Perfluorosulfonic Acid Polymer Research Articles

Orientation Control of Perfluorosulfonic Acid Films via Addition of 1,2,4-Triazole during Casting.

Perfluorosulfonic acid (PFSA) polymers are used as electrolyte membranes in polymer electrolyte fuel cells. To investigate the effect on proton conductivity through structural orientation control, we added 1,2,4-triazole to PFSA films during casting to impart anisotropy to the ion-cluster structure of the films. The proton conductivities of the films were found to be high in the film-surface direction and low in the film-thickness direction. Structural analysis using small-angle X-ray scattering suggested that the anisotropy in proton conductivity was due to anisotropy in the ion-cluster structure, which in turn was attributed to the formation of a phase-separated structure via strong bonding between sulfonic acid groups and 1,2,4-triazole during cast film formation and the surface segregation of fluorine. We expect the findings of this study to aid in the fabrication of PFSA films with controlled ion clusters.

The Hybridization of Polymers with Metal Oxide Clusters for the Design of Non-Fluorinated Proton Exchange Membranes.

As the key component of various energy storage and conversion devices, proton exchange membranes (PEMs) have been attracting significant interest. However, their further development is limited by the high cost of perfluorosulfonic acid polymers and the poor stability of acid-dopped non-fluorinated polymers. Recently, a new group of PEMs has been developed by hybridizing polyoxometalates (POMs), a group of super acidic sub-nanoscale metal oxide clusters, with polymers. POMs can serve simultaneously as both proton sponges and stabilizing agents, and their complexation with polymers can further improve polymers' mechanical performance and processability. Enormous efforts have been focused on studying supramolecular complexation or covalent grafting of POMs with various polymers to optimize PEMs in terms of cost, mechanical properties and stabilities. This concept summarizes recent advances in this emerging field and outlines the design strategies and application perspectives employed for using POM-polymer hybrid materials as PEMs.

Enhancing Impregnability in Reinforced Composite Membrane Using Greener Dispersion

Perfluorosulfonic acid (PFSA) polymer commonly offer high ionic conductivity, chemical and physical properties, and rapid response, making them widely used in energy conversion technologies like fuel cell and water electrolysis. Industrial commercialization of the polymer electrolyte membranes for water electrolysis depends not only on sufficient electrochemical performance but also requires gas barrier properties and high dimensional stability. To improve the properties of these polymer electrolyte membranes selection of an appropriate dispersion solvent and optimization of its composition ratio are very important. However, PFSA polymer limits the types of dispersion solvents due to its unique structure, which consist of combining a hydrophilic perfluorovinyl ether side chain with sulfonate groups onto a hydrophobic tetrafluoroethylene backbone.Here, we have introduced a new greener mixture system for the fabrication of PFSA-reinforced composite membranes for water electrolysis and compared it with conventional solvent systems. Our solvent system not only produced a more densely packed support layer but also relaxed the anisotropy of the reinforced composite membrane. As a result, the compressive strength and tensile strain increased, making it possible to compensate for the shortcomings caused by the support. Also, this increased impregnability resulted in relatively low gas permeability and high ionic conductivity. The water electrolysis performance was comparable with those prepared using an NMP-based solvent. These results demonstrate a method for preparing PFSA dispersions for reinforced composite membrane and their potential to replace hazardous solvents used in fabrication processes.

(Invited) Novel Polymer and Membrane Development Strategies for Water Electrolysis

