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Chemical stability and the trade-off between ion conductivity and dimensional stability are two primary challenges for the development of suitable anion exchange membranes (AEMs). Herein, a series of non-crosslinked poly(norbornene derivatives)-based AEMs containing a bulky steric hindrance hydrophobic arylene substituent were prepared by vinyl addition polymerization (VAP), ring-opening metathesis polymerization (ROMP), and ROMP followed post-hydrogenation, respectively. Compared with ROMP and hydrogenated type membranes, VAP-type membranes, especially the VAP-N-50, exhibited excellent dimensional stability with limited swelling ratio (SR = 27.9 %) while higher water uptake (WU = 213.8 %) at 80 °C, which is attributed to its rigid VAP-type cyclic chain backbone. Microtopography study demonstrated the existence of nanoscale phase separation in VAP-type AEMs and its association with water uptake and swelling behavior. VAP-N-60 showed excellent hydroxide conductivity up to 105.5 mS cm−1 at 80 °C, while exhibited superior alkaline stability that was not found in ROMP-type membrane ROMP-N-50 and the hydrogenated-type membrane H-ROMP-N-50. After being immersed in 2 M NaOH solution at 80 °C for 1200 h, the hydroxide conductivity loss of VAP-N-60 was only 3.0 %. Furthermore, a H 2 /O 2 single cell using VAP-N-50 membrane achieved the highest peak power density of 722 mW cm−2 at 60 °C without back pressure. [Display omitted] • A novel VAP-type poly (norbornene derivatives)-based AEMs were explored. • The performance of the VAP-type AEMs were compared with those of the ROMP-type and theirs hydrogenated AEMs. • The VAP-type AEMs exhibited excellent dimensional stability and alkaline stability. • The VAP-type AEMs exhibited high ionic conductivity and peak power density. [ABSTRACT FROM AUTHOR]

Carbazole and its derivatives have recently shown considerable potential for application in anion exchange membranes (AEMs), yet only a few studies have been reported so far. Herein, a carbazole derivative with multiple phenyls was synthesized, which was copolymerized into the polymer backbone, subsequently by densely piperidinium-functionalized, yielding a series of copolymers named PIP-PAESK-Cz- x as AEMs. The prepared membranes indicated well-defined microscopic morphology due to the drastic polarity contrast between the hydrophilic units and hydrophobic polymer backbone. Furthermore, compared with another analogous AEM, the presence of rigid carbazole significantly improved the water adsorption and alleviated the aggressiveness of OH− for PIP-PAESK-Cz- x. Consequently, the PIP-PAESK-Cz-25 membrane demonstrated decent hydroxide conductivity of 61.5 mS cm−1 at 80 °C, and stable performance upon treatment with harsh alkaline environments at 30 °C or 60 °C. In addition, a maximum power density of 407.8 mW cm−2 in the H 2 /O 2 fuel cell was also achieved. This work presented a novel strategy to exploit the carbazole, which is expected to provide additional ideas for more carbazole-based AEMs in the future. [Display omitted] • A novel strategy to exploit the carbazole for AEMs is investigated. • Densely piperidinium-modified carbazole derivatives are formed in the main chain. • Well-defined microscopic morphology promotes the hydroxide conductivity of AEMs. • Carbazole alleviates the aggressiveness of OH− toward adjacent cationic groups. [ABSTRACT FROM AUTHOR]

Anion-exchange membranes (AEMs) have gained widespread attention as another rising star among the core components of fuel cells. However, the disadvantages of low electrical conductivity and poor chemical stability greatly limit its development. Here, indeno carbazole monomers were introduced into the ether-free backbone and hydrophilic alkoxy side chains were suspended from the side chains to prepare a series of poly (indeno carbazolyl-aryl) piperidine membranes. Indeno carbazole is a nitrogen-containing heterocyclic compound with a large conjugation system, which provides a large volume of space to avoid close stacking of polymer molecules, and provides a place for the aggregation of water molecules without excessive swelling. The hydrophilic alkoxy side chain, as a hydrophilic group, absorbs a large amount of water and at the same time the oxygen atom will form cation-dipole interactions with the cation to induce cation aggregation. In addition, the polarity difference between the hydrophobic main chain and the hydrophilic side chain creates an obvious microphase separation structure, and the high-water absorption generated by the two can also reduce the attack of alkali on the cations, thus further improving the chemical stability of the membrane. At 80 °C, the relatively low IEC qPTP-IC-O-9% membrane instead achieved the highest ionic conductivity (137.5 mS cm−1) and peak power density (406 mW cm−2), and the conductivity retention was at 97.9% after 1300 h of immersion in 3 M NaOH at 80 °C. In addition, the qPTP-IC-O-9% membrane maintained 71.7% of the initial voltage after 30 h durability test at 80 °C, 0.05 A cm−2. To sum up, the qPTP-IC-O-9% membrane has a very bright future in promoting the further rapid development of hydroxide fuel cells. [Display omitted] • Introduction of bulky monomers to increase free volume and cation clusters. • Grafting alkoxy chains build polar differences and cation-dipole interactions. • Main and side chains synergistically optimize conductivity and alkali stability. [ABSTRACT FROM AUTHOR]

