Facile synthesis of morphology-controlled hybrid structure of ZnCo2O4 nanosheets and nanowires for high-performance asymmetric supercapacitors

Abstract

Controllable synthesis of electrode materials with desirable morphology and size is of significant importance and challenging for high-performance supercapacitors. Herein, we propose an efficient hydrothermal approach to controllable synthesis of hierarchical porous three-dimensional (3D) ZnCo₂O₄ composite films directly on Ni foam substrates. The composite films consisted of two-dimensional (2D) nanosheets array anchored with one-dimensional (1D) nanowires. The morphologies of ZnCo₂O₄ arrays can be easily controlled by adjusting the concentration of NH₄F. The effect of NH₄F in the formation of these 3D hierarchical porous ZnCo₂O₄ nanosheets@nanowires films is systematically investigated based on the NH₄F-independent experiments. This unique 3D hierarchical structure can help enlarge the electroactive surface area, accelerate the ion and electron transfer, and accommodate structural strain. The as-prepared hierarchical porous ZnCo₂O₄ nanosheets@nanowires films exhibited inspiring electrochemical performance with high specific capacitance of 1289.6 and 743.2 F g⁻¹ at the current density of 1 and 30 A g⁻¹, respectively, and a remarkable long cycle stability with 86.8% capacity retention after 10 000 cycles at the current density of 1 A g⁻¹. Furthermore, the assembled asymmetric supercapacitor using the as-prepared ZnCo₂O₄ nanosheets@nanowires films as the positive electrode and active carbon as negative electrode delivered a high energy density of 39.7 W h kg⁻¹ at a power density of 400 W kg⁻¹. Our results show that these unique hierarchical porous 3D ZnCo₂O₄ nanosheets@nanowires films are promising candidates as high-performance electrodes for energy storage applications.