Environmentally friendly plasticized electrolyte based on chitosan (CS): Potato starch (PS) polymers for EDLC application: Steps toward the greener energy storage devices derived from biopolymers

Abstract

Biopolymer membranes derived from natural resources are environmentally friendly materials and their use for electrochemical energy storage devices has attracted a great deal of attention. Here, chitosan (CS) and potato starch (PS) doped with ammonium thiocyanate (NH4SCN) were used as host electrolyte. Various weight percent of glycerol (Gly) as a non-toxic plasticizer are used to prepare novel plasticized solid biopolymer electrolytes (PSBEs) through solution casting method, which is subsequently used as a mediator in electric double-layer capacitor (EDLC) application. Inclusion of Gly participated significantly in minimizing the crystallinity nature of the membranes as revealed by the X-ray diffraction (XRD) patterns. Fourier transform infrared (FTIR) spectroscopy revealed the complexation among the constituents of the electrolyte. Ion transport parameters determined by FTIR and electrochemical impedance spectroscopy (EIS) techniques have shown comparable results. The optimum composition of PSBE is achieved when 24 wt% of Gly is added (CPNHG3), which has shown the best ion conductivity (1.62×10−3Scm−1) from the EIS study. This film has exhibited also an excellent ion transference number (tion) of (0.989) and a large electrochemical potential stability (2.1 V) measured by transfer number measurement (TNM) and linear sweep voltammetry (LSV) methods. The restriction to ion movement was observed for the samples overloaded with Gly (32 and 40 wt%) due to the blockage effect, which reflected on ion conductivity and transport parameters. The assembled EDLC device provided a specific capacitance (Cspc) of 16.1 F/g at 10 mV/s scan rate with no sign of redox reaction, which was proven by either cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques. Further, the cyclic stability and high performance of the EDLC regarding energy density, power density, and coulombic efficiency were confirmed throughout the 2500 cycles.