The Role of the Copper Oxidation State in the Electrocatalytic Reduction of CO2 into Valuable Hydrocarbons

Redox-active copper catalysts with accurately prepared oxidation states (Cu0, Cu+, and Cu2+) and high selectivity to C2 hydrocarbon formation, from electrocatalytic cathodic reduction of CO2, were fabricated and characterized. The electrochemically prepared copper-redox electro-cathodes yield higher activity for the production of hydrocarbons at lower oxidation state. By combining advanced X-ray spectroscopy and in situ microreactors, it was possible to unambiguously reveal the variation in the complex electronic structure that the catalysts undergo at different stages (i.e., during fabrication and electrocatalytic reactions). It was found that the surface, subsurface, and bulk properties of the electrochemically prepared catalysts are dominated by the formation of copper carbonates on the surface of cupric-like oxides, which prompts catalyst deactivation by restraining effective charge transport. Furthermore, the formation of reduced or partially reduced copper catalysts yields the key dissociative proto...