fig2

Figure 2. (A) Schematic atomic model of asymmetrical expansion from RuN₄ to RuN₄S. Reproduced with permission^[21]. Copyright 2022, American Chemical Society. Comparison of Ru K-edge XANES spectrum (B) and the E-space derivation (C) between the experimental and theoretical fitting. Reproduced with permission^[21]. Copyright 2022, American Chemical Society. (D) Content of Fe moieties with varied spin polarization deriving from ⁵⁷Fe Mössbauer spectroscopy. Reproduced with permission^[23]. Copyright 2021, John Wiley and Sons. (E) The correlation between ORR overpotential (η_ORR) and OH* adsorption free energy (ΔG_OH*) on Fe moieties with distinct local configurations. Reproduced with permission^[23]. Copyright 2021, John Wiley and Sons. (F) Schematic illustration of the formation of Fe single-atom sites with different numbers and locations of S doping. Reproduced with permission^[26]. Copyright 2019, American Chemical Society. Charge density difference of Fe₁N₄P₁ (G) and Fe₁N₄P₂ (H). The brown, blue, and golden spheres represent carbon, nitrogen, and iron atoms, respectively. Reproduced with permission^[28]. Copyright 2023, Elsevier.