Neutron Imaging of Isothermal Sub-Zero Degree Celsius Cold-Starts of a Polymer Electrolyte Fuel Cell (PEFC)

Start-ups of a polymer electrolyte fuel cell (PEFC) isothermally maintained at subfreezing temperatures were visualized using dynamic in-plane neutron imaging. The results obtained strongly suggest that the water produced stays in liquid state for most of the cold-starts realized between-20°C and-10°C. The presence of super-cooled water is retained as assumption for explaining this. Moreover, the freezing of super-cooled water is thought to be responsible for the sudden water accumulation observed in the catalyst layer during the final voltage drop. This would confirm the hypothesis that the apparition of ice abruptly impedes the access of oxygen to the active site so that the voltage finally drops. More than 400 cold-starts were further realized without imaging. The widely spread and unpredictable working times obtained strongly support the fact that super-cooled water is rather the rule than the exception, at least at temperatures between-10°C and 0°C