Fig. 4
Electrocatalytic oxygen reduction reaction performance. a Oxygen reduction reaction (ORR) polarization curves for single iron atomic sites supported on a nitrogen, phosphorus and sulfur co-doped hollow carbon polyhedron (Fe-SAs/NPS-HC), N, P, S co-doped solid carbon polyhedron with isolated Fe atomic sites (Fe-SAs/NPS-C), iron-free N, P, S co-doped hollow carbon polyhedron (NPS-HC) and 20% Pt/C. b Comparison of J k at 0.85 V and E 1/2 of Fe-SAs/NPS-HC and the corresponding reference catalysts. c The Tafel plots for Fe-SAs/NPS-HC and the corresponding reference catalysts. d Nyquist plots of electrochemical impedance spectroscopy (EIS) over Fe-SAs/NPS-HC, Fe-SAs/NPS-C, NPS-HC and 20% Pt/C catalysts in 0.1 M KOH. e The ORR polarization curves at different rotating rates of Fe-SAs/NPS-HC (inset: K−L plots and electron-transfer numbers). f Electron-transfer number (n) (top) and H2O2 yield (bottom) vs. potential. g Cyclic voltammetry (CV) data for Fe-SAs/NPS-HC in O2-saturated 0.1 M KOH without and with 1.0 M CH3OH. h ORR polarization curves of Fe-SAs/NPS-HC before and after 5000 cycles. i Fe K-edge X-ray absorption near-edge structure (XANES) spectra of Fe-SAs/NPS-HC at various potentials during ORR catalysis in O2-saturated 0.1 M KOH (inset: the enlarged Fe K-edge XANES spectra)
