electronic and optical properties, because of potential applications for energy storage, photocatalysis and photovoltaics. Here, we disclose a facile method, inspired by geochemical process, which gives rise to mesoporous anion-doped metal oxides. As a model system, we demonstrate that simple calcination of a multinuclear coordination cluster results in synchronic chemical reactions: thermal oxidation of Ti8O10(4-aminobenzoate)12 and generation of gases including amino-group fragments. The gas generation during the thermal oxidation of Ti8O10(4-aminobenzoate)12 creates mesoporosity in TiO2. Concurrently, nitrogen atoms contained in the gases are doped into TiO2, thus leading to the formation of mesoporous N-doped TiO2. The mesoporous N-doped TiO2 can be easily synthesized by calcination of the multinuclear coordination cluster, but shows better photocatalytic activity than the one prepared by a conventional sol-gel method. Owing to an intrinsic designability of coordination compounds, this facile synthetic will be applicable to a wide range of metal oxides and anion dopants. PMID:26681104

  15. Effects of erbium doping of indium tin oxide electrode in resistive random access memory

    NASA Astrophysics Data System (ADS)

    Chen, Po-Hsun; Chang, Kuan-Chang; Chang, Ting-Chang; Tsai, Tsung-Ming; Pan, Chih-Hung; Lin, Chih-Yang; Jin, Fu-Yuan; Chen, Min-Chen; Huang, Hui-Chun; Lo, Ikai; Zheng, Jin-Cheng; Sze, Simon M.

    2016-03-01

    Identical insulators and bottom electrodes were fabricated and capped by an indium tin oxide (ITO) film, either undoped or doped with erbium (Er), as a top electrode. This distinctive top electrode dramatically altered the resistive random access memory (RRAM) characteristics, for example, lowering the operation current and enlarging the memory window. In addition, the RESET voltage increased, whereas the SET voltage remained almost the same. A conduction model of Er-doped ITO is proposed through current-voltage (I-V) measurement and current fitting to explain the resistance switching mechanism of Er-doped ITO RRAM and is confirmed by material analysis and reliability tests.

  16. Influence of the metal precursor on the catalytic behavior of Pt/ceria catalysts in the preferential oxidation of CO in the presence of H₂ (PROX).

    PubMed

    Jardim, Erika O; Rico-Francés, Soledad; Coloma, Fernando; Anderson, James A; Silvestre-Albero, Joaquín; Sepúlveda-Escribano, Antonio

    2015-04-01

    The effect of the metal precursor (presence or absence of chlorine) on the preferential oxidation of CO in the presence of H2 over Pt/CeO2 catalysts has been studied. The catalysts are prepared using (Pt(NH3)4)(NO3)2 and H2PtCl6, as precursors, in order to ascertain the effect of the chlorine species on the chemical properties of the support and on the catalytic behavior of these systems in the PROX reaction. The results show that chloride species exert an important effect on the redox properties of the oxide support due to surface chlorination. Consequently, the chlorinated catalyst exhibits a poorer catalytic activity at low temperatures compared with the chlorine-free catalyst, and this is accompanied by a higher selectivity to CO2 even at high reaction temperatures. It is proposed that the CO oxidation mechanism follows different pathways on each catalyst. PMID:25531415

  17. Electrocatalytic oxidation of Epinephrine and Norepinephrine at metal oxide doped phthalocyanine/MWCNT composite sensor

    PubMed Central

    Mphuthi, Ntsoaki G.; Adekunle, Abolanle S.; Ebenso, Eno E.

    2016-01-01

    Glassy carbon electrode (GCE) was modified with metal oxides (MO = Fe3O4, ZnO) nanoparticles doped phthalocyanine (Pc) and functionalized MWCNTs, and the electrocatalytic properties were studied. Successful synthesis of the metal oxide nanoparticles and the MO/Pc/MWCNT composite were confirmed using FTIR, Raman and SEM techniques. The electrodes were characterized using cyclic voltammetry (CV) technique. The electrocatalytic behaviour of the electrode towards epinephrine (EP) and norepinephrine (NE) oxidation was investigated using CV and DPV. Result showed that GCE-MWCNT/Fe3O4/2,3-Nc, GCE-MWCNT/Fe3O429H,31H-Pc, GCE-MWCNT/ZnO/2,3-Nc and GCE-MWCNT/ZnO/29H,31H-Pc electrodes gave enhanced EP and NE current response. Stability study indicated that the four GCE-MWCNT/MO/Pc modified electrodes were stable against electrode fouling effect with the percentage NE current drop of 5.56–5.88% after 20 scans. GCE-MWCNT/Fe3O4/29H,31H-Pc gave the lowest limit of detection (4.6 μM) towards EP while MWCNT/ZnO/29H,31H-Pc gave the lowest limit of detection (1.7 μM) towards NE. The limit of detection and sensitivity of the electrodes compared well with literature. Electrocatalytic oxidation of EP and NE on GCE-MWCNT/MO/Pc electrodes was diffusion controlled with some adsorption of electro-oxidation reaction intermediates products. The electrodes were found to be electrochemically stable, reusable and can be used for the analysis of EP and NE in real life samples. PMID:27245690

  18. Electrocatalytic oxidation of Epinephrine and Norepinephrine at metal oxide doped phthalocyanine/MWCNT composite sensor.

    PubMed

    Mphuthi, Ntsoaki G; Adekunle, Abolanle S; Ebenso, Eno E

    2016-01-01

    Glassy carbon electrode (GCE) was modified with metal oxides (MO = Fe3O4, ZnO) nanoparticles doped phthalocyanine (Pc) and functionalized MWCNTs, and the electrocatalytic properties were studied. Successful synthesis of the metal oxide nanoparticles and the MO/Pc/MWCNT composite were confirmed using FTIR, Raman and SEM techniques. The electrodes were characterized using cyclic voltammetry (CV) technique. The electrocatalytic behaviour of the electrode towards epinephrine (EP) and norepinephrine (NE) oxidation was investigated using CV and DPV. Result showed that GCE-MWCNT/Fe3O4/2,3-Nc, GCE-MWCNT/Fe3O429H,31H-Pc, GCE-MWCNT/ZnO/2,3-Nc and GCE-MWCNT/ZnO/29H,31H-Pc electrodes gave enhanced EP and NE current response. Stability study indicated that the four GCE-MWCNT/MO/Pc modified electrodes were stable against electrode fouling effect with the percentage NE current drop of 5.56-5.88% after 20 scans. GCE-MWCNT/Fe3O4/29H,31H-Pc gave the lowest limit of detection (4.6 μM) towards EP while MWCNT/ZnO/29H,31H-Pc gave the lowest limit of detection (1.7 μM) towards NE. The limit of detection and sensitivity of the electrodes compared well with literature. Electrocatalytic oxidation of EP and NE on GCE-MWCNT/MO/Pc electrodes was diffusion controlled with some adsorption of electro-oxidation reaction intermediates products. The electrodes were found to be electrochemically stable, reusable and can be used for the analysis of EP and NE in real life samples. PMID:27245690

  19. Electrocatalytic oxidation of Epinephrine and Norepinephrine at metal oxide doped phthalocyanine/MWCNT composite sensor

    NASA Astrophysics Data System (ADS)

    Mphuthi, Ntsoaki G.; Adekunle, Abolanle S.; Ebenso, Eno E.

    2016-06-01

    Glassy carbon electrode (GCE) was modified with metal oxides (MO = Fe3O4, ZnO) nanoparticles doped phthalocyanine (Pc) and functionalized MWCNTs, and the electrocatalytic properties were studied. Successful synthesis of the metal oxide nanoparticles and the MO/Pc/MWCNT composite were confirmed using FTIR, Raman and SEM techniques. The electrodes were characterized using cyclic voltammetry (CV) technique. The electrocatalytic behaviour of the electrode towards epinephrine (EP) and norepinephrine (NE) oxidation was investigated using CV and DPV. Result showed that GCE-MWCNT/Fe3O4/2,3-Nc, GCE-MWCNT/Fe3O429H,31H-Pc, GCE-MWCNT/ZnO/2,3-Nc and GCE-MWCNT/ZnO/29H,31H-Pc electrodes gave enhanced EP and NE current response. Stability study indicated that the four GCE-MWCNT/MO/Pc modified electrodes were stable against electrode fouling effect with the percentage NE current drop of 5.56–5.88% after 20 scans. GCE-MWCNT/Fe3O4/29H,31H-Pc gave the lowest limit of detection (4.6 μM) towards EP while MWCNT/ZnO/29H,31H-Pc gave the lowest limit of detection (1.7 μM) towards NE. The limit of detection and sensitivity of the electrodes compared well with literature. Electrocatalytic oxidation of EP and NE on GCE-MWCNT/MO/Pc electrodes was diffusion controlled with some adsorption of electro-oxidation reaction intermediates products. The electrodes were found to be electrochemically stable, reusable and can be used for the analysis of EP and NE in real life samples.

  20. Method of Fabrication of High Power Density Solid Oxide Fuel Cells

    DOEpatents

    Pham, Ai Quoc; Glass, Robert S.

    2008-09-09

    A method for producing ultra-high power density solid oxide fuel cells (SOFCs). The method involves the formation of a multilayer structure cells wherein a buffer layer of doped-ceria is deposited intermediate a zirconia electrolyte and a cobalt iron based electrode using a colloidal spray deposition (CSD) technique. For example, a cobalt iron based cathode composed of (La,Sr)(Co,Fe)O(LSCF) may be deposited on a zirconia electrolyte via a buffer layer of doped-ceria deposited by the CSD technique. The thus formed SOFC have a power density of 1400 mW/cm.sup.2 at 600.degree. C. and 900 mW/cm.sup.2 at 700.degree. C. which constitutes a 2-3 times increased in power density over conventionally produced SOFCs.

  1. Photocatalytic and photoelectrochemical water oxidation over metal-doped monoclinic BiVO(4) photoanodes.

    PubMed

    Parmar, Kanak Pal Singh; Kang, Hyun Joon; Bist, Amita; Dua, Piyush; Jang, Jum Suk; Lee, Jae Sung

    2012-10-01

    The visible-light-induced water oxidation ability of metal-ion-doped BiVO(4) was investigated and of 12 metal ion dopants tested, only W and Mo dramatically enhanced the water photo-oxidation activity of bare BiVO(4); Mo had the highest improvement by a factor of about six. Thus, BiVO(4) and W- or Mo-doped (2 atom %) BiVO(4) photoanodes about 1 μm thick were fabricated onto transparent conducting substrate by a metal-organic decomposition/spin-coating method. Under simulated one sun (air mass 1.5G, 100 mW cm(-2)) and at 1.23 V versus a reversible hydrogen electrode, the highest photocurrent density (J(PH)) of about 2.38 mA cm(-2) was achieved for Mo doping followed by W doping (J(PH) ≈ 1.98 mA cm(-2)), whereas undoped BiVO(4) gave a J(PH) value of about 0.42 mA cm(-2). The photoelectrochemical water oxidation activity of W- and Mo-doped BiVO(4) photoanodes corresponded to the incident photon to current conversion efficiency of about 35 and 40 % respectively. Electrochemical impedance spectroscopy and Mott-Schottky analysis indicated a positive flat band shift of about 30 mV, a carrier concentration 1.6-2 times higher, and a charge-transfer resistance reduced by 3-4-fold for W- or Mo-doped BiVO(4) relative to undoped BiVO(4). Electronic structure calculations revealed that both W and Mo were shallow donors and Mo doping generated superior conductivity to W doping. The photo-oxidation activity of water on BiVO(4) photoanodes (undopeddopeddoped) was in accordance with the results from electrochemical impedance spectroscopy, Mott-Schottky analysis, and theoretical electronic structural calculations. Thus, Mo or W doping enhanced the photocatalytic and photoelectrochemical water oxidation activity of monoclinic BiVO(4) by drastically reducing its charge-transfer resistance and thereby minimizing photoexcited electron-hole pair recombination. PMID:22927058

  2. Growth of semiconducting single-walled carbon nanotubes by using ceria as catalyst supports.

    PubMed

    Qin, Xiaojun; Peng, Fei; Yang, Feng; He, Xiaohui; Huang, Huixin; Luo, Da; Yang, Juan; Wang, Sheng; Liu, Haichao; Peng, Lianmao; Li, Yan

    2014-02-12

    The growth of semiconducting single-walled carbon nanotubes (s-SWNTs) on flat substrates is essential for the application of SWNTs in electronic and optoelectronic devices. We developed a flexible strategy to selectively grow s-SWNTs on silicon substrates using a ceria-supported iron or cobalt catalysts. Ceria, which stores active oxygen, plays a crucial role in the selective growth process by inhibiting the formation of metallic SWNTs via oxidation. The so-produced ultralong s-SWNT arrays are immediately ready for building field effect transistors. PMID:24392872

  3. Multi-wavelength Raman scattering of nanostructured Al-doped zinc oxide

    SciTech Connect

    Russo, V.; Ghidelli, M.; Gondoni, P.

    2014-02-21

    In this work we present a detailed Raman scattering investigation of zinc oxide and aluminum-doped zinc oxide (AZO) films characterized by a variety of nanoscale structures and morphologies and synthesized by pulsed laser deposition under different oxygen pressure conditions. The comparison of Raman spectra for pure ZnO and AZO films with similar morphology at the nano/mesoscale allows to investigate the relation between Raman features (peak or band positions, width, relative intensity) and material properties such as local structural order, stoichiometry, and doping. Moreover Raman measurements with three different excitation lines (532, 457, and 325 nm) point out a strong correlation between vibrational and electronic properties. This observation confirms the relevance of a multi-wavelength Raman investigation to obtain a complete structural characterization of advanced doped oxide materials.

  4. Electrochemical synthesis and properties of ceria films grown on stainless steel

    NASA Astrophysics Data System (ADS)

    Živković, Lj. S.; Lair, V.; Lupan, O.; Ringuedé, A.

    2011-12-01

    Electrochemical synthesis of ceria films was performed on a stainless steel substrate in view of Solid Oxide Fuel Cells (SOFC) applications. Films were obtained from aqueous nitrate solutions via cathodic deposition method at room temperature. A constant potential value of -0.8 V/(SCE) was applied to reduce the molecular oxygen as hydroxide precursor, leading to a formation of adherent, homogeneous and covering films in 20 min deposition time. Structure, morphology and composition of as-grown coatings were studied by X-ray diffraction, Raman and energy-dispersive X-ray spectroscopy, as well as scanning electron microscopy. Cubic fluorite-type nanostructured ceria of leaf-like particles was synthesized. Thermal annealing (600°C, 1 h) was found to enhance ceria crystallinity.

  5. Formation of N3(-) during interaction of NO with reduced ceria.

    PubMed

    Mihaylov, Mihail Y; Ivanova, Elena Z; Aleksandrov, Hristiyan A; St Petkov, Petko; Vayssilov, Georgi N; Hadjiivanov, Konstantin I

    2015-04-01

    We show that the first stages of interaction between NO and reduced ceria comprise the formation of azides, N3(-), with simultaneous oxidation of Ce(3+) to Ce(4+). This finding imposes revision on some current views of catalytic NO conversion and may contribute to design of new deNOx materials and processes. PMID:25714684

  6. One - Step synthesis of nitrogen doped reduced graphene oxide with NiCo nanoparticles for ethanol oxidation in alkaline media.

    PubMed

    Kakaei, Karim; Marzang, Kamaran

    2016-01-15

    Development of anode catalysts and catalyst supporting carbonaceous material containing non-precious metal have attracted tremendous attention in the field of direct ethanol fuel cells (DEFCs). Herein, we report the synthesis and electrochemical properties of nitrogen-doped reduced graphene oxide (NRGO) supported Co, Ni and NiCo nanocomposites. The metal NRGO nanocomposites, in which metal nanoparticles are embedded in the highly porous nitrogen-doped graphene matrix, have been synthesized by simply and one-pot method at a mild temperature using GO, urea choline chloride and urea as reducing and doping agent. The fabricated NiCo/NRGO exhibit remarkable electrocatalytic activity (with Tafel slope of 159.1mVdec(-1)) and high stability for the ethanol oxidation reaction (EOR). The superior performance of the alloy based NRGO is attributed to high surface area, well uniform distribution of high-density nitrogen, metal active sites and synergistic effect. PMID:26454373

  7. Contact doping of silicon wafers and nanostructures with phosphine oxide monolayers.

    PubMed

    Hazut, Ori; Agarwala, Arunava; Amit, Iddo; Subramani, Thangavel; Zaidiner, Seva; Rosenwaks, Yossi; Yerushalmi, Roie

    2012-11-27

    Contact doping method for the controlled surface doping of silicon wafers and nanometer scale structures is presented. The method, monolayer contact doping (MLCD), utilizes the formation of a dopant-containing monolayer on a donor substrate that is brought to contact and annealed with the interface or structure intended for doping. A unique feature of the MLCD method is that the monolayer used for doping is formed on a separate substrate (termed donor substrate), which is distinct from the interface intended for doping (termed acceptor substrate). The doping process is controlled by anneal conditions, details of the interface, and molecular precursor used for the formation of the dopant-containing monolayer. The MLCD process does not involve formation and removal of SiO(2) capping layer, allowing utilization of surface chemistry details for tuning and simplifying the doping process. Surface contact doping of intrinsic Si wafers (i-Si) and intrinsic silicon nanowires (i-SiNWs) is demonstrated and characterized. Nanowire devices were formed using the i-SiNW channel and contact doped using the MLCD process, yielding highly doped SiNWs. Kelvin probe force microscopy (KPFM) was used to measure the longitudinal dopant distribution of the SiNWs and demonstrated highly uniform distribution in comparison with in situ doped wires. The MLCD process was studied for i-Si substrates with native oxide and H-terminated surface for three types of phosphorus-containing molecules. Sheet resistance measurements reveal the dependency of the doping process on the details of the surface chemistry used and relation to the different chemical environments of the P═O group. Characterization of the thermal decomposition of several monolayer types formed on SiO(2) nanoparticles (NPs) using TGA and XPS provides insight regarding the role of phosphorus surface chemistry at the SiO(2) interface in the overall MLCD process. The new MLCD process presented here for controlled surface doping

  8. Electrodeposition of zinc oxide nanowires: Growth, doping, and physical properties

    NASA Astrophysics Data System (ADS)

    Thomas, Matthew Allan

    As a transparent, wide bandgap semiconductor, ZnO offers an expansive range of potential uses in various technological arenas such as electronics, optoelectronics, photonics, sensors, and energy conversion. However, a current obstacle to the realization of ZnO based electronics and optoelectronics is the lack of a reliable and reproducible method for fabricating high quality p-type ZnO. In addition, there remains a difficulty in tuning the various properties of ZnO materials, especially nanostructures, via low cost and low temperature deposition techniques. In this work, some of these deficiencies have been addressed. Undoped and Ag-doped ZnO nanowires, as well as highly uniform and dense ZnO films, were obtained by an inexpensive, low temperature, electrochemical technique in aqueous solution. The effects of electrochemical growth conditions and Ag-doping on the structural, optical, and electrical properties of the ZnO nanowires were investigated in detail. Ag-doping was found to induce significant changes in the various physical properties of the ZnO nanowires. Importantly, a range of experimental and theoretical results indicate Ag is doped into the ZnO nanowire structure and leads to p-type properties of the nanowires. The room temperature photoluminescence (PL) of the nanowires illustrates bandgap reduction, while intense emissions from a free electron to neutral acceptor were induced in the low temperature PL upon Ag-doping. The electrical properties of the Ag-doped nanowires were probed with photoelectrochemical cell measurements, providing further evidence for their p-type nature. The mechanism of Ag-doping in the nanowires was explored with cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Interestingly, the presence of Ag+ in the growth process catalyzes and enhances the electrochemistry, shifting the ZnO growth conditions to an O-rich environment. These conditions enable a more efficient Ag

  9. Surfactant-assisted ultrasonic spray pyrolysis of nickel oxide and lithium-doped nickel oxide thin films, toward electrochromic applications

    NASA Astrophysics Data System (ADS)

    Denayer, Jessica; Bister, Geoffroy; Simonis, Priscilla; Colson, Pierre; Maho, Anthony; Aubry, Philippe; Vertruyen, Bénédicte; Henrist, Catherine; Lardot, Véronique; Cambier, Francis; Cloots, Rudi

    2014-12-01

    Lithium-doped nickel oxide and undoped nickel oxide thin films have been deposited on FTO/glass substrates by a surfactant-assisted ultrasonic spray pyrolysis. The addition of polyethylene glycol in the sprayed solution has led to improved uniformity and reduced light scattering compared to films made without surfactant. Furthermore, the presence of lithium ions in NiO films has resulted in improved electrochromic performances (coloration contrast and efficiency), but with a slight decrease of the electrochromic switching kinetics.

  10. Fluorine-Doped and Partially Oxidized Tantalum Carbides as Nonprecious Metal Electrocatalysts for Methanol Oxidation Reaction in Acidic Media.

    PubMed

    Yue, Xin; He, Chunyong; Zhong, Chengyong; Chen, Yuanping; Jiang, San Ping; Shen, Pei Kang

    2016-03-16

    A nonprecious metal electrocatalyst based on fluorine-doped tantalum carbide with an oxidative surface on graphitized carbon (TaCx FyOz/(g)C) is developed by using a simple one-pot in situ ion exchange and adsorption method, and the TaCxFyOz/(g)C shows superior performance and durability for methanol oxidation reaction and extreme tolerance to CO poisoning in acidic media. PMID:26779940

  11. N + doping of gallium arsenide by rapid thermal oxidation of a silicon cap

    NASA Astrophysics Data System (ADS)

    Sadana, D. K.; de Souza, J. P.; Cardone, F.

    1990-10-01

    Shallow (<200 nm) Si profiles with doping levels in excess of 2×1018 cm-3 were reproducively obtained in GaAs by rapid thermal oxidation (RTO) of Si caps (50 or 160 nm) in 0.1% O2/Ar ambient at 850-1050 °C. The doping level as well as distribution of the diffused Si can be controlled by the thickness of the Si cap, RTO temperature, RTO time, and oxygen level in the annealing ambient. It appears that the generation of Si interstitials at the oxidizing surface of the Si cap during RTO is responsible for the Si diffusion into the underlying GaAs substrate.

  12. Design and simulation of oxide and doping engineered lateral bipolar junction transistors for high power applications

    NASA Astrophysics Data System (ADS)

    Loan, Sajad A.; Bashir, Faisal; Akhoon, M. Saqib; Alamoud, Abdulrahman M.

    2016-01-01

    In this paper, we propose new structures of lateral bipolar junction transistor (LBJT) on silicon on insulator (SOI) with improved performance. The proposed devices are lateral bipolar transistors with multi doping zone collector drift region and a thick buried oxide under the collector region. Calibrated simulation studies have revealed that the proposed devices have higher breakdown voltage than the conventional device, that too at higher drift doping concentration. This has resulted in improved tradeoff between the on-resistance and the breakdown voltage of the proposed devices. It has been observed that the proposed device with two collector drift doping zones and a buried oxide thick step results in ∼190% increase in the breakdown voltage than the conventional device. The further increase in the number of collector drift doping zones from two to three has increased the breakdown voltage by 260% than the conventional one. On comparing the proposed devices with the buried oxide double step devices, it has been found that an increase of ∼15-19% in the breakdown voltage is observed in the proposed devices even at higher drift doping concentrations. The use of higher drift doping concentration reduces the on-resistance of the proposed device and thus improves the tradeoff between the breakdown voltage and the on-resistance of the proposed device in comparison to buried oxide double step devices. Further, the use of step doping in the collector drift region has resulted in the reduction of kink effect in the proposed device. Using the mixed mode simulations, the proposed devices have been tested at the circuit level, by designing and simulating inverting amplifiers employing the proposed devices. Both DC and AC analyses of the inverting amplifiers have shown that the proposed devices work well at the circuit level. It has been observed that there is a slight increase in ON delay in the proposed device; however, the OFF delay is more or less same as that of the

  13. Magnetic and electrical properties of transition-metal-doped oxide thin films

    NASA Astrophysics Data System (ADS)

    Lam, Ching Yee

    In this research programme, the electrical and magnetic properties of PLD and room temperature grown TM-doped TiO2 and TM-doped Cu xO thin films have been investigated. We used Co and Fe as the TM dopants for the TiO2 based films. Mn was however used to dope the Cu xO materials systems. Among the various electrical properties, resistive switching of transition-metal oxide thin films and electrical rectifying property of an all-oxide p-n diode have been studied. The resistive switching of anatase phase TM-doped TiO 2 has been determined using two top-down configurations of Ag/TM-doped TiO2/Pt and In/TM-doped TiO2/TiN. Despite the fact that same transition-metal oxide was used, the switching characteristics of these two configurations were significantly different. For example, both the unipolar and bipolar switching were observed in pure TiO2 films. Heterostructures of Ag/TiO2/Pt have also been deposited on flexible PET substrates at room temperature by PLD. These oxide films on flexible substrate not only show resistive switching, but produce an average switching ratio as high as over 6 orders of magnitude. The resistive switching in In/CuxO/Pt and In/Mn-doped CuxO/Pt films have also been demonstrated in the present study. Our results indicate clearly that the switching stability of the In/CuxO/Pt systems is improved by the Mn-doping. Our ultimate goal is to produce a ferromagnetic all-oxide p-n junction diode. We obtained room-temperature ferromagnetism in the epitaxially grown anatase n-type Co-doped TiO2 and possible p-type Fe-doped TiO 2 thin films. At the same time, the 3.7 at.% Mn-doped Cu2O epitaxial films have been prepared. They are p-type conducting and have been properly utilized to form good rectifying all-oxide heterojunction with the n-type Nb-SrTiO3 substrates. The p-type Mn-doped Cu2O films that we have made so far, although exhibit ferromagnetism at low temperatures <50K, do not reveal any room temperature ferromagnetic characteristics. It is

  14. Electrical and Optical Properties of Hydrogen Doped Aluminum-Doped Zinc Oxide Thin Films for Low Cost Applications.

    PubMed

    Park, Yong Seob; Park, Young; Kwon, Samyoung; Kim, Eung Kwon; Choi, Wonseok; Kim, Donguk; Kim, Minha; Lee, Jaehyeong

    2016-05-01

    Aluminum-doped zinc oxide (AZO) thin films were prepared on glass substrate using a magnetron sputtering system. In this work, a powder target was used as a source material for low cost applications, instead of a conventional sintered ceramic target. The effects of the hydrogen gas ratio on the electrical and optical properties of the AZO films. The hydrogen doped AZO (AZO:H) films had a hexagonal polycrystalline structure. A small amount of hydrogen gas deteriorated the electrical and optical properties of the AZO:H films. However, these properties improved, as the H2/(H2 + Ar) gas ratio increased. The AZO:H films grown at an H2/(H2+Ar) ratio of 10% showed good properties for low cost applications, such as a low resistivity of 1.35 x 10(-3) Ω-cm, high average transmittance of 83.1% in the visible range of light. PMID:27483879

  15. Zirconium doped nano-dispersed oxides of Fe, Al and Zn for destruction of warfare agents

    SciTech Connect

    Stengl, Vaclav; Houskova, Vendula; Bakardjieva, Snejana; Murafa, Nataliya; Marikova, Monika; Oplustil, Frantisek; Nemec, Tomas

    2010-11-15

    Zirconium doped nano dispersive oxides of Fe, Al and Zn were prepared by a homogeneous hydrolysis of the respective sulfate salts with urea in aqueous solutions. Synthesized metal oxide hydroxides were characterized using Brunauer-Emmett-Teller (BET) surface area and Barrett-Joiner-Halenda porosity (BJH), X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDX). These oxides were taken for an experimental evaluation of their reactivity with sulfur mustard (HD or bis(2-chloroethyl)sulfide), soman (GD or (3,3'-Dimethylbutan-2-yl)-methylphosphonofluoridate) and VX agent (S-[2-(diisopropylamino)ethyl]-O-ethyl-methylphosphonothionate). The presence of Zr{sup 4+} dopant can increase both the surface area and the surface hydroxylation of the resulting doped oxides, decreases their crystallites' sizes thereby it may contribute in enabling the substrate adsorption at the oxide surface thus it can accelerate the rate of degradation of warfare agents. Addition of Zr{sup 4+} converts the product of the reaction of ferric sulphate with urea from ferrihydrite to goethite. We found out that doped oxo-hydroxides Zr-FeO(OH) - being prepared by a homogeneous hydrolysis of ferric and zirconium oxo-sulfates mixture in aqueous solutions - exhibit a comparatively higher degradation activity towards chemical warfare agents (CWAs). Degradation of soman or VX agent on Zr-doped FeO(OH) containing ca. 8.3 wt.% of zirconium proceeded to completion within 30 min.

  16. Relationship Between Iron Whisker Growth and Doping Amount of Oxide During Fe2O3 Reduction

    NASA Astrophysics Data System (ADS)

    Gong, Xuzhong; Zhao, Zhilong; Wang, Zhi; Zhang, Ben; Guo, Lei; Guo, Zhancheng

    2016-04-01

    Iron whisker growth during Fe2O3 doped with oxide reduced by CO was investigated by using in situ observation and scanning electron microscopy. The results indicated that the minimum doping amount (MDA) of various oxides, hindering the iron whisker growth, was different. The MDA of Al2O3, Li2O, Na2O, and K2O was 0.5, 0.4, 4, and 12 pct, respectively. From the reduction rate, it was found that Li2O, MgO, and Al2O3 had some suppressive effects on the Fe2O3 reduction process, thus, confining the growth of iron whisker. However, other oxides had some catalytic effects on the Fe2O3 reduction process (Fe2O3-Fe3O4-FeO-Fe), such as CaO, SrO, BaO, Na2O, and K2O. As long as their doping amount was enough, these oxides could inhibit the diffusion of the Fe atom. When the metal ionic radius in doped oxide was bigger than that of Fe3+, such as Ca2+, Sr2+, Ba2+, Na+, and K+, there were lots of spaces left in Fe2O3 doped with oxide after reduction, improving Fe atom diffusion. Consequently, their MDA was more than that of small radius to restrain the growth of iron whisker. Finally, the relationship between corresponding metal ionic radius, electron layer number, valence electron number, and MDA of oxide was expressed by using data fitting as follows: N_{{{{A}}y {{O}}x }} = 1.3 × 10^{ - 5} × {r_{{{{A}}^{x + } }}2 × √{n_{{{{A}}^{x + } }} } }/{f_{q }}

  17. Influences of indium doping and annealing on microstructure and optical properties of cadmium oxide thin films

    NASA Astrophysics Data System (ADS)

    Zhu, Yuankun; Lei, Pei; Zhu, Jiaqi; Han, Jiecai

    2016-04-01

    The influences of indium doping and subsequent annealing in nitrogen and air atmospheres on the microstructure and optical properties of cadmium oxide films were studied in detail with the aid of various characterizations. X-ray photoelectronic spectroscopy analysis shows that indium atom forms chemically oxidized bonds in Cd-O matrix. X-ray diffraction results demonstrate that CdO structure remains FCC structure with indium doping, whereas the preferential orientation transforms from (222) into (200) orientation. Indium doping prevents the large crystalline growth, and this role still works under both nitrogen and air annealing processes. Similarly, CdO films show rough surface under annealing conditions, but the force has been greatly weakened at high doping level. It is clear that refractive index and extinction coefficient are closely correlated with crystalline size for undoped films, whereas it turns to the doping level for doped films, which can be performed by the mechanism of indium atom substitution. This work provides a very useful guild for design and application of optical-electronic devices.

  18. Detection of Aeromonas hydrophila DNA oligonucleotide sequence using a biosensor design based on Ceria nanoparticles decorated reduced graphene oxide and Fast Fourier transform square wave voltammetry.

    PubMed

    Jafari, Safiye; Faridbod, Farnoush; Norouzi, Parviz; Dezfuli, Amin Shiralizadeh; Ajloo, Davood; Mohammadipanah, Fatemeh; Ganjali, Mohammad Reza

    2015-10-01

    A new strategy was introduced for ssDNA immobilization on a modified glassy carbon electrode. The electrode surface was modified using polyaniline and chemically reduced graphene oxide decorated cerium oxide nanoparticles (CeO2NPs-RGO). A single-stranded DNA (ssDNA) probe was immobilized on the modified electrode surface. Fast Fourier transform square wave voltammetry (FFT-SWV) was applied as detection technique and [Ru(bpy)3](2+/3+) redox signal was used as electrochemical marker. The hybridization of ssDNA with its complementary target caused a dramatic decrease in [Ru(bpy)3](2+/3+) FFT-SW signal. The proposed electrochemical biosensor was able to detect Aeromonas hydrophila DNA oligonucleotide sequence encoding aerolysin protein. Under optimal conditions, the biosensor showed excellent selectivity toward complementary sequence in comparison with noncomplementary and two-base mismatch sequences. The dynamic linear range of this electrochemical DNA biosensor for detecting 20-mer oligonucleotide sequence of A. hydrophila was from 1 × 10(-15) to 1 × 10(-8) mol L(-1). The proposed biosensor was successfully applied for the detection of DNA extracted from A. hydrophila in fish pond water up to 0.01 μg mL(-1) with RSD of 5%. Besides, molecular docking was applied to consider the [Ru(bpy)3](2+/3+) interaction with ssDNA before and after hybridization. PMID:26454462

  19. Nitrogen and carbon doped titanium oxide as an alternative and durable electrocatalyst support in polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    Dhanasekaran, P.; Vinod Selvaganesh, S.; Bhat, Santoshkumar D.

