Fabrication and electrochemical properties of hollow cage-like nickel cobalt layered hydroxides with porous structure

Supercapacitors have attracted extensive attention in various storage devices due to their high power density, long life and friendly environment. Hence, improving the energy storage performances of electrode materials are of great significance for supercapacitors. Functional materials with specific nanostructures, as energy storage materials, can display excellent electrochemical performances, for they will provide rich electrochemically active sites, high specific surface area and enhance electrolyte contact area. Consequently, hollow cage-like nickel cobalt layered hydroxides (NiCo-LDH) are prepared via nitrate etching of ZIF-67 nanocrystals, and investigated as electrode materials of supercapacitor. The morphology, structure and electrochemical properties of the obtained materials are investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, N ₂ adsorption/desorption and a series of electrochemical tests (including cyclic voltammetry, galvanostatic charge and discharge and AC impedance). The results show that the NiCo-LDH samples assembled by nanosheets present a porous structure with hollow cages and high specific area surfaces, which conduces to increasing the electroactive sites, enhancing the contact between the electrolyte and the electrode material, and thus significantly improving the electrochemical performance of the materials. With the mass ratio of nickel to cobalt salt being 1∶1, the specific capacitance of Ni ₁Co ₁-LDH is 801 F·g ^–1 at a current density of 0.5 A·g ^–1, and a specific capacitance of 582 F·g ^–1 can still be maintained at a high current density of 10 A·g ^–1. Moreover, the specific capacitance retention of Ni ₁Co ₁-LDH is 100.2% after 2000 cycles at a current density of 15 A·g ^–1, displaying good electrochemical performance and great potential in supercapacitor applications.