Cross-linked Anion Exchange Membranes Research Articles

β-Cyclodextrin-enabled, densely cross-linked anion-exchange membranes for fuel cell applications

Polyarylpiperidinium anion exchange membranes (AEMs) have been widely studied in anion exchange membrane fuel cells and alkaline electrolyzed water due to their excellent alkali resistance stability. In this work, we report the design and fabrication of poly(p-triphenylene-piperidinyl) (PTP) AEMs quaternized and cross-linked by bromo-β-cyclodextrin (β-CD-Br7). In this type of membranes, the densely cross-linked and quaternized sites derived from β-CD-Br7 can help to construct continuous ion transport channels to facilitate ion conduction. Although the ion exchange capacity (IEC) tended to decrease with increasing cross-linking degree, the qPTP-CD5 membrane with 5 % cross-linking (IEC = 2.3 mmol g−1) produced the most significant microphase separation and the highest conductivity (125.6 mS cm−1 at 80 °C). The membrane also exhibited impressive alkaline stability, with 94.6 % conductivity retention in 1 M NaOH at 80 °C after 1000 h and 90.7 % conductivity retention after 1500 h. Finally, the peak power density of the fuel cell assembled with qPTP-CD5 membranes was 1.216 W cm−2 at 80 °C and there was no significant voltage degradation when operated at 200 mA cm−2 current density for 40 h. This work demonstrates that β-CD can function as a good “platform” for simultaneous cross-linking and quaternization to fabricate high performance AEM.

Side Chain Crosslinked Anion Exchange Membrane for Acid Concentration by Electrodialysis

Side Chain Crosslinked Anion Exchange Membrane for Acid Concentration by Electrodialysis

Novel Crosslinked Anion Exchange Membranes Based on Thermally Cured Epoxy Resin: Synthesis, Structure and Mechanical and Ion Transport Properties.

Limitations in existing anion exchange membranes deter their use in the efficient treatment of industrial wastewater effluent. This work presents an approach to fabricating novel anion-conducting membranes using epoxy resin monomers like hydrophobic or hydrophilic diglycidyl ether and quaternized polyethyleneimine (PEI). Manipulating the diglycidyl ether nature, the quantitative composition of the copolymer and the conditions of quaternization allows control of the physicochemical properties of the membranes, including water uptake (20.0-330%), ion exchange capacity (1.5-3.7 mmol/g), ionic conductivity (0.2-17 mS/cm in the Cl form at 20 °C), potentiostatic transport numbers (75-97%), as well as mechanical properties. A relationship was established between copolymer structure and conductivity/selectivity trade-off. The higher the quaternized polyethyleneimine, diluent fraction, and hydrophilicity of diglycidyl ether, the higher the conductivity and the lower the permselectivity. Hydrophobic diglycidyl ether gives a much better conductivity/selectivity ratio since it provides a lower degree of hydration than hydrophilic diglycidyl ether. Different mesh and non-woven reinforcing materials were also examined. The developed membranes demonstrate good stability in both neutral and acidic environments, and their benchmark characteristics in laboratory electrodialysis cells and batch-mode dialysis experiments are similar to or superior to, commercial membranes such as Neosepta© AMX, FujiFilm© Type1, and Fumasep FAD-PET.

A simple method to prepare anion exchange membrane by PVA/EVOH/MIDA for acid recovery by diffusion dialysis.

Given the substantial environmental pollution from industrial expansion, environmental protection has become particularly important. Nowadays, anion exchange membranes (AEMs) are widely used in wastewater treatment. With the use of polyvinyl alcohol (PVA), ethylene-vinyl alcohol (EVOH) copolymer, and methyl iminodiacetic acid (MIDA), a series of cross-linked AEMs were successfully prepared using the solvent casting technique, and the network structure was formed in the membranes due to the cross-linking reaction between PVA/EVOH and MIDA. Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to analyze the prepared membranes. At the same time, its comprehensive properties which include water uptake, linear expansion rate, ion exchange capacity, thermal stability, chemical stability, and mechanical stability were thoroughly researched. In addition, diffusion dialysis performance in practical applications was also studied in detail. The acid dialysis coefficient (UH+) ranged from 10.2 to 35.6 × 10-3 m/h. Separation factor (S) value ranged from 25 to 38, which were all larger than that of the commercial membrane DF-120 (UH+: 8.5 × 10-3 m/h, S: 18.5). The prepared membranes had potential application value in acid recovery.

