The Experts below are selected from a list of 4113 Experts worldwide ranked by ideXlab platform
Sanjeev Mukerjee - One of the best experts on this subject based on the ideXlab platform.
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activation energies for oxygen reduction on Platinum Alloys theory and experiment
Journal of Physical Chemistry B, 2005Co-Authors: Alfred B Anderson, Sanjeev Mukerjee, Jerome Roques, Vivek S Murthi, Nenad M Markovic, Vojislav R StamenkovicAbstract:A combined theoretical and experimental analysis of the electrode potential dependencies of activation energies is presented for the first step in oxygen reduction over Platinum and Platinum alloy catalysts in both polycrystalline and carbon supported form. Tafel data for several of the catalysts are used to predict potential-dependent activation energies for oxygen reduction over the 0.6-0.9 V range in strong and weak acid. Comparisons with the theoretical curve show good agreement above 0.8 V, suggesting a fairly constant preexponential factor. Arrhenius determinations of activation energies over the 0.7-0.9 V range yield little trend for weak acid, possibly because of the larger uncertainties in the Arrhenius fits, but the strong acid results have smaller uncertainties and for them the measured activation energies trend up with potential.
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Enhanced electrocatalysis of oxygen reduction on Platinum Alloys in proton exchange membrane fuel cells
Journal of Electroanalytical Chemistry, 1993Co-Authors: Sanjeev Mukerjee, Supramaniam SrinivasanAbstract:Enhanced electrocatalysis of the oxygen reduction reaction (ORR) on carbon-supported binary and ternary Alloys of Pt in phosphoric acid fuel cells has been reported previously. This investigation focuses on the electrocatalysis of the ORR on some binary Alloys of Pt (Pt+Ni, Pt+Cr and Pt+Co) at interfaces with proton exchange membranes (Dow perfluorinated sulfonic acids). Comparison of the results of these studies with those on carbon-supported Pt electrocatalysts (electrodes containing same Pt loading of 0.3 mg/cm2) revealed enhanced activities, lower activation energies and different reaction orders for all the Alloys. X-ray powder diffraction showed lattice contractions for the Alloys, the predominant phase being Pt3M (LI2) f.c.c. crystalline. X-ray photoelectron spectroscopy studies on the constituent elements of the electrocatalyst showed no chemical energy shifts owing to alloying and/or the presence of oxides on the surface. Lifetime evaluations of proton exchange membrane fuel cells, using both electrochemical as well as scanning electron microscopy/energy-dispersive X-ray analysis techniques, revealed only small amounts of dissolution of the more oxidizable component during the testing periods, which ranged from 400 to 1200 h. Therefore, the enhanced electrocatalysis exhibited by the binary Pt Alloys appears to originate primarily as a result of changes in the lattice structure owing to alloying and the unique environment of the supported catalyst in the particle size range 35–75 A.
Jürgen Merker - One of the best experts on this subject based on the ideXlab platform.
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high temperature mechanical properties of the Platinum group metals elastic properties of Platinum rhodium and iridium and their Alloys at high temperatures
2001Co-Authors: Jürgen Merker, David Lupton, W C Heraeus, Michael Topfer, Harald KnakeAbstract:The Platinum group metals are well suited for use at extremely high temperatures under mechanical loads and simultaneous corrosive attack. They have high melting points, excellent chemical stability and are highly resistant to oxidation. When using these materials in the design of components it is necessary to have data available on their elastic properties as a function of temperature. In this paper, investigations are presented into the temperature dependence of Young’s modulus, the modulus of rigidity and Poisson’s ratio for Platinum, Platinum Alloys, rhodium and iridium. Measurements were carried out at the Friedrich Schiller University, Jena, using a resonance technique. Influences from both the microstructure and the alloying elements on the elastic properties and their temperature dependence were found.
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high temperature mechanical properties of the Platinum group metals stress rupture strength and creep behaviour at extremely high temperatures
Platinum Metals Review, 1999Co-Authors: Bernd Fischer, David Lupton, Andreas Behrends, Dietmar Freund, Jürgen MerkerAbstract:There is a constantly increasing need for metallic materials with melting points over 1700°C for use at very high temperatures. In contrast to the refractory metals: tantalum, niobium, tungsten, molybdenum and rhenium, which also have very high melting points, the metals of the Platinum group, particularl-y Platinum, rhodium and iridium, are characterised by outstanding chemical stability, oxidation resistance and resistance to many molten oxides. The p latinum group metals are therefore ideal materials for using at high temperatures while undergoing simultaneous chemical attack and mwhanical loading. However, for o ptimum effective employment of these metals, it is necessary to know their strength and deformation behaviour at extremely high temperatures. Data have therefore been collected from comparative investigations of Platinum, Platinum Alloys, dispersion hardenedPlatinum materials, rhodium and iridium. and the compilations are presented here.
