Polysulfone-based Anion Exchange Membranes Research Articles

Effect of one- and two-dimensional nanomaterials on polysulfone-based anion exchange membranes for fuel cells

To investigate nanoparticle morphology's impact on the performance of composite anion exchange membrane (AEM), one-dimensional quaternized branched polyethyleneimine @multi-walled carbon nanotubes (QBPEI@MWCNTs) and two-dimensional quaternized branched polyethyleneimine @graphene oxide sheets (QBPEI@GO) were prepared and incorporated into quaternized polysulfone (QPSF) matrices to form QQ-x-MWCNTs and QQ-x-GO AEMs. These AEMs exhibited superior mechanical properties due to the flexible QBPEI cross-linking and nanoparticle reinforcement. Moreover, QBPEI facilitated microphase separation and ion cluster formation along the surface of nanoparticles, enhancing OH− transport. As a result, QQ-1.0%-MWCNTs and QQ-0.7%-GO AEMs both showed high ionic conductivity (83.19 mS/cm and 76.14 mS/cm at 80 °C). QQ-x-MWCNTs AEMs displayed higher conductivity than QQ-x-GO AEMs over the entire temperature range (20–80 °C) at the same level of ion exchange capacity. QQ-0.7%-MWCNTs AEM excelled, achieving a peak power density of 102.44 mW/cm2 in an H2/O2 fuel cell (80 °C, 40 % RH), surpassing QQ-0.5%-GO AEM (86.50 mW/cm2). Evidently, one-dimensional MWCNTs are effective for establishing long-range interconnected ion transport channels, making them excellent AEM fillers.

Polysulfone-Based Anion-Exchange Membranes for Alkaline Water Electrolyzers

Polysulfone-Based Anion-Exchange Membranes for Alkaline Water Electrolyzers

Internally Cross-Linked Polysulfone-Based Anion Exchange Membranes with pH Stability for Carboxylate Separation

Internally Cross-Linked Polysulfone-Based Anion Exchange Membranes with pH Stability for Carboxylate Separation

Alkaline enrichment via electrodialysis with alkaline stable side-chain-type polysulfone-based anion exchange membranes

• Two series of side-chain-type polysulfone-based AEMs were prepared via menshutkin reaction. • The optimized AEM exhibits the low area resistance, and good alkaline stability in ED process. • The optimized AEM show the better NaOH enrichment performance than commercial AEM. • The investigation on AEM of this type suggests its potential ED application for alkali enrichment. To meet the need of efficient resource utilization, developing stable and efficient anion exchange membranes (AEMs) for alkaline enrichment application is of significance. In this work, we designed four polysulfone-based side-chain-type AEMs with several cations and different length of spacers per chain, to explore the structure-property relationship and obtained AEMs with high performance for alkaline enrichment via electrodialysis (ED). Our investigation demonstrates that, the optimized AEM (CM-TQ6Q6Q-1, 1.38 mmol·g −1 ) exhibits low swelling ratio of 8.9%, low area resistance of 2.48 Ω·cm 2 , acceptable OH – conductivity of 13.7 mS·cm −1 . In addition, this AEM also shows relatively good alkaline stability with the IEC retention of 96.7% relative to the original IEC, suggesting the potential application of alkaline enrichment via electrodialysis (ED). After 5-times NaOH enrichment tests in ED, CM-TQ6Q6Q-1 AEM shows an efficient ED performance with alkaline concentration times of ~1.8 (current efficiency: ~90.0%; energy consumption: 8.47 kWh·kg −1 ), and maintains 96.4% of its original IEC, which are even comparable to those from commercial AEM (Neosepta AHA). The results demonstrate that the as-prepared AEM shows the promising potential ED application for alkali enrichment from the alkaline waste water.

Dependable polysulfone based anion exchange membranes incorporating triazatriangulenium cations

A convenient approach for the fabrication of robust anion exchange membranes designed for electrochemical applications is presented. A triazatriangulenium carbocation (i.e., 4,8,12-tri-ethano-4,8,12-triazatriangulenium tetrafluoroborate) with a pKR+ above 20 was used as hydroxide anion and negative charge carrier in polysulfone anion exchange membranes. Morphological analysis of these membranes using high resolution scanning electron microscopy (HRSEM) and small angle X-ray scattering (SAXS) confirmed a phase separation casting process resulting in electrolyte exposed cations. It appears that 4,8,12-tri-ethano-4,8,12-triazatriangulenium brings about an extensive carbocation network within the polysulfone matrix, allowing smooth transport of hydroxide anions with low activation energy value (6.56 kJ mol−1), substantial ion conductivity (23.5 mS cm−1 at 90 °C), and good ion exchange capacity (2.44 ± 072 meq/g). The high stability of the triazatriangulenium cation contributes to the retention of 88% of the initial membrane conductivity for the tested period of 35 days at 60 °C in a 3 M KOH solution. This class of unique carbocations serve as a model system for stable charge carriers in alkaline exchange membranes for electrochemicaltio applications.

