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A new series of poly(arylene piperidinium)-based anion exchange membranes (AEMs) are proposed for vanadium redox flow batteries (VRFBs). The AEMs are fabricated via the Menshutkin reaction between poly(arylene piperidine) without ether bonds in the backbone and various quaternizing agents, including iodomethane, 1-bromopentane, and (5-bromopentyl)-trimethylammonium bromide. The properties of the AEMs are investigated in terms of sulfuric acid doping content, swelling, vanadium permeability, ion selectivity, area-specific resistance, mechanical properties, VRFB performance, and cyclic testing. Particularly, a method of measuring the H+ permeability of the AEM is developed. It demonstrates that the poly(p-terphenyl-N-methylpiperidine)-quaternary ammonium (PTP-QA) membrane with a QA cation-tethered alkyl chain exhibits high H+ permeability, resulting in low area resistance. Combined with its low vanadium permeance, the PTP-QA membrane achieves nearly 370 times higher ion selectivity than Nafion 115. The VRFB based on PTP-QA-based AEM displays high Coulombic efficiencies above 99% at current densities of 80–160 mA cm−2. The higher energy efficiency of 89.8% is achieved at 100 mA cm−2 (vs. 73.6% for Nafion 115). Meanwhile, the PTP-QA-based AEM shows good cycling stability and capacity retention, proving great potential as the ion exchange membrane for VRFB applications.

The polybenzimidazoles represent a large family of high-performance polymers containing benzimidazole groups as part of the structural repeat unit. New application areas in electrochemical cells and separation processes have emerged during the last two decades, which has been a major driver for the tremendous development of new polybenzimidazole chemistries and materials in recent years. This comprehensive treatise is devoted to an investigation of the structural scope of polybenzimidazole derivatives, polybenzimidazole modifications and the acid-base behavior of the resulting materials. Advantages and limitations of different synthetic procedures and pathways are analyzed, with focus on homogeneous solution polymerization. The discussion extends to the solution properties of the obtained polybenzimidazoles and the challenges that are faced in connection to molecular weight determination and processing. Methods for polybenzimidazolegrafting or crosslinking, in particular by N-coupling, are reviewed and successful polymer blend strategies are identified. The amphoteric nature of the benzimidazole groups further enriches the chemistry of the polybenzimidazoles, as cationic or anionic ionenes are obtained depending on the pH. In the presence of protic acids, such as phosphoric acid, cationic ionenes in the form of protic polybenzimidazoliums are obtained. The acid sorption dramatically changes the physicochemical properties of the material, which is discussed and analyzed in detail. Cationic ionenes are also obtained by full N-alkylation of a polybenzimidazole to the corresponding poly(dialkyl benzimidazolium), which has been intensively explored as a new direction in the field of anion exchange membranes recently. In the higher end of the pH scale in aqueous hydroxide solutions, anionic ionenes in the form of polybenzimidazolides are obtained as a result of the deprotonation of the benzimidazole groups. The ionization of the polymer results in dramatically changed physicochemical properties as compared with the pristine material, which is described and discussed. From a technological point of view, performance and stability targets continue to motivate further research and development of new polybenzimidazole chemistries and energy materials The overall aim of this review is therefore to identify challenges and opportunities in this area from synthetic chemistry and materials science perspectives to serve as a solid basis for further development prospects. &nbsp

Two ether-free poly(bis-alkylimidazolium) ionenes with imidazolium cations as part of the main chain were synthesized from 1,4-bis(imidazolyl)butane and 1,4-dibromobutane or 1,4-bis(bromomethyl)benzene via nucleophilic substitution polymerization. Anion exchange membranes (AEMs) were prepared by co-casting with polybenzimidazole (PBI), producing visually homogeneous and mechanically robust blend AEMs. The ion exchange capacity (IEC), water uptake and ion conductivity could be balanced by adjusting the molar ratio of the poly(bis-alkylimidazolium) to PBI polymer in the blend. For example, the blend AEM of PBuIm-37%/PBI prepared from the oligomer derived from 1,4-dibromobutane with an IEC of 1.36 mmol g−1 showed a tensile strength of 5.3 MPa at room temperature and a hydroxide conductivity of 74 mS cm−1 at 80 °C and excellent stability over 500 h in 1 mol L−1 KOH at 60 °C. The present work opens up a new route towards ether-free AEM design and fabrication with a wide potential structural scope.

