Light-Driven Active Separation Sustains a Transmembrane Proton-Activity Difference for Electrochemical Microenvironment Regulation

Abstract Electrochemical water technologies often require spatially distinct proton activities, yet passive membranes allow these microenvironments to equilibrate. Here we construct a topology-defined series of donor–acceptor covalent organic framework (COF) membranes with rhombic, honeycomb, and kagome lattices and establish a connection between local photoinduced responses and membrane-scale active ion transport. Among them, rhombic COF-PY-BT exhibits the strongest local photoresponse and the largest light-induced transmembrane bias under one-sided illumination. Crossed-control experiments establish that the direction of the macroscopic response follows the illumination direction, while periodic Berry-phase calculations reveal framework-dependent retention and cancellation of dipolar components. The resulting transmembrane bias counteracts proton back-diffusion and enables uphill proton transport, helping sustain a bulk ΔpH > 4 between near-neutral anodic and acidic cathodic compartments. When integrated as an active separator in a two-compartment electrolysis cell, COF-PY-BT lowers the apparent full-cell voltage by approximately 45% under dilute conditions and improves voltage stability. These results establish light-driven active membrane regulation as a strategy for sustaining nonequilibrium proton environments during electrochemical operation.