Properties of ab-PBI Membranes for Fuel Cells

Abstract

Poly(2,5-benzimidazole) (ab-PBI) membranes were characterized for use as electrolytes in fuel cells operating at elevated temperatures (100 to 200°C). The conductivity of phosphoric acid-doped ab-PBI was as high as 0.12 S cm⁻¹ at temperatures below 120°C, but it decreased to 0.025 S cm⁻¹ above 150°C due to a dehydration of the doped acid. Using the H₃PO₄-doped ab-PBI, H₂/O₂ fuel cell could be operated at 120°C with a low humidification of reactant gases, although it was necessary to keep the acid-doping level high in both the membrane and the electrodes.