Unraveling the roles of pressure, oxidation state, and morphology in CO electroreduction to C gaseous products over copper oxides.

This study provides compelling experimental evidence of the synergistic effects of reaction pressure, oxidation state, and catalyst morphology on the C selectivity of copper (Cu) oxide catalysts in electrochemical CO 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() with characteristic micro- and nano-morphologies. The optimal CO pressure for maximizing C 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 C selectivity such that all three oxidation states could produce ethylene. More importantly, the nanostructured Cu() 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 C products. This work provides important insights into the key factors influencing C selectivity in Cu-based catalysts, establishing the basis for an informed design to yield high-energy density products.