High electrochemical performance of 3D highly porous Zn0.2Ni0.8Co2O4 microspheres as an electrode material for electrochemical energy storage

We report on the structural properties and electrochemical performances of 3D highly porous Zn0.2Ni0.8Co2O4 microspheres prepared by a hydrothermal route. The Brunauer-Emmett-Teller (BET) specific surface area of the sample is found to be about 96 m(2) g(-1) with a bimodal pore size distribution. This distribution reveals maxima at pore size diameters of about 10 nm and 19 nm. The phase purity of the sample is confirmed by X-ray photoelectron spectroscopy and X-ray diffraction. A spinel-type crystal structure with a lattice parameter of 8.1233(3) angstrom is obtained. Electron microscopy reveals that the highly porous microspheres are built from randomly arranged porous nanorods and these porous rods are made up of nanoparticles. The electrochemical performances of the sample as an electrode in a supercapacitor and lithium ion battery (LIB) were investigated by means of cyclic voltammetry, galvanostatic charge-discharge cycling and impedance spectroscopy. As a result, the mesoporous spinel-type sample exhibits high specific capacitance (2081 F g(-1) at 2.5 A g(-1)), high rate capacity (1321 F g(-1) at 10 A g(-1)) and good cycling behaviours in supercapacitor studies. Furthermore the initial discharge capacity of the sample as an anode in the LIB is 1482 mAh g(-1) with a reversible capacity retention of 681 mAh g(-1) after 40 cycles. These results indicate that the mesoporous Zn0.2Ni0.8Co2O4 microspheres could be promising candidates for electrochemical energy storage device applications.