Synthesis Of Anion Exchange Membranes Research Articles

Quaternized poly(vinyl toluene-co-α-methyl styrene)/poly(vinyl alcohol) interpenetrating anion exchange membrane for efficient acid reclamation

With increasing urbanization and better lifestyle, more industries are being set up worldwide. Eco-friendly treatment of industrial waste is one of the major challenges to be resolved. Membrane can be a better option to treat industrial waste in sustainable manner. Herein, we report synthesis of anion exchange membrane (AEM) via. interpenetrating type crosslinked-network of N-methyl morpholine functionalized poly(vinyl toluene-co-α-methyl styrene) (PVM) and poly(vinyl alcohol) (PVA). The composition of QPVM to PVA varied from 1:1, 1:1.25, and 1:1.50 to optimize for better membrane performance in terms of ionic conductivity, proton diffusion coefficient and selectivity towards metal ions. AEM with composition of 1:1.25 PVA:QPVM (PVM-1.25) exhibits overall better physicochemical and electrochemical traits bearing ∼63% of water uptake and ⁓10.5 mS cm-1 of ionic conductivity (IC) with counter-ion transport number of 0.93. The structural and functional group analysis of prepared membranes were performed by 1H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. All synthesized AEMs were systematically evaluated for acid reclamation application, and results were corroborated in terms of proton diffusion coefficient (UH+), metal diffusion coefficient (UMn+)and separation factor (Sf) using variable divalent and trivalent metal ions in simulant acidic waste models. PVM-1.25 membrane showed highest proton diffusion coefficient of 39.35 × 10−3 m h−1 with separation factor of 42.57 in presence of Al3+ ions, which is ∼42% and ∼66% higher than Fe2+ (UH+= 27.71 × 10−3 m h−1 and Sf=19.87) and Zn2+ (UH+= 23.62 × 10−3 m h−1 and Sf=12.27), respectively. PVM-1.25 membrane also showed chemical, thermal and mechanical stability. Based on the results, PVM-1.25 can be considered a good candidate for reclamation of acid from industrial waste stream.

Microstructural orientation of anion exchange membrane through mechanical stretching for improved ion transport

Synthesis of anion exchange membranes (AEMs) with orientated nano/micro-structure and with tunable ion-channels is of great interest for applications in fuel cells, water electrolyzers, and redox flow batteries. However, there is still a dearth of work in the detailed understanding of anion conductivity from a polymer structure‒property perspective. Herein, we demonstrate an easy and versatile strategy to fabricate highly conductive AEMs. By stretching the AEMs, an improvement in OH− conductivities of AEMs is achieved. The effect of elongation at different water contents on polymer structures and OH− conductivities was investigated by a combination of molecular dynamics (MD) simulation and experimental study, giving insights into macromolecular orientation at the atomic level. The morphological changes, which consist of oriented polymer chains and elongated water clusters, are quantified by a combination of two dimensional small angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and radial distribution functions. Detailed analyses of interatomic distances reveal morphological variations of hydrophilic domains and their interactions with water and OH− under elongation at different hydration levels. Furthermore, the OH− conductivities of our synthesized quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) AEMs increased significantly after stretching to 20% elongation at all water contents. Specifically, OH− conductivity of stretched QPPO was 2.24 times more than the original AEM at 60% RH. The higher relative increase in OH− conductivity at lower water content may be caused by the lower flexibility of side chains at lower hydrated level. This work verifies the significance of porous and/or oriented AEM structure in the improvement on anion conductivity and water transport efficiency.

Synthesis of Anion Exchange Membranes Containing PVDF/PES and Either PEI or Fumion®.