Water electrolysis processes play a crucial role in transitioning to a climate-friendly society. They facilitate the integration of renewable energy, offer a clean and versatile energy carrier, decarbonize industries, improve energy storage and grid stability, and support the development of sustainable transportation solutions. As technology advances and economies of scale are realized, electrolysis is expected to play an increasingly significant role in the clean energy landscape, contributing to a more sustainable and resilient future.Various water-splitting electrolysis processes currently exist, including alkaline, solid oxide, proton exchange membrane (PEM), anion exchange (AEM), acidic-alkaline amphoteric, microbial, and photoelectrochemical methods [1]. In our research group, we are actively involved in membrane development for both PEM and AEM water electrolysis.In PEM electrolysis membrane development, our group explores several approaches, such as (a) aromatic main-chain block copolymers[2],(b) acid-base blend membranes using sulfonated and partially fluorinated aromatic polyether, polybenzimidazole, and a PSU-derived basic polymer[2], (c) poly(fluorene)-based sulfonated ionomers, (d) sulfonated and phosphonated poly(pentafluorostyrene) polymers with flexible side groups, and (d) nanophase-separated block copolymers based on phosphonated[3] or sulfonated pentafluorostyrene and octylstyrene. Additionally, we investigate (e) H+-conductive fiber-mat reinforced perfluorosulfonic acid (PFSA) polymers[4].The development of anion exchange membranes in our research group includes (a) polystyrene-based side chain anion exchange polymers and their blends with polybenzimidazole[5], (b) polynorbornene-based optionally ionically and covalently crosslinked anion exchange polymers and membranes, (c) side chain anion exchange polymers and membranes prepared by polyhydroxyalkylation[6], and (d) anion exchange blend membranes made from polydiallyldimethylammonium salts and polybenzimidazole.This contribution highlights the application of two polymer types in PEM and AEM membrane water electrolysis, respectively:(A) PEM Water Electrolysis (PEMWE): Membranes from PEM types (a) and (b) demonstrated good performance. PEM (a) achieved 2.2 V@6 A/cm2, and PEM (b) reached 2.26 V@6 A/cm2 (compared to Nafion212: 2.26 V@6 A/cm2)[2]. These performances were accomplished with non-optimized membrane-electrode assemblies using Nafion as the electrode ionomer. Further performance improvements are expected with optimized electrodes containing the same ionomers as used in the membrane.(B) AEM Water Electrolysis (AEMWE): Blend membranes from AEM type (a) exhibited excellent alkali stability (no conductivity decrease after 1000 hrs of storage in 1M KOH@85°C) and good AEMWE performance (CuCo anode catalyst, 1M KOH, 70°C, 2 V@3 A/cm2)[5]. Type (c) AEMs were applied to a seawater electrolysis cell at 60°C, achieving a performance of 2 V@1 A/cm2 using completely noble metal-free catalysts in both the anode and cathode[6].[1] M. F. Ahmad Kamaroddin, N. Sabli, T. A. Tuan Abdullah, S. I. Siajam, L. C. Abdullah, A. Abdul Jalil, A. Ahmad, Membranes 2021, 11.[2] J. Bender, B. Mayerhöfer, P. Trinke, B. Bensmann, R. Hanke-Rauschenbach, K. Krajinovic, S. Thiele, J. Kerres, Polymers 2021, 13.[3] S. Auffarth, M. Wagner, A. Krieger, B. Fritsch, L. Hager, A. Hutzler, T. Böhm, S. Thiele, J. Kerres, ACS Materials Lett. 2023, 5, 2039.[4] M. S. Mu'min, M. Komma, D. Abbas, M. Wagner, A. Krieger, S. Thiele, T. Böhm, J. Kerres, Journal of Membrane Science 2023, 685, 121915.[5] L. Hager, M. Hegelheimer, J. Stonawski, A. T. S. Freiberg, C. Jaramillo-Hernández, G. Abellán, A. Hutzler, T. Böhm, S. Thiele, J. Kerres, J. Mater. Chem. A 2023.[6] M. L. Frisch, T. N. Thanh, A. Arinchtein, L. Hager, J. Schmidt, S. Brückner, J. Kerres, P. Strasser, ACS Energy Lett. 2023, 8, 2387.

(Invited) Recycling of Perfluorosulfonic-Acid Polymers, into Commercial Viable Second-Use Applications

This presentation will describe our efforts to commercialize our technology to re-deploy spent perfluorosulfonic acid (PFSA) polymer materials from end-of-life Hydrogen Economy energy conversion systems into second-use applications.The challenge in any recycling effort for the PFSA materials is to find a marketable application for the recovered polymer. This is in stark contrast to the situation for the precious group metals; where any recycling/recovery effort for PGM materials can be quickly and easily brought back to the market and converted to cash. This is why so much of the current end-of-life PGM bearing scrap is currently incinerated in order to recover the PGM value only. We will report on the development of several applications from polymer that we have purified and recovered from end-of-life Hydrogen Economy systems.