    2016-02-01

    Nitrogen and carbon doped titanium oxide as an alternative and ultra-stable support to platinum catalysts is prepared and its efficiency is determined by polymer electrolyte fuel cell. Nitrogen and carbon doped titanium oxide is prepared by varying the melamine ratio followed by calcination at 900 °C. Platinum nanoparticles are deposited onto doped and undoped titanium oxide by colloidal method. The doping effect, surface morphology, chemical oxidation state and metal/metal oxide interfacial contact are studied by X-ray diffraction, Raman spectroscopy, high resolution transmission electron microscopy and X-ray photo electron spectroscopy. The nitrogen and carbon doping changes both electronic and structural properties of titanium oxide resulting in enhanced oxygen reduction reaction activity. The platinum deposited on optimum level of nitrogen and carbon doped titanium oxide exhibits improved cell performance in relation to platinum on titanium oxide electrocatalysts. The effect of metal loading on cathode electrocatalyst is investigated by steady-state cell polarization. Accelerated durability test over 50,000 cycles for these electrocatalysts suggested the improved interaction between platinum and nitrogen and carbon doped titanium oxide, retaining the electrochemical surface area and oxygen reduction performance as comparable to platinum on carbon support.

  20. Preparation of metal oxide doped ACNFs and their adsorption performance for low concentration SO2

    NASA Astrophysics Data System (ADS)

    Yu, Hong-quan; Wu, Yan-bo; Song, Tie-ben; Li, Yue; Shen, Yu

    2013-11-01

    Metal oxide (TiO2 or Co3O4) doped activated carbon nanofibers (ACNFs) were prepared by electrospinning. These nanofibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunner-Emmett-Teller method (BET). The results show that the average diameters of ACNFs were within the range of 200-500 nm, and the lengths were several tens of micrometers. The specific surface areas were 1146.7 m2/g for TiO2-doped ACNFs and 1238.5 m2/g for Co3O4-doped ACNFs, respectively. The electrospun nanofibers were used for adsorption of low concentration sulfur dioxide (SO2). The results showed that the adsorption rates of these ACNFs increased with an increase in SO2 concentration. When the SO2 concentration was 1.0 μg/mL, the adsorption rates of TiO2-doped ACNFs and Co3O4-doped ACNFs were 66.2% and 67.1%, respectively. The adsorption rate also increased as the adsorption time increased. When the adsorption time was 40 min, the adsorption rates were 67.6% and 69.0% for TiO2-doped ACNFs and Co3O4-doped ACNFs, respectively. The adsorption rate decreased as the adsorption temperature increased below 60°C, while it increased as the adsorption temperature increased to more than 60°C.

  1. Harnessing the Cancer Radiation Therapy by Lanthanide-Doped Zinc Oxide Based Theranostic Nanoparticles.

    PubMed

    Ghaemi, Behnaz; Mashinchian, Omid; Mousavi, Tayebeh; Karimi, Roya; Kharrazi, Sharmin; Amani, Amir

    2016-02-10

    In this paper, doping of europium (Eu) and gadolinium (Gd) as high-Z elements into zinc oxide (ZnO) nanoparticles (NPs) was designed to optimize restricted energy absorption from a conventional radiation therapy by X-ray. Gd/Eu-doped ZnO NPs with a size of 9 nm were synthesized by a chemical precipitation method. The cytotoxic effects of Eu/Gd-doped ZnO NPs were determined using MTT assay in L929, HeLa, and PC3 cell lines under dark conditions as well as exposure to ultraviolet, X-ray, and γ radiation. Doped NPs at 20 μg/mL concentration under an X-ray dose of 2 Gy were as efficient as 6 Gy X-ray radiation on untreated cells. It is thus suggested that the doped NPs may be used as photoinducers to increase the efficacy of X-rays within the cells, consequently, cancer cell death. The doped NPs also could reduce the received dose by normal cells around the tumor. Additionally, we evaluated the diagnostic efficacy of doped NPs as CT/MRI nanoprobes. Results showed an efficient theranostic nanoparticulate system for simultaneous CT/MR imaging and cancer treatment. PMID:26771200

  2. The Role of Dextran Coatings on the Cytotoxicity Properties of Ceria Nanoparticles Toward Bone Cancer Cells

    NASA Astrophysics Data System (ADS)

    Yazici, Hilal; Alpaslan, Ece; Webster, Thomas J.

    2015-04-01

    Cerium oxide nanoparticles have demonstrated great potential as antioxidant and radioprotective agents for nanomedicine applications especially for cancer therapy. The surface chemistry of nanoparticles is an important property that has a significant effect on their performance in biological applications including cancer diagnosis, cancer treatment, and bacterial infection. Recently, various nanosized cerium oxide particles with different types of polymer coatings have been developed to improve aqueous solubility and allow for surface functionalization for distinct applications. In this study, the role of ceria nanoparticles coated with dextran on the cytotoxicity properties of bone cancer cells was shown. Specifically, 0.1 M and 0.01 M dextran-coated, <5-nm ceria nanoparticles, were synthesized. The cytotoxicity of 0.1 M and 0.01 M dextran-coated ceria nanoparticles was evaluated against osteosarcoma cells. A change in cell viability was observed when treating osteosarcoma cells with 0.1 M dextran-coated ceria nanoparticles in the 250 -1000 μg/mL concentration range. In contrast, minimal toxicity to bone cancer cells was observed for the 0.01 M dextran coating after 3 days compared with the 0.1 M dextran coating. These results indicated that surface dextran functionalization had a positive impact on the cytotoxicity of cerium oxide nanoparticles against osteosarcoma cells.

  3. Sulfur-doped graphene via thermal exfoliation of graphite oxide in H2S, SO2, or CS2 gas.

    PubMed

    Poh, Hwee Ling; Šimek, Petr; Sofer, Zdeněk; Pumera, Martin

    2013-06-25

    Doping of graphene with heteroatoms is an effective way to tailor its properties. Here we describe a simple and scalable method of doping graphene lattice with sulfur atoms during the thermal exfoliation process of graphite oxides. The graphite oxides were first prepared by Staudenmaier, Hofmann, and Hummers methods followed by treatments in hydrogen sulfide, sulfur dioxide, or carbon disulfide. The doped materials were characterized by scanning electron microscopy, high-resolution X-ray photoelectron spectroscopy, combustible elemental analysis, and Raman spectroscopy. The ζ-potential and conductivity of sulfur-doped graphenes were also investigated in this paper. It was found that the level of doping is more dramatically influenced by the type of graphite oxide used rather than the type of sulfur-containing gas used during exfoliation. Resulting sulfur-doped graphenes act as metal-free electrocatalysts for an oxygen reduction reaction. PMID:23656223

  4. Microstructure, toughness and flexural strength of self-reinforced silicon nitride ceramics doped with yttrium oxide and ytterbium oxide.

    PubMed

    Zheng, Y. S.; Knowles, K. M.; Vieira, J. M.; Lopes, A. B.; Oliveira, F. J.

    2001-02-01

    Self-reinforced silicon nitride ceramics with additions of either yttrium oxide or ytterbium oxide have been investigated at room temperature after various processing heat treatments. Devitrification of the intergranular phase in these materials is very sensitive to the heat treatment used during processing and does not necessarily improve their strength and toughness. Hot-pressed ceramics without a subsequent devitrification heat treatment were the strongest. The ytterbium oxide-doped silicon nitride ceramics were consistently tougher, but less strong, than the yttrium oxide-doped silicon nitride ceramics. In all the ceramics examined, the fracture toughness showed evidence for R-curve behaviour. This was most significant in pressureless sintered ytterbium oxide-doped silicon nitride ceramics. A number of toughening mechanisms, including crack deflection, bridging, and fibre-like grain pull-out, were observed during microstructural analysis of the ceramics. In common with other silicon nitride-based ceramics, thin amorphous films were found at the grain boundaries in each of the ceramics examined. Arrays of dislocations left in the elongated silicon nitride grains after processing were found to belong to the {101;0}<0001> primary slip system. PMID:11207926

  5. Effect of Gadolinium Doping on the Air Oxidation of Uranium Dioxide

    SciTech Connect

    Scheele, Randall D.; Hanson, Brady D.; Cumblidge, Stephen E.; Jenson, Evan D.; Kozelisky, Anne E.; Sell, Rachel L.; MacFarlan, Paul J.; Snow, Lanee A.

    2004-12-04

    Researchers at the Pacific Northwest National Laboratory (PNNL) investigated the effects of gadolinia concentration on the air oxidization of gadolinia-doped uranium dioxide using thermogravimetry and differential scanning calorimetry to determine if such doping could improve uranium dioxide's stability as a nuclear fuel during potential accident scenarios in a nuclear reactor or during long-term disposal. We undertook this study to determine whether the resistance of the uranium dioxide to oxidation to the orthorhombic U3O8 with its attendant crystal expansion could be prevented by addition of gadolinia. Our studies found that gadolinium has little effect on the thermal initiation of the first step of the reported two-step air oxidation of UO2; however, increasing gadolinia content does stabilize the initial tetragonal or cubic product allowing significant oxidation before the second expansive step to U3O8 begins.

  6. Electrochemical impedance spectroscopy studies of lithium diffusion in doped manganese oxide

    SciTech Connect

    Johnson, B.J.; Doughty, D.H.; Voigt, J.A.; Boyle, T.J.

    1996-06-01

    Cathode performance is critical to lithium ion rechargeable battery performance; effects of doping lithium manganese oxide cathode materials on cathode performance are being investigated. In this paper, Li diffusion in Al-doped LiMn{sub 2}O{sub 4} was studied and found to be controlled by the quantity of Al dopant. Electrochemical cycling was conducted at 0.5mA/cm{sub 2}; electrochemical impedance spectra were taken at open circuit potential, with impedance being measured at 65 kHz-0.01 Hz. As the Al dopant level was increased, the Li diffusion rate decreased; this was attributed to the decreased lattice parameter of the doped oxide.

  7. Preparation of Carbon-Platinum-Ceria and Carbon-Platinum-Cerium catalysts and its application in Polymer Electrolyte Fuel Cell: Hydrogen, Methanol, and Ethanol

    NASA Astrophysics Data System (ADS)

    Guzman Blas, Rolando Pedro

    This thesis is focused on fuel cells using hydrogen, methanol and ethanol as fuel. Also, in the method of preparation of catalytic material for the anode: Supercritical Fluid Deposition (SFD) and impregnation method using ethylenediaminetetraacetic acid (EDTA) as a chelating agent. The first part of the thesis describes the general knowledge about Hydrogen Polymer Exchange Membrane Fuel Cell (HPEMFC),Direct Methanol Fuel Cell (DMFC) and Direct Ethanol Fuel Cell (DEFC), as well as the properties of Cerium and CeO2 (Ceria). The second part of the thesis describes the preparation of catalytic material by Supercritical Fluid Deposition (SFD). SFD was utilized to deposit Pt and ceria simultaneously onto gas diffusion layers. The Pt-ceria catalyst deposited by SFD exhibited higher methanol oxidation activity compared to the platinum catalyst alone. The linear sweep traces of the cathode made for the methanol cross over study indicate that Pt-Ceria/C as the anode catalyst, due to its better activity for methanol, improves the fuel utilization, minimizing the methanol permeation from anode to cathode compartment. The third and fourth parts of the thesis describe the preparation of material catalytic material Carbon-Platinum-Cerium by a simple and cheap impregnation method using EDTA as a chelating agent to form a complex with cerium (III). This preparation method allows the mass production of the material catalysts without additional significant cost. Fuel cell polarization and power curves experiments showed that the Carbon-Platinum-Cerium anode materials exhibited better catalytic activity than the only Vulcan-Pt catalysts for DMFC, DEFC and HPEMFC. In the case of Vulcan-20%Pt-5%w Cerium, this material exhibits better catalytic activity than the Vulcan-20%Pt in DMFC. In the case of Vulcan-40% Pt-doped Cerium, this material exhibits better catalytic activity than the Vulcan-40% Pt in DMFC, DEFC and HPEMFC. Finally, I propose a theory that explains the reason why the

  8. Nonaqueous synthesis of metal oxide nanoparticles: Short review and doped titanium dioxide as case study for the preparation of transition metal-doped oxide nanoparticles

    SciTech Connect

    Djerdj, Igor Arcon, Denis; Jaglicic, Zvonko; Niederberger, Markus

    2008-07-15

    The liquid-phase synthesis of metal oxide nanoparticles in organic solvents under exclusion of water is nowadays a well-established alternative to aqueous sol-gel chemistry. In this article, we highlight some of the advantages of these routes based on selected examples. The first part reviews some recent developments in the synthesis of ternary metal oxide nanoparticles by surfactant-free nonaqueous sol-gel routes, followed by the discussion of the morphology-controlled synthesis of lanthanum hydroxide nanoparticles, and the presentation of structural peculiarities of manganese oxide nanoparticles with an ordered Mn vacancy superstructure. These examples show that nonaqueous systems, on the one hand, allow the preparation of compositionally complex oxides, and, on the other hand, make use of the organic components (initially present or formed in situ) in the reaction mixture to tailor the morphology. Furthermore, obviously even the crystal structure can differ from the corresponding bulk material like in the case of MnO nanoparticles. In the second part of the paper we present original results regarding the synthesis of dilute magnetic semiconductor TiO{sub 2} nanoparticles doped with cobalt and iron. The structural characterization as well as the magnetic properties with special attention to the doping efficiency is discussed. - Graphical abstract: In the first part of this article, nonaqueous sol-gel routes to ternary metal oxide nanoparticles are briefly reviewed, followed by the discussion of the morphology-controlled synthesis of lanthanum hydroxide nanoparticles, and the appearance of an unprecedented superstructure in MnO nanoparticles. In the second part, doping experiments of TiO{sub 2} with Fe and Co are presented, along with their characterization including magnetic measurements.

  9. Effect of preparation conditions on physic-chemical properties of tin-doped nanocrystalline indium oxide

    NASA Astrophysics Data System (ADS)

    Malinovskaya, T. D.; Sachkov, V. I.; Zhek, V. V.; Nefedov, R. A.

    2016-01-01

    In this paper the results of investigation of phase formation and change of concentration of free electrons (Ne) in indium tin oxide system during heat treatment of coprecipitated hydroxides of indium and tin from nitric and hydrochloric solutions and also, for comparison melts of salts nitrates by an alkaline reactant (NH4OH) are considered.The performed investigation allowed to set the optimal condition of preparation of polycrystalline tin-doped indium oxide with maximal electron concentration.

  10. Cross-beam pulsed laser fabrication of Free-Standing Nanostructured Carbon Nanotubes-Pt-Ceria Anode with unprecedented electroactivity and durability for ethanol oxidation

    NASA Astrophysics Data System (ADS)

    Wang, Youling; Tabet-Aoul, Amel; Gougis, Maxime; Mohamedi, Mohamed

    2015-01-01

    Owing to its inherent properties such as great capacity to store and release oxygen, lattice oxygen that has a key role in removing the CO poisoning effect, non-toxicity, abundance, low cost and low temperature processing, CeO2 is emerging as a unique class of electrode material for low temperature polymer electrolyte fuel cells such as direct ethanol fuel cells (DEFCs). However, the maximal exploitation of its functional properties is strictly reliant on the availability of optimized synthesis routes that allow tailor-designing, architecturing and manipulation of CeO2 in a precise manner when it is combined with other functional materials. Here we use the cross-beam pulsed laser deposition (CBPLD) technique to synthesize free-standing (binderless) Pt-CeO2 nanostructured thin films onto carbon nanotubes as anodes for ethanol oxidation reaction. Further significance of this work is that it establishes the importance in the design of the catalyst layer architecture. Indeed, we demonstrate here that when CeO2 material is beneath or when it is mixed with Pt, the interactions between Pt with CeO2 are not similar leading inevitably to different electrocatalytic performances. Given proper tailoring synthesis conditions, CBPLD-developed Pt-CeO2 thin films are remarkably stable and provide electrochemical performance much greater than the layer onto layer CeO2/Pt architecture.

  11. Magnetic and Magneto-Optical Properties of Doped Oxides

    NASA Astrophysics Data System (ADS)

    Alqahtani, Mohammed

    This thesis describes the growth, structural characterisation, magnetic and magneto-optics properties of lanthanum strontium manganite (LSMO), GdMnO3 and transition metal (TM)-doped In2O3 thin films grown under different conditions. The SrTiO3 has been chosen as a substrate because its structure is suitable to grow epitaxial LSMO and GdMnO3 films. However, the absorption of SrTiO3 above its band gap at about 3.26 eV is actually a limitation in this study. The LSMO films with 30% Sr, grown on both SrTiO3 and sapphire substrates, exhibit a high Curie temperature (Tc) of 340 K. The magnetic circular dichroism (MCD) intensity follows the magnetisation for LSMO on sapphire; however, the measurements on SrTiO3 were dominated by the birefringence and magneto-optical properties of the substrate. In the GdMnO3 thin films, there are two well-known features in the optical spectrum; the charge transfer transition between Mn d states at 2 eV and the band edge transition from the oxygen p band to d states at about 3 eV; these are observed in the MCD. This has been measured at remanence as well as in a magnetic field. The optical absorption at 3 eV is much stronger than at 2 eV, however, the MCD is considerably stronger at 2 eV. The MCD at 2 eV correlates well with the Mn spin ordering and it is very notable that the same structure appears in this spectrum, as is seen in LaMnO3. The results of the investigations of Co and Fe-doped In2O3 thin films show that TM ions in the films are TM2+ and substituted for In3+. The room temperature ferromagnetism observed in TM-doped In2O3 is due to the polarised electrons in localised donor states associated with oxygen vacancies. The formation of Fe3O4 nanoparticles in some Fe-doped films is due the fact that TM-doped In2O3 thin films are extremely sensitive to the growth method and processing condition. However, the origin of the magnetisation in these films is due to both the Fe-doped host matrix and also to the nanoparticles of Fe3O4.

  12. Application of High Surface Area Tin-Doped Indium Oxide Nanoparticle Films as Transparent Conducting Electrodes

    SciTech Connect

    Hoertz, Paul G.; Chen, Zuofeng; Kent, Caleb A.; Meyer, Thomas J.

    2010-08-16

    Metal complex derivatized, optically transparent nanoparticle films of Sn(IV)-doped In2O3 (nanoITO) undergo facile interfacial electron transfer allowing for rapid, potential controlled color changes, direct spectral (rather than current) monitoring of voltammograms, and multilayer catalysis of water oxidation.

  13. A hydrophobic three-dimensionally networked boron-doped diamond electrode towards electrochemical oxidation.

    PubMed

    He, Yapeng; Lin, Haibo; Wang, Xue; Huang, Weimin; Chen, Rongling; Li, Hongdong

    2016-06-28

    A boron-doped diamond electrode with a three-dimensional network was fabricated on a mesh titanium substrate. Properties such as higher surface area, enhanced mass transfer and a hydrophobic surface endowed the prepared electrode with excellent electrochemical oxidation ability towards contaminants. PMID:27264247

  14. Effects of Doping on Thermal Conductivity of Pyrochlore Oxides for Advanced Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Zhu, Dongming; Eslamloo-Grami, Maryam

    2006-01-01

    Pyrochlore oxides of general composition, A2B2O7, where A is a 3(+) cation (La to Lu) and B is a 4(+) cation (Zr, Hf, Ti, etc.) have high melting point, relatively high coefficient of thermal expansion, and low thermal conductivity which make them suitable for applications as high-temperature thermal barrier coatings. The effect of doping at the A site on the thermal conductivity of a pyrochlore oxide La2Zr2O7, has been investigated. Oxide powders of various compositions La2Zr2O7, La(1.7)Gd(0.3)Zr2O7, La(1.7)Yb(0.3)Zr2O7 and La(1.7)Gd(0.15)Yb(0.15)Zr2O7 were synthesized by the citric acid sol-gel method. These powders were hot pressed into discs and used for thermal conductivity measurements using a steady-state laser heat flux test technique. The rare earth oxide doped pyrochlores La(1.7)Gd(0.3)Zr2O7, La(1.7)Yb(0.3)Zr2O7 and La(1.7)Gd(0.15)Yb(0.15)Zr2O7 had lower thermal conductivity than the un-doped La2Zr2O7. The Gd2O3 and Yb2O3 co-doped composition showed the lowest thermal conductivity.

  15. A novel composite cathode Er0.4Bi1.6O3-Pr0.5Ba0.5MnO3-δ for ceria-bismuth bilayer electrolyte high performance low temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Hou, Jie; Bi, Lei; Qian, Jing; Gong, Zheng; Zhu, Zhiwen; Liu, Wei

    2016-01-01

    A novel composite cathode consisting of A-site disordered Pr0.5Ba0.5MnO3-δ (PBM) and Er0.4Bi1.6O3 (ESB) is developed for solid oxide fuel cells (SOFCs) with ceria-bismuth bilayer electrolyte. Based on Sm0.075Nd0.075Ce0.85O2-δ|ESB (SNDC|ESB) bilayer structured film, the single cell NiO-SNDC|SNDC|ESB|ESB-PBM achieves an encouraging performance with the maximum power density (MPD) of 994 mW cm-2 and an interfacial polarization resistance (Rp) of 0.027 Ω cm2 at 650 °C. Although a possible reaction between ESB and PBM has been identified in the cathode, the ascendant electrochemical performance including the very high fuel cell performance and Rp obtained here can demonstrate that the novel cobalt-free composite cathode ESB-PBM is a preferable alternative for ceria-bismuth bilayer electrolyte high performance low temperature SOFCs (HPLT-SOFCs) and the interfacial reaction in the cathode seems not to be detrimental to the electrochemical performance.

  16. Effect of W and WC on the oxidation resistance of yttria-doped silicon nitride

    NASA Technical Reports Server (NTRS)

    Schuon, S.

    1980-01-01

    The effect of tungsten and tungsten carbide contamination on the oxidation and cracking in air of yttria-doped silicon nitride ceramics is investigated. Silicon nitride powder containing 8 wt % Y2O3 was doped with 2 wt % W, 4 wt % W, 2 wt % WC or left undoped, and sintered in order to simulate contamination during milling, and specimens were exposed in air to 500, 750 and 1350 C for various lengths of time. Scanning electron and optical microscopy and X-ray diffraction of the specimens in the as-sintered state reveals that the addition of W or WC does not affect the phase relationships in the system, composed of alpha and beta Si3N4, melilite and an amorphous phase. Catastrophic oxidation is observed at 750 C in specimens containing 2 and 4 wt % W, accompanied by the disappearance of alpha Si3N4 and melilite from the structure. At 1350 C, the formation of a protective glassy oxide layer was observed on all specimens without catastrophic oxidation, and it is found that pre-oxidation at 1350 C also improved the oxidation resistance at 750 C of bars doped with 4 wt % W. It is suggested that tungsten contamination from WC grinding balls may be the major cause of the intermediate-temperature cracking and instability frequently observed in Si3N4-8Y2O3.

  17. Subwavelength structure for sound absorption from graphene oxide-doped polyvinylpyrrolidone nanofibers

    NASA Astrophysics Data System (ADS)

    Qamoshi, Khadijeh; Rasuli, Reza

    2016-09-01

    We study the sound absorption of the reinforced polyvinylpyrrolidone nanofibers with graphene oxide. It is shown that reinforced nanofibers can acquire impedance-matched surface to airborne sound at special frequencies. To obtain such surface, nanofibers were spun with polyvinylpyrrolidone polymer that was doped by graphene oxide with concentrations of 0, 6 and 12 wt%. It was found that fibers without graphene oxide were spun continuously and randomly, whereas by doping with graphene oxide, the mode of fibers is changed and some nodes form on the fibers coating. The sound absorption coefficient was measured by an impedance tube based on 105341-1 ISO standard. Measurements in the frequency range from 700 to 1600 Hz show that use of graphene oxide as a reinforcing phase increases sound absorption coefficient of the samples at a frequency ~1500 Hz up to ~40 %. Angular eigenfrequency and dissipation coefficient of the samples were obtained by impedance measurement for the prepared samples. Results show that doping the polymer with graphene oxide causes an increase in the angular eigenfrequency and the dissipation coefficient.

  18. Nanostructured ceria based thin films ({<=}1 {mu}m) As cathode/electrolyte interfaces

    SciTech Connect

    Hierso, J.; Boy, P.; Valle, K.; Vulliet, J.; Blein, F.; Laberty-Robert, Ch.; Sanchez, C.

    2013-01-15

    Gadolinium doped cerium oxide (CGO: Ce{sub 0,9}Gd{sub 0,1}O{sub 2-{delta}}) films were used as an oxygen anion diffusion layer at the cathode/electrolyte interface of Solid Oxide Fuel Cells (SOFCs), between LSCF (lanthanum strontium cobalt ferrite) and YSZ (yttria-stabilized zirconia). Thin ({approx}100 nm) and thick ({approx}700 nm) mesoporous CGO layers were synthesized through a sol-gel process including organic template coupled with the dip-coating method. Structural and microstructural characterizations were performed, highlighting a well-bonded crystalline CGO nanoparticles network which delineates a 3-D inter-connected mesoporous network. Their electrical behaviors were investigated by impedance spectroscopy analysis of YSZ/mesoporous-CGO/LSCF half-cell. Anode-supported SOFCs, operating at 800 Degree-Sign C, with either dense or mesoporous CGO dip-coated interlayers were also fabricated [NiO-YSZ anode/YSZ/CGO/LSCF cathode]. The impact of the mesoporous CGO interlayers on SOFCs performances was investigated by galvanostatic analysis and compared to the behavior of a dense CGO interlayer. The polarization curves revealed an enhancement in the electrical performance of the cell, which is assigned to a decrease of the polarization resistance at the cathode/electrolyte interface. The integrity and connectivity of the CGO nanoparticles bonded network facilitates O{sup 2-} transport across the interface. - Graphical abstract: Thin and thick CGO films have been prepared through a sol-gel process and their potential application as SOFC cathode/electrolyte interlayer in SOFC has been investigated. Highlights: Black-Right-Pointing-Pointer Mesoporous ceria based thin films exhibit interesting performances for Solid Oxide Fuel Cell. Black-Right-Pointing-Pointer Mesoporous films were synthesized through the sol-gel process combined with the dip-coating. Black-Right-Pointing-Pointer Integrity and connectivity of the nanoparticles facilitates O{sup 2-} transport across the

  19. Nonstoichiometric zinc oxide and indium-doped zinc oxide: Electrical conductivity and {sup 111}In-TDPAC studies

    SciTech Connect

    Wang, R.; Sleight, A.W.; Platzer, R.; Gardner, J.A.

    1996-02-15

    Indium-doped zinc oxide powders have been prepared which show room-temperature electrical conductivities as high as 30 {Omega}{sup {minus}1} cm{sup {minus}1}. The indium doping apparently occurs as Zn{sub 1-x}In{sub x}O,Zn{sub 1-y}In{sub y}O{sub 1+y/2}, or a combination of these. Optimum conductivity occurs for Zn{sub 1-x}In{sub x}O where the maximum value of x obtained was about 0.5 at%. The degrees of sample reduction were determined by iodimetric titration. Time differential perturbed angular correlation (TDPAC) spectroscopy on indium doped zinc oxide is consistent with indium substituting at normal zinc sites in the ZnO lattice. TDPAC studies on zinc oxide annealed under zinc vapors show a second environment for the {sup 111}In probe. In this case, there is an unusually high temperature dependence of the electric field gradient which may be caused by a nearby zinc interstitial. An important conclusion of this work is that zinc interstitials are not ionized and do not therefore contribute significantly to the increased conductivity of reduced zinc oxide.

  20. Dynamic formation of single-atom catalytic active sites on ceria-supported gold nanoparticles

    PubMed Central

    Wang, Yang-Gang; Mei, Donghai; Glezakou, Vassiliki-Alexandra; Li, Jun; Rousseau, Roger

    2015-01-01

    Catalysis by gold supported on reducible oxides has been extensively studied, yet issues such as the nature of the catalytic site and the role of the reducible support remain fiercely debated topics. Here we present ab initio molecular dynamics simulations of an unprecedented dynamic single-atom catalytic mechanism for the oxidation of carbon monoxide by ceria-supported gold clusters. The reported dynamic single-atom catalytic mechanism results from the ability of the gold cation to strongly couple with the redox properties of the ceria in a synergistic manner, thereby lowering the energy of redox reactions. The gold cation can break away from the gold nanoparticle to catalyse carbon monoxide oxidation, adjacent to the metal/oxide interface and subsequently reintegrate back into the nanoparticle after the reaction is completed. Our study highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in catalysis. PMID:25735407

  1. Magnesium-doped zinc oxide nanorod-nanotube semiconductor/p-silicon heterojunction diodes

    NASA Astrophysics Data System (ADS)

    Caglar, Yasemin; Görgün, Kamuran; Ilican, Saliha; Caglar, Mujdat; Yakuphanoğlu, Fahrettin

    2016-08-01

    Nanostructured zinc oxide material is usable in electronic device applications such as light-emitting diodes, heterojunction diode, sensors, solar cell due to its interesting electrical conductivity and optical properties. Magnesium-doped zinc oxide nanorod (NR)-nanotube (NT) films were grown by microwave-assisted chemical bath deposition to fabricate ZnO-based heterojunction diode. It is found that ZnO hexagonal nanorods turn into hexagonal nanotubes when the Mg doping ratio is increased from 1 to 10 %. The values of the optical band gap for 1 % Mg-doped ZnO NR and 10 % Mg-doped ZnO NT films are found to be 3.14 and 3.22 eV, respectively. The n-ZnO:Mg/p-Si heterojunction diodes were fabricated. The diodes exhibited a rectification behavior with ideality factor higher than unity due to the presence of surface states in the junction and series resistance. The obtained results indicate that Mg doping improves the electrical and optical properties of ZnO.

  2. Method of forming supported doped palladium containing oxidation catalysts

    SciTech Connect

    Mohajeri, Nahid

    2014-04-22

    A method of forming a supported oxidation catalyst includes providing a support comprising a metal oxide or a metal salt, and depositing first palladium compound particles and second precious metal group (PMG) metal particles on the support while in a liquid phase including at least one solvent to form mixed metal comprising particles on the support. The PMG metal is not palladium. The mixed metal particles on the support are separated from the liquid phase to provide the supported oxidation catalyst.

  3. Chromium and Ruthenium-Doped Zinc Oxide Thin Films for Propane Sensing Applications

    PubMed Central

    Gómez-Pozos, Heberto; González-Vidal, José Luis; Torres, Gonzalo Alberto; Rodríguez-Baez, Jorge; Maldonado, Arturo; de la Luz Olvera, María; Acosta, Dwight Roberto; Avendaño-Alejo, Maximino; Castañeda, Luis

    2013-01-01

    Chromium and ruthenium-doped zinc oxide (ZnO:Cr) and (ZnO:Ru) thin solid films were deposited on soda-lime glass substrates by the sol-gel dip-coating method. A 0.6 M solution of zinc acetate dihydrate dissolved in 2-methoxyethanol and monoethanolamine was used as basic solution. Chromium (III) acetylacetonate and Ruthenium (III) trichloride were used as doping sources. The Ru incorporation and its distribution profile into the films were proved by the SIMS technique. The morphology and structure of the films were studied by SEM microscopy and X-ray diffraction measurements, respectively. The SEM images show porous surfaces covered by small grains with different grain size, depending on the doping element, and the immersions number into the doping solutions. The sensing properties of ZnO:Cr and ZnO:Ru films in a propane (C3H8) atmosphere, as a function of the immersions number in the doping solution, have been studied in the present work. The highest sensitivity values were obtained for films doped from five immersions, 5.8 and 900, for ZnO:Cr and ZnO:Ru films, respectively. In order to evidence the catalytic effect of the chromium (Cr) and ruthenium (Ru), the sensing characteristics of undoped ZnO films are reported as well. PMID:23482091

  4. Facile synthesis of antimony-doped tin oxide nanoparticles by a polymer-pyrolysis method

    SciTech Connect

    Li, Yuan-Qing; Wang, Jian-Lei; Fu, Shao-Yun; Mei, Shi-Gang; Zhang, Jian-Min; Yong, Kang

    2010-06-15

    In this article, antimony-doped tin oxide (ATO) nanoparticles was synthesized by a facile polymer-pyrolysis method. The pyrolysis behaviors of the polymer precursors prepared via in situ polymerization of metal salts and acrylic acid were analyzed by simultaneous thermogravimetric and differential scanning calorimetry (TG-DSC). The structural and morphological characteristics of the products were studied by powder X-ray diffraction (XRD) and transmission electron microscope (TEM). The results reveal that the ATO nanoparticles calcined at 600 {sup o}C show good crystallinity with the cassiterite structure and cubic-spherical like morphology. The average particle size of ATO decreases from 200 to 15 nm as the Sb doping content increases from 5 mol% to 15 mol%. Electrical resistivity measurement shows that the resistivity for the 10-13 mol% Sb-doped SnO{sub 2} nanoparticles is reduced by more than three orders compared with the pure SnO{sub 2} nanoparticles. In addition, due to its versatility this polymer-pyrolysis method can be extended to facile synthesis of other doped n-type semiconductor, such as In, Ga, Al doped ZnO, Sn doped In{sub 2}O{sub 3}.

  5. Chromium and ruthenium-doped zinc oxide thin films for propane sensing applications.

    PubMed

    Gómez-Pozos, Heberto; González-Vidal, José Luis; Torres, Gonzalo Alberto; Rodríguez-Baez, Jorge; Maldonado, Arturo; Olvera, María de la Luz; Acosta, Dwight Roberto; Avendaño-Alejo, Maximino; Castañeda, Luis

    2013-01-01

    Chromium and ruthenium-doped zinc oxide (ZnO:Cr) and (ZnO:Ru) thin solid films were deposited on soda-lime glass substrates by the sol-gel dip-coating method. A 0.6 M solution of zinc acetate dihydrate dissolved in 2-methoxyethanol and monoethanolamine was used as basic solution. Chromium (III) acetylacetonate and Ruthenium (III) trichloride were used as doping sources. The Ru incorporation and its distribution profile into the films were proved by the SIMS technique. The morphology and structure of the films were studied by SEM microscopy and X-ray diffraction measurements, respectively. The SEM images show porous surfaces covered by small grains with different grain size, depending on the doping element, and the immersions number into the doping solutions. The sensing properties of ZnO:Cr and ZnO:Ru films in a propane (C3H8) atmosphere, as a function of the immersions number in the doping solution, have been studied in the present work. The highest sensitivity values were obtained for films doped from five immersions, 5.8 and 900, for ZnO:Cr and ZnO:Ru films, respectively. In order to evidence the catalytic effect of the chromium (Cr) and ruthenium (Ru), the sensing characteristics of undoped ZnO films are reported as well. PMID:23482091

  6. Boron-doped cadmium oxide composite structures and their electrochemical measurements

    SciTech Connect

    Lokhande, B.J.; Ambare, R.C.; Mane, R.S.; Bharadwaj, S.R.

