Durable Anion Exchange Membrane Research Articles

Development of Pore-Filling Anion Exchange Membranes for Anion Exchange Membrane Water Electrolysis: Enhancement of Alkaline Stability

Water electrolysis is a process that uses electricity to decompose water into oxygen and hydrogen. There are several types of ion exchange membrane can be used, anion exchange membrane, proton exchange membrane and bipolar membrane for water electrolysis. Alkaline based water electrolysis has several advantages to use non-precious electrocatalysts. However, the development of low resistance and durable anion-exchange membranes is of importance. In this study, several anion-exchange membranes were developed to enhance alkaline stability. Pore-filling anion exchange composite membranes with different contents of cross-linkers were prepared by mixing an electrolyte having good anion conducting ability. The mixture of monomers into a porous polyethylene (PE) substrate were polymerized by UV curing. The pore-filling reinforced composite membranes have been investigated in terms of good chemical stability properties, in particular, the variation of conductivity and mechanical strength in 1 M KOH at 60 oC. Characterization in terms of ion exchange capacity, water uptake, swelling ratio, and mechanical strength were also investigated. Acknowledgments This research was supported in part by "Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ016253)" Rural Development Administration, Republic of Korea, by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040520) and by 2022 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Development of Pore-Filling Anion Exchange Membranes for Anion Exchange Membrane Water Electrolysis: Enhancement of Resistance

Water electrolysis is a process that uses electricity to decompose water into oxygen and hydrogen. There are several types of ion exchange membrane can be used, anion exchange membrane, proton exchange membrane and bipolar membrane for water electrolysis. Alkaline based water electrolysis has several advantages to use non-precious electrocatalysts. However, the development of low resistance and durable anion-exchange membranes is of importance. In this study, several anion-exchange membranes were developed to enhance areal resistance, in other words, to minimize areal resistance. Pore-filling anion exchange composite membranes with different contents of cross-linkers were prepared by mixing an electrolyte having good anion conducting ability. The mixture of monomers into a porous polyethylene (PE) substrate were polymerized by UV curing. The pore-filling reinforced composite membranes have been investigated in terms of good electrochemical properties, in particular, areal resistance. The conductivity and areal specific resistance were measured in both in-plane cell and through-plane cell at 80 ℃ and at room temperature, respectively. Characterization in terms of ion exchange capacity, water uptake, swelling ratio, and mechanical strength were also investigated. Acknowledgments This research was supported in part by "Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ016253)" Rural Development Administration, Republic of Korea, by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040520) and by 2022 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Superior Performance and Durability Water Electrolysis with a Highly Conductive and Stable Anion-Exchange Membrane

The commercialization of anion-exchange membrane water electrolysis (AEMWE) is important to produce low-cost and high-purity hydrogen. However, water electrolysis with an anion-exchange membrane (AEM) has limitations such as its poor stability and ionic conductivity, leading to low durability and performance of AEMWE. In this study, we developed superior-performance and stable AEMWE by employing an AEM without aryl-ether backbone structure. To achieve superior -performance and durable AEMWE, the effect of various parameters that is suitable for the adapted AEM was estimated. As a result, the AEM adapted in this work showed much better and was more durable than the conventional AEM (FAA-3). Moreover, it exhibited high efficiency under pure water feeding conditions. These results were contributed to high-efficient and durable AEM caused by its absence of aryl-ether backbone. This work suggests the potential use of polyphenylene structure as aryl-ether free backbone of AEM on AEMWE under alkaline solution and/or pure water condition.

Efficient and Durable Anion Exchange Membrane Water Electrolysis for a Commercially Available Electrolyzer Stack using Alkaline Electrolyte

Efficient and Durable Anion Exchange Membrane Water Electrolysis for a Commercially Available Electrolyzer Stack using Alkaline Electrolyte

(Energy Technology Division Graduate Student Award sponsored by BioLogic) Design Principles for High-performance and Durable Anion Exchange Membrane water Electrolyzers

