Electrochemical conversion of CO2 to the syngas hybrid with the Fischer–Tropsch (FT) process is a promising way to produce synthetic fuels from renewable energy sources. The product distribution in liquid hydrocarbons produced by FT synthesis has strong dependence on the CO/H2 ratio of the syngas feedstock. Herein, we demonstrated the feasibility of tuning the CO/H2 ratio at a wide range by developing nanoparticle-assisted Ni–Co binary single-atom catalysts for electrocatalytic production of syngas. By controlling the elemental proportion of Ni–Co in the composite catalysts, electrochemical reduction of CO2 to syngas with a tunable CO/H2 ratio from 0.3 to 27.6 was achieved. For the binary catalysts with a Ni–Co ratio of 1:1, the CO/H2 ratio maintains at 1.3–1.5 in a broad potential range from −0.59 to −0.83 V versus reversible hydrogen electrode (RHE) and the total current density reaches ∼32.2 mA/cm2 at −1.0 V versus RHE. The promotion effect of nanoparticles on Ni–Co single-atom catalysts was validated by partial removal of nanoparticles and further density functional theory (DFT) calculations. As revealed by DFT calculations, nanoparticles incorporated in single-atom sites take essential roles in facilitating the adsorption of CO2 and the formation of *COOH. The origin of CO2RR and hydrogen evolution reaction reactivities can be identified as Ni–N4 and Co–N4 single-atom sites, respectively. The dual active sites allow the facile control of the CO/H2 ratio of electrochemical converted syngas, and it will be beneficial to downstream production of diverse chemicals.
Despite the various strategies for achieving metal–nitrogen–carbon (M–N–C) single-atom catalysts (SACs) with different microenvironments for electrochemical carbon dioxide reduction reaction (CO2RR), the synthesis–structure–performance correlation remains elusive due to the lack of well-controlled synthetic approaches. Here, we employed Ni nanoparticles as starting materials for the direct synthesis of nickel (Ni) SACs in one spot through harvesting the interaction between metallic Ni and N atoms in the precursor during the chemical vapor deposition growth of hierarchical N-doped graphene fibers. By combining with first-principle calculations, we found that the Ni-N configuration is closely correlated to the N contents in the precursor, in which the acetonitrile with a high N/C ratio favors the formation of Ni-N3, while the pyridine with a low N/C ratio is more likely to promote the evolution of Ni-N2. Moreover, we revealed that the presence of N favors the formation of H-terminated edge of sp2 carbon and consequently leads to the formation of graphene fibers consisting of vertically stacked graphene flakes, instead of the traditional growth of carbon nanotubes on Ni nanoparticles. With a high capability in balancing the *COOH formation and *CO desorption, the as-prepared hierarchical N-doped graphene nanofibers with Ni-N3 sites exhibit a superior CO2RR performance compared to that with Ni-N2 and Ni-N4 ones.
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