Steering Electrochemical CO₂ Reduction Selectivity toward CH₄ or C₂H₄ on N-Doped Carbon-Coated Cu/Cu₂O Composite Catalysts

Understanding the catalytic mechanism is crucial for the rational design of efficient catalysts. However, the dynamic reconstruction of copper (Cu) catalysts under harsh electrochemical CO2 reduction reaction (CO2RR) conditions poses great challenges for studying the mechanism. Herein, we prepared a series of N-doped carbon-coated Cu/Cu2O composite catalysts with varying Cu/Cu2O ratios and N-doping levels by annealing copper acetylacetonate (Cu(acac)2) with different amounts of potassium nitrate (KNO3), which can steer CO2RR toward either CH4 or C2+ (mainly C2H4) production. The in situ formed carbon layer effectively stabilized the Cu catalyst structures under cathode potentials, facilitating mechanistic studies of CO2RR. Through CO temperature-programmed desorption (TPD) and in situ infrared spectroscopy characterizations, it is revealed that the coexistence of Cu0 and Cu+ sites promoted the generation of a high-coverage, strongly adsorbed *CO intermediate on the catalytic surface, thereby enhancing C–C coupling to generate C2+ products. Conversely, the surface with only Cu0 sites exhibited a low-coverage and weakly adsorbed *CO, benefiting its hydrogenation/deoxygenation toward CH4 production.