The acid doping behavior of polybenzimidazole membranes in phosphoric acid for proton exchange membrane fuel cells

The acid doping behavior of poly(2,2'-(m-phenylene)-5,5'-bibenzimidazole) (PBI) membranes in aqueous phosphoric acid was studied at room temperature. It was found that doping phosphoric acid in the membrane obeyed a multimolecular layer absorption mechanism proposed in this work. Equation, i.e., 1/[L (T) ] (B) =(1 - C (0)/17.5)/2.1, was presented to describe the relationship of the acid doping level of membranes and the concentration of the doping acid in a range of 2-14 mol L-1. The acid doping kinetics as well as the influence of the doped acids on the conductivity and mechanical strength of the PBI membranes was investigated.