Partial fluorinated silica incorporated with tuneable alkyl cross-linker based multi-cationic alkaline membrane for vanadium redox flow battery

Herein, we report partial fluorinated polymer (poly(vinylidene fluoride-co-hexafluoropropylene); PVDF-co-HFP)-based multi-cationic (quaternary ammonium, and imidazolium groups) cross-linked (tuneable carbon chain cross-linker) anion exchange membrane (AEM) incorporated with functionalized silica to avoid any structural deformations under harassed environment. Prepared membranes are cross-linked using different cross-linking agents, to study the effect of cross-linker chain length on the membrane performance. Incorporation of functionalized silica by acid-catalyzed sol-gel process improves membrane properties and stabilities. Reported PVIm-C10-APS AEM shows high conductivity (7.20 × 10−2 S/cm), and ion exchange capacity (1.48 meq/g). Well optimized positively charged PVIm-C10-APS AEM exhibits extremely low permeability of vanadium cations because of “Donnan exclusion” (9.80 × 10−7 cm2/s). During VRFB operation, PVIm-C10-APS AEM exhibits 98.10% coulombic efficiency (CE) and 77.60% voltage efficiency at 100 mA/cm2 without any significant deterioration up to 300 charge-discharge cycles. Further, PVIm-C10-APS membrane also shows >1.50 V OCV and 345 mW/cm2 peak power density at 400 mA/cm2. Reported AEM has been bench-marked with other membranes reported in the literature, and assessed as a promising material for VRFB or membrane separator for energy devices.

Optimization of the mass ratio of siloxane crosslinkers for poly(2,6-dimethyl-1,4-phenylene oxide) anion exchange membranes to improve acid enrichment by electrodialysis

Proton blocking anion exchange membranes (AEMs), which are employed in electrodialysis technology, show promise in acid recovery from industrial waste. A series of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) membranes were prepared using (3-aminopropyl)trimethoxysilane (APTMS) and weakly functionalized bases including N-butylimidazole (N-BuIm). Were networked to create AEMs with low leak rates. It was discovered that the appropriate concentration of siloxane crosslinker raised the membrane matrix's density and lowered the AEM matrix's hydrophilicity. Thermogravimetric measurements and water absorption have confirmed this, and the membranes in this series even swell up to 8.61 %. The maximum H+ concentration concentrated by the cross-linked AEM (BPPO/5Si) during the ED with a current density of 10 mA∙cm−2 was 2.35 M, which was higher than the concentration concentrated by the uncross-linked AEM (BPPO/OSi), which was 1.90 M (beginning concentration: 1.00 M). The current efficiency was 44.8 % and the energy consumption was only 1.81 kW ∙h∙kg−1. A balance between proton blocking and SO42− ions transport was achieved by the optimized AEM, which exhibited increased hydrophobicity and smaller ion clusters. The improved AEM was found to have fewer ionic clusters and greater hydrophobicity. For cross-linked AEMs, a trade-off between SO42− ions transport and proton blocking was thus accomplished. This work is thought to offer direction for developing sophisticated proton blocking AEMs.

Dimensionally Stable Anion Exchange Membranes Based on Macromolecular-Cross-Linked Poly(arylene piperidinium) for Water Electrolysis.

The advancement of anion exchange membranes (AEMs) with superior ionic conductivity has been greatly hindered due to the inherent "trade-off" between membrane swelling and ionic conductivity. To resolve this dilemma, macromolecular covalently cross-linked C-FPVBC-x AEMs were fabricated by combining partially functionalized ether-bond-free polystyrene (FPVBC) with poly(arylene piperidinium). The results from atomic force microscopy reveal that an increase in the ratio of FPVBC promotes the fabrication of microphase separation morphology, resulting in a high ionic conductivity of 40.15 mS cm-1 (30 °C) for the C-FPVBC-1.7 membrane. Molecular dynamics simulations further examine the ionic conduction effect of cross-linked AEMs. Besides, the unique cross-linking structure significantly improves mechanical and alkaline stability. After treatment in 1 M KOH at 50 °C for 1200 h, the C-FPVBC-1.7 membrane shows only a 6.9% decrease in conductivity. The C-FPVBC-1.7 AEM-based water electrolyzer achieves a high current density of 890 mA cm-2 at 2.4 V (80 °C) and maintains good stability, enduring over 100 h at 100 mA cm-2 (50 °C). These results demonstrate the significant potential of macromolecularly cross-linked AEMs for practical applications in water electrolysis.

