Low-crystalline Ni/Co-oxyhydroxides nanoarrays on carbon cloth with high mass loading and hierarchical structure as cathode for supercapacitors
Menghua Pan, Weiliang Zeng, Hongying Quan, Jingmiao Cui, Guo Yao, Yunying Wang, Dezhi Chen
Abstract
Compared with the crystalline transition metal oxyhydroxide, low-crystalline structure is conducive to high electrochemical performance due to its more grain boundaries and ion diffusion channels. However, the manufacture of low-crystalline oxyhydroxides remains challenging, especially those with multiple transition metals. Herein, high mass loading (~9 mg cm−2) and low-crystalline Ni/Co-oxyhydroxides nanoarrays on carbon cloth (CC) were prepared by electrochemical reconstruction. The low-crystalline Ni/Co-oxyhydroxides nanoarrays possessed a hierarchical structure, which were consist of flake-like (Co0.25, Ni0.75)O(OH) single-crystals and needle-like Ni-doped CoO(OH) polycrystalline. Both single crystal nanoflakes and polycrystalline nanoneedles contained a lot of defects. Owing to the unique structure, the mutual doping of Ni and Co atoms, and the abundant defects, the nanoarrays of Ni/Co-3500 showed excellent electrochemical performance with a high specific capacitance of 8.87 F cm−2 at 5 mA cm−2 and a high rate retention of 69.33% at 50 mA cm−2, as well as a high cycle stability remaining 91.6% of initial capacitance after 2000 galvanostatic charge–discharge cycles at a current density of 20 mA cm−2. Furthermore, the assembled asymmetric supercapacitor of Ni/Co-3500//oxidized CC delivered a high areal capacitance of 1.48 F cm−2 and a volumetric capacitance of 14.8 F cm−3 at 8 mA cm−2, as well as 1.11 F cm−2 (11.1 F cm−3) even at 50 mA cm−2. The energy density of Ni/Co-3500//oxidized CC device was up to 4.35 mWh cm−3 at the powder density of 60.1 mW cm−3. It indicates that the as-prepared low-crystalline Ni/Co-oxyhydroxides arrays on CC is a promising electrode for high energy density supercapacitors.