fig2

Figure 2. (A) Illustration of the preparation process of single iron atomic sites supported on nitrogen, phosphorus, and sulfur co-doped hollow carbon polyhedron (Fe-SAs/NPS-HC) by pyrolysis combined with a heteroatom doping strategy; Reproduced from Ref.^[33] with permission from Springer Nature. Electrochemical and physical characterization of different catalysts. (B) Pt L₃-edge XANES for Pt SACs and corresponding Pt foil, PtO₂; (C) The k²-weighted R-space FT spectra from EXAFS for Pt SACs and corresponding Pt foil, PtO₂; (D) High-angle annular dark field scanning transmission electron microscope (HAADF-STEM) image to show the distribution of Pt atoms on carbon defects. Reproduced from Ref.^[39] with permission from Wiley-VCH.