Ni Single Atoms/Fe3N Nanoparticles Supported by N-Doped Carbon Hollow Nanododecahedras with Nanotubes on the Surface for Efficient Electro-Reduction of CO2 to CO.

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The transition metal single atoms (SAs)-based catalysts with M-NX coordination environment have shown excellent performance in electrocatalytic reduction of CO2, and they have received extensive attention in recent years. However, the presence of SAs makes it very difficult to efficiently improve the coordination environment. In this paper, a method of direct high-temperature pyrolysis carbonization of ZIF-8 adsorbed with Ni2+ and Fe2+ ions is reported for the synthesis of Ni SAs and Fe3N nanoparticles (NPs) supported by the N-doped carbon (NC) hollow nanododecahedras (HNDs) with nanotubes (NTs) on the surface (Ni SAs/Fe3N NPs@NC-HNDs-NTs). The synergistic effect between Ni SAs and Fe3N NPs can obviously improve the proton-coupled electron transfer step of CO2 reduction reaction and promotes the process of electrocatalytic reduction of CO2 to CO. The fabricated Ni SAs/Fe3N NPs@NC-HNDs-NTs exhibits a high CO selectivity of up to 94% in the potential range of -0.41--0.81 V versus Reversible Hydrogen Electrode (vs RHE), and an optimal CO Faraday efficiency (FECO) of ≈97.31% at -0.68 V (vs RHE) in the reduction reaction CO2 to CO. In the theoretical calculation results, due to the non-bonding synergy effect between Ni SAs and Fe3N NPs, the free energy of *COOH formation is greatly reduced and the adsorption of *CO is obviously improved, which will efficiently promote the conversion between the intermediates in the reaction step and accelerate electro-reduction process of CO2. This work will provide a new method for constructing a mutually optimized coordination environment between Ni SAs and Fe3N NPs to improve the catalytic performance of CO2RR by synergistic complementarity between the dual active sites.