Geometric‐Topology‐Driven Membrane Design for Suppressing Polysulfide Crossover in Aqueous Redox Flow Batteries

Abstract

ABSTRACT Developing highly selective ion‐exchange membranes to suppress active‐species crossover remains a critical challenge in aqueous redox flow batteries (ARFBs). Unfortunately, their practical performance is often compromised by hydration‐induced membrane swelling, giving rise to non‐selective water channels that facilitate catholyte‐anolyte crossover. Herein, we show that geometric topology is a previously overlooked but decisive parameter governing membrane microstructure, hydration behavior, and ion selectivity. Using a coarse‐grained molecular dynamics framework, we reveal a geometry‐driven phase‐separation mechanism under membrane hydration. Isotropic 0D geometric motifs remain uniformly dispersed and promote the formation of highly interconnected yet spatially confined hydration networks, whereas anisotropic one‐ and 2D geometric motifs exhibit a strong propensity to bundle and aggregate, inducing phase separation and interfacial voids that promote non‐selective transport. Guided by this principle, a membrane incorporating 0D geometric motifs simultaneously achieves high cationic conductivity and strong polysulfide rejection, enabling stable operation of a polysulfide‐based aqueous redox flow battery for over 700 h with Coulombic efficiencies exceeding ∼99.5% and peak power densities of ∼138 mW cm − 2 , dramatically outperforming conventional commercial membranes and demonstrating the effectiveness of the geometry‐guided membrane design principle in advancing future membrane engineering.