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 2 μm large openings, increasing the membrane surface by one dimension. The thickness of the porous layer is typically <5 μm. 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 24 h equilibration, 30–35 μm thick P-Nafion gave 10–16% higher current density, reaching 858 mA/cm2 at 0.4 V and 50% rh. N211 and P-Nafion equilibrated for 8 min showed peak power densities of 56 and 208 mW/cm2 under anhydrous conditions, respectively, indicating that drying processes are slowed down. The stability of a MEA was tested for 240 h at 0.4 V 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 141 m2/g Pt. Also influence of the pores on water transport through a membrane and stability against membrane–electrode delamination were considered.