Unraveling the Role of Pressure, Oxidation State, and Morphology in CO2 Electroreduction to C2+ Products over Copper Oxides

Abstract

This study presents compelling experimental evidence on the synergistic effects of reaction pressure, oxidation state, and catalyst morphology on C2+ selectivity of copper (Cu) oxide electrocatalysts for electrochemical CO2 reduction (ECR). By using femtosecond laser structuring and thermal treatments, we demonstrate the synthesis of Cu(0), Cu(I), Cu(II), and a mixed oxidation state catalyst Cu(x) with distinct micro and nanomorphologies. The optimal CO2 pressure for maximizing C2+ productivity in aqueous bicarbonate media is determined by analyzing reaction products at various pressures in a specially designed, pressurizable two-compartment cell. Among Cu(0), Cu(I), and Cu(II), only thermally produced Cu(I) was an unstructured catalyst that showed ethylene gas-phase selectivity. Laser surface nanostructuring is shown to improve C2+ selectivity, allowing all three oxidation states to produce ethylene. The nanostructured Cu(x), mainly consisting of a Cu(II) matrix with well-dispersed Cu(I) (~22 at%) and Cu(0) (~7 at%), produced both ethylene and ethane. This outcome is linked to the synergistic effects of low-coordinated Cu states, which stabilize reaction intermediates and facilitate charge transfer, leading to the formation of longer C2+ products. Our findings provide deep insights into the factors that influence C2+ selectivity in Cu-based catalysts and lay the groundwork for designing high-energy density long chain products.