789 research outputs found
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Novel Intermetallic Catalysts to Enhance PEM Membrane Durability
The research examined possible sources of degradation of platinum based anode catalysts under long term use. Scientists at the United Technologies Research Center had shown that the anode as well as the cathode catalysts degrade in hydrogen fuel cells. This goal of this research was to see if mechanisms of anode degradation could be understood using forefront electrochemical techniques in an aqueous system. We found that this method is limited by the very low levels of impurities (perhaps less than a part per trillion) in the electrolyte. This limitation comes from the relatively small catalyst surface area (a few sq cm or less) compared to the electrolyte volume of 10 to 25 ml. In real fuel cells this ratio is completelyreversed: high catalyst surface area and low electrolyte violume, making the system much less sensitive to impurities in the electrolyte. We conclude that degradation mechanisms should be studied in real fuel cell systems, rather than in ex-situ, large electrolyte volume experiments
Properties of HxTaS2
The preparation of Hx TaS2 (0 \u3c x \u3c 0.87) is described. The compounds are only marginally stable at room temperature, slowly evolving H2S and H2 (and possibly Hp in air). Magnetic susceptibility data show that a low temperature transformation in 2H ... TaS2 (at so•K) is suppressed with the addition of hydrogen, and· at the same time the superconducting transition temperature T c rises from 0.8 to ~4.2•K at x = 0.11. Heat capacity measurements near this concentration show the superconductivity to be a bulk effect. Finally, by correlation of this data with susceptibility and T c measurements in other intercalation compounds, we suggest that the rise of T c (at low electron transfer) is due to suppression of the low temperature transformation and not due to an excitonic mechanism of superconductivity
Alkaline Earth Metal Oxyhalides Revisited -Syntheses and Crystal Structures of Sr 4 OBr 6 , Ba 4 OBr 6 and Ba 2 OI 2
Single crystals of the compounds Ca 4 OCl 6 , Sr 4 OBr 6 , Ba 4 OBr 6 , and Ba 2 OI 2 were obtained by solid-state reactions. The crystals of Ba 2 OI 2 are transparent and colorless and isopointal to K 2 ZnO 2 adopting the orthorhombic space group Ibam (no. 72, Z = 4) with the cell parameters a = 747.20(9), b = 1392.02(18), and c = 678.12(9) pm. Sr 4 OBr 6 and Ba 4 OBr 6 are isotypic to Ba 4 OCl 6 (or isopointal to K 6 ZnO 4 ) and crystallize in the hexagonal space group P6 3 mc (no. 186, Z = 2) exhibiting the cell parameters a = 982.20(4) and c = 750.41(7) pm for Sr 4 OBr 6 and a = 1030.10(2) and c = 785.92(4) pm for Ba 4 OBr 6 . In the ternary systems Ca-O-X (X = Cl, Br or I) the only compound found other than the starting materials was the already known Ca 4 OCl 6 which is also isotypic to Ba 4 OCl 6 crystallizing in the hexagonal space group P6 3 mc (no. 186, Z = 2) with the cell parameters a = 903.30(6) and c = 683.27(8) pm
Cornell Fuel Cell Institute: Materials Discovery to Enable Fuel Cell Technologies
The discovery and understanding of new, improved materials to advance fuel cell technology are the objectives of the Cornell Fuel Cell Institute (CFCI) research program. CFCI was initially formed in 2003. This report highlights the accomplishments from 2006-2009. Many of the grand challenges in energy science and technology are based on the need for materials with greatly improved or even revolutionary properties and performance. This is certainly true for fuel cells, which have the promise of being highly efficient in the conversion of chemical energy to electrical energy. Fuel cells offer the possibility of efficiencies perhaps up to 90 % based on the free energy of reaction. Here, the challenges are clearly in the materials used to construct the heart of the fuel cell: the membrane electrode assembly (MEA). The MEA consists of two electrodes separated by an ionically conducting membrane. Each electrode is a nanocomposite of electronically conducting catalyst support, ionic conductor and open porosity, that together form three percolation networks that must connect to each catalyst nanoparticle; otherwise the catalyst is inactive. This report highlights the findings of the three years completing the CFCI funding, and incudes developments in materials for electrocatalyts, catalyst supports, materials with structured and functional porosity for electrodes, and novel electrolyte membranes. The report also discusses developments at understanding electrocatalytic mechanisms, especially on novel catalyst surfaces, plus in situ characterization techniques and contributions from theory. Much of the research of the CFCI continues within the Energy Materials Center at Cornell (emc2), a DOE funded, Office of Science Energy Frontier Research Center (EFRC)
Cosputtered composition-spread reproducibility established by high-throughput x-ray fluorescence
We describe the characterization of sputtered yttria-zirconia composition spread thin films by x-ray fluorescence (XRF). We also discuss our automated analysis of the XRF data, which was collected in a high throughput experiment at the Cornell High Energy Synchrotron Source. The results indicate that both the composition reproducibility of the library deposition and the composition measurements have a precision of better than 1 atomic percent
Transport and Magnetic Properties of FexVse2 (x = 0 - 0.33)
We present our results of the effect of Fe intercalation on the structural,
transport and magnetic properties of 1T-VSe2. Intercalation of iron, suppresses
the 110K charge density wave (CDW) transition of the 1T-VSe2. For the higher
concentration of iron, formation of a new kind of first order transition at
160K takes place, which go on stronger for the 33% Fe intercalation.
Thermopower of the FexVSe2 compounds (x = 0 - 0.33), however do not show any
anomaly around the transition. The intercalation of Fe does not trigger any
magnetism in the weak paramagnetic 1T-VSe2, and Fe is the low spin state of
Fe3+.Comment: 7 pages, 8 figures, 2 table
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