Composite Anion Exchange Membranes Research Articles

Simultaneously enhanced hydroxide conductivity and mechanical properties of quaternized chitosan/functionalized carbon nanotubes composite anion exchange membranes

Low-cost biopolymer chitosan has received considerable attention in the field of anion exchange membranes (AEMs) because it can be easily quaternized and avoids the carcinogenic chloromethylation step. Simultaneously increasing the ionic conductivity and improving mechanical properties of quaternized chitosan (QCS) is key for its high-performance application. In this study, new composite AEMs consisting of QCS and functionalized carbon nanotubes (CNTs) were prepared. CNTs were coated with a thick silica layer onto which high-density quaternary ammonium groups were then grafted. The insulator silica coating effectively prohibits electron conduction among nanotubes and the grafted –NR3+ provides new OH− conductive sites. Incorporating 5 wt% functionalized CNTs into the matrix enhanced ionic conductivity to 42.7 mS cm−1 (80 °C) which was approximately 2 times higher than that of pure QCS. The effective dispersion of CNTs and appropriate interfacial bonding between nanofiller and QCS improved the mechanical properties of AEMs, including both the strength and toughness of the composite membranes. An alkaline direct methanol fuel cell equipped with the composite membrane (5% functionalized CNTs loading) produced an maximum power density of 80.8 mW cm−2 (60 °C), which was 57% higher than that of pure QCS (51.5 mW cm−2). This study broadens the application of natural polymers and provides a new way to design and fabricate composite AEMs with both improved mechanical properties and electrochemical performance.

Arc-bridge polydimethylsiloxane grafted graphene incorporation into quaternized poly(styrene-b-isobutylene-b-styrene) for construction of anion exchange membranes

A novel robust quaternized poly(styrene-b-isobutylene-b-styrene) (QSIBS)-based anion exchange membrane (AEM) could be achieved via quaternization and cross-linking reaction of chloromethylated SIBS with amines in the presence of graphene sheets grafted with polydimethylsiloxane arc-bridges (G-g-Arc PDMS). The resulting cross-linked QSIBS/G-g-Arc PDMS composite membranes exhibit significantly high ion conductivity (σ) and dynamic mechanical properties, marked by low methanol permeability, together with improved chemical stability. The σ of composite AEM with 0.25 wt% of graphene loading reached remarkably to 1.81 × 10−2 S cm−1 at 60 °C, compared to that (1.15 × 10−2 S cm−1) of QSIBS. This membrane also behaves high storage modulus of 236 MPa even at 150 °C, while Nafion 115 lost its modulus at 150 °C. The homogeneous dispersion of G-g-Arc PDMS in QSIBS matrix leads to a great decrease in methanol permeability to 3.81 × 10−7 cm2 s−1, which is much lower than that of Nafion 115.

Pendent piperidinium-functionalized blend anion exchange membrane for fuel cell application

Alkaline anion exchange membrane fuel cell has fast cathode reactions and thus allows the use of low cost electrocatalysts. However, its practical application is hindered by the low hydroxide ion conductivity and alkaline stability of AEM. In this study, pendent piperidinium functionalized polyetheretherketone is synthesized and blended with polybenzimidazole for fabrication of composite anion exchange membrane. The pendent piperidinium functionalized side chains can create well-connected ionic transporting channels and thus impart the blend membranes high hydroxide conductivity (61.5–72.8 mS cm−1 at 80 °C) and good tensile strength (42.8–58.9 MPa). Due to the strong interactions between polybenzimidazole and piperidinium groups of the polymers as confirmed by Fourier transform infrared spectroscopy, the piperidinium functionalized blend anion exchange membrane can retain 95% of its original OH− conductivity value when treated in 1 M KOH at 60 °C for 576 h. The single fuel cell assembled with the membrane can yield a peak power density of 87 mW cm−2 at 80 °C. Our work provides a new and effective method to balance the hydroxide conductivity and alkaline stability of anion exchange membranes.