Water electrolysis powered by renewable sources such as wind or solar produces clean hydrogen gas, which is used for many industrial processes and will be essential in a future clean energy economy. Alkaline water electrolysis (AWE) and proton exchange membrane (PEM) electrolysis are mature technologies at megawatt to gigawatt scale. AWE uses earth abundant electrode and catalyst materials submerged in caustic liquid electrolyte (usually KOH or NaOH) separated by a porous diaphragm. This configuration can suffer from gas crossover and shunt current limitations. PEM electrolyzers circumvent these barriers by using an ionically-conductive solid electrolyte membrane that reduces gas crossover and allows for pure water operation that eliminates shunt currents. However, these membranes create a locally acidic environment that necessitates the use of expensive platinum-group-metal (PGM) catalyst materials and hardware coatings. Anion exchange membrane (AEM) electrolysis is an emerging technology that has the potential to combine the benefits of liquid alkaline and PEM. AEM electrolyzers use an anion-selective membrane, maintaining the pure water operation of PEM but creating a locally-alkaline environment allowing for the use of non-PGM materials. However, AEM electrolysis is still immature. In particular, the hydroxide-conducting membrane and ionomer have not yet achieved sufficient stability in pure water to compete with PEM systems. The specific dominant degradation mechanism and location has also not been conclusively identified. Further, while non-PGM catalysts such as Ni- and Fe-based oxyhydroxide catalysts out-compete PGM catalysts in three-electrode KOH studies, this performance does not carry to the pure water electrolyzer configuration. In my talk I report AEM electrolyzer performance below 2 V at 1 A·cm-2 in pure water for both PGM and non-PGM anode catalysts. I will also discuss the specific degradation mechanism of the ionomer and membrane during electrolyzer operation with both catalysts. Understanding the differences in performance and durability with precious metal and earth abundant materials is key for AEMs to compete with current electrolyzer technologies. I compare the performance and stability of five Ni-, Co-, and Fe-based catalysts and compare to IrOx. XPS and cross-sectional SEM data show oxidation of the ionomer binder at the anode for all catalysts, which results in significant degradation and performance loss. I also show additional degradation is induced by introducing soluble Fe species, indicating separate mechanisms beyond ionomer degradation are present in the non-PGM systems. In addition to the fundamental insights into the dynamic behavior of non-PGM catalysts and oxidative durability of ionomeric polymer materials, these findings contribute to bringing low-cost AEM electrolyzer technology to scale. Figure 1

Long-term durable anion exchange membranes based on imidazole-functionalized poly(ether ether ketone) incorporating cationic metal−organic framework

In this work, poly(ether ether ketone) (PEEK) was synthesized by direct polycondensation reaction. Subsequently, PEEK was functionalized by 1-vinylimidazole to prepare the polymer matrix (Im-PEEK). Cationic UiO-66-NH 2 metal-organic frameworks (C-MOF) were synthesized as fillers. The structure of the C-MOF and the morphology of the membranes were verified by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The prepared hybrid membranes exhibited excellent alkali stability, among which Im-PEEK/C-MOF-1% could retain 89.2% of the conductivity compared to the original membrane after immersing in 1 ​mol ​L −1 NaOH solution for 320 ​h at 60 ​°C. In addition, the ionic conductivity of Im-PEEK/C-MOF-1% was 73 ​mS ​cm −1 at 80 ​°C, which was higher than that of pure Im-PEEK under the same condition (44.3 ​mS ​cm −1 at 80 ​°C). The results showed that the hybrid membranes have great potential for application in the field of anion exchange membranes.

Effect of catalyst layer designs for high-performance and durable anion-exchange membrane water electrolysis

Development of anode design is crucial for highly efficient and durable anion-exchange membrane water electrolysis (AEMWE) as the kinetic of oxygen evolution reaction (OER) is sluggish. In this study, a macroporous catalyst layer (macroporous_CL) was proposed as an anode design for AEMWE to enhance the catalyst utilization. A macroporous_CL contains pores of two main size ranges: hundreds of nanometers and hundreds of micrometers. It is prepared using a spraying method to form nanometer-sized pores. The use of a stainless-steel (SUS) porous transport layer (PTL) as the substrate of the spraying method produces micrometer-sized macropores. In an investigation of the effects of the macroporous_CL and conventional catalyst layer (plain_CL) on AEMWE using two different kinds of oxygen evolution reaction (OER) catalysts, the macroporous_CL exhibited higher performance with lower ohmic and charge-transfer resistances compared to the plain_CL. This performance enhancement was attributed to the improved catalyst utilization and electron transport. Also, the macroporous_CL showed better durability compared to the plain_CL. Therefore, the macroporous_CL has been considered as an alternative anode design for AEMWE.

