N-doped CuO with the tunable Cu and Cu sites for selective CO electrochemical reduction to ethylene.

The electrochemical carbon dioxide reduction reaction (CORR) to high value-added fuels or chemicals driven by the renewable energy is promising to alleviate global warming. However, the selective CO reduction to C products remains challenge. Cu-based catalyst with the specific Cu and Cu sites is important to generate C products. This work used nitrogen (N) to tune amounts of Cu and Cu sites in CuO catalysts and improve C-product conversion. The controllable Cu/Cu ratio of CuO catalyst from 0.16 to 15.19 was achieved by adjusting the N doping amount using NH/Ar plasma treatment. The major theme of this work was clarifying a volcano curve of the ethylene Faraday efficiency as a function of the Cu/Cu ratio. The optimal Cu/Cu ratio was determined as 0.43 for selective electroreduction CO to ethylene. X-ray spectroscopy and density functional theory (DFT) calculations were employed to elucidate that the strong interaction between N and Cu increased the binding energy of NCu bond and stabilize Cu, resulting in a 92.3% reduction in the potential energy change for *CO-*CO dimerization. This study is inspiring in designing high performance electrocatalysts for CO conversion.