Regulation of the Charge Distribution in the Confined Channels of Anion Exchange Membranes Enables Efficient Ion Transport

ABSTRACT Ion exchange membranes enable ion transport in electrochemical devices (such as fuel cells, flow batteries, water electrolysis), where ion conductivity is critical for efficient operation. Conventional membranes relying on microphase separation face a selectivity‐conductivity trade‐off. However, current designs primarily introduce charges onto the walls of sub‐nanometer channels, which may lead to the formation of an excessively strong hydrogen‐bond network due to excessive water uptake, thereby reducing the self‐diffusion coefficients of water molecules and ions. This work proposes a strategy for introducing charge into the middle of sub‐nano channels via rigid side chains and has developed a membrane (QPAEPi‐3) to form a continuous hydrogen‐bond network while maintaining high diffusion coefficients for water and ions. Concurrently, membranes without side chains (QPAEPi‐1) and with flexible side chains (QPAEPi‐2) were also designed and investigated in parallel. Charges located far from the pore walls reduce the uptake of water molecules but induce the formation of hydrogen‐bond network more similar to that of bulk water, thereby increasing the self‐diffusion coefficients of water and ions. This achieves the highest chloride ion conductivity (42 mS cm −1 @ 30°C) and energy efficiency of pH‐neutral aqueous organic redox flow battery (55% @ 500 mA cm −2 ).