Structural, thermal, and ion dynamics studies of PVA-CS-NaI-based biopolymer electrolyte films

Abstract

A series of biopolymer blend electrolytes (BPBEs) based on ((100-x)PVA-xCS)-NaI, viz. BPBE-1 to BPBE-5 (x = 10, 20, 30, 40, 50 in wt%), respectively, were prepared using solution cast technique. Prepared samples have been characterized using XRD, ATR-FTIR, TGA, and AC impedance spectroscopic techniques. ATR-FTIR results reveal the interactions between the constituents of PVA/CS with salt, NaI. XRD results show the semi-crystalline nature of PVA-CS polymer blend and %degree of crystallinity (Xc) was found to be minimum for sample BPBE-1. TGA and its 1st derivative (DTGA) results show that BPBE films decompose in multi-steps. The decomposition temperature peak (Td, peak) associated with CS-PVA polymer blend and the interactions between CS-PVA-NaI have been discussed using TGA analysis. Temperature-dependent dc conductivity (σdc) and relaxation frequency (fr) follow the Arrhenius type mechanism. The optimum σdc ~ 1.2 × 10−5 S/cm at 30 °C was received for sample, BPBE-1. The ac conductivity spectra for all samples follow the Jonscher’s power law (JPL). Dielectric permittivity and electric modulus studies have also been done for understanding the charge storage properties and conductivity relaxation. Ionic transference number (ITN) measurement has been carried out for knowing the ionic/electronic nature of charge species. Cyclic voltammetry (CV) measurement has been done to study the electrochemical behavior of the optimized sample.