Increasing the permanent conductivity of PBI membranes for HT-PEMs

Polybenzimidazole-based membranes are the best candidates to substitute Nafion in polymer fuel cells operating above 100 C. These membranes are activated with phosphoric acid as the proton donor, and one of the related problems is acid leaching during fuel cell operation, which can easily reduce the permanent conductivity up to 5–6 orders of magnitude, and it is relevant chiefly in case of thin films. Here we discuss two different strategies to reduce the acid leaching, in order to improve the membrane permanent conductivity. The development of new monomers allows to improve the conductivity up to 100 times, whereas the preparation of composite membranes with active fillers may lead to up to a 3 orders-of-magnitude increase.