    2013-08-01

    Graphical abstract: Conducting nano-fibrous 3% boron doped cadmium oxide thin films were prepared by SILAR and its super capacitive properties were studied. - Highlights: • Samples are of nanofibrous nature. • All samples shows pseudocapacitive behavior. • 3% B doped CdO shows good specific capacitance. • 3% B doped CdO shows maximum 74.93% efficiency at 14 mA/cm{sup 2}. • 3% B doped CdO shows 0.8 Ω internal resistance. - Abstract: Boron-doped and undoped cadmium oxide composite nanostructures in thin film form were prepared onto stainless steel substrates by a successive ionic layer adsorption and reaction method using aqueous solutions of cadmium nitrate, boric acid and 1% H{sub 2}O{sub 2}. As-deposited films were annealed at 623 K for 1 h. The X-ray diffraction study shows crystalline behavior for both doped and undoped films with a porous topography and nano-wires type architecture, as observed in SEM image. Wettability test confirms the hydrophilic surface with 58° contact angle value. Estimated band gap energy is around 1.9 eV. Electrochemical behavior of the deposited films is attempted in 1 M KOH electrolyte using cyclic voltammetry (CV), electrochemical impedance spectroscopy and galvanostatic charge–discharge tests. Maximum values of the specific capacitance, specific energy and specific power obtained for 3% B doped CdO film at 2 mV/s scan rate are 20.05 F/g, 1.22 Wh/kg and 3.25 kW/kg, respectively.

  7. Endohedrally doped gold nanocages: efficient catalysts for O2 activation and CO oxidation.

    PubMed

    Manzoor, Dar; Krishnamurty, Sailaja; Pal, Sourav

    2016-03-14

    Gold nanocages are the most attractive catalytic materials as all the atoms in the cage type clusters reside on the surface, making them available for chemisorption by reacting molecules. Due to a hollow space at the center, their chemical and catalytic properties can be tuned effectively and easily by endohedral doping. While a significant experimental and theoretical understanding is currently available on the structural and electronic properties of doped gold cages, very little information is available on their reactivity and catalytic behavior. In the present work, with the help of density functional theory calculations we demonstrate that endohedral doping leads to a notable increase in the binding energy of molecular oxygen on the gold nanocages. The enhancement in the O2 binding energy on the doped gold cages is also confirmed by a significant decrease in the Au-O and an increase in the O-O bond lengths, corroborated by a red shift (∼250 cm(-1)) in the O-O stretching frequency as compared to the pristine cage. Furthermore, interestingly, the doped gold cages show very low activation barriers for the environmentally important CO oxidation reaction as compared to the pristine gold cage. Importantly, the decrease in the barrier height is comparatively greater for the rate limiting step of O-O-C-O intermediate formation and as a result the CO oxidation is expected to be more facile on the doped gold cages. Thus, the current study highlights the role of heteroatom doping in imparting new chemical and catalytic properties to gold cages and is expected to spur further research in the design of efficient gold nanocatalysts. PMID:26628077

  8. Sol-gel deposition and plasma treatment of intrinsic, aluminum-doped, and gallium-doped zinc oxide thin films as transparent conductive electrodes

    NASA Astrophysics Data System (ADS)

    Zhu, Zhaozhao; Mankowski, Trent; Balakrishnan, Kaushik; Shikoh, Ali Sehpar; Touati, Farid; Benammar, Mohieddine A.; Mansuripur, Masud; Falco, Charles M.

    2015-09-01

    Zinc oxide and aluminum/gallium-doped zinc oxide thin films were deposited via sol-gel spin-coating technique. Employing plasma treatment as alternative to post thermal annealing, we found that the morphologies of these thin films have changed and the sheet resistances have been significantly enhanced. These plasma-treated thin films also show very good optical properties, with transmittance above 90% averaged over the visible wavelength range. Our best aluminum/gallium-doped zinc oxide thin films exhibit sheet resistances (Rs) of ~ 200 Ω/sq and ~ 150 Ω/sq, respectively.

  9. Si-doped graphene: A promising metal-free catalyst for oxidation of SO2

    NASA Astrophysics Data System (ADS)

    Esrafili, Mehdi D.; Saeidi, Nasibeh; Nematollahi, Parisa

    2016-04-01

    This study reports favorable reaction mechanisms of SO2 oxidation by molecular O2 over Si-doped graphene by means of DFT calculations. The SO2 oxidation reaction proceeds through the following elementary steps (a) SO2 + O2 → Oads + SO3 and (b) Oads + SO2 → SO3. It is found that the first and second steps are fulfilled via the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms, with an activation energy of 4.7 and 9.5 kcal/mol, respectively. Results show that the low-cost Si-doped graphene can be used as an efficient catalyst for SO2 oxidation at room temperature.

  10. Cu4 Cluster Doped Monolayer MoS2 for CO Oxidation

    PubMed Central

    Chen, Z. W.; Yan, J. M.; Zheng, W. T.; Jiang, Q.

    2015-01-01

    The catalytic oxidation of CO molecule on a thermodynamically stable Cu4 cluster doped MoS2 monolayer is investigated by density functional theory (DFT) where the reaction proceeds in a new formation order of COOOCO* (O2* + 2CO* → COOOCO*), OCO* (COOOCO* → CO2 + OCO*), and CO2 (OCO* → CO2) desorption with the corresponding reaction barrier values of 0.220 eV, 0.370 eV and 0.119 eV, respectively. Therein, the rate-determining step is the second one. This low barrier indicates high activity of this system where CO oxidation could be realized at room temperature (even lower). As a result, the Cu4 doped MoS2 could be a candidate for CO oxidation with lower cost and higher activity without poisoning and corrosion problems. PMID:26052674

  11. Oxidative Recession, Sulfur Release, and Al203 Spallation for Y-Doped Alloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    2001-01-01

    Second-order spallation phenomena have been noted for Y-doped Rene'N5 after long term oxidation at 1150 degrees C. The reason for this behavior has not been conclusively identified. A mass equivalence analysis has shown that the surface recession resulting from oxidation has the potential of releasing about 0.15 monolayer of sulfur for every 1 mg/sq cm of oxygen reacted for an alloy containing 5 ppmw of sulfur. This amount is significant in comparison to levels that have been shown to result in first-order spallation behavior for undoped alloys. Oxidative recession is therefore speculated to be a contributing source of sulfur and second-order spallation for Y-doped alloys.

  12. Oxidation studies on small atom doped TI*5*SI*3*

    SciTech Connect

    Thom, Andrew

    1995-01-01

    This report described the oxidation and oxidation resistance of Ti{sub 5}Si{sub 3}, along with a discussion on general material properties. Single crystal studies of Ti{sub 5}Si{sub 3}Z{sub x} are included.

  13. Alkaline earth metal doped tin oxide as a novel oxygen storage material

    SciTech Connect

    Dong, Qiang; Yin, Shu; Yoshida, Mizuki; Wu, Xiaoyong; Liu, Bin; Miura, Akira; Takei, Takahiro; Kumada, Nobuhiro; Sato, Tsugio

    2015-09-15

    Alkaline earth metal doped tin oxide (SnO{sub 2}) hollow nanospheres with a diameter of 50 nm have been synthesized successfully via a facial solvothermal route in a very simple system composed of only ethanol, acetic acid, SnCl{sub 4}·5H{sub 2}O and A(NO{sub 3}){sub 2}·xH{sub 2}O (A = Mg, Ca, Sr, Ba). The synthesized undoped SnO{sub 2} and A-doped SnO{sub 2} hollow nanospheres were characterized by the oxygen storage capacity (OSC), X-ray diffraction, transmission electron microscopy and the Brunauer–Emmet–Teller (BET) technique. The OSC values of all samples were measured using thermogravimetric-differential thermal analysis. The incorporation of alkaline earth metal ion into tin oxide greatly enhanced the thermal stability and OSC. Especially, Ba-doped SnO{sub 2} hollow nanospheres calcined at 1000 °C for 20 h with a BET surface area of 61 m{sup 2} g{sup −1} exhibited the considerably high OSC of 457 μmol-O g{sup −1} and good thermal stability. Alkaline earth metal doped tin oxide has the potential to be a novel oxygen storage material.

  14. Manganese Doping of Magnetic Iron Oxide Nanoparticles: Tailoring Surface Reactivity for a Regenerable Heavy Metal Sorbent

    SciTech Connect

    Warner, Cynthia L.; Chouyyok, Wilaiwan; Mackie, Katherine E.; Neiner, Doinita; Saraf, Laxmikant; Droubay, Timothy C.; Warner, Marvin G.; Addleman, Raymond S.

    2012-02-28

    A method for tuning the analyte affinity of magnetic, inorganic nanostructured sorbents for heavy metal contaminants is described. The manganese-doped iron oxide nanoparticle sorbents have a remarkably high affinity compared to the precursor material. Sorbent affinity can be tuned toward an analyte of interest simply by adjustment of the dopant quantity. The results show that following the Mn doping process there is a large increase in affinity and capacity for heavy metals (i.e., Co, Ni, Zn, As, Ag, Cd, Hg, and Tl). Capacity measurements were carried out for the removal of cadmium from river water and showed significantly higher loading than the relevant commercial sorbents tested for comparison. The reduction in Cd concentration from 100 ppb spiked river water to 1 ppb (less than the EPA drinking water limit of 5 ppb for Cd) was achieved following treatment with the Mn-doped iron oxide nanoparticles. The Mn-doped iron oxide nanoparticles were able to load 1 ppm of Cd followed by complete stripping and recovery of the Cd with a mild acid wash. The Cd loading and stripping is shown to be consistent through multiple cycles with no loss of sorbent performance.

  15. Structural and optical properties of Nd3+ doped gadolinium oxide 1D nanorods

    NASA Astrophysics Data System (ADS)

    Boopathi, G.; Raj, S. Gokul; Kumar, G. Ramesh; Mohan, R.

    2014-04-01

    Neodymium doped gadolinium hydroxide [Nd:Gd(OH)3] nanorods were successfully synthesized at 60 °C through co-precipitation method. The dopant percentage was maintained at 5% and calcination was done at 750 °C temperature for 1 hour to form the respective neodymium doped gadolinium oxide [Nd:Gd2O3] nanorods. The as-formed and annealed products were investigated in detail by using powder X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM) with an energy dispersive X-ray spectrum (EDX), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectrophotometry.

  16. Origin of ferromagnetism enhancement in bi-layer chromium-doped indium zinc oxides

    SciTech Connect

    Hsu, C. Y.

    2012-08-06

    This work demonstrates that by controlling the rapid thermal annealing temperature, amorphous chromium-doped indium zinc oxide films develop an amorphous-crystalline bi-layer structure and show magnetization up to {approx}30 emu/cm{sup 3}. The crystalline layer arises from significant out-diffusion of Zn from surfaces, leading to a large difference in the Zn:In ratio in amorphous and crystalline layers. Doped Cr ions in amorphous and crystalline layers form different valence configurations, creating a charge reservoir which transfers electrons through amorphous-crystalline interfaces and in turn enhances ferromagnetism.

  17. Structural, morphological and optical investigations on Sm{sup 3+} doped gadolinium oxide nanorods

    SciTech Connect

    Boopathi, G.; Mohan, R.; Raj, S. Gokul; Kumar, G. Ramesh

    2014-04-24

    One dimensional uniform Sm{sup 3+} doped gadolinium hydroxide nanorods have been prepared via simple co– precipitation technique at 60 °C temperature for 1 hour. The samples were calcinated at 750 °C to obtain Sm{sup 3+} doped gadolinium oxide nanorods. The 1D nanorods were then subjected to different characterization techniques to ascertain its structural stability and its morphology were investigated using high–resolution transmission electron microscopy. Photoluminescence (PL) spectrophotometry was investigated and the obtained results were discussed in detail.

  18. Structural and optical properties of Nd{sup 3+} doped gadolinium oxide 1D nanorods

    SciTech Connect

    Boopathi, G. Mohan, R.; Raj, S. Gokul; Kumar, G. Ramesh

    2014-04-24

    Neodymium doped gadolinium hydroxide [Nd:Gd(OH)3] nanorods were successfully synthesized at 60 °C through co-precipitation method. The dopant percentage was maintained at 5% and calcination was done at 750 °C temperature for 1 hour to form the respective neodymium doped gadolinium oxide [Nd:Gd{sub 2}O{sub 3}] nanorods. The as-formed and annealed products were investigated in detail by using powder X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM) with an energy dispersive X-ray spectrum (EDX), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectrophotometry.

  19. Preparation of Cu-doped nickel oxide thin films and their properties

    SciTech Connect

    Gowthami, V.; Meenakshi, M.; Anandhan, N.; Sanjeeviraja, C.

    2014-04-24

    Copper doped Nickel oxide film was preferred on glass substrate by simple nebulizer technique keeping the substrate temperature at 350°C and characterized by X-ray diffraction (XRD), Photoluminescence (PL) and Four probe resistivity measurements. XRD studies indicated cubic structure and the crystallites are preferentially oriented along the [111] direction. Interesting results have been obtained from the study of PL spectra. A peak corresponding to 376nm in the emission spectra for 0%, 5% and 10% copper doped samples. The samples show sharp and strong UV emission corresponding to the near band edge emission under excitation of 275nm.

  20. Synthesis and characterization of lanthanum doped zinc oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Kumar, Vinod; Sonia, Suman, Kumar, Sacheen; Kumar, Dinesh

    2016-05-01

    La doped ZnO (Zn1-xLaxO, x = 0, 3, 6 and 9) were prepared via chemical co-precipitation method using Zinc Acetate, Lanthanum Acetate and Sodium Hydroxide at 50°C. Hydrate nanoparticles were annealed in air at 300°C for 3 hours. The synthesized samples have been characterized by powder X-ray diffraction and UV-Visiblespectrophotometer. The XRD measurement revealsthat the prepared nanoparticles have different microstructure without changing a hexagonal wurtzite structure. The result shows the change in nanoparticles size with the increment of lanthanum concentration for lower concentration for x = 0 to 6 and decreases at x = 9.

  1. Doped, porous iron oxide films and their optical functions and anodic photocurrents for solar water splitting

    SciTech Connect

    Kronawitter, Coleman X.; Mao, Samuel S.; Antoun, Bonnie R.

    2011-02-28

    The fabrication and morphological, optical, and photoelectrochemical characterization of doped iron oxide films is presented. The complex index of refraction and absorption coefficient of polycrystalline films are determined through measurement and modeling of spectral transmission and reflection data using appropriate dispersion relations. Photoelectrochemical characterization for water photo-oxidation reveals that the conversion efficiencies of electrodes are strongly influenced by substrate temperature during their oblique-angle physical vapor deposition. These results are discussed in terms of the films' morphological features and the known optoelectronic limitations of iron oxide films for application in solar water splitting devices.

  2. Investigation of the properties of Sb doping on tin oxide SNO2 materials for technological applications

    NASA Astrophysics Data System (ADS)

    Hachoun, Z.; Ouerdane, A.; Bouslama, M.; Ghaffour, M.; Abdellaoui, A.; Caudano, Y.; benamara, A. Ali

    2016-04-01

    The conductivities of the oxide SnO2 is dependent on the nature of the surrounding gas. This property stems from the adsorption or desorption on the surface of oxide grains. These phenomena are usually accompanied by electronic transfer between the adsorbed molecule and the semiconductor material, changing its conductivity. Tin oxidation and Sb doping were realized without and with heating process. The XPS technique and the TEM microscopy showed the synthesized nanocrystals. Simulated Monte Carlo program Casino is used for a scanning its profile. The surface characteristics are highlighted in the aim to be used as spatial gas sensors.

  3. Dielectric Properties of Rare-Earth-Oxide-Doped BaTiO3 Ceramics Fired in Reducing Atmosphere

    NASA Astrophysics Data System (ADS)

    Okino, Yoshikazu; Shizuno, Hisamitsu; Kusumi, Shinya; Kishi, Hiroshi

    1994-09-01

    In order to gain an understanding of highly reliable electrical characteristics for the Ho-doped multilayer ceramic capacitors with Ni electrodes, dielectric properties of various rare-earth-oxide-doped BaTiO3 ceramics were studied. The smaller ionic radius rare-earth-oxide (Dy, Ho, Er)-doped samples showed lower resistivity in reducing atmosphere, but higher resistivity in oxidizing atmosphere at the cooling stage, compared with the larger-ion (La, Sm, Gd)-doped samples. Multilayer ceramic capacitors with Ni electrodes using the smaller-ion-doped materials showed smaller aging rate and longer lifetime. We developed Ni-electrode MLCs with X7R specification as 1 µ F in the 2125 type.

  4. Visible-Light-Induced Photocatalytic Inactivation of Bacteria by Composite Photocatalysts of Palladium Oxide and Nitrogen-Doped Titanium Oxide

    PubMed Central

    Wu, Pinggui; Xie, Rongcai; Imlay, James A.; Shang, Jian Ku

    2011-01-01

    Composite photocatalysts of palladium oxide and nitrogen-doped titanium oxide (PdO/TiON) were synthesized by a solgel process, as convenient forms of nanopowder or immobilized powder on nanofiber. The PdO/TiON catalysts were tested for visible-light-activated photocatalysis using different bacterial indicators, including gram-negative cells of Escherichia coli and Pseudomonas aeruginosa, and gram-positive cells of Staphylococcus aureus. Disinfection data indicated that PdO/TiON composite photocatalysts have a much better photocatalytic activity than either palladium-doped (PdO/TiO2) or nitrogen-doped titanium oxide (TiON) under visible-light illumination. The roles of Pd and N were discussed in terms of the production and separation of the charge carriers under visible light illumination. The photocatalytic activity was thus dependent on dopants and light intensity. Microscopic characterization demonstrated that visible-light photocatalysis on PdO/TiON caused drastic damage on the bacteria cell wall and the cell membrane. PMID:21423793

  5. Visible-Light-Induced Photocatalytic Inactivation of Bacteria by Composite Photocatalysts of Palladium Oxide and Nitrogen-Doped Titanium Oxide.

    PubMed

    Wu, Pinggui; Xie, Rongcai; Imlay, James A; Shang, Jian Ku

    2009-05-20

    Composite photocatalysts of palladium oxide and nitrogen-doped titanium oxide (PdO/TiON) were synthesized by a solgel process, as convenient forms of nanopowder or immobilized powder on nanofiber. The PdO/TiON catalysts were tested for visible-light-activated photocatalysis using different bacterial indicators, including gram-negative cells of Escherichia coli and Pseudomonas aeruginosa, and gram-positive cells of Staphylococcus aureus. Disinfection data indicated that PdO/TiON composite photocatalysts have a much better photocatalytic activity than either palladium-doped (PdO/TiO(2)) or nitrogen-doped titanium oxide (TiON) under visible-light illumination. The roles of Pd and N were discussed in terms of the production and separation of the charge carriers under visible light illumination. The photocatalytic activity was thus dependent on dopants and light intensity. Microscopic characterization demonstrated that visible-light photocatalysis on PdO/TiON caused drastic damage on the bacteria cell wall and the cell membrane. PMID:21423793

  6. Effect of W and WC on the oxidation resistance of yttria-doped silicon nitride

    NASA Technical Reports Server (NTRS)

    Schuon, S.

    1980-01-01

    The effect of W and WC contamination on the oxidation and cracking in air of sintered Si3N4 - 8 w/o Y2O3 ceramics at 500, 750, and 1350 C is examined. A mixture of Si3N4 - 8Y2O3, milled with alumina balls, was divided into four portions. Three portions were doped with 2 w/o WC W, and 4 w/o W respectively, in order to simulate contamination during milling. The fourth portion was undoped and used on a control. The addition of W or WC did not affect the phase relationships in the system, as all bars with or without additions contained melilite as the major Si-Y-O-N phase after sintering. At 750 C, instability (rapid oxidation and cracking) of W-doped bars appears to have occurred as a result of oxidation of the tungsten containing melilite phase. No intermediate temperature instability was observed in bars containing 2 w/o WC or in bars with no additive. Specimens exposed at 1350 C had good oxidation resistance due to the formation of a protective siliceous oxide layer. A specimen containing 4 w/o W which was preoxidized at 1350 C had improved oxidation resistance at 750 C. The tendency towards oxidation and cracking of Si3N4 - 8 Y2O3 at 750 C is concluded to be related to tungsten content of the sintered bars.

  7. Fully transparent thin film transistors based on zinc oxide channel layer and molybdenum doped indium oxide electrodes

    NASA Astrophysics Data System (ADS)

    MÄ dzik, Mateusz; Elamurugu, Elangovan; Viegas, Jaime

    2016-03-01

    In this work we report the fabrication of thin film transistors (TFT) with zinc oxide channel and molybdenum doped indium oxide (IMO) electrodes, achieved by room temperature sputtering. A set of devices was fabricated, with varying channel width and length from 5μm to 300μm. Output and transfer characteristics were then extracted to study the performance of thin film transistors, namely threshold voltage and saturation current, enabling to determine optimal fabrication process parameters. Optical transmission in the UV-VIS-IR are also reported.

  8. Pd doped reduced graphene oxide for hydrogen storage

    SciTech Connect

    Das, Tapas; Banerjee, Seemita; Sudarsan, V.

    2015-06-24

    Pd nanoparticles dispersed reduced graphene oxide sample has been prepared by a simple chemical method using hydrazine as the reducing agent. Based on XRD and {sup 13}C MAS NMR studies it is confirmed that, Pd nanoparticles are effectively mixed with the reduced graphene oxide sample. Maximum hydrogen storage capacity has been estimated to be ∼1.36 wt % at 123K. Improved hydrogen storage capacity of Pd incorporated sample can be explained based on the phenomenon of spillover of atomic hydrogen.

  9. Thermoelectric properties of hot-pressed and PECS-sintered magnesium-doped copper aluminum oxide

    SciTech Connect

    Liu, Chang; Morelli, Donald T

    2011-02-03

    Copper aluminum oxide (CuAlO{sub 2}) is considered as a potential candidate for thermoelectric applications. Partially magnesium-doped CuAlO{sub 2} bulk pellets were fabricated using solid-state reactions, hot-pressing, and pulsed electric current sintering (PECS) techniques. X-ray diffraction and scanning electron microscopy were adopted for structural analysis. High-temperature transport property measurements were performed on hot-pressed samples. Electrical conductivity increased with Mg doping before secondary phases became significant, while the Seebeck coefficient displayed the opposite trend. Thermal conductivity was consistently reduced as the Mg concentration increased. Effects of Mg doping, preparation conditions, and future modification on this material’s properties are discussed.

  10. Solvothermal synthesis of gallium-doped zinc oxide nanoparticles with tunable infrared absorption

    NASA Astrophysics Data System (ADS)

    Zhou, Haifeng; Wang, Hua; Tian, Xingyou; Zheng, Kang; Xu, Fei; Su, Zheng; Tian, Konghu; li, Qiulong; Fang, Fei

    2014-12-01

    The doping of ZnO nanoparticles (NPs) has been attracting a lot of attention both for fundamental studies and potential applications. In this manuscript, we report the preparation of gallium doped zinc oxide (GZO) NPs through the solvothermal method. In order to obtain the effective Ga doping in the ZnO crystalline lattice, we identified the optimal reaction conditions in terms of different Zn precursors, temperature, and heating rate. The results show that GZO NPs with tunable infrared absorption can be received using different molar ratios of Ga(NO3)3 and zinc stearate (Zn[CH3(CH2)16COO]2, ZnSt2) kept in the sealed autoclaves at 160 °C for 8 h. Furthermore, the growth of the GZO NPs was investigated by monitoring the optical absorption spectral and the corresponding chemical composition of aliquots extracted at different reaction time intervals.

  11. Effect of nitrogen doping of graphene oxide on hydrogen and hydroxyl adsorption

    NASA Astrophysics Data System (ADS)

    Min, Byeong June; Jeong, Hae Kyung

    2014-05-01

    We investigate how nitrogen-doping affects the hydrogen (H) and the hydroxyl (OH) adsorption on graphene oxide (GO) and on nitrogen-doped GO (NGO) via pseudopotential plane wave density functional calculations within the local spin density approximation. We find that the nitrogendoping brings about drastic changes in the hydrogen and the hydroxyl adsorption energetics, but its effects depend sensitively on the nitrogen configuration in NGO. The H and the OH adsorption energies are comparable only for pyrrolic NGO. In GO and quarternary NGO, the H adsorption energy is greater than the OH adsorption energy while the trend is reversed in pyridinic NGO. Also, the OH adsorption process is less affected by nitrogen-doping than the H adsorption is.

  12. The single cell of low temperature solid oxide fuel cell with sodium carbonate-SDC (samarium-doped ceria) as electrolyte and biodiesel as fuel

    NASA Astrophysics Data System (ADS)

    Rahmawati, F.; Nuryanto, A.; Nugrahaningtyas, K. D.

    2016-02-01

    In this research NSDC (composite of Na2CO3-SDC) was prepared by the sol-gel method to produce NSDC1 and also by the ceramic method to produce NSDC2. The prepared NSDC then were analyzed by XRD embedded with Le Bail refinement to study the change of characteristic peaks, their crystal structure, and their cell parameters. Meanwhile, the measurement of impedance was conducted to study the electrical conductivity of the prepared materials. A single cell was prepared by coating NSDC-L (a composite of NSDC with Li0.2Ni0.7Cu0.1O2) on both surfaces of NSDC. The NSDC-L was used as anode and cathode. The ionic conductivity of NSDC1 and NSDC2 at 400 oC are 4.1109 x 10-2 S.cm-1 and 1.6231 x 10-2 S.cm-1, respectively. Both electrolytes have ionic conductivity higher than 1 x 10-4 S.cm-1, therefore, can be categorized as good electrolyte [1]. However, the NSDC1 shows electrodeelectrolyte conduction. It indicates the existence of electronic migration from electrolyte- electrode or vice versa. Those may cause a short circuit during fuel cell operation and will reduce the fuel cell performance fastly. The single cell tests were conducted at 300, 400, 500 and 600 °C. The single fuel cell with NSDC1 and NSDC2 as electrolyte show maximum power density at 400 °C with the power density of 3.736 x 10-2 mW.cm-2 and 2.245 x 10-2 mW.cm-2, respectively.

  13. Improved performance of ceria-based solid oxide fuel cell using doped LaGaO3 films deposited by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Qian, Jing; Zhu, Zhiwen; Jiang, Guoshun; Liu, Wei

    2014-01-01

    A dense La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) film is fabricated using the pulsed laser deposition (PLD) technique on a Ce0.8Sm0.2O2-δ (SDC) electrolyte which is prepared using a co-pressing process on a NiO-SDC anode substrate. The LSGM/SDC bilayer electrolyte cell with Sm0.5Sr0.5CoO3-δ-Ce0.8Sm0.2O2-δ (SSC-SDC, 70:30 wt.%) cathode achieves significantly enhanced cell performance, yielding open circuit voltage (OCV) value of 0.89 V and maximum power density of 758 mW cm-2 at 700 °C. The electrical current leakage in the SDC single layer cell caused by the reduction of Ce4+ to Ce3+ in reducing environment has been eliminated by depositing the LSGM thin film as a blocking layer; besides, the reaction between NiO and LSGM can be prevented due to the dense SDC electrolyte layer. The influence of oxygen pressure and post-annealing temperature on the crystallinity, microstructure and surface roughness of the LSGM films are studied for obtaining a high quality film. Characterization analysis of the cell shows that the bilayer electrolyte deposited by the PLD technique have retained the chemical, mechanical and structural integrity of the cell.

  14. p type doping of zinc oxide by arsenic ion implantation

    SciTech Connect

    Braunstein, G.; Muraviev, A.; Saxena, H.; Dhere, N.; Richter, V.; Kalish, R.

    2005-11-07

    p type doping of polycrystalline ZnO thin films, by implantation of arsenic ions, is demonstrated. The approach consisted of carrying out the implantations at liquid-nitrogen temperature ({approx}-196 deg. C), followed by a rapid in situ heating of the sample, at 560 deg. C for 10 min, and ex situ annealing at 900 deg. C for 45 min in flowing oxygen. p type conductivity with a hole concentration of 2.5x10{sup 13} cm{sup -2} was obtained using this approach, following implantation of 150 keV 5x10{sup 14} As/cm{sup 2}. A conventional room-temperature implantation of 1x10{sup 15} As/cm{sup 2}, followed by the same ex situ annealing, resulted in n type conductivity with a carrier concentration of 1.7x10{sup 12} cm{sup -2}.

  15. Morphological Control and Characterization of Monodispersed Ceria Particles

    SciTech Connect

    Minamidate, Y.; Yin, S.; Devaraju, M. K.; Sato, T.

    2010-11-24

    The morphological control of cerium oxide particles was carried out by a homogeneous precipitation followed by calcination in air at 400 deg. C. The effects of pre-aging temperature, aging time and precipitation reagents on the morphologies of final products were investigated. When urea was used as a precipitation reagent, monodispersed spherical and flake-like cerium carbonate hydroxide precursor was precipitated in the solution at 90 deg. C for 2 h after pre-aging at 25 deg. C - 50 deg. C for 24-72 h. On the other hand, monodispersed nanosize rod-like cerium hydroxide particles were obtained using triethanolamine as precipitation reagent. Ceria particles with the same morphologies and slightly smaller particle size than those of as-prepared cerium precursor could be obtained after calcination in air at 400 deg. C. Physical-chemical characteristics of the monodispersed cerium oxide particles were evaluated.

  16. Hydrodeoxygenation of Guaiacol over Ceria-Zirconia Catalysts.

    PubMed

    Schimming, Sarah M; LaMont, Onaje D; König, Michael; Rogers, Allyson K; D'Amico, Andrew D; Yung, Matthew M; Sievers, Carsten

    2015-06-22

    The hydrodeoxygenation of guaiacol is investigated over bulk ceria and ceria-zirconia catalysts with different elemental compositions. The reactions are performed in a flow reactor at 1 atm and 275-400 °C. The primary products are phenol and catechol, whereas cresol and benzene are formed as secondary products. No products with hydrogenated rings are formed. The highest conversion of guaiacol is achieved over a catalyst containing 60 mol % CeO2 and 40 mol % ZrO2 . Pseudo-first-order activation energies of 97-114 kJ mol(-1) are observed over the mixed metal oxide catalysts. None of the catalysts show significant deactivation during 72 h on stream. The important physicochemical properties of the catalysts are characterized by X-ray diffraction (XRD), temperature-programmed reduction, titration of oxygen vacancies, and temperature-programmed desorption of ammonia. On the basis of these experimental results, the reasons for the observed reactivity trends are identified. PMID:26036450

  17. Embedded Ceria Nanoparticles in Crosslinked PVA Electrospun Nanofibers as Optical Sensors for Radicals.

    PubMed

    Shehata, Nader; Samir, Effat; Gaballah, Soha; Hamed, Aya; Elrasheedy, Asmaa

    2016-01-01

    This work presents a new nanocomposite of cerium oxide (ceria) nanoparticles embedded in electrospun PVA nanofibers for optical sensing of radicals in solutions. Our ceria nanoparticles are synthesized to have O-vacancies which are the receptors for the radicals extracted from peroxide in water solution. Ceria nanoparticles are embedded insitu in PVA solution and then formed as nanofibers using an electrospinning technique. The formed nanocomposite emits visible fluorescent emissions under 430 nm excitation, due to the active ceria nanoparticles with fluorescent Ce(3+) ionization states. When the formed nanocomposite is in contact with peroxide solution, the fluorescence emission intensity peak has been found to be reduced with increasing concentration of peroxide or the corresponding radicals through a fluorescence quenching mechanism. The fluorescence intensity peak is found to be reduced to more than 30% of its original value at a peroxide weight concentration up to 27%. This work could be helpful in further applications of radicals sensing using a solid mat through biomedical and environmental monitoring applications. PMID:27571083

  18. Investigation of electrical properties of Mn doped tin oxide nanoparticles using impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Azam, Ameer; Ahmed, Arham S.; Chaman, M.; Naqvi, A. H.

    2010-11-01

    Manganese doped tin oxide nanoparticles with manganese content varying from 0 to 15 mol % were synthesized using sol-gel method. The structural and compositional analysis was carried out using x-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive x-ray analysis (EDAX). Dielectric and impedance spectroscopy was carried out at room temperature to explore the electrical properties of Mn doped SnO2. XRD analysis indicated the formation of single phase rutile type tetragonal structure of all the samples. The crystallite size was observed to vary from 16.2 to 7.1 nm as the Mn content was increased. The XRD, SEM, and EDAX results corroborated the successful doping of Mn in the SnO2 matrix. Complex impedance analysis was used to distinguish the grain and grain boundary contributions to the system, suggesting the dominance of grain boundary resistance in the doped samples. The dielectric constant ɛ', dielectric loss tan δ and ac conductivity σac were studied as a function of frequency and composition and the behavior has been explained on the basis of Maxwell-Wagner interfacial model. All the dielectric parameters were found to decrease with the increase in doping concentration. Moreover, it has been observed that the dielectric loss approaches to zero in case of high dopant concentration (9%, 15%) at high frequencies.

