Simple preparation of ZnCo2O4 porous quasi-cubes for high performance asymmetric supercapacitors

Abstract

Novel ZnCo2O4 quasi-cubes (ZnCo2O4 QCs) constructed by porous layered sheets were successfully prepared through two-step process. The precursor was initially obtained by solvothermal reaction in a combined solution of glycerin and water, and then the precursor was converted to porous ZnCo2O4 QCs after direct thermal annealing procedure in air. The ZnCo2O4 QCs were assembled by a substantial proportion of nanoparticles with an average size of 8 nm, and possessed large surface area of 83.9 m2 g−1. The size and shape of the ZnCo2O4 samples were greatly influenced by the volume ratio of water to glycerin as well as the concentration of starting zinc salt. The electrochemical performance of such porous ZnCo2O4 QCs was investigated in a standard three-electrode cell using 2 M of KOH electrolyte, and these QCs delivered a remarkable capacitance of 804 F g−1 at 1 A g−1, a superior rate of 74.5% at 16 A g−1 and an exceptional long-term cycling stability with 79.2% capacitance retention after 3000 cycles at 5 A g−1. Furthermore, the constructed ZnCo2O4 QCs//AC ASC exhibits a high energy density of 34.4 W h kg−1 at a power density of 860.1 W kg−1, along with an outstanding cycling performance of 112.4% capacitance retention after 3000 cycles at 5 A g−1. Such impressive electrochemical performances make ZnCo2O4 QCs a promising candidate as superior electrode material for the next-generation advanced supercapacitors.