Tris(2-benzimidazolylmethyl)amine-Directed Synthesis of Single-Atom Nickel Catalysts for Electrochemical CO Production from CO 2

The electrochemical reduction of carbon dioxide (CO ) to value-added products is a promising approach to reducing excess CO in the atmosphere. However, the development of electrocatalysts for highly selective and efficient electrochemical CO reduction has been challenging because protons are usually easier to reduce than CO in an aqueous electrolyte. Recently, single-atom catalysts (SACs) have been suggested as candidate CO reduction catalysts due to their unique catalytic properties. To prepare single-atom metal active sites, the stabilization of metal atoms over conductive supports such as graphene sheets to prevent metal aggregation is crucial. To address this issue, a facile method was developed to prepare single-atom nickel active sites on reduced graphene oxide (RGO) sheets for the selective production of carbon monoxide (CO) from CO . The tris(2-benzimidazolylmethyl)amine (NTB) ligand was introduced as a linker that can homogeneously disperse nickel atoms on the graphene oxide (GO) sheets. Because the NTB ligands form strong interactions with the GO sheets by π-π interactions and with nickel ions by ligation, they can effectively stabilize nickel ions on GO sheets by forming Ni(NTB)-GO complexes. High-temperature annealing of Ni(NTB)-GO under inert atmosphere produces nickel- and nitrogen-doped reduced graphene oxide sheets (Ni-N-RGO) with single-atom Ni-N active sites. Ni-N-RGO shows high CO reduction selectivity in the reduction of CO to CO with 97 % faradaic efficiency at -0.8 V vs. RHE (reversible hydrogen electrode).