Unprecedented dependence of the oxygen reduction activity on Co content at Pt Skin/Pt–Co(111) single crystal electrodes

Abstract

The kinetically controlled area-specific activities, jk, for the oxygen reduction reaction (ORR) were evaluated at well-defined Pt-skin/Pt100−xCox(111) single crystal electrodes as a function of Co content by use of the rotating disk electrode method. The Pt-skin layer formed by annealing under a pure H2 atmosphere was clarified to consist of atomically flat terraces with the same atomic arrangement as the underlying crystal. At 25 atom%-Co, the jk value reached a maximum as high as 3.0mAcm−2 at 0.9V vs. RHE, which is ca. 25 times larger than that on pure Pt(111). Such an enhanced ORR activity of Pt-skin/Pt–Co(111) electrodes cannot be explained on the basis of decreased OH poisoning, because the surface oxidation charge densities measured at 0.9V in N2-purged solution were nearly constant.