Fabrication of chitosan/zwitterion functionalized titania–silica hybrid membranes with improved proton conductivity

Experimental determination of the mechanical and hydrolytic properties of chitosan/rice husk ash composite membranes

Chitosan-based membranes are promising alternatives to synthetic membranes in a number of specialized use cases, including water purification and electrochemical devices. In application, excessive swelling when hydrated can lead to poor mechanical integrity, necessitating modifications to the polymer so as to counter this effect. Embedding inorganic fillers within an organic polymer matrix is one method of combining excellent mechanical stability with good performance. This study investigated the effect of rice husk ash (RHA) on the mechanical and hydrolytic properties of chitosan-based composite membranes. We incorporated varying amounts of RHA into a chitosan solution and prepared thin film membranes via solution casting. We performed structural, chemical, and mechanical characterizations on the ash and membranes, observing 82.84 % water uptake in the 1.5 weight percent (wt%) RHA-doped membrane and 13.93 MPa tensile strength in the 2.0 wt% loaded composite. As the RHA content increased, the swelling ratio of the composites with RHA loadings greater than 1.0 wt% decreased, indicating an enhancement in mechanical strength. The observed results demonstrate that combining improved mechanical strength with increased water absorption and reduced swelling can lead to optimal membrane characteristics.

Hybrid Membrane of Sulfonated Poly(aryl ether ketone sulfone) Modified by Molybdenum Clusters with Enhanced Proton Conductivity

Developing novel proton exchange membranes (PEMs) with low cost and superior performance to replace Nafion is of great significance. Polyoxometalate-doped sulfonated poly(aryl ether ketone sulfone) (SPAEKS) allows for the amalgamation of the advantages in each constituent, thereby achieving an optimized performance for the hybrid PEMs. Herein, the hybrid membranes by introducing 2MeIm-{Mo132} into SPAEKS are obtained. Excellent hydrophilic properties of 2MeIm-{Mo132} can help more water molecules be retained in the hybrid membrane, providing abundant carriers for proton transport and proton hopping sites to build successive hydrophilic channels, thus lowering the energy barrier, accelerating the proton migration, and significantly fostering the proton conductivity of hybrid membranes. Especially, SP-2MIMo132-5 exhibits an enhanced proton conductivity of 75 mS cm-1 at 80 °C, which is 82.9% higher than pristine SPAEKS membrane. Additionally, this membrane is suitable for application in proton exchange membrane fuel cells, and a maximum power density of 266.2 mW cm-2 can be achieved at 80 °C, which far exceeds that of pristine SPAEKS membrane (54.6 mW cm-2). This work demonstrates that polyoxometalate-based clusters can serve as excellent proton conduction sites, opening up the choice of proton conduction carriers in hybrid membrane design and providing a novel idea to manufacture high-performance PEMs.

Surface Segregation Methods toward Molecular Separation Membranes

As a highly promising approach to solving the issues of energy and environment, membrane technology has gained increasing attention in various fields including water treatment, liquid separations, and gas separations, owing to its high energy efficiency and eco-friendliness. Surface segregation, a phenomenon widely found in nature, exhibits irreplaceable advantages in membrane fabrication since it is an in situ method for synchronous modification of membrane and pore surfaces during the membrane forming process. Meanwhile, combined with the development of synthesis chemistry and nanomaterial, the group has developed surface segregation as a versatile membrane fabrication method using diverse surface segregation agents. In this review, the recent breakthroughs in surface segregation methods and their applications in membrane fabrication are first briefly introduced. Then, the surface segregation phenomena and the classification of surface segregation agents are discussed. As the major part of this review, the authors focus on surface segregation methods including free surface segregation, forced surface segregation, synergistic surface segregation, and reaction-enhanced surface segregation. The strategies for regulating the physical and chemical microenvironments of membrane and pore surfaces through the surface segregation method are emphasized. The representative applications of surface segregation membranes are presented. Finally, the current challenges and future perspectives are highlighted.

Characteristics and performance studies of a composite polymer electrolyte membrane based on chitosan/glycerol-sulfosuccinic acid modified montmorillonite clay

In this study, chitosan (CS) doped sulphosuccinic acid (SSA)-glycerol (Gly) and modified montmorillonite clay (MMT) were successfully fabricated. The membranes were prepared using the solution casting method. Analysis of morphology and topography using scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the composite membrane with 3 wt% MMT filler, namely CS/MMT-1, possessed the most adequate surface roughness compared to the other fabricated membranes. Furthermore, mechanical characterization of the CS/MMT-1 composite membrane showed that the membrane achieved satisfactory mechanical strength with a value of 39.23 MPa. Proton conductivity of the composite membranes increased as the temperature was increased. The proton conductivity of the CS/MMT-1 composite membrane increased from 1.75 × 10-2 S cm-1 at 25 °C up to 3.57 × 10-2 S cm-1 at 80 °C. The CS/MMT-1 composite membrane also exhibited a methanol permeability value that was significantly lower than that of pristine CS, namely 1.22 × 10-7 cm2 s-1 and 12.49 × 10-7 cm2 s-1, respectively. The results of this study show that the fabricated composite membrane can be used as an alternative polymer electrolyte membrane (PEM) for DMFC applications.

