Microwave synthesis of ZIF-67 derived nickel-cobalt hydroxide and its electrochemical performance

Microwave-assisted heating method was used to rapidly prepare three-dimensional hollow nickel-cobalt hydroxide (Ni-Co LDH) by using zeolite dimethyl imidazolium cobalt (ZIF-67) as template and cobalt source. The effect of microwave reaction time on the morphology and electrochemical properties of the materials was investigated. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and specific surface and aperture analyzer (BET) were used to investigate the effect of microwave reaction time on the structure and morphology of the samples. The electrochemical properties of Ni-Co LDH electrode materials were analyzed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The results showed that the electrochemical properties of Ni-Co LDH-15 min electrode were the best. The specific capacitance was 2371.0 F/g at 0.5 A/g. The Ni-Co LDH-15 min also possessed excellent capacity retention of 78.5% when the current density increased by 20 times. An asymmetric supercapacitor (Ni-Co LDH//AC) was assembled by using Ni-Co LDH as the positive electrode and AC as the negative electrode. The Ni-Co LDH//AC device delivered a high energy density of 19.17 W·h/kg at the power density of 448.05 W/kg. Furthermore, the capacitance retention rate still maintained 88.7% after 5000 cycles. These results showed that Ni-Co LDH was a kind of electrode material for supercapacitor with excellent electrochemical performance and practical application potential.