Supramolecular Sidechain Topology Mediated Pseudo‐Nanophase Separation Engineering for High‐Performance Redox Flow Battery Membranes

Abstract Pseudo‐nanophase separation enabled by supramolecular‐interaction‐grafted sidechains proves a promising alternative for constructing high‐performance commercially viable membranes with quick ion transport, excellent chemical stability, and simplified membrane manufacturing. Nonetheless, the concept of pseudo‐nanophase separation is still in nuce, and determinants for controlling pseudo‐nanophase separation remain somewhat opaque. In this contribution, supramolecular sidechain topology is found critical to engineering pseudo‐nanophase separation. Three supramolecular sidechain topological (viz. linear, branched, and cyclic) structures are investigated using experimental and theoretical protocols, and the underlying mechanisms by which supramolecular sidechain topology alters the microstructure and ion‐conducting behaviors of the membranes are proposed. Consequently, the cyclic sidechain‐mediated membrane achieves the highest proton conductivity with an area resistance as low as 0.10 Ω cm 2 . The resulting membrane endows an acidic aqueous redox flow battery with an energy efficiency of up to 80.7% even at high current densities of 220 mA cm −2 , breaking the record set by the pseudo‐nanophase separation strategy constructed membranes and ranking among the highest values ever documented. This study advances the understanding of supramolecular sidechain topology for the design and preparation of high‐performance membranes via pseudo‐nanophase separation engineering for flow batteries and beyond.