Tailored porous PBI membranes featuring efficient proton conduction pathways and multi-barrier systems for high-rate vanadium flow batteries

The development of high-performance ion-selective membranes is essential for advancing vanadium flow batteries (VFBs). In this study, we present a novel porous polybenzimidazole (PBI) membrane featuring a distinctive architecture aimed at significantly enhancing ion selectivity. The porous structure was constructed using Fe₂O₃ nanoparticles as a hard template and etched with HCl. This design facilitates efficient proton transport, achieving a reduced area resistance (<0.20 Ω cm 2 ). Simultaneously, the multiple polymer/electrolyte interfaces within the design introduce energy barriers that effectively block vanadium ion transport, resulting in ultralow vanadium ion permeability (<10 −8  cm 2  min −1 ). The PBI-10Fe₂O₃ membrane demonstrated outstanding electrochemical performance, achieving a high energy efficiency (EE) of 81.4 % at a current density of 300 mA cm⁻ 2 . This study demonstrates the effectiveness of tailored porous PBI membranes in achieving both high proton conductivity and strong vanadium ion blocking performance. Moreover, the unique design approach highlights the potential to overcome the trade-off between ion selectivity and proton conductivity, paving the way for next-generation energy storage applications.