A facile fabrication of functionalized rGO crosslinked chemically stable polysulfone-based anion exchange membranes with enhanced performance

Introducing more ionic conductive groups in polymer-based anion exchange membranes (AEMs) can improve the ion exchange capacity and further overcome the disadvantage of low ion conductivity for AEMs. However, the excessive swelling of AEMs caused by exorbitant IEC value may reduce the dimensional stability of membranes. So it is extremely important to modify the structures of AEMs. Herein, we proposed a facile strategy to construct reduced graphene oxide (rGO) stable crosslinked polysulfone-based AEMs with improved properties. rGO was non-covalently modified with pyrene-containing tertiary amine small molecule and polymer via π-π interactions. The as-prepared functionalized rGO (TrGO and PrGO) as both cross-linkers and fillers to fabricate quaternized polysulfone (QPSU)-based AEMs (CQPSU-X-TrGO and CQPSU-X-PrGO) for the first time. The cross-linked membranes can tighten the internal packing structure, and enhance the alkaline resistance, ion conductivity and oxidative stability of AEMs. Furthermore, the hydrophilicity and flexibility of the CQPSU-X-PrGO membranes were significantly improved as compared with that of CQPSU-X-TrGO membranes. PrGO-crosslinked membranes (CQPSU-2%-PrGO, σ_OH⁻ = 117.7 mS/cm) displayed higher ionic conductivities at 80 °C than TrGO-crosslinked membranes (CQPSU-1%-TrGO, σ_OH⁻ = 87.2 mS/cm). The remarkable nanophase separation can be observed in the CQPSU-X-PrGO membranes by TEM. This feasible strategy can be efficiently used to prepare new type of crosslinked organic-inorganic nanohybrid AEMs with excellent chemical stability and high ionic conductivity.     

Branched poly(ether ether ketone) based anion exchange membrane for H2/O2 fuel cell

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 H₂/O₂ fuel cell with BPEEK-3-Pip-53 membrane reached 133 mW cm⁻² at 260 mA cm⁻².     

Novel self-cross-linked multi-imidazolium cations long flexible side chains triblock copolymer anion exchange membrane based on ROMP-type polybenzonorbornadiene

A novel benzonorbornadiene derivative (BenzoNBD-Bis(Im⁺Br⁻-Im⁺I⁻)) grafted by multi-imidazolium cations side-chains combined the rigid alkyl spacer and flexible alkoxy spacer is designed and synthesized. Then, the BenzoNBD-Bis(Im⁺Br⁻-Im⁺I⁻) monomer is copolymerized with the epoxy functionalized norbornene monomer (NB-MGE) and norbornene (NB) via ring-opening metathesis polymerization (ROMP) using Grubbs 3rd catalyst. All as-designed triblock copolymer membranes (TBCMs) show a thermal decomposition temperature beyond 310 °C and can well be dissolved in common organic solvents. The self-cross-linked structure of anion exchange membrane (AEM) is confirmed by gel fraction and tensile measurement. The water uptake and swelling ratio of TBCMs and AEMs are also measured. Major properties required for AEMs such as ion exchange capacity (IEC), hydroxide conductivity and alkaline stability are investigated. AEM-9.09 shows a hydroxide conductivity of 100.74 mS cm⁻¹ at 80 °C. Besides, the micro-phase separated morphology of AEM is confirmed by TEM, AFM and SAXS analyses, AEMs formed distinct micro-phase separation. The as-prepared AEM exhibits a peak power density of 174.5 mW cm⁻² at 365.1 mA cm⁻² tested in a H₂/O₂ single-cell anion exchange membrane fuel cell (AEMFC) at 60 °C. The newly developed strategy of self-cross-linked multi-imidazolium cations long side-chains triblock benzonorbornadiene copolymer provides an effective method to develop high-performance AEMs.     