In order to improve the ionic conductivity and durability of anion exchange membranes (AEMs), novel ether free AEMs are prepared based on 6-bromo-1-hexanol quaternized poly(terphenyl piperidine)s by construction of a star-branched crosslinking structure via a crosslinker of 1,3,5-tris(bromomethyl)benzene. The star-branched crosslinking network enhances the dimensional stability and mechanical property without occupying the active sites for cation production. Suitable microphase separations with ionic cluster spacing within 19.68–20.72 nm are formed according to the SAXS results. The proposed AEMs exhibit hydroxide ion (OH‾) conductivity ranging from 118 to 136 mS cm−1 at 80 °C. The dense crosslinking structure and flexible side chains endow the AEMs with excellent resistance against the attack of OH‾ ions. About 80% of the conductivity retention rate is achieved after immersing the AEMs in 1 mol L−1 KOH aqueous solutions at 80 °C for 1600 h. A single H 2 /O 2 fuel cell employing the prepared membrane as the electrolyte exhibits a peak power density of 639 mW cm−2 at 60 °C without back pressure. [Display omitted] • Construction of star-branched crosslinking structure for polymer membranes. • A conductivity 136 mS cm−1 is reached at 80 °C by the prepared membrane. • Retain about 80% of conductivity after aging in 1 mol L−1 KOH at 80 °C for 1600 h. • Demonstration of the potential uses of the membranes as the electrolyte in fuel cells. [ABSTRACT FROM AUTHOR]

High hydroxide conductivity and sufficient dimensional/alkaline/mechanical stability are highly desired for practical applications of anion exchange membranes (AEMs). Herein, a new di -quaternized side-chain precursor (EDQA) was firstly designed and synthesized. Then novel AEMs (DBTF-4QA-x) based on poly(fluorenylene alkylene)s containing dual Y-shaped side-chains were prepared from EDQA by an efficient click reaction. Benefiting from several structural advantages of EDQA, DBTF-4QA-x membranes possessed high hydroxide conductivities up to 154.8 mS cm−1 at 80 °C, while maintained high dimensional stability. The membranes exhibited robust mechanical properties with tensile strengths and elongation at break up to 107.4 MPa and 46.4%, respectively. Furthermore, the membranes showed high alkaline stability with the conductivity loss below 11.4% after immersing in 4 M aq. NaOH at 80 °C for 40 days. In addition, DBTF-4QA-0.5 membrane achieved the maximum peak power density of 836.4 mW cm−2 in H 2 /O 2 fuel cells at 60 °C. [Display omitted] • Novel ether-free AEMs with dual Y-shaped side-chains are designed and prepared. • High ionic conductivity up to 64.8 mS/cm at 20 °C and 154.8 mS/cm at 80 °C. • High dimensional stability and good mechanical properties. • Excellent alkaline stability in 4 M NaOH at 80 °C for 40 days. [ABSTRACT FROM AUTHOR]

In alkaline environment, cationic membranes regularly experience degradation because of OH− attack on the cation in anion exchange membrane fuel cells (AEMFCs). Unlike quaternized amine (alicyclic and aliphatic) cations, aromatic cations are unaffected by Hofmann ß-elimination, however, because of planar geometry they are highly susceptible to nucleophilic substitution reaction. A series of polysulfone (PSU) based anion exchange membranes (AEMs) was fabricated carrying pendant pyridinium cation with different substituent groups to shield the cation against OH− ions attack. The pyridinium cations were C-2 substituted, C-4 substituted and simultaneously C-2 and C-6 substituted with either –NH 2 , –OH or –CH 3. Chloromethylation, azidation and CuAAC reactions were employed to synthesize the copolymers. The collaborative analysis of 1H NMR and FT-IR spectroscopy was used to confirm the successful preparation of the desired product. All membranes exhibited adequate thermo-mechanical stabilities and sufficient hydration level without any serious swelling at all ranges of temperature (20–80 °C). The highest recorded ionic conductivity, peak power density and current density were 59.6 mS cm−1, 486.8 mW cm−2 and 1481.8 mA cm−2 respectively. The alkaline stability results suggest that simultaneous protection of pyridinium cation at C-2 and C-6 turns the membrane thoroughly resistant to OH− attack while the ones with exposed cations degrade at accelerated rate at elevated temperature. This study is aimed at providing a broader understanding of designing durable AEMs with promising performance by exploring the influence of changes in structural configuration of aromatic cations with different functional groups on the overall performance of AEMs and how the cations withstand the nucleophilic attack in AEMFCs. [Display omitted] • Polysulfone based AEMs with pendant pyridinium derivatives were synthesized. • Chloromethylation and azidation were employed to functionalize the polymer. • The copolymers were synthesized via CuAAC reaction. • Simultaneous C-2 and C-6 protection of the cation resulted in High alkaline stability. • High ionic conductivity and fuel cell performance were achieved. [ABSTRACT FROM AUTHOR]

