Novel methanol-blocking proton exchange membrane achieved via self-anchoring phosphotungstic acid into chitosan membrane with submicro-pores

Fabrication of Dual-Functional Bacterial-Cellulose-Based Composite Anion Exchange Membranes with High Dimensional Stability and Ionic Conductivity

Anion exchange membranes (AEMs) are increasingly becoming a popular research area due to their ability to function with nonprecious metals in electrochemical devices. Nevertheless, there is a challenge to simultaneously optimize the dimensional stability and ionic conductivity of AEMs due to the "trade-off" effect. Herein, we adopted a novel strategy of combining filling and cross-linking using functionalized bacterial cellulose (PBC) as a dual-functional porous support and brominated poly(phenylene oxide) (Br-PPO) as the cross-linking agent and filler. The PBC nanofiber framework together with cross-linking can provide a reliable mechanical support for the subsequent filled polymer, thus improving the mechanical properties and effectively limiting the size change of the final quaternized-PPO (QPPO)-filled PBC composite membrane. The composite membrane showed a very low swelling ratio of only 10.35%, even at a high water uptake (81.83% at 20 °C). Moreover, the existence of multiple -NR3+ groups in the cross-link bonds between BC and Br-PPO can provide extra OH- ion transport sites, contributing to the increase in ionic conductivity. The final membrane demonstrated a hydroxide ion conductivity of 62.58 mS cm-1, which was remarkably higher than that of the pure QPPO membrane by up to 235.93% (80 °C). The successful preparation of the PBC3/QPPO membrane provides an effective avenue to tackle the trade-off effect through a dual-functional strategy.

Composite proton exchange membrane for fuel cells based on chitosan modified by acid-base amphoteric nanoparticles

Currently, achieving a simultaneous improvement in proton conductivity and mechanical properties is a key challenge in using chitosan (CS) as a proton exchange membrane (PEM) substrate in direct methanol fuel cells (DMFCs). Herein, a novel nanofiller-zwitterionic molecule, (3-(3-aminopropyl) dimethylammonio) propane-1-sulfonate, ADPS)-modified polydopamine (PDA) (PDA-ADPS) was synthesized by the Michael addition reaction and was incorporated into a CS matrix to prepare CS/PDA-ADPS composite membranes. PDA-ADPS, which contains an acid-based ion pair can create new proton conduction channels in the composite membrane, improving proton conductivity. The proton conductivity of the CS/PDA-ADPS composite membrane was as high as 38.4 mS cm-1 at 80 °C. Moreover, due to the excellent compatibility and dispersibility of PDA-ADPS in the CS matrix, the obtained CS/PDA-ADPS composite membranes exhibited favorable mechanical properties. Such outstanding proton conductivity and mechanical properties guarantee good performance of the composite membranes in fuel cells. The peak power density of the CS/PDA-ADPS composite membranes was 30.2 mW cm-2 at 70 °C. This work provides a new strategy for fabricating high-performance CS based PEMs for DMFCs.

Performance Enhancement of Kaolin/Chitosan Composite-Based Membranes by Cross-Linking with Sodium Tripolyphosphate: Preparation and Characterization

A new family of environmentally friendly and low-cost membranes based on readily available mineral and polymeric materials has been developed from cast suspensions of kaolin and chitosan using aqueous phase separation and polyethylene glycol as a pore-forming agent. The as-fabricated membranes were further cross-linked with sodium tripolyphosphate (STPP) in order to strengthen the properties of the obtained samples. The functional groups determined by FTIR and EDX confirmed that the reaction occurred. A detailed study of the effects of cross-linking time on the physicochemical, surface and permeation properties showed that a 30-minute reaction enabled the composite membrane to be stable in acidic media (up to pH 2) and increased the mechanical strength twofold compared to the non-cross-linked membrane. A similar morphology to that generally observed in polymeric membranes was obtained, with a sponge-like surface overlaying a finger-like through structure. The top layer and cross-section thicknesses of the membranes increased during STPP post-treatment, while the pore size decreased from 160 to 15 nm. At the same time, the molecular weight cut-off and permeance decreased due to the increase in cross-linking density. These results observed in a series of kaolin/chitosan composite membranes showed that STPP reaction can provide control over the separation capability range, from microfiltration to ultrafiltration.

Advancements of Polyvinylpyrrolidone-Based Polymer Electrolyte Membranes for Electrochemical Energy Conversion and Storage Devices

Polymer electrolyte membranes (PEMs) play vital roles in electrochemical energy conversion and storage devices, such as polymer electrolyte membrane fuel cell (PEMFC), redox flow battery, and water electrolysis. As the crucial component of these devices, PEMs need to possess high ion conductivity and electronic insulation, remarkable mechanical and chemical stability, and outstanding isolation function for the materials on both sides of the cathode and anode. Polyvinylpyrrolidone has received widespread attention in the research of PEMs owing to its tertiary amine basic groups and exceptional hydrophilic properties. This review focuses on the application status of polyvinylpyrrolidone-based PEMs in PEMFC, vanadium redox flow battery, and alkaline water electrolysis, and describes in detail the key scientific problems in these fields, providing constructive suggestions and guidance for the application of polyvinylpyrrolidone-based PEMs in electrochemical energy conversion and storage devices.

