fig4

Figure 4. (A) LSV tests of Co-N₄-C, Co-N₄Cl-C, Pt/C, and NC collected after the electrolyte is saturated with O₂; (B) Literature comparison chart about ORR performance of Co-N₄Cl-C with reported catalysts; (C) Tafel plots of Co-N₄-C, Co-N₄Cl-C, Pt/C, NC; (D) Mass activity and TOF at 0.80 V (vs. RHE) for Co-N₄-C and Co-N₄Cl-C catalysts. ORR polarization curves of (E) Co-N₄Cl-C and (F) Co-N₄-C at various rotational speeds; the inset shows a fitting illustration of the K-L formula across various voltages; (G) Current-time chronoamperometric responses of Co-N₄Cl-C, Co-N₄-C, and Pt/C. LSV: Linear sweep voltammetry; ORR: oxygen reduction reaction; TOF: turnover frequency.