Chitosan‐based composite membranes containing chitosan‐coated carbon nanotubes for polymer electrolyte membranes

Abstract

Considering the poor dispersion and inert ionic conduction ability of carbon nanotubes (CNTs), functionalization of CNTs is a critical issue for their application in polymer electrolyte membranes.Herein, CNTs were functionalized by the polyelectrolyte, chitosan (CS), via a facile noncovalent surface-deposition method. The obtained CS-coated CNTs (CS@CNTs) were then incorporated into the CS matrix and fabricated composite membranes. The CS coating can enhance the compatibility between CNTs and the matrix, thus ensuring the homogenous dispersion of CS@CNTs and effectively improved the mechanical properties of the composites. Moreover, the CS coating can make CS@CNTs act as an additional proton-conducting pathway through the membranes.The CS/CS@CNTs-1 composite shows the highest proton conductivity of 3.46 × 10 −2 S cmat 80°C, which is about 1.5-fold of the conductivity of pure CS membrane. Consequently, the single cell equipped with CS/CS@CNTs-1 membrane exhibits a peak power density of 47.5 mW cm −2 , which is higher than that of pure CS (36.1 mW cm −2 ).

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

“…In addition to silica and clay nanoparticles, CNTs have been used as nanofillers for the fabrication of high-performance polymer nanocomposites [79,80], because they have high flexibility, low mass density and extremely high aspect ratio, tensile modulus, and mechanical strength [81,82]. However, polymer/CNT composites are rarely favored, because they exhibit poor dispersion, inert ionic conduction [83], strong π-π interactions, and the ability to form electronic channels in PEMs due to their exquisite electrical conductivity, thereby promoting the risk of short-circuiting in fuel cells. In addition, CNTs must be dispersed uniformly in a polymer matrix considering the strength of the basic Van der Waals interaction amongst tubes.…”

“…Hence, to overcome these hindrances, the surface of CNTs are functionalized with simple acid groups [84,85] and inorganic materials [33,86], such as carboxylic acid-functionalized CNTs [87], sulphonated CNTs [88], phosphonated CNTs [85] and Naf-, ion-, and polybenzimidazole-functionalized CNTs [89], which are used as inorganic fillers to alter PEMs. Moreover, polyelectrolyte-functionalized CNTs present new proton conducting pathways for rapid proton transport, increased compatibility with polymer matrixes, and additional modification sites [83].…”

“…Single test results and DMFC performances have shown that the OCV and maximum power density of the CS/CS@CNTs-1 membrane increased to 0.72 V and 47.5 mW cm −2 , whereas pure CS membrane had values of 0.63 V and 36.1 mW cm −2 , respectively. Considering their simple preparation method and good performance, the fabricated CS/CS@CNT composite membranes are promising PEMs for fuel cell applications [83].…”

Novel sulfonated multi‐walled carbon nanotubes filled chitosan composite membrane for fuel‐cell applications

“…In recent years, multi‐walled carbon nanotubes (MWCNTs) have become excellent electrochemical materials for their high thermal and mechanical stability, high flexibility, low density, and phenomenal electrochemical activity . However, it is very difficult to disperse carbon nanotube (CNT) homogeneously in the polymer matrix due to the strong Van der waals force; and an ionic channel can be formed in PEM due to the high electronic conductivity of CNT, which may lead to short‐circuiting in PEMFCs . To overcome these problems, Si, Ti, Zr, and phosphonate functionalized CNT are commonly used for modification of PEM .…”

Quaternized chitosan/functionalized carbon nanotubes composite anion exchange membranes

“…Chitosan (CS) is the product generated from the deacetylation of chitin, and has been extensively studied in the field of polymer electrolyte membranes because of the following benefits: (1) CS has many functional groups (e.g., NH 2 and OH) that easily allow chemical modification to tailor its properties for fuel cell application; (2) the hydrophilicity of CS is a desirable property for the ion transport under the condition of low humidity; (3) CS possesses high alcohol fuel barrier ability, which can decrease the fuel consumption and thus increase the fuel cell efficiency; and (4) CS is low cost, eco‐friendly, and abundant in environment. Moreover, when a CS membrane is swollen in water, the conduction of hydroxyl ions in it becomes possible because the amino groups of CS can be protonated and simultaneously leave OH − free.…”