fig4

Figure 4. (A) Schematic illustration of pyrrolic-, pyridinic- and graphitic-N on the carbon support. (B) Identification of ORR intermediates adsorbed on pyrrole-type active sites derived from Mössbauer spectroscopy. Reproduced with permission^[48]. Copyright 2022, American Chemical Society. (C) Contour plot showing adsorption energy of OH* on pyridinic FeN₄ sites as a function of pH and potential. Reproduced with permission^[49]. Copyright 2022, American Chemical Society. (D) Comparison of adsorption energy of ORR intermediates between pyrrole-type and pyridine-type active sites. Reproduced with permission^[49]. (E) Coordination or structural changes of pyrrole-type and pyridine-type active sites under operando conditions. Reproduced with permission^[53]. Copyright 2020, Springer Nature. (F) Comparison of ΔG of demetallation between pyrrolic FeN₄ and monosymmetric FeN₂ + N’₂. Reproduced with permission^[55]. (G) ORR activity of Fe-N-C catalysts prepared at different temperatures (600-1,100 °C). Reproduced with permission^[57]. Copyright 2017, American Chemical Society. (H) Correlation between ORR activity and content of varied types of nitrogen altered with temperature. Reproduced with permission^[57]. Copyright 2017, American Chemical Society.