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Tuning the hydrophilic/hydrophobic nanophase-separated morphology to enhance the conductivity is a considerable challenge in the field of anion exchange membranes (AEMs). Here, a series of novel aliphatic-aromatic copolymer AEMs were designed by embedding flexible alkyl chains of different lengths into rigid main chain of poly(ether sulfone). Compared to traditional aromatic polymer, the aliphatic-aromatic copolymers had more flexible main chains and longer hydrophobic segments, both of which promoted the nanophase separation and the formation of ionic clusters. Increasing aliphatic chain length made the ionic clusters larger and more interconnected, but too long aliphatic chain led to the formation of smaller ionic clusters because the ionic groups were far away from each other. An optimum length of the aliphatic chain (8 C) existed for the nanophase-separated morphology with the biggest ionic clusters (around 8 nm), with which the membrane showed the highest conductivity. A peak power density of 159 mW cm −2 was obtained for the cell incorporating the 8 C membrane. Based on these, this study reveals a new direction to create a tunable nanophase-separated morphology for high-performance AEMs. [ABSTRACT FROM AUTHOR]

A new series of thermoplastic interpenetrating polymer network (TIPN) anion exchange membranes (AEMs) based on poly [2,2′- (p-oxydiphenylene) −5, 5′-bibenzimidazole] (OPBI) and poly(1, 2-dimethy-3-allylimidazolium) (PDAIm) (PBI/DAIm TIPN) has been developed. With 1, 2-dimethy-3-allylimidazolium (DAIm) polymerization in presence of OPBI polymer chains, two kinds of uncrosslinked polymer chains, i.e. PDAIm and OPBI interpenetrate with each other to form a physically crosslinking network. Small steric hindrance effect of the DAIm monomer and non-covalent crosslinking interpenetrating polymer chains contribute to better compatibility and chains flexibility in the TIPN compared with the blend and semi-interpenetrating networks, which are evidenced by SEM and SAXS, promote the aggregation of hydrophilic groups and induce connective ionic conductive channels. PBI/DAIm TIPN membranes achieve well-balanced performance between high hydroxide conductivity and dimensional stability because of the dynamically forced compatibility feature of TIPN. Especially, the PBI/DAIm TIPN-65/0.5 membrane exhibits high hydroxide conductivity (96.7 mS cm −1 ) and low swelling ratio (4.4%) at 80 °C. With low overall alkali uptake (2.89%) and IEC (0.63 mmol g −1 ) of functional groups, it exhibits excellent chemical stability in 1 M KOH at 60 °C for 96 h (94.0% retention) and high tensile strength (48.2 MPa) in hydrated state. These observations suggest TIPN structure provides a promising solution to the electrochemical-mechanical balance of AEMs. [ABSTRACT FROM AUTHOR]

A novel approach is proposed to design anion exchange membranes (AEMs) containing pendent imidazolium side chains with flexible ether-containing spacer by the Williamson etherification between chloromethylated polysulfone and as-synthesized hydroxyl-bearing imidazolium. The introduction of long flexible ether-containing spacer chains enhances the mobility of terminated imidazolium groups and ion interactions. It facilitates the formation of a good hydrophilic/hydrophobic micro-phase separation structure, which is confirmed by the scattering peak of SAXS. As a result, the membranes exhibit high conductivity and excellent anti-swelling ability. The membrane with IEC of 1.55 mmol g −1 shows considerable hydroxide conductivity (72 mS cm −1 , 60 °C), low swelling ratio (7.3%, 60 °C), and great tensile strength in hydrated state (43.4 MPa, 20 °C). The existence of long spacer chain also improved the alkaline stability. After immersion in 60 °C, 1 M KOH solution for 168 h, hydroxide conductivity and tensile strength of the membrane remain constant. The ether-containing side chains fabricated in this work provides a universal promising method to balance hydroxide conductivity and dimensional and alkaline stability. [ABSTRACT FROM AUTHOR]