Dithiolate-Based Scorpion Arm Ligand Synthesis and Characterization

Redox flow batteries (RFBs) play a vital role in the efficient and reliable utilization of renewable energy sources by providing a means to capture and store excess energy for later use.1–6 The synthesis and characterization of a novel scorpionate arm ligand, i-mntPy- (2,2-dicyano-1-pyridin-2-ylmethyl-1,1-dithiolate), are presented in this study. The ligand i-mntPy- was synthesized through a multistep synthetic route, starting from commercially available precursors. The chemical structure of the ligand was confirmed using various spectroscopic techniques, including NMR spectroscopy, ESI-MS, and Elemental analysis. Furthermore, the coordination ability of i-mntPy- to facilitate 2e- transfer in M(II/IV) coordination environment was investigated by the computational study and addition of Ni(II) and Pd(II) ions in the i-mntPy- solution. The results demonstrate the successful synthesis and characterization of the novel scorpionate arm ligand i-mntPy-, which coordinates with d8 metal centers and holds promise for future applications in coordination chemistry and energy storage. References (1) Mazumder, Md. M. R.; Jadhav, R. G.; Minteer, S. D. Phenyl Acrylate-Based Cross-Linked Anion Exchange Membranes for Non-Aqueous Redox Flow Batteries. ACS Mater. Au 2023. https://doi.org/10.1021/acsmaterialsau.3c00044.(2) Rahaman Mazumder, M. M.; Islam, R.; Khan, M. A. R.; Anis‐Ul‐Haque, K. M.; Rahman, M. M. Efficient AcFc‐[Fe III (Acac) 3 ] Redox Couple for Non‐aqueous Redox Flow Battery at Low Temperature. Chem. – Asian J. 2023, 18 (1). https://doi.org/10.1002/asia.202201025.(3) Mazumder, Md. M. R.; Dalpati, N.; Pokkuluri, P. R.; Farnum, B. H. Zinc-Catalyzed Two-Electron Nickel(IV/II) Redox Couple for Multi-Electron Storage in Redox Flow Batteries. Inorg. Chem. 2022, 61 (48), 19039–19048. https://doi.org/10.1021/acs.inorgchem.2c03124.(4) Mazumder, Md. M. R.; Burton, A.; Richburg, C. S.; Saha, S.; Cronin, B.; Duin, E.; Farnum, B. H. Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate. Inorg. Chem. 2021, acs.inorgchem.1c01699. https://doi.org/10.1021/acs.inorgchem.1c01699.(5) MAZUMDER MDMOTIURRAHAMAN, Islam R. Temperature-dependent study of AcFc-FeIII(acac)3 redox couple for non-aqueous redox flow battery. ChemRxiv. Cambridge: Cambridge Open Engage; 2022; https://doi.org/10.26434/chemrxiv-2022-3177p(6) Islam, R.; Mazumder, M. M. R.; Farnum, B. H. Solvent Dependent Spectroscopic and Electrochemical Studies of Nickel (II) Diethyldithiocarbamate for Energy Storage. ECS Meet. Abstr. 2021, MA2021-01 (1), 54–54. https://doi.org/10.1149/ma2021-01154mtgabs. Figure 1

Elastic and Conductive Cross-linked Anion Exchange Membranes Based on Polyphenylene Oxide and Poly(vinyl alcohol) for H2 -O2 Fuel Cells.

A series of cross-linked AEMs (c-DQPPO/PVA) are synthesized by using rigid polyphenylene oxide and flexible poly(vinyl alcohol) as the backbones. Dual cations are grafted on the PPO backbone to improve the ion exchange capacity (IEC), while glutaraldehyde is introduced to enhance compatibility and reduce swelling ratio of AEMs. In addition to the enhanced mechanical properties resulting from the rigid-flexible cross-linked network, c-DQPPO/PVA AEMs also exhibit impressive ionic conductivity, which can be attributed to their high IEC, good hydrophilicity of PVA, and well-defined micro-morphology. Additionally, due to confined dimension behavior and ordered micro-morphology, c-DQPPO/PVA AEMs demonstrate excellent chemical stability. Specifically, c-DQPPO/PVA-7.5 exhibits a wet-state tensile strength of 12.5 MPa and an elongation at break of 53.0 % at 25 °C. Its OH- conductivity and swelling degree at 80 °C are measured to be 125.7 mS cm-1 and 8.2 %, respectively, with an IEC of 3.05 mmol g-1 . After 30 days in a 1 M NaOH solution at 80 °C, c-DQPPO/PVA-7.5 experiences degradation rates of 12.8 % for tensile strength, 27.4 % for elongation at break, 14.7 % for IEC, and 19.2 % for ion conductivity. With its excellent properties, c-DQPPO/PVA-7.5 exhibits a peak power density of 0.751 W cm-2 at 60 °C in an H2 -O2 fuel cell.