In this work, the preparation of dense blended membranes, from blends of poly(vinylidene fluoride) (PVDF), poly(ether sulfone) (PES) and polyethyleneimine (PEI) or Fumion®, with possible applications in alkaline fuel cell (AEMFC) is reported. The blended PEI/Fumion® membranes were prepared under a controlled air atmosphere by a solvent evaporation method, and were characterized regarding water uptake, swelling ratio, thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), ion exchange capacity (IEC), OH− conductivity and novel hydroxide ion exchange rate (HIER), which is related to the mass transport capacity of the OH− ions through the membrane. The effect of the chemical composition on its morphological and anion exchange properties was evaluated. It was expected that the usage of a commercial ionomer Fumion®, in the blended membranes would result in better features in the electrical/ionic conductivity behaviour. However, two of the membranes containing PEI exhibited a higher HIER and OH− conductivity than Fumion® membranes, and were excellent option for potential applications in AEMFC, considering their performance and the cost of Fumion®-based membranes.

Anion Exchange Membranes for Alkaline Polymer Electrolyte Fuel Cells-A Concise Review.

Solid anion exchange membrane (AEM) electrolytes are an essential commodity considering their importance as separators in alkaline polymer electrolyte fuel cells (APEFC). Mechanical and thermal stability are distinguished by polymer matrix characteristics, whereas anion exchange capacity, transport number, and conductivities are governed by the anionic group. The physico-chemical stability is regulated mostly by the polymer matrix and, to a lesser extent, the cationic head framework. The quaternary ammonium (QA), phosphonium, guanidinium, benzimidazolium, pyrrolidinium, and spirocyclic cation-based AEMs are widely studied in the literature. In addition, ion solvating blends, hybrids, and interpenetrating networks still hold prominence in terms of membrane stability. To realize and enhance the performance of an alkaline polymer electrolyte fuel cell (APEFC), it is also necessary to understand the transport processes for the hydroxyl (OH−) ion in anion exchange membranes. In the present review, the radiation grafting of the monomer and chemical modification to introduce cationic charges/moiety are emphasized. In follow-up, the recent advances in the synthesis of anion exchange membranes from poly(phenylene oxide) via chloromethylation and quaternization, and from aliphatic polymers such as poly(vinyl alcohol) and chitosan via direct quaternization are highlighted. Overall, this review concisely provides an in-depth analysis of recent advances in anion exchange membrane (AEM) and its viability in APEFC.

Anion-exchange membranes derived from main group and metal-based cations

The design and synthesis of anion-exchange membranes (AEMs) has attracted a great deal of attention given the potential utility of these materials for ion transport in electrochemical energy systems. AEMs are polymer electrolytes with positively charged groups covalently bound to a polymer backbone that can conduct either hydroxide or other anions. The vast majority of AEMs are based on ammonium groups (+NR4) but questions surrounding the long-term stability of these functionalities to hydroxide has led to examination of other cation alternatives. In this review, we highlight some of the recent efforts towards AEMs with cations derived from inorganic elements, with a specific emphasis on phosphonium, sulfonium, and metal-based cations. These studies demonstrate the potential of inorganic building blocks for construction of novel AEMs, with unique properties relative to their ammonium analogues.

Polyetherimide based anion exchange membranes for alkaline fuel cell: Better ion transport properties and stability

Alkaline anion exchange membrane (AAEM) is the key component for alkaline exchange membrane fuel cells (AEMFCs). AAEMs with good ionic conductivity, excellent thermo-mechanical and alkaline stability were synthesized by chloromethylation and quaternization followed by alkalization of polyetherimide. Chloromethylation of polyetherimide, a key step in the synthesis of anion exchange membranes based on polyetherimide, frequently involves cancer-causing chemicals. Here, an approach towards the use of non-carcinogenic reagent has been implemented for the synthesis of AAEMs. Physiochemical properties of prepared membranes are tuned by varying tertiary amines. Derivatives during the membrane synthesis are characterized by proton NMR spectroscopy. FTIR spectroscopy confirms the successful quaternization of polyetherimide, and dense nature of membranes is cross-checked by SEM imaging. Synthesized anion exchange membranes show ionic conductivity in order of 2.68–3.22 × 10−2 S/cm complemented by ion exchange capacity of 1.58–2.07 meq/g. Under strong alkaline conditions 1 M KOH at 60 °C and 5 M KOH at room temperature, membranes are stable without losing their integrity. Based on preliminary studies, it is anticipated that functionalized polyetherimide may be a suitable candidate as an anion exchange membrane in fuel cell applications.

