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

Abstract

Electrochemical CO 2 reduction (CO 2 R) to valuable multicarbon (C2+) products is an attractive means for upgrading waste CO 2 . One of the intensively studied strategies is to apply concentrated KOH solution to extensively proceed with CO 2 R to C2+ products; however, the undesired carbonate formation at the cathode consumes majority of the input CO 2 . 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 CO 2 R on bulk OH – concentration. However, tailoring a stable surface hydroxylation reaction microenvironment near the catalyst surface throughout the extended CO 2 R 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 Cu 2 O 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 CO 2 R 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.

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