Nanocomposite Perfluorosulfonic Acid/Montmorillonite-Na+ Polymer Membrane as Gel Electrolyte in Hybrid Supercapacitors.

Solid-state supercapacitors with gel electrolytes have emerged as a promising field for various energy storage applications, including electronic devices, electric vehicles, and mobile phones. In this study, nanocomposite gel membranes were fabricated using the solution casting method with perfluorosulfonic acid (PFSA) ionomer dispersion, both with and without the incorporation of 10 wt.% montmorillonite (MMT). MMT, a natural clay known for its high surface area and layered structure, is expected to enhance the properties of supercapacitor systems. Manganese oxide, selected for its pseudocapacitive behavior in a neutral electrolyte, was synthesized via direct co-precipitation. The materials underwent structural and morphological characterization. For electrochemical evaluation, a two-electrode Swagelok cell was employed, featuring a carbon xerogel negative electrode, a manganese dioxide positive electrode, and a PFSA polymer membrane serving as both the electrolyte and separator. The membrane was immersed in a 1 M Na2SO4 solution before testing. A comprehensive electrochemical analysis of the hybrid cells was conducted and compared with a symmetric carbon/carbon supercapacitor. Cyclic voltammetric curves were recorded, and galvanostatic charge-discharge tests were conducted at various temperatures (20, 40, 60 °C). The hybrid cell with the PFSA/MMT 10 wt.% exhibited the highest specific capacitance and maintained its hybrid profile after prolonged cycling at elevated temperatures, highlighting the potential of the newly developed membrane.

Advanced Nafion/nanofiller composite proton exchange membranes for fuel cell applications

Proton exchange membrane fuel cells (PEMFCs) exhibit increasing potential in a variety of applications, from automotive to stationary power generation, due to their superior advantages such as high efficiency, quick start-up and low emissions. The cell performance and operation life of PEMFCs are directly affected by the proton exchange membranes (PEMs). Nafion, a well-known perfluorosulfonic acid polymer, represents the state of the art of PEMs. To further improve the performance of Nafion, various nanofillers are incorporated into Nafion matrices, leading to the formation of composite PEMs with enhanced proton conductivity, mechanical strength and chemical stability. This review summarizes the recent advancements in Nafion composite PEMs based on four typical kinds of nanofillers: framework nanomaterials, carbon nanomaterials, polyoxometalate nanoclusters, and inorganic oxide nanoparticles. The preparation strategy, structure-property relationship and fuel cell applications of these membranes are discussed comprehensively, particularly focusing on the synergistic effect between Nafion and nanofillers. This review can provide an instructive insight for designing high-performance PEMs towards emerging energy technologies.

Determination of diethylstilbestrol in environmental water based on electrochemical senser modified with vanadium based metal organic framework material composite

In this research, the MIL-47/ACET/Nafion/GCE electrochemical senser for the determination of diethylstilbestrol (DES) was prepared with vanadyl sulfate (VOSO4·nH2O) and terephthalic acid (H2BDC) as the main raw materials, compounded with acetylene black (ACET) and perfluorosulfonic acid polymer (Nafion). The compound DES belongs to the category of estrogens, and prolonged exposure to the environment can have detrimental effects on the physiological functioning of both humans and animals. Due to the strong DES enrichment performance of MIL-47(V-MOFs) with large specific surface area, in addition to the excellent conductivity and electrocatalysis of composite materials, this modified senser had good electrochemical response to DES. With differential pulse voltammetry, in optimum condition of 0.1 M NaH2PO4–Na2HPO4 at pH = 7.0, potential interval of −1.0 to 1.0 V, enrichment time of 120 s and enrichment potential of 0.2 V, there was a good linear relationship between peak current and the concentration of DES over the range of 0.1 and 50 μM, and the limit of detection was 0.008 μM. The sensor accurately detected DES in actual water samples, with recovery rates ranging from 89.21% to 105.3%. The electrochemical sensor was simple to prepare and had practical significance for the detection of DES in water. The research results of the sensor provide another alternative analytical means for the sensitive detection of DES in the environment, which is important for maintaining public health.

