| Abstract
| - To clarify the CO-tolerant mechanism at Pt-based alloy anode catalysts, surface-enhanced infrared reflection−absorption spectroscopy with the attenuated total reflection technique (ATR-SEIRAS), coupled with CVmeasurement, was used to observe the oxidation process of adsorbed CO on a typical Pt−Fe (Pt−Fe =0.27/0.73) alloy. The alloy electrode exhibits a lower saturated coverage of CO (θCO = 0.55) than that ofpure Pt (θCO = 1.0). The dominating linear CO is observed around 2000 cm-1 when the equilibrium adlayerof CO covers the alloy electrode; however, linear and bridged CO and also COOH were found at the pure Ptelectrode at the same CO coverage in the non-steady-state. On the basis of our previous results that a Pt skinis formed during the repetitive potential cycling due to the dissolution of Fe on the alloy surface and the skinexhibits less electronic density in the d band, it can be explained that the lowered linear CO coverage andalmost no bridged CO are obtained as the result of the lowered back-donation of d electrons from the Pt skinto adsorbates on the alloy surface. The wavenumber shift of the linear CO stretching to a lower value at thealloy, which is not simply predicted by the lowering of the back-donation of the d electron, is ascribed to theweakening of the C−Pt bond. As a presumable effect of the electronic structure change at the Pt skin, thedissociation−oxidation of adsorbed water as well as a formation of adsorbed HOOH species are clearly observedbeyond 0.6 V in the electrolyte solution without CO, which is different from that at the pure Pt electrode.Carbonate species can also be detected around 1300−1450 cm-1, which are possibly produced by the surfacereaction of CO2 with water.
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