Ionomer Membranes Research Articles

Investigating the Electro-Osmotic Coefficients of PFSA and Anion-Exchange Ionomers Using Microelectrodes

The electro-osmotic coefficient of ionomer membranes is a significant water management property that quantifies the number of water molecules dragged with the mobile ion (typically a proton) when that ion moves due to the operation of an electrochemical cell or an electric field. This coefficient becomes critical when attempting to model water distribution and movement in fuel cells and electrolyzers, where water is an important factor influencing device performance. However, there is disagreement on the value of the electro-osmotic coefficient for PFSA membranes and little significant study of the coefficient in anion exchange membranes (AEMs). Here we present an electrochemical, two-electrode method of determining the electro-osmotic coefficient of ionomers using differential relative humidity (RH) measurements. This approach allows for more accurate determination of the electro-osmotic coefficient. We present the electro-osmotic coefficient as a function of temperature and mobile ion for a variety of ionomers, including Nafion, sulfonated polystyrene, Versogen,, and Sustainion. In addition, a model based on the Maxwell-Stefan-Onsager framework is developed for the AEMs, enabling calculation of the membrane water permeability via fitting of the electro-osmotic coefficient. These coefficients will allow for more accurate models of water transport in electrochemical systems, leading to a greater understanding of the inefficiencies in these systems and, hopefully, insight into how to improve them. This work was supported by the HydroGEN Advanced Water Splitting Materials consortium, which is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, under contract number DE-AC02-05CH11231.

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/

Comparative Analysis of Degradation of Pristine Nafion and Catalyst Coated Membrane Subjected to Ex-Situ Fenton's Test Approach

Polyfluorinated sulfonic –acid ionomer membranes (e.g Nafion) are extensively used today as the benchmark materials for the electrolyte membrane in PEM water electrolysis. It is broadly accepted that the state of the health of PFSA membranes are adversely impacted by the chemical degradation occured during operation of PEMWE. The crossover gases on the catalytic surface generate Hydrogen Peroxide which is homolytically or in the presence of ferrous salts produce reactive oxygen species like hydroperoxyl (HO.) and hydroxyl (HO.) radicals. These radicals attack the ionomer subsequently leading to chain scission, unzipping and loss of functional groups and release of HF in the effluent water.Other than Fe3+, several transition metal ions Cu2+, Ni2+, Ti3+, Cu+, can poison the membrane significantly. The fact that membrane degradation is accelerated owing to introduction of ferrous ions is fervently implemented in ex-situ degradation tests (known as Fentons tests) to evaluate the durability of membrane materials.This work depicts a systematic investigation of degradation of pristine Nafion and catalyst coated Nafion membrane using a Fentons accelerated aging experiment. The durability of Nafion 117 and catalyst coated Nafion membrane with various counter ions against H2O2 was explored as a degradation factor of polymer electrolyte water electrolyser. Two distinct variations of the experiments were compared : (1) Nafion and CCM were dipped in only hydrogen peroxide solution, (2) Nafion and CCM were exposed to a solution containing ferrous ions and peroxide. Accelerated aging experiments were conducted over 3-7 days. The difference in degradation phenomena with and without Fe ions were evaluated in terms of the fluoride ion release. For both cases, to quantify the effect of water activity in Nafion and CCM chemical structure on both water diffusion and interfacial transport, pulse field gradient spin echo nuclear magnetic resonance (PFGSE-NMR) technique has been employed. Furthermore the equivalent weight of the Nafion and CCM can vary in presence of aforementioned chemical stressors which can be accurately quantitatively studied by confocal Raman spectroscopy. Morphological characteristic before and after aging test was also investigated. Role of H2O2 and ferous ion in mechanical behaviour of Nafion and CCM were also analyzed. The same experiment was repeated for different transition metal ions. This work sheds light on decomposition mechanism of Nafion and CCM in more detail.