Mussel-inspired strategy towards functionalized reduced graphene oxide-crosslinked polysulfone-based anion exchange membranes with enhanced properties

Chemical crosslinking is regard as an effective method to balance the ionic conductivity and dimensional stability of anion exchange membranes (AEMs). In this work, a series of crosslinked AEM composite membranes based on polydopamine-functionalized reduced graphene oxide (PDArGO) were constructed from quaternized polysulfone (QPSU) with amino groups via mussel-inspired chemistry strategy. On the one hand, as the dopant, the hydrogen bonding interaction between PDArGO and a large number of amino groups on the side chains of QPSU can enhance the water uptake of the membranes and has a positive influence on the ionic conductivity of composite membranes. On the other hand, PDArGO also acts as the crosslinker, which can form a micro-crosslinked structure with the amino groups on the side chains of the polymer through the Michael addition/schiff base reactions. Under the combined influence of the above two factors, the crosslinked composite AEMs exhibited special delightful properties. In general, the crosslinking reaction will lead to the decrease of the ionic conductivity of the membranes, but as for the membranes prepared by us, the ionic conductivity had been improved to some extent. Especially, the QPSU-1.5%-PDArGO exhibited 57% improvement in the hydroxide conductivity than that of pure QPSU membrane and reached the highest value of 61 mS cm−1 at 80 °C. Besides, the crosslinked membranes also exhibited strong dimensional stability, good mechanical strength, comparable alkaline stability and improved methanol permeability.

Layered Double Hydroxides Containing an Ionic Liquid: Ionic Conductivity and Use in Composite Anion Exchange Membranes

AbstractZinc‐aluminum layered double hydroxide (LDH) containing an ionic liquid, 1‐butyl‐3‐methylimidazolium hydrogen sulfate (BmimSO4), has been synthesized by a co‐precipitation method. This strategy enabled the intercalation of the ionic liquid (IL) into the interlamellar space of LDH with the aim of increasing the ionic conductivity and reducing its dependence on water content. Pure and IL‐intercalated LDHs have been characterized by Fourier‐Transform Infrared (FTIR) spectroscopy and X‐ray diffraction. Electrochemical Impedance Spectroscopy (EIS) measurements showed that the addition of IL enhanced the ionic conductivity of LDH by a factor of 15 at low humidity and by a factor of 9 at high humidity conditions. As a possible application, LDHs were dispersed as a guest filler in a composite anion exchange membrane (AEM) based on polysulfone‐DABCO. In this case, the addition of IL remarkably improved the ionic conductivity of the membrane from 1.0 ⋅ 10−9 to 2.4 ⋅ 10−7 S/cm at low humidity. At high humidity, the membranes reached a conductivity of 25 mS/cm at 25 °C in OH form. Stability tests of composite AEM confirmed the positive effect of LDH nanoparticles.

Quaternized poly (2.6 dimethyl – 1.4 phenylene oxide)/Polysulfone anion exchange membrane reinforced with graphene oxide for methanol alkaline fuel cell application

Composite anion exchange membranes (AEM) based on quaternized poly (phenylene) oxide and polysulfone blend (QPPO/PSF) were successfully fabricated and characterized for methanol alkaline fuel cell application. To make a composite AEM, increasing graphene oxide (GO) wt.% ratios was introduced in the polymer blend. The membrane properties were enhanced by the addition of GO in comparison to the bare QPPO/PSF blend. The addition of GO resulted to a higher ion exchange capacity (IEC) of 3.21 mmol.g−1 and an ion conductivity increase of up to 63.67 mS.cm−1 at 80 °C. The QPPO/PSF/2%GO composite membrane reached a peak power density of 112 mW.cm−2, which is about five (5) times more than the parent QPPO membrane at room temperature. The above results indicate that QPPO/PSF/GO is a good candidate as an anion exchange membrane for alkaline fuel cell application.

Poly (2,6-dimethyl-1,4-phenylene oxide)/ionic liquid functionalized graphene oxide anion exchange membranes for fuel cells