Simultaneously enhanced hydroxide conductivity and mechanical properties of quaternized chitosan/functionalized carbon nanotubes composite anion exchange membranes

Low-cost biopolymer chitosan has received considerable attention in the field of anion exchange membranes (AEMs) because it can be easily quaternized and avoids the carcinogenic chloromethylation step. Simultaneously increasing the ionic conductivity and improving mechanical properties of quaternized chitosan (QCS) is key for its high-performance application. In this study, new composite AEMs consisting of QCS and functionalized carbon nanotubes (CNTs) were prepared. CNTs were coated with a thick silica layer onto which high-density quaternary ammonium groups were then grafted. The insulator silica coating effectively prohibits electron conduction among nanotubes and the grafted –NR₃⁺ provides new OH⁻ conductive sites. Incorporating 5 wt% functionalized CNTs into the matrix enhanced ionic conductivity to 42.7 mS cm⁻¹ (80 °C) which was approximately 2 times higher than that of pure QCS. The effective dispersion of CNTs and appropriate interfacial bonding between nanofiller and QCS improved the mechanical properties of AEMs, including both the strength and toughness of the composite membranes. An alkaline direct methanol fuel cell equipped with the composite membrane (5% functionalized CNTs loading) produced an maximum power density of 80.8 mW cm⁻² (60 °C), which was 57% higher than that of pure QCS (51.5 mW cm⁻²). This study broadens the application of natural polymers and provides a new way to design and fabricate composite AEMs with both improved mechanical properties and electrochemical performance.     

Preparation and characterization of a polyvinyl alcohol grafted bis-crown ether anion exchange membrane with high conductivity and strong alkali stability

A new type of symmetrical bis-crown ether is prepared by connecting dibenzo-18-crown-6 ether on both sides of the chromotropic acid, and then grafting the aforementioned bis-crown ether onto polyvinyl alcohol matrix to prepare a series of anion exchange membranes (AEMs), which their have high conductivity and strong alkali stability. These synthesized membranes were named B-C_X%-P AEMs (x is the mass percentage of the symmetrical bis-crown ether (B–C)). Then, the chemical structure of aforementioned AEMs were verified by means of ¹H NMR, FT-IR and UV. Meanwhile, the OH⁻ conductivity, alkaline stability and single cell performance of the synthesized membrane were also investigated. The results revealed that the conductivity of B–C_30%-P membrane is the highest at 80 °C (235 mS cm⁻¹), and the power density is also the highest (197 mW cm⁻²), and the alkali stability of the membrane synthesized in this paper was also improved. The conductivity at 80 °C was only reduced by 4%, which was obtained by immersing the B–C_30%-P membrane immersed in 6 mol L⁻¹ KOH solution for 168 h, which the aforementioned results proved that the synthesized membrane in this research had excellent OH⁻ conductivity and alkaline stability.     

End-group crosslinked hexafluorobenzene contained anion exchange membranes

A kind of anion exchange membranes (AEMs) with CC bond end-group crosslinked structure was synthesized successfully. Unlike the traditional aliphatic AEMs, the AEMs were prepared in this work by a strategy to realize the CC bond thermal end-group crosslinking reaction, exhibiting an obvious microphase separation structure and a suitable dimensional stability. The well-defined ion channels constructed in the AEMs guarantee the fast OH⁻ conduction, as confirmed via physical and chemical characterization. The conductivity was dramatically enhanced due to the effective ion channels and increased ion exchange capacity. Among the as-prepared AEMs, the PHFB-VBC-DQ-80% AEM has a conductivity of 135.80 mS cm⁻¹ at 80 °C. The single cell based on PHFB-VBC-DQ-80% can achieve a power density of 141.7 mW cm⁻² at a current density of 260 mA cm⁻² at 80 °C. The AEMs show good thermal stability verified by a thermogravimetric analyzer (TGA). Furthermore, the ionic conductivity of PHFB-VBC-DQ-80% only decreased by 7.1% after being soaked in a 2 M NaOH solution at 80 °C for 500 h.     

