Fig. 4

a CV curves of Fe–N–S/CFs tested in O₂ or N₂ saturated 0.1 M KOH. b LSV curves of Fe–N–S/CFs, Fe–N/CFs, Fe/CFs and Pt/C tested at the rotating speed of 1600 rpm. c Tafel plots of Fe–N–S/CFs, Fe–N/CFs and Pt/C measured at the rotating speed of 1600 rpm. d LSV curves of Fe–N–S/CFs with rotating speed ranging from 400 to 2500 rpm. e K–L plots of Fe–N–S/CFs, Fe–N/CFs and Pt/C at 0.4 V vs. RHE. f H₂O₂ yielding and electron transfer number curves of Fe–N–S/CFs, Fe–N/CFs and Pt/C