Homogeneous trimethylamine-quaternized polysulfone-based anion exchange membranes with crosslinked structure for electrodialysis desalination

A series of trimethylamine quaternized crosslinked anion-exchange membranes (AEMs) based on polysulfone has been prepared by using an ultraviolet cross-linking method, which avoids the uneven reaction and undesirable aggregation of the basic functional groups (trimethylamine) by heterogeneous quaternization. The ultraviolet cross-linking method makes the reaction simpler and more controllable, compared with traditional method. By crosslinking, at 40 °C, the water uptakes of as-prepared AEMs decrease from 62.6% to 36.9%, while the linear expansion ratios reducing from 26.3% to 13.4% without significantly sacrificing the surface area resistance (increased 2.32 Ω cm2 to 2.98 Ω cm2). In addition, the introduced crosslinking yields the more robust AEMs with increased tensile strength from 4.32 to 11.89 MPa and increased elongation at break in a range of 13.8–30.9%. The significantly reduced water absorption, enhanced (dimensional and mechanical) stabilities suggest crosslinkers with more acrylate groups could promote high crosslinking within AEMs. For electrodialysis (ED) application, the optimized AEM exhibits an enhanced NaCl removal ratio of 75.0%, current efficiency of 92.7% and energy consumption of 6.06 kWh Kg−1, compared with AEM without cross-linking (61.4%; 75.9%; 6.20 kWh Kg−1). This investigation demonstrates that the as-proposed strategy has certain guiding significance for the development of advanced AEMs.

Electrochemical performance and enhanced nitrate removal of homogeneous polysulfone-based anion exchange membrane applied in membrane capacitive deionization cell

This paper aims to investigate different strategies toward the enhancement of nitrate removal in a membrane capacitive deionization cell using different membrane functionalizing agents such as trimethylamine, triethylamine, and N,N,N′,N′-tetramethyl-1,6-hexanediamine as well as a double-layer, novel homogeneous polysulfone-based anion exchange membrane. The prepared membranes exhibited nitrate versus chloride transport number ratio in the range of 0.96–1.52. The salt adsorption capacity for the NaNO3 feed was about 1.4-fold compared to that of using NaCl in case of triethylamine functionalized membrane under individual feeding solutions of 30 mL NaCl or NaNO3 during 30 min, and adsorption/desorption voltages of 1.6/0.0 V process conditions. At the same time, this parameter was about 1.2-fold weaker for the cell with a double-layer membrane. Based on the experiments, it can be inferred that the affinity toward nitrate could be promoted as the chain length of the alkyl group increases (i.e., increasing hydrophobicity of the groups). However, due to decrement in water uptake, the overall electrochemical performance of the membranes tended to weaken as the affinity toward nitrate increased. Results showed that the prepared membranes are suitable substitutions to conventional polystyrene-based ones utilized in membrane capacitive deionization cells.

Alkaline stable thermal responsive cross-linked anion exchange membrane for the recovery of NaOH by electrodialysis

We report synthesis of acrylonitrile-vinylimidazole copolymer (PVACN) as novel cross-linking agent, for the fabrication of highly conducting stable and thermal responsive cross-linked polysulfone based anion exchange membrane (AEM) for the recovery caustic soda from industrial waste by electrodialysis. Reported cross-linker (PVACN) showed synergised properties aliphatic carbon chain and grafted ionic groups, while structural features of cross-linked AEM impart conductive and stable nature. Cross-linked architecture of the AEM also formed tight and dense structure. Reported PSCr (cross-linked polysulfone) AEMs possessed imidazolium quaternized groups to avoid Hoffmann elimination reaction (E2), while relatively less number of OH− attacking sites also showed membrane stability under alkaline medium. Suitable optimized PSCr/3 AEM exhibited 1.21 meq g−1 ion-exchange capacity (IEC), 5.5 × 10−2 S/cm ionic conductivity along with 21.7% swelling ratio, and assessed to be highly suitable for alkali recovery by electrodialysis. Electrodialytic recovery of NaOH was performed by increasing the concentrations about 5-times, while about 80% of treated water was also recovered as spin-off. Electro-dialyzer showed 1.33 kWh/kg energy consumption, 75.7% current efficiency at 35 °C, which were significantly improved with increase in feed temperature. Reported AEM provides sustainable and feasible alternative for applying ED for alkali separation/recovery from the industrial waste water.

