Membrane failures at catalyst layer edges in proton exchange membrane fuel cell (PEMFC) membrane electrode assemblies (MEAs) were investigated using MEAs with segmented electrodes. A mathematical model was developed to predict the potential distribution at the edge of the MEA with misaligned electrodes. Control experiments were performed using an accelerated membrane durability test protocol and significant membrane degradation was observed in the region where the cathode overlaps the anode. The model-experiment comparisons suggest that a high cathode potential contributes to the membrane failure. A dependence of membrane degradation on relative humidity (RH) was observed in the experiments, regardless of the electrode overlap. The observed membrane degradation in the overlap region of MEAs with an anode catalyst overlap, run at low RH, is not explained by the model and needs further investigation. (c) 2007 The Electrochemical Society.