Advanced hybrid supercapacitors assembled with beta-Co(OH)2 microflowers and microclews as high-performance cathode materials

Abstract

Supercapacitors (SCs) have received increasing attention thanks to their high power density, cyclic stability, and quick charging capability. Herein, a battery-type beta-Co(OH)2 electrode materials including two types of microstructures of nanosheets-assembled microflowers (MFs) and nanowires-based microclews (MCs) have been prepared through a three-step synthetic method, which contains an initial solvothermal reactions, aging the precursor in water, and final hydrothermal treatment. The mixed solvent of glycerol and isopropanol with different volume ratio in the first solvothermal stage has a crucial impact on the formation of different microstructures. Both the MFs and MCs possess huge surface area, and may provide abundant electro-active sites for further Faradic reactions. After they were tested in different electrode systems, it was found that the β-Co(OH)2 MFs presented a specific capacity of 396.5 C g−1 (1 A g−1) along with a rate of 81.2% at 10 A g−1, and the MCs exhibited an inferior capacity of 303.9 C g−1. In order to further assess the potential of practical applications in SCs, a hybrid supercapacitor (HSC) device was designed by choosing activated carbon (AC) as negative electrode. The β-Co(OH)2 MFs//AC device exhibited 158.6 C g−1 and an energy density (Ed) of 43.6 W h kg−1. In contrast, the β-Co(OH)2 MCs//AC HSC showed lower Ed of 34.1 W h kg−1 at 954.7 W kg−1. Both HSCs exhibited brilliant cycling stability over 5000 continuous cycles at 6 A g−1. Such impressive electrochemical response of β-Co(OH)2 MFs & MCs makes them the suitable candidates to assemble advanced HSC devices with high-performance, and may anticipate their promising application prospect in the near future.