Synthesis and characterization of modified chitosan membranes for applications in electrochemical capacitor

Abstract

Chitosan-based membranes were formed by a casting method from a CS (chitosan) acetic acid solution, and then modified. Sodium hydroxide (NaOH) and glutaraldehyde (GA) solutions were used as covalent or ionic crosslinking agents respectively. The physicochemical properties of crosslinked CS membranes were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Changes in surface hydrophilicity as a result of the crosslinking process were investigated by means of contact angle measurements. In addition, for both modified and unmodified CS membranes, tensile and electrolyte solution swelling ratio tests were performed. All of the obtained chitosan-based membranes were used in electric double layer capacitor (EDLC) cells to study their applicability as gel electrolytes and membranes. 2 M LiOAc (lithium acetate) water solution was used as an electrolyte in the EDLC cells. Electrochemical characteristics of EDLC cells containing chitosan membranes were determined by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) methods. The results show that the CS crosslinking agent type may improve the mechanical properties and limit electrolyte absorption by the membranes. All tested EDLC cells with CS membranes exhibited very good electrochemical performance. The specific capacitances for EDLC cells with modified chitosan (CS) membranes are equal 106 F g−1 after the 10 000th discharge cycle for both CS/GA and CS/NaOH capacitor cells.