Reinforced poly(fluorenyl-co-terphenyl piperidinium) anion exchange membranes for fuel cells

Mechanically tough and durable anion exchange membranes (AEMs) are vital materials for AEM fuel cells (AEMFCs). Here, we report a series of high-performance high density polyethylene (PE)-reinforced in-house AEMs based on poly(fluorenyl-co-terphenyl piperidinium) (PFTP@PE) using EtOH as an assistant co-solvent. We found that EtOH showed low contact angle and interface tension on the PE substrate, which improved the penetration efficiency of polymer solutions in the PE substrate. Specifically, 15% EtOH-assisted PFTP@PE membranes displayed ∼100% visible light transmittance and outstanding tensile strength greater than 120 MPa (along with ∼50% elongation at break) compared to PFTP@PE without EtOH assistance (51% light transmittance and 80 MPa tensile strength). Moreover, the peak power densities of PFTP@PE-based AEMFCs reach 1.7 W cm −2 in H 2 –O 2 and 1.08 W cm −2 in H 2 -air(CO 2 free) at 80 °C. The present work provides a facile and scalable method to fabricate high-performance reinforced AEMs. • Reinforced PFTP membranes (RCM) were prepared with a porous polyethylene substrate. • Ethanol aids the preparation of RCM due to the low contact angle and surface tension. • PFTP RCMs displayed excellent mechanical stability and transparency. • The power densities of RCM AEMFCs reached 1.7 W cm −2 in H 2 –O 2 and 1.08 W cm −2 in H 2 -air at 80 °C.

High-performance and durable water electrolysis using a highly conductive and stable anion-exchange membrane

The commercialization of anion-exchange membrane water electrolysis (AEMWE) is crucial to produce low-cost and high-purity hydrogen. However, water electrolysis with an anion-exchange membrane (AEM) has limitations such as its low ionic conductivity and stability, leading to low performance and durability of AEMWE. In this study, we developed high-performance and stable AEMWE employing an AEM without aryl-ether backbone structure. To achieve high-performance and durable AEMWE, the effect of various parameters that is suitable for the adapted AEM was investigated. As a result, the AEM adapted in this work performed much better and was more durable than the conventional AEM (FAA-3). Moreover, it exhibited high efficiency under pure water feeding conditions. These results were attributed to high-efficient and durable AEM caused by its absence of aryl-ether backbone. This work suggests the potential use of polyphenylene structure as aryl-ether free backbone of AEM on AEMWE operated using alkaline solution and/or pure water. • Highly conductive and stable anion-exchange membrane is proposed. • Effect of aryl-ether on polymer backbone is investigated. • The aryl-ether free anion-exchange membrane shows superior performance and stability. • The aryl-ether free membrane has a potential to operating with pure water.

Single-Step Hydrothermal-Deposited Ni-Co Phosphites as a Noble-Metal Free Catalyst for the Durable Anion-Exchange Membrane Water Electrolyzer Cell

Single-Step Hydrothermal-Deposited Ni-Co Phosphites as a Noble-Metal Free Catalyst for the Durable Anion-Exchange Membrane Water Electrolyzer Cell

Three-Dimensional Unified Electrode Design Using a NiFeOOH Catalyst for Superior Performance and Durable Anion-Exchange Membrane Water Electrolyzers

Three-Dimensional Unified Electrode Design Using a NiFeOOH Catalyst for Superior Performance and Durable Anion-Exchange Membrane Water Electrolyzers

(Invited) Poly(aryl-co-aryl piperidinium) Copolymers for High-Performance Anion Exchange Membrane Fuel Cells

Poly(aryl piperidinium)s (PAPs) have attracted great attention as durable anion exchange membrane (AEMs) and ionomers for AEM fuel cells (AEMFCs). However, most of PAP AEMs display poor microphase morphology, and ionomer research on PAPs is still lacking to date. Here, we report a series of high-performance poly(aryl-co-aryl piperidinium) copolymers (c-PAPs) for AEMs and ionomers, along with improving AEMFC performance (Figure 1). Compared with PAPs, c-PAP AEMs possess higher ion conductivity (>200 mS cm-1), enhanced mechanical properties (tensile strength>80 MPa), lower hydrogen permeability (<10 Barrer) and optimized microphase morphology. On the other hand, c-PAP ionomers display lower ionomer adsorption on platinum-group-metal (PGM) catalysts and higher electrochemical performance than PAP ionomers. Based on poly(diphenyl-co-terphenyl piperidinium) AEMs (PDTP) and poly(fluorenyl-co-biphenyl piperidinium) (PFBP) ionomers, the peak power density (PPD) of presented AEMFCs reaches 2.67 W cm-2 in H2-O2 and 1.38 W cm-2 in H2-air (CO2 free) at 80 oC based on optimized c-PAP AEMs and ionomers. Moreover, c-PAP based AEMFCs reach >1000 h in-situ durability under 1 A cm-2 current density in H2-O2 at 60oC. The presented works provide insight into c-PAP AEMs and ionomers. Figure 1. Chemical structure of c-PAP AEMs and ionomers, along with high PPDs of AEMFCs over 2.6 W cm-2. Reference [1] N. J. Chen and Y. M. Lee. Progress in Polymer Science. 2021, 113, 101345.[2] N. J. Chen, C. Hu, Y. M. Lee, et al. Angew. Chem. Int. Ed. 2021, 60, 7710-7718.[3] N. J. Chen, H. H. Wang, Y. M. Lee, et al. Nat. Commun. 2021. DOI. Figure 1

