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Abstract Friedel-Crafts alkylation route is proposed to synthesis polysulfone based anion exchange membrane (AEM) containing pendent imidazolium-functionalized side chain with the purpose of avoiding conventional carcinogenic chloromethylation. It has no special functional group requirements on the polymer materials, which has advantage over those reported chloromethylation free routes. A novel flexible alkylation reagent containing -(CH 2) 4 - spacer, (1-chlorobutyl-2,3-dimethylimidazole chloride) is synthesized and promotes hydrophilic/hydrophobic micro-phase separation structure in the membranes proved by small angle X-ray scattering (SAXS) and transmission electron microscopy image (TEM). The imidazolium-functionalized polysulfone AEMs prepared by the Friedel-Crafts alkylation route in this study exhibit first level properties compared to other AEMs prepared without chloromethylation. The ion conductivity-normalized swelling ratio (0.08% cm mS−1 at 80 °C) is the lowest, while exhibits higher or equivalent IEC normalized ion conductivity (56.8 S g cm−1 mol−1 at 80 °C). The membranes prepared in this work also display good thermal, mechanical and alkaline stabilities. Graphical abstract fx1 Highlights • Friedel-Crafts alkylation route to synthesis polysulfone based AEM. • A novel flexible alkylation reagent containing -(CH 2) 4 - spacer. • Obvious hydrophilic/hydrophobic micro-phase separation structure. • Low ion conductivity-normalized swelling ratio. [ABSTRACT FROM AUTHOR]

A novel amphoteric membrane was prepared using imidazolium-functionalized polysulfone (ImPSf) as the base polymer and sulfonated poly (ether ether ketone) (SPEEK) as the acid polymer for vanadium flow battery applications. The introduction of the ImPSf effectively resists the migration of vanadium ions owing to the Donnan repelling effect of the imidazolium cations on the vanadium ions and the low swelling ratio of the amphoteric membranes due to the ionic cross-linked interactions between the imidazolium and sulfonic groups. The amphoteric membrane with an ImPSf mass ratio of 17% shows a vanadium permeability of 1.5 × 10 −8 cm 2 s −1 that is much lower than that of Nafion212 (21 × 10 −8 cm 2 s −1 ). Having a high IEC of 2.04 mmol g −1 , it also exhibits a low area resistance of 0.48 Ω cm −2 that is comparable to that of Nafion212 membrane (0.41 Ω cm −2 ). As a result, the VFB cell with the amphoteric membrane exhibits high performances even at high current densities, i.e. at a current density of 200 mA cm −2 , and the amphoteric membrane achieves a coulombic efficiency of 97.5% and an energy efficiency of 77.3%, both of which are higher than those of Nafion212 (92.4% and 73.4%). These results indicate that the ImPSf/SPEEK amphoteric membrane is promising for VFB applications. [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]

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]

Abstract: A series of quaternary phosphonium-functionalized poly(ether ether ketone)s (PEEK-QPOHs) have been synthesized by phosphorization reaction, and their membranes have been prepared by a solution casting method. Ion exchange capacity (IEC) of PEEK-QPOH membranes ranges from 0.89 to 1.19mmolg−1 with the degree of chloromethylation from 70% to 126%. Not only are PEEK-QPOH polymers soluble in typical high-boiling-point membrane-forming solvents, but also they are soluble in some low-boiling-point water-miscible solvents (low alcohols), implying their ability to serve as both membranes and ionomers. PEEK-QPOH membranes showed high hydroxide conductivity, e.g., a PEEK-QPOH 126% membrane (with IEC of 1.19mmolg−1) exhibited 61 and 89mScm−1 at 20°C and 60°C, respectively. Based on the same polymer backbone of PEEK, quaternary phosphonium-functionalized PEEK membranes are more hydroxide-conductive and more alkali-stable than quaternary ammonium- and imidazolium-functionalized counterparts. All these properties indicate PEEK-QPOH is one of the most promising HEM materials for potential applications in alkaline membrane fuel cells. [Copyright &y& Elsevier]

