Sustainable PVA-based plasticized electrolyte filled with TiO₂ nanofiller for an electric double-layer capacitor with enhanced energy storage performance

The design and characterization of a sustainable proton-conducting solid polymer electrolyte (SPE) based on poly(vinyl alcohol) (PVA), ammonium thiocyanate (NH₄SCN), glycerol, and TiO₂ nanoparticles are presented. The electrolyte films were prepared by solution casting, with glycerol employed as the plasticizer and TiO₂ as an inorganic nanofiller. XRD analysis showed progressive suppression of structural ordering and enhancement of the amorphous character with glycerol incorporation and subsequent addition of 3 wt% TiO₂. FTIR spectral changes, including modification of the PVA hydrogen-bonding environment and attenuation of the ν(C N) band of SCN − , were consistent with changes in polymer–salt interactions. Electrochemical impedance spectroscopy showed that incorporation of TiO₂ into the highly plasticized PVA-based electrolyte reduced the bulk resistance and increased the ionic conductivity to 2.03 × 10 −3 S cm −1 . Linear sweep voltammetry indicated electrochemical stability up to approximately 2.1 V , while dielectric and electric-modulus analyses revealed composition-dependent changes in permittivity and relaxation behavior. The fabricated EDLC exhibited stable cycling performance over 2000 cycles, with a specific capacitance of 68.66 F g −1 from cyclic voltammetry and an initial energy density of approximately 23.8 Wh kg −1 from galvanostatic charge–discharge measurements. These results demonstrate the potential of the developed PVA-based nanocomposite electrolyte for sustainable solid-state energy-storage applications. Biodegradation of the electrolyte and complete device was not experimentally evaluated in this study.