Transport properties and fuel cell performance of sulfonated poly(imide) proton exchange membranes

Selective sulfonated poly(imide)s with high proton conductivity and low methanol permeability were tested for their performance as proton exchange membranes in direct methanol fuel cells (DMFC). The proton to methanol transport selectivity of the poly(imide) membranes correlated well with the self-diffusion coefficients of water in the membranes as determined by pulsed-field gradient nuclear magnetic resonance. The poly(imide) membranes showed improved fuel cell device performance, however high interfacial resistance between the membranes and electrodes decreased the membrane electrode assembly (MEA) conductivity to methanol crossover selectivity, likely due to the use of NAFION ^®-based electrodes. The maximum power densities of SPI-50, SPI-75, and NR-212 based MEAs were 75, 72, and 67 mW cm ^-2, respectively, with a methanol feed concentration of 2 M at a cell temperature of 60 °C.