Feasibility of using thin polybenzimidazole electrolytes in high-temperature proton exchange membrane fuel cells

The use of thin polybenzimidazole membranes in high-temperature polymer electrolyte membrane fuel cells is explored. Membranes in thickness of 10–40 μm are prepared, doped and characterized, including fuel cell test. High molecular weight polymers enable fabrication of membranes as thin as 10 μm with sufficient mechanical strength. The thin membranes, upon acid doping, exhibit comparable conductivity and hence decreased ohmic resistance. Membrane electrode assemblies with thin membranes down to 10 μm show slightly lower open-circuit voltages than that for reference 40 μm but all above 0.97 V. This is in good agreement with the hydrogen permeability measurements, which show a value around 10⁻¹² mol cm⁻¹ s⁻¹ bar⁻¹, corresponding to a crossover current density of <1 mA cm⁻². The acid transferred from the membrane to the catalyst layer seems constant, as the iR-free polarization plots are nearly the same for membranes of varied thicknesses. The acid remaining in the membrane after the break-in period is estimated, showing an acid inventory issue when thin membranes are used. This is verified by using the membranes of higher acid doping levels.