Sulfonic acid (-HSO3) functionalization effect on graphene oxide membrane by (3 mercaptopropyl) trimethoxysilane and their applications in hydrogen membrane fuel cells

Conventional proton exchange membrane fuel cells (PEMFCs) use a perfluorinated ionomer membrane, e.g., Nafion®, which is expensive and subject to a rigorous synthesis process. Graphene oxide membrane (GOM) is acknowledged as a promising alternative electrolyte due to its hydrophilic nature and attractive proton conductivity in wet conditions. However, GOM loses its negative surface functional groups by hydrogen gas at the anode during operation in PEMFCs, resulting in increased electronic conductivity. In addition, two-dimensional graphene oxide (GO) nanosheets exhibited a larger anisotropy difference in proton conductivity compared to Nafion®. In this study, (3-mercaptopropyl)trimethoxysilane (MPTS, HS(CH2)3Si(OCH3)3) was reacted with the surface of GO nanosheet (M-GOM) by vigorous stirring, where unreacted MPTS was partially removed by a rinsing cycle except the M-GOM powder. Reactive MPTS has two essential reactions which were carried out by forming a hydrolysis reaction (Si-OCH3 to Si-OH) and a condensation reaction (Si-OH to Si-O-Si). The thiol groups of MPTS were oxidized to sulfonic acid groups (-HSO3) to provide high proton conducting stations with GO functional groups (M-GOM/oxid) and compared with non-oxidized thiol groups in a GO matrix (M-GOM/unoxid). The superior –HSO3 effect on M-GOM have reported for proton conductivity, physicochemical properties, ion exchange capacity, thermal stability, gas permeability and fuel cell performance. Furthermore, a hydrogen-permeable metal layer was deposited by a DC magnetron sputter to increase mechanical strength and reduce fuel crossover. A dual-layer membrane composed of M-GOM/unoxid or M-GOM/oxid and Pd thin film was analyzed as an electrolyte for a hydrogen membrane fuel cell (HMFC), which simultaneously performs two roles, an anode catalyst and an electrolyte.

Simulated and Experimental Trends Regarding Water Uptake in Polymeric Electrolyte Membranes.

Polymeric membranes in an anion or a proton exchange membrane fuel cell need sufficient hydration in order to provide a high hydroxide ion or proton conductivity. The water uptake for six model ionomer membranes, all of the same ion exchange capacity, is modeled by dissipative particle dynamics. The architectures cover three types of families that are of potential interest in fuel cell membrane research. All architectures consist of connected hydrophobic backbone A beads, to which side chains are grafted. For the type I family, the hydrophilic (functional) C beads are pendent on (amphiphilic) [AxC] side chains. The type II architecture contains both hydrophobic [A4] and short hydrophilic [C] side chains. For type III, the C beads are embedded along various locations within the [AxCAy] side chains (x + y = constant). For similar equilibrium time, the membrane water volume fraction increases with side chain length x for type I, and for type III, it increases with the distance x that C beads are separated from the backbone. Among the architectures (types I and III) for which the number of covalent C-A bonds are the same, the water uptake increases with the average number of A-A and A-C bonds (dpd springs) between A beads and the nearest C bead. A picture emerges in which for similar ion exchange capacity model membranes water uptake increases as a function of ⟨Nbondphob-phyl⟩.

NMR characterization of proton exchange membranes in controlled hygrometry conditions

NMR methods are highly sensitive to the state of water adsorbed in ionomer membranes for PEM fuel cells and electrolyzers. This study demonstrates the potential of NMR and MRI to reliably and accurately determine a wide range of water parameters such as proton chemical shift, transverse relaxation time, water content, and membrane thickness. Measurements are carried out in-situ in membranes in contact with humid air flows that are precisely controlled in terms of flow rate, temperature, and humidity. This precise management of the climatic conditions makes it possible to detect very small variations in the parameters measured, linked to the hydrothermal history of the membrane described in the literature. This history is erased when the membrane is humidity cycled several times. In addition, we demonstrate the use of this MRI imaging method to determine the resistance to water transfer across the membrane/humid air interface under steady-state conditions. Finally, we propose a refinement of the imaging method that reduces acquisition time by a factor of two, without degrading the 1D water content profile. This improvement gives us access to the study of transient hydration regimes typical of PEMFC and PEME operation.