To prepare high-performance anion exchange membrane, a twisted ether-free polyarylene piperidinium (QMter-co-Mpi) has been successfully synthesized via simple and controllable acid-catalyzed polycondensation reaction for alkaline water electrolysis. The hydroxide conductivity of QMter-co-Mpi membrane reaches 37 mS cm−1 at 30 °C owing to the fact that an efficient ion-conducting channels are formed by means of this unique molecular structure. Furthermore, the IEC and hydroxide conductivity of the membrane can remain above 80% of the original values after alkali treatment for more than 1000 h, indicating exceptional alkaline stability. As a result, the QMter-co-Mpi based cell presents a high current density of 1064 mA cm−2 at 2.5 V under 1 M KOH and 50 °C and the high frequency resistance of the cell is only 0.165 Ω cm−2 at 1.8 V. The durability test is performed at current density of 200 mA cm−2 for more than 500 h and the voltage is basically remained at 2.1 V, showing excellent electrochemical performance. All these demonstrate a good application prospect for QMter-co-Mpi membrane in water electrolysis. • Twisted ether-free polymer based alkaline membrane has been successfully synthesized. • The membrane showed decent conductivity and exceptional alkaline stability. • The cell with this membrane exhibited excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

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-Br 7). In this type of membranes, the densely cross-linked and quaternized sites derived from β-CD-Br 7 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-CD 5 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-CD 5 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. [Display omitted] • A series of novel β-CD-modified cross-linked polyarylpiperidine polymer membranes were prepared. • The membrane shows a conductivity of 125.61 mS cm−1 at 80 °C. • The membrane has a conductivity retention of 90.7 % in 1 M NaOH at 80 °C after 1500 h. • The membrane gives a H 2 /O 2 fuel cell peak power density of 1.216 W cm−2. [ABSTRACT FROM AUTHOR]

Exploring anion exchange membranes (AEMs) with high conductivity and satisfactory stability is very meaningful for the advancement of alkaline fuel cells. Herein, a novel class of intrinsic microporous AEMs with pendent piperazinium are systematically fabricated for alkaline fuel cell performance testing. Contorted and rigid spirobisindane backbone structure expands the free volume of AEMs, inducing broad and interconnected ion transport channels. This unique feature endows membranes a leading advantage for the efficient transmission of hydroxide ions. Consequently, the prepared membrane displays excellent normalized hydroxide conductivity of 78.99 mS g cm−1 mmol−1 at 80 °C. Meanwhile, the hydroxide conductivity degrades by only 8.3 % after treatment in 1 M NaOH for 1000 h at 80 °C. Moreover, the peak power density of H 2 /O 2 single cell employing this membrane exhibits 1.06 W cm−2 at 80 °C and the cell can preserve 93.0 % of its initial voltage after operating for 18 h. [Display omitted] • A systematic approach is developed to prepare intrinsic microporous poly (phenyl-alkane)s containing piperazinium. • The spirobisindane structure facilitates the construction of well-developed ion channels in AEMs. • The intrinsic microporous membrane shows normalized hydroxide conductivity of as high as 78.99 mS g cm−1 mmol−1. • The prepared membrane shows excellent H 2 /O 2 fuel cell performance and durability. [ABSTRACT FROM AUTHOR]

Anion exchange membrane (AEM) with high ionic conductivity and stable dimension is urgently needed to improve cost-effective anion exchange membrane fuel cells (AEMFC). In this study, a dibenzofuran-containing poly(terphenyl furan piperidinium) (QPTFP) membrane is successfully synthesized in large quantities with a yield exceeding 500 g for the purpose of large-scale AEM production. The introduction of non-rotatable dibenzofurans results in an acceptable swelling ratio of 25 % and high ionic conductivity of 155 mS cm−1 at 80 °C. It also exhibits a favorable tensile strength of 52.6 MPa and excellent alkaline stability of 2200 h at 80 °C in 1 M KOH. Furthermore, the AEMFC employing QPTFP membrane achieves remarkable peak power densities at 80 °C for H 2 –O 2 (2 W cm−2) and H 2 -Air (1.2 W cm−2), and demonstrates excellent stability of over 90 h at 70 °C and a current density of 0.2 A cm−2. [Display omitted] • Poly(aryl furan piperidinium)s are prepared for the continuous production of anion exchange membranes. • The membrane shows the highest conductivity of 155 mS cm−1 and excellent stability of >2200 h. • The fuel cell exhibits the highest peak power density of 2 W cm−2 (H 2 –O 2) and 1.3 W cm−2 (H 2 -Air). • The QPTFP-25 AEM is stabilized of fuel cell operation for 90 h at 70 °C. [ABSTRACT FROM AUTHOR]