Cross-Linked Anion Exchange Membranes for Non-Aqueous Redox Flow Battery

The development of redox flow batteries (RFBs) has been one of the primary responses to the need to store harvested renewable energy for improving grid reliability and utilization.1–6 In this study, we synthesized and characterized different Bromobutyl Norbornene backbone-based anion-exchange membranes (AEM) with different Tetramethyl hexadiamine crosslinker amounts and explored the performance of AEMs in non-aqueous redox flow batteries under ideal conditions. Performance was compared based on high stability in a non-aqueous solvent, high permeability to the charge-carrying ion, low electric cell resistance, low cross-over of the redox-active molecules, high mechanical property, and low cost. 100 cycles battery data indicates that Bromobutyl Norbornene-based AEM performance is far better than the commercial best membrane Fuma-375. The best membrane will be found which will show no cross-over of redox-active electrolytes after 1000 battery cycle experiments and exhibit low resistance and high structural/chemical stability in MeCN solvent. References (1) Mazumder, Md. M. R.; Burton, A.; Richburg, C. S.; Saha, S.; Cronin, B.; Duin, E.; Farnum, B. H. Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate. Inorg. Chem. 2021, 60 (17), 13388–13399. https://doi.org/10.1021/acs.inorgchem.1c01699.(2) Mazumder, M. M. R.; Farnum, B. H. Two One Electron vs One Two-Electron Redox System of Nickel Diethyldithiocarbamate for Redox Flow Battery; ACS, 2021. https://doi.org/10.1021/scimeetings.1c00951.(3) Mazumder, M. M. R. Ni(IV/II) Redox Couple 2e- Reversibility Improvement for Redox Flow Battery. ECS Meet. Abstr. 2021, MA2021-02 (5), 1855–1855. https://doi.org/10.1149/ma2021-0251855mtgabs.(4) Islam, R.; Mazumder, M. M. R.; Farnum, B. H. Solvent Dependent Spectroscopic and Electrochemical Studies of Nickel (II) Diethyldithiocarbamate for Energy Storage. ECS Meet. Abstr. 2021, MA2021-01 (1), 54–54. https://doi.org/10.1149/ma2021-01154mtgabs.(5) Rahaman Mazumder, M. M.; Islam, R.; Khan, M. A. R.; Anis‐Ul‐Haque, K. M.; Rahman, M. M. Efficient AcFc‐[Fe III (Acac) 3 ] Redox Couple for Non‐aqueous Redox Flow Battery at Low Temperature. Chem. – Asian J. 2023, 18 (1). https://doi.org/10.1002/asia.202201025.(6) Mazumder, Md. M. R.; Dalpati, N.; Pokkuluri, P. R.; Farnum, B. H. Zinc-Catalyzed Two-Electron Nickel(IV/II) Redox Couple for Multi-Electron Storage in Redox Flow Batteries. Inorg. Chem. 2022, 61 (48), 19039–19048. https://doi.org/10.1021/acs.inorgchem.2c03124.

Phenyl Acrylate-Based Cross-Linked Anion Exchange Membranes for Non-aqueous Redox Flow Batteries

Phenyl Acrylate-Based Cross-Linked Anion Exchange Membranes for Non-aqueous Redox Flow Batteries

Dithiol cross-linked polynorbornene-based anion-exchange membranes with high hydroxide conductivity and alkaline stability

