Interfacial microenvironment engineering in CO₂ electroreduction: mechanisms, advances, and perspectives

Electrochemical CO₂ reduction reaction (CO₂RR) provides a promising route for converting CO₂ into value-added chemicals and fuels, but its practical application is still limited by competing hydrogen evolution, sluggish reaction kinetics, and poor selectivity toward specific products, especially multicarbon (C₂₊) products. Increasing evidence shows that these limitations are governed not only by the intrinsic properties of catalysts, but also by the interfacial microenvironment where electrolyte ions, solvent molecules, proton donors, adsorbed intermediates, surface modifiers, and catalytic sites dynamically interact. Interfacial microenvironment engineering therefore offers an effective strategy to regulate local electric fields, ion distribution, solvation structure, proton availability, water activity, hydrogen-bond networks, mass transport, and interfacial wettability, thereby reshaping elementary CO₂RR pathways. In this review, we first define the interfacial microenvironment in CO₂RR as a potential-dependent local reaction zone and summarize its key physicochemical quantities. We then discuss recent advances in microenvironment regulation for suppressing the hydrogen evolution reaction, enhancing CO₂-to-CO conversion kinetics, and promoting C-C coupling toward C₂₊ products. Particular emphasis is placed on the mechanistic roles of electrolyte composition, molecular additives and surface functionalization. Finally, we highlight current challenges and future opportunities, including the decoupling of overlapping microenvironment effects, operando characterization under realistic conditions, long-term interfacial stability, and translation from model systems to high-current-density flow cells and membrane-electrode assemblies.