Synthesis of NiCo2O4@NiCo2O4 Layered Nanoflake Arrays on Nickel Foam for Supercapacitor Application

Abstract

With the advent of the energy crisis and the environmental pollution, the development of clean and renewable and new energy technology is one of the most decisive influence in the future world economy. Among the various energy storage devices, supercapacitor is the most promising one. It is a kind of electrochemical energy storage device, has drawn particular attention because of its high energy density, long cycle life and fast charging and discharging. The electrochemical properties of the materials of supercapacitors are determined by materials composition, crystalline morphological and specific area. Thus, controllable syntheses of electrodes with desirable composition and special architecture are expected to have remarkable potential for generating high-performance supercapacitors. Spinel nickel cobaltite (NiCo2O4) has been conceived as a promising cost-effective and scalable alternative since it offers many advantages such as high specific capacitance, excellent electronic conductivity and environmental friendliness. However, some obstacles such as low utilization ratio, non-uniform pore distribution and structural instability of NiCo2O4 always harass the applications in energy storage. Therefore, development of methods for enhancing the value of specific surface and electrode reaction kinetics of NiCo2O4 materials is crucial to improve the storage ability of electrode materials. In this paper, the NiCo2O4@NiCo2O4 laminated nanoflake arrays electrode materials are successfully synthesized via hydrothermal, electro-deposition and followed by calcination. The main contents are as follows： Porous NiCo2O4 nanoflake structured arrays are produced by hydrothermal method. The morphology of the arrays changes with the growth time. The porous NiCo2O4 nanoflakes exhibits excellent pseudocapacitive properties in 2 M KOH, and the specific capacitance can achieve a maximum of 920.5 F g-1 at 2 A g-1, which can still retain 80.8% after 5000 cycles. Hierarchical NiCo2O4@NiCo2O4 laminated nanoflake arrays on nickel foam are synthesized by a two-step method which involves in hydrothermal process and electro-deposition. The obtained laminated nanoflakes have a combined structure of the first nanoflakes and the second nanoflakes as well as the hierarchical porosity morphologies. Compare with the NiCo2O4 nanoflake arrays, the laminated electrode displays better pseudocapacitive behaviors in 2 M KOH which can achieve a maximum of 1398.7 F g-1 at 2 A g-1. It can retain 83.5% after 5000 cycles. The electrode showed excellent pseudocapacitive behaviors owing to the porous laminated nanoflake arrays architecture and synergistic effect.