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Research paper : Basic materials research for the development of ubiquitous-energy devices (M. Kohyama et al.)−50−Synthesiology - English edition Vol.2 No.1 (2009) The deterioration test was conducted by activating the fuel cell under various conditions. By TEM, the increase of the diameter of the catalyst metal particles was observed, the preference dissolution of Ru from the Pt-Ru particles was detected, and the precipitation and growth of catalyst metal particles within the electrolyte film far from the electrode was observed, depending on the test condition (Fig. 6). The particle diameter distribution and particle space distribution changed by altering the type of gas supplied to the negative and positive electrodes and by changing the thickness of the electrolyte film. It was clarified for the first time, that such dissolution and precipitation behaviors of the catalyst metal particles were factors of the deterioration phenomena, along with oxidation of carbon material. The TEM observation of microscopic structures and deterioration of the electrode catalyst of a polymer-electrolyte fuel cell was done for the first time in the world (Table 1).On the other hand, first-principles calculation is important in understanding the function and nanostructure of the Pt/C electrode. We are working on first-principles calculations of basic interface reactions for various forms of Pt metals or clusters deposited on carbon (graphene sheet) (Fig. 7)[14]. The reactivity of the bond surface of the graphene sheet is small. The interactive (bonding) energy between Pt-C reaches maximum for single Pt atom, then decreases as the coordination number and size increase for Pt clusters, and reaches minimum for the crystal surface. Using this calculation data, it is possible to simulate the mesoscale structure of the Pt/C electrode. We obtained comparable results in the TEM observation, and this is important as theory of metal/inorganic nano-hetero interfaces[15].The above results were only possible with daily collaborations and discussions with the group that was actually creating the electrode catalyst for fuel cells and conducting the deterioration test.4.3 Mechanism of gold/oxide nano-hetero catalystsGold is generally inactive, but shows distinctive catalytic activities such as CO low temperature oxidation and water gas shift reaction (reaction to remove CO from hydrogen gas, CO + H2O CO2 + H2) when it is supported on the surface of oxides such as TiO2 and CeO2 in nano-particle form[16]. To clarify the mechanism of how inactive gold is activated should contribute to the development of designing technology of novel metal/inorganic nano-hetero catalysts. We have been engaging in the basic analysis combining TEM observation, surface science, and first-principles calculation, under close collaboration with the catalyst development group.In the Au/TiO2 system, the strong interaction between Au and TiO2 could be inferred since there is preferred orientation relationship at the interface observed by TEM. From surface science experiments such as SPM observation, it was found that the Au-TiO2 interaction is stronger in the reduced surface (Ti-rich surface) with oxygen deficiency compared to the normal stoichiometric surface of TiO2 (surface with equal amount of anion and cation). On the other hand, it was indicated from the first-principles calculation that the interfacial bond becomes much stronger when the interface is non-stoichiometric as Ti-rich or O-rich, revealing stronger orbital hybridization and electron transfer between Au and TiO2, which would affect the catalyst activities[17][18]. For further investigation, we conducted detailed observation of atomic arrangement at the interface using the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) (a method for obtaining the image of atomic column through high-angle scattered wave from atoms by scanning with focused electron beam), and succeeded for the first time in detailed observation that allowed the identification of the atomic columns. On the other hand, from the first-principles calculation of atomic and electronic structures of the interface based on such observation model, it was clarified that Ti-rich or O-rich interfaces might be stabilized according to the atmosphere, and that Ti-rich or O-rich interfaces have unique electronic states.Fig. 8 TEM observation of a Au/CeO2 catalyst system. Upper: High-resolution TEM image of a Au nano-particle boned on CeO2. Lower, left: HAADF-STEM observation of the same structure. Lower. Right: Analysis of inter-layer distances by the profile of integrated HAADF-STEM image intensity along each atomic layer.Table 1 Recent awards from academic societies and conferences. Position (nm)Intensity (arb. unts)00.51.01.52.02.53.0Satoshi Ichikawa, Japan Institute of Metals 2004 Fall Meeting, Best Poster Award (EM)Tomoki Akita, MRS 2004 Fall Meeting Poster Award (EM)Satoshi Ichikawa, MRS 2004 Fall Meeting Poster Award (EM)Shingo Tanaka, MRS-J 2004 Symposium Encouragement Award (Computation)Tomoki Akita, Catalysis Society of Japan Poster Award (EM)Shingo Tanaka, MRS-J 2005 Symposium Encouragement Award (Computation)Tomoki Akita, International Federation of Societies for Microscopy ICM-16 Poster Award (EM)Tomoki Akita, IUMRS-ICA 2006 Best Paper Award (EM)Koji Tanaka, Japan Institute of Metals, Metallographic Contest in Division B 1st Prize(EM)Jun Kikkawa, The 63th Annual Meeting of the Japanese Society of Microscopy, Poster Award (EM)Jun Kikkawa, The 14th International Meeting on Lithium Batteries, Most Excellent Poster Paper Award (EM)Tomoki Akita, ICC-14 Pre-Symposium, Best Poster Presentation Award (EM)FY 2004 FY 2005FY 2006FY 2007FY 2008

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