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.

Graphical abstractNovel urchin-like Ni(OH)2–Co(OH)2 hollow microspheres synthesized by a microwave-incorporated hydrothermal method exhibited much better electrochemical reversibility and specific capacitance retention than that of the single Ni(OH)2 at high current densities. Furthermore, a high specific capacitance of 169 F g−1 at 1 A g−1 and good reversibility over 1000 cycles were maintained at high charge–discharge current densities for the designed Ni(OH)2–Co(OH)2/graphene asymmetric supercapacitor.Figure optionsDownload full-size imageDownload as PowerPoint slide