Constructing high-performance poly(terphenyl pyridinium) membranes through efficient acid doping and controllable crosslinking for vanadium flow batteries

Abstract

The development of membranes is crucial for advancing vanadium flow battery (VFB), however, designing high-performance membranes to achieve high-selectivity ion transport and excellent stability remains a significant challenge. Herein, we present an innovative design of crosslinked acid-doped poly(triphenyl pyridinium) membranes centered on balancing the ratio of the two triphenylene isomers (meso and para) and incorporating efficient sulfuric acid doping and controllable crosslinking strategies. Specifically, precisely balanced rigid and flexible segments make the polymer chains more loosely packed, enhancing acid absorption of the membrane. The uniformly distributed hydrophilic regions and abundant hydrogen bond network within the membrane significantly improve the transport of charge-balanced ions. Meanwhile, the Donnan repulsion effect from the pyridinium groups and the spatial barrier effect from the densely arranged polymer chains synergistically prevent vanadium penetration. The resulting membrane exhibits high ion selectivity (18.49 × 10⁵ S min cm⁻³). Furthermore, the robust ether-free backbone and non-weak-bond pyridinium in combination with the crosslinked structure achieve outstanding mechanical and chemical stability. The VFBs based on these membranes offer excellent energy efficiency (over 82 %) at high current density, and exhibit ultra-low capacity decay (0.056 % decay rate per cycle) and sustained stability (over 1600 cycles) at 120 mA cm⁻². This study provides a new perspective on the design of high-performance membranes for VFBs