Abstract Under strong oxidative environment of vanadium redox flow batteries (VRFB), membrane instability is a serious challenge. Anion exchange membranes (AEMs) are expected to reduce vanadium ion permeability due to Donnan exclusion. Herein, we report long alkyl chain grafted quaternized graphene oxide bonded poly(ether sulfone) by 1,4-diazabicyclo[2,2,2]octane (DABCO) coupling, which provides plenty of amine groups. This helps to improve the ionic conductivity. Whereas, long alkyl chain (C16) grafted quaternized graphene oxide causes well phase separation (hydrophilic-hydrophobic) and decent ionic pathway for ionic transportation. The reported AEMs showed good stabilities under harassed acidic/oxidative conditions due to the bulky nature of chemically grafted QG with the main polymer backbone. This results steric hindrance to resist the attack of oxidative species. Suitably optimized PS-DTQG-5 AEM, showed 32.46% water uptake, 2.14 meq/g ion exchange capacity, 6.06 × 10−2 S/cm ionic conductivity, and 18.93 × 105 S min cm−3 selectivity for VRFB. The VRFB assembled with PS-DTQG-5 AEM, displayed extremely good efficiencies (coulombic (98.06%), energy (76.4%), and voltage (78.0%)) at 60 mA cm−2, higher than those for Nafion 117 membrane. Further, stabilities under ex-situ oxidation conditions and in-situ cycle test (approx. 80) in VRFB operating environment make PS-DTQG-5 AEM as an attractive candidate. Graphical abstract fx1 Highlights • Grafting of quaternized graphene oxide containing C16 chain by DABCO coupling. • Acid/oxidative stable AEMs based on poly(ether sulfone) with plenty of amine groups. • AEMs with good conductivity and impervious for vanadium ion due to Donnan exclusion. • Well-architected PS-DTQG-5 membrane with good efficiencies and durability for VRFB. [ABSTRACT FROM AUTHOR]

A series of photocrosslinkable multi-block poly(arylene ether sulfone) copolymers containing various block lengths of hydrophilic segments were synthesized. For comparison, a series of random poly(arylene ether) copolymers were also synthesized. The anion exchange membranes(AEMs) were fabricated and in-situ photocrosslinking was carried out by UV irradiation in a swollen state. The microphase-separated morphologies of the multi-block membranes were characterized by SAXS and TEM experiments, and the membrane properties were investigated by measuring ion exchange capacity (IEC), water uptake, water swelling ratio, ionic conductivity, methanol permeability and alkaline stability. IECs and water uptakes of the crosslinked multi-block membranes were in the range of 1.11–1.42 meq g −1 and 14.36–31.01% at 20 °C, respectively. The hydroxide conductivity was in the range of 11.38–25.00 mS cm −1 at 20 °C, and showed a maximum value of 178.77 mS cm −1 at 100 °C. The multi-block membranes exhibited low methanol permeability (2.75 × 10 −7 cm 2 s −1 ) at room temperature, which is one order of magnitude lower than that of Nafion® 117 (23.8 × 10 −7 cm 2 s −1 ). The crosslinked membranes showed excellent dimensional stability and alkaline stability with only a slight decrease in ionic conductivity. All the multi-block membranes showed superior properties compared to their corresponding random copolymers. [ABSTRACT FROM AUTHOR]

With the aim to enhance the hydrophilic–hydrophobic separation and thus improve the anion conductivity of diblock copolymer anion exchange membranes (AEMs), a fluorinated hydrophobic block was introduced into quaternized diblock copolystyrene. Two fluoro-containing monomers (i.e., 4-fluorostyrene (4FS) and 2, 3, 4, 5, 6-pentafluorostyrene (PFS)) were polymerized into a poly(4-vinyl benzyl chloride)-based macroinitiator (Macro-PVBC 263 ) via reversible addition–fragmentation chain transfer (RAFT) polymerization. This route led to the corresponding diblock copolymers PVBC 263 - b -P4FS y and PVBC 263 - b -PPFS y , which served to prepare AEMs (i.e., PVBC 263 - b -PPFS y -OH and PVBC 263 - b -P4FS y -OH, respectively) via quaternization with trimethyl amine (TMA) and subsequent ion-exchange. As expected, the as-obtained AEMs showed well-defined lamellar morphologies, as revealed by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). Consequently, all the fluorinated diblock copolymer-based AEMs showed high anion conductivities. PVBC 140 - b -P4FS 38 -OH showed the highest hydroxide conductivity (86.1 mS/cm) with an ion exchange capacity (IEC) of 4.27 meq/g. Interestingly, despite its high IEC, PVBC 263 - b -P4FS 38 -OH showed a reasonable water uptake (WU) of 37.5% as a result of the presence of hydrophobic fluorinated block segments. Thus, proper ion conducting channels are believed to be built by facilitating hydrophilic–hydrophobic phase separation processes driven by the fluoro-substituted functionalities. Despite their high IEC values in terms of hydrophobicity, the WU and swelling ratio of the AEMs prepared herein did not increase significantly, especially at elevated temperatures. All the AEMs preserved over 86% of their initial hydroxide conductivity after 20 d of alkaline stability testing (1 M aqueous NaOH) at 80 °C. [ABSTRACT FROM AUTHOR]

A high performance of anion exchange membranes (AEMs) is highly demanded in anion exchange membrane fuel cells (AEMFCs) and has been extensively studied. However, the poor ionic conductivities and the alkaline stability might limit their applications. Herein, we developed a novel strategy to improve the ionic conductivity and alkaline stability of AEMs by introducing hydrophilic oligo(ethylene glycol)(OEG) groups. Continuous ion-conducting channels were efficiently formed thanks to the dynamic aggregation of water molecules assisted by the hydrophilic side chains. The resultant AEMs with low IEC values showed significant enhancement in hydroxide conductivity compared to the AEMs functionalized by the conventional 1,2-dimethylimidazolium (PSf-Im), as the hydroxide conductivity of PSf-2 membrane with an IEC of 1.05 mmol g −1 was 59.5 mS·cm −1 at 60 °C while the hydroxide conductivity of PSf-Im membrane with an IEC of 1.27 mmol g −1 was 36.7 mS·cm −1 . In addition, the alkaline stability and the mechanical properties of the resultant AEMs were improved remarkably. The density functional theory (DFT) study showed that the introduction of OEG part can significantly increase the LUMO energy of functional group and then enhance the alkaline stability. [ABSTRACT FROM AUTHOR]