Recent development in polyolefin-based anion exchange membrane for fuel cell application

Anion exchange membrane (AEM) plays a critical role in many environmental and energy devices and processes, such as fuel cell, redox flow battery, and electrodialysis. In particular, when polymeric AEMs are exploited in alkaline fuel cells to replace liquid electrolytes, AEM fuel cells (AEMFC) have attracted worldwide attention because of several inherent advantages over proton exchange membrane fuel cells, e.g. the utilization of less expensive metallic catalysts and enhanced kinetics of oxygen reduction. Among different kinds of AEMs, polyolefin-based AEMs showed great potential for large-scale commercialization because of their excellent chemical stability, easy processability, and low cost. The strategies to synthesize polyolefin anion exchange membrane materials included direct (co)polymerization with functionalized monomers and post-modification of polyolefins. Generally, the ring-opening metathesis polymerization and Ziegler-Natta catalyst mediated polymerization techniques have been successfully employed to synthesized polyolefin AEMs, using the functional monomers including the α-olefin, norbornene, and cyclooctene. Therefore, the chemical structure and composition can be readily tuned to achieve the optimized properties of the resulting AEMs. However, the functional monomers that need complex synthetic procedure have greatly hampered its further commercialization. Radiation-grafting polymerization of vinylbenzyl chloride (VBC) on the polyolefin backbone has been confirmed as another effective method to produce AEMs. Both (partially or fully) fluorinated and hydrocarbon-based polyolefin have been grafted with poly(VBC) under high energy radiation (such as commercial electron-beam accelerators or 60Co γ-ray facilities), and subsequent quaternization allow the synthesis of AEMs with different ionic head-group. In order to produce high-performance AEMs, high irradiation doses were used to get high degree of grafting, which in turn results in a detrimental reduction in the mechanical properties of the resulting AEMs. Therefore, it is necessary to optimise the conditions of grafting reactions. The physicochemical properties of polyolefin-based AEMs are investigated in detail by the measurement of ion exchange capacity, water uptake, swelling ratio, and ionic conductivity, which are well corelated to their chemical structure and microstructure. Moreover, H2/O2 AEMFC assembled from polyolefin-based AEMs (especially for radiation-grafted AEMs) are tested under various conditions in terms of types of electrochemical catalysts, cell temperature, gas flow rate, and so on. Thus, this review summarized the recent developments of polyolefin-based AEMs from the synthetic methods to the properties of AEMs and their performance in H2/O2 fuel cell. The relationship between chemical structure, properties and morphology of polyolefin-based AEMs will be discussed. At last, we extend the discussion of AEMs to their performance in H2/O2 fuel cell, as dramatic improvements of AEM fuel cell performance is accomplished when using high- performance polyolefin-based AEMs.

Facile synthesis of Br-PPO/f GO based polymer electrolyte membranes for electrochemical applications

We report the synthesis of anion exchange membrane based on brominated poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) and polyethyleneimine (PEI) modified graphene oxide (GO). The prepared membrane are characterized electrochemically in terms of ion exchange capacity (IEC), water uptake (Wt), dimensional stability (Sd), and membrane ionic conductivity (ɸ). The surface morphology and structural analysis of membrane were performed by using AFM, TEM, FT-IR, XRD and 1HNMR. Thermal and mechanical analysis was done by using TGA, DMA and UTM. QP-5 membrane show good thermal and mechanical stability among all prepared membranes. The ionic conductivity and IEC value was found maximum in QP-5 and the value is 7.1 × 10−2 S cm−1 and 3.59 meq g−1. Mechanical study was determined by universal testing machine (UTM) analysis shows QP-5 membrane best among the membranes with modulus 6.5 MPa. The methanol crossover resistance for QP-5 membrane is calculated to be 2.27 × 10−7 cm2/s with the selectivity of 3.4 × 104. The power consumption during salt removal is also found to be lower compared to other synthesized membranes.