Supramolecular complexation of metal oxide clusters in PVDF-PVP blends for large scale fabrication of proton exchange membranes for fuel cells

The perfluorosulfonic acid (PFSA) polymers have achieved great success as proton exchange membranes (PEMs) in various energy storage and conversion devices; nevertheless, the improvements regarding PEMs' synthetic cost, mechanical properties, stability and processability are still urgently required. Herein, 1 nm super acidic metal oxide cluster, H3PW12O40 (PW12), is complexed with the blends of polyvinylpyrrolidone (PVP) and polyvinylidene fluoride (PVDF) to afford nanocomposite PEMs that enables the stable and effective operation of hydrogen fuel cell devices. As the polymer matrix, the PVDF is blended with PVP via inter-chain hydrogen bonding to provide mechanical support for the nanocomposite PEMs. The further introduced PW12 clusters can interact strongly with PVP via electrostatic attraction to enhance the PEMs' mechanical strength (E = 231 MPa) and prevent the leaching of PW12 for long-term stability. Meanwhile, the incorporation of the super acidic PW12 can facilitate the fast proton transportation and therefore, lead to the significant increasement of proton conductivity to 9.8 × 10−3 S cm−1 at 70 °C and 100% RH. Due to the excellent mechanical properties and the supramolecular interaction among the components, the PEMs’ thickness can be controlled to be challenging ∼10μm for feasible large-scale continuous processing. Finally, the molecular design enables the successful fabrication of the nanocomposite PEMs into fuel cell devices with the power density as 342.8 mW cm−2. The studies not only shed light on the structure-properties of polymer nanocomposites, but also pave avenues to the design of robust composite PEMs for fuel cell appliacations.

ZIF67-ZIF8@MFC-Derived Co-Zn/NC Interconnected Frameworks Combined with Perfluorosulfonic Acid Polymer as a Highly Efficient and Stable Composite Electrocatalyst for Oxygen Reduction Reactions.

The development of precious metal-free (M-N-C) catalysts for the oxygen reduction reaction (ORR) is considered crucial for reducing fuel cell costs. Herein, Co-Zn/NC interconnected frameworks with uniformly dispersed Co nanoparticles and graphitic carbon are designed and successfully synthesized through the in situ growth of zeolitic imidazolate frameworks (ZIF67 and ZIF8) along with biomass nano-microfibrillar cellulose (MFC), followed by pyrolysis. A Co-Zn/NC composite is prepared by combining Co-Zn/NC with a perfluorosulfonic acid polymer. The Co-Zn/NC composite catalyst exhibits excellent ORR catalytic activity (E0 = 0.974 V vs. RHE, E1/2 = 0.858 V vs. RHE) and good long-term durability, with 90% current retention after 10000s, surpassing that of commercial Pt/C in alkaline media. The hierarchical porous structure, coupled with the uniform distribution of Co nanoparticles and nitrogen doping, contributes to superior electrocatalytic performance, while the interconnected frameworks and graphitic carbon ensure good stability. Additionally, the Co-Zn/NC composite demonstrates promising applications in acidic media. This strategy offers significant guidance to develop advanced non-precious metal carbon-based catalysts for highly efficient and stable ORR.

Insight into oxygen diffusion mechanism in ionomer film on catalyst surface with varying perfluorosulfonic acid and water contents

Classic molecular dynamics (MD) simulations were performed to explore the effects of perfluorosulfonic acid (PFSA) polymers and water content on the nanostructures of ionomer film on Pt/C surfaces and the corresponding oxygen diffusion mechanisms.

(Keynote) Polyoxometallate Functionalized Membranes for Next Generation Fuel Cells, Electrolyzers and Other Devices

