Growth of vertically aligned nanosheet-like structured nickel–cobalt hydroxide thin films and their electrochemical properties

Nickel–cobalt (Ni–Co) hydroxide thin films were directly prepared on the fluorine-doped tin oxide (FTO)-coated glass substrates using the facile and cost-effective wet-chemical method at a low-temperature of 75–90 °C with different growth durations. The nanosheet-like structures were interconnected with each other and vertically aligned on the surface of the FTO/glass substrate, leading to the formation of a porous thin film. As the growth time increased, the morphology of the nanosheet-like structures was well-preserved. The growth of vertically aligned nanosheet-like structures of the Ni–Co hydroxide grown at 90 °C was faster than that of the sample grown at 75 °C. The distribution of the nanosheet-like structures became denser with increasing temperature and time. The mass- and area-specific capacitances of the Ni–Co hydroxide thin film grown at 90 °C for 8 h were ~ 528 F/g and ~ 42.3 mF/cm2, respectively, at a scan rate of 2 mV/s and reasonably good capacitance retention of ~ 94% at a scan rate of 50 mV/s over 1500 cycles, which indicated superior electrochemical performance compared with that of the sample grown at 75 °C for 8 h. This shows that the vertically well-aligned nanosheet-like structured Ni–Co hydroxide thin films have great potential as cost-effective electrochemical capacitance electrodes.