Synthesis of Anion Exchange Membranes with Side-Chain-Type Benzylic Cationic Groups Using Chloromethylbenzoylation

To circumvent the shortcomings of traditional synthetic routes relying on chloromethylation or bromination of benzylic methyl groups, a novel approach, chloromethylbenzoylation, has been proposed to synthesize commercially available poly(aryl ether)s (PAEs) with side-chain-type benzylic cationic groups for anion exchange membranes (AEMs). Previous works have demonstrated that adding alkyl side chain to PAE backbones can improve the alkaline stability of the AEMs. In this work, side-chain-type benzylchloride groups have been directly introduced onto poly resorcinol ketone (PRK) via an acylation reaction between 4-(chloromethyl)benzoic acid and PRK in P2O5/CH3SO3H at 60 oC. 1H NMR and GPC confirm that 100% substitution occurred, without side reactions such as crosslinking or degradation. Robust AEMs were then obtained through amination upon introduction of trimethylammonium (TMA+) groups. The chloride ionic conductivity of the AEM was 8.8 mS/cm at 30 °C, which is competitive with that of a commercial TokuyamaÒ A201 membrane at similar IEC values. In summary, this approach represents a simple and straightforward route capable of quantitative introduction of side-chain-type benzylchloride groups without using expensive or toxic reagents, with potential applications of the resultant AEMs in energy conversion and storage and other fields.

Anion exchange membrane prepared from simultaneous polymerization and quaternization of 4-vinyl pyridine for non-aqueous vanadium redox flow battery applications

A simple, single step and environmentally friendly process is developed for the synthesis of anion exchange membrane (AEM) by simultaneous polymerization and quaternization, unlike the conventional membrane synthesis which consists of separate polymerization and quaternization step. The membrane synthesis is carried out by dissolving polyvinyl chloride (PVC) in cyclohexanone along with 4-vinyl pyridine (4VP) and 1,4-dibromobutane (DBB) in the presence of thermal initiator benzoyl peroxide, followed by film casting to get thin and flexible AEMs. The membrane properties such as ion exchange capacity, ionic conductivity and swelling behaviour are tuned by varying the degree of crosslinking. These AEMs exhibit low vanadium permeability, while retaining good dimensional and chemical stability in an electrolyte solution, making them appropriate candidates for non-aqueous vanadium acetylacetonate redox flow battery (VRFB) applications. The optimized membrane displays ion exchange capacity and ionic conductivity of 2.0 mequiv g−1 and 0.105 mS cm−1, respectively, whereas the efficiency of 91.7%, 95.7% and 87.7% for coulombic, voltage and energy parameter in non-aqueous VRFB, respectively. This study reveals that the non-aqueous VRFB performance is greatly influenced by membrane properties; therefore the optimal control over the membrane properties is advantageous for the improved performance.

Alkali doped polyvinyl alcohol/graphene electrolyte for direct methanol alkaline fuel cells

Despite the intensive effort directed at the synthesis of anion exchange membranes (AEMs) only a few studies show enhanced ionic conductivity with simultaneous suppression of unfavourable mass transport and improved thermal and mechanical properties. Here we report an alkaline nanocomposite membrane based on fully exfoliated graphene nanosheets and poly(vinyl alcohol) (PVA) prepared by a simple blending process. The composite membrane shows improved ionic transport due to the homogeneous distribution of the graphene nanosheets which are able to form continuous, well-connected ionic channels. Significant enhancement of the ionic conductivity for the prepared graphene/PVA composite membranes is observed with a 0.7 wt% graphene loading resulting in a ∼126% improvement in ionic conductivity and a ∼55% reduction in methanol permeability. The resulting maximum power density obtained by incorporating the membrane in a cell is increased by ∼148%. A higher graphene loading (1.4 wt%) enhances the adhesion of the nanofiller–matrix, giving a ∼73% improvement in the tensile strength. This study provides a simple route to designing and fabricating advanced AEMs.

