Conductivity Of Anion Exchange Membranes Research Articles

Machine Learning-Aided Design of Highly Conductive Anion Exchange Membranes for Fuel Cells and Water Electrolyzers.

Alkaline anion exchange membrane (AEM)-based fuel cells (AEMFCs) and water electrolyzers (AEMWEs) are vital for enabling the efficient and large-scale utilization of hydrogen energy. However, the performance of such energy devices is impeded by the relatively low conductivity of AEMs. The conventional trial-and-error approach to designing membrane structures has proven to be both inefficient and costly. To address this challenge, a fully connected neural network (FCNN) model is developed based on acid-catalyzed AEMs to analyze the relationship between structure and conductivity among 180,000 AEM variations. Under machine learning guidance, anilinium cation-type membranes are designed and synthesized. Molecular dynamics simulations and Mulliken charge population analysis validated that the presence of a large anilinium cation domain is a result of the inductive effect of N+ and benzene rings. The interconnected anilinium cation domains facilitated the formation of a continuous ion transport channel within the AEMs. Additionally, the incorporation of the benzyl electron-withdrawing group heightened the inductive effect, leading to high conductivity AEM variant as screened by the machine learning model. Furthermore, based on the highly active and low-cost monomers given by machine learning, the large-scale synthesis of anilinium-based AEMs confirms the potential for commercial applications.

Towards high conductivity and stability diblock poly(norbornene)s-based anion exchange membranes crosslinked with alkyl quaternary ammonium cationic clusters

Anion exchange membranes (AEMs) with exceptional comprehensive performance, combining high conductivity, alkaline and dimensional stability, have been indispensable for the practical application in fuel cells. Herein, a robust addition poly(norbornene)s-based AEMs with an all-carbon-hydrogen bicyclic skeleton were fabricated by cross-linking of alkyl quaternary ammonium cationic clusters and further quaternization. The partially crosslinked AEMs adopt a synergistic strategy that combines diblock copolymer backbone, cationic cluster crosslinking structure, and long flexible spacer suspended with cationic head groups. Benefiting from these structural design advantages, the prepared AEMs possessed excellent hydroxide conductivity (133.9–146.9 mS cm−1) and low swelling ratio (SR ≦ 20%) at 80 °C. The robust crosslinked AEMs exhibited good mechanical properties and high thermostability, with onset of decomposition temperatures up to 240 °C. Furthermore, after 44 days treatment in 1 M NaOH solution at 80 °C, the hydroxide conductivity of AEMs maintained at 79.4–85.7% of the initial value depending on the crosslinking degree, demonstrating excellent alkaline stability. In addition, the H2/O2 single cell equipped with CL20-aPNB-TAT-QA-1.75 achieved a peak power density of 338.0 mW cm−2 at 80 °C. The study provided a meaningful insight to exploit the practical application of multi-cation clusters crosslinked addition poly(norbornene)s-based AEMs in fuel cells.

Preparation of highly conductive anion exchange membranes by introducing dibenzothiophene monomer into the polymer backbone

The poly(aryl piperidinium) backbone has outstanding electrical conductivity and chemical stability, which is ideal for the preparation of anion exchange membranes (AEMs). Hence, in this research we prepared a series of high performance AEMs by introducing electron-rich dibenzothiophene (DBT) monomer into poly(aryl piperidinium) polymer backbone. The larger conjugated surface of the DBT monomer and the presence of heteroatoms facilitated intermolecular interactions between the polymers, which induced the generation of highly efficient ion-transport channels within the membranes, as evidenced by atomic force microscopy (AFM) images. The highest molar addition of DBT monomer, QPDBTTP-25 membrane, showed the highest conductivity (190.90 mS cm−1 at 80 °C) while maintaining robust dimensional stability (swelling ratio was 23.66 % at 80 °C). Owing to the advantages of the poly(aryl piperidinium) polymer backbone, the QPDBTTP-25 membrane also exhibited excellent mechanical properties (tensile strength of 53.03 MPa under fully hydrated condition) and durable chemical stability (conductivity retention remained at 93.2% after being immersed in 2 M NaOH solution at 80 °C for 1500 h). The H2/O2 fuel cell test based on QPDBTTP-25 membrane resulted in a peak power density of 384 mW cm−2 at 80 °C.