  19. Influence of neodymium concentration on excitation and emission properties of Nd doped gallium oxide nanocrystalline films

    NASA Astrophysics Data System (ADS)

    Podhorodecki, A.; Banski, M.; Misiewicz, J.; Lecerf, C.; Marie, P.; Cardin, J.; Portier, X.

    2010-09-01

    Gallium oxide and more particularly β-Ga2O3 matrix is an excellent material for new generation of devices electrically or optically driven as it is known as the widest band gap transparent conductive oxide. In this paper, the optical properties of neodymium doped gallium oxide films grown by magnetron sputtering have been analyzed. The influence of the Nd ions concentration on the excitation/emission mechanisms of Nd ions and the role of gallium oxide matrix have been investigated. The grain size reduction into gallium oxide films have been observed when concentration of Nd increases. It has been found for all samples that the charge transfer is the main excitation mechanism for Nd ions where defect states play an important role as intermediate states. As a consequence Nd emission efficiency increases with temperature giving rise to most intensive emission at 1087 nm at room temperature.

  20. Influence of neodymium concentration on excitation and emission properties of Nd doped gallium oxide nanocrystalline films

    SciTech Connect

    Podhorodecki, A.; Banski, M.; Misiewicz, J.; Lecerf, C.; Marie, P.; Cardin, J.; Portier, X.

    2010-09-15

    Gallium oxide and more particularly {beta}-Ga{sub 2}O{sub 3} matrix is an excellent material for new generation of devices electrically or optically driven as it is known as the widest band gap transparent conductive oxide. In this paper, the optical properties of neodymium doped gallium oxide films grown by magnetron sputtering have been analyzed. The influence of the Nd ions concentration on the excitation/emission mechanisms of Nd ions and the role of gallium oxide matrix have been investigated. The grain size reduction into gallium oxide films have been observed when concentration of Nd increases. It has been found for all samples that the charge transfer is the main excitation mechanism for Nd ions where defect states play an important role as intermediate states. As a consequence Nd emission efficiency increases with temperature giving rise to most intensive emission at 1087 nm at room temperature.

  1. Growth and Characterization of Co-Doped Fluorine and Antimony in Tin Oxide Thin Films Obtained by Ultrasonic Spray Pyrolysis

    NASA Astrophysics Data System (ADS)

    Gaewdang, Thitinai; Wongcharoen, Ngamnit

    Fluorine (F)-doped, antimony (Sb)-doped, fluorine and antimony co-doped tin oxide (SnO2) thin films were prepared by ultrasonic spray pyrolysis technique using SnCl2, NH4F and SbCl3 as precursors of Sn, F and Sb elements respectively. F and Sb doping concentrations carried out from 1 to 20 wt% and 1 to 4 wt% in F-doped and Sb-doped SnO2 films respectively. In F and Sb co-doped SnO2 films, the proportions of F and Sb to Sn in starting solution were 15 and 2 wt% respectively. XRD patterns showed that the preferred orientation of SnO2:F, SnO2:Sb and SnO2:F, Sb is dependent on the doping concentration. The variation of doping concentration and preferred orientation of the films was reflected in their morphology as investigated by SEM. The electrical properties of the films were performed by Hall effect measurements in van der Pauw configuration. The minimum resistivity values of SnO2:F and SnO2:Sb were found in the films doped with 15 wt% of F and 2 wt% of Sb. However, The minimum of resistivity value of F and Sb co-doped SnO2 films is not better than neither the one of F-doped nor the one of Sb-doped SnO2 films. The optical transmission of SnO2:F films was found to increase with increasing in F doping concentration. Whereas the optical transmission of SnO2:Sb was found to decrease with increasing in Sb concentration. The F and Sb co-doped SnO2 films annealed in three different conditions at 500°C show the lower transmission values than the value obtained in the as-prepared SnO2:F, Sb films.

  2. Reactivity enhancement of oxide skins in reversible Ti-doped NaAlH{sub 4}

    SciTech Connect

    Delmelle, Renaud; Borgschulte, Andreas; Gehrig, Jeffrey C.; Züttel, Andreas

    2014-12-15

    The reversibility of hydrogen sorption in complex hydrides has only been shown unambiguously for NaAlH{sub 4} doped with transition metal compounds. Despite a multitude of investigations of the effect of the added catalyst on the hydrogen sorption kinetics of NaAlH{sub 4}, the mechanism of catalysis remains elusive so far. Following the decomposition of TiCl{sub 3}-doped NaAlH{sub 4} by in-situ X-ray photoelectron spectroscopy (XPS), we link the chemical state of the dopant with those of the hydride and decomposition products. Titanium and aluminium change their oxidation states during cycling. The change of the formal oxidation state of Al from III to zero is partly due to the chemical reaction from NaAlH{sub 4} to Al. Furthermore, aluminium oxide is formed (Al{sub 2}O{sub 3}), which coexists with titanium oxide (Ti{sub 2}O{sub 3}). The interplay of metallic and oxidized Ti with the oxide skin might explain the effectiveness of Ti and similar dopants (Ce, Zr…)

  3. Interfacial control of oxygen vacancy doping and electrical conduction in thin film oxide heterostructures

    PubMed Central

    Veal, Boyd W.; Kim, Seong Keun; Zapol, Peter; Iddir, Hakim; Baldo, Peter M.; Eastman, Jeffrey A.

    2016-01-01

    Oxygen vacancies in proximity to surfaces and heterointerfaces in oxide thin film heterostructures have major effects on properties, resulting, for example, in emergent conduction behaviour, large changes in metal-insulator transition temperatures or enhanced catalytic activity. Here we report the discovery of a means of reversibly controlling the oxygen vacancy concentration and distribution in oxide heterostructures consisting of electronically conducting In2O3 films grown on ionically conducting Y2O3-stabilized ZrO2 substrates. Oxygen ion redistribution across the heterointerface is induced using an applied electric field oriented in the plane of the interface, resulting in controlled oxygen vacancy (and hence electron) doping of the film and possible orders-of-magnitude enhancement of the film's electrical conduction. The reversible modified behaviour is dependent on interface properties and is attained without cation doping or changes in the gas environment. PMID:27283250

  4. Optical constants of amorphous, transparent titanium-doped tungsten oxide thin films.

    PubMed

    Ramana, C V; Baghmar, Gaurav; Rubio, Ernesto J; Hernandez, Manuel J

    2013-06-12

    We report on the optical constants and their dispersion profiles determined from spectroscopic ellipsometry (SE) analysis of the 20%-titanium (Ti) doped of tungsten oxide (WO3) thin films grown by sputter-deposition. The Ti-doped WO3 films grown in a wide range of temperatures (25-500 °C) are amorphous and optically transparent. SE data indicates that there is no significant interdiffusion at the film-substrate interface for a W-Ti oxide film growth of ~90 nm. The index refraction (n) at λ = 550 nm vary in the range of 2.17-2.31 with a gradual increase in growth temperature. A correlation between the growth conditions and optical constants is discussed. PMID:23682744

  5. Interfacial control of oxygen vacancy doping and electrical conduction in thin film oxide heterostructures.

    PubMed

    Veal, Boyd W; Kim, Seong Keun; Zapol, Peter; Iddir, Hakim; Baldo, Peter M; Eastman, Jeffrey A

    2016-01-01

    Oxygen vacancies in proximity to surfaces and heterointerfaces in oxide thin film heterostructures have major effects on properties, resulting, for example, in emergent conduction behaviour, large changes in metal-insulator transition temperatures or enhanced catalytic activity. Here we report the discovery of a means of reversibly controlling the oxygen vacancy concentration and distribution in oxide heterostructures consisting of electronically conducting In2O3 films grown on ionically conducting Y2O3-stabilized ZrO2 substrates. Oxygen ion redistribution across the heterointerface is induced using an applied electric field oriented in the plane of the interface, resulting in controlled oxygen vacancy (and hence electron) doping of the film and possible orders-of-magnitude enhancement of the film's electrical conduction. The reversible modified behaviour is dependent on interface properties and is attained without cation doping or changes in the gas environment. PMID:27283250

  6. 2.7 μm emission in heavy metal oxide glasses doped with erbium ions

    NASA Astrophysics Data System (ADS)

    Ragin, Tomasz; Zmojda, Jacek; Kochanowicz, Marcin; Miluski, Piotr; Jelen, Piotr; Sitarz, Maciej; Dorosz, Dominik

    2015-12-01

    In this paper, heavy metal oxide glasses based on bismuth, germanate and gallium elements doped with Er3+ have been synthesized. Composition of glass matrix has been developed in terms of low phonon energy (724 cm-1), low absorption coefficient in the infrared region (1.2 cm-1), good mechanical and chemical properties. Synthesis of glasses has been performed under a low vacuum condition, which has reduced the OH- ions to 50 ppm. Glasses were doped with (0.25 - 1 mol%) Er2O3 to obtain emission at the wavelength of 2.7 μm (4I11/2 → 4I13/2) under 980 nm laser diode excitation. Obtained results demonstrate that developed heavy metal oxide glass is an attractive material for mid-infrared applications.

  7. Acetone Sensing Properties of a Gas Sensor Composed of Carbon Nanotubes Doped With Iron Oxide Nanopowder

    PubMed Central

    Tan, Qiulin; Fang, Jiahua; Liu, Wenyi; Xiong, Jijun; Zhang, Wendong

    2015-01-01

    Iron oxide (Fe2O3) nanopowder was prepared by a precipitation method and then mixed with different proportions of carbon nanotubes. The composite materials were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. A fabricated heater-type gas sensor was compared with a pure Fe2O3 gas sensor under the influence of acetone. The effects of the amount of doping, the sintering temperature, and the operating temperature on the response of the sensor and the response recovery time were analyzed. Experiments show that doping of carbon nanotubes with iron oxide effectively improves the response of the resulting gas sensors to acetone gas. It also reduces the operating temperature and shortens the response recovery time of the sensor. The response of the sensor in an acetone gas concentration of 80 ppm was enhanced, with good repeatability. PMID:26569253

  8. Interfacial control of oxygen vacancy doping and electrical conduction in thin film oxide heterostructures

    NASA Astrophysics Data System (ADS)

    Veal, Boyd W.; Kim, Seong Keun; Zapol, Peter; Iddir, Hakim; Baldo, Peter M.; Eastman, Jeffrey A.

    2016-06-01

    Oxygen vacancies in proximity to surfaces and heterointerfaces in oxide thin film heterostructures have major effects on properties, resulting, for example, in emergent conduction behaviour, large changes in metal-insulator transition temperatures or enhanced catalytic activity. Here we report the discovery of a means of reversibly controlling the oxygen vacancy concentration and distribution in oxide heterostructures consisting of electronically conducting In2O3 films grown on ionically conducting Y2O3-stabilized ZrO2 substrates. Oxygen ion redistribution across the heterointerface is induced using an applied electric field oriented in the plane of the interface, resulting in controlled oxygen vacancy (and hence electron) doping of the film and possible orders-of-magnitude enhancement of the film's electrical conduction. The reversible modified behaviour is dependent on interface properties and is attained without cation doping or changes in the gas environment.

  9. Tungsten-doped tin oxide thin films prepared by pulsed plasma deposition

    SciTech Connect

    Huang Yanwei; Zhang Qun Li Guifeng; Yang Ming

    2009-05-15

    Transparent conductive oxide tungsten-doped tin oxide thin films were deposited on glass substrates from ceramic targets by the pulsed plasma deposition method. The structural, electrical and optical properties have been investigated as functions of tungsten doping content and oxygen partial pressure. The lowest resistivity of 2.1 x 10{sup -3} {omega}{center_dot}cm was reproducibly obtained, with carrier mobility of 30 cm{sup 2}V{sup -1}s{sup -1} and carrier concentration of 9.6 x 10{sup 19} cm{sup -3} at the oxygen partial pressure of 1.8 Pa. The average optical transmission was in excess of 80% in the visible region from 400 to 700 nm, with the optical band gap ranging from 3.91 to 4.02 eV.

  10. Co-doped titanium oxide foam and water disinfection device

    DOEpatents

    Shang, Jian-Ku; Wu, Pinggui; Xie, Rong-Cai

    2016-01-26

    A quaternary oxide foam, comprises an open-cell foam containing (a) a dopant metal, (b) a dopant nonmetal, (c) titanium, and (d) oxygen. The foam has the advantages of a high surface area and a low back pressure during dynamic flow applications. The inactivation of Escherichia coli (E. coli) was demonstrated in a simple photoreactor.

  11. Direct ethanol solid oxide fuel cell operating in gradual internal reforming

    NASA Astrophysics Data System (ADS)

    Nobrega, S. D.; Galesco, M. V.; Girona, K.; de Florio, D. Z.; Steil, M. C.; Georges, S.; Fonseca, F. C.

    2012-09-01

    An electrolyte supported solid oxide fuel cell (SOFC) using standard electrodes, doped-lanthanum manganite cathode and Ni-cermet anode, was operated with direct (anhydrous) ethanol for more than 100 h, delivering essentially the same power output as running on hydrogen. A ceria-based layer provides the catalytic activity for the gradual internal reforming, which uses the steam formed by the electrochemical oxidation of hydrogen for the decomposition of ethanol. Such a concept opens up the way for multi-fuel SOFCs using standard components and a catalytic layer.

  12. Resistance Measurements and Activation Energies Calculations of Pure and Platinum Doped Stannic Oxide Ceramics in Air

    SciTech Connect

    Ibrahim, Zuhairi; Othman, Zulkafli; Karim, Mohd Mustamam Abd; Holland, Diane

    2007-05-09

    Pure SnO2 and Pt-SnO2 ceramics were fabricated by the dry pressing method using a pressure of 40 Mpa and sintered at 1000 deg. C. Electrical resistance measurements were made using an impedance analyzer, in air and temperatures between 25 deg. C and 450 deg. C. The change in resistance in both pure and platinum-doped stannic oxide ceramics was discussed.

  13. Distribution, elimination, and biopersistence to 90 days of a systemically introduced 30 nm ceria-engineered nanomaterial in rats.

    PubMed

    Yokel, Robert A; Au, Tu C; MacPhail, Robert; Hardas, Sarita S; Butterfield, D Allan; Sultana, Rukhsana; Goodman, Michael; Tseng, Michael T; Dan, Mo; Haghnazar, Hamed; Unrine, Jason M; Graham, Uschi M; Wu, Peng; Grulke, Eric A

    2012-05-01

    Nanoceria is used as a catalyst in diesel fuel, as an abrasive in printed circuit manufacture, and is being pursued as an antioxidant therapeutic. Our objective is to extend previous findings showing that there were no reductions of cerium in organs of the mononuclear phagocyte (reticuloendothelial) system up to 30 days after a single nanoscale ceria administration. An ~5% aqueous dispersion of citrate-stabilized 30 nm ceria, synthesized and characterized in-house, or vehicle, was iv infused into rats terminated 1, 7, 30, or 90 days later. Cageside observations were obtained daily, body weight weekly. Daily urinary and fecal cerium outputs were quantified for 2 weeks. Nine organs were weighed and samples collected from 14 tissues/organs/systems, blood and cerebrospinal fluid for cerium determination. Histology and oxidative stress were assessed. Less than 1% of the nanoceria was excreted in the first 2 weeks, 98% in feces. Body weight gain was initially impaired. Spleen weight was significantly increased in some ceria-treated groups, associated with abnormalities. Ceria was primarily retained in the spleen, liver, and bone marrow. There was little decrease of ceria in any tissue over the 90 days. Granulomas were observed in the liver. Time-dependent oxidative stress changes were seen in the liver and spleen. Nanoscale ceria was persistently retained by organs of the mononuclear phagocyte system, associated with adverse changes. The results support concern about the long-term fate and adverse effects of inert nanoscale metal oxides that distribute throughout the body, are persistently retained, and produce adverse changes. PMID:22367688

  14. Highly conducting and crystalline doubly doped tin oxide films fabricated using a low-cost and simplified spray technique

    NASA Astrophysics Data System (ADS)

    Ravichandran, K.; Muruganantham, G.; Sakthivel, B.

    2009-11-01

    Doubly doped (simultaneous doping of antimony and fluorine) tin oxide films (SnO 2:Sb:F) have been fabricated by employing an inexpensive and simplified spray technique using perfume atomizer from aqueous solution of SnCl 2 precursor. The structural studies revealed that the films are highly crystalline in nature with preferential orientation along the (2 0 0) plane. It is found that the size of the crystallites of the doubly doped tin oxide films is larger (69 nm) than that (27 nm) of their undoped counterparts. The dislocation density of the doubly doped film is lesser (2.08×10 14 lines/m 2) when compared with that of the undoped film (13.2×10 14 lines/m 2), indicating the higher degree of crystallinity of the doubly doped films. The SEM images depict that the films are homogeneous and uniform. The optical transmittance in the visible range and the optical band gap of the doubly doped films are 71% and 3.56 eV respectively. The sheet resistance (4.13 Ω/□) attained for the doubly doped film in this study is lower than the values reported for spray deposited fluorine or antimony doped tin oxide films prepared from aqueous solution of SnCl 2 precursor (without using methanol or ethanol).

  15. Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte.

    PubMed

    Zhuang, Zhongbin; Giles, Stephen A; Zheng, Jie; Jenness, Glen R; Caratzoulas, Stavros; Vlachos, Dionisios G; Yan, Yushan

    2016-01-01

    The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells. PMID:26762466

  16. Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte

    PubMed Central

    Zhuang, Zhongbin; Giles, Stephen A.; Zheng, Jie; Jenness, Glen R.; Caratzoulas, Stavros; Vlachos, Dionisios G.; Yan, Yushan

    2016-01-01

    The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells. PMID:26762466

  17. Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte

    DOE PAGESBeta

    Zhuang, Zhongbin; Giles, Stephen A.; Zheng, Jie; Jenness, Glen R.; Caratzoulas, Stavros; Vlachos, Dionisios G.; Yan, Yushan

    2016-01-14

    The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizesmore » the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Here, owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells.« less

  18. Hydrogen Doped Metal Oxide Semiconductors with Exceptional and Tunable Localized Surface Plasmon Resonances.

    PubMed

    Cheng, Hefeng; Wen, Meicheng; Ma, Xiangchao; Kuwahara, Yasutaka; Mori, Kohsuke; Dai, Ying; Huang, Baibiao; Yamashita, Hiromi

    2016-07-27

    Heavily doped semiconductors have recently emerged as a remarkable class of plasmonic alternative to conventional noble metals; however, controlled manipulation of their surface plasmon bands toward short wavelengths, especially in the visible light spectrum, still remains a challenge. Here we demonstrate that hydrogen doped given MoO3 and WO3 via a facile H-spillover approach, namely, hydrogen bronzes, exhibit strong localized surface plasmon resonances in the visible light region. Through variation of their stoichiometric compositions, tunable plasmon resonances could be observed in a wide range, which hinge upon the reduction temperatures, metal species, the nature and the size of metal oxide supports in the synthetic H2 reduction process as well as oxidation treatment in the postsynthetic process. Density functional theory calculations unravel that the intercalation of hydrogen atoms into the given host structures yields appreciable delocalized electrons, enabling their plasmonic properties. The plasmonic hybrids show potentials in heterogeneous catalysis, in which visible light irradiation enhanced catalytic performance toward p-nitrophenol reduction relative to dark condition. Our findings provide direct evidence for achieving plasmon resonances in hydrogen doped metal oxide semiconductors, and may allow large-scale applications with low-price and earth-abundant elements. PMID:27384437

  19. Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte

    NASA Astrophysics Data System (ADS)

    Zhuang, Zhongbin; Giles, Stephen A.; Zheng, Jie; Jenness, Glen R.; Caratzoulas, Stavros; Vlachos, Dionisios G.; Yan, Yushan

    2016-01-01

    The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells.

  20. Tailoring ferromagnetism in chromium-doped zinc oxide

    NASA Astrophysics Data System (ADS)

    Haq, Bakhtiar Ul; Ahmed, Rashid; Goumri-Said, Souraya

    2014-03-01

    The simultaneous manipulation of both charge and spin has made diluted magnetic semiconductors (DMS) a potential material for the fabrication of spintronic devices. We report DMSs based on ZnO doped with Cr in wurtzite (WZ) and zinc-blend (ZB) geometries. The injection of Cr impurities at a concentration of 6.25% has successfully tuned ferromagnetism in ZnO. To recognize the nature of magnetic interactions, two spatial configurations are investigated, where the impurity atoms are placed at minimum and maximum separation distances. The material favors the short-range magnetic coupling and has a tendency towards Cr clustering. The injection of a Cr impurity into ZnO strongly influences the electronic properties in terms of band structure, dependent on the impurity spatial distribution. It is half metallic for both structural geometries when impurity atoms have minimum separation and is metallic when they are placed far apart. Moreover, replacing Zn with Cr does not show a significant effect on the structural geometries. Our results endorse that Cr:ZnO can be efficiently used for spin-polarized transport and other spin-dependent applications in both hexagonal and cubic phases.

  1. Microstructure of the Native Oxide Layer on Ni and Cr-doped Ni Nanoparticles

    SciTech Connect

    Wang, Chong M.; Baer, Donald R.; Bruemmer, Stephen M.; Engelhard, Mark H.; Bowden, Mark E.; Sundararajan, J. A.; Qiang, You

    2011-10-01

    Metallic or alloy nanoparticles exposed to air at room temperature will be instantaneously oxidized and covered by an oxide layer. However, for most cases, the true structural nature of the oxide layer formed at this stage is hard to determine. In this paper, we report the structure, morphology, and electronic structure (the density of state of both valence and conduction bands measured by a combination of XPS and EELS) of pure Ni and Cr-doped Ni nanoparticles synthesized using a cluster deposition process. Structural characterization carried out at the atomic level using aberration corrected high resolution transmission electron microscopy (HRTEM) in combination with electron and x-ray diffractions reveals that both pure Ni and Cr-doped Ni particles exposed to air at room temperature similarly possesses a core-shell structure of metal core covered by an oxide layer of typically 1.6 nm in thickness. There exists a critical size of ~ 6 nm, below which the particle is fully oxidized. The oxide particle corresponds to the rock-salt structured NiO and is faceted on the (001) planes. XPS of O-1s shows a strong peak that is attributed to (OH)-, which in combination with the atomic level HRTEM imaging indicates that the very top layer of the oxide is hydrolyzed as Ni(OH)2. Chemical composition analysis using EDS, EELS, and XPS indicates that the Cr dopant at the level of ~ 5at% forms solid solution with the Ni lattice. The Cr shows no segregation on the surface or preferential oxidation during the initial oxidation.

  2. Low driving voltage and high stability organic light-emitting diodes with rhenium oxide-doped hole transporting layer

    NASA Astrophysics Data System (ADS)

    Leem, Dong-Seok; Park, Hyung-Dol; Kang, Jae-Wook; Lee, Jae-Hyun; Kim, Ji Whan; Kim, Jang-Joo

    2007-07-01

    The authors report a promising metal oxide-doped hole transporting layer (HTL) of rhenium oxide (ReO3)-doped N ,N'-diphenyl-N ,N'-bis (1,1'-biphenyl)-4,4'-diamine (NPB). The tris(8-hydroxyquinoline) aluminum-based organic light-emitting diodes with ReO3-doped NPB HTL exhibit driving voltage of 5.2-5.4V and power efficiency of 2.2-2.3lm/W at 20mA/cm2, which is significantly improved compared to those (7.1V and 2.0lm/W, respectively) obtained from the devices with undoped NPB. Furthermore, the device with ReO3-doped NPB layer reveals the prolonged lifetime than that with undoped NPB. Details of ReO3 doping effects are described based on the UV-Vis absorption spectra and characteristics of hole-only devices.

  3. Comparison of beryllium oxide and pyrolytic graphite crucibles for boron doped silicon epitaxy

    SciTech Connect

    Ali, Dyan; Richardson, Christopher J. K.

    2012-11-15

    This article reports on the comparison of beryllium oxide and pyrolytic graphite as crucible liners in a high-temperature effusion cell used for boron doping in silicon grown by molecular beam epitaxy. Secondary ion mass spectroscopy analysis indicates decomposition of the beryllium oxide liner, leading to significant incorporation of beryllium and oxygen in the grown films. The resulting films are of poor crystal quality with rough surfaces and broad x-ray diffraction peaks. Alternatively, the use of pyrolytic graphite crucible liners results in higher quality films.

  4. Structure and Morphology Study of Cobalt Oxide Doped Silica Nanocomposite Films

    NASA Astrophysics Data System (ADS)

    Drasovean, Romana; Monteiro, Regina; Cherif, Mourad

    2010-01-01

    Cobalt oxide doped silica films were synthesized by a dip-coating technique. Initial compounds were cobalt acetate Co(CH3COO)2ṡ4H2O and tetraethoxysilane Si(OC2H5)4. The chemical composition was studied by X-ray diffraction and UV-Vis spectroscopy. The morphology analyses were carried out by means of atomic force microscopy. The average diameter of cobalt oxide dispersed particles increases with the molar ratio Co:Si and with the aging time of the initial colloidal solution.

  5. Characterization and catalytic performance of pure and Li 2O-doped CuO/CeO 2 catalysts

    NASA Astrophysics Data System (ADS)

    Deraz, N. M.

    2009-01-01

    Pure and Li 2O-doped CuO/CeO 2 catalysts calcined at 500 °C were prepared by impregnation method. The catalysts are characterized by DTA, TG-DTG, XRD, IR, TEM, nitrogen adsorption at -196 °C and the catalytic decomposition of hydrogen peroxide at 30 °C. The effects of molar ratio, heat treatment time and the doping on the structural, surface and catalytic properties of nanocrystalline Cu/Ce-mixed oxides system have been studied. It was found that the catalytic activity of ceria-supported copper oxide catalysts increased by increasing both the heat treatment time and dopant content. However, the pure Cu/Ce-mixed oxide solids containing 10 wt.% CuO exhibited the best performance. The characterization results indicated that the higher surface area, the formation of solid solution between copper and cerium oxides, and the high dispersion of copper species on the ceria were responsible for the high catalytic activity of the CuO/CeO 2 catalysts.

  6. Dopant induced bandgap narrowing in Y-doped zinc oxide nanostructures.

    PubMed

    Yogamalar, Rajeswari; Venkateswaran, Pedinti S; Benzigar, Mercy R; Ariga, Katsuhiko; Vinu, Ajayan; Bose, A Chandra

    2012-01-01

    In this report, hydrothermal synthesis and the absorption properties of the cubic shaped zinc oxide nanostructures doped with different amount of yttrium (Y) metal cation (0 to 15 at.%) are demonstrated. The structural and optical properties of chemically synthesized pure and Y doped ZnO powders are investigated by using powder X-ray diffraction (XRD), field emission scanning electron spectroscopy (FESEM) and transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorbance, photoluminescence (PL), and Fourier transform infra-red spectroscopy (FT-IR). It is found that the dopant ions stabilize in wurtzite hexagonal phase of ZnO upto the concentration of less than 6 at.%, which is mainly due to the fact that the ZnO lattice expands and the optical bandgap energy decreases at this level. Increasing the dopant concentration to greater than 6 at.% leads to a contraction of the lattice, which in turn produces a significant structural disorder evidenced by shift in the XRD peaks due to additional interstitial incorporation of Y. The vibrational modes of the metal oxide groups have been identified from the IR transmission spectra. The optical absorption results show that the optical bandgap energy of Y:ZnO nanocrystals is much less as compared to that of the pure bulk ZnO particles. Doping ZnO with trivalent Y produces excess number of electrons in the conduction band and thus, shifts the absorption edge and narrows down to 80 meV approximately. PL spectra are used to study the dependence of doping on the deep-level emission, which show an enhanced blue emission after Y doping. The existence of near band edge (NBE) emission and blue emission, related to zinc interstitials are observed in the luminescence spectra of Zn(1-x)Y(x)O nanostructures. PMID:22523948

  7. Spinel Mn-Co oxide in N-doped carbon nanotubes as a bifunctional electrocatalyst synthesized by oxidative cutting.

    PubMed

    Zhao, Anqi; Masa, Justus; Xia, Wei; Maljusch, Artjom; Willinger, Marc-Georg; Clavel, Guylhaine; Xie, Kunpeng; Schlögl, Robert; Schuhmann, Wolfgang; Muhler, Martin

    2014-05-28

    The notorious instability of non-precious-metal catalysts for oxygen reduction and evolution is by far the single unresolved impediment for their practical applications. We have designed highly stable and active bifunctional catalysts for reversible oxygen electrodes by oxidative thermal scission, where we concurrently rupture nitrogen-doped carbon nanotubes and oxidize Co and Mn nanoparticles buried inside them to form spinel Mn-Co oxide nanoparticles partially embedded in the nanotubes. Impressively high dual activity for oxygen reduction and evolution is achieved using these catalysts, surpassing those of Pt/C, RuO2, and IrO2 and thus raising the prospect of functional low-cost, non-precious-metal bifunctional catalysts in metal-air batteries and reversible fuel cells, among others, for a sustainable and green energy future. PMID:24815686

  8. Determination of active doping in highly resistive boron doped silicon nanocrystals embedded in SiO2 by capacitance voltage measurement on inverted metal oxide semiconductor structure

    NASA Astrophysics Data System (ADS)

    Zhang, Tian; Puthen-Veettil, Binesh; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-10-01

    We investigate the Capacitance-Voltage (CV) measurement to study the electrically active boron doping in Si nanocrystals (ncSi) embedded in SiO2. The ncSi thin films with high resistivity (200-400 Ω cm) can be measured by using an inverted metal oxide semiconductor (MOS) structure (Al/ncSi (B)/SiO2/Si). This device structure eliminates the complications from the effects of lateral current flow and the high sheet resistance in standard lateral MOS structures. The characteristic MOS CV curves observed are consistent with the effective p-type doping. The CV modeling method is presented and used to evaluate the electrically active doping concentration. We find that the highly boron doped ncSi films have electrically active doping of 1018-1019 cm-3 despite their high resistivity. The saturation of doping at about 1.4 × 1019 cm-3 and the low doping efficiency less than 5% are observed and discussed. The calculated effective mobility is in the order of 10-3 cm2/V s, indicating strong impurity/defect scattering effect that hinders carriers transport.

  9. Determination of active doping in highly resistive boron doped silicon nanocrystals embedded in SiO{sub 2} by capacitance voltage measurement on inverted metal oxide semiconductor structure

    SciTech Connect

    Zhang, Tian Puthen-Veettil, Binesh; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-10-21

    We investigate the Capacitance-Voltage (CV) measurement to study the electrically active boron doping in Si nanocrystals (ncSi) embedded in SiO{sub 2}. The ncSi thin films with high resistivity (200–400 Ω cm) can be measured by using an inverted metal oxide semiconductor (MOS) structure (Al/ncSi (B)/SiO{sub 2}/Si). This device structure eliminates the complications from the effects of lateral current flow and the high sheet resistance in standard lateral MOS structures. The characteristic MOS CV curves observed are consistent with the effective p-type doping. The CV modeling method is presented and used to evaluate the electrically active doping concentration. We find that the highly boron doped ncSi films have electrically active doping of 10{sup 18}–10{sup 19 }cm{sup −3} despite their high resistivity. The saturation of doping at about 1.4 × 10{sup 19 }cm{sup −3} and the low doping efficiency less than 5% are observed and discussed. The calculated effective mobility is in the order of 10{sup −3} cm{sup 2}/V s, indicating strong impurity/defect scattering effect that hinders carriers transport.

  10. Luminescence of europium-doped anode oxide films on titanium-aluminum composites

    NASA Astrophysics Data System (ADS)

    Sokol, V. A.; Pinaeva, M. M.; Gurskaya, E. A.; Stekol'Nikov, A. A.

    2000-03-01

    The luminescence of europium in anode oxide films (AOF) on titanium-aluminum film composites is investigated. It is shown that the intensity distribution in the continuous and line luminescence spectra of europium introduced into the AOF directly in the process of anodic oxidation essentially depends on the sequence of arrangement of the layers of metal films and on the temperature of their heat treatment preceding the process of anodic oxidation. It is established that the nature of the luminescence spectrum of the AOF correlates with the chronovoltammetry diagrams of anodic oxidation. Composites with a high degree of europium doping are found and methods of searching for composites for creating new materials of electronic technology are outlined.

  11. Spectroscopic properties of doped and defective semiconducting oxides from hybrid density functional calculations.

    PubMed

    Di Valentin, Cristiana; Pacchioni, Gianfranco

    2014-11-18

    CONSPECTUS: Very rarely do researchers use metal oxides in their pure and fully stoichiometric form. In most of the countless applications of these compounds, ranging from catalysis to electronic devices, metal oxides are either doped or defective because the most interesting chemical, electronic, optical, and magnetic properties arise when foreign components or defects are introduced in the lattice. Similarly, many metal oxides are diamagnetic materials and do not show a response to specific spectroscopies such as electron paramagnetic resonance (EPR) spectroscopy. However, doped or defective oxides may exhibit an interesting and informative paramagnetic behavior. Doped and defective metal oxides offer an expanding range of applications in contemporary condensed matter science; therefore researchers have devoted enormous effort to the understanding their physical and chemical properties. The interplay between experiment and computation is particularly useful in this field, and contemporary simulation techniques have achieved high accuracies with these materials. In this Account, we show how the direct comparison between spectroscopic experimental and computational data for some selected and relevant materials provides ways to understand and control these complex systems. We focus on the EPR properties and electronic transitions that arise from the presence of dopants and defects in bulk metal oxide materials. We analyze and compare the effect of nitrogen doping in TiO2 and ZnO (two semiconducting oxides) and MgO (a wide gap insulator) and examine the effect of oxygen deficiency in the semiconducting properties of TiO2-x, ZnO1-x, and WO3-x materials. We chose these systems because of their relevance in applications including photocatalysis, touch screens, electrodes in magnetic random access memories, and smart glasses. Density functional theory (DFT) provides the general computational framework used to illustrate the electronic structure of these systems. However

  12. Tuning the Electrical and Thermal Conductivities of Thermoelectric Oxides through Impurity Doping

    NASA Astrophysics Data System (ADS)

    Torres Arango, Maria A.

