Novel three-dimensional NiCo2O4 hierarchitectures: solvothermal synthesis and electrochemical properties

Abstract

Three-dimensional flower-like NiCo₂O₄ hierarchitectures have been successfully prepared on a large scale via a facile solvothermal method followed by an annealing process. The as-synthesized NiCo₂O₄ flower-like architectures have uniform diameters of about 500 nm assembled by numerous nanosheets radially grown from the center. The possible growth mechanism of the unique structures has been investigated. Both the poly(vinylpyrrolidone) (PVP) surfactant and the formation of metal glycolate play important roles in the formation of these novel three-dimensional flower-like hierarchitectures. With a large surface specific area of 212.6 m² g⁻¹, this novel NiCo₂O₄ material exhibited a superior specific capacitance of 1191.2 F g⁻¹ and 755.2 F g⁻¹ at current densities of 1 and 10 A g⁻¹, respectively, which suggests that 63.4% of the capacitance is still retained when the charge–discharge rate is increased from 1 A g⁻¹ to 10 A g⁻¹. This superior electrochemical performance of NiCo₂O₄ as an electrode material for supercapacitors can be ascribed to the synergetic effect of the porous structure and the small diffusion lengths in the nanosheet building blocks. The simple, versatile and cost-effective route reported here may provide a general methodology for the high-yield synthesis of metal cobaltite nanostructures featuring improved properties and structures.