Hong Yang - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and electrocatalytic property of cubic and spherical nanoparticles of cobalt Platinum Alloys
Frontiers of Chemical Engineering in China, 2010Co-Authors: Xiaowei Teng, Hong YangAbstract:This paper describes the morphological control and electrocatalytic property of CoPt nanoparticles. Both cubic and spherical CoPt nanoparticles were made using cobalt carbonyl and Platinum 2,4-pentanedionate under different reaction temperatures in the presence of capping reagents, which included adamantanecarboxylic acid and hexadecylamine. Effects of heterogeneous species on shape of the CoPt nanoparticles were examined by replacing cobalt carbonyl with silver acetylacetonate. Our results suggest that the formation of different shapes of CoPt particles could be attributed to the affinity between cobalt and Platinum, and the effects of capping agents. The size and shape dependent electrocatalytic properties of these nanoparticles were examined based on the direct methanol oxidation reaction.
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designer Platinum nanoparticles control of shape composition in alloy nanostructure and electrocatalytic property
Nano Today, 2009Co-Authors: Zhenmeng Peng, Hong YangAbstract:Summary Recent advances in the design and preparation of Platinum-based nanostructures and their applications as electrocatalysts for low-temperature fuel cells are reviewed. Discussions are focused on the fundamental understanding and new experimental designs in the control of shape, composition and nanoscale structure of Platinum and its alloy particles in colloidal systems. We explain the formation of various heteronanostructures using the Frank–van der Merwe (FM), Volmer–Weber (VW) and Stranski–Krastanov (SK) growth modes. Phenomena that exist in nanometer-sized regime, such as the disappearance of miscibility gaps for certain Platinum Alloys are given special attentions. The relationship between electronic structure or surface atomic arrangement and catalytic properties of Platinum-based nanostructures is discussed.
Regis Chenitz - One of the best experts on this subject based on the ideXlab platform.
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Recent Advances in Electrocatalysts for Oxygen Reduction Reaction
Chemical Reviews, 2016Co-Authors: Minhua Shao, Qiaowan Chang, Regis ChenitzAbstract:The recent advances in electrocatalysis for oxygen reduction reaction (ORR) for proton exchange membrane fuel cells (PEMFCs) are thoroughly reviewed. This comprehensive Review focuses on the low- and non-Platinum electrocatalysts including advanced Platinum Alloys, core-shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts, and metal-free catalysts. The recent development of ORR electrocatalysts with novel structures and compositions is highlighted. The understandings of the correlation between the activity and the shape, size, composition, and synthesis method are summarized. For the carbon-based materials, their performance and stability in fuel cells and comparisons with those of Platinum are documented. The research directions as well as perspectives on the further development of more active and less expensive electrocatalysts are provided.
Charles J Oconnor - One of the best experts on this subject based on the ideXlab platform.
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magnetic properties of iron and iron Platinum Alloys synthesized via microemulsion techniques
Journal of Applied Physics, 2000Co-Authors: Everett E Carpenter, J Sims, J A Wienmann, Weilie L Zhou, Charles J OconnorAbstract:In this article, metallic iron, and iron/Platinum Alloys nanoparticles have been synthesized via chemical assembly and magnetically characterized. Fabrication of iron and iron/Platinum particles was achieved by reducing 0.1 M aqueous metal salts confined in the polar portions of inverse micelles of cetyltrimethylammonium bromide with borohydride. The dc susceptibility of a sample of 8 nm iron nanoparticles exhibits a blocking temperature of 54 K and coercivity of 200 G at 10 K. The presence of the gold coatings prevented oxidation and allowed the samples to be manipulated without additional precautions to prevent oxidation. Two iron/Platinum Alloys have been synthesized and verified by x-ray powder diffraction and transmission electron microscopy. Magnetic characterization is performed using superconducting quantum interference device magnetometry.