Proton conducting membranes based on semi-interpenetrating polymer network of Nafion® and polybenzimidazole

A new strategy to prepare the reinforced composite membranes for polymer electrolyte membrane fuel cells (PEMFCs), which can work both in humidified and anhydrous state, was proposed via constructing semi-interpenetrating polymer network (semi-IPN) structure from polybenzimidazole (PBI) and Nafion (R) 212, with N-vinylimidazole as the crosslinker. The crosslinkable PBI was synthesized from poly (2,2'-(m-phenylene)-5,5'-bibenzimidazole) and p-vinylbenzyl chloride. The semi-IPN structure was formed during the membrane preparation. The composite membranes exhibit excellent thermal stability, high-dimensional stability, and significantly improved mechanical properties compared with Nafion (R) 212. The proton transport in the hydrated composite membranes is mainly contributed by the vehicle mechanism, with proton conductivity from similar to 10(-2) S/cm to similar to 10(-1) S/cm. When the temperature exceeds 100 C, the proton conductivity of the semi-IPN membranes decreases quickly due to the dehydration of the membranes. Under anhydrous condition, the proton conductivity of the membranes will drop to similar to 10(-4) S/cm, which is also useful for intermediate temperature (100-200 degrees C) PEMFCs. The benzimidazole structure of PBI and the acidic component of Nafion (R) provide the possibility for the proton mobility via structure diffusion involving proton transfer between the heterocycles with a corresponding reorganization of the hydrogen bonded network. (C) 2010 Elsevier Ltd. All rights reserved.