Abstract OH− conduction involved in the hydrophilic channel of anion exchange membrane strongly depends on the water uptake. To investigate the effect of water uptake on the hydrogen bond network for OH− conduction, a series of molecular dynamics simulations based on all-atom force field were performed on the hydrated imidazolium-g-PPO membranes with different water uptakes. The systems were well verified by comparing the membrane density and OH− conductivity with previous experiments. By means of local structural properties and pair-potential energy, reasonable hydrogen bond criteria were determined to describe the hydrogen bond network confined in the membrane. Increasing water uptake enhances the hydration structures of water and OH−, and facilitates the reorganization of the hydrogen bond network. Water and OH− are nearly saturated with water when the water uptake reaches λ = 10, where well-connected hydrogen bond network is produced. Further increasing water uptake has much less contribution to improving the hydrogen bond network, but inevitably swells the membrane channel. This work provides a molecular-level insight into the effect of water uptake on the hydrogen bonding structures and dynamics of OH− and water confined in the imidazolium-g-PPO membrane. Highlights • We investigated Im-g-PPO membrane with various water uptakes. • We explored the effect of water uptake on the hydrogen bond network in the membrane. • Topology and connectivity of the hydrophilic membrane channel are closely related with water uptake. • Hydrogen bond network in low-hydrated membrane could be much more regulated by water uptake than high-hydrated membrane. • We find the Im-g-PPO membrane with the water uptake of λ = 10 has the superior performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • The poly(aryl ether piperidinium) membranes are prepared by super acid catalysis with less amount of catalyst. • The membrane shows the highest conductivity of 140 mS cm−1 and excellent stability of greater than 2000 h. • The fuel cell exhibits the highest peak power density of 1.2 W cm−2. • The polymers can be easily prepared into larger widths of membranes. Poly(aryl piperidinium) is considered a promising material for the preparation of anion exchange membranes (AEM) with considerable conductivity and excellent chemical stability for anion exchange membrane fuel cells (AEMFC). In this research, we report a range of biphenyl ether-containing poly(aryl ether piperidinium) unlike previous ones to increase the conductivity of AEMs and the peak power density (PPD) of fuel cells, and the alkaline stability of ether bonds in the polymer backbone is demonstrated. All of the poly(aryl ether piperidinium) membranes possess comparable mechanical properties and inherent viscosity derived from the high activity of biphenyl ethers in superacid-catalyzed reactions, which means that large-width AEMs can be prepared. The data demonstrated that the poly (ether p-terphenyl piperidinium) (QPEPTpi-35) exhibited a conductivity of 140 mS cm−1 at 80 ℃ compared to the original poly (p-terphenyl piperidinium) (QPTPpi) membrane owning to optimized micro-phase separation structure and higher water uptake. Meanwhile, QPEPTpi-35 membrane conductivity retention is greater than 85% after immersion in 1 M KOH for 2000 h at 80 ℃. Moreover, the PPD of the QPEPTpi-35 membrane reaches 1.2 W cm−2 in H 2 /O 2 fuel cells, which is much higher than that of the QPTPpi membrane (0.51 W cm−2). The durability of MEA prepared by the catalyst-coated substrate (CCS) method manifests over 20 h under 0.2 A cm−2 at 60 °C. [ABSTRACT FROM AUTHOR]

