Fig. 2
a ORR theoretical onset potential versus ΔGOH* on carbon-based SMACs with different metal atomic centers. b Theoretical and experimental ORR onset potentials versus the descriptor φ. c The trend in the theoretical ORR overpotential of metalloporphyrin-based catalysts plotted against ΔGOH* − 1.23 eV. d–f Linear sweep voltammetry (LSV) curves of carbon-based SMACs with different metal atomic centers in O2-saturated 0.1 M KOH. g LSV curves of carbon-based SMACs with different metal atomic centers in O2-saturated 0.1 M HClO4. h LSV curves of carbon-based SMACs with different metal atomic centers in O2-saturated 0.5 M H2SO4. i ORR activity versus O2 binding energy of carbon-based SMACs with different metal atomic centers. a, b Reproduced with permission from Ref. [75]. Copyright 2018, Nature Publishing Group. c Reproduced with permission from Ref. [76]. Copyright 2017, Royal Society of Chemistry. d, g Reproduced with permission from Ref. [78]. Copyright 2014, American Chemical Society. e Reproduced with permission from Ref. [79]. Copyright 2020, American Chemical Society. f Reproduced with permission from Ref. [80]. Copyright 2016, Elsevier. h, i Reproduced with permission from Ref. [81]. Copyright 2017, American Chemical Society