A polymer membrane with integrated microphase separation and intrinsic microporosity for aqueous organic redox flow batteries

The aqueous organic redox flow battery (AORFB) is a promising electrochemical technology for large-scale and long-duration energy storage, requiring highly conductive and selective ion-exchange membranes. Traditional porous and microphase-separated membranes often present a tradeoff between high ion conductivity and low crossover of active species, remaining a persistent research challenge. Here, we propose a key design strategy that integrates size-confined microphase separation and intrinsic microporosity within a solution-processable Tröger’s base (TB) framework. By introducing a delayed implementation of a three-armed branch linker and a semi-rigid polymer backbone in a sequential synthesis, the resulting branched TB membrane b-DPM-N3, demonstrates both high conductivity and selectivity (as low as 10⁻¹² cm²/s permeability of various active materials) and showcases its efficiency in AORFBs with record power density and up to 42% energy efficiency under 300 mA/cm² current density. This design concept offers broad potential for membrane applications in electrochemical devices.