Microphase-Engineered Homologous Ion-Exchange Layers for High-Current-Density Bipolar Membrane Electrolysis

Bipolar membranes (BPMs) maintain separated acidic and alkaline environments via water dissociation at the junction, but high-current-density operation remains challenging because rapid hydrated H+/OH– migration away from the junction must be coupled with sufficient water replenishment toward it. A transport imbalance between these opposing processes causes interfacial dehydration and limits long-term operation. Here, we develop microphase-engineered homologous ion-exchange layers to balance this coupled transport. These layers are fabricated from homologous multiblock poly(biphenyl alkylene) ionomers sharing a common backbone and block architecture, promoting interlayer compatibility and interconnected ionic domains. The hydrated pathways accelerate water replenishment and ion transport, thereby maintaining a stably hydrated junction. The resulting BPM enables pure-water electrolysis at 2.11 V at 1000 mA cm–2 and sustains high-purity hydrogen production for over 1100 h at 500 mA cm–2. This work establishes molecularly engineered ion-exchange layers as an effective approach for improving mass transport in high-current-density BPM systems.