Nafion membranes with a porous surface

Nafion membranes with a monolayer of pores on one surface (P-Nafion) were prepared by casting a Nafion SE20092 dispersion containing ortho-dichlorobenzene. The pores are not connected but provide 2μm large openings, increasing the membrane surface by one dimension. The thickness of the porous layer is typically <5μm. In catalyst coated membranes the catalyst layer penetrated the pores well. The effect on the performance of a polymer electrolyte fuel cell (PEFC) was investigated at 95°C. The porous layer formed the cathode, to enhance water back diffusion. After 24h equilibration, 30-35μm thick P-Nafion gave 10-16% higher current density, reaching 858mA/cm² at 0.4V and 50% rh. N211 and P-Nafion equilibrated for 8min showed peak power densities of 56 and 208mW/cm² under anhydrous conditions, respectively, indicating that drying processes are slowed down. The stability of a MEA was tested for 240h at 0.4V and 50% rh (anode/cathode), without observable degradation. Under fully humidified conditions, the electrochemical surface area (ECSA) increased 40% in comparison to a N211 based MEA. At 65°C, the ECSA more than doubled, showing 141m²/g Pt. Also influence of the pores on water transport through a membrane and stability against membrane-electrode delamination were considered.