Assessment of proton conductivity, dielectric relaxation and other physicochemical properties of LTA zeolite blended chitosan composites for membrane applications

Abstract

Novel chitosan biopolymer based solid electrolyte system consisting of surfactant-modified zeolite A are fabricated via simple solvent-casting technique to yield thin film proton exchange membrane. The zeolite LTA (Linde type-A) is synthesized and then it is impregnated with a surfactant, sodium dodecyl sulfate. The interfacial compatibility as well as the strong interaction in the polymer-filler system, modification of zeolite-A as well as its elemental composition is confirmed using FTIR, XRD and SEM-EDAX analysis. The physicochemical characteristics of the prepared membranes such as water uptake, IEC, hydration number and dimensional stability found to increase with increasing concentrations of the doped zeolitic filler. The appreciable mechanical as well as oxidative stability displayed by the membranes is due to the strong H-bond interaction between the polymer and modified zeolite. Overall, CSA-1.0 composite membrane showed the highest proton conductivity of 4.45 mS cm−1 at 80 °C, good thermal stability with Tmax = 217 °C and lesser gas permeability around 5 barrer. By determining the bound water content of the membranes using TGA analysis, the self-humidification characteristics were investigated. Good compatibility and interfacial interaction in the composite membranes has resulted in the creation of non-tortuous pathways for efficient proton transfer predominantly through Grotthus type mechanism. The relevant mechanism for the proton transfer along the membranes is evaluated in terms of complex impedance analysis, dielectric permittivity and electric modulus spectra. On the whole, the results obtained from various analysis suggests that the fabricated composite membranes are good alternatives as proton exchange membranes for fuel cell applications.