Polybenzimidazole membrane with dual proton transport channels for vanadium flow battery applications

Polybenzimidazole membranes with dual proton transport channels (B-PBI) are designed and fabricated for vanadium flow battery (VFB) applications. The dual channels are established by introducing pyridine groups (channel-1) in the PBI chain (B-PBI), which contains imidazole rings (channel-2). The proton transport channels can endow the B-PBI membrane with dramatically enhanced proton conductivity, while the repulsion between the positively charged pyridine and imidazole nitrogens after doping with protons and the vanadium ions can afford the membrane with excellent ion selectivity. Hence, the prepared B-PBI membrane delivers an excellent performance in terms of high proton conductivity, ion selectivity and chemical stability. A VFB with a B-PBI membrane exhibits a coulombic efficiency (CE) of 99.16% and a voltage efficiency (VE) of 88.86% at a current density of 80 mA cm(-2), which is much higher than does a battery with a pristine PBI membrane (CE of 98.54%, VE of 84.10%) and with a Nafion 115 membrane (CE of 95.13%, VE of 87.05%). The chemical stability of the B-PBI is confirmed by a stable performance of 600 cycles at 160 mA cm(-2) and the ex-situ oxidation stability test. These results suggest that the B-PBI membrane with dual proton transport channels can be served as promising candidate for vanadium flow battery.