Increasing CO Binding Energy and Defects by Preserving Cu Oxidation State via O<sub>2</sub>-Plasma-Assisted N Doping on CuO Enables High C<sub>2+</sub> Selectivity and Long-Term Stability in Electrochemical CO<sub>2</sub> Reduction
Abstract
Cu is considered as the most promising catalyst for the electrochemical carbon dioxide reduction reaction (CO2RR) to produce C2+ hydrocarbons, but achieving high C2+ product selectivity and efficiency with long-term stability remains one of great challenges. Herein, we report a strategy to realize the CO2RR catalyst allowing high C2+ product selectivity and stable catalytic properties by utilizing the benefits of oxygen-plasma-assisted nitrogen doping on CuO. It is exhibited that the defects such as oxygen vacancies and grain boundaries suitable for CO2RR are generated by N2 plasma radicals on CuO. Also, the oxidation state of Cu is maintained without Cu reduction by O2 plasma. Indeed, ON–CuO synthesized through oxygen-plasma-assisted nitrogen doping is demonstrated to enable a high C2+ product selectivity of 77% (including a high C2H4 selectivity of 56%) with a high current density of −34.6 mA/cm2 at −1.1 V vs RHE, as well as a long-term stability for 22 h without performance degradation. High CO2RR performances are ascribed to the increased CO binding energy and catalytic sites in N-doped CuO. Furthermore, an in situ X-ray absorption near-edge structure analysis reveals that the defects in ON–CuO are favorable for C–C coupling leading to C2+ products.