Electrooxidation of H 2, CO and H 2/CO on well-characterized Au(1 1 1)–Pd surface alloys

Abstract

Electroooxidation of H 2, CO and 1000 ppm CO/H 2 oxidation was studied on two well-defined Au(1 1 1)–Pd surface alloys prepared and characterized in ultrahigh vacuum. Preparation was done using Pd vapor deposition. Characterization was done using Auger electron spectroscopy and low-energy ion scattering. After deposition, Pd always (partly) diffuses into the Au(1 1 1) crystal and forms stable surface alloys. Two surface alloys with Pd surface concentrations of ca. 38 and 65% were transferred into the electrochemical environment. Three major findings from the electrocatalytic study can be summarized as follows: (i) hydrogen oxidation on Au(1 1 1)–Pd surface alloys is ca. one order of magnitude slower as compared to Pt(1 1 1); (ii) Au(1 1 1)–Pd surface alloys show finite and stable activity for the continuous oxidation of pure CO at potentials below 0.2 V with a positive reaction order with respect to solution phase CO; (iii) the oxidation of 1000 ppm CO in H 2 at potentials below 0.2 V is governed by the slow H 2 oxidation kinetics and the unfavorable partial pressure dependence. At potentials above 0.2 V, however, the steady-state activity of a high-surface area Au–Pd catalyst can be reached.