Anchoring Water Soluble Phosphotungstic Acid by Hybrid Fillers to Construct Three-Dimensional Proton Transport Networks

Phosphotungstic acid (HPW)-filled composite proton exchange membranes possess high proton conductivity under low relative humidity (RH). However, the leaching of HPW limits their wide application. Herein, we propose a novel approach for anchoring water soluble phosphotungstic acid (HPW) by polydopamine (PDA) coated graphene oxide and halloysite nanotubes (DGO and DHNTs) in order to construct hybrid three-dimensional proton transport networks in a sulfonated poly(ether ether ketone) (SPEEK) membrane. The introduction of PDA on the surfaces of the hybrid fillers could provide hydroxyl groups and secondary amine groups to anchor HPW, resulting in the uniform dispersion of HPW in the SPEEK matrix. The SPEEK/DGO/DHNTs/HPW (90/5/5/60) composite membrane exhibited higher water uptake and much better conductivity than the SPEEK membrane at low relative humidity. The best conductivity reached wass 0.062 S cm-1 for the composite membrane, which is quite stable during the water immersion test.

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

(1) Background: Ionotropic gelation of cost-effective and eco-friendly biopolymer chitosan (Chit) is a novel and promising approach to the one-step synthesis of proton-conducting fuel cell bio-membranes.The method discovered by the author in 2011 and subsequently drowned among very few papers. This work aimed to relaunch this method through clear and effective communication of new unpublished results emphasizing the key aspects of this topic for successful dissemination of the results and significant future developments. (2) Methods and results: The mechanism of in-situ ionotropic gelation of Chit on an alumina substrate by phosphotungtate anions (PWA3-) was discussed and analyzed. The study sheds light on the effect of prolonged post-treatment in phosphotungstic acid (PWA) solution on the obtained chitosan/phosphotungstate (Chit-PWA) flat structures. Methods used included combined structural (XRD), thermal-gravimetric (DTG), electrochemical (in-situ EIS), compositional (EDX),morphological analysis (SEM), as well as the performances in a low temperature H2/O2 fuel cell(4) Conclusions: This contribution discloses novel possibilities aimed at increasing the impact of ionotropic gelation of chitosan on the scientific community working on the synthesis of novel proton conductive bio-composite membranes and structures.

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.

Polyoxometalate-Polymer Hybrid Materials as Proton Exchange Membranes for Fuel Cell Applications

As one of the most efficient pathways to provide clean energy, fuel cells have attracted great attention in both academic and industrial communities. Proton exchange membranes (PEMs) or proton-conducting electrolytes are the key components in fuel cell devices, which require the characteristics of high proton conductivity as well as high mechanical, chemical and thermal stabilities. Organic-inorganic hybrid PEMs can provide a fantastic platform to combine both advantages of two components to meet these demands. Due to their extremely high proton conductivity, good thermal stability and chemical adjustability, polyoxometalates (POMs) are regarded as promising building blocks for hybrid PEMs. In this review, we summarize a number of research works on the progress of POM-polymer hybrid materials and related applications in PEMs. Firstly, a brief background of POMs and their proton-conducting properties are introduced; then, the hybridization strategies of POMs with polymer moieties are discussed from the aspects of both noncovalent and covalent concepts; and finally, we focus on the performance of these hybrid materials in PEMs, especially the advances in the last five years. This review will provide a better understanding of the challenges and perspectives of POM-polymer hybrid PEMs for future fuel cell applications.

A highly proton-/vanadium-selective perfluorosulfonic acid membrane for vanadium redox flow batteries

The polar clusters of Nafion are blocked by the incorporation of the nanohybrid, which contributes to suppress vanadium ions crossover.

Graphene oxide based nanohybrid proton exchange membranes for fuel cell applications: An overview

In the context of many applications, such as polymer composites, energy-related materials, sensors, 'paper'-like materials, field-effect transistors (FET), and biomedical applications, chemically modified graphene was broadly studied during the last decade, due to its excellent electrical, mechanical, and thermal properties. The presence of reactive oxygen functional groups in the grapheme oxide (GO) responsible for chemical functionalization makes it a good candidate for diversified applications. The main objectives for developing a GO based nanohybrid proton exchange membrane (PEM) include: improved self-humidification (water retention ability), reduced fuel crossover (electro-osmotic drag), improved stabilities (mechanical, thermal, and chemical), enhanced proton conductivity, and processability for the preparation of membrane-electrode assembly. Research carried on this topic may be divided into protocols for covalent grafting of functional groups on GO matrix, preparation of free-standing PEM or choice of suitable polymer matrix, covalent or hydrogen bonding between GO and polymer matrix etc. Herein, we present a brief literature survey on GO based nano-hybrid PEM for fuel cell applications. Different protocols were adopted to produce functionalized GO based materials and prepare their free-standing film or disperse these materials in various polymer matrices with suitable interactions. This review article critically discussed the suitability of these PEMs for fuel cell applications in terms of the dependency of the intrinsic properties of nanohybrid PEMs. Potential applications of these nanohybrid PEMs, and current challenges are also provided along with future guidelines for developing GO based nanohybrid PEMs as promising materials for fuel cell applications.