Fig. 8
a Linear fitting curve of oxidation state for Fe-ISA/SNC and reference materials. The insert is the molecular structure of Fe-N4S2 active site in Fe-ISA/SNC. b Free energy diagrams of ORR on Fe-ISA/SNC and Fe-ISA/NC. c Comparison of Jk at 0.85 V and E1/2 of Fe-ISA/SNC, Fe-ISA/NC, and Pt/C. d Geometric structure of Fe/SNC-7.3. e Free energy diagram of ORR on Fe/NC and Fe/SNC. f Schematic interfacial model of Cu-SA/SNC. g LSV curves of Cu-SA/SNC, Cu-SA/NC, SNC, NC, and Pt/C catalysts in O2-saturated 0.1 M KOH solution. h Schematic model of Fe-SAs/NPS-HC, Fe (orange), N (blue), P (green), S (yellow) and C (gray). i LSV curves of Fe-SAs/NPS-HC, Fe-SAs/NPS-C, NPS-HC, and Pt/C catalysts in O2-saturated 0.1 M KOH solution. a-c Reproduced with permission from Ref. [119]. Copyright 2018, Wiley-VCH. d, e Reproduced with permission from Ref. [115]. Copyright 2017, Wiley-VCH. f, g Reproduced with permission from Ref. [118]. Copyright 2019, Royal Society of Chemistry. h, i Reproduced with permission from Ref. [32]. Copyright 2018, Nature Publishing Group