Fig. 2: Morphology and structure characterizations.

a HAADF TEM image of pFeSAN. b Elemental mapping of C, Fe, N, and O elements of pFeSAN. c HAADF-STEM image of pFeSAN showing the atomically dispersed Fe single atom sites as bright dots (yellow cycles marked single atoms). d EELS spectra of pFeSAN. e Pore size distribution curves of C, FeSAN and pFeSAN. f Raman spectra of as-prepared C, FeSAN and pFeSAN. g EPR spectrum of FeSAN and pFeSAN. h The corresponding percentage of N configurations for FeSAN and pFeSAN. Three times each morphology characterization was repeated independently with similar results. Representative images are shown. Source data are provided as a Source Data file.