成果報告書詳細
管理番号100013129
タイトル平成19年度-平成20年度成果報告書 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 高活性な構造規制表面と金属ナノ微粒子触媒の研究開発
公開日2009/3/27
報告書年度2007 - 2008
委託先名国立大学法人千葉大学
プロジェクト番号P05011
部署名燃料電池・水素技術開発部
和文要約(1)水素酸化反応を活性化するPt高指数面の研究n(111)-(111),n(100)-(110),n(100)-(111)系列のPt高指数面を用い,水素飽和した0.1MHClO4中のボルタモグラムから,水素酸化反応の交換電流密度j0を求めた。25℃では,テラス原子列数nが9の面までステップ原子密度の増加に応じてj0は上昇するものの,nが9以下ではj0は一定となった。-5℃-45℃の間でj0を測定しアレニウスプロットを取ることで,水素酸化反応の活性化エネルギーと頻度因子を求めた。活性化エネルギーはステップ原子密度の増加とともに単調に減少し,ステップが反応活性を向上させている傾向を示している。その反面,頻度因子はステップ原子密度の増加とともに減少し,nが9以下でほぼ一定となった。以上のことは,水素酸化反応においてステップが活性サイトであるものの,水素酸化に関与するのは一部のステップ原子のみであることを示す。(2)酸素過電圧低下させる表面構造の研究Pd基本指数面の酸素還元活性を,酸素還元電流の立ち上がり電位で評価すると,Pd(110)
英文要約(1) Pt high index planes enhancing the activity of hydrogen oxidation reaction Exchange current densities j0 of the hydrogen oxidation reaction have been measured on n(111)-(111), n(100)-(110) and n(100)-(111) surfaces of Pt in 0.1 M HClO4 saturated with hydrogen. The values of jo increase with the increase of the step atom density on the surfaces with n>9 on all the series, but they do not depend on the step atom density on the surfaces with n-9. The values of j0 have been measured between -5 and 45°C. Activation energies decrease with the increase of the step atom density, showing step sites enhance the activity of hydrogen oxidation reaction. However, pre-exponential factors drop with the increase of step atom density, becoming almost constant on the surfaces with n-9. These results show that step atoms are active sites for the hydrogen oxidation reaction, but not all the step atoms are related with the hydrogen oxidation. (2) Surface structures enhancing the activity of oxygen reduction reaction The onset potentials of the oxygen reduction reaction strongly depend on the crystal orientation on the low index planes of Pd in 0.1 M HClO4, giving activity series: Pd(110) < Pd(111) < Pd(100). This series completely differs from that on Pt electrodes: Pt(100) < Pt(111) < Pt(110). Pd(100) has higher activity for the oxygen reduction than Pt(110). The oxygen reduction reaction has been also studied on n(100)-(111) series of Pd. The onset potentials of oxygen reduction do not depend on the crystal orientation between n=3 and ∞. The activity of oxygen reduction drops at n=2. The (100) terrace with the terrace atomic rows more than 3 is the active site for the oxygen reduction on Pd. Oxygen reduction reaction has been studied on monolayer Pt/Pd(hkl). Pt/Pd(111) and Pt/Pd(110) have higher activity for the oxygen reduction than bare surfaces, however, the activity of Pt/Pd(100) becomes lower than Pd(100). The activity for the oxygen reduction reaction are estimated using the current density at 0.90 V(RHE). Following activity series is obtained: Pt(110) - Pt/Pd(100) < Pt/Pd(111) - Pt/Pd(110). Pd electrodes covered with monolayer of Pt have the activity for the oxygen reduction as high as genuine Pt electrodes. Ag electrode is the core of model core shell electrodes. Oxygen reduction reaction has been studied on the low index planes of Ag in 0.01 M NaOH, giving the activity series Ag(100) < Ag(110) - Ag(111). (3) AFM of shape controlled Pt nano-particles in electrochemical environments Real structure of cubic Pt nano-particle (~10 nm) has been successfully imaged in electrochemical environments with the use of atomic force microscopy (AFM). The cubic nano-particles are supported on a polished Pt plate. The electrolytic solution is 0.1 M NaClO4. The shape of the cubic nano-particles is unchanged up to the onset potential of the oxygen evolution (1.7 V(RHE)). The upper terrace of the nano-particle begins to be dissolved at 2.1 V(RHE).
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