Figure 4. (a) Schematic illustration for the formation of the Ni-NC@Ni catalyst. In the green circle: the possible atomic structure of the Ni–N species. HAADF-STEM image of NC with (b) Ni NPs and (c) atomic dispersion of Ni atoms in the carbon skeleton. Reproduced with permission.[78] Copyright 2020, Elsevier. (d) The CO FEs and CO partial current densities comparison of Ni0.037-NG and Ni0.037-NG-H catalysts at independent potentials from −0.5 to −1.2 V (vs RHE). (e) Calculation model and charge density difference graph of NGR@Ni and 3NGR@Ni (left: side view; right: top view; Yellow and blue represent the charge accumulation and depletion, respectively). (f) Difference in limiting potentials between ECR and HER for Ni-N4, Ni-N1, NGR, NGR@Ni, and 3NGR@Ni. Reproduced with permission.[79] Copyright 2021, Wiley-VCH. (g) Partial CO currents plotted against different potentials from NiSA/NP, NiSA, and NiNP. (h) Top and side views of the deformation electronic densities of NiN3@Ni (111). The Δq indicates the increased number of electrons of the Ni single atom on NiN3@Ni (111). Reproduced with permission.[81] Copyright 2022, Wiley-VCH. (i) A proposed reaction mechanism for CO production via ECR. Ni yellow, N blue, O pink, C gray, H red. (j) Illustration of synthesis process of Ni@NiNCM. Reproduced with permission.[82]Copyright 2021, Wiley-VCH.