Synchrotron Resonant X-Ray Scattering Reveals New Multiscale Ionomer Morphology

Ion-conducting polymer, or ionomer, membranes play a key role as the ion-conducting electrolyte in electrochemical devices, including fuel cells and electrolyzers. The performance of ionomers, for example, its proton conductivity, is defined by its unique molecular structure and multiscale morphology. Perfluorinated sulfonic acid ionomers are the most used ionomers, and they are cast into membranes and thin films from alcohol-rich dispersions. In this work, we examine the connections between the dispersion solvent used for casting and resulting membrane properties. Understanding and controlling the hierarchical phase separated morphology of ionomer membranes and elucidating its relationship to transport properties is crucial for improving device performance. Synchrotron-based x-ray scattering is well-suited to probe the morphology in polymers that lack a high degree of long-range order, including ionomer membranes. However, it is still challenging for conventional high energy hard x-ray scattering to resolve all the morphological details in chemically heterogeneous ionomers. Here, we use emerging synchrotron tender resonant x-ray scattering (TReXS) near the sulfur K-edge to improve scattering contrast and enhance chemical specificity to the sulfonate groups in perfluorinated sulfonic acid ionomers. We find that TReXS reveals unique energy-dependent mesoscale morphological features not apparent in hard x-ray scattering, and these features depend on dispersion composition and ionomer chemistry. These structure-property relationships can be used to guide design of next-generation ionomers for energy applications. Furthermore, this work highlights synchrotron resonant x-ray scattering as an emerging tool for structural characterization of ionomers and electrochemically active polymers in general.

Modelling and Experimental Validation of the Flow and Mixing Processes in a Microfluidic Membraneless X-Cell with Flowing Vanadium Electrolytes

Microfluidic devices are characterized by submillimeter channel cross-sections and tiny flow rates, typically below 100 µL/min. This results in rather small Reynolds numbers that maintain the flow laminar and steady, preventing chaotic mixing from turbulence [1-4]. This orderly flow can be used to remove the ionomeric membrane in redox flow batteries, generating membraneless microfluidic cells with low internal electric resistance. These devices could be manufactured at a lower cost than their macro counterparts. However, without a membrane, the mixing region where the electrolytes come into contact must be accurately controlled to avoid unwanted interface deflections leading to increased cross-contamination of liquid and species.In this work, we compare experimental and CFD realizations of the flow in a membraneless microfluidic flow channel [5], including in the simulations the effect of viscosity variations across the positive and negative vanadium electrolytes. The apparatus includes a microfluidic control system that uses piezoelectric pumps and valves for flow regulation, an X-cell as flow channel, and small tanks with discharged positive (VIV) and negative (VIII) electrolytes. We use a UV/Visible spectrometer to measure the amount of mixing at the outlet of the cell [6]. This allows us to validate the CFD model against the experimentally measured cross-contamination and liquid transfer. To our knowledge, these results are unique in using spectrometry data to quantify the mixing ratio of VIII/VIV, and provide valuable data to validate CFD models that could later be used to engineer the flow in membraneless microfluidic vanadium redox flow batteries. Acknowledgments This work has been partially funded by FEDER/Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación Projects PID2019-106740RB-I00 and RTC-2017-5955-3/AEI/10.13039/501100011033, and by Grant IND2019/AMB-17273 of the Comunidad de Madrid.

Understanding the Role of Cu Electocatalyst, Binder, and Membrane Interfaces in CO2 Electrolyzer Durability

Carbon dioxide electrolyzers capable of maintaining stable performance for thousands of hours are necessary for commercial electrochemical reduction of CO2 to two-carbon products such as ethanol and ethylene. Currently, most studies containing CO2 reduction to two-carbon products have been for durations of under 20h. Only a few (<5) instances of CO2 reduction to two-carbon products at durations over 100h have been reported. Common cell failure mechanisms, such as carbonate salt precipitation and cathode flooding, can be mitigated by tuning the operating conditions of the reactor. Beyond these modes of failure, there are practical limitations related to materials' durabilities and long-term stabilities, including ionomeric membranes' operating lifetimes, gas diffusion cathodes, anodes, and other MEA components.In this presentation, we explore the role of CO2, water, and ion transport on cell performance over extended periods of operation. The polymeric anion exchange membrane and conductive binder have been identified as crucial components in tuning the transport properties of electrolyzer systems and, thus, will be the focus of this study. We consider several types of anion exchange membranes (e.g., imidazolium, ammonium, piperindinium) and conductive binders (e.g., Nafion, PVDF, PTFE, PSMIM) for use in the direct reduction of CO2 to two-carbon products at nanoscale Cu electrodes (150mA/cm2, 0.01M KHCO3 anolyte). This work improves upon previous analysis of membrane and binder transport properties by testing a wider variety of materials for >100h durations and reporting specific cell failure times and causes. We will discuss the balances between carbonate precipitation, flooding, and other membrane or electrode failures as a function of materials, MEA preparation, and operating conditions. A comprehensive set of failure standards based on electrolyzer performance (pressure, outlet mass flow, two-carbon product Faradaic efficiencies, energy efficiency, carbon efficiency) is introduced, and electrolyzer configurations are tested in triplicate to produce statistically significant failure data. Overall, this provides insight into CO2, ion, and water transport's role in electrolyzer cell performance and failure mechanisms. Figure 1

