Microwave synthesis of nickel/cobalt double hydroxide ultrathin flowerclusters with three-dimensional structures for high-performance supercapacitors

The hydrothermal method was mostly used for the preparation of metallic double hydroxides. However, it is very time-consuming and energy-consuming. In this study, we for the first time reported a facile, rapid and cost-effective microwave strategy to fabricate nickel/cobalt double hydroxides (Ni/Co-DH). Four solvents, including water, ethanol, isopropanol and tertbutanol, were used for the synthesis of Ni/Co-DH to examine effect of the reaction medium. The study demonstrated that the Ni/Co-DH prepared in the aqueous solution exists as the mixture of alpha-Ni(OH)(2) and beta-Co(OH)(2). However, the Ni/Co-DH prepared in the organic solvent studied has a hydrotalcite-like structure. Moreover, the Ni/Co-DH prepared in ethanol offers ultrathin flowercluster structure with a three-dimensional morphology. Owing to the greatly improved Faradaic redox reaction and mass transfer, the Ni/Co-DH electrode exhibits excellent pseudo-capacitance performance, including high specific capacitance and rate capability, good charge/discharge stability and long-term cycling life. Its maximum specific capacitance was up to 1887.5 Fg(-1) at the current density of 1 Ag-1, which is more than 2.4-fold that of the Ni/Co-DH prepared in the aqueous solution. The specific capacitance can remain 1187.5 Fg(-1) when the current density increases to 10 Ag-1. The capacitance can keep at least 99.7% at the current density of 8 Ag-1 after 3000 cycles. This work also provides a promising approach for the synthesis of various metallic double hydroxide materials with largely enhanced supercapacitor behavior, which can be potentially applied in energy storage/conversion devices. (C) 2013 Published by Elsevier Ltd.