Unraveling the roles of pressure, oxidation state, and morphology in CO2 electroreduction to C2+ gaseous products over copper oxides†

Abstract

This study provides compelling experimental evidence of the synergistic effects of reaction pressure, oxidation state, and catalyst morphology on the C₂₊ selectivity of copper (Cu) oxide catalysts in electrochemical CO₂ reduction (ECR). We employed femtosecond laser structuring and thermal treatments to synthesize Cu(0), Cu(I), Cu(II), and a mixed oxidation state catalyst Cu(x) with characteristic micro- and nano-morphologies. The optimal CO₂ pressure for maximizing C₂₊ productivity in aqueous bicarbonate media was established by assessing the reaction products at different imposed pressures in a custom-designed, pressurizable two-compartment cell. Among Cu(0), Cu(I), and Cu(II), thermally produced Cu(I) was the only unstructured catalyst exhibiting ethylene gas-phase selectivity. Nanostructuring enhanced the C₂₊ selectivity such that all three oxidation states could produce ethylene. More importantly, the nanostructured Cu(x) comprising well-dispersed Cu(0), Cu(I), and Cu(II), exhibited ethylene as well as ethane production – a characteristic associated with the synergistic effects of undercoordinated Cu states in stabilizing reaction intermediates and facilitating charge transfer to yield longer C₂₊ products. This work provides important insights into the key factors influencing C₂₊ selectivity in Cu-based catalysts, establishing the basis for an informed design to yield high-energy density products.