Preparation and properties of PPO-based anion exchange membranes with flexible side chains for fuel cells

Poor alkali resistance and low ionic conductivity are the crux of the matter that hinder the commercialization applications of anion exchange membranes (AEMs). Here, we designed and synthesized a range of poly(phenylene oxide) (PPO)-based AEMs with benzyl free side-chain type. After that, the influences of different cationic functional groups, such as quaternary ammonium, imidazole and piperidine, on the membrane performances were examined systemically. The introduction of ether bond-containing side chains to build micro-phase separation structures enhanced the conductivity of AEMs (64 mS·cm−1 at 80 °C). At the same time, the side-chain without benzyl structures effectively avoids the influence of electron withdrawing groups on PPO main chains. Moreover, the steric hindrance effect of the benzene ring can further alleviate the attack of OH−, thereby improving the alkali resistance of the membrane. Molecular dynamics simulations revealed that a well-developed hydrogen bonding network was formed between ether linkages and water molecules in the side-chain structures, which enhanced the electrical conductivity of the membrane. Meanwhile, the prepared membranes owned a good water uptake and a certain dimensional stability. These results provide a basis for the subsequent enhancement of membrane performances.

Fabrication of Dual-Functional Bacterial-Cellulose-Based Composite Anion Exchange Membranes with High Dimensional Stability and Ionic Conductivity.

Anion exchange membranes (AEMs) are increasingly becoming a popular research area due to their ability to function with nonprecious metals in electrochemical devices. Nevertheless, there is a challenge to simultaneously optimize the dimensional stability and ionic conductivity of AEMs due to the "trade-off" effect. Herein, we adopted a novel strategy of combining filling and cross-linking using functionalized bacterial cellulose (PBC) as a dual-functional porous support and brominated poly(phenylene oxide) (Br-PPO) as the cross-linking agent and filler. The PBC nanofiber framework together with cross-linking can provide a reliable mechanical support for the subsequent filled polymer, thus improving the mechanical properties and effectively limiting the size change of the final quaternized-PPO (QPPO)-filled PBC composite membrane. The composite membrane showed a very low swelling ratio of only 10.35%, even at a high water uptake (81.83% at 20 °C). Moreover, the existence of multiple -NR3+ groups in the cross-link bonds between BC and Br-PPO can provide extra OH- ion transport sites, contributing to the increase in ionic conductivity. The final membrane demonstrated a hydroxide ion conductivity of 62.58 mS cm-1, which was remarkably higher than that of the pure QPPO membrane by up to 235.93% (80 °C). The successful preparation of the PBC3/QPPO membrane provides an effective avenue to tackle the trade-off effect through a dual-functional strategy.

Poly(arylene alkylene)s Carrying Quaternary Ammoniums via Flexible Phenylpropyl Spacers as Hydroxide Conducting Membranes

