This study examines the effect of hydrogen peroxide (H2O2) on the open-circuit voltage (OCV) of a proton exchange membrane fuel cell (PEMFC) and the reduction of H2O2 in the membrane using a ruthenium/carbon catalyst (Ru/C) at the anode. Each cathode and anode potential of the PEMFC in the presence of H2O2 is examined by constructing a half-cell using 1.0 M H2SO4 solution as an electrolyte and Ag/AgCl as the reference electrode. H2O2 is added to the H2SO4 solution and the half-cell potential is measured at each H2O2 concentration. The cathode potential is affected by the H2O2 concentration while the anode potential remains stable. A Ru catalyst is used to reduce the level of H2O2 formation through O-2 cross-over at the interface of a membrane and the anode. The Ru catalyst is known to produce less H2O2 through oxygen reduction at the anode of PEMFC than a Pt catalyst. A Ru/C layer is placed between the Nafion (R) 112 membrane and anode catalyst layer and the cell voltage under open-circuit condition is measured. A single cell is constructed to compare the OCV of the Pt/C only anode with that of the Ru/C-layered anode. The level of hydrogen cross-over and the OCV are determined after operation at a current density of 1 A cm(-2) for 10 h and stabilization at open-circuit for 1 h to obtain an equilibrium state in the cell. Although there is an increase in the OCV of the cell with the Ru/C layer at the anode, excessive addition of Ru/C has an adverse effect on cell performance. (c) 2007 Elsevier B.V. All rights reserved.