To improve the overall performance of anion exchange membranes (AEMs) for fuel cells, a series of composite AEMs was prepared via a facile approach using ionic liquid-functionalized graphene oxide (IL-GO) and imidazolium-functionalized poly (2,6-dimethyl-1,4-phenylene oxide) (ImPPO). The prepared ImPPO/IL-GO-0.5% (0.5% refers to the weight percentage of IL-GO) membranes with an ionic exchange capacity (IEC) of 1.9 meq g−1 achieved a hydroxide conductivity of 78.5 mS cm−1. The high conductivity of ImPPO/IL-GO-0.5% is due to the fact that the ionic cluster size of composite membranes (3.43–3.58 nm) is larger than that of the pristine membrane (3.30 nm). The ionic cluster morphology is confirmed by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). Moreover, the AEMs retained approximately 70% of their initial hydroxide conductivity after the alkaline stability test in a 2 M aqueous NaOH at 80 °C for 480 h, indicating a good alkaline stability. A single cell using ImPPO/IL-GO-0.5% exhibits a peak power density of 136 mW cm−2 at 60 °C under 100% related humidity, thereby having a great potential for fuel cells.

Facile and green fabrication of polybenzoxazine-based composite anion-exchange membranes with a self-cross-linked structure

A new type of composite anion-exchange membrane is fabricated using benzoxazine (Bz) monomer and polytetrafluoroethylene (PTFE) via a green and facile method. Membrane fabrication is achieved via in situ ring-opening polymerization of Bz within the PTFE matrix, followed by quaternization and ion-exchange reactions. The quaternized PBz works as a self-cross-linked and anion conductive polymer. The synthesized membranes show improved conductivity (26 to 70 mS/cm) at a reasonable water uptake and a low swelling ratio; they also show improved alkaline stability for 150 h at 60 °C in 1 M KOH solution, the decrease in conductivity being only ca. 10%. Our method of AEM fabrication is advantageous over conventional ones due to facile process and the avoidance of chloro- or bromomethylation as well as the self-cross-linked structure; the resulting membranes show relatively good performance as compared with some of those obtained from conventional techniques.

Composite anion exchange membrane made by layer-by-layer method for selective ion separation and water migration control

Abstract In ion exchange membrane processes (e.g. electrodialysis), improving ion selectivity and reducing water permeance are two key concerns, which drive new membrane fabrication methods. Preparation of composite ion exchange membrane with functional layers may be a solution to elevate its performance. In this study, composite anion exchange membranes (C-AEM) were prepared by using layer-by-layer (LbL) method, and were characterized with regard to membrane surface properties, selectivity, as well as water permeance. Results indicate that monovalent ion selectivity increased with the number of assembled layers. More specifically, when the membrane was modified with 10.5 layers, P SO 4 2 - Cl - reached over 10, which was much higher than the commercially available monovalent selective membrane (ACS, P SO 4 2 - Cl - around 5). Besides, the C-AEMs also showed a good performance on organic ion selectivity and water migration control. This work proves that LbL method is an effective way to prepare functionalized ion exchange membrane by controlling membrane surface properties (surface potential and pore size). Furthermore, this work provides an investigation of transport mechanisms of ions with different charge, different size and different hydration number by penetrating functional membranes with layered top structure. The prepared C-AEMs showed a good separation efficiency of monovalent ions and organic acids with controlled water migration, this may be potentially used in desalination, wastewater treatment, chemical separation, or other related fields.

Preparation and characterization of quaternized poly(vinyl alcohol)/chitosan/MoS2 composite anion exchange membranes with high selectivity

In this study, a series of novel quaternized poly(vinyl alcohol)/chitosan/molybdenum disulfide (QPVA/CS/MoS2) anion exchange membranes (AEMs) were prepared for direct methanol alkaline fuel cell (DMAFC). The composite membrane was synthesized by adding different amounts of MoS2 nanosheets (0, 0.1, 0.2, 0.5 and 1wt%) into QPVA/CS mixture solution and using the solution casting method. The crystallinity, thermal and mechanical properties, ion conductivity and resistance to methanol of the QPVA/CS/MoS2 membranes were characterized by X-ray diffraction, thermogravimetric analysis, tensile testing, ion exchange capacity, and methanol permeability measurements, respectively. The MoS2 was homogeneously dispersed in the membranes. The mechanical strength of the composite membranes was enhanced with the addition of MoS2. With the addition of 1.0wt% MoS2, the QPVA/CS/MoS2 composite membrane has the lowest methanol permeability of 0.210×10−7cm2·s−1. This study confirmed that the novel QPVA/CS/MoS2 membrane would be a potential candidate for the application in DMAFCs.