Cross-linked anion exchange membranes with flexible,long-chain,bis-imidazolium cation cross-linker

Herein, poly (phenylene) oxide (PPO)-based cross-linked anion exchange membranes (AEMs) with flexible, long-chain, bis-imidazolium cation cross-linkers are designed and synthesized. Although the cross-linked membranes possess high ion exchange capacity (IEC) values of up to 3.51–3.94 meq g⁻¹, they have a low swelling degree and good mechanical strength because of their cross-linked structure. Though the membranes with the longest flexible bis-imidazolium cation cross-linker (BMImH-PPO) possess the lowest IEC among these PPO-based AEMs, they show the highest conductivity (24.10 mS cm⁻¹ at 20 °C) and highest power density (325.7 mW cm⁻² at 60 °C) because of the wide hydrophilic/hydrophobic microphase separation in the membranes that promote the construction of ion transport channels, as confirmed by atom force microscope (AFM) images and the small angle X-ray scattering (SAXS) analyses. Furthermore, the BMImH-PPO samples exhibit good chemical stability (10% and 6% decrease in IEC and conductivity, respectively, in 2 M KOH at 80 °C for 480 h, and a 22% decrease in weight in Fenton's reagent at 60 °C for 120 h), making such cross-linked AEMs potentially applicable in alkaline anion exchange membrane fuel cells.     

Anion exchange membranes of bis-imidazolium cation crosslinked poly(2,6-dimethyl-1,4- phenylene oxide) with enhanced alkaline stability

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.     

Novel quaternized carbon dots modified polysulfone-based anion exchange membranes with improved performance

At present, low conductivity and poor chemical stability are still the biggest challenges in the research on anion exchange membranes (AEMs). Herein, novel nanocomposite AEMs were first constructed by introducing quaternized carbon dots (QCDs) into the imidized polysulfone matrix (Im-PSU). QCDs were synthesized by quaternization of CDs derived from citric acid and ethylenediamine. The physicochemical properties and electrochemical properties of the nanocomposite AEMs were significantly improved due to the introduction of QCDs. It was found that the QCDs can improve the ion transport channel of the nanocomposite AEMs. Compared with pure Im-PSU AEM, the OH⁻ conductivity and physicochemical properties of the nanocomposite membranes were enhanced, and the OH⁻ conductivity of ImPSU-1.0%-QCDs composite membrane can reach 109.3 mS cm⁻¹ at 80 °C, and 61.2% initial OH⁻ conductivity was maintained in 1.0 M NaOH solution for 500 h at 60 °C. Our research proves that the nanofiller with a small size can better improve the performance of composite AEMs, and provide an efficient strategy for future research work in the design and preparation of AEMs.     

Poly(isatin-piperidinium-terphenyl) anion exchange membranes with improved performance for direct borohydride fuel cells

In this work, an effective design strategy for anion exchange membranes (AEMs) incorporating ether-bond free and piperidinium cationic groups promote chemical stability. A series of poly (isatin-piperidium-terphenyl) based AEMs were synthesized by superacid catalyzed polymerization reaction, followed by quaternization. The effect of functionalization on the performance of poly (isatin-N-dimethyl piperidinium triphenyl) (PIDPT-x) AEMs was investigated. Highly reactive N-propargylisatin was introduced into the backbone to achieve high molecular weight polymers (η_a = 2.06–3.02 dL g⁻¹) leading to robust mechanical properties, as well as modulating 1.78–2.00 mmol g⁻¹ of the ion exchange capacity (IEC) of the AEMs by feeding. Apart from that, the rigid non-ionized isatin-terphenyl segment provides AEMs improved dimensional stability with a swelling ratio of less than 12% at 80 °C. Among them, PIDPT-90 exhibited a higher OH⁻ conductivity of 105.6 mS cm⁻¹ at 80 °C. The alkali-stabilized PIDPT-85 AEM was presented, in which OH⁻ conductivity retention maintained 85.6% in a 2 M NaOH at 80 °C after 1632 h. Afterward, the direct borohydride fuel cells (DBFC) with PIDPT-90 membrane as a separator showed an open-circuit voltage of 1.63 V and a peak power density of 75.5 mWcm⁻² at 20 °C. This work demonstrates the potential of poly (isatin- N-dimethyl piperidinium triphenyl) as AEM for fuel cells.     

