Fig. 2: HER performance.

a HER polarization curves and (b) Tafel slopes in 1 M KOH. (c) Plot of ratio of Δη/ΔLog|j | (η: overpotential) as a function of current density. Error bars represent standard deviation. d ECSA-corrected polarization curves (hollow) against apparent activity (solid). e Multistep chronopotentiometry of Ni(OH)2@Ni-N/Ni-C/NF and Ni(HO)2/NF as well as HER polarization of Ni(OH)2@Ni-N/Ni-C/NF before and after 1000 CV cycles. f Stability of Ni(OH)2@Ni-N/Ni-C/NF at fixed current densities.