Microwave-Assisted\nSynthesis of a Defect-Rich CuO\nElectrode for Selective Electrochemical CO<sub>2</sub> Reduction to\nC<sub>2+</sub> Products

Electrochemical reduction\nof CO<sub>2</sub> to valuable\nC<sub>2+</sub> chemicals using renewable energy is a crucial pathway\nfor sustainable\ndevelopment, replacing traditional nonrenewable feedstocks. In this\nstudy, CuO-based materials were synthesized with and without microwave\nheating as electrocatalysts for CO<sub>2</sub> reduction. The CuO\nsynthesized under microwave irradiation (MW-CuO) showed a similar\nmorphology to the conventionally heated samples but exhibited a higher\ndensity of defect sites with increased grain boundaries (GBs). MW-CuO\nelectrodes with a Cu<sup>2+</sup> and CO<sub>3</sub><sup>2–</sup> reactant ratio of 1.1 showed superior catalytic performance under\nidentical reaction conditions. In particular, the catalytic activity\nof the MW-CuO electrode at −1.04 V vs RHE for the C<sub>2+</sub> products is 49.3% higher than that of the CuO electrode. A faradaic\nefficiency (FE) of 71.9% is achieved for C<sub>2+</sub> products,\nwhich is among the highest yields reported for OD-Cu catalysts. The\nspent MW-CuO electrode exhibited a significantly higher Cu<sup>+</sup> to Cu<sup>0</sup> ratio compared to the CuO electrode. The synergy\nof Cu(I) species and defective surface features is speculated to be\nresponsible for the improved CO<sub>2</sub>ER selectivity toward multicarbon\nproducts. However, the activity decreased for longer reactions, which\nwas attributed to the loss of defect sites and Cu agglomerations.\nThis study highlights the effectiveness of a simple synthesis approach\n for the production of defect-rich electrocatalysts that improve the\nefficiency and selectivity of CO<sub>2</sub> reduction.