Effect of Wettability of Micro-porous Layer on Microscopic Water Transport Phenomena in PEFC

The wettability of the micro-porous layer (MPL) is attractive as a key to improve the performance of a polymer electrolyte fuel cell (PEFC). This paper directly observed the cross-sectional distribution of liquid water inside the cathode MPL to elucidate the effect of wettability of the MPL on microscopic water transport phenomena in the PEFC. The performances of cells with hydrophobic and hydrophilic MPLs were measured, and the internal water distributions of the MPLs were observed by using the freezing method and cryo-scanning electron microscope (cryo-SEM). The results show that the water exists inside the hydrophilic MPL as liquid even during the high temperature operation while no liquid water exists inside the hydrophobic MPL under the same condition. It is estimated that the hydrophilic MPL drains liquid water from the catalyst layer (CL) and promote liquid water transport through the MPL.