Developing high temperature proton exchange membranes (HT-PEMs) with high conductivity and mechanical strength simultaneously is a considerable challenge for the HT-PEM fuel cell (HT-PEMFC). Herein, a 1-(3-aminopropyl)imidazole (APIm) functionalized low-cost poly(vinyl chloride) (PVC) membrane (PVC-APIm) with superior phosphoric acid (PA) doping content and high proton conductivity is synthesized via a gentle and facile method with no need for the chloromethylation procedure. The poly(ether ketone cardo) (PEK-C) polymer is blended with PVC-APIm to provide sufficient mechanical robustness. Interestingly, blending PEK-C not only improves the mechanical stability, but also increases the PA doping content of membranes. As a result, PA doped PVC-APIm/x%PEK-C membranes possess increased tensile strength and upgraded conductivity simultaneously. The PVC-APIm/10%PEK-C/166%PA membrane exhibits a low area swelling of 45%, high conductivity of 0.132 S cm−1 at 180 °C and suitable tensile strength of 11.8 MPa at room temperature. The single cell performance of this membrane demonstrates the technical feasibility of the PVC-APIm/x%PEK-C/PA membrane for the HT-PEMFC.

Partially crosslinked anion exchange membranes (AEMs) with imidazolium-based cationic functionalities were fabricated based on a poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) matrix. The PPO was activated by bromomethylation and functionalized with methylimidazole and 1,4-bis(imidazolyl)butane at different ratios through a gentle and facile heat curing method. The use of 1,4-bis(imidazolyl)butane resulted in a membrane with cationic functionalities incorporated in covalent crosslinks, which allowed for high ion exchange capacities (IECs) without compromising on mechanical robustness. Comprehensive characterizations were performed in terms of thermal stability, water uptake, IEC, swelling, conductivity, mechanical properties and alkaline stability to investigate the correlation of the structure and physicochemical properties. Comparing with the un-crosslinked imidazolium PPO membrane, crosslinked membranes exhibited improved mechanical robustness and alkaline stabilities. The membrane with a crosslinking degree of 10% displayed an IEC of around 1.5 mmol g−1, tensile strength of 4.1 MPa, hydroxide ion conductivity of 40.5 mS cm−1, and a retained ratio in conductivity of 40% after tolerance test of nearly 150 h in 1 mol L−1 KOH (aq.) at 60 °C.

The inhibition mechanism of a high-efficiency corrosion inhibitor (sodium dodecyl sulfate, SDS) is unveiled and the strategy to design effective inhibitors for Mg alloys is suggested. It was found that SDS is chemically absorbed on the cathodic intermetallics to inhibit micro-galvanic corrosion. Anodic Mg dissolution is also kinetically suppressed by physisorption of SDS since the long hydrophobic tail of the surfactant contributes to building up a protective corrosion layer. Utilization and synthesis of such green inhibitors can pave the way for a wider range of applications for Mg alloy and provide active corrosion protection for coated Mg surfaces.

Developing anion exchange membranes (AEMs) with a long lifespan is a considerable challenge for the electrolyte material in the alkaline water electrolysis. Herein, the methylpyrrolidinium cation functionalized poly(vinyl benzyl chloride) (PVBC-MPy) membrane with high alkaline stability and ion conductivity simultaneously was synthesized through a facile, gentle and non-carcinogenic chemical method. A poly(ether ketone-cardo) (PEK-cardo) polymer was blended with PVBC-MPy to provide sufficient mechanical robustness for integration and testing in AEM water electrolysis. The PVBC-MPy/x%PEK-cardo membranes showed excellent alkaline stability with no obvious degradation after immersing in 1 mol L−1 KOH at 60 °C and 80 °C for more than 500 h. The PVBC-MPy/35%PEK-cardo membrane exhibited a good balance between high ion conductivity and mechanical strength, and was down-selected for electrolysis testing in 1 M KOH at 60 °C. The cell polarization curves of the AEM water electrolysis indicated that the membrane displayed good cell performance with a current density of 500 mA cm−2 at 2 V at 60 °C. Moreover electrochemical impedance spectroscopy and the cell voltage lifetime test illustrated the feasibility of the membrane operating under mildly alkaline conditions.

