fig7

Figure 7. (A) Structure of CoNi-SAs/NC. Free-energy diagrams of (B) two models at 0 and 1.23 V and (C) OER processes on NC, Ni-N and Co-Ni-N at 1.57 V. Reproduced with permission: Copyright 2019, Wiley^[125]. (D) Overall bifunctional performance for different catalysts based on Tafel slope in 1 M KOH/0.1 M O₂-saturated KOH. Proposed mechanisms for (E) ORR and (F) OER. Black, blue, green, golden, red and pink balls represent C, N, Ni, Fe, O and H atoms, respectively. Reproduced with permission: Copyright 2020, Elsevier^[126]. (G) Free-energy diagram of ORR on Fe, Mn-N/C under an 0.33 V overpotential. (H) Differential charge density illustrating the increase (olive color) and decrease (cyan color) in electron distributions. (I) Bader charge analysis. Reproduced with permission: Copyright 2018, Royal Society of Chemistry^[127]. ORR: oxygen reduction reaction; OER: oxygen evolution reaction.