Ligand environment engineering of nickel single atomic sites for efficient electrochemical carbon dioxide reduction reaction†

The electrochemical carbon dioxide reduction reaction (CO₂RR) is considered one of the feasible options for a net reduction of CO₂ emissions, especially when coupled with renewable energy resources. Many techno-economical assessments on the CO₂RR have concluded that the production of syngas (CO/H₂), a precursor for Fischer–Tropsch synthesis, is beneficial. Thus, cost-effective and durable catalysts are needed to selectively promote the CO₂RR to produce syngas. Ni-based single-atom catalysts (Ni-SACs) have gained significant interest for the CO₂RR towards syngas production. However, there is still a lack of understanding of the physicochemical properties of isolated Ni atomic sites with different ligand environments and the resultant CO₂RR performance. In this study, we combined experimental measurements, in situ X-ray absorption fine structure analyses, and density functional theory calculations to study a series of Ni-SACs with controlled Ni configuration and N-coordination and revealed that Ni–N_x sites with less than 4 N coordination are the catalytically active sites for the selective CO₂RR process. This study provides fundamental insights into the rational design for Ni-SACs for enhanced CO₂RR activity and selectivity based on their structure–property relationship.