Synthesis and characterization of tungsten suboxide in W18O49 composition and investigation of their electrical properties for supercapacitors

The decreasing energy resources in the world and the increasing global energy demand are driving researchers to work intensively on the development of energy storage technologies. Among energy storage devices, supercapacitors are seen as an important energy storage source for areas such as electric cars, unmanned aerial vehicles, drones and robot technologies, which are increasingly used today, thanks to their high energy density and high power density. W18O49 is one of the suboxide forms formed at the W+5 oxidation level among the oxygenated compounds of tungsten and is a new generation material whose electrical conductivity has only been discovered in the last decade due to its structural properties. It is the compound with the most oxygen deficiency in its structure compared to other tungsten suboxides and its crystal network is woven with trigonal, tetragonal and hexagonal channels. These channels play a major role in increasing the electrical conductivity and the amount of stored energy in n-type transitions by significantly improving electron conductivity. However, the optimization, characterization and chemical properties of W18O49 are missing in the literature for supercapacitor electrodes. In this thesis, electrode materials in W18O49 were synthesized by solvothermal method for supercapacitors. Solvothermal parameters such as precursor concentration, synthesis temperature and synthesis time were optimized. Structural properties were elucidated by SEM, EDS, XRD, FTIR and BET analyses. The effects of these properties on electrochemical behavior were investigated in detail by conducting CV, GCD and EIS tests using Ag/AgCl - Pt and W18O49 based working electrodes in 1M H2SO4 in a three-electrode setup. In addition, changes in structural and electrochemical properties were investigated in detail by adding samarium (Sm+3) and iron (Fe+3) to the optimized W18O49 compound. According to the results, the optimized W18O49 electrode showed quite high specific capacitance values of 605.6 Fg-1 at 1 mVs-1 scan rate and 198.9 Fg-1 at 1.75 Ag-1 current density. In addition, with 5 wt% Fe+3 addition, the specific capacitance of the optimized electrode was increased by 50.17% at 1 mVs-1 and 70.12% at 2.00 Ag-1, and with 1 wt% Sm+3 addition, it was increased by 57.7% at 1 mVs-1 and 99.6% at 1.25 Ag-1.