fig2

Figure 2. (A) Schematic illustration of the synthetic procedure of metal-ISASs/CN; (B-D) EDX measurements and (E-G) High-resolution AC HAADF-STEM images of Fe-ISASs/CN, Co-ISASs/CN and Ni-ISASs/CN, respectively. The (A-G) are quoted with permission from Wei et al.^[51]; (H) Schematic illustration of preparation procedure for SA-Fe^III/SNPC catalyst; (I-K) SEM, TEM, and HAADF-STEM of SA-Fe^III/SNPC catalyst; (L) Fe XANES spectra and (M) Fe FT-EXAFS signal of SA-Fe^III/SNPC and reference samples. The (H-M) are quoted with permission from Zheng et al.^[33]. XANES: X-ray absorption near edge structure; FT-EXAFS: Fourier transform of extended X-ray absorption fine structure; EDX: Energy-dispersive X-ray; AC HAADF-STEM: Aberration-corrected high-angle annular dark field scanning transmission electron microscopy; SNPC: Sulfur and nitrogen co-doped porous carbon; SEM: Scanning electron microscopy; TEM: Transmission electron microscopy; SAs: Single atoms; CN: Carbon nitride; ISAs: Isolated single-atom sites.