Hydrophobic Nanoporous Copper Oxide for Electrochemical CO ₂ Reduction

Copper-based electrocatalysts have attracted significant attention for the electrochemical reduction of CO 2 into value-added chemicals, such as ethanol. However, their practical application is limited by poor selectivity and stability under operating conditions along with the low faradaic efficiency. In this work, we demonstrate enhanced CO 2 RR performance through surface restructuring and local microenvironment manipulation via defect engineering. A controlled thermal annealing process was employed to induce hydrophobic microchannels within nanoporous copper oxide, thereby promoting the selective reduction of CO 2 to ethanol. CO-TPD and water contact angle measurements confirmed that the sample with the highest hydrophobicity exhibited superior CO 2 RR activity, which remained stable under long-term chronoamperometry. The optimized catalyst achieved exceptional selectivity toward ethanol production, delivering a maximum yield of 10.05 mmol cm –2 h –1 g –1 at −1 V (vs RHE), with a faradaic efficiency of 41% of ethanol production. Postcatalytic characterization revealed that both the microstructure and hydrophobicity were preserved along with the changes in the oxidation state as a result of the applied reduction potential. This work demonstrates a strategic manipulation of the microenvironment to improve faradaic efficiency of a solid–liquid–gas interfacial electron transfer reaction.