Alkaline Stability of Novel Aminated Polyphenylene-Based Polymers in Bipolar Membranes

This research investigated stability of two novel aminated polyphenylene polymers as anion exchange layers in bipolar membranes. Bipolar membrane stability was tested under operating conditions of 50 mA/cm2, and under conditions of soaking in room temperature 1 M NaOH. The stability of the custom made bipolar membranes was compared with those for two commercial membranes. For the polyphenylene-based membranes, there was no measurable increase in operating voltage when run continuously at a current density of 50 mA/cm2. For the two commercial membranes, the operating voltages increased by 3.2 to 4.4 mV per day when operated continuously over an 85 day testing period. Commercial membrane degradation in 1 M NaOH was similar to that under real operating conditions, with average rates of voltage increase of 3.2 to 3.5 mV/d. The custom made membrane containing a quaternary ammonium-tethered poly(biphenylalkylene) (PBPA) anion exchange layer did not show any loss in performance in either stability test. Density functional theory (DFT) simulations were used to calculate activation barriers and reaction energies for nucleophilic attack on the polymer backbones and cation functional groups on each of the four anion exchange polymers. Cation loss from all four polymers was thermodynamically favorable, with activation barriers ranging from 64 to 138 kJ/mol. The two commercial polysulfone-based anion exchange membranes were susceptible to cleavage of the ether bonds. However, the polyphenylene-based anion exchange polymers were considerably more stable with respect to backbone cleavage. The DFT calculations showing that the PBPA polymer was the most stable confirmed the results of the stability tests.

Novel quaternized carbon dots modified polysulfone-based anion exchange membranes with improved performance

At present, low conductivity and poor chemical stability are still the biggest challenges in the research on anion exchange membranes (AEMs). Herein, novel nanocomposite AEMs were first constructed by introducing quaternized carbon dots (QCDs) into the imidized polysulfone matrix (Im-PSU). QCDs were synthesized by quaternization of CDs derived from citric acid and ethylenediamine. The physicochemical properties and electrochemical properties of the nanocomposite AEMs were significantly improved due to the introduction of QCDs. It was found that the QCDs can improve the ion transport channel of the nanocomposite AEMs. Compared with pure Im-PSU AEM, the OH− conductivity and physicochemical properties of the nanocomposite membranes were enhanced, and the OH− conductivity of ImPSU-1.0%-QCDs composite membrane can reach 109.3 mS cm−1 at 80 °C, and 61.2% initial OH− conductivity was maintained in 1.0 M NaOH solution for 500 h at 60 °C. Our research proves that the nanofiller with a small size can better improve the performance of composite AEMs, and provide an efficient strategy for future research work in the design and preparation of AEMs.

A facile fabrication of functionalized rGO crosslinked chemically stable polysulfone-based anion exchange membranes with enhanced performance

Introducing more ionic conductive groups in polymer-based anion exchange membranes (AEMs) can improve the ion exchange capacity and further overcome the disadvantage of low ion conductivity for AEMs. However, the excessive swelling of AEMs caused by exorbitant IEC value may reduce the dimensional stability of membranes. So it is extremely important to modify the structures of AEMs. Herein, we proposed a facile strategy to construct reduced graphene oxide (rGO) stable crosslinked polysulfone-based AEMs with improved properties. rGO was non-covalently modified with pyrene-containing tertiary amine small molecule and polymer via π-π interactions. The as-prepared functionalized rGO (TrGO and PrGO) as both cross-linkers and fillers to fabricate quaternized polysulfone (QPSU)-based AEMs (CQPSU-X-TrGO and CQPSU-X-PrGO) for the first time. The cross-linked membranes can tighten the internal packing structure, and enhance the alkaline resistance, ion conductivity and oxidative stability of AEMs. Furthermore, the hydrophilicity and flexibility of the CQPSU-X-PrGO membranes were significantly improved as compared with that of CQPSU-X-TrGO membranes. PrGO-crosslinked membranes (CQPSU-2%-PrGO, σOH− = 117.7 mS/cm) displayed higher ionic conductivities at 80 °C than TrGO-crosslinked membranes (CQPSU-1%-TrGO, σOH− = 87.2 mS/cm). The remarkable nanophase separation can be observed in the CQPSU-X-PrGO membranes by TEM. This feasible strategy can be efficiently used to prepare new type of crosslinked organic-inorganic nanohybrid AEMs with excellent chemical stability and high ionic conductivity.

