Promoting CO2 electroreduction to C2H4 product by promoting water molecules activation on MgO/CuO catalyst

Electrocatalytic CO₂ reduction reaction (CO₂RR) to ethylene (C₂H₄) represents a promising approach to reducing CO₂ emissions and producing high-value chemicals. The ethylene productivity is always limited by the slow reaction kinetics and the high-performance catalysts are significantly desired. Many efforts have been made to develop a catalyst to activate CO₂ molecules. However, as another reactant, H₂O activation does not receive the attention it deserves. In particular, slow H₂O dissociation kinetics limit the rate of proton supply, severely impairing the production of C₂H₄. Here, we designed a MgO-modified CuO catalyst (MgO/CuO), which can promote H₂O dissociation and enhance CO₂ adsorption at the same time to realize the efficient ethylene production. The optimal catalyst exhibits a Faraday efficiency for C₂H₄ reached 54.4% at −1.4 V vs. RHE in an H-cell, which is 1.4 times that of pure CuO (37.9%), and it was further enhanced to a 56.7% in a flow cell, with a high current density of up to 535.9 mA cm⁻² at −1.0 V vs. RHE. Experimental and theoretical calculations show that MgO/CuO plays a bifunctional role in the CO₂RR, which facilitates the adsorption and activation of CO₂ by CuO and simultaneously accelerates H₂O dissociation by MgO doping. The in situ XRD experiments demonstrate that the introduction of MgO protects CuO active phase to avoid overreduction and preserves the active centers for CO₂RR. In combination with in situ FTIR and DFT calculations, the protonation process from *CO to *COH and asymmetric C–C coupling step are promoted by the enhanced water activation and proton coupling on MgO/CuO. This work provides new insights into the CO₂ and H₂O coactivation mechanism in CO₂RR and a potential universal strategy to design ethylene production electrocatalysts.