Anion exchange membranes (AEM)s are attracting growing research interests as central components in various alkaline energy conversion and storage devices such as AEM fuel cells and water electrolyzers.1,2 Compared to the devices operated under acidic conditions, the alkaline conditions open up for possibilities to use, e.g., nickel and iron catalysts instead of platinum. However, the insufficient hydroxide conductivity and long-term stability of AEMs at elevated temperatures are still hindering a widespread application of these devices.3 An effective strategy to improve AEM properties by structure design is to functionalize hetero-atom free polymer backbones with quaternary ammonium cations via flexible spacers.4-6 In the present work, we have synthesized a series of AEM materials by tethering three different quaternary ammonium cations to poly(arylene alkylene)s via a phenylpropyl spacer (Figure 1a). The Friedel-Crafts acylation and polyhydroxyalkylation employed in the monomer and polymer syntheses are both free of noble metals and have excellent yields. All the polymers prepared in this way formed robust membranes reaching high hydroxide conductivities – up to 175 mS/cm at 80 °C (Figure 1b). PpT-DMP, carrying dimethyl piperidinium cations, was found to have the highest alkaline stability with less than 7% ionic loss after treatment in 7 M aq. NaOH at 90 oC during 240 h. The hydroxide conductivity of PpT-DMP reached 104 mS/cm at an ion exchange capacity (IEC) of 1.79 mequiv./g., which is still quite high. Atom force microscope (AFM) phase imaging revealed a phase separated morphology of PpT-DMP, most probably involving ion-clustering (Figure 1c). In this presentation we will further discuss the synthesis of these polymers, and influence of the phenylpropyl spacer on AEM properties.[1] Xue, J.; Zhang, J.; Liu, X.; Huang, T.; Jiang, H.; Yin, Y.; Qin, Y.; Guiver, M. D. Toward alkaline-stable anion exchange membranes in fuel cells: cycloaliphatic quaternary ammonium-based anion conductors. Electrochem. Energy Rev. 2022, 5, 348-400.[2] Chatenet, M.; Pollet, B. G.; Dekel, D. R.; Dionigi, F.; Deseure, J.; Millet, P.; Braatz, R. D.; Bazant, M. Z.; Eikerling, M.; Staffell, I.; Balcombe, P.; Horn, Y. S.; Schafer, H. Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments. Chem. Soc. Rev. 2022, 51, 4583-4762.[3] Varcoe, J. R.; Atanassov, P.; Dekel, D. R.; Herring, A. M.; Hickner, M. A.; Kohl, P. A.; Kucernak, A. R.; Mustain, W. E.; Nijmeijer, K. N.; Scott, K.; Xu, T.; Zhuang, L. Anion-exchange membranes in electrochemical energy systems. Energy Environ. Sci. 2014, 7, 3135-3197.[4] Dang, H. S.; Jannasch, P. Exploring different cationic alkyl side chain designs for enhanced alkaline stability and hydroxide ion conductivity of anion-exchange membranes. Macromolecules 2015, 48, 5742-5751.[5] Allushi, A.; Pham, T. P.; Olsson, J. S.; Jannasch, P. Ether-free polyfluorenes tethered with quinuclidinium cations as hydroxide exchange membranes. J. Mater. Chem. A 2019, 7, 27164-27174.[6] Lee, W. H.; Kim, Y. S.; Bae, C. Robust Hydroxide Ion Conducting Poly(biphenyl alkylene)s for Alkaline Fuel Cell Membranes. ACS Macro Lett. 2015, 4, 814-818. Figure 1. a) Poly(arylene alkylene)s tethered with different quaternary ammonium cations via phenylpropyl spacers, b) hydroxide conductivity of the AEMs in the fully hydrated state, and c) an AFM phase image of PpT-DMP. Figure 1

A Hybrid Direct Ammonia Fuel Cell

Ammonia has emerged as a highly promising energy carrier [1], primarily because it offers a noticeable economic benefit over hydrogen in terms of source-to-tank expenses, owing to reduced transmission, distribution, and dispensation costs [2]. Direct ammonia fuel cells (DAFCs) are capable of directly converting the chemical energy stored in ammonia into electrical energy. With its quick start-up advantage, this fuel cell technology holds great potential in the field of zero-emission transportation [3]. Although promising, this fuel cell performance needs to be much improved before the widespread commercialization becomes possible. The limiting factors include the sluggish kinetics of ammonia oxidation and the poor conductivity of anion exchange membranes. In addition, another important factor that limits the cell performance is that thermodynamically, its theoretical voltage is low (1.17 V). In this work, a hybrid direct ammonia fuel cell is developed, which consists of an alkaline anode, a cation exchange membrane, and an acid cathode. This hybrid fuel cell offers a theoretical voltage of as high as 2.55 V. The experimental results have shown that it exbibits an open-circuit voltage of 1.35 V and a peak power density of 437.1 mW cm−2 at 90 °C. Acknowledgement This work was fully supported by a grant from the National Natural Science Foundation of China (Project No. 52022003).

