Visualization of Water Transport and Freezing Process in a Gas Diffusion Layer of PEFC During Low Temperature Operation

During low temperature operation of polymer electrolyte fuel cell (PEFC), water flooding in a cathode electrode is a critical barrier to achieve high power density, because liquid water condensed in the porous gas diffusion layer (GDL) blocks oxygen transport to the active reaction sites. Furthermore, during startup below the freezing point, liquid water in the cathode GDL or on the catalyst layer (CL) surface is frozen and the cell voltage is suddenly decreased. In this study, we experimentally investigate liquid water transport and freezing process in a cathode GDL of PEFC at low temperature operations using an optical diagnostic. The results showed that liquid water behavior and ice formation at the cathode electrode are largely affected by operating parameters such as current density and ambient temperature. Furthermore, in order to prevent water flooding, we propose the structure of cathode GDL that has several slits for water removal. With this cathode GDL structure, it was found that liquid water accumulated inside the cathode electrode is rapidly removed and cell voltage is improved.