<p>Ternary nanocomposites are important in the field of energy storage devices (ESDs). In this work, an in situ chemical oxidative polymerization method is applied to produce polymer nanocomposites filled with polythiophene (PTh) and WO₃/TiO₂. Three combinations of samples are synthesized using different concentrations of metal oxides (MOs). Various characterization techniques, including x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy (EDX), elemental mapping, and x-ray photoelectron spectroscopy (XPS), are employed to characterize the structure and morphology of the synthesized nanocomposites. A potentiostat is used to perform the electrochemical measurement including cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). The combination of WO₃ and TiO₂ with PTh was found to enhance the specific capacitance (<i>C</i>_sp) of the nanocomposites. The <i>C</i>_sp of the PWT5 electrode was calculated as 244 F g⁻¹ at 1 A g⁻¹ in 1&#xa0;M NaNO₃ solution. The <i>C</i>_sp of the PWT5 symmetric supercapacitor (SSC) was measured as 96.7 F g⁻¹ at 1 A g⁻¹ in PVA-NaNO₃ gel. The SSC exhibited outstanding cyclic performance, retaining 84% of its initial capacitance after 1000 cycles. Energy density of 30.2 Wh kg⁻¹ was measured at power density of 749.8 W kg⁻¹ at 1 A g⁻¹. The combined MOs improved the conductivity of the fabricated device, increasing the <i>C</i>_sp of the PTh-based SC, providing a promising ESD.</p> Graphical Abstract <p></p>