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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]

Hydroxide exchange membrane fuel cells (HEMFCs) are attracting growing interest owing to their advantages such as low cost and high power density. However, their applications are hindered due to the poor stability of the membrane. Here, we proposed a novel strategy to improve the alkaline stability of hydroxide exchange membranes (HEMs) using the interactions between strongly polar nitrile groups and side-chain functional cations. A poly(ether nitrile) (PEN) was synthesized by the polycondensation of bisphenol A and 2,6-difluorobenzonitrile, and then imidazolium and morpholinium functional groups were integrated by the typical chloromethylation-functionalization method. The existence of the interactions between nitrile groups and cation groups i.e. imidazolium and morpholinium, was proved by the density functional theory calculations. The interactions have two positive effects that contribute to the improvement of the alkaline stability of the PEN based membranes. On the one hand, they increase the LUMO energies of the functional groups; and on the other hand they reduce the free volume around hydrated cationic groups. As a result, PEN based membranes showed much better alkaline stabilities compared to the membrane based on commercial polysulfone that has a similar chemical structure. In addition, given similar swelling ratios, PEN based membranes exhibited higher hydroxide conductivities than simple polysulfone based ones. [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]

A novel anion exchange membrane with tri-quaternized side chain has been developed in the present work. Di-cationic quaternary ammonium salt, 1-(4′-{1″-azonia-4″-azabicyclo [2.2.2] octyl} butyl) azonia-4-azabicyclo [2.2.2] octane (AABAA), is synthesized and used as tri-quaternization reagent. The tri-quaternized side chains enhance ionic interactions, which induce good micro-phase separation and excellent swelling resistance. Better aggregation of ionic clusters is observed in transmission electron microscopy (TEM) image in the tri-quaternized poly (ether sulfone) membrane (tri-QPESOH) compared to that in the mono-quaternized membrane (mono-QPESOH). Tri‐QPESOH membranes achieve a well-balanced performance between high hydroxide conductivity and dimensional stability. Especially, the tri-QPESOH membrane with IEC 2.31 mmol g −1 exhibits high hydroxide conductivity of 45.9 mS cm −1 at 25 °C and 130.9 mS cm −1 at 80 °C, and low swelling ratio of 21.5% even at 80 °C. Tri-QPESOH membranes also show improved thermal, mechanical and chemical stabilities. These observations suggest that the tri-cationic side chains provide a promising solution to the electrochemical-mechanical balance of anion exchange membranes. [ABSTRACT FROM AUTHOR]

An imidazolium-functionalized poly(ether ether ketone) containing a long spacer chain between imidazolium group and polymer main-chain (PEEK-AeImBr) was synthesized by the reaction of chloromethylated PEEK and self-synthesized 1-Aminoethyl-2,3-dimethylimidazolium bromide. 1 H NMR spectra confirmed the successful synthesis of PEEK-AeImBr. The corresponding PEEK-AeImOH HEM was prepared by casting the PEEK-AeImBr solution and subsequent ion-exchange process. Ion exchange capacity (IEC) of PEEK-AeImOH membranes ranges from 1.50 to 2.07 mmol g −1 with the degree of chloromethylation from 58% to 92%. Hydroxide conductivity of PEEK-AeImOH membranes increases with increasing IEC. PEEK-AeImOH membrane with IEC of 2.07 mmol g −1 has the highest conductivity of 48 mS cm −1 . The spacer-modified PEEK-AeImOH membrane maintained good alkali stability at 60 °C. The H 2 /O 2 single cell with the PEEK-AeImOH membrane exhibits high open circuit voltage of 1.02 V and peak power density of 120 mW cm −2 at room temperature. [ABSTRACT FROM AUTHOR]

High-performance anion exchange membranes (AEMs) are in need for practical application of AEM fuel cells. Novel branched poly(ether ether ketone) (BPEEK) based AEMs were prepared by the copolymerization of phloroglucinol, methylhydroquinone and 4,4′-difluorobenzophenone and following functionalization. The effects of the branched polymer structures and functional groups on the membrane's properties were investigated. The swelling ratios of all the membranes were kept below 15% at room temperature and had good dimensional stability at elevated temperatures. The branching degree has almost no effect on the dimensional change, but plays a great role in tuning the nanophase separation structure. The cyclic ammonium functionalized membrane showed a lower conductivity but a much better stability than imidazolium one. The BPEEK-3-Pip-53 membrane with the branching degree of 3% and piperidine functionalization degree of 53% showed the best performances. The ionic conductivity was 43 mS cm−1 at 60 °C. The ionic conductivity in 1 M KOH at 60 °C after 336 h was 75% of its initial value (25% loss of conductivity), and the IEC was 83% of its initial value (17% loss of IEC), suggesting good alkaline stability. The peak energy density (60 °C) of the single H 2 /O 2 fuel cell with BPEEK-3-Pip-53 membrane reached 133 mW cm−2 at 260 mA cm−2. • A novel branched poly(ether ether ketone) based AEM was prepared. • The branched AEMs showed high conductivity and low swelling ratio. • A high peak power density was achieved for single cell with the branched AEM. [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]