A facile approach to prepare crosslinked polysulfone-based anion exchange membranes with enhanced alkali resistance and dimensional stability.

Novel anion exchange membranes with enhanced ion exchange capacity, dimensional stability and alkali stability were prepared by a facile synthesis method. Internal crosslinking networks in the resulting membranes were achieved by reacting chloromethylated polysulfone with 4,4′-trimethylene bis(1-methylpiperidine) (BMP), where BMP was used as both a quaternization reagent and crosslinker without requirement of post-functionalization. In order to evaluate the alkali resistance and dimension stability performance of the resulting membranes, the molar ratio of BMP in the resulting membranes was fixed at four different contents: 40%, 60%, 80% and 100%. The obtained membranes were accordingly denoted as CAPSF-N, in which N = 40, 60, 80 and 100, respectively. Due to the dense internal network structure and spatial conformation of the six-membered rings, the resulting CAPSF-N AEMs showed enhanced dimensional structures (at 60 °C, the water uptakes and swelling ratios of CAPSF-N were 8.42% to 14.84% and 2.32% to 5.93%, respectively, whereas those for the commercial AEM Neosepta AMX were 44.23% and 4.22%, respectively). In addition, after soaking in 1 M KOH solution at 60 °C for 15 days, the modified membranes exhibited excellent alkaline stability. The CAPSF-100 membrane showed the highest alkali stability (retained 85% of its original ion exchange capacity and 84% of its original OH− conduction after the alkaline stability test), whereas the non-crosslinked APSF broke into pieces. Additionally, compared to the commercial Neosepta AMX membrane under the same test conditions, the desalination efficiency of CAPSF-100 was enhanced, and the energy consumption was lower.

Friedel-Crafts alkylation route for preparation of pendent side chain imidazolium-functionalized polysulfone anion exchange membranes for fuel cells

Friedel-Crafts alkylation route is proposed to synthesis polysulfone based anion exchange membrane (AEM) containing pendent imidazolium-functionalized side chain with the purpose of avoiding conventional carcinogenic chloromethylation. It has no special functional group requirements on the polymer materials, which has advantage over those reported chloromethylation free routes. A novel flexible alkylation reagent containing -(CH2)4- spacer, (1-chlorobutyl-2,3-dimethylimidazole chloride) is synthesized and promotes hydrophilic/hydrophobic micro-phase separation structure in the membranes proved by small angle X-ray scattering (SAXS) and transmission electron microscopy image (TEM). The imidazolium-functionalized polysulfone AEMs prepared by the Friedel-Crafts alkylation route in this study exhibit first level properties compared to other AEMs prepared without chloromethylation. The ion conductivity-normalized swelling ratio (0.08% cm mS−1 at 80 °C) is the lowest, while exhibits higher or equivalent IEC normalized ion conductivity (56.8 S g cm−1 mol−1 at 80 °C). The membranes prepared in this work also display good thermal, mechanical and alkaline stabilities.

Functionalized rGO as covalent crosslinkers for constructing chemically stable polysulfone-based anion exchange membranes with enhanced ion conductivity

Anion exchange membranes (AEMs) still remains a povital issue such as low ion conductivity, which hinders the practical applications. Therefore, constructing cross-linking structure in AEMs is considered as an effective strategy to balance the comprehensive properties including chemical stability and ion conductivity. However, the cross-linking may hinder the ion transport and decrease the ion conductivity unsatisfactorily. Herein we prepared highly ion conductive quaternized polysulfone (QPSU)-based AEMs (CQPSU-X-rGO) cross-linked by reduced graphene oxide (rGO) functionalized with different-chain length small molecules. The cross-linked QPSU AEMs (CQPSU-n) with organic small molecules as cross-linkers were also prepared to serve as control samples. Compared with AEMs cross-linked by short-chain cross-linkers, the cross-linked membranes with elastic long-chain cross-linkers (PTMHDA) and their modified rGO (LrGO) displayed higher ion conductivity due to the generation of more quaternary ammonium groups and nanophase separated morphology. Especially, the functionalized rGO-cross-linked composite membranes (CQPSU-X-LrGO and CQPSU-X-SrGO) exhibited better conductivity and chemical stability as compared with cross-linked polymer membranes (t-CQPSU-n and p-CQPSU-n) with small molecule cross-linkers. The highest ion conductivity was achieved for rGO-cross-linked AEMs (CQPSU-2%-LrGO, σOH- = 139.7 mS/cm at 80 °C). Thus, the functionalized rGO has been demonstrated to be a potential cross-linker and filler for preparing cross-linked AEMs with improved properties.

