Figure 8. (a) Schematic of the synthesis of H-Ni/NC. (b) Schematic diagram of the formation of attachment of a hydroxyl group via OH to the carbon atom next to a pyridinic N. (c) The calculated free-energy diagrams on different catalysts with active sites. (d) Schematic of the synthesis process for Ni–N4/C–NH2. Reproduced with permission.[102] Copyright 2020, Royal Society of Chemistry. (e) CO2adsorption isotherm of Ni–N4/C and Ni–N4/C–NH2. (f) Projected DOS of Ni 3d and (g) free-energy diagram of CO2 electroreduction to CO over Ni–N4/C and Ni–N4/C–NH2. Reproduced with permission.[103] Copyright 2021, Royal Society of Chemistry.
In addition, a series of ionic liquids with different combinations of cations and anions was restricted into the nanopore size of the Ni-N-C material, solving the problem of high viscosity and low conductivity of ionic liquids for ECR reaction by Zhao’s group.[104] When the target catalyst is applied to dilute CO2 reduction, the optimal Ni-N-C/[Bmim][PF6] hybrid exhibits nearly 100% CO selectivity at −0.8 V, significantly superior to the initial Ni-N-C catalyst. As expected, the [Bmim]+ cation can coordinate with free CO2* to form [Bmim]-CO2 complex, enhancing the adsorption of CO2. The high solubility of ionic liquid CO2, the inherent activity of single-atom Ni sites, and the large surface area of carbon nanotubes jointly promote the rapid electron/mass transport and the co-catalytic ECR effect of ionic liquid.