Synergetic Effect of Three-Dimensional Co 3 O 4 @Co(OH) 2 Hybrid Nanostructure for Electrochemical Energy Storage

A novel three-dimensional (3D) Co3O4@Co(OH)2 hybrid nanostructure is synthesized by using two-step hydrothermal and electrodeposition methods. The composite can be employed as an efficient electrode of a high-performance supercapacitor. Scanning electron microscopy and high-resolution transmission electron microscopy images show that Co(OH)2 nanosheets can grow both in the space and on the tops of Co3O4 nanotubes. In comparison with the sole Co3O4 nanotubes and Co(OH)2 nanosheets, the hybrid Co3O4@Co(OH)2 electrode with a naturally formed nanostructure exhibits much improved battery-type performances in a 3 mol L−1 KOH electrolyte solution, as evidenced by the high specific capacity of 1876 C g−1 at a current density of 5 mA cm−2. A good retention capability is also demonstrated, 83.1% of initial capacity value is maintained after 1000 cycles at a current density of 25 mA cm−2. The observed high performances of Co3O4@Co(OH)2 hybrid electrode with the 3D nanostructure make it attractive for the development of high-efficiency electrochemical energy storage devices.