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

The kinetically controlled area-specific activities, j(k), 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 H-2 atmosphere was clarified to consist of atomically flat terraces with the same atomic arrangement as the underlying crystal. At 25 atom%-Co, the j(k) value reached a maximum as high as 3.0 mA cm(-2) at 0.9 V 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 0.9 V in N-2-purged solution were nearly constant. (C) 2016 Elsevier B.V. All rights reserved.