Microphase separation structures facilitated by dipole molecules and hydrogen bonding in poly (biphenyl piperidine-isatin) anion exchange membranes

The anion exchange membranes (AEMs) have the important function of blocking fuel and conducting OH− to make the cell form a circuit, so its alkali stability directly affects the performance of alkaline fuel cells. Currently, AEMs face a “trade-off” between ionic conductivity and stability. In order to solve this problem, we optimize the alkali resistance and conductivity of AEMs by introducing dipole-interacting side chains and hydrophilic hydroxyl side chains acting simultaneously on a rigid polymer backbone. By adopting the design strategy of “1 + 1>2″, the ion channel efficiency also makes a high-speed leap from a “two-wheeled bicycle” to a “four-wheeled car”. This effective microscopic modulation is clearly demonstrated by transmission electron microscope (TEM), where the AEMs after molecular design carry out a more obvious microphase separation structure at 200 nm. Through the PBP-54-IS- [OPD-100-OH-0] membrane, the maximum ionic conductivity is 100.62 mS cm−1 at 80 °C. After 1000 h at 80 °C, the retention rate of OH− conductivity of all AEMs was over 88.24 %. We also test its fuel cell performance for analysis. When the temperature of the two poles is 75 °C/72 °C, the power density is 147.28 mW cm−2. These are in line with the inherent requirements of AEMs for fuel cell applications.

Highly conductive anion-exchange membrane based on poly(acenaphthylenyl aryl piperidinium) π-π self-assembly

The use of strong intermolecular interaction force to promote the formation of ion transport channels is one of the common methods to increase the conductivity of AEMs. In this work, a series of poly(acenaphthylenyl aryl piperidinium) membranes and ionomer were prepared by ultra-strong acid-catalyzed polymerization. The π-π self-assembly of acenaphthylene monomer promoted the aggregation of piperidinium cation and the formation of efficient ion transport channel, which was confirmed by well aggregated transmission electron micrographs of the ion clusters. Therefore, the prepared membrane had desirable conductivity (173.38 mS cm−1 at 80 °C). Meanwhile, the membrane exhibited excellent alkaline stability (99 % retention of conductivity in 3 M NaOH solution immersed at 80 °C for 1000 h), acceptable dimensional stability (swelling rate < 27.78 % at 80 °C), and high mechanical properties (tensile strength >33.9 MPa). The H2/O2 fuel cell assembled based on the prepared QPANTP-20 membrane and ionomer exhibited peak power density of 266 mW cm−2 at 80 °C.

Molecular Assembly of Alkylated Fused Expanded Pyridinium for a Highly Conductive Anion-Exchange Membrane

Molecular Assembly of Alkylated Fused Expanded Pyridinium for a Highly Conductive Anion-Exchange Membrane

Predicting the anion conductivities and alkaline stabilities of anion conducting membrane polymeric materials: development of explainable machine learning models

ABSTRACT Anion exchange membranes (AEMs) are core components in fuel cells and water electrolyzers, which are crucial to realize a sustainable hydrogen society. The low anion conductivity and durability of AEMs have hindered the commercialization of AEM-based devices, and research and development (R&D) to improve AEM materials is often resource-intensive. Although machine learning (ML) is commonly used in many fields to accelerate R&D while reducing resource consumption, it is rarely used in the AEM field. Three problems hinder the adoption of ML models, namely, the low explainability of ML models; complication with expressing both homopolymers and copolymers in unity to train a single ML model; and difficulty in building a single ML model that comprehends various polymer types. This study presents the first ML models that solve all three problems. Our models predicted the anion conductivity for a diverse set of unseen AEM materials with high accuracy (root mean squared error = 0.014 S cm−1), regardless of their state (freshly synthesized or degraded). This enables virtual pre-synthesis screening of novel AEM materials, reducing resource consumption. Moreover, human-comprehensible prediction logic revealed new factors affecting the anion conductivity of AEM materials. Such capability to reveal new important variables for AEM materials design could shift the paradigm of AEM R&D. This proposed method is not limited to AEM materials, instead it presents a technology that is applicable to the diverse set of polymers currently available.

