Lavender-like cobalt hydroxide nanoflakes deposited on nickel nanowire arrays for high-performance supercapacitors

Hierarchical nanostructured electrodes with excellent electronic properties and high specific surface areas have promising applications in high-performance supercapacitors. However, high active mass loading and uniform structure are still crucial in fabricating such architectures. Herein, Co(OH)₂ nanoflakes were homogeneously deposited on nickel nanowire arrays (NNA) through a hydrothermal approach to form an NNA@Co(OH)₂ (NNACOH) composite electrode. The as-synthesized one dimensional (1D) system had a lavender-like structure with a high mass loading of 5.42 mg cm^-2 and a high specific surface area of 74.5 m² g^-1. Due to the unique electrode structure characteristics, the electrode could deliver a high specific capacitance of 891.2 F g^-1 at the current density of 1 A g^-1 (corresponding to an areal capacitance of 4.83 F cm^-2 at 5.42 mA cm^-2). The capacitance could still maintain a high value of 721 F g^-1 when the current density is increased to 50 A g^-1. In addition, the electrode showed superior cycle stability with a capacitance retention of 89.3% after charging/discharging at the current density of 10 A g^-1 for 20 000 cycles. A flexible asymmetric supercapacitor (ASC) was assembled by employing NNACOH as the positive electrode and activated carbon (AC) as the negative electrode. It delivered a maximum energy density of 23.1 W h kg^-1 at the power density of 712 W kg^-1 and an energy density of 13.5 W h kg^-1 at the maximum power density of 14.7 kW kg^-1 (based on the total mass of the electrodes), showing the state-of-the-art energy storage ability of the Co(OH)₂ cathode material at device level.