(Invited) Partially Fluorinated Anion Exchange Membranes for Electrochemical Applications

There has been a considerable effort to develop high performance and durable anion exchange membranes (AEMs) for the electrochemical applications such as fuel cells, electrolyzers, and redox flow batteries. When these devices are operated under alkaline conditions, possible use of non-precious metal catalysts is advantageous. Although a number of AEMs have been proposed in the literature, chemical and mechanical stability in alkaline media still remains an issue for long-term, reliable operation of the devices. In the pursuit of more stable AEMs, we have recently reported some new polymer structures. Combination of absence of heteroatom linkages such as ether, sulfide, and sulfone in the main chain and employing pendant ammonium groups contributed to improvement of the alkaline and mechanical stability of AEMs. A typical example is QPAF-4 copolymers composed of perfluoroalkylene/phenylene main chain and hexylammonium head groups, which exhibited high hydroxide ion conductivity and alkaline stability.1 In the present paper, we report effect of other fluorinated components for our AEMs. We have developed a novel series of quaternized aromatic copolymers (BAF-QAFs) containing hexafluoroisopropylidene groups.2 Similar to QPAF-4 copolymer membranes, BAF-QAF copolymers had good solubility in polar organic solvents, membrane forming capability, and phase-separated morphology. Hexafluoroisopropylidene groups contributed to efficient anion transport as BAF-QAF membranes showed lower water uptake and higher hydroxide ion conductivity than those of QPAF-4 membranes. BAF-QAF membranes were thermally stable up to 95 °C and 90% RH with no obvious glass transition behavior in DMA analyses, while the elongation of BAF-QAF membranes were smaller than that of QPAF-4 membranes. BAF-QAF membranes were alkaline stable in 1 and 4 M KOH at 80 °C for 1000 h. A hydrogen/oxygen fuel cell with the BAF-QAF as a membrane and an electrode binder was successfully operated. The maximum power density reached 319 mW/cm2 at a current density of 702 mAcm2 with O2. The fuel cell with BAF-QAF copolymers were better in cathode performance than QPAF-4 cell most probably because of the higher hydroxide ion conductivity and better interfacial contact between the membrane and the catalyst layer. Acknowledgements This project was partly supported by NEDO through the Advanced Research Program for Energy and Environmental Technologies, JST through SICORP project, and JSPS/SNSF under the Joint Research Projects (JRPs) program. References Ono, T. Kimura, A. Takano, K. Asazawa, J. Miyake, J. Inukai, K. Miyatake, J. Mater. Chem. A, 5, 24804 (2017).Kimura, A. Matsumoto, J. Inukai, K. Miyatake, ACS Appl. Energy Mater., 3, 469-477 (2020). Figure 1

Novel polyolefin based alkaline polymer electrolyte membrane for vanadium redox flow batteries

Low conductivity and stability of anion exchange membranes limited the durability and performance of corresponding fuel cells despite their unique advantages in compared to the proton exchange membrane fuel cells. In this work, we present a simple and efficient method to fabricate highly durable anion exchange membranes from commercial porous hydrocarbon substrates. Polyethylene/polypropylene (PE/PP) microfibers is employed as a substrate and radiation induced emulsion grafting is utilized to introduce poly(vinylbenzyl chloride) side chains. The grafted substrates with flexible content of side chains are converted to anion exchange membranes by converting into dense membranes and introducing quaternary amine groups. The dense membranes are characterized and employed in vanadium redox flow battery (VRFB) application. Developed membranes demonstrate high anion conductivity, low vanadium permeability and good chemical and mechanical stability. In compare to Nafion 117, superior performance is achieved for the developed membranes as the undesired vanadium ion permeability is reduced by 16 times and the energy efficiency significantly enhanced by 9% at current density of 80 mA cm−2. Such enhanced performance of the developed membrane is attributed to the presence of positive charged ionic groups in the membrane structure.

