Characterization of defect structures in nanoscaled W-doped $${\text {TiO}_2}$$ tested as supercapacitor electrode materials

In this work, Tungsten(W)-doped $${\text {TiO}_2}$$ nanoparticles were synthesized using the sol–gel method and were used as electrode materials in supercapacitor applications. The structural and morphological properties of the prepared samples were analyzed by means of XRD, STEM, TEM, and XPS. The analysis of the defect centers was carried out using EPR spectroscopy. The electrochemical analysis of the assembled supercapacitor was done using cyclic voltammetry, galvanostatic cycling with potential limitation technique, potentiostatic electrochemical impedance spectroscopy, and voltage-holding experiments. All the presented samples showed paramagnetic defects in the EPR analysis, while 0.5% W-doped $${\text {TiO}_2}$$ showed a maximum signal intensity. The supercapacitor performance from the synthesized electrode material showed highly encouraging results. The equivalent series resistance (R $$_{\text{s}}$$ ) value for all the designs showed values under “1 $$\Omega$$ ,” which reflects high conductivity. As the maximum EPR intensity comes from $${\text {TiO}_2}$$ doped with 0.5% W, the supercapacitor performance of this sample was tested with a newly designed five-electrode system. This design showed superior performance compared to any other used designs with a specific capacitance of 25.5 F g $$^{-1}$$ , with an energy density of 14.16 Wh kg $$^{-1}$$ at 302 kW kg $$^{-1}$$ .