Chitosan-Based Anion Exchange Membranes for Direct Ethanol Fuel Cells

Abstract

A series of novel cross-linked highly quaternized chitosan and quaternized poly (vinyl alcohol) membranes were successfully synthesized to be applied in alkaline direct ethanol fuel cells. Cross-linking was accomplished using two different cross-linking agents and an additional thermal process to improve both chemical and thermal properties. Equivalent blends of chitosan and poly (vinyl alcohol) membranes with various degrees of cross-linking were prepared by using different amounts of glutaraldehyde and ethylene glycol diglycidyl ether as cross-linkers. To investigate their applicability in direct ethanol fuel cells, the membranes were characterized in terms of their structural properties, chemical, thermal and alkaline stability, ion transport and ionic properties using following methods: Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, thermogravimetric analysis, water uptake by mass change, ethanol permeability in the diffusion cell, back titration method (ion exchange capacity) and electrochemical impedance spectroscopy (anion conductivity). Despite the high degree of quaternization of the applied materials and regardless of the thin film thickness of the blend membranes, the novel cross-linked products displayed outstanding mechanical stability. The lower crosslinked membranes exhibited the best transport and ionic properties with a high anion conductivity of 0.016 S cm-1 and a high ion exchange capacity of 1.75 meq g-1 , whereas membranes with a higher degree of cross-linking performed superior in terms of reduced ethanol permeability of 3.30•10-7 cm 2 s-1 at 60°C. The blend membranes-chemically and thermally cross-linked-provide excellent thermal stability with an onset degradation temperature above 280°C and superb alkaline stability in 1.0 M KOH at 60°C for 650 h. Therefore, these composite membranes exhibit high potential for application as alkaline electrolytes in fuel cells.

Preparation and Characterization of PVA/PDDA/Nano-Zirconia Composite Anion Exchange Membranes for Fuel Cells

“…Water clusters can provide transport channels for anions inside the anion-exchange membrane, in this way improving the ionic conductivity [32]. On the other hand, excessive water uptake can induce a severe swelling of the membrane, which leads to a decline of the dimensional stability and possibly restricts the preparation of membrane electrode assembly (MEA) by reducing contact between the active layer of the electrodes and the membrane [34].…”

“…The OH − conductivity was determined by an AC impedance method using Gamry Reference 600 potentiostat [34]. The membrane at a size of 2.5 × 1.0 cm was alkalized in a 1.0 M KOH solution for 24 h, washed, then immersed in ultra-pure water for 24 h. Impedance was measured over a frequency range of 0.1 Hz to 10 kHz (50 mV amplitude) with the samples placed into the four-electrode configuration of the conductivity clamp (Bekktech BT110 LLC, Scribner Associates, Southern Pines, NC, USA) that was immersed in ultra-pure water at ambient temperatures.…”

Quaternized Polysulfone Cross-Linked N,N-Dimethyl Chitosan-Based Anion-Conducting Membranes

“…Chitosan is an inexpensive and abundantly available natural material which has good film formation ability, aptitude for facile modification, excellent mechanical strength, and is environmentally benign. Chitosan contains an anime group attached to its backbone, which can be quaternized and directly used in different applications such as biomedical applications [35,36], membrane design [37,38,39], and water purification. Owing to its hydrophilicity, chitosan is structurally immiscible with organic polymers; consequently, phase separation on the micro- or nano-levels is possible.…”

Imidazolium functionalized poly(vinyl alcohol) membranes for direct methanol alkaline fuel cell applications

“…Figure 4 shows the 1 H NMR spectrum of PVA‐QAm. In addition to chemical shifts for PVA, the newly appearing peaks between 3.2 and 3.4 ppm are ascribed to the methyl protons of the quaternary ammonium group 36 . The NMR results confirmed the successful addition of the quaternary ammonium group into the PVA chain.…”