The lifetime of PEM fuel cells is limited due to degradation of its components, which depend on material choice and operational conditions. A stack can also suffer from off- spec conditions due to system failures, like: 1. Malfunctioning of the gas humidifying hardware, resulting in (local) drying out of the membrane; 2. Gas accumulation in the cooling circuit causing a hotspot; 3. (local) fuel or oxidant starvation resulting from a malfunctioning air supply system, a gas leakage, or a (partial) blockage of the gas supply by water droplets. The impact of these off-spec conditions on an MEA is studied using a large area (400 cm2) cell while monitoring the current density distribution over 864 individual spots of the cell. This monitoring technique helps to identify the places of the MEA that suffer most from off- spec operation, for subsequent post test analysis by SEM and TEM. Operation of the cell at a fixed current density without humidifying the incoming air, having humidified hydrogen in counter flow, shows a gradually decreasing local current density at the cathode inlet region. In time this region also increases, while at the same time the cell voltage decreases. Decreasing the anode or cathode stoichiometry from 2 down to 1 results in a change of the current density distribution. The effect is largest at the cathode. Lowering of the air stoichiometry results in tilting of the current density distribution, more and more current is produced at the cathode inlet region. Upon lowering of the anode stoichiometry only a minor change in distribution is observed until the stoichiometry is close to 1. The effect of operation at stoichiometries below 1 will also be presented in combination with post-test analyses.
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