In Polymer electrolyte membrane fuel cells (PEFCs), freezing of produced water induces the extreme deterioration of cell performance below zero. This phenomenon is a serious problem in cold regions and is needed to be solved to achieve the practical use of PEFCs. In this study, we investigated ice distribution at the cold start in a PEFC using an optical microscope and a CRYO-SEM to clarify the freezing mechanism. The observation results showed that the cold start at −10°C makes ice at the interface between the cathode catalyst layer (CL) and the micro porous layer of gas diffusion layer. Little ice was, however, observed in the cold start at −20°C, which indicated the ice formation inside the CL. The CRYO-SEM observation was conducted at −20°C to investigate the ice formation inside the CL, and this identified the effects of the current density and the cathode gas species on the ice distribution.

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