Multichannel Proton-Conducting Polybenzimidazole/Sulfonated UiO-66 Hybrid Membranes for High-Performance Vanadium Redox Flow Batteries

Polybenzimidazole (PBI) membranes are promising for vanadium redox flow batteries (VRFBs) but are limited by low proton conductivity. We address this by integrating flexible-ether PBI (OPBI) with a zirconium-based sulfonated MOF (UiO-66-N-SO3H, PSM) to form OPBI/PSM hybrid membranes. PSM constructs hierarchical proton pathways and size-exclusion barriers to vanadium, increasing proton conductivity from 7.3 (OPBI) to 28.4 mS cm–1 (OPBI/PSM5, 289% improvement), reducing vanadium permeation, and boosting tensile strength to 89.0 MPa. In VRFB cells, OPBI/PSM5 delivers ∼90–77% energy efficiency from 40 to 160 mA cm–2, outperforming both Nafion 212 (∼79–68%) and neat OPBI (∼86–68%). The cell shows a self-discharge time of 371 h (vs 21 h for Nafion 212) and maintains an ∼80% energy efficiency after 2150 cycles at 140 mA cm–2. This study proposes a viable strategy for advancing high-performance VRFB membrane development.