PEM fuel cells degrade over time. The loss of cell potential is the most obvious
symptom of degradation. Degradation may affect either one of the four major losses in fuel cells, namely activation polarization, ohmic losses, concentration polarization and hydrogen crossover losses. The report first addresses these symptoms, and then degradation mechanisms of different fuel cell components are discussed, namely catalyst and catalyst layer, membrane, and gas diffusion layer. For each of these some mitigation strategies are discussed. For each of degradation mechanism the key stressors are identified and standardized accelerated test protocols are presented. Experiments that were conducted at FESB with the goal of gaining practical experience and understanding of underlying degradation mechanisms. Two series of experiments were conducted with two of the most severe stressors, namely prolonged exposure to open circuit voltage, and potential cycling