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]

An effective soft-template strategy using Zn2+ metal ions is proposed to construct well-ordered ionic conductive channels in the imidazolium (Im+) functionalized polysulfone anion exchange membranes (AEMs). The divalent Zn2+ ion possesses strong electrostatic interactions to induce better microphase separation. The further removal of the sub-nanoscale water-soluble Zn2+ ions introduces free volumes to connect ionic pathways, meanwhile promotes the secondary aggregation of Im+ groups. Experiment and simulation show that Zn2+ ions organize into Zn2+ self-aggregations and interact with Im+ groups via an electrostatic anion-bridged configuration in the Zn2+ incorporated membranes, and the subsequent Zn2+ removal increases the free volume and induces the rearrangement of Im+ groups to form bigger ionic clusters (up to 7.7 nm) than those in the pristine membrane. By optimizing Zn2+ content, the induced ionic conductive channels are tailored, yielding a 50% improvement of hydroxide conductivity and achieving the top level in the previously reported polysufone-based main-chain-type AEMs. This study suggests a novel and scalable route for regulating micro-phase separations in AEMs and provides theoretical exploration for selecting effective template molecules. [Display omitted] • Ionic channels in the AEMs are constructed using Zn2+ ions as the soft template. • Im+ groups are electrostatically assembled surrounding the Zn2+ template. • The removal of the Zn2+ template enlarges Im+ clusters and free volume. • Ionic channels are optimized by Zn2+ content, enhancing ion transport in the AEMs. [ABSTRACT FROM AUTHOR]

Morpholinium-functionalized cross-linked poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) anion exchange membranes were prepared using a crosslinking/post-functionalization method. 4,4'-(oxybis(ethane-2,1-diyl)) dimorpholine (OEDM) having a flexible long chain and hydrophilic ether bond was for the first time used as the crosslinker. The brominated PPO reacted with OEDM, forming a crosslinked structure and accomplishing partial functionalization. Further functionalization was carried out by immersion in N-methylmorpholine aqueous solution. The degree of crosslinking was controlled by varying the proportion of brominated PPO to OEDM because excessive bromomethyl groups ensured the occurrence of crosslinking reaction. The cross-linked structure promoted the formation of micro-phase separation and effectively limited swelling. The crosslinked membrane shows much higher conductivity and lower swelling ratio compared to non-crosslinked one at similar IEC. The highest hydroxide conductivity that the crosslinked membrane achieves is 35 mS cm−1 at 20 °C. The power density for the H 2 /O 2 single cell assembled with this membrane is up to 193 mW cm−2. In addition, the crosslinked PPO-MmOH-Cr membrane exhibits good alkaline stability with conductivity loss of less than 15% after soaking in 1 M KOH for 96 h. • A crosslinking/post-functionalization method was proposed to prepare crosslinked AEM. • The conductivity and swelling resistance were simultaneously improved. • The single cell with this membrane showed a decent power density. [ABSTRACT FROM AUTHOR]

N-spirocyclic cations containing anion exchange membranes (AEMs) possess excellent alkaline stability, but poor mechanical and conductive properties due to the rigid N-spirocyclic structure and lack of flexible side chain structural design. In this work, a flexible ether spaced N-spirocyclic quaternary ammonium functionalized side chain is proposed, in which hydroxyl substituted N-spirocyclic cation provides active grafting site with chloromethylated polysulfone through Williamson etherification. The flexible ether-oxygen spacer promotes aggregation of the rigid spirocyclic cations and thus significantly improves conductivity. The uniformly in-situ thermal crosslinking between benzene rings and the residue chloromethyl groups in polysulfone greatly enhances mechanical properties of the membranes. Constrained ring conformation of N-spirocyclic cation, ether spaced benzyl-free side chain, as well as the OH− blocking crosslinked networks endow an excellent alkaline stability to the membranes. The ether spaced N-spirocyclic containing membranes exhibit well micro-phase separation structure, up to around 85.7 mS cm−1 of hydroxide conductivity at 80 oC, around 10.5 MPa of tensile strength in hydrated state and around 95.6% conductivity retention after immersion in 1 M KOH at 80 oC for 720 h. The performance is among the best N-spirocyclic functionalized AEMs reported in the literature. Image 1 • Crosslinked AEMs with ether spaced N-spirocyclic cationic side chain are proposed. • Flexible ether spacer promotes rigid spirocyclic cations to aggregate into cluster. • In-situ thermal treatment provides crosslinking networks for mechanical properties. • Benzyl-free spirocyclic cation and OH− blocked crosslinking endow alkaline stability. [ABSTRACT FROM AUTHOR]

