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.