Poly(vinylpyrrolidone) (PVP), as the low-cost and commercial material, exhibits superior phosphoric acid doping capability due to the presence of heterocycle and carbonyl groups in the repeat unit. However, it can’t be used as the high temperature polymer electrolyte membrane (HT-PEM) alone because of its significant hydrophilicity and poor mechanical stability. In the present work, polyethersulfone (PES), polysulfone (PSU), polyetherketone-cardo (PEK-c), polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride-co-hexafluoropropylene) (PHFP), five kinds of engineering thermoplastics with excellent mechanical properties and chemical inertness, are chosen to prepare a series of PVP blend membranes by the polymer blending method in order to enhance the dimensional and mechanical stabilities of PVP based membranes. The influence of structures of enhanced polymers on properties of HT-PEMs was investigated systematically. PVP blend membranes with aromatic polymers (i.e. PES, PSU and PEK-c) exhibited decreased volume swellings, increased acid doping contents, superior conductivities and improved mechanical strengths, which determined that they are more suitable for electrolytes of fuel cell applications comparing with PVP/PVDF and PVP/PHFP membranes blended with aliphatic polymers.

Anion exchange membranes with star main chains or side chains were prepared by grafting the 1-butyl-2-methylimidazole and/or 1-aminopropyl-2-methyl-3-butylimidazolium hydroxide onto branched or linear poly(aryl ether ketone) polymers. In order to know the influence of the star structures on the physicochemical properties of the prepared membranes, comprehensive characterizations were made including ion exchange capacity, conductivity, mechanical property and alkaline stability. All the membranes exhibit conductivities of about 40 mS cm−1 at 60 °C and about 60 mS cm−1 at 80 °C, respectively. The durability of the membranes in alkaline medium was detected by monitoring the changes in conductivity, ion exchange capacity and contact angle with water. The results indicate that the introduced star structures of both main chains and side chains are effective to enhance the tensile strength and alkaline stability of the membranes. The membranes with star main chains exhibited a tensile stress at break of 45 MPa and retained a conductivity of 36.1 mS cm−1 at 60 °C after exposed to 1 M KOH at 80 °C for 300 h.

In this work, we propose a sulfonated poly (ether ether ketone) (SPEEK) composite proton-conductive membrane based on a 3-(1-hydro-imidazolium-3-yl)-propane-1-sulfonate (Him-pS) additive to break through the trade-off between conductivity and selectivity of a vanadium redox flow battery (VRFB). Specifically, Him-pS enables an oriented distribution of the SPEEK matrix to construct highly conductive proton nanochannels throughout the membrane arising from the noncovalent interaction. Moreover, the "acid-base pair" effect from an imidazolium group and a sulfonic group further facilitates the proton transport through the nanochannels. Meanwhile, the structure of the acid-base pair is further confirmed based on density functional theory calculations. Material and electrochemical characterizations indicate that the nanochannels with a size of 16.5 nm are vertically distributed across the membrane, which not only accelerate proton conductivity (31.54 mS cm-1) but also enhance the vanadium-ion selectivity (39.9 × 103 S min cm-3). Benefiting from such oriented proton-conductive nanochannels in the membrane, the cell delivers an excellent Coulombic efficiency (CE, ≈ 98.8%) and energy efficiency (EE, ≈ 78.5%) at 300 mA cm-2. More significantly, the cell maintains a stable energy efficiency over 600 charge-discharge cycles with only a 5.18% decay. Accordingly, this work provides a promising fabrication strategy for a high-performance membrane of VRFB.

Development of high temperature polymer electrolyte membranes is essential for advanced energy conversion and storage technologies. Herein, an imidazolium type ionic liquid (BPMIm) with a long side-chain of 5-bromopentyl is synthesized and employed as the quaternization reagent for ether-free poly(p-terphenyl-co-N-methyl-piperidine) (PTP). Grafting the flexible long side-chain imidazolium group into the ether-free polymer backbone not only improves the polymer solubility in organic solvents but also provides acid-base interaction sites for the following phosphoric acid doping that supports proton conductivity at above 100 °C. Compared with pure and iodomethane quaternized PTP membranes (i.e. PTP and PTP-Me), the prepared imidazolium ionic liquid grafted PTP membrane (i.e. PTP-PMIm) exhibits an enhanced phosphoric acid uptake and hence a superior anhydrous proton conductivity of 138 mS cm−1 at 180 °C. The technical feasibility of the PTP-PMIm membrane is demonstrated in H2-air fuel cells at temperatures from 160 °C–200 °C, which reaches a high peak power density of around 456 mW cm−2 at 200 °C at ambient pressure.

