The durabilities of membrane-electrode assemblies based on sulfonated polyimide membranes containing triazole groups (SPI-8) were evaluated at various cell currents in polymer electrolyte fuel cells. The electrochemical properties and drain water collected from the anode and cathode were monitored during the test, followed by post-test analyses of the membranes. The percentages remaining of the original weight-averaged molecular weight (M(w))(orig) of the SPI-8 membranes after not only an open circuit potential (OCP) test but also a high current test were lower than that after a low current test, which implied that the OCP test accelerated the oxidative degradation of the SPI-8 membrane due to the generation of radical species, and the high current test accelerated the hydrolytic degradation of the membrane due to the increased water generation. Also, during the durability tests, decomposition products of the SPI-8 membranes adsorbed specifically on the cathode catalysts, which caused decreases in the reduction charge of the catalyst surface oxide (Q(red)), as determined from cyclic voltammograms. In addition, the mass activity, evaluated from the current-potential (I-E) curves and the Q(red) showed a good correlation, i.e., the adsorption of decomposition products on the cathode catalyst led to decreased performance. (C) 2011 Elsevier Ltd. All rights reserved.