New insight into high-temperature driven morphology reliant CoMoO4 flexible supercapacitors

Abstract

A facile hydrothermal method has been successfully developed for the synthesis of cobalt molybdate (CoMoO₄). The morphology of the CoMoO₄ was tailored by varying the growth conditions, and as a result different morphologies have been achieved such as cauliflower, brick and nano-sphere structures. The proposed potential use of the CoMoO₄ as an electrode material for flexible supercapacitor applications was examined using cyclic voltammetry (CV) and galvanostatic charge–discharge measurements. It was observed that the specific capacitance of CoMoO₄ depends on its morphology. A specific capacitance of 169 F g⁻¹ in 3 M KOH at a current of 1 mA was observed for the nano-sphered CoMoO₄. The effect of the electrolyte (LiOH, NaOH and KOH) on the electrochemical properties of the CoMoO₄ was also investigated. The specific capacitance depends on the type of electrolyte and showed the highest value of 259 F g⁻¹ in a 3 M NaOH electrolyte. Furthermore, these electrodes showed excellent cyclic stability. We have fabricated a flexible supercapacitor device by sandwiching two electrodes separated by an ion-transporting layer. The device shows no degradation in its capacitive properties upon bending and shows improved stability with the number of cyclic CV performances. The effect of temperature on the charge storage properties of the device was also investigated for high temperature applications. The specific capacitance of the device significantly increased when the operational temperature of the device was elevated from 10 to 70 °C. Hence, this study provides an ultimate facile method to synthesize morphology controlled cobalt molybdate for applications in the next generation of flexible energy storage devices, which can perform more efficiently at a higher temperature.