Low-crystalline Ni/Co-oxyhydroxides nanoarrays on carbon cloth with high mass loading and hierarchical structure as cathode for supercapacitors

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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.