Capacity estimation of a curbside bus stop is essential to evaluation of its operation, reliability and performance. Arrival buses and served buses will form an overflow queue and an interlocking queue in loading areas with high frequencies. Therefore, bus stop blockage may reduce the stop capacity. The capacity of a bus stop is modelled as a function of the blockage probability, the arrival of buses, and the service time, while considering the no-overtaking principle and allowable-overtaking principle. This study aims to estimate the capacity, minimum arrival time and maximum service time based on the blockage probability and number of berths. The results indicate that congestion can be effectively alleviated by increasing the number of berths when the demand for loaded buses is low due to the significantly changing probability threshold for a NO stop. A congestion and stopping principle is important when multiple bus routes converge at the same bus stop. By combination with an actual case, an optimal overtaking principle is obtained using a computer program written in the MATLAB environment. The developed methodology can be practically applied to determine the loading principle and designated stopping berths for multi-route buses.

Novel high temperature proton exchange membranes, quaternized poly(aryl ether sulfone) (QPAES), were prepared using triethylamine (TEA) as quaternization reagent and (N,N-diethyl-3-aminopropyl) trimethoxysilane (EPMS) as the crosslinking agent, respectively. To improve the mechanical strength and dimensional stability of the membranes, the crosslinked structure of Si O Si network was formed by hydrolyzing siloxane groups of EPMS. Compared with the non-crosslinked membrane, the crosslinked PAES membranes displayed significantly enhanced mechanical properties, improved dimensional stabilities as well as high conductivities. The QPAES-10EPMS-90TEA membrane with a phosphoric acid doping level of 12.1 exhibited a tensile strength of 9.16 MPa at room temperature, and a conductivity of 74.8 mS cm−1 at 180 °C under no humidification conditions.

We employed four radical inhibitors to investigate their influences on the degradation of poly (4-vinylbenzyl chloride-styrene) based anion exchange membranes (AEMs) in alkaline solutions. It is found that the presence of the radical inhibitors could effectively restrain the nucleophilic attack of hydroxide ions to the AEMs according to the conductivity measurements, especially the one p -ethyl phenol (PEP), which could significantly protect the AEMs against the attack. More evidences including water uptake, swelling ratio as well as FT-IR analysis further proved this phenomenon by comparison those properties of the membranes before and after the stability test in 8 M KOH at 80 °C for 24 h. According to the 1 H NMR spectra, the quaternary ammonium groups of the AEMs were mainly degraded into tertiary amines in the hot alkaline solutions; while in the presence of PEP, this degradation was restrained and the quaternary ammonium groups maintained by reaction with PEP. Fenton test results further indicated that high oxidative stability of the AEMs benefited from the presence of a small amount of PEP, which could reduce the generation of the oxidants. Thus an inhibition reaction mechanism of the radical inhibitors preventing the AEMs from alkaline degradation is proposed.

The blend polymer membranes were synthesized from the methylimidazolium poly (aromatic ether ketone) (MeIm-PAEK) and fluoropolymers (PVDF and PVDF-HFP) with excellent thermal stability and improved dimensional stabilities for high-temperature polymer electrolyte fuel cells. The MeIm-PAEK exhibited good compatibility with PVDF or PVDF-HFP without phase separation. High phosphoric acid doping contents of the blend membranes were achieved at elevated temperatures with acceptable swellings. The acid doped blend membranes displayed lower dimensional swellings and higher mechanical strength compared to the MeIm-PAEK membrane, which allowed the blend membranes to obtain higher acid doping contents and proton conductivities. The MeIm-PAEK/10%PVDF membrane with a phosphoric acid doping content of 700 wt% showed a proton conductivity as high as 0.192 S cm−1 at 180 °C under the non-humidified condition and a tensile strength of 4.3 MPa at room temperature.