Fluorinated poly(p-triphenyl piperidine) anion exchange membranes with robust dimensional stability for fuel cells

Anion exchange membrane fuel cells (AEMFCs), which are more economical than proton exchange membrane fuel cells (PEMFCs), stand out in the context of the rapid development of renewable energy. Superacid-catalyzed ether-free aromatic polymers have recently received a lot of attention due to their exceptional performance, but their development has been hampered by the trade-off between the dimensional stability and ionic conductivity of anion exchange membranes (AEMs). Here, we introduced fluoroketones containing different numbers of fluorinated groups (x = 0, 3 and 6) in the main chain of p-terphenyl piperidine because of the favorable hydrophobic properties of fluorinated groups. The results show that fluorinated AEMs can enhance OH− conductivity by building more aggregated hydrophilic channels while ensuring dimensional stability. The PTF6-QAPTP AEM with more fluorinated groups has the most excellent performance at 80 °C with an OH− conductivity of 142.7 mS cm−1 and a swelling ratio (SR) of only 4.55 %. Additionally, it exhibits good alkali durability, with the OH− conductivity and quaternary ammonium (QA) cation retaining at 93.45% and 92.6%, respectively, after immersion in a 2 M NaOH solution at 80 °C for 1200 h. In addition, the power density of the PTF6-QAPTP based single cell reaches 849 mW cm−2 when the current density is 1600 mA cm−2. The PTF6-QAPTP based cell has a voltage retention of 88% after 80 h of stability testing at a constant current density of 300 mA cm−2 at 80 °C.

Highly alkaline stability poly(aryl ether piperidinium) anion exchange membranes with partial aryl ether segments

Poly(aryl piperidinium) is considered a promising material for the preparation of anion exchange membranes (AEM) with considerable conductivity and excellent chemical stability for anion exchange membrane fuel cells (AEMFC). In this research, we report a range of biphenyl ether-containing poly(aryl ether piperidinium) unlike previous ones to increase the conductivity of AEMs and the peak power density (PPD) of fuel cells, and the alkaline stability of ether bonds in the polymer backbone is demonstrated. All of the poly(aryl ether piperidinium) membranes possess comparable mechanical properties and inherent viscosity derived from the high activity of biphenyl ethers in superacid-catalyzed reactions, which means that large-width AEMs can be prepared. The data demonstrated that the poly (ether p-terphenyl piperidinium) (QPEPTpi-35) exhibited a conductivity of 140 mS cm−1 at 80 ℃ compared to the original poly (p-terphenyl piperidinium) (QPTPpi) membrane owning to optimized micro-phase separation structure and higher water uptake. Meanwhile, QPEPTpi-35 membrane conductivity retention is greater than 85% after immersion in 1 M KOH for 2000 h at 80 ℃. Moreover, the PPD of the QPEPTpi-35 membrane reaches 1.2 W cm−2 in H2/O2 fuel cells, which is much higher than that of the QPTPpi membrane (0.51 W cm−2). The durability of MEA prepared by the catalyst-coated substrate (CCS) method manifests over 20 h under 0.2 A cm−2 at 60 °C.

Anion Exchange Membranes for Fuel Cells: Equilibrium Water Content and Conductivity Characterization

AbstractThe ionic conductivity of anion exchange membranes (AEMs) directly determines the performance of anion exchange membrane fuel cells (AEMFCs), which highly depends on the hydration level of the membrane. A better understanding of the relationship between hydration level and membrane ionic conductivity is essential for membrane development and for water and thermal management analyses of AEMFCs. In this study, the effects of water activity and temperature on water uptake, equilibrium water content, and ionic conductivity of three high‐performance AEMs (Alkymer, Orion, and Pention) are quantitatively characterized via the designed experiments. The results show that Orion exhibits the lowest water uptake and highest ionic conductivity among the three membranes at high water activity and Alkymer exhibits good water‐retention capability and the highest ionic conductivity at low water activity. Empirical equations combining water activity and equilibrium water content are proposed based on fitted experimental data to define the hydration level. Empirical equations combining ionic conductivity, equilibrium water content, and temperature are fitted to illustrate the relationship between ionic conductivity and hydration level. The findings of this study can provide solid guidelines and support for the future experimental characterization and water and thermal management analyses of AEMFCs.

