Abstract The performance of a ten-cell 50 cm 2 100 W polymer electrolyte membrane fuel cell (PEMFC) stack was evaluated under dynamic load cycling conditions utilizing the 2005 United States Department of Energy durability test protocol for PEFCs. An enhancement of performance was observed during the first 240 h, while an irreversible degradation of stack performance was observed after 480 h (∼4700 cycles). In particular, the stack voltage at 100 mA cm − 2 was decreased by 2.8% after 480 h and individual cell voltage was decreased up to 8%. An analysis of cell overpotentials for activation, Ohmic, and mass transport losses revealed that the predominant source of performance degradation was due to kinetic losses. The loss of catalyst utilization was estimated to be 39% based on the electrochemically active surface area (ECSA) measurements. Electron microscopic images of some of the cells showed growth in cathode Pt particle size from 5.3 to 6.2 nm. However, these microscopic images did not show any membrane damage or electrode thinning. Severe degradation of both the anode and cathode silicone gasket seals was observed during the durability test.