Chitosan-PVA-Mg(NO3)2 based biopolymer blend electrolyte membranes for EDLC applications: Structural, thermal and electrical transport properties study

Abstract

Solid biopolymer electrolytes have low ionic conductivity at room temperature. Biopolymer-polymer blending is one promising approach for improving ionic conductivity. The biopolymer Chitosan (CS) has the methyl, amide, and amine groups attached to its backbone, which is responsible for the interaction with the additive/polymer. Biopolymer blend electrolytes (BPBEs) based on [CS-PVA-PEG-200] + xwt% Mg(NO₃)₂ were prepared and described using techniques XRD, FTIR, SEM, TGA and Electrochemical impedance spectroscopy(EIS). XRD and SEM results show an increase in the amorphousness of polymer electrolytes with salt, Mg(NO₃)₂ content upto 30 wt% salt due to the interactions between the functional groups of PVA/CS as observed in IR analysis. Multi-step thermal decomposition peaks were observed in TGA analysis, and BPBE membranes are thermally stable up to 120 °C. The optimized sample, BPBE-4, has the maximum bulk dc conductivity ∼ 1.20 × 10⁻⁴ Scm⁻¹ at 30 °C with the lowest activation energy, ionic transference number ∼ 0.99, and electrochemical stability window ∼ 4 Volt. The electrical conductivity and dielectric relaxation frequency of BPBEs show a temperature-dependent behavior that follows Arrhenius-type characteristics. All membranes show conductivity spectra that depend on frequency. These spectra follow Jonscher’s power law (JPL). Dielectric permittivity studies indicate that electrode polarisation is effective at low frequencies. The fabricated EDLC, based on the optimal sample, has been analysed using CV and GCD measurements.