Boosting Electrochemical CO2 Reduction via Surface Hydroxylation over Cu-Based Electrocatalysts

Electrochemical CO2 reduction (CO2R) to valuable multicarbon (C2+) products is an attractive means for upgrading waste CO2. One of the intensively studied strategies is to apply concentrated KOH solution to extensively proceed with CO2R to C2+ products; however, the undesired carbonate formation at the cathode consumes majority of the input CO2. Therefore, it is crucial to seek a new strategy to improve the local environment at the electrode and thus eliminate or reduce dependence of the selectivity of CO2R on bulk OH- concentration. However, tailoring a stable surface hydroxylation reaction microenvironment near the catalyst surface throughout the extended CO2R operation process is still a challenge. Here, we implement the concept of molecular surface modification experimentally by applying a hydroxyl-functionalized surface strategy (i.e., capping hydroxyl-rich molecules over a set of Cu2O catalysts) to enhance the formation of C2+ products. Electrochemical experiments and operando characterizations confirm the stable presence of hydroxyl species near the catalyst surface during the CO2R operation and its advantage in converting absorbed *CO into C2+ products. As a result, the Faradaic efficiency of C2+ products of 81.5% and the cathodic energy efficiency of 43.1% were achieved with a partial current density of 285 mA cm(-2) in a flow cell. Using a cation-exchange membrane electrode assembly device, we demonstrated the stable production of ethylene over 100 h at an average current density of 151 mA cm(-2). Theoretical analyses also show that hydroxyl-rich molecules such as gluconic acid can lead to the electron loss of the Cu sites, which is beneficial for *CO adsorption and thus the formation of C2+ products. Our results reveal the significance of tailoring a stable local reaction microenvironment over the catalyst surface in an electrochemical system.