Developments of new proton conducting membranes based on different polybenzimidazole structures for fuel cells applications

The current goal on PEMFCs research points towards the optimization of devices working at temperatures above 100 °C and at low humidity levels. Acid-doped polybenzimidazoles are particularly appealing because of high proton conductivity without humidification and promising fuel cells performances. In this paper we present the development of new proton conducting membranes based on different polybenzimidazole (PBI) structures. Phosphoric acid-doped membranes, synthesized from benzimidazole-based monomers with increased basicity and molecular weight, are presented and discussed. Test of methanol crossover and diffusion were performed in order to check the membrane suitability for DMFCs. Both the acid doping level and proton conductivity remarkably increase with the membrane molecular weight and basicity, which strictly depend on the amount of NH-groups as well as on their position in the polymer backbone. In particular, a conductivity value exceeding 0.1 S cm−1 at RH = 40% and 80 °C was reached in the case of the pyridine-based PBI.