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.

A polysulfone-based anion exchange membrane for phosphoric acid concentration and purification by electro-electrodialysis

A series of quaternary ammonium polysulfone (QAPSU) anion exchange membranes used the chlorotrimethylsilane instead of toxic chloromethyl methyl ether and quaternized-functionalized by trimethylamine ethanol solution were prepared. The effect of chloromethylation reaction time on membrane morphologies and physiochemical properties such as ion exchange capacity, water swelling, and membrane area resistance, mechanical and thermal stabilities was investigated. When being applied in electro-electrodialysis (EED) for purifying phosphoric acid solution, the QAPSU membranes exhibit high purification efficiency, especially all the metal ions (Fe, Mg, Ca) removal rates reach over 60%, which suggests that the QAPSU membranes have a high potential for EED application.

Benzimidazolium functionalized polysulfone-based anion exchange membranes with improved alkaline stability

The stability of anion exchange membranes (AEMs) is an important feature of alkaline exchange membrane fuel cells (AEMFCs), which has been extensively studied. However it remains a real challenge due to the harsh working condition. Herein, we developed a novel type of polysulfone-based AEMs with three modified 1,2-dimethylbenzimidazoliums containing different substitutes at C4- and C7-position. The results showed that the introduction of the substitutes could obviously improve the dimensional and alkaline stabilities of the corresponding membranes. The swelling ratios of resultant AEMs were all lower than 10% after water immersion. The membrane with 4,7-dimethoxy-1,2-dimethylbenzimidazolium group exhibited the highest alkaline stability. Only 9.2% loss of hydroxide conductivity was observed after treating the membrane in 1 mol·L−1 KOH solution at 80 °C for 336 h. Furthermore, the density functional theory (DFT) study on the three functional group models showed that the substitutes at C4- and C7-position affected the lowest unoccupied molecular orbital (LUMO) energies of the different 1,2-dimethylbenzimidazolium groups.

Facile construction of crosslinked anion exchange membranes based on fluorenyl-containing polysulfone via click chemistry

Crosslinked fluorenyl-containing polysulfone based anion exchange membranes have been successfully synthesized via click chemistry with improved properties by controlling the crosslinking degree and micro-phase structure.

Preparation of a Chemically Stable Polysulfone-based Anion Exchange Membrane Using DABCO as the Quaternization Agent

Preparation of a Chemically Stable Polysulfone-based Anion Exchange Membrane Using DABCO as the Quaternization Agent Xu Wang, Yuan Wang, Bernard T. Goldings, Eileen Hao Yu, Keith Scott a School of Resources and Environmental Sciences, Wuhan University, 430072, China; b School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK; c School of Chemical Engineering and Advanced Materials, Merz Court, Newcastle upon Tyne, NE1 7RU, UK. xu.wang@whu.edu.cn

Mechanism of Polysulfone-Based Anion Exchange Membranes Degradation in Vanadium Flow Battery.

The stability of hydrocarbon ion exchange membranes is one of the critical issues for a flow battery. However, the degradation mechanism of ion exchange membranes has been rarely investigated especially for anion exchange membranes. Here, the degradation mechanism of polysulfone based anion exchange membranes, carrying pyridine ion exchange groups, under vanadium flow battery (VFB) medium was investigated in detail. We find that sp(2) hybrid orbital interactions between pyridinic-nitrogen in 4,4'-bipyridine and benzylic carbon disrupt the charge state balance of pristine chloromethylated polysulfone. This difference in electronegativity inversely induces an electrophilic carbon center in the benzene ring, which can be attacked by the lone pair electron on the vanadium(V) oxygen species, further leading to the degradation of polymer backbone, while leaving the 4,4'-bipyridine ion exchange groups stable. This work represents a step toward design and construction of alternative type of chemically stable hydrocarbon ion exchange membranes for VFB.