Steering the products distribution of CO2 electrolysis: A perspective on extrinsic tuning knobs

The bigger pictureThe reactivity and selectivity of CO2 electrolysis depend on the intrinsic physicochemical properties of catalysts, as well as on the extrinsic reaction environment in the vicinity of cathode. Compared with delicately controlled intrinsic tuning knobs, regulation on the local reaction environment has attracted growing interest in past years given its merits of versatility and scalability.Challenges and opportunities:•Molecular-level insights into the reactive species evolution at cathode–catholyte interface and the resultant mass transport within the hydrodynamic boundary layer are in high demand to clarify the local reaction environment effect•Systematic optimization on CO2 mass transport, electrode surface treatment, and electrolyte composition provides opportunities for more selective CO2-to-C2+ conversion•Multiphysics simulations and inspirations from the fuel cells community could aid the optimal design of heat, mass, and electron transfer for industrial-scale CO2 electrolysisSummaryUsing renewable electricity to electrochemically convert CO2 into value-added chemicals and fuels is a promising way to curb anthropogenic carbon emissions. In past years, exciting achievements have been witnessed on the robust and selective electrochemical CO2 reduction reaction, via either the delicate design of electrocatalytic materials or the local reaction environment engineering toward a practical system integration. In this perspective, we overview recent advances of extrinsic reaction environment effects in promoting CO2-to-C2+ conversion from three spatial aspects: (1) the chemical and physical surface modification, (2) the electrolyte composition and adjoint concentration gradient for both cations and anions, and (3) the mass transport regulation. Prevailing hypotheses, together with experimental and/or theoretical progress, have been critically assessed along with a deepened mechanism understanding of those extrinsic tuning knobs. Finally, challenges and future opportunities for more efficient C2+ production are provided in terms of fundamental interface engineering and technical electrolyzer implementation.Graphical abstract