Study on the partially cross-linked poly(styrene-b-(ethylene-co-butylene)-b-styrene) anion exchange membrane remotely (spaced hexyl) grafted double cation separated by different alkyl groups

In order to improve the alkali stability and OH⁻ conductivity of Poly (styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS)-based anion exchange membranes (AEMs), double cations with different alkyl intervals are remotely grafted onto the SEBS skeleton with hexyl as a linker through reactions such as acylation and ketone reduction. Then, SEBS-0.8Cn-0.2C6 cross-linked membranes were prepared to study the effect of the length of the alkyl chain between the dications on the ion transport and other properties. The OH⁻ conductivity of SEBS-0.8C4-0.2C6 cross-linked membrane can reach 85.27 mS cm⁻¹ at 80 °C, and the peak power density can reach 225 mW cm⁻² at a current density of 450 mA cm⁻². As the dicationic spacer alkyl chains became longer, the swelling rate and water uptake of the membranes increased, resulting in significant improvements in mechanical properties and chemical stability. After soaking in 2 M NaOH solution at 80 °C for 1200 h, the conductivity of SEBS-0.8C6-0.2C6 decreased by only 5.76%. Optimizing the side chain structure of SEBS skeleton can effectively improve the comprehensive performance of AEM.     

Dense 1,2,4,5-tetramethylimidazolium-functionlized anion exchange membranes based on poly(aryl ether sulfone)s with high alkaline stability for water electrolysis

Anion exchange membranes with enough alkaline stability and ionic conductivity are essential for water electrolysis. In this work, a class of anion exchange membranes (PAES-TMI-x) with dense 1,2,4,5-tetramethylimidazolium side chains based on poly(aryl ether sulfone)s are prepared by aromatic nucleophilic polycondensation, radical substitution and Menshutkin reaction. Their chemical structure and hydrophilic/hydrophobic phase morphology are characterized by hydrogen nuclear magnetic resonance (¹H NMR) and atomic force microscope (AFM), respectively. The water uptake, swelling ratio and ionic conductivity for PAES-TMI-x are in the range of 23.8%–48.3%, 8.3%–14.3% and 18.22–96.31 mS/cm, respectively. These AEMs exhibit high alkaline stability, and the ionic conductivity for PAES-TMI-0.25 remains 86.8% after soaking in 2 M NaOH solution at 80 °C for 480 h. The current density of 1205 mA/cm² is obtained for the water electrolyzer equipped with PAES-TMI-0.25 in 2 M NaOH solution at 2.0 V and 80 °C, and the electrolyzer also has good operation stability at current density of 500 mA/cm². This work is expected to provide a valuable reference for the selection and design of cations in high-performance AEMs for water electrolysis.     

Enhanced ionic conductivity of anion exchange membranes by grafting flexible ionic strings on multiblock copolymers

A new strategy to prepare high-conductivity anion exchange membranes (AEMs) is presented here. A series of phenolphthalein-based poly(arylene ether sulfone nitrile) multiblock AEMs has been synthesized by selectively grafting flexible ionic strings on hydrophilic segments to form ionic regions. Moreover, the phenolphthalein groups are introduced to force chains apart and create additional interchain spacing. In addition, the nitrile groups suspended on main chains are aimed at enhancing the anti-swelling behavior of as-prepared AEMs. Along these processes, well-defined phase separation has been attained, forming excellent ion-transport channels. The effective phase separation has been confirmed by atomic force microscopy. Finally, as-prepared AEMs exhibit a high hydroxide conductivity, ranging from 40.1 to 121.6 mS cm⁻¹ in the temperature range of 30–80 °C, and superior ionic conductivity to IEC ratio at 80 °C. Furthermore, excellent thermal stability and desirable mechanical strength have been rendered by as-prepared AEMs. However, the alkaline stability of as-prepared AEMs requires further optimization.     

Highly durable and conductive poly(arylene piperidine) with a long heterocyclic ammonium side-chain for hydroxide exchange membranes

Recently, the preparation of hydroxide exchange membranes (HEMs) without ether bonds have attracted much attention because of their high chemical stability. Hence, ether-bond free, highly durable, and conductive poly(arylene piperidine)s (PAPips) tethered with heterocyclic ammonium via hexyl spacer chains were prepared successfully for HEMs via a facile synthetic procedure. The effect of the cationic groups (quaternary ammonium, piperidinium, and morpholinium) on the properties of the corresponding PAPip-based HEMs, including the morphology, hydroxide conductivity, and alkaline and chemical stability were systematically investigated. The as-designed PAPip-based membranes exhibited excellent overall performance. The membranes attached with piperidinium (IEC = 1.64 mmol g⁻¹) exhibited a hydroxide conductivity of 0.082 S cm⁻¹ at 80 °C and exhibited significant alkaline stability which maintained 80.1% of its conductivity after immersion in 1 M NaOH at 80 °C for 1500 h. The as-prepared membrane also presented a peak power density of 76 mW cm⁻² at 80 °C in a H₂/O₂ HEMFC. The resulting HEMs also showed excellent mechanical properties, thermal stability, and well-defined phase separation.     

