Increasing CO Binding Energy and Defects by Preserving Cu Oxidation State via O₂-Plasma-Assisted N Doping on CuO Enables High C₂₊ Selectivity and Long-Term Stability in Electrochemical CO₂ Reduction

Abstract

Cu is considered as the most promising catalyst for the electrochemical carbon dioxide reduction reaction (CO 2 RR) to produce C 2+ hydrocarbons, but achieving high C 2+ product selectivity and efficiency with long-term stability remains one of great challenges. Herein, we report a strategy to realize the CO 2 RR catalyst allowing high C 2+ 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 CO 2 RR are generated by N 2 plasma radicals on CuO. Also, the oxidation state of Cu is maintained without Cu reduction by O 2 plasma. Indeed, ON−CuO synthesized through oxygen-plasma-assisted nitrogen doping is demonstrated to enable a high C 2+ product selectivity of 77% (including a high C 2 H 4 selectivity of 56%) with a high current density of −34.6 mA/cm 2 at −1.1 V vs RHE, as well as a long-term stability for 22 h without performance degradation. High CO 2 RR 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 C 2+ products. KEYWORDS: electrochemical CO 2 reduction to C 2+ product, O 2 -plasma-assisted N doping, increasing CO binding energy and defect sites, preserving Cu oxidation state, in situ X-ray absorption spectroscopy

Sub-1 nm Cu2O Nanosheets for the Electrochemical CO2 Reduction and Valence State–Activity Relationship

“…However, the Δ G for the transition from *COOH to *CO on Cu 2 O-NS and CuO-NS is larger than the corresponding value on Cu-NS, which indicates that the adsorption capacity of Cu for CO is significantly improved after oxidation. According to the electron cloud structure of CO bonding, CO is given to the electron side during the bonding process between CO and Cu, so the higher oxidation state of Cu, the stronger adsorption capacity for CO. The theoretical calculation results in Figure a are consistent with the experimental results.…”

“…The electron back-donation weakens the internal connections between C and O because the 2π* orbital is vacant and antibonding. Depending on the level of electron back-donation, the surface of Cu will adsorb CO molecules to varying degrees. , As shown in Figure h,k, some of the electrons on Cu of Cu-NS are transferred to form an oxidized state, so that they can adsorb CO and OCCHO. Unlike Cu-NS, Cu on the surfaces of Cu 2 O-NS and CuO-NS is already in an oxidized state, and Cu as an electron acceptor can effectively reduce the σ repulsion of *CO.…”

“…For example, in the Cu 0.50 Zn 0.5 O x electrocatalyst designed by Chang et al, Zn δ+ O can act as a Lewis acid site to receive electrons, adsorb *CO, and stabilize the oxidation state of Cu . Kang et al regulated the adsorption capacity of Cu to *CO by doping N atoms, and also utilized O atom doping to suppress the reduction of N to the oxidized state of Cu, thereby achieving the stability of Cu + …”

Materials Design for Photocatalytic CO2 Conversion to C2+ Products

“…46,47 Moreover, recent advancements have shown that defect engineering can also be employed to modulate the selectivity of products generated during photocatalytic CO 2 conversion. 48 This opens significant opportunities for the production of C 2+ products, further underscoring the versatility and potential of defect engineering in this field.…”

“…These irregularities can either naturally manifest during the material growth or be intentionally introduced through post-treatment processes. , Due to their ease of introduction, defects have found extensive use in studies related to photocatalytic CO 2 conversion. Their functions, such as optimizing the separation of photogenerated charge carriers, expanding the range of light absorption, and providing abundant catalytic sites, have demonstrated their effectiveness in enhancing the process of photocatalytic CO 2 conversion. , Moreover, recent advancements have shown that defect engineering can also be employed to modulate the selectivity of products generated during photocatalytic CO 2 conversion . This opens significant opportunities for the production of C 2+ products, further underscoring the versatility and potential of defect engineering in this field.…”