High‐performance Poly(biphenyl piperidinium) Type Anion Exchange Membranes with Interconnected Ion Transfer Channels: Cooperativity of Dual Cations and Fluorinated Side Chains

AbstractThe performance of alkaline fuel cells is severely limited by substandard anion exchange membranes (AEMs) due to the lower ionic conductivity compared to the proton exchange membranes. The ionic conductivity of AEMs can be effectively improved by regulating the microphase structure, but it still cannot meet the practical use requirements. Here, enhanced microphase‐separated structures are constructed by the cooperativity of highly hydrophilic dual cations and highly hydrophobic fluorinated side chains. Meanwhile, the introduction of O enhances the flexibility of side chains and facilitates the formation of ion transport channels. The dual piperidinium cation functionalized membrane (PB2Pip‐5C8F) which is grafted with the ultra‐hydrophobic fluorocarbon chain exhibits a high conductivity of 74.4 mS cm−1 at 30 °C and 168.46 mS cm−1 at 80 °C. Furthermore, the PB2Pip‐5C8F membrane achieves the highest peak power density of 718 mW cm−2 at 80 °C under a current density of 1197 mA cm−2 without back pressure. A long‐term life cell test of this AEM shows a low voltage decay rate of 1.68 mV h−1 over 70 h of operation at 80 °C.

Highly conductive, anti-freezing, and adhesive hydrogels containing pores constructed by cation–dipole interactions

The low ionic conductivity of most hydrogels limits their application in various fields. Boosting ion conductivity in anion exchange membranes (AEMs) using dipole-ion interactions (electrostatic attraction between anions and neutral dipole molecules) with exceptional interaction energies of 20 to 200 kJ mol−1 is the best way to create ion channels in anion exchange membranes (AEMs). In this study, intending to increase the ionic conductivity of hydrogels, the antifreeze crosslinked PVA/PVP hydrogels (5, 10, and 15% Cr-PVA) were prepared using 1,10-dibromodecane (DBD) to crosslink PVA and PVP via SN2 reaction to create multiple pores morphology in the hydrogels by cation-dipole interactions. Moreover, the prepared hydrogels contain cationic groups facilitating ion transport through the hopping mechanism. There was a significant difference in ionic conductivity between the 10% Cr-PVA hydrogel (2.63 S m−1) and the PVA hydrogel (0.76 S m−1) at room temperature due to the multiple pores created with cation-dipole interaction. Despite excellent mechanical properties, 10% Cr-PVA at −20 °C (1.25 S m−1) has a higher ionic conductivity than most antifreeze conductive hydrogels. Eventually, the 10% Cr-PVA hydrogel with gauge factor 1.97 demonstrated the desired sensitive response performance for sensor applications.

Effects of the crown ether cavity on the performance of anion exchange membranes

Anion exchange membrane fuel cells (AEMFCs) have emerged as a promising alternative to proton exchange membrane fuel cells (PEMFCs) due to their adaptability to low-cost stack components and non-noble-metals catalysts. However, the poor alkaline resistance and low OH− conductivity of anion exchange membranes (AEMs) have impeded the large-scale implementation of AEMFCs. Herein, the preparation of a new type of AEMs with crown ether macrocycles in their main chains via a one-pot superacid catalyzed reaction was reported. The study aimed to examine the influence of crown ether cavity size on the phase separation structure, ionic conductivity and alkali resistance of anion exchange membranes. Attributed to the self-assembly of crown ethers, the poly (crown ether) (PCE) AEMs with dibenzo-18-crown-6-ether (QAPCE-18-6) exhibit an obvious phase separated structure and a maximum OH− conductivity of 122.5 mS cm−1 at 80 °C (ionic exchange capacity is 1.51 meq g−1). QAPCE-18-6 shows a good alkali resistance with the OH− conductivity retention of 94.5% albeit being treated in a harsh alkali condition. Moreover, the hydrogen/oxygen single cell equipped with QAPCE-18-6 can achieve a peak power density (PPD) of 574 mW cm−2 at a current density of 1.39 A cm−2.