    Waste heat and thermal gradients available at power plants can be harvested to power wireless networks and sensors by using thermoelectric (TE) generators that directly transform temperature differentials into electrical power. Oxide materials are promising for TE applications in harsh industrial environments for waste heat recovery at high temperatures in air, because they are lightweight, cheaply produced, highly efficient, and stable at high temperatures in air. Ca3Co4O9(CCO) with layered structure is a promising p-type thermoelectric oxide with extrapolated ZT value of 0.87 in single crystal form [1]. However the ZT values for the polycrystalline ceramics remain low of ˜0.1-0.3. In this research, nanostructure engineering approaches including doping and addition of nanoinclusions were applied to the polycrystalline CCO ceramic to improve the energy conversion efficiency. Polycrystalline CCO samples with various Bi doping levels were prepared through the sol-gel chemical route synthesis of powders, pressing and sintering of the pellets. Microstructure features of Bi doped ceramic bulk samples such as porosity, development of crystal texture, grain boundary dislocations and segregation of Bi dopants at various grain boundaries are investigated from microns to atomic scale. The results of the present study show that the Bi-doping is affecting both the electrical conductivity and thermal conductivity simultaneously, and the optimum Bi doping level is strongly correlated with the microstructure and the processing conditions of the ceramic samples. At the optimum doping level and processing conditions of the ceramic samples, the Bi substitution of Ca results in the increase of the electrical conductivity, decrease of the thermal conductivity, and improvement of the crystal texture. The atomic resolution Scanning Transmission Electron Microscopy (STEM) Z-contrast imaging and the chemistry analysis also reveal the Bi-segregation at grain boundaries of CCO

  13. Impacts of a Nanosized Ceria Additive on Diesel Engine Emissions of Particulate and Gaseous Pollutants

    PubMed Central

    Zhang, Junfeng; Nazarenko, Yevgen; Zhang, Lin; Calderon, Leonardo; Lee, Ki-Bum; Garfunkel, Eric; Schwander, Stephan; Tetley, Teresa D.; Chung, Kian Fan; Porter, Alexandra E.; Ryan, Mary; Kipen, Howard; Lioy, Paul J.; Mainelis, Gediminas

    2014-01-01

    Fuel additives incorporating nanosized ceria have been increasingly used in diesel engines as combustion promoters. However, few studies have assessed the impact of these nanotechnology-based additives on pollutant emissions. Here, we systematically compare emission rates of particulate and gaseous pollutants from a single-cylinder, four-cycle diesel engine using fuel mixes containing nanoceria of varying concentrations. The test fuels were made by adding different amounts of a commercial fuel additive Envirox into an ultralow-sulfur diesel fuel at 0 (base fuel), 0.1-, 1-, and 10-fold the manufacturer-recommended concentration of 0.5 mL Envirox per liter of fuel. The addition of Envirox resulted in ceria-concentration-dependent emission reductions of CO2, CO, total particulate mass, formaldehyde, acetaldehyde, acrolein, and several polycyclic aromatic hydrocarbons. These reductions at the manufacturer-recommended doping concentration, however, were accompanied by a substantial increase of certain other air pollutants, specifically the number of ultrafine particles (+32%), NOx (+9.3%), and the particle-phase benzo[a]pyrene toxic equivalence quotient (+35%). Increasing fuel ceria concentrations also led to decreases in the size of emitted particles. Given health concerns related to ultrafine particles and NOx, our findings call for additional studies to further evaluate health risks associated with the use of nanoceria additives in various engines under various operating conditions. PMID:24144266

  14. Impacts of a nanosized ceria additive on diesel engine emissions of particulate and gaseous pollutants.

    PubMed

    Zhang, Junfeng; Nazarenko, Yevgen; Zhang, Lin; Calderon, Leonardo; Lee, Ki-Bum; Garfunkel, Eric; Schwander, Stephan; Tetley, Teresa D; Chung, Kian Fan; Porter, Alexandra E; Ryan, Mary; Kipen, Howard; Lioy, Paul J; Mainelis, Gediminas

    2013-11-19

    Fuel additives incorporating nanosized ceria have been increasingly used in diesel engines as combustion promoters. However, few studies have assessed the impact of these nanotechnology-based additives on pollutant emissions. Here, we systematically compare emission rates of particulate and gaseous pollutants from a single-cylinder, four-cycle diesel engine using fuel mixes containing nanoceria of varying concentrations. The test fuels were made by adding different amounts of a commercial fuel additive Envirox into an ultralow-sulfur diesel fuel at 0 (base fuel), 0.1-, 1-, and 10-fold the manufacturer-recommended concentration of 0.5 mL Envirox per liter of fuel. The addition of Envirox resulted in ceria-concentration-dependent emission reductions of CO2, CO, total particulate mass, formaldehyde, acetaldehyde, acrolein, and several polycyclic aromatic hydrocarbons. These reductions at the manufacturer-recommended doping concentration, however, were accompanied by a substantial increase of certain other air pollutants, specifically the number of ultrafine particles (+32%), NO(x) (+9.3%), and the particle-phase benzo[a]pyrene toxic equivalence quotient (+35%). Increasing fuel ceria concentrations also led to decreases in the size of emitted particles. Given health concerns related to ultrafine particles and NO(x), our findings call for additional studies to further evaluate health risks associated with the use of nanoceria additives in various engines under various operating conditions. PMID:24144266

  15. Preparation of high purity doped oxides for fundamental studies

    NASA Astrophysics Data System (ADS)

    Morrissey, Amy L.

    Yttria-stabilized zirconia (YSZ) is an important ceramic and is critical in electrochemical applications. Small amounts of transition metal dopants are shown to influence mechanical and electronic properties of YSZ. In this work, a novel method was used to synthesize 0.01, 0.1, 0.5, and 1.0 mol % NiO, Co3O4, and Fe2O3-doped YSZ from all acetate precursors. The synthesized materials were calcined at temperatures between 600°C and 1000°C to produce powders that were then pressed into compacts and sintered at 1500°C The powders and compacts were evaluated with x-ray diffraction, electron microscopy, and SQUID magnetometry. The particle size was observed to increase with increasing calcination temperature and a correlation between the particle size and formation of NiO was noted. In particular, NiO is absent as a second phase in the finer particle size material (lower calcination temperatures) but present in coarser material (calcination temperature at 1000°C), even when the concentration is well below the known solid solubility limit of NiO in YSZ. The results suggest Ni 2+ ions dissolve readily in nanoscale YSZ, but form NiO once the grains are larger than about 150 nm. When all materials are sintered at 1500°C, NiO dissolves fully into YSZ. Thus, the dissolution of NiO in YSZ occurs in two stages: at temperatures up to 1000°C, Ni2+ ions dissolve only in the grain boundaries of YSZ; at 1500°C, Ni2+ ions dissolve in the bulk YSZ. The results of initial experiments for Co3 O4-10YSZ and Fe2O3-10YSZ systems are reported and show an increased complexity compared with NiO-YSZ, likely because the dopant solubilities are not well-known and the effect of multivalent dopant ions existing simultaneously in YSZ is not well-characterized. This work shows that magnetometry is extremely useful for characterizing the dopant concentration in all stages of processing.

  16. Multi-Walled Carbon Nanotube-Doped Tungsten Oxide Thin Films for Hydrogen Gas Sensing

    PubMed Central

    Wongchoosuk, Chatchawal; Wisitsoraat, Anurat; Phokharatkul, Ditsayut; Tuantranont, Adisorn; Kerdcharoen, Teerakiat

    2010-01-01

    In this work we have fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walled carbon nanotube (MWCNT)-doped tungsten oxide (WO3) thin films by means of the powder mixing and electron beam (E-beam) evaporation technique. Hydrogen sensing properties of the thin films have been investigated at different operating temperatures and gas concentrations ranging from 100 ppm to 50,000 ppm. The results indicate that the MWCNT-doped WO3 thin film exhibits high sensitivity and selectivity to hydrogen. Thus, MWCNT doping based on E-beam co-evaporation was shown to be an effective means of preparing hydrogen gas sensors with enhanced sensing and reduced operating temperatures. Creation of nanochannels and formation of p-n heterojunctions were proposed as the sensing mechanism underlying the enhanced hydrogen sensitivity of this hybridized gas sensor. To our best knowledge, this is the first report on a MWCNT-doped WO3 hydrogen sensor prepared by the E-beam method. PMID:22163623

  17. Gd-doped BaSnO3: A transparent conducting oxide with localized magnetic moments

    NASA Astrophysics Data System (ADS)

    Alaan, Urusa S.; Shafer, Padraic; N'Diaye, Alpha T.; Arenholz, Elke; Suzuki, Y.

    2016-01-01

    We have synthesized transparent, conducting, paramagnetic stannate thin films via rare-earth doping of BaSnO3. Gd3+ (4f7) substitution on the Ba2+ site results in optical transparency in the visible regime, low resistivities, and high electron mobilities, along with a significant magnetic moment. Pulsed laser deposition was used to stabilize epitaxial Ba0.96Gd0.04SnO3 thin films on (001) SrTiO3 substrates, and compared with Ba0.96La0.04SnO3 and undoped BaSnO3 thin films. Gd as well as La doping schemes result in electron mobilities at room temperature that exceed those of conventional complex oxides, with values as high as 60 cm2/V.s (n = 2.5 × 1020 cm-3) and 30 cm2/V.s (n = 1 × 1020 cm-3) for La and Gd doping, respectively. The resistivity shows little temperature dependence across a broad temperature range, indicating that in both types of films the transport is not dominated by phonon scattering. Gd-doped BaSnO3 films have a strong magnetic moment of ˜7 μB/Gd ion. Such an optically transparent conductor with localized magnetic moments may unlock opportunities for multifunctional devices in the design of next-generation displays and photovoltaics.

  18. Structural and photoluminescence properties of terbium-doped zinc oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Ningthoujam Surajkumar, Singh; Shougaijam Dorendrajit, Singh; Sanoujam Dhiren, Meetei

    2014-05-01

    We present in this paper a study of the structural and photoluminescence (PL) properties of terbium (Tb) doped zinc oxide (ZnO) nanoparticles synthesized by a simple low temperature chemical precipitation method, using zinc acetate and terbium nitrate in an isopropanol medium with diethanolamine (DEA) as the capping agent at 60 °C. The as-prepared samples were heat treated and the PL of the annealed samples were studied. The prepared nanoparticles were characterized with X-ray diffraction (XRD). The XRD patterns show the pattern of typical ZnO nanoparticles and correspond with the standard XRD pattern given by JCPDS card No. 36-1451, showing the hexagonal phase structure. The PL intensity was enhanced due to Tb3+ doping, and it decreased at higher concentrations of Tb3+ doping after reaching a certain optimum concentration. The PL spectra of Tb3+ doped samples exhibited blue, bluish green, and green emissions at 460 nm (5D3 - 7F3), 484 nm (5D4 - 7F6), and 530 nm (5D4 - 7F5), respectively, which were more intense than the emissions for the undoped ZnO sample. Based on the results, an energy level schematic diagram was proposed to explain the possible electron transition processes.

  19. Impact of hole doping on spin transition in perovskite-type cobalt oxides.

    PubMed

    Che, Xiangli; Li, Liping; Hu, Wanbiao; Li, Guangshe

    2016-06-28

    Series of perovskite PrCo1-xNixO3-δ (x = 0-0.4) were prepared and carefully investigated to understand the spin state transition driven by hole doping and further to reveal the effect of spin state transition on electronic conduction. It is shown that with increasing doping level, the transition temperature Ts for Co(3+) ions from low-spin (LS) to intermediate-spin (IS) reduces from 211.9 K for x = 0 to 190.5 K for x = 0.4. XPS and FT-IR spectra demonstrate that hole doping promoted this transition due to a larger Jahn-Teller distortion. Moreover, a thermal activation of spin disorder caused by thermal population of the spin states for Co ions has a great impact on the electrical transport of these perovskite samples. This work may shed light on the comprehension of spin transition in cobalt oxides through hole doping, which is promising for finding new strategies of enhancing electronic conduction, especially for energy and catalysis applications. PMID:27049837

  20. Charge transfer and formation of reduced Ce3+ upon adsorption of metal atoms at the ceria (110) surface

    NASA Astrophysics Data System (ADS)

    Nolan, Michael

    2012-04-01

    The modification of cerium dioxide with nanoscale metal clusters is intensely researched for catalysis applications, with gold, silver, and copper having been particularly well studied. The interaction of the metal cluster with ceria is driven principally by a localised interaction between a small number of metal atoms (as small as one) and the surface and understanding the fundamentals of the interaction of metal atoms with ceria surfaces is therefore of great interest. Much attention has been focused on the interaction of metals with the (111) surface of ceria, since this is the most stable surface and can be grown as films, which are probed experimentally. However, nanostructures exposing other surfaces such as (110) show high activity for reactions including CO oxidation and require further study; these nanostructures could be modified by deposition of metal atoms or small clusters, but there is no information to date on the atomic level details of metal-ceria interactions involving the (110) surface. This paper presents the results of density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U) calculations of the adsorption of a number of different metal atoms at an extended ceria (110) surface; the metals are Au, Ag, Cu, Al, Ga, In, La, Ce, V, Cr, and Fe. Upon adsorption all metals are oxidised, transferring electron(s) to the surface, resulting in localised surface distortions. The precise details depend on the identity of the metal atom. Au, Ag, Cu each transfer one electron to the surface, reducing one Ce ion to Ce3+, while of the trivalent metals, Al and La are fully oxidised, but Ga and In are only partially oxidised. Ce and the transition metals are also partially oxidised, with the number of reduced Ce ions possible in this surface no more than three per adsorbed metal atom. The predicted oxidation states of the adsorbed metal atoms should be testable in experiments on ceria nanostructures modified with metal atoms.

  1. Continuous Precipitation of Ceria Nanoparticles from a Continuous Flow Micromixer

    SciTech Connect

    Tseng, Chih Heng; Paul, Brian; Chang, Chih-hung; Engelhard, Mark H.

    2013-01-01

    Cerium oxide nanoparticles were continuously precipitated from a solution of cerium(III) nitrate and ammonium hydroxide using a micro-scale T-mixer. Findings show that the method of mixing is important in the ceria precipitation process. In batch mixing and deposition, disintegration and agglomeration dominates the deposited film. In T-mixing and deposition, more uniform nanorod particles are attainable. In addition, it was found that the micromixing approach reduced the exposure of the Ce(OH)3 precipates to oxygen, yielding hydroxide precipates in place of CeO2 precipitates. Advantages of the micro-scale T-mixing approach include shorter mixing times, better control of nanoparticle shape and less agglomeration.

  2. Comparative structural and optical properties of different ceria nanoparticles.

    PubMed

    Nikolic, A S; Boskovic, M; Fabian, M; Bozanic, D K; Vucinic-Vasic, M; Kremenovic, A; Antic, B

    2013-10-01

    Herein a comparative study of five nanocrystalline cerium oxides (CeO(2-delta)) synthesised by different methods and calcined at 500 degrees C is reported. XRPD analysis showed that stoichiometry parameter delta, crystallite size/strain and lattice constant were only slightly affected by the method utilized. All ceria nanoparticles are nearly spherical in shape with faceted morphology, free of defects and with a relatively uniform size distribution. The average microstrain was found to be approximately 10 times higher than that of bulk counterpart. The absorption edge of nanocrystalline materials was shifted towards a higher wavelengths (red shift) in comparison with bulk counterpart, and band gap values were in the range 2.7-3.24 eV (3.33 eV for bulk counterpart). PMID:24245144

  3. Ceria Nanotube Formed by Sacrificed Precursors Template through Oswald Ripening

    PubMed Central

    Pang, Laixue; Wang, Xiaoying; Tang, Xinde

    2015-01-01

    Controllable preparation of ceria nanotube was realized by hydrothermal treatment of Ce(OH)CO3 precursors. The gradually changing morphologies and microstructures of cerium oxide were characterized by X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. A top-down path is illuminated to have an insight to the morphological transformation from nanorod to nanotube by adjusting the reaction time. The growth process is investigated by preparing a series of intermediate morphologies during the shape evolution of CeO2nanostructure based on the scanning electron microscopy image observation. On the basis of the time-dependent experimental observation, the possible formation mechanism related to oriented attachment and Oswald ripening was proposed, which might afford some guidance for the synthesis of other inorganic nanotubes. PMID:26151866

  4. P-Doped Porous Carbon as Metal Free Catalysts for Selective Aerobic Oxidation with an Unexpected Mechanism.

    PubMed

    Patel, Mehulkumar A; Luo, Feixiang; Khoshi, M Reza; Rabie, Emann; Zhang, Qing; Flach, Carol R; Mendelsohn, Richard; Garfunkel, Eric; Szostak, Michal; He, Huixin

    2016-02-23

    An extremely simple and rapid (seconds) approach is reported to directly synthesize gram quantities of P-doped graphitic porous carbon materials with controlled P bond configuration. For the first time, it is demonstrated that the P-doped carbon materials can be used as a selective metal free catalyst for aerobic oxidation reactions. The work function of P-doped carbon materials, its connectivity to the P bond configuration, and the correlation with its catalytic efficiency are studied and established. In direct contrast to N-doped graphene, the P-doped carbon materials with higher work function show high activity in catalytic aerobic oxidation. The selectivity trend for the electron donating and withdrawing properties of the functional groups attached to the aromatic ring of benzyl alcohols is also different from other metal free carbon based catalysts. A unique catalytic mechanism is demonstrated, which differs from both GO and N-doped graphene obtained by high temperature nitrification. The unique and unexpected catalytic pathway endows the P-doped materials with not only good catalytic efficiency but also recyclability. This, combined with a rapid, energy saving approach that permits fabrication on a large scale, suggests that the P-doped porous materials are promising materials for "green catalysis" due to their higher theoretical surface area, sustainability, environmental friendliness, and low cost. PMID:26751165

  5. Aqueous Co-precipitation of Pd-doped Cerium Oxide Nanoparticles: Chemistry Structure and Particle Growth

    SciTech Connect

    Liang H.; Zhang L.; Raitano J.M.; He G.; Akey A.J.; Herman I.P.; Chan S.-W.

    2012-01-01

    Nanoparticles of palladium-doped cerium oxide (Pd-CeO{sub 2}) have been prepared by aqueous co-precipitation resulting in a single phase cubic structure after calcination according to X-ray diffraction (XRD). Inhomogeneous strain, calculated using the Williamson-Hall method, was found to increase with palladium content, and the lattice contracts slightly, relative to nano-cerium oxide, as palladium content is increased. Moreover, high resolution transmission electron microscopy reveals some instances of defective microstructure. These factors combined imply that palladium is in solid solution with CeO{sub 2} in these nanoparticles, but palladium (II) oxide (PdO) peaks in the Raman spectra indicate that solid solution formation is partial and that highly dispersed PdO is present as well as the solid solution. Nevertheless, the addition of palladium to the CeO{sub 2} lattice inhibits the growth of the 6% Pd-CeO{sub 2} particles compared to pure CeO{sub 2} between 600 and 850 C. Activation energies for grain growth of 54 {+-} 7 and 79 {+-} 8 kJ/mol were determined for 6% Pd-CeO{sub 2} and pure CeO{sub 2}, respectively, along with pre-exponential Arrhenius factors of 10 for the doped sample and 600 for pure cerium oxide.

  6. Dysprosium-doped cadmium oxide as a gateway material for mid-infrared plasmonics

    DOE PAGESBeta

    Sachet, Edward; Shelton, Christopher T.; Harris, Joshua S.; Gaddy, Benjamin E.; Irving, Douglas L.; Curtarolo, Stefano; Donovan, Brian F.; Hopkins, Patrick E.; Sharma, Peter A.; Sharma, Ana Lima; et al

    2015-02-16

    The interest in plasmonic technologies surrounds many emergent optoelectronic applications, such as plasmon lasers, transistors, sensors and information storage. Although plasmonic materials for ultraviolet–visible and near-infrared wavelengths have been found, the mid-infrared range remains a challenge to address: few known systems can achieve subwavelength optical confinement with low loss in this range. With a combination of experiments and ab initio modelling, here we demonstrate an extreme peak of electron mobility in Dy-doped CdO that is achieved through accurate ‘defect equilibrium engineering’. In so doing, we create a tunable plasmon host that satisfies the criteria for mid-infrared spectrum plasmonics, and overcomesmore » the losses seen in conventional plasmonic materials. In particular, extrinsic doping pins the CdO Fermi level above the conduction band minimum and it increases the formation energy of native oxygen vacancies, thus reducing their populations by several orders of magnitude. The substitutional lattice strain induced by Dy doping is sufficiently small, allowing mobility values around 500 cm2 V–1 s–1 for carrier densities above 1020 cm–3. As a result, our work shows that CdO:Dy is a model system for intrinsic and extrinsic manipulation of defects affecting electrical, optical and thermal properties, that oxide conductors are ideal candidates for plasmonic devices and that the defect engineering approach for property optimization is generally applicable to other conducting metal oxides.« less

  7. Dysprosium-doped cadmium oxide as a gateway material for mid-infrared plasmonics

    NASA Astrophysics Data System (ADS)

    Sachet, Edward; Shelton, Christopher T.; Harris, Joshua S.; Gaddy, Benjamin E.; Irving, Douglas L.; Curtarolo, Stefano; Donovan, Brian F.; Hopkins, Patrick E.; Sharma, Peter A.; Sharma, Ana Lima; Ihlefeld, Jon; Franzen, Stefan; Maria, Jon-Paul

    2015-04-01

    The interest in plasmonic technologies surrounds many emergent optoelectronic applications, such as plasmon lasers, transistors, sensors and information storage. Although plasmonic materials for ultraviolet-visible and near-infrared wavelengths have been found, the mid-infrared range remains a challenge to address: few known systems can achieve subwavelength optical confinement with low loss in this range. With a combination of experiments and ab initio modelling, here we demonstrate an extreme peak of electron mobility in Dy-doped CdO that is achieved through accurate ‘defect equilibrium engineering’. In so doing, we create a tunable plasmon host that satisfies the criteria for mid-infrared spectrum plasmonics, and overcomes the losses seen in conventional plasmonic materials. In particular, extrinsic doping pins the CdO Fermi level above the conduction band minimum and it increases the formation energy of native oxygen vacancies, thus reducing their populations by several orders of magnitude. The substitutional lattice strain induced by Dy doping is sufficiently small, allowing mobility values around 500 cm2 V-1 s-1 for carrier densities above 1020 cm-3. Our work shows that CdO:Dy is a model system for intrinsic and extrinsic manipulation of defects affecting electrical, optical and thermal properties, that oxide conductors are ideal candidates for plasmonic devices and that the defect engineering approach for property optimization is generally applicable to other conducting metal oxides.

  8. Bismuth doped lanthanum ferrite perovskites as novel cathodes for intermediate-temperature solid oxide fuel cells.

    PubMed

    Li, Mei; Wang, Yao; Wang, Yunlong; Chen, Fanglin; Xia, Changrong

    2014-07-23

    Bismuth is doped to lanthanum strontium ferrite to produce ferrite-based perovskites with a composition of La(0.8-x)Bi(x)Sr0.2FeO(3-δ) (0 ≤ x ≤ 0.8) as novel cathode material for intermediate-temperature solid oxide fuel cells. The perovskite properties including oxygen nonstoichiometry coefficient (δ), average valence of Fe, sinterability, thermal expansion coefficient, electrical conductivity (σ), oxygen chemical surface exchange coefficient (K(chem)), and chemical diffusion coefficient (D(chem)) are explored as a function of bismuth content. While σ decreases with x due to the reduced Fe(4+) content, D(chem) and K(chem) increase since the oxygen vacancy concentration is increased by Bi doping. Consequently, the electrochemical performance is substantially improved and the interfacial polarization resistance is reduced from 1.0 to 0.10 Ω cm(2) at 700 °C with Bi doping. The perovskite with x = 0.4 is suggested as the most promising composition as solid oxide fuel cell cathode material since it has demonstrated high electrical conductivity and low interfacial polarization resistance. PMID:24971668

  9. Reconsidering the possibility of room temperature ferromagnetism in Mn-doped zirconium oxide

    NASA Astrophysics Data System (ADS)

    Chakraborty, Akash; Bouzerar, Georges

    2013-12-01

    The possibility to induce long-range ferromagnetic order by doping oxides with transition metal ions has become a very exciting challenge in the last decade. Theoretically, it has been claimed that Mn-doped ZrO2 could be a very promising spintronic candidate and that high critical temperatures could be already achieved even for a low Mn concentration. Some experiments have reported room temperature ferromagnetism (RT-FM) whilst some others only paramagnetism. When observed, the nature of RT-FM appears to be controversial and not clearly understood. In this study, we propose to clarify and shed light on some of theses existing issues. A detailed study of the critical temperatures and low-energy magnetic excitations in Mn-doped ZrO2 is performed. We show that the Curie temperatures were largely overestimated previously, due to the inadequate treatment of both thermal and transverse fluctuations, and disorder. It appears that the Mn-Mn couplings cannot explain the observed RT-FM. We argue, that this can be attributed to the interaction between large moments induced in the vicinity of the manganese. This is similar to the non-magnetic defect-induced ferromagnetism reported in oxides, semiconductors and graphene/graphite.

  10. Antimony-Doped Tin Oxide Thin Films Grown by Home Made Spray Pyrolysis Technique

    NASA Astrophysics Data System (ADS)

    Yusuf, Gbadebo; Babatola, Babatunde Keji; Ishola, Abdulahi Dimeji; Awodugba, Ayodeji O.; Solar cell Collaboration

    2016-03-01

    Transparent conducting antimony-doped tin oxide (ATO) films have been deposited on glass substrates by home made spray pyrolysis technique. The structural, electrical and optical properties of the ATO films have been investigated as a function of Sb-doping level and annealing temperature. The optimum target composition for high conductivity and low resistivity was found to be 20 wt. % SnSb2 + 90 wt. ATO. Under optimized deposition conditions of 450oC annealing temperature, electrical resistivity of 5.2×10-4 Ω -cm, sheet resistance of 16.4 Ω/sq, average optical transmittance of 86% in the visible range, and average optical band-gap of 3.34eV were obtained. The film deposited at lower annealing temperature shows a relatively rough, loosely bound slightly porous surface morphology while the film deposited at higher annealing temperature shows uniformly distributed grains of greater size. Keywords: Annealing, Doping, Homemade spray pyrolysis, Tin oxide, Resistivity

  11. Direct oxidation of waste vegetable oil in solid-oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhou, Z. F.; Kumar, R.; Thakur, S. T.; Rudnick, L. R.; Schobert, H.; Lvov, S. N.

    Solid-oxide fuel cells with ceria, ceria-Cu, and ceria-Rh anode were demonstrated to generate stable electric power with waste vegetable oil through direct oxidation of the fuel. The only pre-treatment to the fuel was a filtration to remove particulates. The performance of the fuel cell was stable over 100 h for the waste vegetable oil without dilution. The generated power was up to 0.25 W cm -2 for ceria-Rh fuel cell. This compares favorably with previously studied hydrocarbon fuels including jet fuels and Pennsylvania crude oil.

  12. Functionally graded composite cathodes for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Hart, N. T.; Brandon, N. P.; Day, M. J.; Lapeña-Rey, N.

    Functionally graded solid oxide fuel cell (SOFC) cathodes have been prepared from mixtures of strontium-doped lanthanum manganite (LSM) and gadolinia-doped ceria (CGO) using slurry spraying techniques. Similar samples were also prepared from mixtures of LSM and ytrria-stabilised zirconia (YSZ). A current collector comprising a mixture of LSM and strontium-doped lanthanum cobaltite (LSCO) was then applied to both cathode types. Samples were characterised using scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Characterisation using EIS techniques showed that cathodes incorporating CGO into the structure gave improved performance over those fabricated using YSZ. These performance gains were most noticeable as the temperature was decreased towards 700 °C, and were maintained during the testing of three cell membrane electrode assemblies fabricated to the Rolls-Royce design.

  13. Comparison study of electrochemical properties of porous zinc oxide/N-doped carbon and pristine zinc oxide polyhedrons

    NASA Astrophysics Data System (ADS)

    Zhou, Zhenfang; Zhang, Kun; Liu, Jinghao; Peng, Hongrui; Li, Guicun

    2015-07-01

    An in-situ calcination strategy has been developed for the synthesis of porous zinc oxide/N-doped carbon (ZnO/NC) polyhedrons, in which zeolitic imidazolate framework-8 (ZIF-8) serves as the precursor. The ZnO/NC polyhedrons with a hierarchical architecture possess a high specific surface area of 390.7 m2 g-1, high nitrogen content (19.99 at%), and robust pore structures. The porous N-doped carbon frameworks can not only increase the electronic conductivity of ZnO, but also provide interior space for the fast diffusion of Li+ ions and accommodate the volume variations during the charge and discharge cycles. When evaluated for lithium storage capacity, the hierarchical ZnO/NC polyhedrons exhibit high reversible discharge capacity (834.3 mAh g-1 at the initial low rate of 0.5C, 1C = 978 mA g-1), superior rate performance (399.2 mAh g-1 at 5C and 253.5 mAh g-1 at 10C), and excellent cycling stability (677.9 mAh g-1 at 1C after 400 cycles). The reasons are explored in terms of the well-confined primary nanocrystals (5 nm), and the finely constructed interconnected pores of the N-doped carbon networks, which facilitate the fast and effective transfer of Li+ ions and electrons, and accommodate the large volume expansions.

  14. Fluorine doped tin oxide film with high haze and transmittance prepared for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Otsuka, Rena; Endo, Takeshi; Takano, Takafumi; Takemura, Shuichiro; Murakami, Ryo; Muramoto, Ryosuke; Madarász, János; Okuya, Masayuki

    2015-08-01

    Fluorine doped tin oxide (FTO) transparent conductive oxide (TCO) film for dye-sensitized solar cell (DSSC) was investigated. Haze of the incident light through TCO film was easily tuned by controlling the surface morphology of FTO deposited on tin doped indium oxide (ITO) nano-particle seed layer pre-coated on a glass substrate, and the light harvest within the cell was effectively enhanced with high haze TCO film. The conversion efficiency of DSSC fabricated with TCO film with the haze of 30.1% reached as high as 7.7%, attributing to the consequence of the effective light harvest with the scattering within the cell.

  15. Nitrogen-doped and simultaneously reduced graphene oxide with superior dispersion as electrocatalysts for oxygen reduction reaction

    SciTech Connect

    Lee, Cheol-Ho; Yun, Jin-Mun; Lee, Sungho; Jo, Seong Mu; Yoo, Sung Jong; Cho, Eun Ae; Khil, Myung-Seob; Joh, Han-Ik

    2014-11-15

    Nitrogen doped graphene oxide (Nr-GO) with properties suitable for electrocatalysts is easily synthesized using phenylhydrazine as a reductant at relatively low temperature. The reducing agent removes various oxygen functional groups bonded to graphene oxide and simultaneously dope the nitrogen atoms bonded with phenyl group all over the basal planes and edge sites of the graphene. The Nr-GO exhibits remarkable electrocatalytic activities for oxygen reduction reaction compared to the commercial carbon black and graphene oxide due to the electronic modification of the graphene structure. In addition, Nr-GO shows excellent dispersibility in various solvent due to the dopant molecules.

  16. Communication: Towards catalytic nitric oxide reduction via oligomerization on boron doped graphene

    NASA Astrophysics Data System (ADS)

    Cantatore, Valentina; Panas, Itai

    2016-04-01

    We use density functional theory to describe a novel way for metal free catalytic reduction of nitric oxide NO utilizing boron doped graphene. The present study is based on the observation that boron doped graphene and O—N=N—O- act as Lewis acid-base pair allowing the graphene surface to act as a catalyst. The process implies electron assisted N=N bond formation prior to N—O dissociation. Two N2 + O2 product channels, one of which favoring N2O formation, are envisaged as outcome of the catalytic process. Besides, we show also that the N2 + O2 formation pathways are contrasted by a side reaction that brings to N3O3- formation and decomposition into N2O + NO2-.

  17. Sulfurization behavior of cerium doped uranium oxides by CS{sub 2}

    SciTech Connect

    Sato, Nobuaki; Kato, Shintaro; Kirishima, Akira; Tochiyama, Osamu

    2007-07-01

    For the recovery of nuclear materials from the spent nuclear fuel, the sulfide process has been proposed and the voloxidation of spent fuel and selective sulfurization rare-earth elements has been proposed. In this paper, cerium was used as a stand-in of plutonium and sulfurization behavior of cerium doped uranium dioxide by CS{sub 2} was studied. UO{sub 2} was oxidized to U{sub 3}O{sub 8} in air, while the Ce doped UO{sub 2} solid solution was formed in the presence of CeO{sub 2} by the heat treatment in air. The effect of heating time, temperature and the ratio of uranium to cerium on the formation of solid solution was analyzed. The results were also compared with those of thermodynamic consideration. (authors)

  18. Nonlinear optical properties of zinc oxide doped bismuth thin films using Z-scan technique

    NASA Astrophysics Data System (ADS)

    Abed, S.; Bouchouit, K.; Aida, M. S.; Taboukhat, S.; Sofiani, Z.; Kulyk, B.; Figa, V.

