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?

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.

Liquid Nitrogen Sources Assisting Gram-Scale Production of Single-Atom Catalysts for Electrochemical Carbon Dioxide Reduction.

Developing metal-nitrogen-carbon (M-N-C)-based single-atom electrocatalysts for carbon dioxide reduction reaction (CO2 RR) have captured widespread interest because of their outstanding activity and selectivity. Yet, the loss of nitrogen sources during the synthetic process hinders their further development. Herein, an effective strategy using 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4 ]) as a liquid nitrogen source to construct a nickel single-atom electrocatalyst (Ni-SA) with well-defined Ni-N4 sites on a carbon support (denoted as Ni-SA-BB/C) is reported. This is shown to deliver a carbon monoxide faradaic efficiency of >95% over a potential of -0.7 to -1.1 V (vs reversible hydrogen electrode) with excellent durability. Furthermore, the obtained Ni-SA-BB/C catalyst possesses higher nitrogen content than the Ni-SA catalyst prepared by conventional nitrogen sources. Importantly, only thimbleful Ni nanoparticles (Ni-NP) are contained in the large-scale-prepared Ni-SA-BB/C catalyst without acid leaching, and with only a slight decrease in the catalytic activity. Density functional theory calculations indicate a salient difference between Ni-SA and Ni-NP in the catalytic performance toward CO2 RR. This work introduces a simple and amenable manufacturing strategy to large-scale fabrication of nickel single-atom electrocatalysts for CO2 -to-CO conversion.