The piperidinium cation exhibited a substantial impact on the improvement of alkaline stability of anion exchange membranes (AEMs), yet the research regarding the micro-block polymer AEMs modified with it has not been conducted. Herein, we report two series of micro-block poly(arylene ether sulfone)s containing densely benzyl- N -methylpiperidinium (TTP- n -PIPPES) and benzyl-trimethyl-ammonium (TTP- n -QAPES) functionalized units for AMEs, respectively, where the n represents the molar ratio of monomer containing tri-tetraphenyl to the employed bisphenol monomers. The content and arrangement of the two types of cations in both polymer backbones were the same. The hydrophilic phases of TTP- n -PIPPES membranes exhibited isolated island states, wrapped with coherent hydrophobic phases. While the TTP- n -QAPES membranes formed continuous hydrophilic channels but fragmented hydrophobic phases. The discrepancy in the microscopic morphology of membranes and the intrinsic nature of cations thus rendered two types of AEMs with different advantages in macroscopic properties. The TTP- n -PIPPES membranes performed better dimensional stability and alkaline stability (low temperature). In contrast, the preferable capabilities of TTP- n -QAPES membranes were water affinity, hydroxide conductivity, and alkaline stability (high temperature). For instance, the TTP-18.2-PIPPES membrane was 11.7%, 11.4%, and 27.4% lower than the TTP-18.2-QAPES membrane at 80 °C in terms of dimensional change, water uptake, and hydroxide conductivity, respectively. [Display omitted] • Effects of quaternary ammonium groups on micro-block AEMs are investigated. • Benzyl N -methylpiperidinium improve dimensional stability, alkali stability (30 °C). • Benzyl trimethyl ammonium promote hydroxide conductivity, alkali stability (60 °C). • Dimensional change of AEM with benzyl N -methylpiperidinium is 11.7% lower at 80 °C. • Ionic conductivity of AEM with benzyl trimethyl ammonium is 27.4% higher at 80 °C. [ABSTRACT FROM AUTHOR]

A series of cross-linked QPBP-HT/OT-X% anion exchange membranes (AEMs) were prepared by introducing unsaturated olefins during the quaternization of poly(biphenyl piperidine) polymers (QPBP), followed by a thiol-ene "Click" reaction with a dithiol cross-linker for diffusion dialysis. In particular, the ethoxy (EO) group in 3,6-dioxa-1,8-octanedithiol (OT) can enhance the hydrophilicity of AEM and the ion-dipole interactions existing with cationic groups can effectively tune the nanostructure within AEM, which is jointly verified by AFM and SAXS. Compared with the original QPBP AEM, the ion exchange capacity of cross-linked QPBP-HT/OT-X% AEMs did not change significantly, but the water uptake and swelling rate showed a decreasing trend, which led to an obvious improvement in dimensional stability. Diffusion dialysis tests showed that QPBP-OT-5% AEM containing EO groups achieved a better dialysis coefficient (U H + ) of 41.72 × 10−3 m h−1 and an excellent separation factor (S) of 103.56, which was significantly superior than QPBP-HT-X% AEMs containing hydrophobic crosslinkers and commercial DF-120 AEM (U H + = 9 × 10−3 m h−1, S = 18.5). These results show that the "trade-off" effect between acid flux and ion selectivity can be effectively balanced by introducing hydrophilic EO groups into the cross-linked network of the polymer, which is a perspective design strategy. [Display omitted] • EO group can effectively modulate the microphase separation structure of AEMs. • The appropriate cross-linking can improve the dimensional stability of AEMs. • The prepared QPBP-HT/OT-X% AEMs showed superior ionic conductivity. • The QPBP-OT-X% AEMs showed significant acid flux and excellent ion selectivity. [ABSTRACT FROM AUTHOR]

As a key constituent of anion exchange membrane fuel cells, anion exchange membrane (AEM) faces a tough challenge to withstand the nucleophilic (OH−) attack on central cation in alkaline atmosphere which causes a constant degradation and thus affects the long term performance of the AEM. Aromatic cations unlike aliphatic amine cations are resistant to Hofmann β-elimination, however due to planar geometry they are more vulnerable to nucleophilic substitution reaction. To understand the problem and to formulate a mechanism to protect the AEM, a series of cationic membranes was fabricated based on poly(arylene ether ketone) having pendant quaternized derivatives of pyrimidinium and pyridazinium cations employing DCC-coupling reaction. The chemical structure characterization of the target products was conducted by 1H NMR and FT-IR spectroscopy. Various physicochemical properties of the membranes were investigated including thermomechanical behavior, ion exchange capacity, water uptake, swelling ratio, ionic conductivity, fuel cell performance and oxidative and chemical stabilities. No serious swelling was observed with adequate water uptake at temperature between 20 °C and 80 °C. The membranes with both pyrimidinium and pyridazinium cations exhibited sufficient ionic conductivity. The highest recorded conductivity was 45.7 mS cm−1 and peak power density was 194 mW cm−2. The oxidative stability of all membranes was high (more than 90%) however, alkaline stability results suggest a different behavior. Pyridazinium cations with substituents simultaneously at C-3 and C-6 positions is thoroughly protected from OH− attack while pyrimidinium (simultaneously protected at C-4 and C-6 positions) degraded at accelerated rate with raising temperature. This work not only explores the possibility of utilizing aromatic cations that weren't used before but also provides a wider understanding of the relationship of aromatic cation structure and membrane stability and performance thus helping in designing stable anion exchange membranes for long-lasting fuel cells. [Display omitted] • Poly(arylene ether ketone) with pendant –COOH group was prepared. • DCC coupling was employed to functionalize the polymer. • Anion exchange membranes with pendant pyrimidinium and pyridazinium were fabricated. • Pyridazinium based AEM were stable in alkaline solution. • High ionic conductivity was achieved. [ABSTRACT FROM AUTHOR]

