fig4
![Heterogeneous single-atom catalysts for energy process: recent progress, applications and challenges](https://image.oaes.cc/412b5842-a04b-4be1-8dae-44815d7d6412/5490.fig.4.jpg)
Figure 4. (A) Schematic illustration of the fabrication process of Ni-doped nanoporous graphene; Reproduced from Ref.[51] with permission from Wiley-VCH. (B) Schematic illustration of the fabrication of Fe SACs; (C) Enlarged HAADF-STEM image of Fe-N-SCCFs. Reproduced from Ref.[52] with permission from the American Chemical Society. Scheme for the construction of high-loading single-atom Pd1/PCN with chemical scissors. (D and H) The models of PCN, (E and I) The models of Pdh/PCN, (F and J) The schemes of selective etching; (G and K) As-synthesized Pd1/PCN. Only bonds between Pd and PCN have remained. (L) Recycling Pd to avoid waste. Reproduced from Ref.[53] with permission from Wiley-VCH.