A Photocurable Covalent Polyoxometalates‐Membrane With Hierarchical Proton Conduction Pathways for High‐Performance Vanadium Flow Batteries

Abstract

ABSTRACT Developing proton exchange membranes (PEMs) that integrate high conductivity, selectivity, and processability is highly challenging. Although polyoxometalates (POMs) are promising proton conductors, their practical application is hindered by poor processability, susceptibility to leaching, and difficulty in forming continuous proton conduction pathways within polymers. Herein, a new photocurable polyoxometalate (POM)‐organic membrane (PAPOM‐AMPS) is synthesized via ultrafast UV‐initiated copolymerization of an acrylamide‐functionalized arsenomolybdate cluster (APOM), 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS), and acrylic acid (AA). This molecular‐level design ingeniously constructs hierarchical proton transport channels: the covalently immobilized APOM clusters serve as long‐range highways, while sulfonic (–SO 3 H) and carboxylic (–COOH) acid groups synergize with water molecules to facilitate efficient proton dissociation and dynamic short‐range hopping. The membrane exhibits an exceptional proton conductivity of 0.417 S·cm −1 at 80°C and 100% RH, surpassing Nafion 117. With confined ionic domains (∼2.27 nm), it achieves ultrahigh proton/vanadium selectivity (18.1 × 10 4 S·min·cm −3 ), 4.6 times that of Nafion 117. When configured into a sandwich‐structured membrane for vanadium flow batteries (VFBs), it delivers outstanding performance, including 98.2% coulombic efficiency, 86.7% energy efficiency, and exceptional cycling stability (0.12% capacity decay per cycle at 120 mA·cm −2 ). This work provides a groundbreaking strategy for next‐generation high‐performance proton‐conductive membranes.