Fig. 6From: Hollow Ni/NiO/C composite derived from metal-organic frameworks as a high-efficiency electrocatalyst for the hydrogen evolution reactiona Polarization curves recorded initially and after 2000 CV cycles of H–Ni/NiO/C. Inset: Current–time response of H–Ni/NiO/C obtained at − 0.198 V for 12 h. b Schematic of the proposed HER mechanism using the H–Ni/NiO/C catalystBack to article page