Two trifunctional bromomethyls containing crosslinkers, 1,3,5-tris(bromomethyl)benzene (B3Br) and 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene (Be3Br), are employed to covalently crosslink polybenzimidazole (PBI) membranes for the high temperature proton exchange membrane fuel cell. The presence of three bromomethyl groups in each crosslinker molecule is expected to create more free volume for acid doping while enhancing the adhesive strength of the PBI chains. In addition, the influence of the two crosslinker structures on the property of the crosslinked membranes is compared and analyzed. All the crosslinked PBI membranes exhibit longer morphology durability over the pristine PBI membrane toward the radical oxidation. Moreover, the crosslinked PBI membranes with the crosslinker Be3Br containing three ethyl groups display superior acid doping level, high conductivity and excellent mechanical strength simultaneously, over those with the crosslinker B3Br and the pristine PBI membrane. Single cell measurements based on the acid doped membrane with a crosslinking degree of 7.5% by Be3Br demonstrate the technical feasibility of the prepared membranes for high temperature proton exchange membrane fuel cells.

A 1-decyl-2-methylimidazole (DMIm) functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) membrane is fabricated and employed to dope phosphoric acid (PA) for use as a high temperature proton exchange membrane. This kind of membrane displayed superior PA doping capability, but poor mechanical properties. In order to improve the dimensional and mechanical stabilities without sacrificing proton conductivities, a series of dual cross-linked membranes are prepared using the poly(styrene-vinylimidazole-divinylbenzene) (poly(St-VIm-DVB)) copolymer as a crosslinker. The reaction of vinylimidazole with benzyl bromide not only constructs a cross-linking network, but also endows the membranes with a PA doping capacity for proton conduction. The reticular polymer chain structure improves the mechanical properties of the membranes, especially at elevated temperatures. As an example, PPO-70%VIm-30%DMIm/180.1%PA achieves a high proton conductivity of 0.067 S cm−1 at 180 °C without humidification, while it displays suitable tensile strengths of 5.0 MPa and 2.1 MPa at room temperature and 120 °C, respectively. These membranes show great potential for use as an electrolyte in high temperature proton exchange membrane fuel cells.

Developing polymer membranes with low cost, high ionic conduction and low vanadium ion permeability simultaneously for the vanadium redox flow battery (VRFB) is a huge challenge to macromolecule design and engineering. Herein, a series of high-performance and low-cost macromolecule cross-linked membranes for VRFB are synthesized from cardo-poly(etherketone) (PEKC) and poly(ethylene imine) (PEI) through a straightforward lactamization reaction between the primary amines in PEI and lactones in PEKC. Owing to the acid-base interaction between amino groups of PEI and sulfonic acid (SA), crosslinked x%PEI-PEKC membranes exhibit excellent SA adsorption capability and low area resistance. Meanwhile, the formed macromolecule multi-crosslinked networks significantly improve the membrane-forming property of PEI and endow membranes with superior mechanical rigidity and low vanadium ion permeability simultaneously. Consequently, the 50%PEI-PEKC membrane exhibit a nearly 90 times higher ion selectivity of 24.71 × 105 S min cm−3 than Nafion 115. The assembled VRFB with 50%PEI-PEKC displays higher battery efficiencies than Nafion 115 at 60–160 mA cm−2, which also possesses superior cycling stability at 100 mA cm−2.

Novel high temperature polymer electrolyte membranes (HT-PEMs) are fabricated from commercial and low-cost poly (ether ketone cardo) (PEK-Cardo). Rather than normal chloromethylation and quaternization procedure to introduce basic groups into poly (arylene ether)s, three different long side-chain basic groups are grafted into PEK-Cardo through a facile one-step lactamization between the cardo phenolphthalein type moiety in PEK-Cardo and amino compounds (i.e. 1-(3-aminopropyl) imidazole (APIm), 1-(3-aminopropyl) pyrrolidin-2-one (APy) and 3-(dimethylamino)-1-propylamine). The obtained lactamized PEK-Cardo membranes exhibit excellent phosphoric acid doping capability and the physicochemical properties are optimized by adjusting the chemical structure and grafting degree of side-chain basic groups. Fuel cell results demonstrate a big potential for HT-PEM fuel cell applications. Thus, this proposal provides a new, straightforward and low-cost method to prepare high-performance HT-PEMs.

