Insights on forming N,O-coordinated Cu single-atom catalysts for electrochemical reduction CO₂ to methane

Single-atom catalysts (SACs) are promising candidates to catalyze electrochemical CO₂ reduction (ECR) due to maximized atomic utilization. However, products are usually limited to CO instead of hydrocarbons or oxygenates due to unfavorable high energy barrier for further electron transfer on synthesized single atom catalytic sites. Here we report a novel partial-carbonization strategy to modify the electronic structures of center atoms on SACs for lowering the overall endothermic energy of key intermediates. A carbon-dots-based SAC margined with unique CuN₂O₂ sites was synthesized for the first time. The introduction of oxygen ligands brings remarkably high Faradaic efficiency (78%) and selectivity (99% of ECR products) for electrochemical converting CO₂ to CH₄ with current density of 40 mA·cm^-2 in aqueous electrolytes, surpassing most reported SACs which stop at two-electron reduction. Theoretical calculations further revealed that the high selectivity and activity on CuN₂O₂ active sites are due to the proper elevated CH₄ and H₂ energy barrier and fine-tuned electronic structure of Cu active sites.