Ether-free polymer based bipolar electrolyte membranes without an interlayer catalyst for water electrolysis with durability at a high current density

In this study, bipolar membranes (BPMs) were fabricated employing the sulfonated poly(fluorine biphenyl indole) based proton exchange membrane (PEM) and the poly(arylene piperidinium) based anion exchange membrane (AEM) for the production of green hydrogen by water electrolysis. As those polymers comprise similar aromatic backbone structures without ether groups, excellent chemical durability of the constituent membranes was expected for the long-term energy efficient operation in a wide pH range. Three BPMs with different ionic conductivity pairs between PEM and AEM were designed to explore its effect on water electrolysis performance. At the fixed anionic conductivity of AEM of 0.0370–0.0923 S cm−1 at 30–70 °C, the proton conductivity of PEMs was tuned as 0.0379–0.1196 S cm−1, 0.0909–0.1598 S cm−1, and 0.1104–0.1739 S cm−1 at 30–70 °C. BPMs were steadily operated at low voltages below 1.5 V in the wide current density range of 0–1500 mA cm−2. Among them, the water electrolytic cell assembled with BPM 80/20 showed the best water electrolysis performance, as the cell voltage of BPM 80/20, BPM 70/30, and BPM 60/40 was 0.75 V, 0.98 V, and 1.08 V, respectively, under the current density of 700 mA cm−2 at 70 °C. It was much lower than that of AEM, 2.24 V and PEM 80/20, 1.81 V even in the absence of interlayer catalyst. Also, the synthesized BPM 80/20 was not only thermally and mechanically stable up to 298 °C and 19.15 MPa (tensile strength), but also chemically stable in the concentrated acidic and basic environment, as its weight loss was less than 5.4 % and 4.62 % in 4 M H2SO4 and 4 M KOH solutions for 4 weeks, respectively.

Development of highly conductive anion exchange membranes based on crosslinked PIM-SEBS with high free volume

x-PIM-SEBS membranes were developed by chemical crosslinking of PIM with SEBS. The developed membrane showed good phase separation and ion conductivity through free volume, and also showed high AEMWE performance of 1.905 A cm−2 at 2.0 V.

Semi-interpenetrating anion exchange membranes using hydrophobic microporous linear poly(ether ketone)

In order to realise high ionic conductivity and improved chemical stability, a series of anion exchange membranes (AEMs) with semi-interpenetrating polymer network (sIPN) has been prepared via the incorporation of crosslinked poly(biphenyl N-methylpiperidine) (PBP) and spirobisindane-based intrinsically microporous poly(ether ketone) (PEK-SBI). The formation of phase separated structures as a result of the incompatibility between the hydrophilic PBP network and the hydrophobic PEK-SBI segment, has successfully promoted the hydroxide ion conductivity of AEMs. A swelling ratio (SR) as low as 12.2 % at 80 °C was recorded for the sIPN containing hydrophobic PEK-SBI as the linear polymer and crosslinked structure with a mass ratio of PBP to PEK-SBI of 90/10 (sIPN-90/10(PEK-SBI)). The sIPN-90/10(PEK-SBI) AEM achieved the highest hydroxide ion conductivity of 122.4 mS cm−1 at 80 °C and a recorded ion exchange capacity (IEC) of 2.26 meq g−1. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) clearly revealed the improved phase separation structure of sIPN-90/10(PEK-SBI). N2 adsorption isotherm indicated that the Brunauer-Emmett-Teller (BET) surface area of the AEMs increased with the increase of microporous PEK-SBI content. Interestingly, the sIPN-90/10(PEK-SBI) AEM showed good alkaline stability for being able to maintain a conductivity of 94.7 % despite being soaked in a 1 M sodium hydroxide solution at 80 °C for 30 days. Meanwhile, a peak power density of 481 mW cm−2 can be achieved by the hydrogen/oxygen single cell using sIPN-90/10(PEK-SBI) as the AEM.