To improve low-efficiency and durability for alkaline membrane water electrolysis, novel piperidinium functionalized SEBS (SEBS-Pi) alkali membrane was prepared. The membrane not only displayed high conductivity (>10 mS cm−1 at 30 °C), but possessed excellent thermal stability and mechanical properties. Alkali resistance test lasts 576 h in 1 M KOH at 80 °C, high retentions of IEC as well as conductivity and no obvious change in FT-IR spectra suggest good alkaline resistance of SEBS-Pi membrane. Good three phase reaction boundary in catalyst layers and packing between the membrane and catalyst layers are formed when SEBS-Pi is used as both membrane and ionomer. A good performance of water electrolysis is achieved (400 mA cm−2 at 2 V, 50 °C). During a long-term electrochemical stability test carried out with current density of 400 mA cm−2 at 50 °C for 105 h, the voltage remained almost constant (around 2.08 V), indicating good cell durability. All these indicate that SEBS-Pi has a good potential for applications in water electrolysis. • Novel piperidinium functionalized SEBS membrane was prepared. • The membrane shows high conductivity and good alkaline stability. • The cell with this membrane shows excellent electrochemical performances. [ABSTRACT FROM AUTHOR]

Abstract Novel electrospun inorganic-organic nanofiber reinforced anion exchange membranes were developed by incorporating imidazolium functionalized multiwalled carbon nanotubes (FMWCNTs) into imidazolium functionalized polysulfone nanofibers via co-electrospinning. Under a high-voltage electrostatic field, FMWCNT inorganic nanofibers were able to align along the axis of the electrospun nanofibers, thereby solving the problem of easy agglomeration of FMWCNTs in cast-composite anion exchange membrane, synergistic with the polymer nanofibers to reinforce the membranes. Small angle x-ray suggests that ion clusters are more likely to aggregate in a co-electrospun composite membrane, indicating continuous and lower-energy-barrier pathways for hydroxide transport. As a result, composite electrospun membranes exhibit higher OH− conductivity and better single fuel cell performance. With an additive amount of 0.4 wt.%, hydroxide conductivity reaches a maximum value of 67.5 mS cm−1 (30 °C). However, the maximum power density (102.5 mWcm−2) is much higher than that of the electrospun (2.1 times) and cast (3.3 times) membranes without FMWCNTs. Fibration of polymer and alignment of multiwalled carbon nanotube nanofibers also greatly enhance the membrane strength. For fully hydrated membranes, tensile stress dramatically increases from 5.6 MPa for a cast membrane without FMWCNTs to 24.4 MPa for an electrospun membrane with 0.4 wt.% FMWCNTs addition. The strategy for co-electrospinning of imidazolium functionalized multiwalled carbon nanotubes/polysulfone presented in this work provides a way to enhance the organic-inorganic interface compatibility, and improve ionic conductivity and mechanical strength of anion exchange membrane simultaneously. Highlights • Electrospun functionalized MWCNT/IMPSf AEM was fabricated by electrospinning. • FMWCNTs align along IMPSf fiber axis, synergistic with the nanofibers to reinforce the membranes. • 2.1 and 3.3 times hydroxide conductivity as that of electrospun and cast AEMs without FMWCNT. • 1.5 times and 3.4 times tensile stress as that of electrospun and cast AEMs without FMWCNT [ABSTRACT FROM AUTHOR]

A novel strategy was proposed to construct a bicontinuous hydrophilic/hydrophobic micro-phase separation structure which is crucial for high hydroxide conductivity and good dimensional stability anion exchange membranes (AEMs). A semi-flexible poly (aryl ether sulfone) containing a flexible aliphatic chain in the polymer backbone with imidazolium cationic group was synthesized by the polycondensation of bis(4-fluorophenyl) sulfone and the self-synthesized 4,4′-[butane-1,4-diylbis(oxy)] diphenol followed by a two-step functionalization. The corresponding membranes were prepared by solution casting. More continuous hydroxide conducting channels were formed in the semi-flexible polymer membranes compared with the rigid based ones as demonstrated by TEM. As a result, given the same swelling ratio, hydroxide conductivity of the semi-flexible polymer membrane was about 2-fold higher than the one of the rigid polymer based membrane (e.g., 45 vs. 22 mS cm −1 with the same swelling ratio of 24% at 20 °C). The highest achieved conductivity for the semi-flexible polymer membranes at 60 °C was 93 mS cm −1 , which was much higher those of other random poly (aryl ether sulfone) based imidazolium AEMs (27–81 mS cm −1 ). The single cell employing the semi-flexible polymer membrane exhibited a maximum power density of 125 mW cm −2 which was also higher than those for other random poly (aryl ether sulfone) based imidazolium AEMs (16–105.2 mW cm −2 ). [ABSTRACT FROM AUTHOR]

