The detaching behavior of catalyst layers in membrane electrode assembly (MEA) for PEM fuel cells could affect the lifetime of both catalyst layers and membranes. However, this issue is always neglected. Therefore, the study of detaching behavior of catalyst layer is very conducive to investigate the failure mechanism of fuel cells. The detaching of catalyst layers was simulated by dipping membrane electrode assemblies (MEAs) into H(2)O(2) solution with or without Fe(2+). We observed the presence of detaching of catalyst layers and found the varied detaching behaviors with different accelerated testing solutions: a layered-type detaching behavior is shown for the catalyst layer treated with 30% H(2)O(2) solution, whereas a crack-like detaching behavior in the case of 30% H(2)O(2) solution with Fe(2+) species (or Fenton's test). At the same time, the layered-type detaching of catalyst layers has a higher detaching rate than the crack-like detaching. These detaching behaviors should have an inherent link to degradation of recast-ionomer (Nafion) films in catalyst layers. In addition, the effect of detaching behaviors of catalyst layers on the lifetime of fuel cells has been studied by hydrogen crossover measurement, and shows that, for the crack-like detaching, the membrane has a shorter lifetime than that for the layered detaching. (c) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.