Using polyoxometalate moieties we are developing proton conducting membranes for proton exchange membrane fuel cells, electrolyzers and other devices that can solve the durability and environmental challenges and temperature limitations facing the state of the state-of-the-art perfluorinated sulfonic acid-based membranes. During recent work with perfluorinated membranes we have shown how to achieve stability enhancement that easily exceeds the Fuel Cell DOE accelerated stress tests (AST) for chemical stability and mechanical durability requirements for light duty vehicles. This indicates the potential of these For this perfluorinated polymer-HPA combination we obtained higher performance than the current state-of-the-art PFSAs under high humidity conditionsHPA moieties to give oxidative stability to hydrocarbon membranes as well. New membrane technology we are working on will utilize covalently bound heteropoly acids (HPA), inorganic super acids, that have both some of the highest proton conductivities when wet and have been proven to catalytically decompose oxygenated radicals that destroy existing membranes. We have already demonstrated similar membranes in fuel cells with high performance and some of the most stable long term durability ever demonstrated. In fuel cells, the materials always performed beyond state-of the-art when in humid conditions but struggled when the cells became dry, as electrolysis applications feeds water to the cell we have very high confidence that we will be able to easily exceed electrolyzer performance targets. We are improving upon this polymer chemistry and are now tailoring it specifically to electrolysis. When configured correctly within a hydrocarbon polymer membrane these HPA-hydrocarbon polymers will outperform perfluorosulfonic acid (PFSA) polymers. The correct HPA chemistry must be chosen, and we have shown that silicotungstic acid derivatives act as strong proton conducting moieties and also catalytically decompose oxygenated radicals. This will then enable hydrocarbon membranes with practical lifetimes and performance using the silicotungstic functionality. We are aiming to control the HPA channel morphology and allow for maximum proton conductivity with minimum water uptake. The engineered structures will facilitate proton conduction from ambient conditions to temperatures in excess of 120°C (the polymeric materials chosen are stable to 200°C when dry and potentially much higher when wet and pressurized), as well as achieving cost and durability targets for PEM membranes in electrolyzer applications. Our approach will also allow for development of an ionomer for optimal interfacing with the electrodes.

Structure, Ionomer and Water Distribution in Catalyst Layer of Proton Exchange Membrane Fuel Cell

Catalyst layer’s (CL) ionomer plays a crucial role in the operation of Proton Exchange Membrane Fuel Cell (PEMFC), not simply because it binds the catalyst nanopowder but mostly because it allows proton transport and affects both gas diffusivity and water management [1]. In the CL, the ionomer is a perfluorosulfonic acid polymer similar to that use in the membrane as electrolyte. It is in the form of a few nanometer thick film dispersed around the carbon support or as aggregates larger than 150 nm within the pores of the carbon network [2,3]. In contrast with bulk ionomer membrane or model thin films that have been extensively studied, still little is known on the distributions of ionomer, and especially of water, within the catalyst layer upon hydration [4]. However, this information is crucial to understand the operation and degradation of PEMFC.In the frame of the project FURTHER-FC [5], we perform extensive analysis of the water sorption properties, and in a more unusual way, of the structure of the catalyst layer as a function of relative humidity for different types of carbon support, using Small Angle Neutron Scattering (SANS). It allows us to estimate qualitatively the distribution of the ionomer, and to quantify the average thickness of the ionomer film coating the catalyst, as well as the location of water within the CL upon hydration. The project FURTHER-FC [2] has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under Grant Agreement No 875025. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research. Jinnouchi, R. et al. Nat. Commun. 12, (2021)Ueda, S. et al., Phys B Condens Matter 551, 309–314 (2018)Morawietz, T. et al., Fuel Cells 18, 239–250 (2018)Kusoglu et al., Chem. Rev. 117, 987−1104 (2017)https://further-fc.eu/

Perfluorosulfonic Acid Polymer Membranes: Microstructure and Basic Functional Properties

The development of modern technologies and the requirements that are imposed on the ecology of production require the producing of new polymeric ion-exchange membrane materials with a set of given properties. Such materials are used in systems of separation and purification of liquids and gases, chemical and electrochemical synthesis, in alternative energy. Membranes based on perfluorosulfonic acid (PFSA) polymers have a set of characteristics necessary for their practical application: good transport properties, strength, elasticity and chemical stability. In this review, the microstructure of PFSA membranes, its change upon sorption of water and solvents, the features of ion and gas transport, mechanical properties as well as the dependence of a number of parameters on the chain length and ionic form of the polymer are discussed.