Recycling of PFSA-Based Membranes and Their Re-Application in PEM Fuel Cells

The commercialization of PEM fuel cells offers a promising opportunity to overcome our dependence on fossil fuels and provides an attractive alternative for automotive and stationary power applications.[1] However, PEMFCs are still costly in production, with the main cost factor due to the fabrication of the perfluorosulfonic acid (PFSA)-based proton exchange membrane and the noble metal catalysts.[2,3] Recycling of these components could increase the economic attractiveness of PEMFCs. However, while the high resistance of the ionomer membrane to thermal and chemical degradation is favorable for their use in fuel cells, it also makes membrane recycling a major challenge.Here, we present a newly developed recycling strategy to recover PFSA-based membranes after operation by a hydrothermal treatment. Both short side chain (SSC) and long side chain (LSC) ionomers with EWs of 800 and 1000 were investigated. In contrast to previously published methods, we were able to recover the PFSA ionomer by using water instead of high-boiling organic solvents, such as DMF or DMSO.[4,5] The recycled membranes were obtained from the recycled PFSA ionomer solution by doctor-blading. They were investigated by in-situ Raman techniques for studying the water uptake and analyzed by IR and small-angle X-ray scattering (SAXS) techniques to get a more detailed insight into their morphology. In single cell tests at standard (80 °C) and enhanced (up to 130 °C) PEMFC operating temperatures, the recycled membranes showed an increased cell performance as compared to the pristine 3M-800EW membrane. Solid-state NMR measurements confirmed that no chemical changes in the membrane occurred due to the heat-treatment process.We assume that the observed performance boost can be attributed to an increased water uptake and retention. Furthermore, a change in the polymer matrix formation may be responsible for the observed behavior, which led to an expanded water filled channel structure, where water can accumulate to facilitate proton diffusion as H3O+ through the channels. To confirm this assumption, the morphology of the recycled membranes will be investigated by in situ SAXS measurements at different temperatures and degrees of hydration.[1] I. Staffell, D. Scamman, A. Velazquez Abad, P. Balcombe, P. E. Dodds, P. Ekins, N. Shah, K. R. Ward, Energy Environ. Sci. 2019, 12, 463–491.[2] J. Fan, M. Chen, Z. Zhao, Z. Zhang, S. Ye, S. Xu, H. Wang, H. Li, Nat. Energy 2021, 6, 475–486.[3] D. Papageorgopoulos, Fuel Cell R&D Overview. 2019 Annual Merit Review and Peer Evaluation Meeting, 2019.[4] Q. Xu, X. Chen, S. Wang, C. Guo, Y. Niu, R. Zuo, Z. Yang, Y. Zhou, C. Xu, Energies 2022, 15, 8717.[5] H. F. Xu, X. Wang, Z. G. Shao, I. M. Hsing, J. Appl. Electrochem. 2002, 32, 1337–1340.

