Direct methanol fuel cell membranes from Nafion–polybenzimidazole blends

Proton conducting membranes for a direct methanol fuel cell (DMFC) were fabricated from blends of Nafion® and polybenzimidazole (PBI) by solution casting. Prior to dissolution in the casting solvent, the sulfonic acid groups of the Nafion component of the blend were partially exchanged with sodium ions. The dependence of membrane proton conductivity and methanol permeability on the extent of proton substitution of Nafion during blending and on the PBI content of the final membrane was studied. It was found that membrane selectivity (the ratio of proton conductivity to methanol permeability) was the highest (four times that of Nafion 117) when fully protonated Nafion was used during blending and when the PBI content was 8%. DMFC performance of Nafion–PBI membranes (approximately 60 μm in thickness) was found to be superior to that of Nafion 117 at 1.0 and 5.0 M methanol feeds.