Porous Sulfonated N-Heterocyclic Poly(aryl ether ketone) Membranes for Vanadium Redox Flow Battery Application

The application of sulfonated poly(aryl ether)-based cation exchange membranes in vanadium redox flow batteries (VRFBs) faces a critical challenge of the trade-off effect on ion conductivity, selectivity, and oxidation resistance. A porous N-heterocyclic poly(aryl ether ketone) incorporating bis-phthalazinone and low-substituted benzenesulfonic group (SPBPEK-P) membrane is prepared by the non-solvent-induced phase separation (NIPS) process based on the coagulation of water. The regulation of the process endows the membranes with a dense skin layer and a porous bottom layer to optimize the equilibrium between ionic conduction and selectivity. All of the SPBPEK-P membranes exhibit sponge-like morphology, and the area resistance reduces to 0.16 Ω cm 2 by the introduction of poly(ethylene glycol) (PEG). The regulation of butanone and evaporation time enhances the ion selectivity to obtain the vanadium ion permeability of 1.6 × 10 −7 cm 2 min −1 . The SPBPEK-P-85 membrane prepared in the evaporation duration of 85 min achieves 81.3% energy efficiency (EE) at 200 mA cm −2, outperforming Nafion 212 (75.0%), and exerts good stability in 300 charge–discharge cycles at 180 mA cm −2 . This work highlights the potential prospect of SPBPEK-P membranes in VRFBs and provides a process strategy for cation porous membranes.