Quaternized polyhedral oligomeric silsesquioxanes (QPOSS) modified polysulfone-based composite anion exchange membranes

A new method was applied to prepare a series of composite anion exchange membranes by incorporating quaternized polyhedral oligomeric silsesquioxanes (QPOSS) into the quaternized polysulfone (QPSU). The highly functional QPOSS were synthesized by epoxide ring opening reaction of Octaammonium POSS (OAPOSS) with glycidyltrimethylammonium chloride (GDTMAC). It has been shown that the hydroxide conductivity of composite membranes was significantly improved when the QPOSS was doped into the QPSU. Especially, the QPSU-3%-QPOSS exhibited 60% improvement in the hydroxide conductivity than that of the pure QPSU membrane and reached the highest value of 53.6mS/cm at 80°C. TEM characterizations indicated that the formed ion clusters and connected ion transport channels are responsible for the improvement of hydroxide conductivity. In addition, the water uptake, alkaline resistance and oxidative stability of composite membranes were also improved after the doping of QPOSS. The other properties of AEMs including mechanical property, thermal stability and methanol permeability were also investigated. Our study indicated that doping highly functional polyhedral oligomeric silsesquioxanes is a simple and effective method to improve the properties of the AEMs.

Composite anion exchange membranes with functionalized hydrophilic or hydrophobic titanium dioxide

Composite anion exchange membranes based on polysulfone with grafted 1,4-diazabicyclo[2.2.2]octane (DABCO) and surface functionalized TiO2 nanoparticles were prepared and characterized. Tri(hydroxymethyl)propane (TMP) was used for hydrophilic and polymethyl-hydrosiloxane (PMHS) for hydrophobic surface functionalization. Thermal analysis (TGA and DSC) showed water loss, the loss of quaternary ammonium groups around 300 °C and the backbone decomposition above 400 °C starting from the quaternary carbon. The decompositions were confirmed by temperature-dependent FTIR spectroscopy. The thermomechanical study (DMA) showed a secondary relaxation, probably due to DABCO side groups motions, around 130 °C followed by the glass transition around 250 °C and by a partial crystallization of the polymer, which is also observed by DSC. The increase of storage modulus observed for the composites is consistent with their reduced hydration, which is confirmed by water uptake measurements. Atomic Force Microscopy observations show a more homogeneous dispersion of hydrophobic TiO2 nanoparticles, which are also well embedded in the polymer, whereas agglomeration is evident for hydrophilic surface treatment. The contact angle with water decreases strongly in composites with TMP-TiO2. The ionic conductivity is higher for PMHS-TiO2, probably related to the more homogeneous filler distribution with lower agglomeration.

Anion exchange composite membrane based on octa quaternary ammonium Polyhedral Oligomeric Silsesquioxane for alkaline fuel cells

A series of novel composite anion exchange membranes were prepared via simple solution casting method using synthesized quaternary ammonium functionalized Polyhedral Oligomeric Silsesquioxane (QA-POSS) with Quaternary polysulfone (QPSU). QA-POSS was synthesized from prepared Cl-POSS and well characterized by FT-IR, NMR, SEM and TEM analyses to confirm the chemical modifications and cubic morphologies. The QA-POSS nano particles have dual role in the membrane providing additional ion conducting groups and reinforcing the membrane in molecular level for the overall improvement of composite membrane. Additionally, the composite membranes were characterized by XRD, SEM, Ion exchange capacity (IEC), water uptake and conductivity to ensure the suitability of its use as an electrolyte in alkaline fuel cell. Finally, membrane electrode assembly (MEA) was fabricated using Pt anode (0.25 mg/cm2), Ag cathode (0.375 mg/cm2) and various synthesized composite membranes, and then it was tested in real time fuel cell setup. The membrane with 15% QA-POSS showed the maximum power density of 321 mW/cm2. The results showed that QA-POSS possess the ability to enhance the performance of the anion exchange membrane significantly.

