An Investigation of PEFC Sub-Zero Startup: Influence of Initial Conditions and ResidualWater

Kurzfassung

Isothermal cold starts of polymer electrolyte fuel cells were performed at sub-zero temperatures and analyzed by means of neutron radiography in order to unravel the relation between the preconditioning of the cell and the cold start capability. It was found out that the initial humidification state of the membrane (determined by its resistance) has a clear correlation with the duration of the initial phase of the cold start, but not with the total duration of startup until cell failure. In the experimental setup the impact of realistic and commercial sealing solutions was taken into account by adding an edge channel. The impact of water accumulations in this region on the cold start capability was assessed. Liquid water located in the outer perimeter of a cell could be directly verified to freeze during cell cool down by a novel dual spectrum neutron radiography method. The amount of water accumulated in the outer cell perimeter showed some correlation with the total duration of the cold start. It was found out that residual water located in the edge channel can initiate freezing of a substantial part of the active area nearby.