    2016-06-01

    ZnO doped Bi thin films were grown on glass substrates by spray ultrasonic technique. This paper presents the effect of Bi doping concentration on structural and nonlinear optical properties of zinc oxide thin films. These thin films were characterized by X-ray diffractometer technique. XRD analysis revealed that the ZnO:Bi thin films indicated good preferential orientation along c-axis perpendicular to the substrate. The nonlinear optical properties such as nonlinear absorption coefficient (β) and third order nonlinear susceptibility (Imχ(3)) are investigated. The calculations have been performed with a Z scan technique using Nd:YAG laser emitting 532 nm. The reverse saturable absorption (RSA) mechanism was responsible for the optical limiting effect. The results suggest that this material considered as a promising candidate for future optical device applications.

  19. Energy-band engineering for tunable memory characteristics through controlled doping of reduced graphene oxide.

    PubMed

    Han, Su-Ting; Zhou, Ye; Yang, Qing Dan; Zhou, Li; Huang, Long-Biao; Yan, Yan; Lee, Chun-Sing; Roy, Vellaisamy A L

    2014-02-25

    Tunable memory characteristics are used in multioperational mode circuits where memory cells with various functionalities are needed in one combined device. It is always a challenge to obtain control over threshold voltage for multimode operation. On this regard, we use a strategy of shifting the work function of reduced graphene oxide (rGO) in a controlled manner through doping gold chloride (AuCl3) and obtained a gradient increase of rGO work function. By inserting doped rGO as floating gate, a controlled threshold voltage (Vth) shift has been achieved in both p- and n-type low voltage flexible memory devices with large memory window (up to 4 times for p-type and 8 times for n-type memory devices) in comparison with pristine rGO floating gate memory devices. By proper energy band engineering, we demonstrated a flexible floating gate memory device with larger memory window and controlled threshold voltage shifts. PMID:24472000

  20. Dissolution and drug release profiles of phosphate glasses doped with high valency oxides.

    PubMed

    El-Meliegy, E; Farag, M M; Knowles, J C

    2016-06-01

    This paper investigates phosphate glasses incorporating vanadium and molybdenum oxides for effective management of dissolution and drug release. These glass formulations are found to reduce the rate of dissolution from the glass surfaces. The drug functional groups of vancomycin molecules loaded by immersion showed stronger hydrogen bonding with Vanadium doped glasses and consequently lower rate of drug release over 2 weeks indicating better surface attachment with the drug molecules and slow drug release profiles. This can be explained by the strong adherence of drug molecules to glass surfaces compared with the molybdenum containing glasses (PM5 and PM10). The strong attachment relates to hydrogen bonding between the amino-functional groups of vancomycin and the hydrated P-O-H groups in the glass network. In conclusion, the rate of dissolution of doped glasses and the rate of drug release can be administered to deliver the drug molecules over weeks. PMID:27117794

  1. Method of making highly porous, stable aluminum oxides doped with silicon

    DOEpatents

    Khosravi-Mardkhe, Maryam; Woodfield, Brian F.; Bartholomew, Calvin H.; Huang, Baiyu

    2016-03-22

    The present invention relates to a method for making high surface area and large pore volume thermally stable silica-doped alumina (aluminum oxide) catalyst support and ceramic materials. The ability of the silica-alumina to withstand high temperatures in presence or absence of water and prevent sintering allows it to maintain good activity over a long period of time in catalytic reactions. The method of preparing such materials includes adding organic silicon reagents to an organic aluminum salt such as an alkoxide in a controlled quantity as a doping agent in a solid state, solvent deficient reaction followed by calcination. Alternatively, the organic silicon compound may be added after calcination of the alumina, followed by another calcination step. This method is inexpensive and simple. The alumina catalyst support material prepared by the subject method maintains high pore volumes, pore diameters and surface areas at very high temperatures and in the presence of steam.

  2. Raman and Photoluminescence Spectroscopy of Er(3+) Doped Heavy Metal Oxide Glasses

    NASA Technical Reports Server (NTRS)

    Dyer, Keith; Pan, Zheng-Da; Morgan, Steve

    1997-01-01

    The potential applications of rare-earth ion doped materials include fiber lasers which can be pumped conveniently by infrared semiconductor laser diodes. The host material systems most widely studied are fluoride crystals and glasses because fluorides have low nonradiative relaxation rates due to their lower phonon energies. However, the mechanical strength, chemical durability and temperature stability of the oxide glasses are generally much better than fluoride glasses. The objective of this research was to investigate the optical and spectroscopic properties of Er(3+)-doped lead-germanate and lead-tellurium-germanate glasses. The maximum vibrational energy of lead-tellurium-germanate glasses are in the range of 740-820/cm, intermediate between those of silicate (1150/cm) and fluoride (530/cm) glasses.

  3. Permanent optical doping of amorphous metal oxide semiconductors by deep ultraviolet irradiation at room temperature

    SciTech Connect

    Seo, Hyungtak; Cho, Young-Je; Bobade, Santosh M.; Park, Kyoung-Youn; Choi, Duck-Kyun; Kim, Jinwoo; Lee, Jaegab

    2010-05-31

    We report an investigation of two photon ultraviolet (UV) irradiation induced permanent n-type doping of amorphous InGaZnO (a-IGZO) at room temperature. The photoinduced excess electrons were donated to change the Fermi-level to a conduction band edge under the UV irradiation, owing to the hole scavenging process at the oxide interface. The use of optically n-doped a-IGZO channel increased the carrier density to approx10{sup 18} cm{sup -3} from the background level of 10{sup 16} cm{sup -3}, as well as the comprehensive enhancement upon UV irradiation of a-IGZO thin film transistor parameters, such as an on-off current ratio at approx10{sup 8} and field-effect mobility at 22.7 cm{sup 2}/V s.

  4. Thermoelectric Properties of Barium Plumbate Doped by Alkaline Earth Oxides

    NASA Astrophysics Data System (ADS)

    Eufrasio, Andreza; Bhatta, Rudra; Pegg, Ian; Dutta, Biprodas

    Ceramic oxides are now being considered as a new class of thermoelectric materials because of their high stability at elevated temperatures. Such materials are especially suitable for use as prospective thermoelectric power generators because high temperatures are encountered in such operations. The present investigation uses barium plumbate (BaPbO3) as the starting material, the thermoelectric properties of which have been altered by judicious cation substitutions. BaPbO3 is known to exhibit metallic properties which may turn semiconducting as a result of compositional changes without precipitating a separate phase and/or altering the basic perovskite crystal structure. Perovskite structures are noted for their large interstitial spaces which can accommodate a large variety of ``impurity'' ions. As BaPbO3 has high electrical conductivity, σ = 2.43x105Ω-1 m-1 at room temperature, its thermopower, S, is relatively low, 23 μV/K, as expected. With a thermal conductivity, k, of 4.83Wm-1K-1, the figure of merit (ZT =S2 σ Tk-1) of BaPbO3 is only 0.01 at T = 300K. The objective of this investigation is to study the variation of thermoelectric properties of BaPbO3 as Ba and Pb ions are systematically substituted by alkaline earth ions.

  5. n-type doping of oxides by hydrogen

    NASA Astrophysics Data System (ADS)

    Kilic, Cetin; Zunger, Alex

    2002-07-01

    First-principles total-energy calculations suggest that interstitial hydrogen impurity forms a shallow donor in SnO2, CdO, and ZnO, but a deep donor in MgO. We generalize this result to other oxides by recognizing that there exist a "hydrogen pinning level" at about 3.0plus-or-minus0.4 eV below vacuum. Materials such as Ag2O, HgO, CuO, PbO, PtO, IrO2, RuO2, PbO2, TiO2, WO3, Bi2O3, Cr2O3, Fe2O3, Sb2O3, Nb2O5, Ta2O5, FeTiO3, and PbTiO3, whose conduction band minimum (CBM) lie below this level (i.e., electron affinity>3.0plus-or-minus0.4 eV) will become conductive once hydrogen is incorporated into the lattice, without reducing the host. Conversely, materials such as BaO, NiO, SrO, HfO2, and Al2O3, whose CBM lie above this level (i.e., electron affinity<3.0plus-or-minus0.4 eV) will remain nonconductive since hydrogen forms a deep impurity.

  6. Microstructure evolution of Al-doped zinc oxide and Sn-doped indium oxide deposited by radio-frequency magnetron sputtering: A comparison

    SciTech Connect

    Nie, Man; Bikowski, Andre; Ellmer, Klaus

    2015-04-21

    The microstructure and morphology evolution of Al-doped zinc oxide (AZO) and Sn-doped indium oxide (ITO) thin films on borosilicate glass substrates deposited by radio-frequency magnetron sputtering at room temperature (RT) and 300 °C were investigated by X-ray diffraction and atomic force microscopy (AFM). One-dimensional power spectral density (1DPSD) functions derived from the AFM profiles, which can be used to distinguish different growth mechanisms, were used to compare the microstructure scaling behavior of the thin films. The rms roughness R{sub q} evolves with film thickness as a power law, R{sub q} ∼ d{sub f}{sup β}, and different growth exponents β were found for AZO and ITO films. For AZO films, β of 1.47 and 0.56 are obtained for RT and 300 °C depositions, respectively, which are caused by the high compressive stress in the film at RT and relaxation of the stress at 300 °C. While for ITO films, β{sub 1} = 0.14 and β{sub 2} = 0.64 for RT, and β{sub 1} = 0.89 and β{sub 2} = 0.3 for 300 °C deposition are obtained, respectively, which is related to the strong competition between the surface diffusion and shadowing effect and/or grain growth. Electrical properties of both materials as a function of film thickness were also compared. By the modified Fuchs-Sondheimer model fitting of the electrical transport in both materials, different nucleation states are pointed out for both types of films.

  7. Microstructure evolution of Al-doped zinc oxide and Sn-doped indium oxide deposited by radio-frequency magnetron sputtering: A comparison

    NASA Astrophysics Data System (ADS)

    Nie, Man; Bikowski, Andre; Ellmer, Klaus

    2015-04-01

    The microstructure and morphology evolution of Al-doped zinc oxide (AZO) and Sn-doped indium oxide (ITO) thin films on borosilicate glass substrates deposited by radio-frequency magnetron sputtering at room temperature (RT) and 300 °C were investigated by X-ray diffraction and atomic force microscopy (AFM). One-dimensional power spectral density (1DPSD) functions derived from the AFM profiles, which can be used to distinguish different growth mechanisms, were used to compare the microstructure scaling behavior of the thin films. The rms roughness Rq evolves with film thickness as a power law, Rq ˜ dfβ, and different growth exponents β were found for AZO and ITO films. For AZO films, β of 1.47 and 0.56 are obtained for RT and 300 °C depositions, respectively, which are caused by the high compressive stress in the film at RT and relaxation of the stress at 300 °C. While for ITO films, β1 = 0.14 and β2 = 0.64 for RT, and β1 = 0.89 and β2 = 0.3 for 300 °C deposition are obtained, respectively, which is related to the strong competition between the surface diffusion and shadowing effect and/or grain growth. Electrical properties of both materials as a function of film thickness were also compared. By the modified Fuchs-Sondheimer model fitting of the electrical transport in both materials, different nucleation states are pointed out for both types of films.

  8. Charge mobility increase in indium-molybdenum oxide thin films by hydrogen doping

    NASA Astrophysics Data System (ADS)

    Catalán, S.; Álvarez-Fraga, L.; Salas, E.; Ramírez-Jiménez, R.; Rodriguez-Palomo, A.; de Andrés, A.; Prieto, C.

    2016-11-01

    The increase of charge mobility in transparent conductive indium molybdenum oxide (IMO) films is correlated with the presence of hydroxyl groups. The introduction of H2 in the chamber during sputtering deposition compensates the excess charge introduced by cationic Mo doping of indium oxide either by oxygen or hydroxyl interstitials. Films present a linear increase of carrier mobility correlated with H2 content only after vacuum annealing. This behavior is explained because vacuum annealing favors the removal of oxygen interstitials over that of hydroxyl groups. Since hydroxyl groups offer lower effective charge and smaller lattice distortions than those associated with interstitial oxygen, this compensation mechanism offers the conditions for the observed increase in mobility. Additionally, the short-range order around molybdenum is evaluated by extended X-ray absorption fine structure (EXAFS) spectroscopy, showing that Mo4+ is placed at the In site of the indium oxide.

  9. A Room Temperature Nitric Oxide Gas Sensor Based on a Copper-Ion-Doped Polyaniline/Tungsten Oxide Nanocomposite

    PubMed Central

    Wang, Shih-Han; Shen, Chi-Yen; Su, Jian-Ming; Chang, Shiang-Wen

    2015-01-01

    The parts-per-billion-level nitric oxide (NO) gas sensing capability of a copper-ion-doped polyaniline/tungsten oxide nanocomposite (Cu2+/PANI/WO3) film coated on a Rayleigh surface acoustic wave device was investigated. The sensor developed in this study was sensitive to NO gas at room temperature in dry nitrogen. The surface morphology, dopant distribution, and electric properties were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy mapping, and Hall effect measurements, respectively. The Cu2+/PANI/WO3 film exhibited high NO gas sensitivity and selectivity as well as long-term stability. At 1 ppb of NO, a signal with a frequency shift of 4.3 ppm and a signal-to-noise ratio of 17 was observed. The sensor exhibited distinct selectivity toward NO gas with no substantial response to O2, NH3 and CO2 gases. PMID:25811223

  10. Characterization of molybdenum doped indium oxide/aluminum doped zinc oxide thin film stacks for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Elamurugu, Elangovan; Flores, Raquel; Janeiro, Ricardo; Dahlem, Marcus; Viegas, Jaime

    2014-03-01

    Multilayer (ML) thin films, based on indium molybdenum oxide (IMO) and aluminum zinc oxide (AZO), having different stacking were deposited using RF sputtering at room temperature (RT). The total-layer thickness of the MLs ranges between 93 nm and 98 nm. The deposited films were characterized by their structural, electrical, microstructural, and optical properties. X-ray diffraction (XRD) peaks obtained at 2θ of around 30.6° and 34.27° are matched with cubic-In2O3 (222) and hexagonal-ZnO (002), respectively. The MLs have both nano-crystalline and polycrystalline structures depending on the layer properties. A conspicuous feature of XRD analysis is the absence of diffraction peak from 50 nm thick IMO layer when it is stacked below 50 nm thick AZO, whereas it appears significantly when the stacking is reversed to place IMO above AZO layer. Hall measurements confirmed that the deposited MLs are n- type conducting and the electrical properties are varied as a function of layer properties. The deposited MLs show high shortwavelength infrared transmittance (SWIRT) even at 3300 nm, which is ranging as high as 75 % - 90 %. Overall, the MLs show high transmittance in the entire Vis-SWIR region. The optical band gap (Eg) calculated using the absorption coefficient (α) and photon energy (hν) of the deposited MLs is ranging between 3.19 eV and 3.56 eV, depending on the layer properties. Selected as- deposited films were annealed in open air at 400 °C for 1 h; the transmittance of annealed films was improved but their electrical properties deteriorated. Atomic force microscopy (AFM) analysis shows that the root-mean-square (RMS) roughness of the MLs ranges between 0.8 nm and 1.5 nm.

  11. Design, synthesis, and characterization of materials for controlled line deposition, environmental remediation, and doping of porous manganese oxide material

    NASA Astrophysics Data System (ADS)

    Calvert, Craig A.

    This thesis covers three topics: (1) coatings formed from sol-gel phases, (2) environmental remediation, and (3) doping of a porous manganese oxide. Synthesis, characterization, and application were investigated for each topic. Line-formations were formed spontaneously by self-assembly from vanadium sol-gels and other metal containing solutions on glass substrates. The solutions were prepared by the dissolution of metal oxide or salt in water. A more straightforward method is proposed than used in previous work. Analyses using optical microscopy, atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray analysis, and infrared spectroscopy showed discreet lines whose deposition could be controlled by varying the concentration. A mechanism was developed from the observed results. Microwave heating, the addition of graphite rods, and oxidants, can enhance HCB remediation from soil. To achieve remediation, a TeflonRTM vessel open to the atmosphere along with an oxidant, potassium persulfate (PerS) or potassium hydroxide, along with uncoated or aluminum oxide coated, graphite rods were heated in a research grade microwave oven. Microwave heating was used to decrease the heating time, and graphite rods were used to increase the absorption of the microwave energy by providing thermal centers. The results showed that the percent HCB removed was increased by adding graphite rods and oxidants. Tungsten, silver, and sulfur were investigated as doping agents for K--OMS-2. The synthesis of these materials was carried out with a reflux method. The doping of K--OMS-2 led to changes in the properties of a tungsten doped K--OMS-2 had an increased resistivity, the silver doped material showed improved epoxidation of trans-stilbene, and the addition of sulfur produced a paper-like material. Rietveld refinement of the tungsten doped K--OMS-2 showed that the tungsten was doped into the framework.

  12. Mechanical properties of mesoporous ceria nanoarchitectures.

    PubMed

    Sayle, Thi X T; Inkson, Beverley J; Möbus, Günter; Parker, Stephen C; Seal, Sudipta; Sayle, Dean C

    2014-12-01

    Architectural constructs are engineered to impart desirable mechanical properties facilitating bridges spanning a thousand meters and buildings nearly 1 km in height. However, do the same 'engineering-rules' translate to the nanoscale, where the architectural features are less than 0.0001 mm in size? Here, we calculate the mechanical properties of a porous ceramic functional material, ceria, as a function of its nanoarchitecture using molecular dynamics simulation and predict its yield strength to be almost two orders of magnitude higher than the parent bulk material. In particular, we generate models of nanoporous ceria with either a hexagonal or cubic array of one-dimensional pores and simulate their responses to mechanical load. We find that the mechanical properties are critically dependent upon the orientation between the crystal structure (symmetry, direction) and the pore structure (symmetry, direction). PMID:25322448

  13. Ti-doped molybdenum-based perovskites as anodes for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    He, Beibei; Wang, Zhenbin; Zhao, Ling; Pan, Xin; Wu, Xiaojun; Xia, Changrong

    2013-11-01

    Ti doping is found to increase the stability of Sr2NiMoO6 perovskite oxides in reducing atmosphere. The composition Sr2TiNi0.5Mo0.5O6 (STNM) is further evaluated as a potential oxide anode for solid oxide fuel cells (SOFCs). Electrical conductivity, thermal expansion coefficient, surface exchange coefficient, chemical diffusion coefficient, and its electrochemical performance in single cells with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolytes are investigated. STNM exhibits a high conductivity of 17.5 S cm-1 at 800 °C at anodic atmosphere. The material shows good chemical and thermal expansion compatibilities with LSGM. To investigate the effect of Ti doping on the conduction properties, first-principle calculations are performed using the Vienna Ab initio Simulation. The strong Ti-O bond is held responsible for the enhanced structural stability of STNM under humidified H2 atmospheres, relative to that of the undoped system. The remarkable cell performance with both H2 and dry CH4 as the fuel indicates the potential ability of STNM to be used as SOFC anodes. These results obtained indicate that Sr2TiNi0.5Mo0.5O6 is a promising material for use as anode for intermediate temperature SOFCs.

  14. High Performance, Low Temperature Solution-Processed Barium and Strontium Doped Oxide Thin Film Transistors

    PubMed Central

    2013-01-01

    Amorphous mixed metal oxides are emerging as high performance semiconductors for thin film transistor (TFT) applications, with indium gallium zinc oxide, InGaZnO (IGZO), being one of the most widely studied and best performing systems. Here, we investigate alkaline earth (barium or strontium) doped InBa(Sr)ZnO as alternative, semiconducting channel layers and compare their performance of the electrical stress stability with IGZO. In films fabricated by solution-processing from metal alkoxide precursors and annealed to 450 °C we achieve high field-effect electron mobility up to 26 cm2 V–1 s–1. We show that it is possible to solution-process these materials at low process temperature (225–200 °C yielding mobilities up to 4.4 cm2 V–1 s–1) and demonstrate a facile “ink-on-demand” process for these materials which utilizes the alcoholysis reaction of alkyl metal precursors to negate the need for complex synthesis and purification protocols. Electrical bias stress measurements which can serve as a figure of merit for performance stability for a TFT device reveal Sr- and Ba-doped semiconductors to exhibit enhanced electrical stability and reduced threshold voltage shift compared to IGZO irrespective of the process temperature and preparation method. This enhancement in stability can be attributed to the higher Gibbs energy of oxidation of barium and strontium compared to gallium. PMID:24511184

  15. PEGylated silver doped zinc oxide nanoparticles as novel photosensitizers for photodynamic therapy against Leishmania.

    PubMed

    Nadhman, Akhtar; Nazir, Samina; Khan, Malik Ihsanullah; Arooj, Syeda; Bakhtiar, Muhammad; Shahnaz, Gul; Yasinzai, Masoom

    2014-12-01

    We describe daylight responsive silver (Ag) doped semiconductor nanoparticles of zinc oxide (DSNs) for photodynamic therapy (PDT) against Leishmania. The developed materials were characterized by X-ray diffraction analysis (XRD), Rutherford backscattering (RBS), diffused reflectance spectroscopy (DRS), and band-gap analysis. The Ag doped semiconductor nanoparticles of zinc oxide were PEGylated to enhance their biocompatibility. The DSNs demonstrated effective daylight response in the PDT of Leishmania protozoans, through the generation of reactive oxygen species (ROS) with a quantum yield of 0.13 by nondoped zinc oxide nanoparticles (NDSN) whereas 0.28 by DSNs. None of the nanoparticles have shown any antileishmanial activity in dark, confirming that only ROS produced in the daylight were involved in the killing of leishmanial cells. Furthermore, the synthesized nanoparticles were found biocompatible. Using reactive oxygen species scavengers, cell death was attributable mainly to 77-83% singlet oxygen and 18-27% hydroxyl radical. The nanoparticles caused permeability of the cell membrane, leading to the death of parasites. Further, the uptake of nanoparticles by Leishmania cells was confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). We believe that these DSNs are widely applicable for the PDT of leishmaniasis, cancers, and other infections due to daylight response. PMID:25266330

  16. High Performance, Low Temperature Solution-Processed Barium and Strontium Doped Oxide Thin Film Transistors.

    PubMed

    Banger, Kulbinder K; Peterson, Rebecca L; Mori, Kiyotaka; Yamashita, Yoshihisa; Leedham, Timothy; Sirringhaus, Henning

    2014-01-28

    Amorphous mixed metal oxides are emerging as high performance semiconductors for thin film transistor (TFT) applications, with indium gallium zinc oxide, InGaZnO (IGZO), being one of the most widely studied and best performing systems. Here, we investigate alkaline earth (barium or strontium) doped InBa(Sr)ZnO as alternative, semiconducting channel layers and compare their performance of the electrical stress stability with IGZO. In films fabricated by solution-processing from metal alkoxide precursors and annealed to 450 °C we achieve high field-effect electron mobility up to 26 cm(2) V(-1) s(-1). We show that it is possible to solution-process these materials at low process temperature (225-200 °C yielding mobilities up to 4.4 cm(2) V(-1) s(-1)) and demonstrate a facile "ink-on-demand" process for these materials which utilizes the alcoholysis reaction of alkyl metal precursors to negate the need for complex synthesis and purification protocols. Electrical bias stress measurements which can serve as a figure of merit for performance stability for a TFT device reveal Sr- and Ba-doped semiconductors to exhibit enhanced electrical stability and reduced threshold voltage shift compared to IGZO irrespective of the process temperature and preparation method. This enhancement in stability can be attributed to the higher Gibbs energy of oxidation of barium and strontium compared to gallium. PMID:24511184

  17. Polaronic contributions to oxidation and hole conductivity in acceptor-doped BaZrO3

    NASA Astrophysics Data System (ADS)

    Lindman, Anders; Erhart, Paul; Wahnström, Göran

    2016-08-01

    Acceptor-doped perovskite oxides like BaZrO3 are showing great potential as materials for renewable energy technologies where hydrogen acts an energy carrier, such as solid oxide fuel cells and hydrogen separation membranes. While ionic transport in these materials has been investigated intensively, the electronic counterpart has received much less attention and further exploration in this field is required. Here, we use density functional theory (DFT) to study hole polarons and their impact on hole conductivity in Y-doped BaZrO3. Three different approaches have been used to remedy the self-interaction error of local and semilocal exchange-correlation functionals: DFT +U , pSIC-DFT, and hybrid functionals. Self-trapped holes are found to be energetically favorable by about -0.1 eV and the presence of yttrium results in further stabilization. Polaron migration is predicted to occur through intraoctahedral transfer and polaron rotational processes, which are associated with adiabatic barriers of about 0.1 eV. However, the rather small energies associated with polaron formation and migration suggest that the hole becomes delocalized and bandlike at elevated temperatures. These results together with an endothermic oxidation reaction [A. Lindman, P. Erhart, and G. Wahnström, Phys. Rev. B 91, 245114 (2015), 10.1103/PhysRevB.91.245114] yield a picture that is consistent with experimental data for the hole conductivity. The results we present here provide new insight into hole transport in acceptor-doped BaZrO3 and similar materials, which will be of value in the future development of sustainable technologies.

  18. Ultrasonic-assisted degradation of phenazopyridine with a combination of Sm-doped ZnO nanoparticles and inorganic oxidants.

    PubMed

    Eskandarloo, Hamed; Badiei, Alireza; Behnajady, Mohammad A; Ziarani, Ghodsi Mohammadi

    2016-01-01

    Pure and samarium doped ZnO nanoparticles were synthesized by a sonochemical method and characterized by TEM, SEM, EDX, XRD, Pl, and DRS techniques. The average crystallite size of pure and Sm-doped ZnO nanoparticles was about 20 nm. The sonocatalytic activity of pure and Sm-doped ZnO nanoparticles was considered toward degradation of phenazopyridine as a model organic contaminant. The Sm-doped ZnO nanoparticles with Sm concentration of 0.4 mol% indicated a higher sonocatalytic activity (59%) than the pure ZnO (51%) and other Sm-doped ZnO nanoparticles. It was believed that Sm(3+) ion with optimal concentration (0.4 mol%) can act as superficial trapping for electrons in the conduction band of ZnO and delayed the recombination of charge carriers. The influence of the nature and concentration of various oxidants, including periodate, hydrogen peroxide, peroxymonosulfate, and peroxydisulfate on the sonocatalytic activity of Sm-doped ZnO nanoparticles was studied. The influence of the oxidants concentration (0.2-1.4 g L(-1)) on the degradation rate was established by the 3D response surface and the 2D contour plots. The results demonstrated that the utilizing of oxidants in combination with Sm-doped ZnO resulting in rapid removal of contaminant, which can be referable to a dual role of oxidants; (i) scavenging the generated electrons in the conduction band of ZnO and (ii) creating highly reactive radical species under ultrasonic irradiation. It was found that the Sm-doped ZnO and periodate combination is the most efficient catalytic system under ultrasonic irradiation. PMID:26384896

  19. Thermodynamic Analysis of Isothermal Redox Cycling of Ceria for Solar Fuel Production

    SciTech Connect

    Bader, R; Venstrom, LJ; Davidson, JH; Lipinski, W

    2013-09-01

    A thermodynamic analysis of continuous fuel production by redox cycling of ceria in a single solar reactor under isothermal conditions is presented. Ceria is partially reduced in a sweep gas flow of purified nitrogen and reoxidized with either steam or carbon dioxide to produce hydrogen or carbon monoxide, respectively. The sweep gas and oxidizer flows are preheated by the product gases. The influence of selected process parameters, including operating temperature, pressure, and the effectiveness of heat recovery, on the solar-to-fuel conversion efficiency is determined. For a solar concentration ratio of 3000, typical of state-of-the-art solar dish concentrators, and operating temperature of 1773 K, 95.5% of the available gas-phase heat must be recovered to reach conversion efficiencies of 10% and 18% for hydrogen and carbon monoxide production, respectively, assuming the flow rate of inert sweep gas is equivalent to that in a counter-current flow arrangement of gas and ceria. The efficiency depends strongly on the gas-phase heat recovery effectiveness and the sweep gas flow rate. Introducing a temperature swing of 150 K between reduction and oxidation steps strongly reduces the sweep gas flow rate and increases the efficiency from 10% to 31.6% for hydrogen production.

  20. CO2 methanation over Ni-Ceria-Zirconia catalysts: effect of preparation and operating conditions

    NASA Astrophysics Data System (ADS)

    Ocampo, F.; Louis, B.; Kiennemann, A.; Roger, A. C.

    2011-03-01

    Ni-Ceria-Zirconia materials with various Ceria/Zirconia ratios were prepared by sol-gel and impregnation methods and were subsequently characterized by means of XRD, BET, TPR and TPO. Their catalytic activity and stability were evaluated in the CO2 methanation reaction. The main parameters which seem to monitor catalytic performance are the capacity of Ni2+ cations to incorporate into the mixed oxide structure and the obtained ratio between incorporated Ni2+ and surface Ni0 species. Catalysts prepared by sol-gel thus exhibited higher methane yield and an improved resistance to deactivation when compared to those obtained by impregnation. The process viability was then investigated in potential industrial conditions. Operating under moderate pressure was beneficial to catalytic activity, whereas working under sub-stoichiometric H2 resulted in a loss of both activity and stability. Even though metal sintering and carbon deposits are believed to cause deactivation, nickel partial reoxidation and site blocking have to be considered.

  1. Dehydrogenation of methanol to formaldehyde catalyzed by pristine and defective ceria surfaces.

    PubMed

    Beste, Ariana; Overbury, Steven H

    2016-04-21

    We have explored the dehydrogenation of methoxy on pristine and defective (111), (100), and (110) ceria surfaces with density functional methods. Methanol conversion is used as a probe reaction to understand structure sensitivity of the oxide catalysis. Differences in reaction selectivity have been observed experimentally as a function of crystallographically exposed faces and degree of reduction. We find that the barrier for carbon-hydrogen cleavage in methoxy is similar for the pristine and defective (111), (100), and (110) surfaces. However, there are large differences in the stability of the surface intermediates on the different surfaces. The variations in experimentally observed product selectivities are a consequence of the interplay between barrier controlled bond cleavage and desorption processes. Subtle differences in activation energies for carbon-hydrogen cleavage on the different crystallographic faces of ceria could not be correlated with structural or electronic descriptors. PMID:27005883

  2. Dehydrogenation of methanol to formaldehyde catalyzed by pristine and defective ceria surfaces

    DOE PAGESBeta

    Beste, Ariana; Overbury, Steven H.

    2016-03-09

    We have explored the dehydrogenation of methoxy on pristine and defective (111), (100), and (110) ceria surfaces with density functional methods. Methanol conversion is used as a probe reaction to understand structure sensitivity of the oxide catalysis. Differences in reaction selectivity have been observed experimentally as a function of crystallographically exposed faces and degree of reduction. We find that the barrier for carbon-hydrogen cleavage in methoxy is similar for the pristine and defective (111), (100), and (110) surfaces. However, there are large differences in the stability of the surface intermediates on the different surfaces. The variations in experimentally observed productmore » selectivities are a consequence of the interplay between barrier controlled bond cleavage and desorption processes. Ultimately, subtle differences in activation energies for carbon-hydrogen cleavage on the different crystallographic faces of ceria could not be correlated with structural or electronic descriptors.« less

  3. Gd-Doped BaSnO3 Thin Films: High Mobility in a Magnetically-Doped Transparent Conducting Oxide

    NASA Astrophysics Data System (ADS)

    Alaan, Urusa; Shafer, Padraic; N'diaye, Alpha; Arenholz, Elke; Suzuki, Yuri

    It has recently been shown that when the perovskite-structure BaSnO3 (BSO) is doped with LaBa', the result is a transparent conducting oxide with room-temperature electron mobilities that are much higher than conventional ternary oxides. The ability to achieve high carrier mobilities in BSO is promising for future perovskite-structure devices. We have used pulsed laser deposition to grow epitaxial thin films of Ba0.96Gd0.04SnO3 (Gd:BSO) and Ba0.96La0.04SnO3 (La:BSO) on (001) SrTiO3 and (001) MgO substrates. At 300 K, Gd:BSO films have ρ ~2 m Ω .cm, μe ~28 cm2/V .s and n ~1.0 × 1020cm-3. At the same temperature, La:BSO films have ρ ~0.4 m Ω .cm, μe ~58 cm2/V .s and n ~2.5 × 1020 cm-3. While La:BSO is diamagnetic, Gd:BSO is paramagnetic with a clear magnetic response that saturates at ~7 μB/Gd3+, and a negative ordinary magnetoresistance at low temperatures. Like La:BSO, Gd:BSO is transparent and colorless in the visible regime. Thus, we have shown that Gd is good dopant for BSO in order to achieve transparency and metallicity that is coincident with a magnetic response. We acknowledge support from the Army Research Office under Grant # W911NF-14-1-0611, the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and the National Science Foundation Graduate Research Fellowship Program.

  4. The effect and mechanism of bismuth doped lead oxide on the performance of lead-acid batteries

    NASA Astrophysics Data System (ADS)

    Chen, H. Y.; Wu, L.; Ren, C.; Luo, Q. Z.; Xie, Z. H.; Jiang, X.; Zhu, S. P.; Xia, Y. K.; Luo, Y. R.