Vinylic-addition polynorbornenes possess high thermal stability, excellent mechanical integrity, and chemically inert backbones. Herein, we conveniently synthesize a series of vinylic-addition polynorbornene copolymers containing pendant alkenes from commercial vinyl-substituted norbornene (VNB) and alkyl-bromide-substituted norbornene (BrNB). Subsequently, the copolymers are photo-crosslinked with dithiol reagents through UV-initiated thiol-ene click reactions followed by quaternization to prepare the cross-linked anion-exchange membranes (AEMs). The extent of cross-linking and the hydrophobicity of the cross-linkers can be easily controlled, so that the absorption of excess water can be inhibited with enhanced membrane strength. The resultant AEMs have ultrahigh hydroxide conductivities (up to 199 mS/cm at 90 °C under humidified conditions) and excellent alkaline stability in 1 M KOH at 80 °C for 1200 h. The vinylic-addition AEMs are also successfully applied in alkaline anion-exchange membrane water electrolyzers with commercial noble-metal-free electrocatalysts.

Cu(I) catalyzed ATRP for the preparation of high-performance poly (vinylidene fluoride)-g-poly 2-(dimethylamino)ethyl methacrylate crosslinked anion exchange membranes for enhanced acid recovery

The exclusive selectivity feature of an anion exchange membrane (AEM) makes it a core component of the diffusion dialysis (DD) process. Herein, we have developed a novel synthetic route for the preparation of AEMs with a controlled graft length and density by grafting 2-(dimethylamino)ethyl methacrylate (DMA) chains from the backbone of poly(vinylidene fluoride) (PVDF) by Cu(I) catalyzed atom transfer radical polymerization to produce PVDF-g-PDMA copolymer, which is converted to AEM by the reaction with α,α’-dichloro-p-xylene (XDC). XDC induces positive charge on the membrane surface and increases the hydrophilicity of the membrane. It also acts as a crosslinker and helps to create a network structure in the membrane, which increases overall membrane stability. The AEMs are used to separate hydrochloric acid from its mixture with metal salts by diffusion dialysis. A representative AEM containing 12% w/w PDMA, abbreviated as ATM-2, show diffusion coefficient (UH+) and separation factors (S) of 0.049 m/h and 117, respectively during the separation of HCl from 2 M HCl + 0.09 M FeCl2 solution. ATM-2 also shows higher UH+ and S values for the separation of HCl with its mixture of different metal salts, i.e., NaCl, CuCl2, and AlCl3. ATM-2 membrane endures a small loss of 1.5% and 3.2% in UH+ and S values, respectively, after submerging in a 2 M acid/salt mixture solution for 60 days. This confirms the good acid stability of the AEM. The results indicate the reasonable potency of the prepared AEMs to be a suitable candidate for DD applications.

Novel piperidinium-functionalized crosslinked anion exchange membrane with flexible spacers for water electrolysis

Anion Exchange membranes (AEM) are core components for alkaline electrochemical energy technology, such as the AEM water electrolysis and AEM fuel cell. They are regarded as promising alternatives for proton exchange membrane-based systems due to the possibility of using noble metal-free electrocatalyst. However, chemical stability and conductivity of the membrane are still the main challenge of the electrolyzer system. Here in we highlight an AEM with styrene-b-ethylene-b-butylene-b-styrene copolymer (SEBS) as its backbone and piperidinium functioned flexible ethylene oxide spacer structure as its side-chains (SEBS-P2O6). This membrane reached 20.8 mS cm−1 hydroxide ion conductivity at room temperature, which is higher compared to previously obtained piperidinium functionalized SEBS with 10.09 mS cm−1[1]. The SEBS-P206 was measured in a single cell AEM electrolysis cell with platinum group metal (PGM) catalyst. Current densities 275 mA cm−2 and 680 mA cm−2 at 60 °C and 2 V cell potential were achieved in ultra-pure ware (UPW) and 0.1 M KOH, respectively. Remarkably, in UPW the degradation rate was only 140 μA h−1 cm−2, which is the lowest reported up to know.

Highly Cross-Linked butene grafted poly (Vinyl Alcohol)–co-Vinyl pyridine based anion exchange membrane for improved acid recovery and desalination efficiency

