Synthesis of Nickel Cobalt Oxide-Reduced Graphene Oxide Nanocomposite using Ammonia for Supercapacitor

Abstract

NiCo₂O₄ has been widely used as the electrode material for pseudocapacitors owing to its abundance in nature, good electrochemical and redox behaviour than Ni oxide and Co oxide [1-5]. Also, reduced graphene oxide has been explored a lot for supercapacitors because of its oxide functional groups [6]. As hybrid supercapacitors provide high energy density along with high power density, so in this work, it is decided to prepare nanocomposite of NiCo₂O₄ and reduced graphene oxide (NC-RGO) by the hydrothermal synthesis technique using ammonia as the reducing agent. Here we have synthesized nanocomposite of NiCo₂O₄ and reduced graphene oxide (NC-RGO) by the hydrothermal synthesis technique using ammonia as the reducing agent. We have used ammonia solution as the reducing agent for GO reduction in aqueous solvent as it is more effective and more environment friendly in comparison to hydrazine hydrate or other poisonous reducing agents [7]. We have synthesized this nanocomposite previously also by using different reducing agents [6, 8, 9]. Our aim is to find the suitable environment friendly material for supercapacitor application. As synthesized material has been characterized by thermo-gravimetric analysis and X-ray diffraction techniques. Thermo-gravimetric analysis of the prepared precursor has been done to find the decomposition temperature. X-ray diffraction has been done to verify the phases present in the material shown in Fig.1. Also, the crystallite size has been calculated using De-bye Scherrer’s formula. The electrochemical behaviour has been studied by cyclic voltammetry and galvanostatic charge-discharge curves in two electrolytic solutions. The measurements of specific capacitance, energy density and power density have been performed in both 1 M Na₂SO₄ and 1 M KOH aqueous electrolytic solutions.It has been observed that the material possesses higher energy density (7 W h kg^-1) in 1 M Na₂SO₄ aqueous solution in comparison to 1 M KOH aqueous solution (0.867 W h kg^-1). Such behaviour is because of larger PW exhibited by the material in 1 M Na₂SO₄ aqueous solution (1.25 V in GCD plots) than in 1 M KOH solution (0.52 V). These results may prove to be very beneficial for further research on such materials.