A series of imidazolium-functionalized poly(ether ether ketone)s (PEEK-ImOHs) were successfully synthesized by a two-step chloromethylation–Menshutkin reaction followed by hydroxide exchange. PEEK-ImOH membranes with ion exchange capacity (IEC) ranging from 1.56 to 2.24 mmol g−1 were prepared by solution casting. PEEK-ImOHs show selective solubility in aqueous solutions of acetone and tetrahydrofuran, but are insoluble in lower alcohols. PEEK-ImOH membranes with IEC of 2.03 mmol g−1 have high hydroxide conductivity (52 mS cm−1 at 20 °C), acceptable water swelling ratio (51% at 60 °C), and great tensile strength (78 MPa), and surprising flexibility (elongation-to-break of 168%), and high thermal stability (Decomposition temperature: 193 °C). In addition, PEEK-ImOH membranes show low methanol permeability (1.3–6.9 × 10−7 cm2 s−1). PEEK-ImOH membrane was tested in methanol/O2 fuel cell as both the HEM and the ionomer impregnated into the catalyst layer; the open circuit voltage is 0.84 V and the peak power density is 31 mW cm−2. [ABSTRACT FROM AUTHOR]

Abstract: Water sorption, water transport and ion transport are compared for polyether–ether ketone polymers functionalized with sulfonic acid, quaternary amine hydroxide, and imidazolium hydroxide. Water sorption in all three ionomers increases modestly with increasing water activity up to a w =0.6 and then increases more rapidly between 0.60.6. The increase in ion conductivity with increasing water activity is 10 times greater for the proton exchanged polymer compared to the hydroxide exchanged polymers. Water permeation from partially saturated vapor streams is primarily diffusion limited for all three ionomers and the permeation rates were approximately the same. Water pervaporation from liquid water appeared to be interfacial transport limited for membranes<120μm thick; the pervaporation rates at 40 and 60°C were independent of membrane thickness. Water sorption and transport show little dependence on the mobile ion while the ion transport appears to depend on both ion size and hydrophilicity of the fixed ion. [Copyright &y& Elsevier]

Abstract: A series of imidazolium-functionalized polysulfones were successfully synthesized by chloromethylation-Menshutkin two-step method. PSf-ImOHs show the desired selective solubility: insoluble in alcohols (e.g., methanol and ethanol), and soluble in 50 vol.% aqueous solutions of acetone or tetrahydrofuran, implying their potential applications for both the alcohol-resistant membranes themselves and the ionomer solutions in low-boiling-point water-soluble solvents. PSf-ImOH also possesses very high thermal stability (T OD: 258 °C), higher than quaternary ammonium and quaternary phosphonium functionalized polysulfones (T OD: 120 °C and 186 °C, repsectively). Ion exchange capacity (IEC) of PSf-ImOH membranes ranges from 0.78 to 2.19 mmol g−1 with degree of chloromethylation from 42% to 132% of original chloromethylated polysulfone. As expected, water uptake, swelling ratio, and hydroxide conductivity increase with IEC and temperatures. With 2.19 mmol g−1 of IEC, the PSf-ImOH 132% membrane exhibits the highest hydroxide conductivity (53 mS cm−1 at 20 °C), higher than those of all other reported polysulfone-based HEMs (1.6–45 mS cm−1) and other imidazolium-functionalized HEMs (19.6–38.8 mS cm−1). In addition, PSf-ImOH membranes have low methanol permeability of 0.8–4.7 × 10−7 cm2 s−1, one order of magnitude smaller than that of Nafion212 membrane. All these properties indicate imidazolium-functionalized polysulfone is very promising for potential applications in alkaline membrane direct alcohol fuel cells. [Copyright &y& Elsevier]

A long-side-chain sulfonated polybenzimidazole (PBI-PS) membrane was successfully prepared by the reaction of PBI with 1, 3-propanesultone for improving the efficiencies of vanadium redox flow battery. The interaction between sulfonic acid and imidazole groups provides the PBI-PS membrane with excellent swelling resistance, leading to a swelling ratio of only 13% for the membrane with IEC of as high as 3.18 mmol g−1. This results in an ultra-low vanadium permeability (6.5 × 10−9 cm2 s−1). The introduction of sulfonic acid-terminated flexible side chain in the membrane also constructs good microphase separation structure, leading to a low area resistance of 0.51 Ω cm2, which is close to Nafion 212 (0.41 Ω cm2). This membrane exhibits excellent cell performance. The voltage and energy efficiencies are up to 90.73% and 89.13% at 80 mA cm−2, respectively. Furthermore, the efficiencies remain constant values for 200 cycles, and no changes in chemical structure and cell efficiencies are observed after 720 h immersion in electrolyte solution. • Long-side-chain sulfonated polybenzimidazole membrane was prepared for RFB. • High conductivity and vanadium resistance were achieved. • The cell with this membrane exhibited high efficiencies and good stability. [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]

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]

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]