Preparation and characterization of imidazolium-based membranes for anion exchange membrane fuel cell applications

New anion exchange membranes (AEMs) with high conductivity, good dimensional and alkaline stability are currently required in order to develop alkaline fuel cells into efficient and clean energy conversion devices. In this study, a series of AEMs based on 1, 2-dimethyl-3-(4-vinylbenzyl) imidazolium chloride ([DMVIm][Cl]) are prepared and investigated. [DMVIm][Cl] is synthesized and used as ion carriers and hydrophilic phase in the membranes. The water uptake, swelling ratio, IEC and conductivity of the AEMs increase with increasing the [DMVIm][Cl]. The imidazolium-based AEMs show excellent thermal stability, sufficient mechanical strength, the membrane which containing 30% mass fraction of [DMVIm][Cl] shows conductivity up to 1.0 × 10^?2 S cm^?1 at room temperature and good long-term alkaline stability in 1 M KOH solution at 80 °C. The results of this study suggest that this type of AEMs have good perspectives for alkaline anion exchange membrane fuel cell applications.     

Synthesis and characterization of a long side-chain double-cation crosslinked anion-exchange membrane based on poly(styrene-b-(ethylene-co-butylene)-b-styrene)

By choosing a triple block polymer, poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), as the backbone and adopting a long side-chain double-cation crosslinking strategy, a series of SEBS-based anion-exchange membranes (AEMs) was successively synthesized by chloromethylation, quaternization, crosslinking, solution casting, and alkalization. The 70C16-SEBS-TMHDA membrane showed high OH⁻ conductivity (72.13 mS/cm at 80 °C) and excellent alkali stability (only 10.86% degradation in OH⁻ conductivity after soaking in 4-M NaOH for 1700 h at 80 °C). Furthermore, the SR was only 9.3% at 80 °C and the peak power density of the H₂/O₂ single cell was up to 189 mW/cm² at a current density of 350 mA/cm² at 80 °C. By introducing long flexible side chains into a polymer SEBS backbone, the structure of the hydrophilic–hydrophobic microphase separation in the membrane was constructed to improve the ionic conductivity. Additionally, network crosslinked structure improved dimensional stability and mechanical properties.     

Preparation and performance of bisimidazole cationic crosslinked addition-type polynorbornene-based anion exchange membrane

The late transition metal catalyst system (η³-allyl)Pd(PPh₃)Cl/Li[B(C₆F₅)₄]·2.5Et₂O (Li[FABA]) was used to catalyze 5-norbornene-2-methylenehexyl ether (NB-MHE) and 5-norbornene-2-methylene-(6-bromohexyl) ether (NB–O–Br) controllable addition copolymerization to obtain post-functionalized vinyl addition-type block copolymer aP(NB-O-Br-b-NB-MHE). 1,6-Bis(2-methylimidazole)hexane (Bis-MeIm) was used as a crosslinking agent to prepare a series of anion exchange membranes (AEMs) CL-aP(NB-O-Br-b-NB-MHE). The initial thermal decomposition temperature of the obtained addition-type polynorbornene-based AEM was about 250 °C. The AEM had moderate water uptake (WU) and swelling ratio (SR), and obvious micro-phase separation structure that could be observed from the AFM phase diagram. It could maintain high OH^? conductivity (85.07 mS cm^?1, 80 °C) and alkali resistance stability (soaking alkali for more than 500 h at 25 °C). In the single cell test of the H₂/O₂ fuel cell assembled by CL5-aP(NB-O-Br-b-NB-MHE), the peak power density was 177 mW cm^?2.     

