fig3

Figure 3. (A) Schematic illustration of the Fe-PANI preparation; (B) AC HAADF-STEM image of Fe-PANI; (C) FT-EXAFS spectra of Fe-PANI. The (A-C) are quoted with permission from Shi et al.^[55]; (D) Synthesis procedure of M-N-C (M: Fe, Co, Ni) SACs; (E-G) HAADF-STEM images of Fe-N-C, Co-N-C, Ni-N-C. The (D-G) are quoted with permission from Wang et al.^[52]; (H) Illustration of the synthesis process used to prepare 2D Fe_y-N-HCNS/rGO-T nanosheets. This figure is quoted with permission from Tan et al.^[56]; (I) Schematic illustration of the preparation process of PCCs. This figure is quoted with permission from Long et al.^[10]. FT-EXAFS: Fourier transform of extended X-ray absorption fine structure; AC HAADF-STEM: Aberration-corrected high-angle annular dark field scanning transmission electron microscopy; PANI: Polyaniline; SACs: Single-atom catalysts; PCCs: Porous carbon catalysts.