Theoretical Study on the Electrocatalytic CO₂ Reduction Mechanism of Single-Atom Co Complexed Carbon-Based (Co–N_χ@C) Catalysts Supported on Carbon Nanotubes

Electrocatalytic CO₂ reduction serves as an effective strategy to tackle energy crises and mitigate greenhouse gas effects. The development of efficient and cost-effective electrocatalysts has been a research hotspot in the field. In this study, we designed four Co-doped single-atom catalysts (Co-N_χ@C) using carbon nanotubes as carriers, these catalysts included tri- and dicoordinated N-doped carbon nanoribbons, as well as tri- and dicoordinated N-doped graphene, respectively denoted as H3(H2)-Co/CNT and 3(2)-Co/CNT. The stable configurations of these Co-N_χ@C catalysts were optimized using the PBE+D3 method. Additionally, we explored the reaction mechanisms of these catalysts for the electrocatalytic reduction of CO₂ into four C1 products, including CO, HCOOH, CH₃OH and CH₄, in detail. Upon comparing the limiting potentials (<i>U</i>_L) across the Co-N_χ@C catalysts, the activity sequence for the electrocatalytic reduction of CO₂ was H2-Co/CNT > 3-Co/CNT > H3-Co/CNT > 2-Co/CNT. Meanwhile, our investigation of the hydrogen evolution reaction (HER) with four catalysts elucidated the influence of acidic conditions on the electrocatalytic CO₂ reduction process. Specifically, controlling the acidity of the solution was crucial when using the H3-Co/CNT and H2-Co/CNT catalysts, while the 3-Co/CNT and 2-Co/CNT catalysts were almost unaffected by the solution's acidity. We hope that our research will provide a theoretical foundation for designing more effective CO₂ reduction electrocatalysts.