Recoverable voltage loss was observed for a PEM fuel cell due to membrane chemical degradation under open circuit voltage (OCV) conditions. The anion analysis of the fuel cell effluent water, collected during both the OCV hold and voltage recovery stages, indicates that sulfate release rate is much higher during recovery than that during the OCV hold. The surge in sulfate anion release occurs simultaneously with the recovery of fuel cell voltage. It was found that the reversible voltage loss, and concurrent sulfate release rate during voltage recovery, is lower for Ce-mitigated NRE211 membrane compared to as-received membrane. The recoverable voltage loss is proposed to be mainly due to the sulfate anion generated by membrane chemical degradation adsorbing onto the platinum catalyst surface. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.063207jes] All rights reserved.