A novel class of alkaline anion exchange membrane (AAEM) is presented, in the form of KOH-modified multilayer graphene oxide paper (GO KOH ). Such membranes can be easily fabricated at large scale with varying thickness using conventional filtration techniques, and have high tensile strength (24.5 MPa). However, a large degree of swelling is observed. SEM investigations show that the morphology of GO changes after KOH-treatment, whilst XPS measurements and XRD analysis confirm successful chemical modification. The hydrogen gas permeability is several orders of magnitude lower than conventional polymer-based ionomer membranes. The maximum anion conductivity is 6.1 mS/cm at 70 °C, and the dominant charge carrier is confirmed to be OH − by utilization of anion and proton-conducting blocking layers. The ion exchange capacity is 6.1 mmol/g, measured by titration. A water-mediated reverse Grotthuss-like mechanism is proposed as the main diffusion mode of OH − ions. Finally, a prototype AAEM fuel cell is fabricated using a GO KOH membrane, confirming the applicability to real systems. [ABSTRACT FROM AUTHOR]

A random copolymer, tris(2,4,6-trimethoxyphenyl) phosphonium functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO–TPQP) was cast from three different solvents: dimethyl sulfoxide (DMSO), ethyl lactate, or a 41:59 vol% mixture of DMSO and ethyl lactate. Solvents were selected via analysis of the Hansen solubility parameters to vary the phase separation of the polymer in the films. An optimized mixture of DMSO and ethyl lactate chosen for film fabrication and this film was contrasted with films cast from the neat constituent solvents. Atomic force microscopy identified domains from nanometer to tens of nanometer sizes, while the light microscopy showed features on the order of micron. SAXS revealed a cation scattering peak with a d-spacing from 7 to 15 Å . Trends in conductivity and water diffusion for the membranes vary depending on the solvent from which they are cast. The mixed solvent cast membrane shows a linear Arrhenius behavior indicating fully dissociated cationic/anionic groups, and has the highest bromide conductivity of 3 mS/cm at 95% RH, 90 °C. The ethyl lactate cast membrane shows a linear Arrhenius relation in conductivity, but a Vogel–Tamman–Fulcher behavior in its water self-diffusion. While water increases bromide dissociation, water and bromide transport in these films seems to be decoupled. This is particularly true for the film cast from ethyl lactate. [ABSTRACT FROM AUTHOR]

Alkaline doped PBI membranes are investigated for their physicochemical properties when employed in alkaline direct alcohol fuel cells. Alkali uptake, water uptake, alcohol permeability, ion conductivity, mechanical strength and evolution of the morphology for the alkaline doped PBI membranes are measured. It is demonstrated that the alkaline doping process has a profound influence on the physicochemical properties of PBI membranes. With a high alkaline doping level, the alkali uptake of alkaline doped PBI membranes reaches 14%. The high alkaline uptake results in a separation of the polymer backbones and partial cleavage of hydrogen bonds, which leads to a reduction in the mechanical strength and an increase the alcohol permeability of alkaline doped PBI membranes. However, the high alkaline doping level is beneficial to the ionic conductivity. The conductivity of alkaline doped PBI membranes increases to 96.1 mS cm −1 at 363.15 K after PBI membranes are doped with 6 M KOH solution. Based on these investigations, a mechanism is proposed to interpret the chemical interaction during the alkaline doping process and its influence on physicochemical properties. The existence of a neutralization reaction and the re-establishment of hydrogen bonding networks should be attributed to the property transformation during the alkaline doping process. [ABSTRACT FROM AUTHOR]

Anion exchange membranes (AEMs) have found numerous electrochemical applications because of their good conductivity and permselectivity. Herein, we are reporting a method to prepare silica modified poly(ethyleneimine) (SMPEI) with 3-Glycidoxypropyl-trimethoxysilan (GPTMS) by epoxide ring opening reaction. Stable AEMs of different compositions were prepared with SMPEI and a plasticizer poly(vinyl alcohol) (PVA) by acid catalyzed sol–gel followed by formal cross-linking. The reported method is simple and a green alternative for the preparation of AEM without the use of hazardous chemicals. Suitability of prepared AEMs for electrodialytic application was assessed by analyzing their physicochemical properties, stabilities under operating conditions, conductivity, electro-osmotic and chronopotentiometry studies. A highly suitable membrane, SMPEI/PVA-40, exhibited 55.32 mS cm −1 conductivity (in equilibration with 0.04 N NaCl solution at 30 °C), ion-exchange capacity (1.31 meq g −1 ) and permselectivity (0.79) with good electrodialytic performance. Preparation protocols and properties of the reported composite AEM represent a promising starting point for architecting highly conducting and stable AEMs, but we have to study the trade-off between properties, stabilities and electro-osmotic mass drag before its commercial exploitation. [ABSTRACT FROM AUTHOR]

