Green synthesis of cobalt oxide thin films as an electrode material for electrochemical capacitor application

Abstract

In this study, we report on the fabrication and characterization of cobalt oxide (Co3O4) thin film that is potentially important for electrochemical capacitor applications. For that purpose, the precursor powder of Co3O4 was prepared using the cost-effective sol-gel synthesis route and heat treatment at a relatively low temperature. A thin film of Co3O4 was prepared on a fluorine-doped tin oxide (FTO) substrate using a simple doctor-blade method. X-ray diffraction and Raman spectroscopy confirmed the formation of pure Co3O4 thin film on FTO, and scanning and transmission electron microscopy confirmed the nanoscale nature of the particles in the film. The electrochemical studies revealed a specific capacitance of 237 ​F ​g-1 for the Co3O4 electrode, with a remarkable cycling stability in 1 ​M NaOH electrolyte, and 77% capacity retention after 2000 cycles at 5 ​mA ​cm-2 current density (833 ​mA ​g-1); this demonstrates that Co3O4 is a promising material for electrochemical devices. Further, the electrochemical impedance measurements revealed an internal (solution) of 10 ​Ω, whereas the charge transfer resistance between the electrode and the electrolyte was roughly 40 ​Ω.