In the present work, new anion exchange membranes (AEMs) are synthesized by using polybenzimidazole (PBI) as the matrix and (5-bromopentyl)-trimethylammonium bromide (BPTMA-Br) as the grafting reagent. The grafted long side-chain quaternary ammonium group endows the PBI membrane with a high ion exchange capacity (IEC) of 1.8 mmol g−1, and increased hydrophilicity and ionic conductivity. The PBI-48%BPTMA membrane shows a gradual decrease in conductivity when immersing in 1 M KOH at 80 °C, and maintains its 65.3% conductivity after 240 h measurement. Nevertheless, the PBI-48%BPTMA membrane displays a large potential in the vanadium redox flow battery (VRFB). The PBI-48%BPTMA membrane possesses a lower area resistance (0.43 Ω cm2) and vanadium ion permeability (6.9 × 10−7 cm2 min−1) than Nafion115 (0.61 Ω cm2 and 3.2 × 10−6 cm2 min−1). Consequently, the assembled VRFB shows higher energy efficiency of 82.7% at 80 mA cm−2 than Nafion115 (77.4%). Meanwhile, the single cell also exhibits almost unchanged performance within the 400 charge-discharge cycles at 100 mA cm−2, demonstrating superior stability of the PBI-BPTMA membrane in VRFB.

Polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) has attracted more and more attention recently for using as the matrix of anion exchange membranes (AEMs) in fuel cells due to its low cost, superior mechanical properties and ether-free total C-C bond backbone. In this work, the short side chain of chloromethyl and long side chain of bromohexanoyl groups are grafted into the SEBS copolymer via the chloromethylation and Friedel-Crafts acylation reactions. After quaternized by different nitrogen heterocyclic compounds including 1-methylimidazole (Im), 1-methylpyrrolidine (Mpy), N-methylpiperidine (Pip) and 2-methyl-1-pyrroline (Mpyl), various SEBSCn-x AEMs are prepared. Combing with small molecule model experiment results, Mpy and Pip cations grafted SEBS membranes are confirmed to possess good alkali resistance, while SEBSC1-x membranes with Im and Mpyl cations are not suitable for AEMs due to their poor alkaline stability. Meanwhile, long side-chain cation grafted SEBSC6-x AEMs with lower ion exchange capacity (IEC) values exhibit higher water uptake, ionic conductivity and mechanical strength simultaneously comparing with short side-chain cation grafted SEBSC1-x AEMs. As an example, the SEBSC6-Pip membrane with an IEC of 0.48 mmol g−1 exhibits a water uptake of 47% at 80 °C, an OH− conductivity of 57.7 mS cm−1 at 80 °C, a tensile strength of 52 MPa at room temperature, and a conductivity retention percent of 75% after 600 h in 1 M KOH at 80 °C, demonstrating a big potential for the AEM fuel cell application.

A concept of macromolecular crosslinking is applied to prepare high temperature proton exchange membranes (HT-PEMs). Through a simple lactamization procedure, a series of crosslinked membranes are synthesized based on poly(ethylene imine) (PEI) and poly(ether ketone cardo) (PEKcardo). PEI with abundant amino groups endows crosslinked membranes with superior phosphoric acid (PA) absorption capability, resulting in high conductivities. The rigid PEKcardo matrix and constructed crosslinking network significantly improve the dimensional and mechanical stabilities. As an example, the 92%PEI-PEKcardo with a PA doping content of 304%PA achieves a conductivity of 0.107 S cm−1 at 180 °C without humidifying and a tensile strength of 4.6 MPa at room temperature. The fuel cell performance of abovementioned membrane demonstrates the technical feasibility of the x%PEI-PEKcardo membrane for the HT-PEM fuel cell. This work provides a straightforward method to prepare low-cost and high-performance electrolyte membranes for both fuel cell and other energy devices, such as the vanadium redox flow battery.