Possessing high ionic conductivity is required to polymer-based membrane electrolytes. However, it is a challenge to evaluate the conductivity based on the structure of the polymer membrane without any measurements. We present a deep learning protocol to predict the hydroxide ion (OH-) conductivity from chemical structure information of poly (2,6-dimethyl phenylene oxide)-based anion exchange membranes (AEMs) grafting with one kind of functional cationic group. The modeling process includes data collection and feature processing, functional cationic group identification, OH- conductivity prediction and scientific law extraction. The established model achieves 99.7% of accuracy for classifying various functional cationic groups. The prediction error in OH- conductivity is ± 0.016 S/cm for quaternary ammonium based AEMs, ± 0.014 S/cm for saturated heterocyclic ammonium based ones, and ± 0.07 S/cm for those possessing imidazolium cations. The proposed protocol is powerful to assist researchers in designing the AEMs with predictable OH- conductivity, and provides a new research paradigm of the AEMs preparation. [Display omitted] • Construction of a deep neutral network model by using an experimental dataset. • Identify functional cationic groups and predict conductivity of anion exchange membranes. • Superior discernibility and predictive power on external dataset. • Feasibly extract scientific rules of specific polymer based membrane electrolytes. [ABSTRACT FROM AUTHOR]

Possessing high ionic conductivity is required to polymer-based membrane electrolytes. However, it is a challenge to evaluate the conductivity based on the structure of the polymer membrane without any measurements. We present a deep learning protocol to predict the hydroxide ion (OH-) conductivity from chemical structure information of poly (2,6-dimethyl phenylene oxide)-based anion exchange membranes (AEMs) grafting with one kind of functional cationic group. The modeling process includes data collection and feature processing, functional cationic group identification, OH- conductivity prediction and scientific law extraction. The established model achieves 99.7% of accuracy for classifying various functional cationic groups. The prediction error in OH- conductivity is ± 0.016 S/cm for quaternary ammonium based AEMs, ± 0.014 S/cm for saturated heterocyclic ammonium based ones, and ± 0.07 S/cm for those possessing imidazolium cations. The proposed protocol is powerful to assist researchers in designing the AEMs with predictable OH- conductivity, and provides a new research paradigm of the AEMs preparation. [Display omitted] • Construction of a deep neutral network model by using an experimental dataset. • Identify functional cationic groups and predict conductivity of anion exchange membranes. • Superior discernibility and predictive power on external dataset. • Feasibly extract scientific rules of specific polymer based membrane electrolytes. [ABSTRACT FROM AUTHOR]

Abstract: Novel benzimidazolium (BIm) functionalized anion exchange membranes (AEMs) are synthesized and characterized for alkaline fuel cells (AFCs). Poly(phenylene oxide) (PPO) is firstly brominated followed by nucleophilic substitution reaction with methylbenzimidazole to obtain the objective BIm-PPO AEMs. Such solution-casting AEMs show good mechanical and thermal stabilities as well as the favorable fuel cell-related indicators, including high ion exchange capacity, proper water uptake and high ionic conductivity. In addition, a single H2/O2 fuel cell test by employing the optimal BIm-PPO-0.54 AEM yields a peak power density of 13mWcm−2 at 35°C, indicating the potential application of BIm-PPO AEMs in AFCs. Compared with the analogous AEMs based on PPO containing the classical pendant quaternary ammonium and imidazolium cations, BIm-PPO AEMs show the advantages in dimensional, mechanical and thermal stabilities, while simultaneously exhibiting the higher ionic conductivity. Compared with polybenzimidazolium based AEMs, where BIm cations distribute within the polymer backbone, AEMs herein present the higher ionic conductivity and power density (produced from a single cell test) due to the better mobility and aggregation abilities of pendant BIm cations attached to the backbone via a side chain relative to those distribute within the polymer backbone. [Copyright &y& Elsevier]

A series of polymer based on spirocyclic quaternary ammonium (QA) cations having 5-/6- and 6-/6- membered rings were designed and prepared from tetrakis(bromomethyl) monomers to investigate the alkaline and fuel cell stability of spirocyclic ionenes. The alkaline stability testing of model compounds and DFT calculations showed that the spirocyclic QA having 5-/6-membered rings based on phenyl and biphenyl showed a better stability than that of the spirocyclic QA with naphthalene 6-/6-membered rings probably due to the strong electro-withdrawing effect of naphthalene rings. Although the high molecular weight polymer with naphthalene rings could not be obtained, the spirocyclic ionenes based on phenyl or biphenyl showed high molecular weight. Thus, the blending membrane with rigid NPBI have been fabricated to mitigate the water solubility of spirocyclic ionenes due to their high IEC values. The blending membrane showed a high ionic conductivity even at elevated temperature without any excessive swelling in spite of its high IEC value. Employing the spirocyclic ionenes as membrane, the H 2 /O 2 single cell at 60 °C was firstly demonstrated. A peak power density of 135 mW cm−2 was achieved for PP80N20 membrane. Surprisingly, the fuel cell device durability provided a counterintuitive data that showed that spirocyclic ionenes with excellent alkaline stability were not superior in device function assessment. A rapid ring-opening degradation as confirmed by NMR technique for the spirocyclic ionenes was observed in device testing. These results that stability investigation gives us new directions for polymer and cations designs for highly durable devices. [Display omitted] • A series of spirocyclic quaternary ammonium (QA) cations were designed and synthesized. • The results indicated that the spirocyclic QA having 5-/6-membered rings based on phenyl have a best alkaline stability. • A maximum power density of 135 mW cm−2 was achieved for PP80N20 membrane. [ABSTRACT FROM AUTHOR]

