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.