Neutral aqueous organic redox flow battery (NAORFB) stands out as one of the most prospective mass energy storage options. The main limitations of large-scale storage regarding the NAORFB lie in the low Na+/Cl− conductivity of membrane in pH7 systems, which leads to a lower voltage efficiency. Herein, quaternary ammonium functionalized fluorinated poly (arylene ether) (QAFPAE-x) anion exchange membrane with hydrophilic and hydrophobic blocks was designed successfully. The results demonstrated that the grafting of quaternary ammonium and fluorine-containing block enables QAFPAE-x membrane low swelling, high Cl− conductivity, and promising chemical stability characteristics. The voltage efficiency of QAFPAE-100 membrane (93.8%–60.7%) is much higher than the AMVN membrane (88.4%–37.8%) at 20–160 mA cm−2. Furthermore, the NAORFB with the QAFPAE-100 membrane steadily runs at 60 mA cm−2 over 1500 cycles. Therefore, the ionic highway induced excellent performance of QAFPAE-100 membrane to render this material a promising candidate for practical NAORFB applications. [Display omitted] • A membrane with hydrophilic groups and hydrophobic block was designed. • The membrane has low swelling, high conductivity and chemical stability. • The membrane support over 1500 cycles of cells. [ABSTRACT FROM AUTHOR]

Crosslinked poly (ether ether ketone) (PEEK) hydroxide exchange membranes are prepared using bi-functional cyclic ammonium, 1,4-diazabicyclo [2,2,2] octane (DABCO), as simultaneous quaternization and crosslinking reagent. Hydroxide conductivity and ion mobility are evaluated as a function of ion concentration, which integrates the counteracting effects of the hydroxide ion amount and crosslinking degree. With the increase of ion concentration, effective mobility of hydroxide ion increases to a high level and then levels off or slightly goes down, suggesting a balance existed between ion concentration and mobility in the crosslinked membranes. As a result, hydroxide conductivity increases rapidly to a high stable level, indicating the applicable range of ion concentration (up to 1.0molL−1) for improving hydroxide conductivity. The crosslinked membranes exhibit high hydroxide conductivity of 33.4mScm−1 at 25°C and low swelling ratio of 48.2% at 60°C. Thermal stability (T onset: 176°C) of the crosslinked membranes is better as compared with the non-crosslinked (T onset: 165°C) and trimethylamine quaternized PEEK membranes. [ABSTRACT FROM AUTHOR]

Octopus-like side chains are introduced in poly(arylene piperidinium)-based alkaline anion exchange membranes (AEMs) to enhance the conductivity and stability. This type of side chain consists of a bulky rigid β-cyclodextrin (β-CD) as the "octopus head", and long flexible piperidinium ionic liquids as the "arms". The β-CD unit can enlarge internal free volume of the AEM to reduce ion transport resistance; the "arms" can interact with adjacent hydrophilic ionic groups and water, constructing continuous ion transport channels. The prepared poly(biphenyl piperidinium) AEM with "octopus" side chains at an ion exchange capacity (IEC) of 1.29 mmol g−1 exhibits higher hydroxide conductivity (121.5 mS cm−1 at 80 °C) than that without the "octopus" structure (57.4 mS cm−1) although the latter has a larger IEC (1.55 mmol g−1). This "octopus" AEM retains 87.2% of its conductivity after being treated in a 1 M NaOH at 80 °C for 480 h. The alkaline H 2 /O 2 fuel cell constructed with this "octopus" AEM produces a peak power density of 469 mW cm−2; the cell voltage can be maintained by 85% during 16 h operation. This work illustrates the advantage of "octopus" side chain for enhancement of AEM performance. [Display omitted] • Octopus-like side chains are grafted on an ether-free backbone for AEM preparation. • The octopus-type side chains can promote micro-phase separation. • The octopus side chain AEM exhibits a high hydroxide ion conductivity (121.5 mS cm−1 at 80 °C). • The H 2 –O 2 fuel cell employing the above AEM yields a power density of 469 mW cm−2 at 60 °C. [ABSTRACT FROM AUTHOR]