Phosphonic acid-imidazolium containing polymer ionomeric membranes derived from poly (phenylene oxide) towards boosting the performance of HT-PEM fuel cells

Phosphoric acid (PA)-dependent proton conductivity and polymer-offered mechanical properties are contradictory in high-temperature proton exchange membranes (HT-PEMs). Microphase separation strategy contributes to achieve a tradeoff between proton conductivity and mechanical properties. Herein, a kind of phosphonic acid-imidazolium containing polymer (PICP) ionomeric membranes, in which acidophilic (imidazolium) and acidophobic groups (-PO3H2) can be induced to form a microphase separation structure by PA, are firstly prepared. The acidophilic phase with adsorbed PA plays the role of proton conduction and the acidophobic phase can not only provides -PO3H2 group synergistically conduct protons but also largely maintains the intrinsic mechanical properties. As a result, the PICP ionomeric membranes with microphase separation structure possess high proton conductivity (48 mS cm−1, 160 °C) and satisfying mechanical strength (16.5 MPa) simultaneously at a moderate PA doping level (130 wt%). The fuel cell based on such HT-PEMs demonstrates a peak power density of 493 mW cm−2 and high voltage stability. This is the first report of phosphonic acid-imidazolium containing ionomeric membranes with satisfactory fuel cell performance and durability, representing a meaningful step towards practical HT-PEM fuel cells.

Start–Stop Cyclic Durability Analysis of Membrane–Electrode Assemblies Using Polyflourene-Based Electrolytes for an Anion-Exchange Membrane Water Electrolyzer

Highly durable anion-exchange membranes and ionomers are essential for developing cost-effective green hydrogen generation. The anion-exchange membrane and ionomer must withstand chemical attacks by OH– ions as well as nonlinear mechanical stress caused by irregular bubble formation when the electrolyzer is coupled with intermittent power sources. Herein, we examined the durability of a trimethylammonium-modified poly(fluorene-alt-tetrafluorophenylene) (PFT-C10-TMA)-based membrane and ionomer under dynamic operation to evaluate its competency to couple with intermittent power sources. The durability of membrane–electrode assembly (MEA) prepared using these polymer membrane and ionomer was evaluated by performing 1000 start–stop voltage cycles in 1 M KOH solution at 80 °C while varying the applied cell voltage. The electrochemical performances of the MEA and electrodes were simultaneously evaluated using an electrolyzer with reference electrodes, and the chemical structure of the polymer was examined before and after the durability test using NMR techniques. The MEA based on a commercial Sustainion XB-7 ionomer and X37-50 RT anion-exchange membranes showed the catalyst leaching during start–stop cycles, resulting in reduced cell performance. On the other hand, the MEAs with the PFT-C10-TMA membrane and ionomer demonstrated promising high chemical and mechanical durability under dynamic start–stop operation, encouraging the development of electrolyzers that can function with intermittent renewable power sources.

Investigation of structural and transport properties of highly oxygen-permeable ionomer in polymer electrolyte membrane fuel cells using molecular dynamics simulations

Understanding the nanostructure of ionomer membranes is important for elucidating the mechanism of their molecular transport properties and for improving the performance of proton exchange membrane fuel cells. In this study, we incorporated a ring structure into the main chain of perfluorinated sulfonic acids ionomers including short side chain (SSC) as a highly oxygen-permeable ionomer and used molecular dynamics simulations to investigate the interrelation between the structural properties of the ionomer and its transport properties. The incorporated ring structure influences the stiffness of the ionomer chain and the nanostructure of the ionomer membrane. To demonstrate the influence of the ionomer structure on the transport properties and the nanostructural features such as water channels, the structure and water volume were analyzed and the water-cluster connectivity was calculated for modified SSC ionomers and long side chain (LSC) ionomer, and the results were compared. Compared with the LSC ionomer, the modified SSC ionomer exhibits better oxygen transport properties but worse water transport properties because of its stiff chain derived from the ring structure.

On-body hypoxia monitor based on lactate biosensors with a tunable concentration range

We report on a noninvasive hypoxia monitor based on a biosensor linearly responding to lactate through its whole concentration range in human sweat. The biosensor is designed with an additional perfluorosulfonated ionomer (Nafion analogue) membrane acting as a diffusion barrier for lactate due to its intrinsic negative charge. The resulting biosensor linearly responds to lactate in the range from 1 to 100 mM and displays significantly improved operational stability, maintaining its initial response during 3 h in human sweat flow. Thus, the elaborated monitor has been validated through on-body continuous sweat analysis during exhaustive physical exercise. In contrast to periodic sweat sampling, the elaborated monitor allows recording of the true extremes of sweat lactate, which are of particular importance for diagnostics.