Synthesis of anion exchange membranes from cellulose: Crosslinking with diiodobutane

Polymer Electrolyte Fuel Cells operating in alkaline media present various advantages. As an alternative to fossil origin polymer electrolytes, the synthesis of crosslinked anion exchange membranes based on cellulose is described in this paper. Using cellulose p-toluenesulfonate derivatives, a carbohydrate polymer bearing quaternary ammonium moieties is synthesized by a reaction with 1,4-diazabicyclo[2.2.2]octane. Membranes are then obtained by crosslinking this cationic polymer with diiodobutane. IR and NMR spectroscopy together with elemental analysis confirmed structures of the different intermediates. In order to complete this study, Ionic Exchange Capacity, Water Uptake and conductimetry data are also provided.

Poly(phenylene)-Based Anion Exchange Membranes for Alkaline Fuel Cells

Cationic polymer membranes that conduct free anions comprise an enabling research area for alkaline membrane fuel cells and other solid-state electrochemical devices that operate at high pH. The synthesis of anion exchange membranes based on a poly(phenylene) backbone prepared by a Diels-Alder reaction is demonstrated as a potential material for alkaline fuel cells. The poly(phenylene)s have benzylic methyl groups that are converted to bromomethyl groups by a radical reaction. Cationic polymers result from conversion of the bromomethyl groups to ionic moieties by quaternization with trimethylamine in the solid state. The conversion to benzyltrimethyl ammonium groups is incomplete as evidenced by the differences between the IEC values measured by titration and the theoretical IECs based on 1H NMR measurements. The anion exchange membranes formed from these polymers have hydroxide ion conductivities as high as 50 mS/cm in liquid water and they are stable under highly basic conditions at elevated temperatures.

Synthesis and Characterization of Poly(phenylene)-Based Anion Exchange Membranes for Alkaline Fuel Cells

Cationic polymer membranes that conduct free anions comprise an enabling area of research for alkaline membrane fuel cells and other solid-state electrochemical devices that operate at high pH. The synthesis of anion exchange membranes based on a poly(phenylene) backbone prepared by a Diels−Alder reaction is demonstrated. The poly(phenylene)s have benzylic methyl groups that are converted to bromomethyl groups by a radical reaction. Cationic polymers result from conversion of the bromomethyl groups to ionic moieties by quaternization with trimethylamine in the solid state. The conversion to benzyltrimethylammonium groups is incomplete as evidenced by the differences between the IEC values measured by titration and the theoretical IECs based on 1H NMR measurements. The anion exchange membranes formed from these polymers have hydroxide ion conductivities as high as 50 mS/cm in liquid water, and they are stable under highly basic conditions at elevated temperatures.

Synthesis of an Ion Exchange Membrane by Radiation-Induced Grafting of Acrylic Acid onto Poly(tetrafluoroethylene)

Acrylic acid was grafted onto a 100-μm thick poly(tetrafluoroethylene) (PTFE) film by simultaneous irradiation method. The effect of the dose rate on the grafting and, the changes in the film thickness, water absorption, and electric resistance of the grafted film were investigated. The results suggested that the nongrafted layer remains in the middle part of the film at lower percent of grafting and then disappears as the grafting proceeds. Interference microscopy of the grafted film revealed that this grafting occurs by a gradual diffusion of the monomer through the successive grafted layers which swell in the reaction medium, i.e., the grafted front moves inward into film.