Hydroxide exchange membrane fuel cells (HEMFCs) receive growing interest due to the usability of non-precious metal catalysts in the basic operating environment. The applications of HEMFCs are hindered by the trade-off between high hydroxide conductivity and good dimensional stability of the HEMs. Here, a novel poly(2,6-dimethyl-1,4-phenylene oxide) with imidazolium-terminated long side chains (PPO-COC 5 H 10 -Im) was synthesized by simple and controllable acetylation reaction of PPO and 6-bromohexanoyl chloride in a moderate condition (at room temperature), followed by the Menshutkin reaction with 1,2-dimethylimidazole. The introduction of long chains between imidazolium groups and polymer main chains facilitates the formation of good hydrophilic/hydrophobic micro-phase separation structure, which is illustrated by TEM. The hydroxide effective mobility in PPO-COC 5 H 10 -Im membrane is almost 2-fold that in short side chain imidazolium functionalized PPO (PPO-CH 2 -Im) membrane at a certain IEC. Given similar swelling ratios (25% vs. 27%), PPO-COC 5 H 10 -Im membrane shows much higher hydroxide conductivity than PPO-CH 2 -Im membrane (62 vs. 42 mS cm −1 ) at 60 °C. It indicates that the PPO-COC 5 H 10 -Im membranes prepared here exhibits highly enhanced conductivity without sacrificing the dimensional stability. [ABSTRACT FROM AUTHOR]

A series of novel bis-imidazolium crosslinked polysulfone membranes (CL-PSf-ImOHs) membranes were prepared through simultaneous quaternization and crosslinking reactions of 4,4′-bis(2-methylimidazole-1-ylmethyl)diphenyl (bis-Im-diPh) and chloromethyl groups on the polymer during the membrane formation. The novel bis-Im-diPh crosslinker possesses a rigid bis-phenyl structure, which creates large free volume and leads to the formation of continuous hydroxide conducting channels in the membrane as demonstrated by TEM. The properties of the crosslinked membrane were controlled by varying the molar ratio ( R d/c ) of bis-Im-diPh and chloromethyl groups from 0.18 to 0.33. With increasing R d/c , the swelling ratio decreases, and the hydroxide conductivity increases. The CL-PSf-ImOH membrane with R d/c of 0.33 exhibits the conductivity of 112 mS cm −1 at 60 °C, much higher than that of non-crosslinked membrane (83 mS cm −1 , losing its morphology at 60 °C) and those of other crosslinked membranes (17–68 mS cm −1 ) prepared with the similar methods. In addition, the CL-PSf-ImOH membranes show good dimensional stability at elevated temperatures. [ABSTRACT FROM AUTHOR]

• A high-strength hydrophobic backbone and a hydrophilic side chains were combined. • Membrane with low swelling, permeability and high stability were achieved. • The VE of NAORFB with the membrane is advantages over other best-performed batteries. Neutral aqueous organic redox flow battery (NAORFB) has been considered as a promising energy-storage device in the stationary storage field. Yet the insufficient Cl− conductivity of anion exchange membrane (AEM) has become a crucial obstacle for neutral energy systems compared to their counterparts, such as H+ and OH– in acidic and alkaline conditions, respectively. Here, by proper microstructure design in AEM, a membrane with high Cl− conductivity is constructed by coupling the hydrophobic fluorinated poly(arylene ether) backbone and hydrophilic piperazinium groups, which exhibits excellent Cl− conductivity up to 55.9 mS cm−1 at room temperature. Moreover, the developed piperazinium functional fluorinated poly(arylene ether) (QPFPAE) membrane exhibits excellent low swelling, low organic redox-active species permeability, and high chemical stability. The constructed NAORFB using QPFPAE membrane shows a remarkable energy efficiency (85.6% at 80 mA cm−2), which has outperformed the other best-performing membranes. In addition, the membrane demonstrates outstanding stability and state-of-the-art performance over 1000 charge–discharge cycles. This work provides a rational design strategy toward high anion-selective conductivity in the membrane for large-scale NAORFB development. [ABSTRACT FROM AUTHOR]

