Cold-Start of a PEFC Visualized with High Resolution Dynamic In-Plane Neutron Imaging

Cold-starts of a polymer electrolyte fuel cell (PEFC), isothermally maintained at various subfreezing temperatures, were visualized using high resolution dynamic in-plane neutron imaging. The results obtained aim to bring new knowledge about the water accumulation mechanisms leading to the voltage drop usually observed in isothermal mode after a given working time, also called voltage failure. In particular, the data presented should be useful for comparison to simulation predictions provided by modeling studies. As main result, water in a condensed phase was observed to accumulate not only in the membrane-electrode-assembly (MEA), but also in the cathode gas diffusion layer (GDL) at −15°C and even in the cathode gas channels at −10°C. Moreover, approximately 400 cold-starts were realized without neutron imaging and revealed stochastic distributions of working times. The presence of water in super-cooled state is discussed and finally retained as only valid explanation of the results obtained. Additionally, the sudden freezing of super-cooled water is thought to cause the rapid water accumulation observed in the MEA during the voltage failure.