Molecularly designed, solvent processable tetraalkylammonium-functionalized fluoropolyolefin for durable anion exchange membrane fuel cells

A new generation of solvent processable fluoropolyolefin was prepared and explored for durable anion exchange membrane fuel cells. By one-pot Ziegler-Natta copolymerization of a fluorinated monomer (1-(but-3-en-1-yl)-4-fluorobenzene) with 11-bromo-1-undecene and subsequent quaternization with trimethylamine, a series of tetraalkylammonium-functionalized fluoropolyolefin was synthesized by varying the molar ratio between monomers. The excellent solubility of the quaternized fluoropolyolefins provided by fluorinated moieties enabled the solvent processability to afford transparent and robust AEMs (PBFB-QA). Compared to heterogeneous quaternized membranes (H-PBFB-QA) and the corresponding non-fluorinated AEMs counterparts, the homogeneous quaternized PBFB-QA membrane showed lower water uptake due to the high hydrophobicity of fluorine atoms and more compact entanglement of polymer chains during solvent casting process. It was found that PBFB-QA membrane with an IEC of 1.47 meq/g showed the highest hydroxide conductivity of 29.2 mS/cm at 20 °C in spite of its low water uptake (11.9 wt%) and hydrated number (λ = 4.4). Thus, fluoropolyolefin AEMs standed out from the other reported polyolefin-based AEMs with the highest λ-normalized hydroxide conductivity, indicating the efficient ion transport in AEMs with the aid of less water. In addition to high ionic conductivity, fluoropolyolefin AEMs also exhibited excellent alkaline stability, and the retention of the conductivity of PBFB-QA-18 membrane was 89.5% after 700 h of aging in 1 M NaOH at 80 °C. More importantly, in contrast to the non-fluorinated polyolefin-based AEMs, fluoropolyolefin AEM showed better initial fuel cell device performance with a maximum power density of 133 mW/cm2 at 60 °C, and impressive device durability of alkaline fuel cell using the fluoropolyolefin AEM was observed with no loss of performance over 80 h of operation at 60 °C at a constant cell voltage of 0.3 V.

An effective strategy to increase hydroxide-ion conductivity through microphase separation induced by hydrophobic-side chains

A highly conductive and durable anion exchange membrane (AEM) is an essential component for alkaline electrochemical conversion and storage systems. Contrary to the conventional wisdom that the ionic conductivity can be improved by increasing the ion exchange capacity (IEC) through a cross-linking process, in this work, a new approach to improve the ionic conductivity by enhancing the ionic mobility is adopted. The microstructure of quaternary ammonia poly (2, 6-dimethyl-1, 4-phenylene oxide) (QAPPO) is manipulated through grafting with hydrophobic side chains, which will drive the well-established hydrophilic/hydrophobic domains and nano-phase separated, well-connected ionic channels. As a result, the local hydroxide concentration is enhanced by the novel microstructure, thereby improving the ionic conductivity of the as-prepared ionomers. The as-prepared ionomers, denoted as self-aggregated QAPPO-CF, with an intermediate IEC value achieved an ionic conductivity of 65 mS cm−1 at 80 °C, outperforming the QAPPO with an even higher IEC value. This result suggests that the microphase separation is an effective approach to enhance the ionic conductivity.

Novel quaternary ammonium functional addition-type norbornene copolymer as hydroxide-conductive and durable anion exchange membrane for direct methanol fuel cells

Novel quaternary ammonium functional addition-type norbornene copolymers, and their anion exchange membranes with effective hydrophilic–hydrophobic separation and well performance suitable for direct methanol fuel cells application are achieved.

Alkaline Durable Anion Exchange Membranes Based on Graft-Type Fluoropolymer Films for Hydrazine Hydrate Fuel Cell

Anion exchange membranes (AEMs) having polyvinylimidazolium grafts were synthesized by radiation-induced graft polymerization of N-vinylimidazole (NVIm) or the coplymerizaiton with styrene onto poly(ethylene-co-tetrafluoro-ethylene) (ETFE) film, followed by N-alkylation and ion exchange reactions. The alkaline durability of the membranes was evaluated in 1M KOH at 60 and 80{degree sign}C. The AEM consisting of the homopolymer and copolymer (1:1 molar ratio) grafts (AEM2 and AEM3) with the ion exchange capacity (IEC) of 0.86 and 1.18 mmol g-1 exhibited ionic conductivity of 23 and 63 mS cm-1, respectively. The homopolymer-type AEM2 showed alkaline stability at 60 {degree sign}C for 270 hours, but degraded at 80 {degree sign}C for ca. 150 hours. In contrast, the copolymer-type AEM3 kept its ion conductivity above 10 mS cm-1 in 1M KOH at 80 {degree sign}C for 250 h. The alkylimidazolium group in the copolymer grafts is a promising anion exchange group in AEMs for highly alkaline durable fuel cells.

Alkaline Durable Anion Exchange Membranes Based on Graft-type Fluoropolymer Films for Hydrazine Hydrate Fuel Cell

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