Hexafluorophosphate-Modulated CuO for Selectivity Enhancement of C₂ Species in Electroreduction of CO₂

Copper (Cu)-based catalysts are widely employed in electroreduction of carbon dioxide (CO₂ER) because of their cost-effectiveness and versatility in producing multi-carbon products. However, improving the product selectivity, especially toward C₂ species (hydrocarbon containing two carbon atoms), remains a significant challenge. Herein, the microwave-assisted synthesis of copper oxide (CuO) is modulated with ammonium hexafluorophosphate (NH₄PF₆), obtaining thin CuO (ca. 12 nm in thickness) nanosheets with the surface adsorbed with hexafluorophosphate, referred as CuO-PF₆. This CuO-PF₆ catalyst could help stabilize the key reaction intermediates during CO₂ER. Therefore, the Faradaic efficiency (FE) of C₂ products (ethylene and ethanol) during CO₂ER could be improved to 75.8% ± 0.5% in an H-type electrochemical cell. This C₂ FE increases to 82.4% in a flow cell. The improved FE toward C₂ species could be attributed to the PF₆-modulated electronic structure of Cu surface and stabilization of key reaction intermediates, especially those involving C₂ production. In addition, CuO-PF₆ also demonstrates a high catalytic stability over 10 h. This work provides a deeper understanding of surface modification strategy for CO₂ER enhancement, promising for designing hybrid electrocatalysts with high efficiency and stability for CO₂-to-fuel conversion.