Conductivity of PBI Membranes for High-Temperature Polymer Electrolyte Fuel Cells

Polybenzimidazole (PBI) film, a candidate polymer electrolyte membrane (PEM) for high-temperature (120-200°C) fuel cells, was cast from solution with constant molecular weight PBI powder and various acid doping levels. Conductivity measurements on these membranes were performed using an ac method under controlled temperature and relative humidity (RH). A complete set of conductivity data for acid-doped PBI is presented as a function of temperature (60-200°C), RH (5-30%), and acid doping level (300-600 mol %). A mechanism of conductivity is proposed for the proton migration in this PBI/acid system based on this and previous work. Proton transfer in this system appears to occur along different paths for…