Hexamethylenetetramine-induced synthesis of hierarchical NiO nanostructures on nickel foam and their electrochemical properties

• NiO as active electrode material direct grows on nickel foam.
• Hexamethylenetetramine is used as both alkaline solvent and complex agent.
• The effect of nickel salts on the morphology and electrochemical performances was investigated.

Uniform NiO hierarchical nanostructures assembled by NiO nanosheets have grown directly on nickel foam substrate via a mild hydrothermal reaction between nickel salts and hexamethylenetetramine (HMT), followed by a subsequent calcinations process. HMT was employed as both alkaline source and complex agent. Several kinds of nickel salts (NiSO4, Ni(NO3)2, NiCl2 or Ni(CH3COO)2) were introduced as nickel source to investigate their effect on the morphology and electrochemical performances of NiO nanostructure. Cyclic voltammetry and constant current charge–discharge measurement illustrated these NiO electrodes presented good electrochemical performance. Especially the electrode with NiSO4 as nickel source gave a maximum specific capacitance of 349 F g−1 at a current density of 0.25 A g−1, which was superior to others owing to the smaller particle size that provided more active sites to ensure sufficient Faradaic reaction.