The enhanced reduction of hydrogen peroxide (H2O2) and electrochemical current oscillatory phenomena during its reduction were observed on a mercury (Hg) adatom-modified An polycrystalline electrode in alkaline, acidic and neutral aqueous solutions. The enhancement of the H2O2 reduction was observed in the potential region from -0.2 to -0.6 V (vs. Ag \ AgCl \ KCl (sat.)). The enhanced reduction of H2O2 was independent of the pH of the solution in the pH region from 3 to 10. The current oscillation occurred in the negative differential resistance potential region (-0.4 to -0.6 V). Its amplitude and the potential width in which the current oscillation was observed depended on the surface coverage of Hg on the Au electrode and the kind of anions in the solution. The observed enhancement of the reduction of H2O2 and the current oscillation were explained by taking into account the local pH increase near the Hg adatom-modified Au electrode as well as the electrode potential-dependent electrocatalytic behavior of the adsorbed species of OH-(OHad) on the electrode surface. (C) 2003 Elsevier Science B.V. All rights reserved.