Two N3-substituted imidazoles 1,2-dimethylimidazole and 1-butyl-2-methylimidazole were chosen to functionalize poly(aryl ether ketone), respectively. The generated imidazolium cations could electrostatically react with sulfonate ions of the sulfonated poly(ether ether ketone) forming the ionic crosslinking structure of the membranes. The changes in crosslinking degree and the alkyl chain-length on N3 site of the imidazoliums could highly affect the properties of the anion exchange membranes (AEMs). The AEMs functionalized by 1-butyl-2-methylimidazole exhibited superior properties compared to those functionalized by 1,2-dimethylimidazole according to the tolerance tests of the AEMs towards hot alkaline solutions. After exposed to 1M KOH at 80°C for 200h, the 1-butyl-2-methylimidazole modified AEMs maintained the ion exchange capacity of above 85%, the conductivity of about 70%, and the tensile stress at break of around 80%, respectively. The hydrophile-lipophile balance of the polymer membranes was calculated and proposed to better understand the correlation between structures and properties of the AEMs. The degradation of the imidazolium functional groups of the AEMs under the attack of hydroxide ions was evidenced by FT-IR analysis.

New high temperature proton exchange membranes are fabricated based on low cost polyvinylchloride (PVC) and 1-(3-aminopropyl)imidazole (APIm) by a facile method (i.e. solution casting method). Due to the presence of chemically active chloride sites in the backbone, PVC reacts with the amino and imidazole groups in APIm directly via the nucleophilic reaction. The fabricated membranes possess good thermal stability, high hydrophilicity and mechanical strength as well as superior phosphoric acid (PA) doping capability due to the acid-base and hydrogen bond interactions between the APIm groups and PA molecules. Incorporating pendant APIm groups into PVC endows membranes with significantly higher acid doping levels than membranes functionalized by mono- and bis-amino or imidazole containing compounds. As a result, the PVC-19%APIm/2.4PA membrane displays an outstanding proton conductivity of 0.26 S cm-1 at 180 °C under anhydrous conditions, which is comparable to the conductivity of Nafion-type membranes (> 0.1 S cm-1 at 80 °C). The polarization curve and durability test demonstrate the technical feasibility of the PVC-x%APIm/PA membrane for the high temperature proton exchange membrane fuel cell.

Developing anion exchange membranes (AEMs) with high ionic conductivity, excellent chemical stability and superior alkaline resistance simultaneously is a remarkable challenge. In this work, a series of high-performance covalently crosslinked AEMs are successfully designed by tethering the flexible methylpyrrolidinium grafted poly (vinyl benzyl chloride) (PVBMPy) backbone and rigid polysulfone (PSF) backbone and employing N,N,N′,N′-tetramethyl-1,6-hexanediamine (TMHDA) as the crosslinker. The PVBMPy ionomer, as the anion conductor, exhibits remarkable alkali resistance while the existence of rigid PSF chain ensures sufficient mechanical strength. The properties of various membranes are optimized through adjusting the adding amount of TMHDA into the casting solution. The fabricated PVBMPy-CL-x%PSF membranes possess a superior oxidative stability against radicals attack, and simultaneously display enhanced dimensional and mechanical stabilities, acceptable conductivity and robust alkaline stability. As an example, the PVBMPy-CL-15%PSF membrane occupies a weight residual rate of 71.3% after immersing in the Fenton solution at 60 °C for 120 h, a volume swelling of 26.2%, a tensile stress at break of 13.1 MPa at room temperature and an ionic conductivity of 32.9 mS cm−1 at 80 °C, and maintains its initial ionic conductivity of 70.5% after exposure for 580 h in 1 M KOH at 80 °C.

One critical issue to phosphoric acid (PA) doped high-temperature proton exchange membranes (HT-PEMs) is to balance the proton conductivity and mechanical properties for overall application performance in fuel cells. Addressing the issue, we prepare durable HT-PEMs having the dual crosslinking structure by employing poly(vinylimidazole-divinylbenzene-styrene) (poly(VIm-DVB-St)) copolymer as a crosslinker and using the poly (aromatic ether ketone) (PAEK) polymer containing four methyl groups as the host membrane matrix. The imidazole groups of poly(VIm-DVB-St) react with benzyl bromide groups of brominated PAEK for both the primary cross-linking network and high PA doping. The divinylbenzene crosslinked poly (styrene-co-vinylimidazole) network generates the secondary cross-linking structure. The formed reticular polymer chain structure brings on low swelling and high mechanical strength of the HT-PEMs. The fuel cell based on the acid doped PAEK41-85%VIm/233.0 PA shows a H2-air fuel cell peak power density of 306 mW cm−2 at 200 °C without back pressure, and a low degradation rate of 3.9 × 10−5 V h−1 during a period of 600 h under a constant current density of 200 mA cm−2 at 160 °C.