Highly conductive and robust composite anion exchange membranes by incorporating quaternized MIL-101(Cr)

With well-defined channels and tunable functionality, metal-organic frameworks (MOFs) have inspired the design of a new class of ion-conductive compounds. In contrast to the extensive studies on proton-conductive MOFs and related membranes attractive for fuel cells, rare reports focus on MOFs in preparation of anion exchange membranes. In this study, chloromethylated MIL-101(Cr) was prepared and incorporated into chloromethylated poly (ether ether ketone) (PEEK) as a multifunctional filler to prepare imidazolium PEEK/imidazolium MIL-101(Cr) (ImPEEK/ImMIL-101(Cr)) anion exchange membrane after synchronous quaternization. The successful synthesis and chloromethylation of MIL-101(Cr) were verified by transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy while the enhanced performance of composite membranes in hydroxide conductivity, mechanical strength and dimensional stability were evaluated by alternating-current impedance, electronic stretching machine and measurement of swelling ratio. Specifically, incorporating 5.0wt% ImMIL-101(Cr) afforded a 71.4% increase in hydroxide conductivity at 20°C, 100% RH. Besides, the composite membranes exhibited enhanced dimensional stability and mechanical strength due to the rigid framework of ImMIL-101(Cr). At room temperature and the ImMIL-101(Cr) content of 10wt%, the swelling ratio of the ImPEEK/ImMIL-101(Cr) was 70.04% lower while the tensile strength was 47.5% higher than that of the pure membrane.

Ionic-Liquid-Functionalized Graphene Nanoribbons for Anion Exchange Membrane Fuel Cells

Ionic-liquid-functionalized graphene nanoribbons (IGNRs) were synthesized, and a novel composite anion exchange membrane (AEM) was then constructed by blending the IGNRs with an ionic-liquid-functionalized perfluorinated anion polymer (I-PFSO2NH2-Cl) in solution, followed by solution casting and anion exchange. FT-IR, NMR, SEM and Raman spectra were applied to analyze the chemical composition and morphology of the composite AEM, confirming their successful synthesis. The composite AEM containing 1.0% IGNRs displayed the highest conductivity of 120.5 mS.cm−1 at 80°C in water, which was 1.7 times higher than that of the pristine membrane. Meanwhile, a new IGNRs/Pt electrocatalyst structure that uses IGNRs as the supporting material was prepared to improve the compatibility between the fillers and the Pt catalyst, and it was effectively used in the anion exchange membrane fuel cell (AEMFC). The single cell of the composite AEM with the IGNRs/Pt electrocatalysts reached a peak power density of 197.2 mW cm−2, which was 1.9 times higher than that of the pristine membrane. Thus, the IGNRs architecture appears to be a promising candidate for membrane fillers and electrocatalyst support materials to enhance the performance of AEMFCs.

Incorporating functionalized silica nanoparticles in polyethersulfone‐based anion exchange nanocomposite membranes

ABSTRACTIn order to investigate for anion exchange membranes (AEMs) with improved properties, four series of polyethersulfone‐based composite AEMs are fabricated by incorporating pristine and three functionalized silica nanoparticles containing propylamine, trimethylpropylamine, and melamine‐based dendrimer amine groups. The results show that by choosing appropriate functional agent, anion exchange membranes with improved parameters can be achieved. The polymeric matrix of the membranes is synthesized by chloromethylation of polyethersulfone using thionyl chloride followed by amination with trimethylamine (TMA). The effectiveness of chloromethylation process is confirmed by 1H NMR analysis. The effects of functional groups on characteristic and transport properties of the prepared composite membranes i.e., SEM, IEC, water uptake, porosity transport properties, and conductivity are investigated. The scanning electron microscope images illustrates that the synthesized membranes possess dense structures. Ion exchange capacity (IEC), water uptake, transport properties, and conductivity of the composite membranes are measured. In addition, the morphology and thermal stability are characterized. IECs and ion conductivities of up to 1.45 meq g−1 and 45.46 mS cm−1 and moderate transport characteristics are obtained from the modified membranes which confirm that these membranes are appropriate for applying in electro‐membrane processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44596.

