Review of Chitosan-Based Polymers as Proton Exchange Membranes and Roles of Chitosan-Supported Ionic Liquids

Abstract

Perfluorosulphonic acid-based membranes such as Nafion are widely used in fuel cell applications. However, these membranes have several drawbacks, including high expense, non-eco-friendliness, and low proton conductivity under anhydrous conditions. Biopolymer-based membranes, such as chitosan (CS), cellulose, and carrageenan, are popular. They have been introduced and are being studied as alternative materials for enhancing fuel cell performance, because they are environmentally friendly and economical. Modifications that will enhance the proton conductivity of biopolymer-based membranes have been performed. Ionic liquids, which are good electrolytes, are studied for their potential to improve the ionic conductivity and thermal stability of fuel cell applications. This review summarizes the development and evolution of CS biopolymer-based membranes and ionic liquids in fuel cell applications over the past decade. It also focuses on the improved performances of fuel cell applications using biopolymer-based membranes and ionic liquids as promising clean energy. Int. J. Mol. Sci. 2020, 21, 632 2 of 52 used to exchange protons from the anode to the cathode [1]. PEMFCs are light, highly efficient, and compact. They operate at relatively low temperatures (≈80 • C), have high power density, and are suitable for various applications. Figure 1 shows that PEMFC consists of various important elements, namely, bipolar plates, diffusion layers, electrodes (anode and cathode), and an electrolyte. The core of a PEMFC is a membrane electrode assembly (MEA) composed of a proton exchange membrane (PEM) placed between two electrodes. Int. J. Mol. Sci. 2019, 20, x FOR PEER REVIEW 2 of 53 Int. J. Mol. Sci. 2020, 21, 632 3 of 52Polysaccharides, such as chitosan (CS) and cellulose, are among the best natural polymer materials because of their abundance in the environment. CS is a linear polysaccharide consisting of randomly distributed β-(1-4)-linked d-glucosamine (deacetylated unit) and N-acetyl-d-glucosamine (acetylated unit), which is produced by the deacetylation of chitin. CS has high water affinity properties as there is the presence of three different polar functional groups, which are hydroxyl (-OH), primary amine (-NH 2 ), and C-O-C groups. CS has a structure that is very similar to cellulose, but the difference among them is that CS contains amine groups and its structure is characterized by its molecular weight and degree of deacetylation, where its solubility is depended on [7].CS has rigid structure and high crystallinity as there are three hydrogen atoms strongly bonded between the amino and hydroxyl groups within the CS monomers, due to the immobilized structure, which leads to its proton conduction limitation. Moreover, CS has attractive physicochemical properties in aqueous solution due to its polycationic nature and this leads to wide range of biological purposes such as antimicrobial activity and disease resistance activities in plants [8]. CS membranes are one of the most preferable and favorable materials to re...

Ionotropic Gelation of Chitosan for Next-Generation Composite Proton Conducting Flat Structures

“…In the past decade, chitosan-based membranes for fuel cell applications have been developed using different methods [16,[27][28][29]. The low proton conductivity of pristine chitosan has been improved to high values by doping the bio-polymer with inorganic fillers (cesium phosphotungstate salt [30], silica-supported silicotungstic acid [31], or calcium oxide [32]).…”

“…It can also be improvedby chemically modifying chitosan (sulphonation, phosphorylation, quaternization, and cross-linking [17,28,29,31,33]). Flat proton-conducting chitosan membranes have been obtained typically by solution-cast techniques [16,23,24,32,33] and chemical neutralization [34,35]. In contrast, ionotropic gelation is a procedure not deservedly developed in fuel cell literature, and thus, is confined to a very few papers [25,26].…”

“…(v) The presence of polar functional groups in the structure, specifically hydroxyl (-OH), primary amine (-NH 2 ), and ether (C-O-C) groups, facilitates the chemical modifications of chitosan and the tailored synthesis of Chit-based materials for specific applications [10][11][12]. Owing to the very low proton conductivity of pristine chitosan (about 1.2 × 10 −2 S cm −1 at 25 • C [8]), chemical modification of the polymer has been intensively exploited in recent years to generate ion-exchange sites to improve proton/ionic conductivity of the composite material [13][14][15][16].…”

Synthesis of Porous Proton Ion Conducting Solid Polymer Blend Electrolytes Based on PVA: CS Polymers: Structural, Morphological and Electrochemical Properties

“…CS has several promising pharmaceutical uses and has been studied as a new carrier material in drug delivery systems and for its wound healing, fat binding, antibacterial, and hypocholesterolemic effects [32]. Biopolymer-based membranes, for example, CS, carrageenan, and cellulose, are considered as some good alternative materials to improve the performance of fuel cells, since they are eco-friendly and cheap [33]. CS is one of the most suitable materials that can be used as a substitute for the Nafion membrane since it has shown enhanced performance in low-temperature fuel cell applications [34,35].…”

Perspectives in the design and application of composites based on graphene derivatives and bio‐based polymers

“…In recent years, CS, alginate and PVA were actively investigated as polyions for polyelectrolyte membranes (PEMs). [127][128][129] Together with other characteristics like biocompatibility and biodegradability, these polymers attract significant interest of researchers as efficient materials for energy-related applications. Like polyelectrolytes, GO behaves as a weak polyacid.…”