1. SEM images of (a) Fe-NC and (b)Fe SA-NC, (c)nitrogen adsorption/desorption plots of Fe SA-NC at 77 K, and (d) pore size distribution of Fe SA-NC

2. (a) TGA curves of hypoxanthine and hypoxanthine with molten salt; (b) Raman spectra and (c) XRD patterns of Fe SA-NC and Fe-NC

3. (a, b) AC HAADF-STEM images, high-resolution X-ray photoelectron spectra (XPS) of (c) N1s and (c) Fe2p of the Fe SA-NC catalyst

4. Fe K-edge (a) XANES spectra (b) k²-weighted FT spectra for the Fe SA-NC, FePc, FeO and Fe₂O₃ and (c) EXAFS fitting curves in R space for Fe SA-NC

5. (a) CV curves of the Fe SA-NC in a N₂-saturated and O₂-saturated 0.1 mol/L KOH solution, respectively; (b) LSV curves of Fe SA-NC, NC and Pt/C in O₂-saturated 0.1 mol/L KOH solution (1600 r/min, 10 mV·s^-1); (c) ORR polarization curves of Fe SA-NC recorded at different rotating speeds; (d) K-L plots derived from Fig. (c); (e) ORR electron transfer number and H₂O₂ yield of Fe SA-NC; (f) Tafel slopes of Fe SA-NC, NC and Pt/C in O₂-saturated 0.1 mol/L KOH solution

6. (a) Durability test and (b) methanol resistance test for Fe SA-NC in O₂-saturated 0.1 mol/L KOH solution (1600 r/min)

Table 1. XPS results of element composition in Fe SA-NC catalyst

Table 2. EXAFS fitting parameters of Fe SA-NC sample