Water treatment and waste acid reclamation are important in present situation due to huge industrialization. Different processes are available for the water treatment and waste treatment. Ion exchange membranes based electrodialysis (ED) and diffusion dialysis (DD) are attracted by the researchers since last decade due to its simplicity and economical operation. Acid reclamation by diffusion dialysis has been gained huge attention due to their absolute selectivity and energy less process. Here, we report the synthesis of efficient anion exchange membrane (AEM) by free radical co-polymerization of butene grafted poly (vinyl alcohol) and 4-vinyl pyridine followed by in-situ quaternization and cross-linking. Different amount 4-vinyl pyridine was chosen for the membrane preparation, and its impact on physiochemical and electrochemical properties has been studied. Structural and chemical characterisation of the membranes were studied using nuclear magnetic resonance (NMR), attenuated total reflectance-infrared spectroscopy (ATR-IR), while surface-phase morphology was investigated through scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermo-mechanical properties of prepared membranes were studied using thermogravimetric analysis (TGA), differential scanning colorimetry (DSC), dynamic mechanical analysis (DMA) and universal testing machine (UTM) analysis. The cross-linked PVA-x membranes showed high acidic stability as well as good antioxidation property. The synthesized membranes were studied for their salt removal performance by electrodialysis and acid recovery by diffusion dialysis. The optimised membrane (PVA-0.8) shows 0.90 kWh kg−1 energy consumption and 93.49 % current efficiency during salt removal from brackish water using electrodialysis. All cross-linked PVA-x membranes have diffusion coefficient of acid are in the range of 0.0556–0.0716 mh−1 and separation factor values are between the 79.51 to 91.33 at 25 °C, which comparable to commercial DF-120B membrane. This result shows that the prepared cross-linked AEMs may be a good candidate for the electrochemical applications.

Poly(phenylene oxide)-Based Anion Exchange Membranes Having Linear Cross-Linkers or Star Cross-Linkers

Linear cross-linked and star cross-linked anion exchange membranes (AEMs) are reported in this work, namely, lcQPPO (linear cross-linked quaternized poly(2,4-dimethyl-1,4-phenylene oxide) (PPO)) and scDQPPO (star cross-linked quaternized PPO) . Compared with original quarternized PPO (QPPO), cross-linked AEMs show a restrained swelling degree. But, due to the hindrance of a cross-linking polymer matrix, lcQPPO membranes show decreased ionic conductivity. For scDQPPO, its wide and connective ion channels are beneficial to the conduction of OH–, exhibiting increased ionic conductivity. Besides, the aggregated and cross-linked polymer networks in scDQPPO enhance the chemical stability and mechanical properties of the AEMs. Specifically, for scDQPPO-40, a high OH– conductivity of 100.7 mS cm–1 and a low swelling degree of 20.7% are achieved at 80 °C. The tensile strength and elongation at break of wet scDQPPO-40 at 25 °C are 16.7 MPa and 18.0%. After immersing in 1 M NaOH at 80 °C for 30 days, the loss of ionic conductivity and weight for scDQPPO-40 is 24.2 and 14.8%, with the degradation of tensile strength and elongation at break of 22.2% and 26.7%, respectively. On the basis of the membrane, a fuel cell performance of 0.577 W cm–2 is demonstrated at 60 °C, while, for QPPO-40 and lcQPPO-60, their fuel cell peak power densities are only 0.250 and 0.215 W cm–2.

Cross-Linked Anion-Exchange Membranes with Dipole-Containing Cross-Linkers Based on Poly(terphenyl isatin piperidinium) Copolymers.

To balance the ionic conductivity and dimensional stability of anion-exchange membranes (AEMs), several cross-linked ether-free poly(terphenyl isatin piperidinium) copolymers were synthesized using 1,2-bis(2-aminoethoxy)ethane as a cross-linker. By introducing an alkyl diamine-based hydrophobic cross-linker as a control, the effects of the dipolar-molecule-containing cross-linker on the comprehensive performance of the membranes were investigated. Cation-dipole interactions between the cations and the hydrophilic ethylene oxide cross-linker enhance the self-assembly capability of the cationic groups. The introduction of the rotatable ethylene oxide cross-linker facilitates the flexibility of the cross-linked networks, thereby promoting hydrophilic/hydrophobic phase separation and inhibiting excessive swelling of the corresponding AEMs simultaneously. The resulting PTPBHIN-O19 membrane showed a high hydroxide conductivity (151.69 mS cm-1) and low swelling ratio (10.53%) at 80 °C. Furthermore, owing to the cross-linked structure and ether-free polymer backbone with high alkali resistance, the membranes treated in 3 M NaOH at 80 °C for 1600 h maintained ≥85% of their hydroxide conductivity, indicating excellent alkaline stability. A H2/O2 fuel cell based on the PTPBHIN-O19 AEM exhibited a maximum power density of 398 mW cm-2 at 515 mA cm-2.