Proton exchange membranes for polymer electrolyte fuel cells: An analysis of perfluorosulfonic acid and aromatic hydrocarbon ionomers

The design of proton-exchange membranes (PEMs) for high-performance, durable fuel cells and related electrochemical devices requires a delicate balance between high ion-exchange capacity and proton conductivity, while ensuring robust mechanical properties and preserving dimensional, chemical and thermal stability. In addition, low species crossover is desirable to reduce hydrogen peroxide formation. Ionomers used in PEMs can be classified into two main groups: (i) perfluorosulfonic acid (PFSA) polymers, and (ii) aromatic hydrocarbon (HC) polymers. In this work, an analysis of key characteristics of both PEM types is presented, including water uptake, proton conductivity, water transport properties, thermal conductivity, permeability, mechanical properties and chemical and thermal stability, among others. Comparatively, PFSA-based PEMs are undoubtedly the commercial standard due to its proven high proton conductivity and good chemical stability, even though PTFE-reinforced aromatic HC-based PEMs have also started to be commercialized recently. In the last decades, a growing trend is identified toward the development of hybrid and composite ultra-thin PEMs (5–20 μm in thickness) with tailored properties, e.g., incorporating microporous fillers to enhance water uptake and layered reinforced microstructures to improve mechanical properties and chemical stability. PEM design is to be accomplished in an environmentally friendly circular economy with facilitated recycling and re-utilization.

Self-sustainable, self-healable sulfonated graphene oxide incorporated nafion/poly(vinyl alcohol) proton exchange membrane for direct methanol fuel cell applications

Nafion, a perfluorosulfonic acid polymer, has been the standard membrane material for direct methanol fuel cells (DMFCs) due to its proton-carrying capabilities, despite its shortcomings as a methanol barrier. To attain self-healing and methanol-blocking properties, the incorporation of poly(vinyl alcohol) (PVA) polymer into Nafion was pursued. However, this strategy resulted in low proton conductivity. Thus, acid functional groups were added to a secondary modifier to boost proton conductivity. In this work, sulfonated graphene oxide (SGO) was assembled with Nafion and PVA through a simple freezing-thawing method to demonstrate a self-healable proton exchange membrane (PEM) without compromising the proton conductivity of Nafion. The synergistic effect of SGO in methanol-blocking and proton transport successfully strode over recast Nafion by hampering 33.2 % of methanol permeation and increasing 19.5 % of proton conductivity. As a result, the selectivity of the best hybrid PEM (N/PVA/SGO1.0) was increased by 1.8 times in comparison to recast Nafion. A single cell passive DMFC made using the novel hybrid membrane exhibited a power density of 6.07 mW cm−2 at a current density of 26.48 mA cm−2, and an open circuit voltage of 0.55 V at room temperature using 4 M methanol. This performance was essentially higher than that achieved by recast Nafion and commercial Nafion 117. The N/PVA/SGO1.0 hybrid membrane also showed remarkable self-healing properties, with 89 % recovery of methanol blocking function through reversible hydrogen bonding, illustrating its tremendous sustainable potential for use in DMFCs.

Evaluation of Phosphoric Acid Leaching in PBI Membranes for High-Temperature PEM Fuel Cells By Ex-Situ and Operando Characterization Methods

High-Temperature PEM Fuel Cells (HT-PEMFCs) based on PA-doped-PBI membranes have become a promising sustainable power generation system due to their high proton conductivity, high tolerance to hydrogen impurities, thermal stability and high utilization of waste heat [1]. Unlike low-temperature fuel cells based on perfluorosulfonic acid polymers (Nafion), HT-PEMFCs do not need water to act as a proton conductor, instead a hydrogen-bonded matrix is established between PA and PBI, negating the need for humidification in the system. As a result, the proton conductivity of the PA-doped PBI membrane is related to its PA loading. When PA is added to the PBI membrane, each PBI repeat unit can only bond with two PA molecules, leading to higher doping levels due to PA distributed in the PBI matrix in a free state. This extra PA leaches from the membrane to the electrodes during cell operation [2] resulting in several problems, the reduction of the proton conductivity of the membrane, blocking of the pathway for the gases to and from catalytically active sites and drive the migration of Pt-based catalyst, resulting in an increase in both mass and charge transfer resistances [3].To prevent acid leaching out of the membrane and the subsequent negative effects on the fuel cell performance, Single Layer Graphene (SLG) has been incorporated as barrier material between the PEM and cathode/anode. SLG acts as sieve material to block all atoms and molecules from passing through with the exception of protons improving the performance and the long-term of the HT-PEMFC [4]. However, although the electrochemical characterization proves this enhancement, the mechanism of the phosphoric acid migration and the effect of the SLG on the leaching is still unknown.In this work, different techniques, X-rat CT [4, 5]y, Raman microscopy [5] and µ-XRF, have been used to evaluate the PA leaching under ex-situ and in-operando conditions to study the mechanism of the migration of the acid and to prove that the electrochemical improvement is due to SLG has a positive effect in the HT-PEMFC.