Anion exchange membrane (AEM) with high ionic conductivity and good stability is of vital importance for developing high-performance alkaline anion-exchange membrane fuel cell (AEMFC). In particular, the performance of AEM largely depends on the microstructure of the basic polymer material. Herein, we have developed a novel strategy to fabricate the AEMs, featuring a star topological structure, via living anionic polymerization and the subsequent functionalization. Thanks to the introduction of well-defined amphiphilic block structure, a distinct micro-phase separation was observed in the synthesized AEMs (AEM-SCP) which were based on star-shaped block copolymers. In comparison to the AEM-LCP membranes based on linear block copolymers, the AEM-SCP membranes exhibited relatively lower water uptake and swelling ratio, but much higher hydroxide conductivity (at 80 °C, 68.1 mS cm−1 for AEM-SCP-3 vs. 38.1 mS cm−1 for AEM-LCP). This is attributed to the efficient aggregation of ionic groups via employing star-shaped block copolymers, which can result in the formation of continuous ion-conducting channels and the facilitated ionic conduction in the AEMs. Furthermore, compared with the AEM-LCP membrane, the dimensional and alkaline stability of the resultant AEM-SCPs have been significantly enhanced. [Display omitted] • A distinct micro-phase separation via employing star-shaped block copolymer. • An enhancement in hydroxide conductivity by efficient aggregation of ionic groups. • The dimensional and alkaline stability were improved comparing to linear membrane. [ABSTRACT FROM AUTHOR]

A series of mechanically robust and highly conducting crosslinked anion-exchange membranes are synthesized by using quaternary phosphonium-functionalized poly(ether ether ketone) (QPPEEK) as base polymer and poly(ethylene glycol) (PEG) as the crosslinker. The crosslinked membrane containing both rigid and flexible polymer constituents (QPPEEK-PEG) revealed better flexibility and mechanical strength, and higher conductivity than the pristine QPPEEK membrane. The mechanical properties and ionic conductivity of the crosslinked membranes are tuned by the mass fractions of the QPPEEK and PEG components. Among the different QPPEEK and PEG compositions, the QPPEEK-PEG 20 (QPPEEK:PEG 80:20) membrane has the best properties, reaching a hydroxide conductivity of 102 mS cm−1 at 80 ᵒC, a tensile strength of 13.7 MPa, and 48% of elongation. The membrane is chemically stable in alkaline environment, retaining 85% of its initial conductivity and mechanical strength after being exposed to 1 M KOH at 80 °C for 400 h. Finally, in the operando anion-exchange membrane fuel cell the QPPEEK-PEG 20 crosslinked membrane performs well, displaying an open-circuit voltage of 1.05 V and a maximum power density of 154 mW cm−2 measured at 0.55 V, showing the potential of PEEK-based membranes for fuel cell applications. [Display omitted] • Mechanically robust, highly conducting crosslinked AEMs are synthesized. • The AEMs have tensile strength of 9–15 MPa and 40–65% elongation. • Hydroxide conductivities up to 102 mS cm−1 are achieved at 80 ᵒC. • The AEMs retain 85% of their initial conductivity after 400 h in 1 M KOH at 80 °C. [ABSTRACT FROM AUTHOR]

Surplus demand for freshwater gained considerable attention towards the development of desalination technologies, of those electrodialysis proved to be able to brackish water desalination. Herein, this article clearly explains the synthesis of poly(vinylidene fluoride-co-hexafluoropropylene) based anion exchange membranes (AEMs) for electrodialysis. Prepared series of AEMs is analyzed for stabilities and ion transport behavior to assess their suitability in electrodialysis. TEM and AFM imaging are used to get further insights about hydrophilic-hydrophobic phase separation and ionic domain clustering, which is critical for the amplification in electrochemical properties. Optimized membrane (AEM-1.0) exhibited notable electrochemical properties with water uptake of 44.3%, ion exchange capacity of 1.56 meq g−1, and ionic conductivity of 21.1 mS cm−1. Relatively high transport number (0.94) and limiting current density (43.7 A m−2) of AEM-1.0 membrane enables a broad window for faster electrodialytic desalination at a higher operating potential. Further, 1.05 kWh kg−1 energy consumption and 87.33% energy efficiency are realized for optimized AEM-1.0 membranes, which proves its efficiency to be employed in electrodialysis for brackish water desalination. Image 1 • Poly (vinylidene fluoride-co-hexafluoropropylene) based partially cross-linked AEMs. • Insights towards phase separation and ionic domain clustering are observed. • Melting temperature and crystallinity percent for AEMs reduced with 4-VP content. • High ionic conductivity at moderate water uptake and ion exchange capacity. • Low energy consumption and high energy efficiency in electrodialysis. [ABSTRACT FROM AUTHOR]

