fig9

Figure 9. (A) The ORR mechanism is shown with the blue arrow for proton/electron transfer and the yellow arrow for the O-O bond break. The illustration is quoted with permission from Wang et al.^[12]; (B) Fe SAC/N-C TEM image; (C) Free energy diagrams of the ORR process of three Fe-SACs in different coordination environments at 0.4 V overpotential, and the volcano plot in the upper right corner. The B and C figures are quoted with permission from Lin et al.^[80]; (D) Illustration of ISAS-Co/HNCS; (E) ISAS-Co/HNCS XANES spectra at the Co K-edge. The D and E are quoted with permission from Han et al.^[81]; (F) SEM images of Ni SAs-NC; (G) LSV curves of different catalysts in O₂ saturated 0.1 M KOH. The F and G are quoted with permission from Jiang et al.^[82]. ORR: Oxygen reduction reaction; TEM: Transmission electron microscopy; SACs: Single-atom catalysts; ISAS-Co/HNCS: Isolated single atomic sites are dispersed on hollow N-doped carbon spheres; XANES: X-ray absorption near edge structure; SEM: Scanning electron microscopy; Ni SAs-NC: Ni SAs dispersed on N-doped carbon nanosheets; SV: