Electrochemistry of TiO2/CdS composite electrodes for supercapacitor applications

Abstract

This paper outlines a sol–gel method for the synthesis of TiO2/CdS composites with different CdS concentrations for use in supercapacitor applications. Composite electrodes of TiO2/CdS containing zinc (0.25, 0.5, 0.75, and 0.1 M) and sulphide (0.5, 0.1, 1.5, and 2 M) in a 1:2 molar ratio were prepared and are labelled TC1, TC2, TC3, and TC4, respectively. The X-ray diffraction patterns displayed peaks for TiO2 and CdS. A gradual change in morphology from rod like to spherical as the CdS content increased was observed using FE-SEM and confirmed by TEM analysis. Furthermore, the electrochemical properties of all prepared electrodes were analysed using techniques such as cyclic voltammetry (CV), galvanostatic charge–discharge (GV), electrochemical impedance spectroscopy (EIS), and cycle life testing. Among the studied electrodes, CV analysis of TC1 indicated a capacitance of 1296 Fg−1 at a low scan rate of 10 mVs−1, whereas GV analysis showed the value to be 1320 Fg−1 at a scan rate of 10 Ag−1. Also, the significant increase in the energy density and power density of the TC1 electrode may open a new path to supercapacitor applications. The improved electrochemical performance of TC1 can be largely attributed to its increased BET parameters, rod-like morphology, and low charge transfer resistance. Furthermore, an asymmetric capacitor (ASC) was fabricated using the TC1 electrode as the cathode material and activated carbon as the anode. The fabricated ASC had a capacitance of 685 Fg−1 at a scan rate of 10 Ag−1 with a high energy density of 219 kWh kg−1. The repeatability test results imply that even after 500 cycles of operation, the as-fabricated ASC exhibits 95% capacitance retention. Additionally, on charging, the as-fabricated ASC has the ability to glow green in a light-emitting diode. Therefore, the TC1 electrode is a suitable cathode material for next-generation supercapacitors in high-energy density storage systems.