Effect of metal ad-layers on Au(111) electrodes on electrocatalytic reduction of oxygen in an alkaline solution

Oxygen reduction reaction was investigated in an O-2-saturated 0.1 M NaOH solution at Au(111) single crystal electrodes modified with various ad-metals (Cu, Ag and Bi) by underpotential deposition (upd). An increase in the catalytic activity was observed upon deposition of metal ad-atoms submonolayer for all prepared electrodes: Cu ad-layer was found, for the first time, to show a very interesting positive catalytic effect in contrast with reported data in acidic media, i.e., an apparent four-electron reduction process due to considerable enhancement of the disproportionation of hydrogen peroxide on the 1/3 monolayer (ML) Cu-modified Au(111) electrode. An interesting catalytic activity was also obtained at the 1/3 ML Ag ad-atoms modified Au(1 11) electrode, where a significant increase in reduction current was shown to suggest a four-electron reduction of oxygen to water. The Bi ad-atoms modified Au(111) electrode, Bi(2 x 2)-Au(111), showed positive catalytic activity by a limiting current of twice higher than at a bare Au(111) electrode with peak potential at ca. -0.38 V vs. Ag|AgCl|KCl(sat). (C) 2004 Elsevier B.V. All rights reserved.