Design of Mg-Ni binary single-atom catalysts for conversion of carbon dioxide to syngas with a wide tunable ratio: Each species doing its own job or working together to win?

[Display omitted] •Mg-Ni dual atomic catalysts are constructed for eCO2RR to produce syngas.•Faradaic efficiency is close to ∼100 % exhibiting the excellent selectivity.•The controllable H2/CO ratio is achieved by tuning Ni content.•Synergistic effect to win instead of each species doing its own job by DFT calculations. Electrochemical carbon dioxide reduction reaction (eCO2RR) to generate syngas is an appealing strategy for CO2 net reduction. However, it suffers from the inferior faradaic efficiency (FE), selectivity, and difficult modulation of hydrogen/carbon monoxide (H2/CO) ratio. To address these issues, a series of magnesium-nickel (Mg-Ni) dual atomic catalysts with different Ni contents are fabricated on the nitrogen-doped carbon matrix (MgNiX-NC DACs) by one-step pyrolysis. MgNi5-NC electrocatalyst generates 0.51–0.79 H2/CO ratios in a potential range of −0.6 to −1.0 V vs. reversible hydrogen electrode (RHE) and the total FE reaches 100 % with good stability. While a wider range of H2/CO (0.95–4.34) is achieved for MgNi3-NC electrocatalyst in the same overpotential range, which is suitable for typical downstream thermochemical reactions. Introduction of Ni species accelerates the generation of CO, however, there is much less influence on the H2 production as compared with Mg-based single atomic electrocatalyst. According to the experimental results and density functional theory (DFT) calculations, the synergistic effect between Mg and Ni achieves the satisfied results rather than each one fulfill its own duty for selective producing H2 and CO, respectively. This work introduces a feasible approach to develop atomic catalysts on main group metal for more controllable CO2RR.