    Flooded automotive and motorcycle lead-acid batteries were manufactured from three kinds of lead oxides including electrolyzed pure lead (99.99 wt.% Pb) oxide, electrolyzed pure lead oxide doped with Bi 2O 3 (0.02 wt.% Bi 2O 3) and bismuth-bearing refined lead (0.02 wt.% Bi) oxide. The first cranking and cold cranking curves of the automotive batteries show that there is no obvious difference among the above lead oxides. Bismuth in lead oxide does not affect the water loss of flooded batteries. However, bismuth results in the improvement of capacity and charge-acceptance capability. In discharge, the positive voltage versus cadmium of plates with bismuth decreases more slowly than that of plates without bismuth. In order to investigate the mechanism of the function of bismuth, three other kinds of test electrodes were prepared from electrolyzed pure lead (99.99 wt.% Pb) oxide, electrolyzed pure lead oxide doped 0.02 wt.% Bi 2O 3 and electrolyzed pure lead oxide doped 0.06 wt.% Bi 2O 3. The cyclic voltammetry curve shows that bismuth has no significant influence on the electrochemical behavior of the positive active-material. There is an opposite result concerning the cathodic polarization curves between bismuth doped in the electrode and Bi 3+ ion doped in the electrolyte. Bismuth doped in the electrode results in a decrease of the hydrogen overpotential. Conversely, Bi 3+ ion doped in the electrolyte results is an increase. The chemical analysis confirms that a trace of Bi 3+ ion exists in sulfuric acid solution (e.g. plates soaking, after formation, after cycling). A higher porosity is observed in the positive active-material containing bismuth by SEM technique. SEM morphology shows that needle-like crystals begin to occur after a few cycles. X-ray diffraction phase analysis proves that the amount of α-PbO 2 is increased by doping bismuth in to lead oxide. The existing forms, chemical characteristics and electrochemical reactions of bismuth during manufacture

  5. CRYSTALLINE CHROMIUM DOPED ALUMINUM OXIDE (RUBY) USE AS A LUMINESCENT SCREEN FOR PROTON BEAMS.

    SciTech Connect

    BROWN,K.A.; GASSNER,D.M.

    1999-03-29

    In our search for a better luminescent screen material, we tested pieces of mono-crystalline chromium doped aluminum oxide (more commonly known as a ruby) using a 24 GeV proton beam. Due to the large variations in beam intensity and species which are run at the Alternating Gradient Synchrotron (AGS), we hope to find a material which can sufficiently luminesce, is compatible in vacuum, and maintain its performance level over extended use. Results from frame grabbed video camera images using a variety of neutral density filters are presented.

  6. Growth of yttria-doped zirconium oxide nitride single crystals by means of reactive skull melting

    NASA Astrophysics Data System (ADS)

    Berendts, Stefan; Lerch, Martin

    2011-12-01

    Reactive skull melting, a method developed for this work and herein presented, combines crystal growth of zirconia-based materials and their direct nitridation in one step. The nitrogen content of nitrided YSZ single crystals strongly depends on the nitrogen solubility in the melt. Stabilization of the tetragonal or cubic phase is mainly determined by the yttria dopant concentration, the amount of incorporated nitrogen, and reduction caused by the low oxygen activity and hydrogen in the gas atmosphere. Yttria-doped zirconium oxide nitride single crystals with a maximum nitrogen content of 0.58(3) wt% and 4 mol% yttria were obtained by this method.

  7. Large-Scale Synthesis of Tin-Doped Indium Oxide Nanofibers Using Water as Solvent

    NASA Astrophysics Data System (ADS)

    Altecor, Aleksey; Mao, Yuanbing; Lozano, Karen

    2012-09-01

    Here we report the successful fabrication of tin-doped indium oxide (ITO) nanofibers using a scalable Forcespinning™ method. In this environmentally-friendly process, water was used as the only solvent for both Polyvinylpyrrolidone (PVP, the sacrificial polymer) and the metal chloride precursor salts. The obtained precursor nanofiber mats were calcinated at temperatures ranging from 500-800°C to produce ITO nanofibers with diameters as small as 400 nm. The developed ITO nanofibers were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction analysis.

  8. Tribological properties of nanolamellar tungsten disulfide doped with zinc oxide nanoparticles.

    PubMed

    An, V; Irtegov, Y; Anisimov, E; Druzyanova, V; Burtsev, N; Khaskelberg, M

    2015-01-01

    Tribological properties of nanolamellar tungsten disulfide doped with zinc oxide nanoparticles were studied. Nanolamellar tungsten disulfide and ZnO nanoparticles produced by electrospark erosion of metal granules in an H2O2 solution were analyzed using the XRD, SEM and TEM techniques. According to the tribological measurements, ZnO nanoparticles did not significantly change the friction coefficient of nanolamellar WS2 at 25 °C in air, whereas they positively impact on wear resistance of nanolamellar WS2 at 400 °C. PMID:26558176

  9. Localized electropolymerization on oxidized boron-doped diamond electrodes modified with pyrrolyl units.

    PubMed

    Actis, Paolo; Manesse, Mael; Nunes-Kirchner, Carolina; Wittstock, Gunther; Coffinier, Yannick; Boukherroub, Rabah; Szunerits, Sabine

    2006-11-14

    This paper describes the functionalization of oxidized boron-doped diamond (BDD) electrodes with N-(3-trimethoxysilylpropyl)pyrrole (TMPP) and the influence of this layer on the electrochemical transfer kinetics as well as on the possibility of forming strongly adhesive polypyrrole films on the BDD interface through electropolymerization. Furthermore, localized polymer formation was achieved on the TMPP-modified BDD interface using the direct mode of a scanning electrochemical microscope (SECM) as well as an electrochemical scanning near-field optical microscope (E-SNOM). Depending on the method used polypyrrole dots with diameters in the range of 1-250 microm are electrogenerated. PMID:17066183

  10. Novel antimony doped tin oxide/carbon aerogel as efficient electrocatalytic filtration membrane

    NASA Astrophysics Data System (ADS)

    Liu, Zhimeng; Zhu, Mengfu; Wang, Zheng; Wang, Hong; Deng, Cheng; Li, Kui

    2016-05-01

    A facile method was developed to prepare antimony doped tin oxide (Sb-SnO2)/carbon aerogel (CA) for use as an electrocatalytic filtration membrane. The preparation process included synthesis of a precursor sol, impregnation, and thermal decomposition. The Sb-SnO2, which was tetragonal in phase with an average crystallite size of 10.8 nm, was uniformly distributed on the CA surface and firmly attached via carbon-oxygen-tin chemical bonds. Preliminary filtration tests indicated that the Sb-SnO2/CA membrane had a high rate of total organic carbon removal for aqueous tetracycline owing to its high current efficiency and electrode stability.

  11. Cerium-modified doped strontium titanate compositions for solid oxide fuel cell anodes and electrodes for other electrochemical devices

    DOEpatents

    Marina, Olga A [Richland, WA; Stevenson, Jeffry W [Richland, WA

    2010-03-02

    The present invention provides novel compositions that find advantageous use in making electrodes for electrochemical cells and electrochemical devices such as solid oxide fuel cells, electrolyzers, sensors, pumps and the like, the compositions comprising cerium-modified doped strontium titanate. The invention also provides novel methods for making and using anode material compositions and solid oxide fuel cells and solid oxide fuel cell assemblies having anodes comprising the compositions.

  12. Cerium-modified doped strontium titanate compositions for solid oxide fuel cell anodes and electrodes for other electrochemical devices

    DOEpatents

    Marina, Olga A [Richland, WA; Stevenson, Jeffry W [Richland, WA

    2010-11-23

    The present invention provides novel compositions that find advantageous use in making electrodes for electrochemical cells and electrochemical devices such as solid oxide fuel cells, electrolyzers, sensors, pumps and the like, the compositions comprising cerium-modified doped strontium titanate. The invention also provides novel methods for making and using anode material compositions and solid oxide fuel cells and solid oxide fuel cell assemblies having anodes comprising the compositions.

  13. Effect of S-doping on structural, optical and electrochemical properties of vanadium oxide thin films prepared by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Mousavi, M.; Kompany, A.; Shahtahmasebi, N.; Bagheri-Mohagheghi, M.-M.

    2013-12-01

    In this research, S-doped vanadium oxide thin films, with doping levels from 0 to 40 at.%, are prepared by spray pyrolysis technique on glass substrates. For electrochemical measurements, the films were deposited on florin-tin oxide coated glass substrates. The effect of S-doping on structural, electrical, optical and electrochemical properties of vanadium oxide thin films was studied. The x-ray diffractometer analysis indicated that most of the samples have cubic β-V2O5 phase structure with preferred orientation along [200]. With increase in the doping levels, the structure of the samples tends to be amorphous. The scanning electron microscopy images show that the structure of the samples is nanobelt-shaped and the width of the nanobelts decreases from nearly 100 to 40 nm with increase in the S concentration. With increase in the S-doping level, the sheet resistance and the optical band gap increase from 940 to 4015 kΩ/square and 2.41 to 2.7 eV, respectively. The cyclic voltammogram results obtained for different samples show that the undoped sample is expanded and the sample prepared at 20 at.% S-doping level has sharper anodic and cathodic peaks.

  14. Effect of nitrogen doping on structural, morphological, optical and electrical properties of radio frequency magnetron sputtered zinc oxide thin films

    NASA Astrophysics Data System (ADS)

    Perumal, R.; Hassan, Z.

    2016-06-01

    Zinc oxide receives remarkable attention due to its several attractive physical properties. Zinc oxide thin films doped with nitrogen were grown by employing RF magnetron sputtering method at room temperature. Doping was accomplished in gaseous medium by mixing high purity nitrogen gas along with argon sputtering gas. Structural studies confirmed the high crystalline nature with c-axis oriented growth of the nitrogen doped zinc oxide thin films. The tensile strain was developed due to the incorporation of the nitrogen into the ZnO crystal lattice. Surface roughness of the grown films was found to be decreased with increasing doping level was identified through atomic force microscope analysis. The presenting phonon modes of each film were confirmed through FTIR spectral analysis. The increasing doping level leads towards red-shifting of the cut-off wavelength due to decrement of the band gap was identified through UV-vis spectroscopy. All the doped films exhibited p-type conductivity was ascertained using Hall measurements and the obtained results were presented.

  15. Chitosan as template for the synthesis of ceria nanoparticles

    SciTech Connect

    Sifontes, A.B.; Gonzalez, G.; Ochoa, J.L.; Tovar, L.M.; Zoltan, T.; Canizales, E.

    2011-11-15

    Graphical abstract: Cerium oxide nanoparticles with cubic fluorite structure were prepared using chitosan as template, cerium nitrate as a starting material and sodium hydroxide as a precipitating agent. Calcinated powders at 350 {sup o}C contain agglomerated particles with average particle size of {approx}4 nm, very high porosity and foam-like morphology formed by open and close pores. Highlights: {yields} Pure CeO{sub 2} nanoparticles can take place using chitosan as template. {yields} A porous material was obtained. {yields} Blueshifts in the ultraviolet absorption spectra have been observed in cerium oxide nanocrystallites. -- Abstract: Cerium oxide (CeO{sub 2}), nanoparticles were prepared using chitosan as template, cerium nitrate as a starting material and sodium hydroxide as a precipitating agent. The resultant ceria-chitosan spheres were calcined at 350 {sup o}C. The synthesized powders were characterized by, XRD, HRTEM, UV-vis, FTIR, and TG-DTA. The average size of the nanoparticles obtained was {approx}4 nm and BET specific surface area {approx}105 m{sup 2} g{sup -1}. Blueshifts in the ultraviolet absorption spectra have been observed in cerium oxide nanocrystallites. The band-gap was found to be 4.5 eV. The blueshifts are well explained for diameters down to less than a few nanometers by the change in the electronic band structure.

  16. Composite Cathode for High-Power Density Solid Oxide Fuel Cells

    SciTech Connect

    Ilwon Kim; Scott Barnett; Yi Jiang; Manoj Pillai; Nikkia McDonald; Dan Gostovic; Zhongryang Zhan; Jiang Liu

    2004-01-31

    Reduction of solid oxide fuel cell (SOFC) operating temperature will play a key role in reducing the stack cost by allowing the use of low-cost metallic interconnects and new approaches to sealing, while making applications such as transportation more feasible. Reported results for anode-supported SOFCs show that cathode polarization resistance is the primary barrier to achieving high power densities at operating temperatures of 700 C and lower. This project aims to identify and develop composite cathodes that could reduce SOFC operating temperatures below 700 C. This effort focuses on study and use of (La,Sr)(Co,Fe)O{sub 3} (LSCF) based composite cathodes, which have arguably the best potential to substantially improve on the currently-used, (La,Sr)MnO{sub 3}-Yttria-stabilized Zirconia. During this Phase I, it was successfully demonstrated that high performances can be achieved with LSCF/Gadolinium-Doped Ceria composite cathodes on Ni-based anode supported cells operating at 700 C or lower. We studied electrochemical reactions at LSCF/Yttria-stabilized Zirconia (YSZ) interfaces, and observed chemical reactions between LSCF and YSZ. By using ceria electrolytes or YSZ electrolytes with ceria diffusion barrier layers, the chemical reactions between LSCF and electrolytes were prevented under cathode firing conditions necessary for the optimal adhesion of the cathodes. The protection provided by ceria layer is expected to be adequate for stable long-term cathode performances, but more testing is needed to verify this. Using ceria-based barrier layers, high performance Ni-YSZ anode supported cells have been demonstrated with maximum power densities of 0.8W/cm2 at 700 C and 1.6W/cm{sup 2} at 800 C. Ni-SDC anode supported cells with SDC electrolytes yielded >1W/cm{sup 2} at 600 C. We speculate that the power output of Ni-YSZ anode supported cell at 700 C and lower, was limited by the quality of the Ceria and Ceria YSZ interface. Improvements in the low

  17. Effects of Titanium Doping Concentration on the Structural and Electrical Properties of Sputtered Indium Oxide Films.

    PubMed

    Ok, Jung-Woo; Oh, Hyung-Seok; Kwak, Dong-Joo; Sung, Youl-Moon; Kim, Sang-Heum

    2015-02-01

    The surface structure and electrical properties of titanium-doped indium oxide (ITiO) films prepared by RF magnetron sputtering were investigated. The doping concentration of TiO2 in the In2O3 target was changed from 1.0 wt.% to 10.0 wt.% with increments of 1.0 wt.%. At a Ti content of 5.0 wt.%, the optimum growth conditions were achieved. The finest value of hall mobility, carrier concentration, and resistivity of the deposited film reached 47.03 cm2Ns, 1.148 x 10(21) cm-3 and 1.14 x 10(-4) Ωcm, respectively. Then the transmittance was achieved up to 82% at 570 nm. The peaks of the XRD spectra became more intense and sharp as the Ti concentration increased up to 2.5 wt.% but a higher Ti content of 10.0 wt.% retarded a growth of In2O3 grains. The surface roughness of the films by examination of surface morphology using AFM also rose with increase of Ti doping concentration. PMID:26353685

  18. Paramagnetic dysprosium-doped zinc oxide thin films grown by pulsed-laser deposition

    SciTech Connect

    Lo, Fang-Yuh Ting, Yi-Chieh; Chou, Kai-Chieh; Hsieh, Tsung-Chun; Ye, Cin-Wei; Hsu, Yung-Yuan; Liu, Hsiang-Lin; Chern, Ming-Yau

    2015-06-07

    Dysprosium(Dy)-doped zinc oxide (Dy:ZnO) thin films were fabricated on c-oriented sapphire substrate by pulsed-laser deposition with doping concentration ranging from 1 to 10 at. %. X-ray diffraction (XRD), Raman-scattering, optical transmission spectroscopy, and spectroscopic ellipsometry revealed incorporation of Dy into ZnO host matrix without secondary phase. Solubility limit of Dy in ZnO under our deposition condition was between 5 and 10 at. % according to XRD and Raman-scattering characteristics. Optical transmission spectroscopy and spectroscopic ellipsometry also showed increase in both transmittance in ultraviolet regime and band gap of Dy:ZnO with increasing Dy density. Zinc vacancies and zinc interstitials were identified by photoluminescence spectroscopy as the defects accompanied with Dy incorporation. Magnetic investigations with a superconducting quantum interference device showed paramagnetism without long-range order for all Dy:ZnO thin films, and a hint of antiferromagnetic alignment of Dy impurities was observed at highest doping concentration—indicating the overall contribution of zinc vacancies and zinc interstitials to magnetic interaction was either neutral or toward antiferromagnetic. From our investigations, Dy:ZnO thin films could be useful for spin alignment and magneto-optical applications.

  19. Structural studies of lithium boro tellurite glasses doped with praseodymium and samarium oxides

    SciTech Connect

    Damas, Pedro; Coelho, João; Hungerford, Graham; Hussain, N. Sooraj

    2012-11-15

    Graphical abstract: [TeO{sub 4}] trigonal bipyramid structural unit, which is formed by two unequivalent pair of oxygen atoms: two equatorial oxygens (O{sub eq}) and two axial oxygens (O{sub ax}). Highlights: ► Pr{sup 3+} and Sm{sup 3+} doped LBT glasses have been prepared and characterized. ► LBT glasses present normal surfaces without metallic clusters. ► Raman spectra revealed the network modifying behaviour of dopant ions. -- Abstract: This paper reports the preparation and structural studies of praseodymium and samarium (0.5, 2 and 4 mol%) oxide doped lithium boro tellurite glasses. These materials were prepared by the quenching technique in a ceramic crucible at 950 °C. Structural characterization was performed by Raman spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-ray spectroscopy techniques. Results from Raman analysis are in good agreement with those reported in the literature, revealing a normal glass structure for the host material. Understanding on how the glasses internal structure changed when the doping concentration increases was also assessed.

  20. Gallium-doped indium oxide nanoleaves: Structural characterization, growth mechanism and optical properties

    NASA Astrophysics Data System (ADS)

    Liu, Lizhu; Chen, Yiqing; Guo, Linliang; Guo, Taibo; Zhu, Yunqing; Su, Yong; Jia, Chong; Wei, Meiqin; Cheng, Yinfen

    2011-11-01

    The novel two-dimensional (2-D) Ga-doped In2O3 nanoleaves are synthesized by a simple one-step carbonthermal evaporation method using Cu-Sn alloy as the substrates. Two basic parts construct this leaf-like nanostructure: a long central trunk and two tapered nanoribbons in symmetric distribution in relation to the trunk. The Ga-In-O alloy particles are located at or close to the tips of the central trunks and serve as catalysts for the central trunk growth by the self-catalytic vapor-liquid-solid (VLS) mechanism. And the homoepitaxial growth of tapered nanoribbon on the surface of the central trunk can be explained by vapor-solid (VS) mechanism. The room-temperature photoluminescence (PL) measurement of this nanoscaled Ga-doped In2O3 transparent conducting oxide (TCO) detected two blue peaks located at 432 nm and 481 nm, respectively, which can be used by Ru-based dye and indicates potential application in dye-sensitized solar cells (DSSCs). The successful preparation of this novel 2-D Ga-doped In2O3 nanoleaves not only enriches the synthesis of TCO materials, but also provides new blocks in future architecture of functional nano-devices.

  1. Application of N-Doped Three-Dimensional Reduced Graphene Oxide Aerogel to Thin Film Loudspeaker.

    PubMed

    Kim, Choong Sun; Lee, Kyung Eun; Lee, Jung-Min; Kim, Sang Ouk; Cho, Byung Jin; Choi, Jung-Woo

    2016-08-31

    We built a thermoacoustic loudspeaker employing N-doped three-dimensional reduced graphene oxide aerogel (N-rGOA) based on a simple template-free fabrication method. A two-step fabrication process, which includes freeze-drying and reduction/doping, was used to realize a three-dimensional, freestanding, and porous graphene-based loudspeaker, whose macroscopic structure can be easily modulated. The simplified fabrication process also allows the control of structural properties of the N-rGOAs, including density and area. Taking advantage of the facile fabrication process, we fabricated and analyzed thermoacoustic loudspeakers with different structural properties. The anlayses showed that a N-rGOA with lower density and larger area can produce a higher sound pressure level (SPL). Furthermore, the resistance of the proposed loudspeaker can be easily controlled through heteroatom doping, thereby helping to generate higher SPL per unit driving voltage. Our success in constructing an array of optimized N-rGOAs able to withstand input power as high as 40 W demonstrates that a practical thermoacoustic loudspeaker can be fabricated using the proposed mass-producible solution-based process. PMID:27532328

  2. Mid- to long-wavelength infrared surface plasmon properties in doped zinc oxides

    NASA Astrophysics Data System (ADS)

    Cleary, Justin W.; Snure, Michael; Leedy, Kevin D.; Look, David C.; Eyink, Kurt; Tiwari, Ashutosh

    2012-09-01

    This work investigates properties of surface plasmons on doped metal oxides in the 2-20 μm wavelength regime. By varying the stoichiometry in pulse laser deposited Ga and Al doped ZnO, the plasmonic properties can be controlled via a fluctuating free carrier concentration. This deterministic approach may enable one to develop the most appropriate stoichometry of ZnAlO and ZnGaO in regards to specific plasmonic applications for particular IR wavelengths. Presented are theoretical and experimental investigations pertaining to ZnAlO and ZnGaO as surface plasmon host materials. Samples are fabricated via pulsed laser deposition and characterized by infrared ellipsometry and Hall-effect measurements. Complex permittivity spectra are presented, as well as plasmon properties such as the field propagation lengths and penetration depths, in the infrared range of interest. Drude considerations are utilized to determine how the optical properties may change with doping. Finite element simulations verify these plasmonic properties. These materials not only offer potential use as IR plasmon hosts for sensor applications, but also offer new integrated device possibilities due to stoichiometric control of electrical and optical properties.

  3. Manganese doped-iron oxide nanoparticle clusters and their potential as agents for magnetic resonance imaging and hyperthermia.

    PubMed

    Casula, Maria F; Conca, Erika; Bakaimi, Ioanna; Sathya, Ayyappan; Materia, Maria Elena; Casu, Alberto; Falqui, Andrea; Sogne, Elisa; Pellegrino, Teresa; Kanaras, Antonios G

    2016-06-22

    A simple, one pot method to synthesize water-dispersible Mn doped iron oxide colloidal clusters constructed of nanoparticles arranged into secondary flower-like structures was developed. This method allows the successful incorporation and homogeneous distribution of Mn within the nanoparticle iron oxide clusters. The formed clusters retain the desired morphological and structural features observed for pure iron oxide clusters, but possess intrinsic magnetic properties that arise from Mn doping. They show distinct performance as imaging contrast agents and excellent characteristics as heating mediators in magnetic fluid hyperthermia. It is expected that the outcomes of this study will open up new avenues for the exploitation of doped magnetic nanoparticle assemblies in biomedicine. PMID:27282828

  4. Defect-mediated magnetism of transition metal doped zinc oxide thin films

    NASA Astrophysics Data System (ADS)

    Roberts, Bradley Kirk

    Magnetism in transition metal doped wide band-gap materials is of interest to further the fundamental science of materials and future spintronics applications. Large inter-dopant separations require mediation of ferromagnetism by some method; carrier-mediated mechanisms are typically applicable to dilute magnetic semiconductors with low Curie temperatures. Dilute magnetic oxides, commonly with poor conductivity and TC above room temperature, cannot be described within this theory. Recent experiment and theory developments suggest that ferromagnetic exchange in these materials can be mediated by defects. This research includes experimental results justifying and developing this approach. Thin films of Cr doped ZnO (band gap ˜3.3 eV) were deposited with several processing variations to enhance the effects of either 0-dimensional (vacancy, hydrogen-related defect) or two-dimensional defects (surface/interface) and thereby affect magnetism and conductivity. We observe surface magnetism in dielectric thin films of oxygen-saturated ZnO:Cr with spontaneous magnetic moment and conductance dropping approximately exponentially with increasing thickness. Uniform defect concentrations would not result in such magnetic ordering behavior indicating that magnetism is mediated either by surface defects or differing concentrations of point defects near the surface. Polarized neutron reflectivity profiling confirms a magnetically active region of ˜8 nm at the film surface. Hydrogen is notoriously present as a defect and carrier dopant in ZnO, and artificial introduction of hydrogen in dielectric ZnO:Cr films results in varying electronic and magnetic behavior. Free carriers introduced with hydrogen doping are not spin-polarized requiring an alternative explanation for ferromagnetism. We find from positron annihilation spectroscopy measurements that hydrogen doping increases the concentration of an altered VZn-related defect (a preliminary interpretation) throughout the film, which

  5. CO and Soot Oxidation over Ce-Zr-Pr Oxide Catalysts

    NASA Astrophysics Data System (ADS)

    Andana, Tahrizi; Piumetti, Marco; Bensaid, Samir; Russo, Nunzio; Fino, Debora; Pirone, Raffaele

    2016-06-01

    A set of ceria, ceria-zirconia (Ce 80 at.%, Zr 20 at.%), ceria-praseodymia (Ce 80 at.%, Pr 20 at.%) and ceria-zirconia-praseodymia (Ce 80 at.%, Zr 10 at.% and Pr 10 at.%) catalysts has been prepared by the solution combustion synthesis (SCS). The effects of Zr and Pr as dopants on ceria have been studied in CO and soot oxidation reactions. All the prepared catalysts have been characterized by complementary techniques, including XRD, FESEM, N2 physisorption at -196 °C, H2-temperature-programmed reduction, and X-ray photoelectron spectroscopy to investigate the relationships between the structure and composition of materials and their catalytic performance. Better results for CO oxidation have been obtained with mixed oxides (performance scale, Ce80Zr10Pr10 > Ce80Zr20 > Ce80Pr20) rather than pure ceria, thus confirming the beneficial role of multicomponent catalysts for this prototypical reaction. Since CO oxidation occurs via a Mars-van Krevelen (MvK)-type mechanism over ceria-based catalysts, it appears that the presence of both Zr and Pr species into the ceria framework improves the oxidation activity, via collective properties, such as electrical conductivity and surface or bulk oxygen anion mobility. On the other hand, this positive effect becomes less prominent in soot oxidation, since the effect of catalyst morphology prevails.

  6. CO and Soot Oxidation over Ce-Zr-Pr Oxide Catalysts.

    PubMed

    Andana, Tahrizi; Piumetti, Marco; Bensaid, Samir; Russo, Nunzio; Fino, Debora; Pirone, Raffaele

    2016-12-01

    A set of ceria, ceria-zirconia (Ce 80 at.%, Zr 20 at.%), ceria-praseodymia (Ce 80 at.%, Pr 20 at.%) and ceria-zirconia-praseodymia (Ce 80 at.%, Zr 10 at.% and Pr 10 at.%) catalysts has been prepared by the solution combustion synthesis (SCS). The effects of Zr and Pr as dopants on ceria have been studied in CO and soot oxidation reactions. All the prepared catalysts have been characterized by complementary techniques, including XRD, FESEM, N2 physisorption at -196 °C, H2-temperature-programmed reduction, and X-ray photoelectron spectroscopy to investigate the relationships between the structure and composition of materials and their catalytic performance. Better results for CO oxidation have been obtained with mixed oxides (performance scale, Ce80Zr10Pr10 > Ce80Zr20 > Ce80Pr20) rather than pure ceria, thus confirming the beneficial role of multicomponent catalysts for this prototypical reaction. Since CO oxidation occurs via a Mars-van Krevelen (MvK)-type mechanism over ceria-based catalysts, it appears that the presence of both Zr and Pr species into the ceria framework improves the oxidation activity, via collective properties, such as electrical conductivity and surface or bulk oxygen anion mobility. On the other hand, this positive effect becomes less prominent in soot oxidation, since the effect of catalyst morphology prevails. PMID:27255898

  7. Isothermal and dynamic oxidation behaviour of Mo-W doped carbon-based coating

    NASA Astrophysics Data System (ADS)

    Mandal, Paranjayee; Ehiasarian, Arutiun P.; Hovsepian, Papken Eh.

    2015-10-01

    The oxidation behaviour of Mo-W doped carbon-based coating (Mo-W-C) is investigated in elevated temperature (400-1000 °C). Strong metallurgical bond between Mo-W-C coating and substrate prevents any sort of delamination during heat-treatment. Isothermal oxidation tests show initial growth of metal oxides at 500 °C, however graphitic nature of the as-deposited coating is preserved. The oxidation progresses with further rise in temperature and the substrate is eventually exposed at 700 °C. The performance of Mo-W-C coating is compared with a state-of-the-art DLC(Cr/Cr-WC/W:C-H/a:C-H) coating, which shows preliminary oxidation at 400 °C and local delamination of the coating at 500 °C leading to substrate exposure. The graphitisation starts at 400 °C and the diamond-like structure is completely converted into the graphite-like structure at 500 °C. Dynamic oxidation behaviour of both the coatings is investigated using Thermo-gravimetric analysis carried out with a slow heating rate of 1 °C/min from ambient temperature to 1000 °C. Mo-W-C coating resists oxidation up to ∼800 °C whereas delamination of DLC(Cr/Cr-WC/W:C-H/a:C-H) coating is observed beyond ∼380 °C. In summary, Mo-W-C coating provides improved oxidation resistance at elevated temperature compared to DLC(Cr/Cr-WC/W:C-H/a:C-H) coating.

  8. Characterization of the Fe-Doped Mixed-Valent Tunnel Structure 2 Manganese Oxide KOMS-2

    SciTech Connect

    Hanson J. C.; Shen X.; Morey A.M.; Liu J.; Ding Y.; Cai J.; Durand J.; Wang Q.; Wen W.; Hines W.A.; Bai J.; Frenkel A.I.; Reiff W.; Aindow M.; Suib S.L.

    2011-11-10

    A sol-gel-assisted combustion method was used to prepare Fe-doped manganese oxide octahedral molecular sieve (Fe-KOMS-2) materials with the cryptomelane structure. Characterization of the nanopowder samples over a wide range of Fe-doping levels (0 {le} Fe/Mn {le} 1/2) was carried out using a variety of experimental techniques. For each sample, Cu K{alpha} XRD and ICP-AES were used to index the cryptomelane structure and determine the elemental composition, respectively. A combination of SEM and TEM images revealed that the morphology changes from nanoneedle to nanorod after Fe doping. Furthermore, TGA scans indicated that the thermal stability is also enhanced with the doping. Anomalous XRD demonstrated that the Fe ions replace the Mn ions in the cryptomelane structure, particularly in the (211) planes, and results in a lattice expansion along the c axis, parallel to the tunnels. Reasonable fits to EXAFS data were obtained using a model based on the cryptomelane structure. Moessbauer spectra for selected Fe-KOMS-2 samples indicated that the Fe is present as Fe{sup 3+} in an octahedral environment similar to Mn in the MnO{sub 6} building blocks of KOMS-2. Magnetization measurements detected a small amount of {gamma}-Fe{sub 2}O{sub 3} second phase (e.g., 0.6 wt % for the Fe/Mn = 1/10 sample), the vast majority of the Fe being in the structure as Fe{sup 3+} in the high-spin state.

  9. First-principles study of doping and band gap anomalies in delafossite transparent conductive oxides

    NASA Astrophysics Data System (ADS)

    Nie, Xiliang; Wei, Su-Huai; Zhang, S. B.

    2002-03-01

    Despite the success of n-type transparent conductive oxides (TCOs) in flat panel display, solar cell, and touch panel applications, p-type TCOs are rare. Recently, however, several p-type TCO films such as SrCu_2O2 and delafossite CuM^IIIO2 where M^III=Al, Ga, and In have been successfully demonstrated. These materials have some very unusual properties: (i) The band gaps increase with increasing atomic number. This contradicts the trend in normal semiconductors including those with the same group III elements. (ii) Bipolar doping (namely both p- and n-type doping) is observed only in the largest band gap CuInO_2. This contradicts the doping limit rule [1] as no similar trend has ever been observed in any other semiconductors. Here, using first-principles method, we calculate the electronic and optical properties of CuM^IIIO_2. We found that the fundamental direct gap decreases with the increase of the atomic number, following the general trend in conventional semiconductors. But the optical band gap (which has been used in the above experiments to define the band gap) follows an opposite trend. This happens because optical transition at the fundamental direct gap is forbidden as both states have the same parity (even). On the other hand, CuInO2 has exceptionally low conduction band minimum (CBM), 1.48 eV lower than CuAlO_2. According to the doping limit rule [1], low CBM implies good n-type dopability. Our findings explain the puzzling combination of good transparency with bipolar dopability in CuInO_2. This work was supported by the U. S. DOE-SC-BES under contract No. DE-AC36-99GO10337. [1] S. B. Zhang, S. -H. Wei, and A. Zunger, J. Appl. Phys. 83, 3192 (1998).

  10. Mineralization of bisphenol A (BPA) by anodic oxidation with boron-doped diamond (BDD) electrode.

    PubMed

    Murugananthan, M; Yoshihara, S; Rakuma, T; Shirakashi, T

    2008-06-15

    Anodic oxidation of bisphenol A (BPA), a representative endocrine disrupting chemical, was carried out using boron-doped diamond (BDD) electrode at galvanostatic mode. The electro-oxidation behavior of BPA at BDD electrode was investigated by means of cyclic voltammetric technique. The extent of degradation and mineralization of BPA were monitored by HPLC and total organic carbon (TOC) value, respectively. The results obtained, indicate that the BPA removal at BDD depends on the applied current density (Iappl), initial concentration of BPA, pH of electrolyte and supporting medium. Galvanostatic electrolysis at BDD anode cause concomitant generation of hydroxyl radical that leads to the BPA destruction. The kinetics for the BPA degradation follows a pseudo-first order reaction with a higher rate constant 12.8x10(-5) s(-1) for higher Iappl value 35.7 mA cm(-2), indicating that the oxidation reaction is limited by Iappl control. Complete mineralization of BPA was achieved regardless of the variables and accordingly the mineralization current efficiency was calculated from the TOC removal measurements. Considering global oxidation process, the effect of supporting electrolytes has been discussed in terms of the electro generated inorganic oxidants. The better performance of BDD anode was proved on a comparative study with Pt and glassy carbon under similar experimental conditions. A possible reaction mechanism for BPA degradation involving three main aromatic intermediates, identified by GC-MS analysis, was proposed. PMID:18023975

  11. Fluorescence in nanocomposites based on polyethylene oxides and block copolymers of polyethylene oxide-polypropylene oxide loaded with rare earth doped fluorides

    NASA Astrophysics Data System (ADS)

    Yust, Brian; Pedraza, Francisco; Sardar, Dhiraj; Saenz, Aaron; Chipara, Mircea

    2015-03-01

    Rare earth doped fluoride nanoparticles with a size of about 25 nm have been synthesized by a solvothermal process. Polymer-based nanocomposites, containing various weight fraction of nanofillers, have been obtained by dissolving the polymeric matrix (polyethylene oxide) within a solvent (deionized water), adding the nanoparticles, sonicating the mixture, and finally removing the solvent. The complete removal of the solvent has been confirmed by Thermogravimetric Analysis. Additional information about the thermal features have been obtained by Differential Scanning Calorimetry, Wide Angle X-Ray Scattering, FTIR, UV-Visible, and Raman. The effect of the loading with nanoparticles on the glass, crystallization, and melting transition temperatures of the polymeric matrix are reported. Fluorescence of rare earth doped nanoparticles dispersed within the polymeric matrix has been tested by laser spectroscopy. The dependence of fluorescence intensity on the concentration of nanofillers and on temperature in the range 300 to 400 K is analyzed.

