Design of a Graphene Nitrene Two-Dimensional Catalyst Heterostructure Providing a Well-Defined Site Accommodating One to Three Metals, with Application to CO2 Reduction Electrocatalysis for the Two-Metal Case.

Recently, the reduction of CO2 to fuels has been the subject of numerous studies, but the selectivity and activity remain inadequate. Progress has been made on single-site two-dimensional catalysts based on graphene coupled to a metal and nitrogen for the CO2 reduction reaction (CO2RR); however, the product is usually CO, and the metal-N environment remains ambiguous. We report a novel two-dimensional graphene nitrene heterostructure (grafiN6) providing well-defined active sites (N6) that can bind one to three metals for the CO2RR. We find that homobimetallic FeFe-grafiN6 could reduce CO2 to CH4 at -0.61 V and to CH3CH2OH at -0.68 V versus reversible hydrogen electrode, with high product selectivity. Moreover, the heteronuclear FeCu-grafiN6 system may be significantly less affected by hydrogen evolution reaction, while maintaining a low limiting potential (-0.68 V) for C1 and C2 mechanisms. Binding metals to one N6 site but not the other could promote efficient electron transport facilitating some reaction steps. This framework for single or multiple metal sites might also provide unique catalytic sites for other catalytic processes.