Permeable intimate membrane electrode interface with optimized micro-environment for CO2 electroreduction in pure water

Pure water-fed membrane electrode assembly (MEA) electrolyzers represent a significant advance for practical deployment of electrochemical CO2 reduction, yet suffer from poor reaction kinetics and high ohmic resistance due to the lack of alkali cations and low intrinsic ionic conductivity. Here, we address interfacial mass transport limitations arising from inefficient H2O and OH- transport in anion exchange membrane (AEM)-based pure water MEAs. A permeable intimate membrane (PIM) electrode is developed by casting ionomer emulsion directly onto the catalyst layer (CL) to form the anion exchange layer (AEL) in situ, which creates an intimately bonded CL/AEL interface and allows the ionomer to permeate the CL, establishing continuous internal channels for efficient H2O and OH− transport. Consequently, the PIM-based MEA achieves over 90% CO selectivity across a wide current density range under pure water conditions, with a system energy efficiency 1.35 times higher than conventional MEAs. Characterization reveals that the intimate catalyst-ionomer interface reconstructs the hydrogen-bonded network of interfacial water, accelerating the hydrogenation kinetics of the key *COO− intermediate. Pure water-fed CO2 electrolyzers promise industrial CO2 electroreduction (ECR) but suffer from slow kinetics and high ohmic resistance. Here, the authors report a permeable intimate electrode interface enabling efficient mass transport and optimized microenvironments for energy-efficient ECR.