Effect of through-plane polytetrafluoroethylene distribution in a gas diffusion layer on a polymer electrolyte unitized reversible fuel cell

The relationship between through-plan polytetrafluoroethylene (PTFE) distribution on a gas diffusion layer (GDL) and unitized reversible fuel cell (URFC) performance was investigated. Titanium (Ti) - felt was used for the oxygen-side GDL and treated with 10wt.% PTFE dispersion to enhance hydrophobicity. The dependence of PTFE distribution on the PTFE drying conditions was examined using scanning electron microscopy (SEM)-based energy dispersive X-ray spectroscopy (EDS) imaging. The EDS image maps revealed that the PTFE distribution strongly depended on the drying condition of the PTFE; drying under atmospheric pressure yielded a highly non-uniform PTFE distribution in the through-plane direction, whereas drying under vacuum pressure yielded a relatively uniform PTFE distribution. The cell performance of URFCs was then evaluated based on measured current-voltage characteristics during both electrolysis and fuel cell operation modes. Results verified that compared with non-uniform PTFE distribution, a uniform distribution in the Ti-felt GDL improved the fuel cell performance under the fully wet condition (relative humidity = 100%). By applying the Ti-felt GDL with uniform PTFE distribution in the through-plane direction, the current density at the cell voltage of 0.6 V was increased by a factor of about 1.9 compared with the Ti-felt with non-uniform PTFE distribution.