High chemical stability anion exchange membrane based on poly(aryl piperidinium): Effect of monomer configuration on membrane properties

In recent years, ether-free polyaryl polymers prepared by superacid-catalyzed Friedel-Crafts polymerization have attracted great research interest in the development of anion exchange membranes(AEMs) due to their high alkali resistance and simple synthesis methods. However, the selection of monomers for high-performance polymer backbone and the relationship between polymer structure construction and properties need further investigated. Herein, a series of free-ether poly(aryl piperidinium) (PAP) with different polymer backbone steric construction were synthesized as stable anion exchange membranes. Meta-terphenyl, p-terphenyl and diphenyl-terphenyl copolymer were chosen as monomers to regulate the spatial arrangement of the polymer backbone, which tethered with stable piperidinium cation to improve the chemical stability. In addition, a multi-cation crosslinking strategy has been applied to improve ion conductivity and mechanical stability of AEMs, and further compared with the performance of uncrosslinked AEMs. The properties of the resulting AEMs were investigated and correlated with their polymer structure. In particular, m-terphenyl based AEMs exhibited better dimensional stability and the highest hydroxide conductivity of 144.2 mS/cm at 80 °C than other membranes, which can be attributed to their advantages of polymer backbone arrangement. Furthermore, the hydroxide conductivity of the prepared AEMs remains 80%–90% after treated by 2 M NaOH for 1600 h, exhibiting excellent alkaline stability. The single cell test of m-PTP-20Q4 exhibits a maximum power density of 239 mW/cm² at 80 °C. Hence, the results may guide the selection of polymer monomers to improve performance and alkaline durability for anion exchange membranes.     

Alkali-doped hyperbranched cross-linked polybenzimidazoles containing benzyltrimethyl ammoniums with improved ionic conductivity as alkaline direct methanol fuel cell membranes

Development of anion exchange membranes (AEMs) with good performance, such as high conductivity, good alkaline stability and mechanical strength, has been a hot topic for the fuel cell application. Here, a novel kind of hyperbranched cross-linker decorated with quaternary ammonium groups was introduced to polybenzimidazole (PBI) membranes and QOPBI-x membranes (where x is the weight ratio of the hyperbranched cross-linker). Compared with the linear OPBI membrane (0.091 S cm⁻¹), QOPBI-x membranes displayed an improved ionic conductivity (up to 0.122 S cm⁻¹) at 60°C after they were doped in 6 M KOH for 7 days. The KOH-doped QOPBI-x membranes also exhibited a high tensile strength (54.5-61.7 MPa) and superior alkaline stability. There is almost no decline in the ionic conductivity after being immersed in a 6 M KOH solution for 30 days. In addition, the alkaline direct methanol fuel cell (ADMFC) performance based on the KOH-doped OPBI and QOPBI-x membranes is described. The QOPBI-15 membrane displayed good performance (75.6 mW cm⁻²), which is 33.3% higher than the OPBI membrane (56.7 mW cm⁻²).     

Macromolecular crosslink of imidazole functionalized poly(vinyl alcohol) and brominated poly(phenylene oxide) for anion exchange membrane with enhanced alkaline stability and ionic conductivity

Anion exchange membranes (AEMs) are important energy conversion device for fuel cell applications, where the overall redox reaction happened. Both alkaline stability and ionic conductivity should be considered in the long-term use of fuel cells. In this work, imidazole functionalized polyvinyl alcohol was designed as the functional macromolecular crosslinking agent to fabricate crosslinked AEMs with brominated poly(phenylene oxide) matrix. Benefitting from the macromolecular crosslinked structure, the membranes displayed enhanced ionic conductivity and alkaline stability at elevated temperature. Moreover, membrane with ion exchange capacity of 1.54 mmol/g displayed ionic conductivity of 78.8 mS/cm at 80 °C, and the conductivity could maintain 75% of the initial value after immersion in 1 M NaOH solution at 80 °C for 1000 h. Moreover, a peak power density of 105 mW/cm² was achieved when the assembled single cell with c-91 was operated at 60 °C. These results indicated that the construction of macromolecular crosslinked AEMs have great potential in the practical application of anion exchange membranes fuel cells.