Mechanism of CO tolerance at Pt-alloy anode catalysts for polymer electrolyte fuel cells

We have found an excellent CO tolerance at Pt anodes alloyed with the secon d metals in spite of the formation of Pt skin layer (ca. 1-2 nm in thicknes s) over the alloy surfaces due to the dissolution of the second metals and proposed a new mechanism for the catalysis. In this study, ATR-SEIRAS, coup led with CV measurement, was used to observe the oxidation process of adsor bed CO on the typical Pt-Fe alloy. The ahoy anode exhibits a lower saturate d coverage with CO than that of pure Pt Linear CO is observed predominantly on the alloy electrode, differing from both of linear and bridged CO besid es COOH on the pure Pt The negative-shift of the wavenumber for the linear CO stretching and the broadening of the half-wave width at the ahoy also in dicate the weakening of metal-CO banding and the increased mobility of the adsorbed CO, respectively. As a presumable effect of the electronic structu re change at the Pt skin, the dissociation/oxidation of adsorbed water as w ell. as a formation of adsorbed HOOH species are clearly observed beyond 0. 6 V in the electrolyte solution without CO. The mechanism of CO tolerance a t the Pt skin on top of the alloy surface with an increased d-band vacancy, proposed previously by us, is supported by the present SEIRAS data as the "detoxification mechanism", featured by an increased mobility of the adsorb ed CO with suppressed coverage.