成果報告書詳細
管理番号20090000000589
タイトル*平成20年度中間年報 固体高分子形燃料電池実用化戦略的技術開発 次世代技術開発 Pt基電極触媒モデルの実験的構築と表面分子挙動観察
公開日2010/3/13
報告書年度2008 - 2008
委託先名国立大学法人東北大学大学院
プロジェクト番号P05011
部署名燃料電池・水素技術開発部 燃料電池グループ
和文要約以下本編抜粋:1.研究開発の内容及び成果等 Pt及びその合金(Pt-X)は燃料電池電極触媒として多用される。しかし、Ptは希少でありまた資源も偏在しているため、その使用量削減と電極触媒能向上の両立が燃料電池の普及へ向けて急務の課題となっている。また、原料水素中の一酸化炭素のような極微量不純物が引き起こす電極表面被毒も問題となっており、耐被毒性に優れた触媒探索も主要課題の一つである。したがって、合金表面固有の格子構造が及ぼす電極触媒表面活性や被毒特性への影響に関する分子論的理解は高活性電極触媒開発の大前提となる。
英文要約Title: Experimental Fabrications and Molecular Behavior of Pt-based-Alloy Model Catalysts for fuel cells FY2008 Annual Report
From a catalytic perspective, numerous studies of Pt-based alloys have been undertaken to develop highly efficient, low-noble-metal-content electrode materials for fuel cells. Indeed, alloying of Pt with Ni,Co, etc. improve their catalytic activities of the oxygen reduction and hydrogen dissociation reactions. However, atomic arrangements and compositions of the outermost alloy surfaces remain as key issues for catalytic activities for the electrode. In this project, we construct an experimental set-up for observing dynamic behavior of molecules on the Pt-based alloy model catalysts and, then, investigate relations between the molecular behavior and the outermost surface structures by using infrared reflection absorption.
The electron diffraction patterns for the 343-K-deposited Ni and Co-deposited Pt(111) reveal Ni(Co) epitaxial growth. The CO exposure to the clean Pt(111) surface engenders linearly bonded and bridge-bonded CO-Pt bands at 2093 and 1850 cm-1. The 343-K-deposited Ni(Co)x/Pt(111) (x=deposition thickness) gives rise to a new band at around 2070-2060 cm-1 in addition to the CO-Pt(111) bands. The new band becomes prominent with increasing substrate temperatures during the depositions: Ni(Co) depositions at above ca. 700K result in a single and sharp absorption band at ~2080 cm-1. The electron diffraction patterns for the Ni(Co)-deposited Pt(111) at 343K reveal incommensurate higher-order extra spots surrounding integer spots originated from the substrate Pt(111). In contrast, the incommensurate pattern changes to its original six-fold symmetry for the 823(843)-K-deposited Ni(Co)x/Pt(111). We therefore assign the ~2080 cm-1 band to CO adsorption on the outermost Pt layer ("Pt skin") formed through the surface segregation of substrate Pt atoms: the Pt skin outermost surface can be generated through thermal annealing of the 343K-deposited Ni(Co)x/Pt(111) surfaces at above 800K. The Pt skin was formed for Cox/Pt(100)-hex surface systems, although the formation temperatures were lower than those for the Cox/Pt(111). The results might come from difference in atomic densities for the (111) and (100) substrate surfaces.
As for D2O adsorption on the clean Pt(111), three absorption bands ascribable to O-D stretch vibrations for a first-adsorption layer of D2O, ice-islands of D2O on the first layer and non-hydrogen-bonded D2O at outermost islands surface are located respectively at 2473, 2553 and 2723 cm-1. On the Pt skin surface (823K-deposited Ni0.3nm/Pt(111)), the first-layer band appears at 2495 cm-1. The O2 exposure to the clean Pt(111) causes dissociative adsorption of O2 to form p(2x2)-O adsorption structure. In contrast, O2 exposure to the Pt skin surface resulted in no regular adsorption structure. The IRRAS spectral measurements indicate different D2O adsorption behaviors on the O2 pre-exposed Pt(111) and Pt skin surfaces. The above-mentioned results suggest that Ni or Co incorporation into the Pt substrate modifies the surface properties, thereby influencing the catalytic activities of the Pt-based alloys.
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