NPM-SACs/CS for OER. (A) The proposed catalytic pathways for oxygen release in an acidic medium or alkaline medium, where * represents the active site. (B) OER reaction mechanism on Fe₁(OH)_x/P-C. The blue, brown, red, and white balls represent Fe, C, O, and H atoms, respectively. (C) LSV curves and (D) TOF at the overpotential of 0.35 V of Fe₁(OH)_x/P-C and control samples in 1.0 mol L⁻¹ KOH. (E) Chronopotentiometric curve of Fe₁(OH)_x/P-C at 10 mA cm^-2 in 1.0 mol L⁻¹ KOH. Reproduced with permission from ref. [199]. Copyright©2021, American Chemical Society. Ball-and-stick model and free energy of (F) Co-N₂C₂, (G) Co-N₃ and (H) Co-N₄. Reproduced with permission from ref. [164]. Copyright©2020, Royal Society of Chemistry.