Microwave-Assisted Synthesis of a Defect-Rich CuO Electrode for Selective Electrochemical CO₂ Reduction to C₂₊ Products

Electrochemical reduction of CO₂ to valuable C₂₊ chemicals using renewable energy is a crucial pathway for sustainable development, replacing traditional nonrenewable feedstocks. In this study, CuO-based materials were synthesized with and without microwave heating as electrocatalysts for CO₂ reduction. The CuO synthesized under microwave irradiation (MW-CuO) showed a similar morphology to the conventionally heated samples but exhibited a higher density of defect sites with increased grain boundaries (GBs). MW-CuO electrodes with a Cu²⁺ and CO₃^2- reactant ratio of 1.1 showed superior catalytic performance under identical reaction conditions. In particular, the catalytic activity of the MW-CuO electrode at −1.04 V vs RHE for the C₂₊ products is 49.3% higher than that of the CuO electrode. A faradaic efficiency (FE) of 71.9% is achieved for C₂₊ products, which is among the highest yields reported for OD-Cu catalysts. The spent MW-CuO electrode exhibited a significantly higher Cu⁺ to Cu⁰ ratio compared to the CuO electrode. The synergy of Cu(I) species and defective surface features is speculated to be responsible for the improved CO₂ER selectivity toward multicarbon products. However, the activity decreased for longer reactions, which was attributed to the loss of defect sites and Cu agglomerations. This study highlights the effectiveness of a simple synthesis approach for the production of defect-rich electrocatalysts that improve the efficiency and selectivity of CO₂ reduction.