[Display omitted] • π-conjugation and steric structural factors of cations contribute to water sorption. • Interchain interactions are enhanced by π-conjugation but weakened by steric effect. • Structural factor also affects cationic hydration and location in the water phase. • Schematic water sorption mechanism and hydrophilic channel morphology are proposed. Water sorption heavily influences the ionic conduction and dimensional stability of anion exchange membranes (AEMs), however, it is extremely difficult to investigate the structural contributions of different cationic groups to water sorption with only experiments. Here, with the aid of density functional theory (DFT) and molecular dynamics (MD) simulations, such typical structural characteristics as π-conjugated ring and steric hindrance were extracted; and trimethylammonium (QA), 1-methylimidazolium (Im) and tris(2,4,6-trimethoxyphenyl) phosphonium (QP) were investigated as the model cations. It was found that water molecules tend to first fill into the free volume of the AEMs, while the equilibrium water content is the overall result of interchain interactions, cationic hydration, and cationic location in the hydrophilic phase. The interchain interactions (Im > QA > QP) are enhanced by the π-conjugated ring but weakened by the steric hindrance, whereas the cationic hydrations (QA > Im > QP) are reduced by the π-conjugation and steric effects. Accordingly, schematics of the water sorption mechanism and hydrophilic channel morphology are proposed to clarify the impact of cationic structural features on ion conductivity. [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]

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]

Anion exchange membranes (AEMs) are an important component in anion exchange membrane fuel cells, and their side chain structures have a significant impact on membrane performance. Here, we construct a series of poly(phenylene oxide) (PPO)-based AEMs with varied side chain structures and investigate the effects of alkyl or alkoxyl extenders (or "tail" of the cation) and spacers (or the link between backbone and cation head group) on AEM performance. Our investigations demonstrate that the simultaneous introduction of alkoxyl extender and spacer can significantly improve water absorption and ion conductivity of membrane; this is attributed to the good hydrophilicity of alkoxyl group and flexibility of spacer that benefit the formation hydrophilic domains. At an IEC (ion exchange capacity) of 1.13 mmol/g, the AEM containing both spacer and alkoxyl extender exhibits a hydroxide conductivity of 87.3 mS/cm (80 °C), which is much higher than that of other spacer-containing membranes at similar IECs. The H 2 /O 2 single cell constructed with this membrane exhibits a good peak power density of 292 mW/cm2 at 60 °C. In addition, the steric hindrance of the extender gives rise to higher alkali stability of the AEM than that of the membrane which does not have the extender. Our work provides a meaningful direction of side chain design which can effectively improve conductivity and alkaline stability of AEMs. Image 1 • Alkoxy extender and alkyl spacer were co-introduced into anion exchange membrane. • Alkoxy extender and alkyl spacer can synergistically improve ion conductivity and chemical stability of membrane. • The highest conductivity of 87.3 mS/cm at 80 °C was obtained at a low IEC of 1.13 mmol/g. • The H 2 –O 2 fuel cell employing the above AEM yielded a power density of 292 mW/cm2 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]

N-spirocyclic cations possess double-cyclic non-planar structure that exhibit the highest alkali stability among quaternary ammonium cations, however, the extremely rigidity usually causes fragile membranes and poor conductivity. In this work, a rod-coil grafts design is proposed for N-spirocyclic anion exchange membranes (AEMs), in which microphase separation of the hydrophilic N-spirocyclic rod grafts is significantly improved by the hydrophobic aggregation of the flexible alkyl coil grafts with polysulfone backbone. Molecular dynamic simulations indicate that the coil grafts contribute to microphase separation but fill in free volume to reduce water reservoir, therefore the rod-coil grafts design provides a way to evaluate the effects of microphase separation and free volume on conductivity. The increasing conductivity with the length of coil grafts suggests a greater contribution of good microphase separation to OH− conduction. With optimized n-octylamine hydrophobic coil graft length, the N-spirocyclic AEM exhibits toughness (elongation at break of about 28.7%) and high OH− conductivity (136.2 mS cm−1 at 80 °C), resulting in high power density (850.1 mW cm−2), which is far greater than that assemble with other N-spirocyclic AEMs, and also bring N-spirocyclic AEMs into the top level of the cycloaliphatic AEMs reported in literatures. Image 1 • Rod-coil grafts for robust, high conductive and alkali stable N-spirocyclic AEMs. • Coil grafts join aggregation of hydrophobic domains to enhance microphase separation. • Microphase separation contributes greater than free volume to promote conductivity. • Highest power density is achieved among different N-spirocyclic based fuel cells. [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]