Crosslinked anion exchange membranes prepared from highly reactive polyethylene and polypropylene intermediates

To obtained polyolefin-based anion exchange membranes (AEMs) with high performance in high efficiency, reactive polyolefin intermediates were prepared via polymerization of ethylene or propylene with 1-iodo-10-undecene (IUD) by single-site rac-ethylenebis(indenyl)Zr(IV) dichloride and dimethyl (pyridylamido)Hf(IV) catalysts, respectively. The catalytic activity for synthesis of these reactive polyolefin intermediates was up to 2.94 × 106 for ethylene copolymers (PEI-x) and 7.20 × 106 gpolymer molcat.−1 h−1 for propylene copolymers (PPI-x), respectively. Moreover, incorporation ratio of IUD in copolymers was high up to 19.8 (PEI-x) and 29.7 mol% (PPI-x), respectively. These copolymers could be well dissolved in o-xylene, make them easily crosslinked and quaternized to give polyolefin-based AEMs. These AEMs with crosslinking structure exhibited high hydroxide conductivity (131 and 143 mS/cm for PEI-20-C100-QA and PPI-30-C70-QA at 80 °C, respectively) and excellent alkaline stability without visible loss in hydroxide conductivity after 1680 h. These AEMs exhibited evident microphase separation via microphase study, presented low swelling ratio even with high water uptake. A H2/O2 fuel cell with PEI-20-C100-QA presented a peak power density of 439 mW cm−2 without optimized membrane electrode assembly fabrication process.

Cross-linked anion-exchange membrane with side-chain grafted multi-cationic spacer for electrodialysis: Imparting dual anti-fouling and anti-bacterial characteristics

Polyimide (SPI) was functionalized using dianhydride with a high electron density in the carbonyl carbon atoms, and on active-sites (2,4,6-tris(dimethylaminomethyl) phenol: TAP) multi-cationic groups were grafted. Further, we fabricated multi-cationic cross-linked anion-exchange membrane (AEM) with tuneable polymer design by varying number of carbon chain in cross-linker spacer. CrQSPI@3 AEM with C3 spacer, exhibited 2.85 meq/g ion-exchange capacity, 21.4% water uptake, 20.7% swelling ratio, 13.87 × 10–2 S/cm membrane conductivity, and assessed as optimized membrane for further experimental analysis. Architectural strategy including cross-linking, and side chain grafting of multi-cationic groups provides fine control over properties, stabilities, hydrophilic-hydrophobic characteristics, anti-fouling and anti-bacterial nature. Anti-fouling nature of CrQSPI@3 AEM were gaged by impedance spectroscopy, chronopotentiometry, and electrodialysis experiments, while anti-bacterial nature was studied against water borne Escherichia coli (E. coli). High electro-dialytic performance of CrQSPI@3 AEM (current efficiency: 97.4%, and energy consumption: 0.92 kW h/kg of NaCl removed) along with better stabilities, anti-fouling and anti-bacterial properties, revealed its suitability for water desalination and other diversified electrochemical applications. Described method provides facile membrane fabrication with superior performance to obtain deep in-sight understanding of structural features.

Construction of macromolecule cross-linked anion exchange membranes containing free radical inhibitor groups for superior chemical stability

In order to achieve high chemical stability of anion exchange membranes (AEMs), polystyrene (PVE) containing free radical inhibitor groups is first used to cross-link fluorinated poly(aryl ether ketone) (PAEK). The crosslinked PAEK is afterwards quaternized with 6-bromohexyltrimethylammonium bromide (QA) to fabricate AEMs. The prepared AEMs show obvious microphase separation with anionic cluster spacing within 8.8–9.3 nm according to the SAXS analysis results. The hydroxide conductivity of the proposed AEMs is in the range of 76.7–97.6 mS cm−1 at 80 °C. It is found that the free radical inhibitor groups as well as the dense cross-linked structure endow the AEMs with excellent resistance against the attack of OH‾ and free radicals. After immersed in 1 mol L−1 KOH at 60 °C for 1000 h, the QPAEK-30PVE membrane exhibits about 75% and 82% of the conductivity and IEC retention rate. Using this membrane as the electrolyte, a peak power density of 329 mW cm−2 is achieved under a cell voltage of 0.66 V at 60 °C by fueling the cell with humidified H2 and O2 without back pressure.