All‐carbon backbone aromatic polymers for proton exchange membranes

AbstractProton exchange membranes (PEMs) play a crucial role in energy storage and conversion technologies such as fuel cells, redox flow batteries, and water electrolysis. Currently, perfluorosulfonic acid polymer (PFSA) membranes are the most commonly used PEM materials. However, PFSA membranes possess certain drawbacks, including the high dependence of proton conductivity on humidity, low glass transition temperatures, and complex synthesis processes. In recent decades, significant efforts have been dedicated to developing various alternative PEM materials, such as the sulfonated products of polyether ether ketone, poly(phenylene oxide), polysulfone, and polyimide. However, the backbones of these polymers often contain heteroatoms that are prone to breaking under practical working conditions, leading to reduced chemical stability. In contrast, all‐carbon backbone aromatic polymers exhibit excellent chemical stability, thermal stability, and mechanical properties, as well as high proton conductivity upon incorporating suitable acidic groups, which makes them promising alternatives for PEM materials. This review aims to summarize the recent research progress about all‐carbon backbone aromatic polymers, with a specific focus on synthesis strategies, structure–performance relationships, and applications in PEMs.

Approaches to the Modification of Perfluorosulfonic Acid Membranes.

Polymer ion-exchange membranes are featured in a variety of modern technologies including separation, concentration and purification of gases and liquids, chemical and electrochemical synthesis, and hydrogen power generation. In addition to transport properties, the strength, elasticity, and chemical stability of such materials are important characteristics for practical applications. Perfluorosulfonic acid (PFSA) membranes are characterized by an optimal combination of these properties. Today, one of the most well-known practical applications of PFSA membranes is the development of fuel cells. Some disadvantages of PFSA membranes, such as low conductivity at low humidity and high temperature limit their application. The approaches to optimization of properties are modification of commercial PFSA membranes and polymers by incorporation of different additive or pretreatment. This review summarizes the approaches to their modification, which will allow the creation of materials with a different set of functional properties, differing in ion transport (first of all proton conductivity) and selectivity, based on commercially available samples. These approaches include the use of different treatment techniques as well as the creation of hybrid materials containing dopant nanoparticles. Modification of the intrapore space of the membrane was shown to be a way of targeting the key functional properties of the membranes.

Tuning Polybenzimidazole‐Derived Crosslinked Interpenetrating Network Membranes for Vanadium Redox Flow Batteries

AbstractNon‐fluorinated ion exchange membranes with high proton selectivity and conductivity are sought as separators for vanadium redox flow batteries (VRFB) to substitute the typically used perfluorosulfonic acid (PFSA) polymer membranes. Polybenzimidazole based membranes offer a promising non‐fluorinated alternative due to their excellent thermomechanical properties, low vanadium crossover, and ionic conductivity in acidic media. In this work, a series of polybenzimidazole‐polyvinylchloride polymer blends were cast and decorated with different quaternary ammonium functionalities. The polymer blends were systematically studied with respect to the blend composition and chemical structure of the quaternary ammonium groups. Assessment of relevant membrane properties for use in an aqueous acidic flow battery was conducted through a combination of VRFB single cell testing, permeability measurements, water/electrolyte uptake, and infrared spectroscopy. The blend with a polybenzimidazole content of 90 % decorated with DABCO (1,4‐diazabicyclo[2.2.2]octane) was found to combine low polarization resistance with low swelling and high stability. The performance was found to be similar to that of a benchmark polybenzimidazole membrane despite being three times thicker. This led to the conclusion that quaternary ammonium functionalized polybenzimidazole‐polyvinylbenzylchloride systems is an excellent candidate for further modification or fabrication of thinner membranes to further reduce the membrane resistance without compromising on vanadium blocking properties.