Preparation and characterization of anion-exchange membranes derived from poly(vinylbenzyl chloride-co-styrene) and intercalated montmorillonite

In this paper, three organic intercalating agents containing cations [hexadecyl trimethyl ammonium bromide (CTAB), poly(acrylamide-co-diallyldimethylammonium chloride), and quaternized polyethyleneimine] are used to prepare intercalated montmorillonites (MMT) by ion-exchange method. Then the modified MMTs are doped with vinylbenzyl chloride and styrene copolymer [poly(vinylbenzyl chloride-co-styrene)] for fabricating composite anion-exchange membranes (AEM). Fourier transform infrared, X-raydiffraction, thermogravimetric analysis, scanning electron microscopy, and Mastersizer laser particle size analyzer are employed to characterize the structure and morphology of MMTs and AEMs. The successful intercalation of MMTs is approved, and the MMT intercalated by CTAB shows an interlayer distance of 2.31 nm. The properties of the composite membranes including water uptake, mechanical property, and ionic conductivity are investigated. Among all the AEMs, the composite membrane containing MMT sheets with CTAB demonstrates better compositive performances. It presents an ionic conductivity of 2.09 × 10−2 S cm−1 at 80°C and good alkaline solution stability. Copyright © 2016 John Wiley & Sons, Ltd.

Composite Anion Exchange Membrane from Quaternized Polymer Spheres with Tunable and Enhanced Hydroxide Conduction Property

In this research, novel quaternized polymer spheres (QPSs) with a high quaternary ammonium (QA) group loading amount and a controllable structure are synthesized and incorporated into a chitosan (CS) matrix to fabricate a composite membrane. Systematic characterizations and molecular simulation are adopted to elaborate the relationship between the QA structure of QPSs and physical-chemical as well as ion conduction properties of composite membranes. The well-dispersed QPSs generate repulsive interaction to CS chains, endowing the composite membrane with promoted chain mobility and water uptake and thereby enhanced hydroxide conductivity. The QPSs work as hydroxide conductors within the membranes, affording a hydroxide conductivity increase over 80%. As the hopping sites in the membrane, the QA group with moderate OH– combination/dissociation capability exhibits higher OH– conductivity. By comparison, the QA group with the highest or lowest potential displays slightly lower OH– conductivity. Besides, exten...

Using diethylamine as crosslinking agent for getting polyepichlorohydrin-based composite membrane with high tensile strength and good chemical stability

A composite anion exchange membrane of crosslinked quaternized polyepichlorohydrin/polytetrafluoroethylene (CQPECH/PTFE) had been prepared via a green and facile method, where diethylamine, 1-methylimidazole and PTFE, respectively, served as crosslinking agent, quaternization reagent and supporting material. The structure and morphology of CQPECH/PTFE membrane were investigated. Water uptake, swelling ratio, ionic exchange capacity, hydroxide conductivity, chemical stability, and thermal and mechanical properties were measured to evaluate its performance in a direct methanol alkaline fuel cell. The results indicated that CQPECH had penetrated into the pores of PTFE membrane, showing a dense and uniform structure without any pore and phase separation. Besides, CQPECH/PTFE membrane exhibited high ionic conductivity, considerable ionic exchange capacity, moderate water uptake and low swelling ratio. More importantly, the obtained composite membrane displayed high tensile strength and good chemical and thermal stability, suggesting the great potential application of CQPECH/PTFE membrane as anion exchange membrane. Crosslinked quaternized polyepichlorohydrin/polytetrafluoroethylene composite anion exchange membrane had been prepared via a green and facile method, where diethylamine served as crosslinking agent. With a dense and uniform structure without any pore and phase separation, the obtained composite membrane exhibited high tensile strength and good chemical stability.

Novel Composite Anion Exchange Membranes Based on Quaternized Polyepichlorohydrin for Electromembrane Application

A series of semi-interpenetrating polymer network (sIPN) composite anion exchange membranes were fabricated depending on immobilized linear PVDF and cross-linked polyepichlorohydrin (PECH), 1,4-diazabicyclo[2.2.2]octane, (DABCO) network through in situ synthetic pathway. A cyclic diamine (DABCO) was used as cross-linking agent and simultaneously improved the ion-exchange capacity by amination. Scanning electron microscopy (SEM) indicated that the composite membranes exhibited a dense and homogeneous structure. Successful formation of PECH-DABCO copolymer within the sIPN membranes was also confirmed by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The PVDF percentage and inherent properties of membranes such as ion exchange capacity (IEC), water uptake (WR), thermal stability, mechanical property, and area resistance were investigated to evaluate their applicability in electrodialysis (ED). The experimental results showed that the composite membrane maintained a good perspec...