Anchoring sea-urchin-like Co(OH)2 microspheres on nickel foam as three-dimensional free-standing electrode for high-performance supercapacitors

Transition metal hydroxides have emerged as promising materials in supercapacitor. In this work, a free-standing supercapacitor electrode was prepared. Sea-urchin-like Co(OH) 2 microspheres were hydrothermally deposited on a Ni foam substrate, showing a hierarchical 3D free-standing structure. The 3D framework endows the as-prepared electrode with improved supercapacitive performances. The influence of the hydrothermal time on the structure and electrochemical performances of the resulting products are investigated systematically. It delivers a capacitance of 1916 F/g (15.9 F/cm 2 ) and 699 F/g (5.8 F/cm 2 ) at 10 mA/cm 2 and 100 mA/cm 2 , respectively, exhibiting excellent rate performance. The capacitance retains about 79.3% after 5000 charging-discharging cycles at 80 mA/cm 2 . Various ill-defined rod-like and stacked plate-like CoOOH materials are obtained from the electrodes after the cycles, which is responsible for the property deterioration of Co(OH) 2 /Ni foam.