Nanoporous PBI membranes by track etching for high temperature PEMs

•Ordered nanoporous PBI films 25 μm thick prepared by track etching for HT PEM.•Nominal porosity values varying from 0.3% to 10% with pore diameters below 50 nm.•Chemical modification of the PBI polymer along the pore walls upon ion beaming.•Enhanced phosphoric acid embedding process for ordered nanoporous PBI films.•Linear decay of activation energy for H+ conduction with external surface area.

This article describes for the first time the preparation of conducting track-etched PBI membranes 25 mm thick with pore diameter values varying from 15 nm to 50 nm and overall porosity up to 10%. The TGA, DSC and FTIR characterization results for the so obtained nanoporous membranes reveal the chemical modification of PBI upon irradiation along the track walls. A clear conduction outperforming is shown by phosphoric acid doped track-etched PBI in comparison with dense PBI counterparts. This behavior could be explained by the effective contribution of additional pathways for proton transport involving shorter benzimidazole fragments, cross-linked PBI nanodomains and free amphoteric phosphoric acid molecules settled on the pore walls.