Microwave-incorporated hydrothermal synthesis of urchin-like Ni(OH)2-Co(OH)2 hollow microspheres and their supercapacitor applications

Urchin-like Ni(OH)(2)-Co(OH)(2) hollow microspheres were successfully synthesized by a microwave-incorporated hydrothermal method. The Ni(OH)(2)-Co(OH)(2) hollow microspheres achieved a high specific capacitance of 2164 F g(-1) at 1 A g(-1) and long-term cycle life. Electrochemical data reveal that the Ni(OH)(2)-Co(OH)(2) hollow microspheres exhibits much better electrochemical reversibility and specific capacitance retention than that of the single Ni(OH)(2) or Co(OH)(2) based on peak potential difference, symmetry of charge-discharge curves, and specific capacitances at high charge-discharge rates. Furthermore, the designed Ni(OH)(2)-Co(OH)(2)/graphene asymmetric supercapacitor displays good reversibility and a high specific capacitance of 169 F g(-1) at 1 A g(-1), 145 F g(-1) at 3 A g(-1), and 116 F g(-1) at 5 A g(-1), indicating a good ability to deliver a high energy density at a high power density. These results proved that the Ni(OH)(2)-Co(OH)(2) hollow microspheres can be promising electroactive materials for supercapacitor and the microwave-incorporated hydrothermal method provided a one-step, template-free, and cost-effective route for fabricating pseudocapacitive materials in 3-D form. (C) 2013 Elsevier Ltd. All rights reserved.