  12. Hydrogen plasma treatment for improved conductivity in amorphous aluminum doped zinc tin oxide thin films

    SciTech Connect

    Morales-Masis, M. Ding, L.; Dauzou, F.; Jeangros, Q.; Hessler-Wyser, A.; Nicolay, S.; Ballif, C.

    2014-09-01

    Improving the conductivity of earth-abundant transparent conductive oxides (TCOs) remains an important challenge that will facilitate the replacement of indium-based TCOs. Here, we show that a hydrogen (H{sub 2})-plasma post-deposition treatment improves the conductivity of amorphous aluminum-doped zinc tin oxide while retaining its low optical absorption. We found that the H{sub 2}-plasma treatment performed at a substrate temperature of 50 °C reduces the resistivity of the films by 57% and increases the absorptance by only 2%. Additionally, the low substrate temperature delays the known formation of tin particles with the plasma and it allows the application of the process to temperature-sensitive substrates.

  13. Indium doped zinc oxide nanowire thin films for antireflection and solar absorber coating applications

    SciTech Connect

    Shaik, Ummar Pasha; Krishna, M. Ghanashyam

    2014-04-24

    Indium doped ZnO nanowire thin films were prepared by thermal oxidation of Zn-In metal bilayer films at 500°C. The ZnO:In nanowires are 20-100 nm in diameter and several tens of microns long. X-ray diffraction patterns confirm the formation of oxide and indicate that the films are polycrystalline, both in the as deposited and annealed states. The transmission which is <2% for the as deposited Zn-In films increases to >90% for the ZnO:In nanowire films. Significantly, the reflectance for the as deposited films is < 10% in the region between 200 to 1500 nm and < 2% for the nanowire films. Thus, the as deposited films can be used solar absorber coatings while the nanowire films are useful for antireflection applications. The growth of nanowires by this technique is attractive since it does not involve very high temperatures and the use of catalysts.

  14. Hydrogen plasma treatment for improved conductivity in amorphous aluminum doped zinc tin oxide thin films

    NASA Astrophysics Data System (ADS)

    Morales-Masis, M.; Ding, L.; Dauzou, F.; Jeangros, Q.; Hessler-Wyser, A.; Nicolay, S.; Ballif, C.

    2014-09-01

    Improving the conductivity of earth-abundant transparent conductive oxides (TCOs) remains an important challenge that will facilitate the replacement of indium-based TCOs. Here, we show that a hydrogen (H2)-plasma post-deposition treatment improves the conductivity of amorphous aluminum-doped zinc tin oxide while retaining its low optical absorption. We found that the H2-plasma treatment performed at a substrate temperature of 50 °C reduces the resistivity of the films by 57% and increases the absorptance by only 2%. Additionally, the low substrate temperature delays the known formation of tin particles with the plasma and it allows the application of the process to temperature-sensitive substrates.

  15. Chemical solution deposition of ferroelectric yttrium-doped hafnium oxide films on platinum electrodes

    SciTech Connect

    Starschich, S.; Griesche, D.; Schneller, T.; Böttger, U.; Waser, R.

    2014-05-19

    Ferroelectric hafnium oxide films were fabricated by chemical solution deposition with a remnant polarization of >13 μC/cm{sup 2}. The samples were prepared with 5.2 mol. % yttrium-doping and the thickness varied from 18 nm to 70 nm. The hafnium oxide layer was integrated into a metal-insulator-metal capacitor using platinum electrodes. Due to the processing procedure, no thickness dependence of the ferroelectric properties was observed. To confirm the ferroelectric nature of the deposited samples, polarization, capacitance, and piezoelectric displacement measurements were performed. However, no evidence of the orthorhombic phase was found which has been proposed to be the non-centrosymmetric, ferroelectric phase in HfO{sub 2}.

  16. Characterization of Monolayer Formation on Aluminum-Doped Zinc Oxide Thin Films

    SciTech Connect

    Rhodes,C.; Lappi, S.; Fischer, D.; Sambasivan, S.; Genzer, J.; Franzen, S.

    2008-01-01

    The optical and electronic properties of aluminum-doped zinc oxide (AZO) thin films on a glass substrate are investigated experimentally and theoretically. Optical studies with coupling in the Kretschmann configuration reveal an angle-dependent plasma frequency in the mid-IR for p-polarized radiation, suggestive of the detection of a Drude plasma frequency. These studies are complemented by oxygen depletion density functional theory studies for the calculation of the charge carrier concentration and plasma frequency for bulk AZO. In addition, we report on the optical and physical properties of thin film adlayers of n-hexadecanethiol (HDT) and n-octadecanethiol (ODT) self-assembled monolayers (SAMs) on AZO surfaces using reflectance FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Our characterization of the SAM deposition onto the AZO thin film reveals a range of possible applications for this conducting metal oxide.

  17. Recent developments in polycrystalline oxide fiber laser materials: production of Yb-doped polycrystalline YAG fiber

    NASA Astrophysics Data System (ADS)

    Lee, HeeDong; Keller, Kristin; Sirn, Brian; Parthasarathy, Triplicane; Cheng, Michael; Hopkins, Frank K.

    2011-09-01

    Laser quality, polycrystalline oxide fibers offer significant advantages over state-of-the-art silica fiber for high energy lasers. Advanced ceramic processing technology, along with a novel powder production process, has potential to produce oxide fibers with an outstanding optical quality for use in the fiber laser applications. The production of contaminant-free green fibers with a high packing density, as well as uniform packing distribution, is a key factor in obtaining laserquality fibers. High quality green fibers are dependent on the powder quality combined with the appropriate slurry formulation. These two fundamental technologies were successfully developed at UES, and used to produce Yb-doped yttrium aluminum garnet (YAG) fibers with high optical quality, high chemical purity, and suitable core diameters down to 20-30 microns.

  18. Determination of the oxidation state and coordination of a vanadium doped chalcogenide glass

    NASA Astrophysics Data System (ADS)

    Hughes, Mark A.; Curry, Richard J.; Hewak, Daniel W.

    2011-01-01

    Vanadium doped chalcogenide glass has potential as an active gain medium, particularly at telecommunications wavelengths. This dopant has three spin allowed absorption transitions at 1100, 737 and 578 nm, and a spin forbidden absorption transition at 1000 nm. X-ray photoelectron spectroscopy indicated the presence of vanadium in a range of oxidation states from V+ to V5+. Excitation of each absorption band resulted in the same characteristic emission spectrum and lifetime, indicating that only one oxidation state is optically active. Arguments based on Tanabe-Sugano analysis indicated that the configuration of the optically active vanadium ion was octahedral V2+. The calculated crystal field parameters (Dq/B, B and C/B) were 1.85, 485.1 and 4.55, respectively.

  19. Synthesis of antimony-doped tin oxide (ATO) nanoparticles by the nitrate-citrate combustion method

    SciTech Connect

    Zhang Jianrong; Gao Lian . E-mail: Liangaoc@online.sh.cn

    2004-12-02

    Antimony-doped tin oxide (ATO) nanoparticles having rutile structure have been synthesized by the combustion method using citric acid (CA) as fuel and nitrate as an oxidant, the metal sources were granulated tin and Sb{sub 2}O{sub 3}. The influence of citric acid (fuel) to metal ratio on the average crystallite size, specific surface area and morphology of the nanoparticles has been investigated. X-ray diffraction showed the tin ions were reduced to elemental tin during combustion reaction. The average ATO crystallite size increased with the increase of citric acid (fuel). Powder morphology and the comparison of crystallite size and grain size shows that the degree of agglomeration of the powder decreased with an increase of the ratio. The highest specific surface area was 37.5 m{sup 2}/g when the citric acid to tin ratio was about 6.

  20. Copper-ceria interaction: A combined photoemission and DFT study

    NASA Astrophysics Data System (ADS)

    Szabová, Lucie; Skála, Tomáš; Matolínová, Iva; Fabris, Stefano; Farnesi Camellone, Matteo; Matolín, Vladimír

    2013-02-01

    Stoichiometric and partially reduced ceria films were deposited on preoxidized Ru(0 0 0 1) crystal by Ce evaporation in oxygen atmosphere of different pressures at 700 K. Copper-ceria interaction was investigated by deposition of metalic copper on both types of substrate. The samples were characterized by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) of core states and resonant photoelectron spectroscopy (RPES) of the valence bands. Copper adsorption on stoichiometric ceria caused reduction of CeO2, while on the oxygen-defficient ceria it partially reoxidized the substrate. This is in agreement with DFT+U calculations of copper adsorption on stoichiometric and defective ceria surfaces.

  1. Implications of the band gap problem on oxidation and hydration in acceptor-doped barium zirconate

    NASA Astrophysics Data System (ADS)

    Lindman, Anders; Erhart, Paul; Wahnström, Göran

    2015-06-01

    Charge carrier concentrations in acceptor-doped proton-conducting perovskites are to a large extent determined by the hydration and oxidation of oxygen vacancies, which introduce protons and holes, respectively. First-principles modeling of these reactions involves calculation of formation energies of charged defects, which requires an accurate description of the band gap and the position of the band edges. Since density-functional theory (DFT) with local and semilocal exchange-correlation functionals (LDA and GGA) systematically fails to predict these quantities this can have serious implications on the modeling of defect reactions. In this study we investigate how the description of band gap and band-edge positions affects the hydration and oxidation in acceptor-doped BaZrO3. First-principles calculations are performed in combination with thermodynamic modeling in order to obtain equilibrium charge carrier concentrations at different temperatures and partial pressures. Three different methods have been considered: DFT with both semilocal (PBE) and hybrid (PBE0) exchange-correlation functionals, and many-body perturbation theory within the G0W0 approximation. All three methods yield similar results for the hydration reaction, which are consistent with experimental findings. For the oxidation reaction, on the other hand, there is a qualitative difference. PBE predicts the reaction to be exothermic, while the two others predict an endothermic behavior. Results from thermodynamic modeling are compared with available experimental data, such as enthalpies, concentrations, and conductivities, and only the results obtained with PBE0 and G0W0 , with an endothermic oxidation behavior, give a satisfactory agreement with experiments.

  2. Investigation of fluorine-doped tin oxide based optically transparent E-shaped patch antenna for terahertz communications

    SciTech Connect

    Anand, S. E-mail: darak.mayur@gmail.com Darak, Mayur Sudesh E-mail: darak.mayur@gmail.com Kumar, D. Sriram E-mail: darak.mayur@gmail.com

    2014-10-15

    In this paper, a fluorine-doped tin oxide based optically transparent E-shaped patch antenna is designed and its radiation performance is analyzed in the 705 – 804 GHz band. As optically transparent antennas can be mounted on optical display, they facilitate the reduction of overall system size. The proposed antenna design is simulated using electromagnetic solver - Ansys HFSS and its characteristics such as impedance bandwidth, directivity, radiation efficiency and gain are observed. Results show that the fluorine-doped tin oxide based optically transparent patch antenna overcomes the conventional patch antenna limitations and thus the same can be used for solar cell antenna used in satellite systems.

  3. Dysprosium-doped cadmium oxide as a gateway material for mid-infrared plasmonics

    SciTech Connect

    Sachet, Edward; Shelton, Christopher T.; Harris, Joshua S.; Gaddy, Benjamin E.; Irving, Douglas L.; Curtarolo, Stefano; Donovan, Brian F.; Hopkins, Patrick E.; Sharma, Peter A.; Sharma, Ana Lima; Ihlefeld, Jon; Franzen, Stefan; Maria, Jon -Paul

    2015-02-16

    The interest in plasmonic technologies surrounds many emergent optoelectronic applications, such as plasmon lasers, transistors, sensors and information storage. Although plasmonic materials for ultraviolet–visible and near-infrared wavelengths have been found, the mid-infrared range remains a challenge to address: few known systems can achieve subwavelength optical confinement with low loss in this range. With a combination of experiments and ab initio modelling, here we demonstrate an extreme peak of electron mobility in Dy-doped CdO that is achieved through accurate ‘defect equilibrium engineering’. In so doing, we create a tunable plasmon host that satisfies the criteria for mid-infrared spectrum plasmonics, and overcomes the losses seen in conventional plasmonic materials. In particular, extrinsic doping pins the CdO Fermi level above the conduction band minimum and it increases the formation energy of native oxygen vacancies, thus reducing their populations by several orders of magnitude. The substitutional lattice strain induced by Dy doping is sufficiently small, allowing mobility values around 500 cm2 V–1 s–1 for carrier densities above 1020 cm–3. As a result, our work shows that CdO:Dy is a model system for intrinsic and extrinsic manipulation of defects affecting electrical, optical and thermal properties, that oxide conductors are ideal candidates for plasmonic devices and that the defect engineering approach for property optimization is generally applicable to other conducting metal oxides.

  4. Electrical and optical properties of molybdenum doped zinc oxide films prepared by reactive RF magnetron sputtering

    SciTech Connect

    Reddy, R. Subba; Sreedhar, A.; Uthanna, S.

    2015-08-28

    Molybdenum doped zinc oxide (MZO) films were deposited on to glass substrates held at temperatures in the range from 303 to 673 K by reactive RF magnetron sputtering method. The chemical composition, crystallographic structure and surface morphology, electrical and optical properties of the films were determined. The films contained the molybdenum of 2.7 at. % in ZnO. The films deposited at 303 K were of X-ray amorphous. The films formed at 473 K were of nanocrystalline in nature with wurtzite structure. The crystallite size of the films was increased with the increase of substrate temperature. The optical transmittance of the films was in the visible range was 80–85%. The molybdenum (2.7 at %) doped zinc oxide films deposited at substrate temperature of 573 K were of nanocrystalline with electrical resistivity of 7.2×10{sup −3} Ωcm, optical transmittance of 85 %, optical band gap of 3.35 eV and figure of merit 30.6 Ω{sup −1}cm{sup −1}.

  5. A novel precursor system and its application to produce tin doped indium oxide.

    PubMed

    Veith, M; Bubel, C; Zimmer, M

    2011-06-14

    A new type of precursor has been developed by molecular design and synthesised to produce tin doped indium oxide (ITO). The precursor consists of a newly developed bimetallic indium tin alkoxide, Me(2)In(O(t)Bu)(3)Sn (Me = CH(3), O(t)Bu = OC(CH(3))(3)), which is in equilibrium with an excess of Me(2)In(O(t)Bu). This quasi single-source precursor is applied in a sol-gel process to produce powders and coatings of ITO using a one-step heat treatment process under an inert atmosphere. The main advantage of this system is the simple heat treatment that leads to the disproportionation of the bivalent Sn(II) precursor into Sn(IV) and metallic tin, resulting in an overall reduced state of the metal in the final tin doped indium oxide (ITO) material, hence avoiding the usually necessary reduction step. Solid state (119)Sn-NMR measurements of powder samples confirm the appearance of Sn(II) in an amorphous gel state and of metallic tin after annealing under nitrogen. The corresponding preparation of ITO coatings by spin coating on glass leads to transparent conductive layers with a high transmittance of visible light and a low electrical resistivity without the necessity of a reduction step. PMID:21541390

  6. Manganese oxide nanowires wrapped with nitrogen doped carbon layers for high performance supercapacitors.

    PubMed

    Li, Ying; Mei, Yuan; Zhang, Lin-Qun; Wang, Jian-Hai; Liu, An-Ran; Zhang, Yuan-Jian; Liu, Song-Qin

    2015-10-01

    In this study, manganese oxide nanowires wrapped by nitrogen-doped carbon layers (MnO(x)@NCs) were prepared by carbonization of poly(o-phenylenediamine) layer coated onto MnO2 nanowires for high performance supercapacitors. The component and structure of the MnO(x)@NCs were controlled through carbonization procedure under different temperatures. Results demonstrated that this composite combined the high conductivity and high specific surface area of nitrogen-doped carbon layers with the high pseudo-capacitance of manganese oxide nanowires. The as-prepared MnO(x)@NCs exhibited superior capacitive properties in 1 M Na2SO4 aqueous solution, such as high conductivity (4.167×10(-3) S cm(-1)), high specific capacitance (269 F g(-1) at 10 mV s(-1)) and long cycle life (134 F g(-1) after 1200 cycles at a scan rate of 50 mV s(-1)). It is reckoned that the present novel hybrid nanowires can serve as a promising electrode material for supercapacitors and other electrochemical devices. PMID:26070189

  7. Boron doped ZnO embedded into reduced graphene oxide for electrochemical supercapacitors

    NASA Astrophysics Data System (ADS)

    Alver, Ü.; Tanrıverdi, A.

    2016-08-01

    In this work, reduced graphene oxide/boron doped zinc oxide (RGO/ZnO:B) composites were fabricated by a hydrothermal process and their electrochemical properties were investigated as a function of dopant concentration. First, boron doped ZnO (ZnO:B) particles was fabricated with different boron concentrations (5, 10, 15 and 20 wt%) and then ZnO:B particles were embedded into RGO sheets. The physical properties of sensitized composites were characterized by XRD and SEM. Characterization indicated that the ZnO:B particles with plate-like structure in the composite were dispersed on graphene sheets. The electrochemical properties of the RGO/ZnO:B composite were investigated through cyclic voltammetry, galvanostatic charge/discharge measurements in a 6 M KOH electrolyte. Electrochemical measurements show that the specific capacitance values of RGO/ZnO:B electrodes increase with increasing boron concentration. RGO/ZnO:B composite electrodes (20 wt% B) display the specific capacitance as high as 230.50 F/g at 5 mV/s, which is almost five times higher than that of RGO/ZnO (52.71 F/g).

  8. Facile synthesis of highly conductive sulfur-doped reduced graphene oxide sheets.

    PubMed

    Tian, Zhengshan; Li, Jitao; Zhu, Gangyi; Lu, Junfeng; Wang, Yueyue; Shi, Zengliang; Xu, Chunxiang

    2016-01-14

    A facile hydrothermal strategy to synthesize sulfur-doped reduced graphene oxide (S-RGO) sheets with good conductivity is proposed by using only graphene oxide (GO) sheets and sodium sulphide (Na2S) as precursors through a hydrothermal reaction process at 200 °C in one pot. The introduced Na2S can act as not only a sulfur dopant, but also as a highly efficient reducing agent in the formation of S-RGO sheets, which dramatically improves the electrical conductivities of the resulting S-RGO sheets compared with previous reports. The current reaches about 50.0 mA at an applied bias of 2.0 V for the optimized sample with 2.22 at% sulfur doping. This current value is much higher than that of RGO sheets (∼1.2 mA) annealed at 200 °C, and very close to that of single-layer graphene sheets (∼68.0 mA) prepared using chemical vapor deposition under the same test conditions. The resulting highly conductive S-RGO sheets offer many promising technological applications such as efficient metal-free electrocatalysts in oxygen reduction reactions in fuel cells and as supercapacitor electrode materials for high-performance Li-ion batteries. PMID:26659603

  9. Preparation and characterization of thermoluminescent aluminium oxide doped with Tb3+ and Tb3+-Mg2+

    NASA Astrophysics Data System (ADS)

    Barros, V. S. M.; Azevedo, W. M.; Khoury, H. J.; Linhares Filho, P.

    2010-11-01

    This paper presents the preparation method and the thermoluminescence analysis of aluminium oxide doped with Tb3+ and Tb3+-Mg2+ obtained by Combustion Synthesis (CS). An aqueous solution containing stoichiometric amounts of aluminium, terbium, magnesium nitrates and urea were mixed and introduced in a muffle furnace pre-heated to 500°C. After combustion, the samples were thermally treated at 1300°C and irradiated with a Co-60 gamma radiation source. The TL glow curves of the annealed Al2O3:Tb and Al2O3:Tb,Mg samples presented a well defined TL peak at approximately 200 °C, whereas the samples without heat-treatment presented a large number of TL peaks in the range from 150 to 500°C. These peaks were attributed to amorphous and phase impurities (γ-Al2O3 mixed with the α-phase) still present in the sample. Dose response analysis showed a linear response in the dose range from 0.5 to 5 Gy. These results strongly suggest that CS is a suitable technique to prepare doped aluminium oxide for TL dosimetric applications.

  10. Effect of doping and chemical ordering on the optoelectronic properties of complex oxide semiconductors

    NASA Astrophysics Data System (ADS)

    Nayyar, Iffat; Sara, Chamberlin; Kaspar, Tiffany; Govind, Niranjan; Chambers, Scott; Sushko, Peter

    2015-03-01

    Transition metal oxide hematite, α-Fe2O3, is of interest in photovoltaic and photoelectrochemical applications due to its natural abundance, narrow band gap and electrochemical stability. Doping of α-Fe2O3 may lead to conductivity enhancement and band-gap reduction. In this work, we have studied the electronic and optical properties of α-(Fe1-xVx)2 O3(0 <= x <= ~0.5) solid-solution epitaxial thin films using advanced theoretical models employing embedded cluster approach and time-dependent density functional theory. We observe that V doping results in localized, occupied V 3d states which are hybridized with Fe 3d and are located in the midgap of pure α-Fe2O3. The lowest energy transitions for α-(Fe1-xVx)2O3 films are the electronic excitations from these levels to the unoccupied Fe 3d* orbitals, reducing the onset of α-Fe2O3photoconductivity by nearly 1.2 eV. Our calculated optical absorption spectra are in good agreement with the experiment. This insight into the atomic, electronic and spin ordering provides guiding principles for the design of new oxide semiconducting materials for efficient visible light harvesting, thus enabling the technological growth of alternate energy sources for solving the renewable solar energy and photo-chemical organic waste remediation problems.

  11. Alcohol vapor sensing by cadmium-doped zinc oxide thick films based chemical sensor

    NASA Astrophysics Data System (ADS)

    Zargar, R. A.; Arora, M.; Chackrabarti, S.; Ahmad, S.; Kumar, J.; Hafiz, A. K.

    2016-04-01

    Cadmium-doped zinc oxide nanoparticles were derived by simple chemical co-precipitation route using zinc acetate dihydrate and cadmium acetate dihydrate as precursor materials. The thick films were casted from chemical co-precipitation route prepared nanoparticles by economic facile screen printing method. The structural, morphological, optical and electrical properties of the film were characterized relevant to alcohol vapor sensing application by powder XRD, SEM, UV-VIS and DC conductivity techniques. The response and sensitivity of alcohol (ethanol) vapor sensor are obtained from the recovery curves at optimum working temperature range from 20∘C to 50∘C. The result shows that maximum sensitivity of the sensor is observed at 25∘C operating temperature. On varying alcohol vapor concentration, minor variation in resistance has been observed. The sensing mechanism of sensor has been described in terms of physical adsorption and chemical absorption of alcohol vapors on cadmium-doped zinc oxide film surface and inside film lattice network through weak hydrogen bonding, respectively.

  12. The influence of magnetic nano metal oxides doping on structure and electrical properties of YBCO superconductor

    NASA Astrophysics Data System (ADS)

    Salama, A. H.; El-Hofy, M.; Rammah, Y. S.; Elkhatib, M.

    2016-03-01

    Superconductor samples of YBa2Cu3O7-δ (YBCO) + x where x = 0.1, 0.2, 0.3, 0.4 and 0.5 wt% of nano metal oxides namely Cr2O3, Co3O4 and Mn3O4 namely are synthesized by the solid-state reaction route. Both x-ray diffraction and electron microscopy have been employed to study the phase identification and the microstructure of these samples. Transition temperature of the samples has been determined by four probe resistivity measurements. The x-ray diffraction patterns indicate that the gross structure of YBCO does not change with the substitution of three types of nano metal oxides with different doping level. The critical transition temperature (Tc) is found to decrease with the increases of doping level. Mn3O4 has highest Tc value which may be due to flux pinning from some defects and the rapid suppression in Tc with increasing concentration of Mn3O4 may be due to the cooper pair breaking and the hole filling in the CuO2 planes.

  13. Metal/metal oxide doped oxide catalysts having high deNOx selectivity for lean NOx exhaust aftertreatment systems

    DOEpatents

    Park, Paul W.

    2004-03-16

    A lean NOx catalyst and method of preparing the same is disclosed. The lean NOx catalyst includes a ceramic substrate, an oxide support material, preferably .gamma.-alumina, deposited on the substrate and a metal promoter or dopant introduced into the oxide support material. The metal promoters or dopants are selected from the group consisting of indium, gallium, tin, silver, germanium, gold, nickel, cobalt, copper, iron, manganese, molybdenum, chromium, cerium, vanadium, oxides thereof, and combinations thereof. The .gamma.-alumina preferably has a pore volume of from about 0.5 to about 2.0 cc/g; a surface area of between about 80 to 350 m.sup.2 /g; an average pore size diameter of between about 3 to 30 nm; and an impurity level of less than or equal to 0.2 weight percent. In a preferred embodiment the .gamma.-alumina is prepared by a sol-gel method, with the metal doping of the .gamma.-alumina preferably accomplished using an incipient wetness impregnation technique.

  14. Synergetic antibacterial activity of reduced graphene oxide and boron doped diamond anode in three dimensional electrochemical oxidation system

    PubMed Central

    Qi, Xiujuan; Wang, Ting; Long, Yujiao; Ni, Jinren

    2015-01-01

    A 100% increment of antibacterial ability has been achieved due to significant synergic effects of boron-doped diamond (BDD) anode and reduced graphene oxide (rGO) coupled in a three dimensional electrochemical oxidation system. The rGO, greatly enhanced by BDD driven electric field, demonstrated strong antibacterial ability and even sustained its excellent performance during a reasonable period after complete power cut in the BDD-rGO system. Cell damage experiments and TEM observation confirmed much stronger membrane stress in the BDD-rGO system, due to the faster bacterial migration and charge transfer by the expanded electro field and current-carrying efficiency by quantum tunnel. Reciprocally the hydroxyl-radical production was eminently promoted with expanded area of electrodes and delayed recombination of the electron–hole pairs in presence of the rGO in the system. This implied a huge potential for practical disinfection with integration of the promising rGO and the advanced electrochemical oxidation systems. PMID:25994309

  15. Synergetic antibacterial activity of reduced graphene oxide and boron doped diamond anode in three dimensional electrochemical oxidation system

    NASA Astrophysics Data System (ADS)

    Qi, Xiujuan; Wang, Ting; Long, Yujiao; Ni, Jinren

    2015-05-01

    A 100% increment of antibacterial ability has been achieved due to significant synergic effects of boron-doped diamond (BDD) anode and reduced graphene oxide (rGO) coupled in a three dimensional electrochemical oxidation system. The rGO, greatly enhanced by BDD driven electric field, demonstrated strong antibacterial ability and even sustained its excellent performance during a reasonable period after complete power cut in the BDD-rGO system. Cell damage experiments and TEM observation confirmed much stronger membrane stress in the BDD-rGO system, due to the faster bacterial migration and charge transfer by the expanded electro field and current-carrying efficiency by quantum tunnel. Reciprocally the hydroxyl-radical production was eminently promoted with expanded area of electrodes and delayed recombination of the electron-hole pairs in presence of the rGO in the system. This implied a huge potential for practical disinfection with integration of the promising rGO and the advanced electrochemical oxidation systems.

  16. Electrocatalytic oxidation of nitrite using metal-free nitrogen-doped reduced graphene oxide nanosheets for sensitive detection.

    PubMed

    Chen, Dong; Jiang, Jingjing; Du, Xuezhong

    2016-08-01

    Nitrite can become poisonous to animals and human beings as it can lead to generation of carcinogenic N-nitrosamines. Metal-free nitrogen-doped reduced graphene oxide (NrGO) exhibited a good electrocatalytic activity toward oxidation of nitrite with the relatively low oxidation potential of 0.68V (v.s. saturated calomel electrode), thus, a facile electrochemical sensor based on metal-free NrGO was fabricated for sensitive detection of nitrite for the first time. The novel sensor showed a wide linear concentration range from 0.5 to 5000μM and a low detection limit of 0.2μM at the signal-to-noise ratio of 3 with good selectivity, stability, and reproducibility. This fabricated sensor was used for the determination of nitrite in pickled garlic and river water. These results demonstrate that the facile metal-free NrGO-modified electrochemical sensor has promising applications for the determination of nitrite in food and environment. PMID:27216690

  17. Nitrogen-doped hierarchical porous carbon with high surface area derived from graphene oxide/pitch oxide composite for supercapacitors.

    PubMed

    Ma, Yuan; Ma, Chang; Sheng, Jie; Zhang, Haixia; Wang, Ranran; Xie, Zhenyu; Shi, Jingli

    2016-01-01

    A nitrogen-doped hierarchical porous carbon has been prepared through one-step KOH activation of pitch oxide/graphene oxide composite. At a low weight ratio of KOH/composite (1:1), the as-prepared carbon possesses high specific surface area, rich nitrogen and oxygen, appropriate mesopore/micropore ratio and considerable small-sized mesopores. The addition of graphene oxide plays a key role in forming 4 nm mesopores. The sample PO-GO-16 presents the characteristics of large surface area (2196 m(2) g(-1)), high mesoporosity (47.6%), as well as rich nitrogen (1.52 at.%) and oxygen (6.9 at.%). As a result, PO-GO-16 electrode shows an outstanding capacitive behavior: high capacitance (296 F g(-1)) and ultrahigh-rate performance (192 F g(-1) at 10 A g(-1)) in 6 M KOH aqueous electrolyte. The balanced structure characteristic, low-cost and high performance, make the porous carbon a promising electrode material for supercapacitors. PMID:26397915

  18. Modeling doped and defective oxides in catalysis with density functional theory methods: room for improvements.

    PubMed

    Pacchioni, Gianfranco

    2008-05-14

    Due to the well-known problem of the self-interaction, standard density functional theory (DFT) methods tend to produce delocalized holes and electrons in defective oxide materials even when there is ample experimental evidence of a strong localization. For late transition metal compounds or rare earth oxides, this results in the incorrect description of the electronic structure of the system (e.g., magnetic insulators are predicted to be metallic). Practical ways to correct this deficiency are based on the use of hybrid functionals or of the DFT+U approach. In this way, most of the limitations related to the self-interaction are removed, and the electronic structure is properly described. What is less clear is to what extent hybrid functionals, DFT+U approaches, or standard DFT functionals can properly describe the strength of the chemical bonds at the surface of an oxide. This is a crucial question if one is interested in the catalytic properties of oxide surfaces. Oxidation reactions often involve oxygen detachment from the surface and incorporation into an organic substrate. Oxides are doped with heteroatoms to create defects and facilitate oxygen removal from the surface, with formation of oxygen vacancies. Do standard DFT calculations provide a good binding energy of the missing oxygen despite the failure in giving the right electronic structure? Can hybrid functionals or the DFT+U approach provide a simple yet reliable way to get accurate reaction enthalpies and energy barriers? In this essay, we discuss these problems by analyzing some case histories and the relatively scarce data existing in the literature. The conclusion is that while modern electronic structure methods accurately reproduce and predict a wide range of electronic, optical, and magnetic properties of oxides, the description of the strength of chemical bonds still needs considerable improvements. PMID:18532790

  19. Boron doped diamond and glassy carbon electrodes comparative study of the oxidation behaviour of cysteine and methionine.

    PubMed

    Enache, T A; Oliveira-Brett, A M

    2011-04-01

    The electrochemical oxidation behaviour at boron doped diamond and glassy carbon electrodes of the sulphur-containing amino acids cysteine and methionine, using cyclic and differential pulse voltammetry over a wide pH range, was compared. The oxidation reactions of these amino acids are irreversible, diffusion-controlled pH dependent processes, and occur in a complex cascade mechanism. The amino acid cysteine undergoes similar three consecutive oxidation reactions at both electrodes. The first step involves the oxidation of the sulfhydryl group with radical formation, that undergoes nucleophilic attack by water to give an intermediate species that is oxidized in the second step to cysteic acid. The oxidation of the sulfhydryl group leads to a disulfide bridge between two similar cysteine moieties forming cysteine. The subsequent oxidation of cystine occurs at a higher potential, due to the strong disulfide bridge covalent bond. The electro-oxidation of methionine at a glassy carbon electrode occurs in two steps, corresponding to the formation of sulfoxide and sulfone, involving the adsorption and protonation/deprotonation of the thiol group, followed by electrochemical oxidation. Methionine undergoes a one-step oxidation reaction at boron doped diamond electrodes due to the negligible adsorption, and the oxidation also leads to the formation of methionine sulfone. PMID:21377428

  20. Composite ceria-coated aerogels and methods of making the same

    DOEpatents

    Eyring, Edward M; Ernst, Richard D; Turpin, Gregory C; Dunn, Brian C

    2013-05-07

    Ceria-coated aerogels can include an aerogel support material having a stabilized ceria coating thereon. The ceria coating can be formed by solution or vapor deposition of alcogels or aerogels. Additional catalytic metal species can also be incorporated into the coating to form multi-metallic compounds having improved catalytic activity. Further, the ceria coated aerogels retain high surface areas at elevated temperatures. Thus, improvements in catalytic activity and thermal stability can be achieved using these ceria-coated composite aerogels.