Structural Effects on the Fuel Cell Reactions on the Stepped Surfaces of Platinum and Palladium

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Structural effects on the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) have been studied on the high index planes of Pt and Pd in 0.1 M HClO4. The exchange current density jo of the HOR increases with the increase of the step atom density dS from n = ∞ to 9 on(n−1)(111)-(110), n(111)-(100), n(100)-(111) and n(100)-(110) surfaces of Pt, where n shows the number of the terrace atomic rows. On the surfaces with n ≤ 9, however, the values of j0 do not depend on dS. These facts support that the step is the active site for the HOR on Pt electrodes, however, only part of the step atoms contributes to the HOR. Pt electrodes of (n−1)(111)-(110) series have the highest activity for the HOR. The activity for the ORR increases with the increase of the terrace atom density dT on Pd electrodes. The step atoms do not affect the ORR. Pd(100) has the highest activity for the ORR. The specific activity of Pd(100) is 4.2 times as high as that of the standard Pt catalyst (TEC10E50E). The mass activity of Pd surfaces covered with monolayer of Pt (Pt/Pd(hkl)) is 7 times as high as that of TEC10E50E.