To break the alkaline stability limitation of aryl-ether cleavage in anion exchange membranes (AEMs), novel electron-withdrawing C O link-free polymer backbone with spacer-tunable branched ionic side-chain is synthesized via the Leuckart-Menshutkin route. Density functional theory studies show that replacing C O links in conventional poly(aryl ether ketone)s (PAEKs) with electron-donating C–NH 2 groups followed by grafting long flexible spacer cationic side chain can not only elevate the barrier height of aryl-ether cleavage by increasing electron cloud density on the ether-connected carbon atom, but also result in higher barrier height of quaternary ammonium (QA) group degradation by providing stronger steric hindrance effect and higher lowest unoccupied molecular orbital (LUMO) energy. Long pendant QAs also facilitate microphase separation and ion conduction. The PEAM-2C6 AEM with flexible hexyl-spacer branched cationic side chain achieves high ion conductivity (128.2 mS cm−1 at 80 °C), as well as excellent alkaline stability (no backbone degradation and 81% retaining of original conductivity) after immersion in 4 M KOH at 80 °C for 400 h. H 2 /O 2 fuel cell assembled with PEAM-2C6 exhibits a maximum peak power density of 499 mW cm−2 at 80 °C. Electron-withdrawing link-free strategy provides an effective way to fabricate alkaline stabilized polyelectrolytes along with high ion conductivity. Image 1 • Novel electron-withdrawing C O links free AEMs with branched cationic side chain. • Resulting AEMs exhibit no backbone degradation at 80 °C for 400 h. • Aryl-ether cleavage is suppressed by higher electronic density on neighboring carbon. • Branched cationic side chain improves microphase-separation and conductivity. • No backbone degradation in 4 M KOH and high conductivity of 128.2 mS cm−1 at 80 °C. [ABSTRACT FROM AUTHOR]

• COF based proton permselective membranes are designed for flow batteries. • Precise H+/Vn+ sieving is achieved by appropriate pore size (0.48 nm) of COF. • No vanadium permeation can be detected for the membrane. • Cell with the membrane shows improved efficiencies and long-term cycle stability. Covalent organic framework (COF) based proton permselective membranes are for the first time designed to break through the trade-off between proton permeability and selectivity for improved efficiencies of acid supporting redox flow batteries (the representative one is all vanadium redox flow battery). The precise hydrated proton (<0.24 nm)/vanadium (>0.6 nm) sieving is achieved originating from the appropriate pore size (0.48 nm) of COF prepared here. As a result, no vanadium permeation can be detected for the membrane. While, the presences of micropores and the amino groups in COF lead to a low area resistance. The cell assembled with this membrane presents very high coulombic efficiency (CE: 98.7–99.6%) and energy efficiency (EE: 93.5–76.4%) at 40–180 mA cm−2. In addition, the membrane is free of ion exchange groups, leading to excellent chemical stability. The membrane structure shows no changes after the cell steadily runs over 500 cycles (>1300 h) at 80 mA cm−2. This work provides a new orientation to design a membrane with an ultrahigh proton permselectivity for redox flow batteries. [ABSTRACT FROM AUTHOR]

Although N-spirocyclic cation exhibits superior alkaline stability, its rigidity leads to low conductivity and mechanical stability in anion exchange membranes (AEMs). Herein, N-spirocyclic cationic side chain with novel -NH-(CH 2) x -NH- spacer is proposed to promote hydrogen bond networks and flexible aggregation of ionic clusters in AEMs. Chloromethyl N-spirocyclic cation is synthesized and bonded with diamines of different lengths to achieve benzyl free N-spirocyclic side chain, as well as to tune the length of the side chains. Molecular dynamic simulation suggests that amino groups induce hydrogen bond networks with water to broaden hydrophilic pathways for hydroxide ions conduction. Trade-off between diffusion coefficient and solubility parameter of the side chain is proposed to demonstrate the side chain-backbone interaction and thus the effects of spacer length on the aggregation of ionic clusters. It coincides well with the experimental results that PSF-C6-ASD with -NH-(CH 2) 6 -NH- spacer exhibits the largest ion clusters (about 8.5 nm) and the highest OH− conductivity (107.1 mS cm−1 at 80 °C), as well as excellent elongation at break (38.3%) and alkaline stability (tolerance to 8 M hot KOH). The properties are better than that of the previously reported N-spirocyclic based AEMs. Image 1 • N-spirocyclic cationic side chains with novel -NH-(CH 2) x -NH- spacer are prepared. • Hydrogen bond networks via -NH- broaden hydrophilic pathways for OH− conduction. • MD simulation demonstrates effect of spacer length on aggregation of ionic clusters. • Membrane properties are better than that of previous reported N-spirocyclic AEMs. [ABSTRACT FROM AUTHOR]