The durability of proton exchange membrane (PEM) fuel cells remains a challenging issue for their long term operational use. Degradation of the PEM related to dissolution of the adjacent catalyst and redeposition into the PEM significantly reduces cell efficiency. We investigate the effects of platinum (Pt) dispersions intended to simulate the re-deposited catalyst on the mechanical durability of the PEM. The bulge technique was applied to characterize the mechanical properties of PEMs simulating pressure loading on fully hydrated membranes in fuel cells. The results showed that with increasing Pt dispersion concentration the stiffness of the PEMs increased, and the membranes became less ductile and inclined to fracture at lower stresses under pressure loading. We also used the out-of-plane tearing test to characterize membrane fracture behavior which revealed the harmful effects of Pt dispersion on the fracture resistance under different environmental conditions. Deterioration in fracture resistance was explained in terms of the Pt distribution and aggregation as defects inside the membranes as characterized by electron microscopy. Fracture was shown to initiate preferentially at the interface of Pt particles and the polymer matrix, and propagate through the defect regions in polymer with lower energy, thus reducing the overall fracture resistance of the PEM. (C) 2011 Elsevier B.V. All rights reserved.