A high-performance solid electrolyte assisted with hybrid biomaterials for lithium metal batteries

The demand for high safety lithium batteries has led to the rapid development of solid electrolytes. However, some inherent limitations of solid polymer electrolytes (SPEs) impede them achieving commercial value. In this work, a novel polyethylene oxide (PEO)-based solid electrolyte is reported. For the first time, biomaterial-based chitosan-silica (CS) hybrid particles serve as fillers, which can interact with polymer matrix to significantly improve the electrochemical performance. The optimized polymer electrolyte exhibits a maximum ion conductivity of 1.91 × 10^-4 S·cm^-1 at 30 °C when the mass ratio of PEO and CS is 4:1 (PCS4). All-solid-state LiFePO₄|PCS4|Li cells deliver a high coulombic efficiency and stable cycling performance, remaining an excellent capacity of more than 96.2 % after 150 cycles. Furthermore, the wide electrochemical window (5.4 V) and steady interfacial stability provide the possibility for high-voltage batteries applications. NCM811|| Li cells are assembled and display reliable charge and discharge cycle properties.

Synthesis of Silica Membranes by Chemical Vapor Deposition Using a Dimethyldimethoxysilane Precursor

Silica-based membranes prepared by chemical vapor deposition of tetraethylorthosilicate (TEOS) on γ-alumina overlayers are known to be effective for hydrogen separation and are attractive for membrane reactor applications for hydrogen-producing reactions. In this study, the synthesis of the membranes was improved by simplifying the deposition of the intermediate γ-alumina layers and by using the precursor, dimethyldimethoxysilane (DMDMOS). In the placement of the γ-alumina layers, earlier work in our laboratory employed four to five dipping-calcining cycles of boehmite sol precursors to produce high H₂ selectivities, but this took considerable time. In the present study, only two cycles were needed, even for a macro-porous support, through the use of finer boehmite precursor particle sizes. Using the simplified fabrication process, silica-alumina composite membranes with H₂ permeance > 10^-7 mol m^-2 s^-1 Pa^-1 and H₂/N₂ selectivity >100 were successfully synthesized. In addition, the use of the silica precursor, DMDMOS, further improved the H₂ permeance without compromising the H₂/N₂ selectivity. Pure DMDMOS membranes proved to be unstable against hydrothermal conditions, but the addition of aluminum tri-sec-butoxide (ATSB) improved the stability just like for conventional TEOS membranes.

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

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.

Self-Assembly DBS Nanofibrils on Solution-Blown Nanofibers as Hierarchical Ion-Conducting Pathway for Direct Methanol Fuel Cells

In this work, we reported a novel proton exchange membrane (PEM) with an ion-conducting pathway. The hierarchical nanofiber structure was prepared via in situ self-assembling 1,3:2,4-dibenzylidene-d-sorbitol (DBS) supramolecular fibrils on solution-blown, sulfonated poly (ether sulfone) (SPES) nanofiber, after which the composite PEM was prepared by incorporating hierarchical nanofiber into the chitosan polymer matrix. Then, the effects of incorporating the hierarchical nanofiber structure on the thermal stability, water uptake, dimensional stability, proton conductivity, and methanol permeability of the composite membranes were investigated. The results show that incorporation of hierarchical nanofiber improves the water uptake, proton conductivity, and methanol permeability of the membranes. Furthermore, the composite membrane with 50% hierarchical nanofibers exhibited the highest proton conductivity of 0.115 S cm-1 (80 °C), which was 69.12% higher than the values of pure chitosan membrane. The self-assembly allows us to generate hierarchical nanofiber among the interfiber voids, and this structure can provide potential benefits for the preparation of high-performance PEMs.

Anatase titania coated CNTs and sodium lignin sulfonate doped chitosan proton exchange membrane for DMFC application

Anatase titania coated CNTs (TCNTs) and sodium lignin sulfonate (SLS) were introduced to chitosan membrane to improve the conductivity based on extra proton transfer channels built by TCNTs and sulfonate groups supplied by SLS. Water uptake, mechanical properties, oxidation stability and methanol-rejecting property of composite membranes were characterized. The results show that TCNTs and SLS doped membranes have enhanced conductivity and the sample with 5% TCNTs and 2% SLS doped (CS/TCNT-5/SLS-2) achieved a conductivity of 0.0367 S cm^-1 at room temperature and 0.0647 S cm^-1 at 60 °C, which is much higher than pure chitosan membrane. Moreover, with TCNTs incorporation, the mechanical properties, oxidation stability and methanol-rejecting property also improved. Overall, selectivity of CS/TCNT-5/SLS-2 sample achieved 28.2 × 10⁴ S s cm^-3 which is much higher than 3.8 × 10⁴ S s cm^-3 of pure chitosan membrane. Thus, with enhanced properties, chitosan composite membrane could be promising as proton exchange membrane (PEM) in the use of direct methanol fuel cell (DMFC).

Bio-functionalized hybrid nanocomposite membranes for direct methanol fuel cells

Featured methanol-blocking characteristics of nanocomposite membrane.

Zwitterionic SiO2 nanoparticles as novel additives to improve the antifouling properties of PVDF membranes

Zwitterionic SiO₂ nanoparticles exhibit great potential for improving the antifouling performance of hydrophobic PVDF membranes.

Novel composite membranes based on sulfonated poly(ether ether ketone) and adenosine triphosphate for enhanced proton conduction

Novel SPEEK/ATP composite membranes were prepared via a facile method, achieving improved proton conductivity under different conditions.