Effect of Alloy Composition and Crystal Face of Pt-Skin/Pt100–xCox [(111), (100), and (110)] Single Crystal Electrodes on the Oxygen Reduction Reaction Activity

Abstract

We have examined and compared for the first time the oxygen reduction reaction (ORR) activities at a series of (111), (100), and (110) faces of Pt100–xCox single crystals as a function of Co content x with rotating disk electrodes in air-saturated 0.1 M HClO4 solution. The low energy electron diffraction and low energy ion scattering indicated that the topmost surfaces of Pt–Co(111), (100), and (110) have well-defined (1×1) Pt-skin layers as a result of annealing in pure H2. Among the three faces examined, the effect of Co content was found to be the most dramatic for the (111) face: specifically, the jk values on the Pt-skin/Pt–Co(111) electrodes increased greatly as x increased and reached a maximum value at x = 27 atom %, which is ca. 27 times larger than that for pure Pt(111). On the Pt-skin/Pt100–xCox(110) electrodes, the jk values reached a maximum at x = 18 atom %, which is 4 times larger than that of pure Pt(110). Unlike other faces, the Pt-skin/Pt–Co(100) electrodes exhibited a weak dependence of...