Structural effects in electrocatalysis. Oxygen reduction on the Au (100) single crystal electrode

Abstract

The kinetics of O2 reduction on the Au (100) single crystal electrode have been examined in alkaline electrolytes using the rotating dise method. A comparison has been made with the Au (110) and Au (111) surfaces. The quality of the surfaces has been determined by Auger electron spectroscopy and LEED. A pronounced effect of the crystallographic orientation on the kinetics and mechanism of O2 reduction has been found. The half-wave potential for the Au (100) face is the most positive. O2 reduction, only on this surface, proceeds with the exchange of four electrons in a "series" pathway in the potential region of AuOH formation. The cathodic and anodic kinetic data for the O2/HO2- and HO2-/OH- couples support the mechanism O2+e-→ O2- (ads) 2 O2- (ads)+H2O HO2-+O2+OH- Further reduction of HO2- is controlled by an initial one-electron transfer: HO2-+e-+H2O→ 2 OH-+OH(ads) OH(ads)+e- OH- The OH species adsorbed on the Au (100) face appears considerably discharged. Such a surface apparently interacts more strongly with O2, O2- and HO2-, and is probably the origin of the high activity of the Au (100) face for O2 and HO2- reduction.