Ni–Co Binary Hydroxide Nanotubes with Three-Dimensionally Structured Nanoflakes: Synthesis and Application as Cathode Materials for Hybrid Supercapacitors

Nickel–cobalt binary hydroxide nanotubes were fabricated by a facile synthetic approach by using Cu₂O nanowires as sacrificial templates. The surface morphology of the binary hydroxide nanotubes can be easily controlled by adjusting the molar ratio of Ni to Co. With increasing Co content, the surfaces of the nanotubes tend to form hierarchical nanoflakes. The obtained nanotubes with high specific surface area exhibit typical battery-like electrochemical behavior. Among them, Ni–Co hydroxide nanotubes with Ni:Co=48:52 showed outstanding electrochemical characteristics, with a specific capacity of 209.9 mAh g⁻¹ at 1 Ag⁻¹ and remarkable cycling stability with 84.4 % capacity retention after 10 000 cycles at 20 A g⁻¹. With the advantages of their unique nanostructure and the synergistic effect of the two elements, the Ni–Co binary hydroxide nanotubes are expected to be effective potential cathode materials for hybrid supercapacitors.