Fig. 3: Electrochemical measurements of HER performances for these electrodes in both acid and alkaline medium.

a Linear sweep voltammetry (LSV) curves and b Tafel slopes of (I) Co4N@CoSA/N-CNT/CC, (II) Co@CoSA/N-CNT/CC, (III) CoSA/N-CNT/CC, (IV) 20wt.% Pt/C, (V) Co4N/CC, and (VI) bare CC. c Comparison of the 1st and 5000th LSV curves of Co4N@CoSA/N-CNT/CC for the HER in a 0.5M H2SO4 medium. Inset in (c) is the current–time curve. d LSV curves and e Tafel slopes of (I) Co4N@CoSA/N-CNT/CC, (II) Co@CoSA/N-CNT/CC, (III) CoSA/N-CNT/CC, (IV) 20wt.% Pt/C, (V) Co4N/CC, and (VI) bare CC. f Comparison of the 1st and 5000th LSV curves of Co4N@CoSA/N-CNT/CC for the HER in a 1.0M KOH medium. Inset in (f) is the current–time curve.