Research on the ion conductivity and mechanical stability of anion exchange membranes (AEMs) has achieved great progress, it is more urgent to prepare AEMs with high alkali stability. Azaspirocyclic cations are among the most alkali-stable cations. In this study, a synthesized long-chain 3-(3-(1-(8-bromooctyl) piperidin-4-yl) propyl)-6-azaspiro[5.5] undecan-6-ium bromide(BOP-ASU) cation was introduced into a portion of a piperidine ring on a PBP backbone to prepare PBP-BOP-ASU, and AEMs based on PBP-ASU and PBP-BOP-ASU were prepared. The structure of each product was characterized (1H NMR, MS), and the prepared anion exchange membrane was also characterized using micromorphology (SEM, TEM, AFM) and performance tests (TGA, WU, SR, ion conductivity, alkali stability). The PBP-BOP-ASU (8% membrane) showed the highest ion conductivity (117.43 mS/cm) at 80 °C. In addition, it showed excellent alkali stability in a test environment of 2 M NaOH solution at 80 °C for 1400 h. Moreover, the introduction of side chain spiro cations could improve the microscopic phase separation structure of the AEMs, and it also increased their ionic conductivity, thus ensuring the potential for their application in anion exchange membrane fuel cells. The PBP grafted side chain BOP-ASU cation has a very good hydrophilic-hydrophobic microphase separation structure, the higher ion conductivity (117.43 mS/cm at 80 °C) and excellent alkali stability(1400h, 2 M NaOH solution at 80 °C). Image 1 • The PBP grafted side chain BOP-ASU cation has a very good hydrophilic-hydrophobic microphase separation structure. • The PBP-BOP-ASU 8% membrane showed the highest ion conductivity (117.43 mS/cm) at 80 ℃Ø 3. The PBP-BOP-ASU 8% membrane showed the excellent alkali stability in a test environment of 2 M NaOH solution at 80 ℃ for 1400 h. [ABSTRACT FROM AUTHOR]

Novel anion exchange membranes (AEMs) with C-C polymer backbones, cardo fragments, flexible alkyl side chains and cyclic quaternary ammonium (QA) groups were designed and synthesized. Cardo poly(oxindolebiphenylylene) polymers with pendent cyclic QAs of different length (POXIA-Br) were prepared by a superacid-catalysed polyhydroxyalkylation reaction and subsequent quaternion functionalization. This preparation process has the advantages of mild reaction conditions, simple operation, low cost and environmental friendliness. The morphology, water uptake (WU), ion conductivity, stabilities and the fuel cell performance were all investigated thoroughly. With the extension of the side chain length, both the microphase separation scale and the ionic conductivity increased. AEMs with longer pendent QAs exhibited decreased WU and better alkaline stability performance than did AEMs with shorter pendent QAs. POXIH-OH (in OH− form) with a hexyl side-chain spacer showed a maximal conductivity of 73.6 mS cm−1 at 80 °C. There was no degradation observed for POXIH-OH except for loss of 9.5% of QA groups after 1200 h in 1 M NaOH at 80 °C. In addition, the AEM fuel cell test performed a high peak power density of 476 mW cm−2 at 60 °C. • Novel cardo poly(oxindolebiphenylylene) AEMs were designed and fabricated. • C-C backbone, flexible alkyl side chain and cyclic QAs were present in AEMs. • The preparation process was simple, low cost and environmental friendly. • POXIH-OH AEMs showed distinct phase separation, high stability and conductivity. • The AEMFC based on POXIH-OH exhibited high performance. [ABSTRACT FROM AUTHOR]

In order to develop anion exchange membranes (AEMs) with high ionic conductivity, low swelling ratio (SR) and long-term alkaline stability, a series of crosslinked polybenzimidazole-based AEMs (FPBI-QPVC x) were prepared. We herein demonstrated that the integration of a partially fluorinated polybenzimidazole and quaternized poly(vinylbenzyl chloride) benefits the fabrication of the AEMs with well-defined hydrophilic/hydrophobic phase-segregated structure, leading to a relative high hydroxide conductivity of 91.7 mS cm−1 at 80 °C for FPBI-QPVC 2.5. The existence of a crosslinking structure endowed the as-prepared AEMs with relatively low water uptake and SR. Besides, the FPBI-QPVC x AEMs also have robust mechanical properties, high thermal decomposition temperature and good alkaline stability. Only 10.7% of conductivity loss was observed after soaking the ether-bond-free AEMs into 1 M a.q. KOH at 80 °C for 480 h. A maximum power density of 197.5 mW cm−2 was determined by a single cell using FPBI-QPVC 2.5 AEM. Image 1 • Novel crosslinked polybenzimidazole-based AEMs were prepared. • The AEMs exhibited well-defined micro-phase separation structures. • The crosslinking structure constrained the water swelling behavior of the AEMs. • The ether-bond-free backbone improved the alkaline stability of the AEMs. • The highest conductivity of 91.7 mS cm−1 was obtained. [ABSTRACT FROM AUTHOR]

A double-network anion exchange membrane (TA/AT-PEK/PVA-x) was prepared by Br-PEK and PVA, 3-amino-1,2,4 triazole forms a cross-linking structure with PVA under the action of 1,4-phthalaldehyde and then triazole can be linked with Br-PEK. The structure of membranes was verified by FT-IR. The composite membrane is uniform and smooth can be seen from the scanning electron microscope (SEM) and exhibit good hydrophilic/hydrophobic micro-phase separation structure proved by Transmission electron micrograph (TEM). The ionic conductivity of TA/AT-PEK/PVA-0.15 is 0.062 S/cm at 80 °C. With the addition of PVA within a certain range, the water uptake, swelling ratio hydroxide conductivity and alkaline stability are increase. The membranes are more flexible. After immersing in 4 M NaOH solutions for 240 h at 80 °C, it remains at least 65% of its initial hydroxide ion conductivity of TA/AT-PEK/PVA-0.3 membrane. With the increasing number of water molecules solvating the hydroxide, its nucleophilicity and basicity were hindered, which enhance alkaline stability of anion exchange membranes. • A series of double-network anion exchange membranes are synthesized. • Exhibit good hydrophilic/hydrophobic micro-phase separation structure. • The anion exchange membranes are flexible and stable under high alkaline solutions. [ABSTRACT FROM AUTHOR]