High-performance eco-friendly tamarind gum-based biopolymer electrolytes for electric double-layer capacitor application

Abstract

Mg⁺-ion-conducting tamarind gum (TG)-based biopolymer electrolytes (BPEs) are prepared by a simple solution-casting technique. XRD and FTIR analyses have revealed the dissociation and complexation of the salt with the polymer host. The glass transition temperature is observed for all the prepared electrolytes using differential scanning calorimetry (DSC). By using AC impedance analysis, the higher ionic conductivity calculated for the sample 1-g TG with 0.5 g of salt (5 TML) is 3.48 × 10⁻³ S/cm. The temperature-dependent conduction mechanism of sample 5 TML follows three models: region I obeys the overlapping-large polaron tunneling (OLPT) model, the quantum mechanical tunneling (QMT) model is observed in region II, and region III obeys the nonoverlapping small polaron tunneling (NSPT) model. The minimum activation energy of 0.045 eV is observed for sample 5 TML according to the Arrhenius plot. The complex dielectric permittivity and dielectric modulus spectra are discussed. The relaxation time (τ) attained by tangent analysis for 5 TML is 7.94 × 10⁻⁷ s. From the transference number measurement, it is concluded that the conductivity is mostly due to the transfer of ions only. Using the 5 TML sample, a symmetrical supercapacitor and an electrochemical cell are fabricated. Cyclic voltammetry (CV) reveals a specific capacitance of 413.05 Fg⁻¹ at a low scan rate of 15 mV/s. From the GCD data, the power and energy density are calculated as 1499 W/kg and 100 Wh/kg, respectively. The cyclic stability is confirmed by the observed constant values of power and energy densities for different cycles.