In Situ Confocal Raman Microscopy of Redox Polymer Films on Bulk Electrode Supports.

A spectroelectrochemical cell is described that enables confocal Raman microscopy studies of electrode-supported films. The confocal probe volume (∼1 μm3) was treated as a fixed-volume reservoir for the observation of potential-induced changes in chemical composition at microscopic locations within an ∼20 μm thickness layer of a redox polymer cast onto a 3 mm diameter carbon disk electrode. Using a Raman system with high collection efficiency and wavelength reproducibility, spectral subtraction achieved excellent rejection of background interferences, opening opportunities for measuring within micrometer-scale thickness redox films on widely available, low-cost, and conventional carbon disk electrodes. The cell performance and spectral difference technique are demonstrated in experiments that detect transformations of redox-active molecules exchanged into electrode-supported ionomer membranes. The in situ measurements were sensitive to changes in the film oxidation state and swelling/deswelling of the polymer framework in response to the uptake and discharge of charge-compensating electrolyte ions. The studies lay a foundation for confocal Raman microscopy as a quantitative in situ probe of processes within electrode-immobilized redox polymers under development for a range of applications, including electrosynthesis, energy conversion, and chemical sensing.

Reinforcement effect in tandemly sulfonated, partially fluorinated polyphenylene PEMs for fuel cells.

The mechanical and chemical durability is one of the most crucial properties for proton exchange membranes in practical fuel cell applications. In the present paper, we report the physical reinforcement of chemically stable, highly proton conductive tandemly sulfonated, partially fluorinated polyphenylenes using porous polyethylene (PE). With the PE pores completely and homogeneously filled by ionomers through a push coating approach, the resulting reinforced membranes were more proton conductive (183.1-389.2 mS cm-1) than the commercial perfluorinated ionomer (Nafion: 120.6-187.2 mS cm-1) membrane at high humidity (80-95% RH). Benefiting from the tough PE supporting layer, the reinforced membranes outperformed the parent ionomer membranes in stretchability with maximum strain up to 453%. The combination of intrinsic chemical stability of partially fluorinated polyphenylene ionomers and physical reinforcement with PE substrates contributed for the reinforced membranes to achieving superior durability to survive more than 20 000 cycles in severe accelerated durability test combining OCV hold and wet/dry frequent cycling.

Improved Hydrolytic and Mechanical Stability of Sulfonated Aromatic Proton Exchange Membranes Reinforced by Electrospun PPSU Fibers.

The hydrolytic stability of ionomer membranes is a matter of concern for the long-term durability of energy storage and conversion devices. Various reinforcement strategies exist for the improvement of the performances of the overall membrane. We propose in this article the stabilization of membranes based on aromatic ion conducting polymers (SPEEK and SPPSU) by the introduction of an electrospun mat of inexpensive PPSU polymer. Characterization data from hydrolytic stability (mass uptake and dimension change) and from mechanical and conductivity measurements show an improved stability of membranes in phosphate buffer, used for enzymatic fuel cells, and in distilled water. The synergistic effect of the reinforcement, together with the casting solvent and the thermal treatment or blending polymers, is promising for the realization of high stability ionomer membranes.

Permeation of Ternary Mixture Containing H2S, CO2 and CH4 in Aquivion® Perfluorosulfonic Acid (PFSA) Ionomer Membranes.

Aquivion® E87-12S Perfluorosulfonated acid ionomer material (PFSA) has been studied as a membrane technology for natural gas sweetening from CO2, H2S due to its interesting chemical and mechanical stability and good separation performance for polar compounds in humid environments. In the present work, permeation of the H2S/CO2/CH4 ternary mixture in this short-side PFSA chain was investigated at pressures up to 10 bar, temperatures up to 50 °C, and in a range of relative humidity (RH) from 20% to 90%. The results obtained confirm the strong dependence of Aquivion® on water activity and temperature, and its ability to separate gases based on their water solubility without substantial differences between pure and mixed gas experiments. Indeed, even when tested in ternary mixture, the permeation behavior remains similar to that observed for pure components and binary mixtures. In particular, the permeability of H2S is higher than that of CO2 and methane CH4, reaching values of 500 Barrer at 50 °C and 80% RH, against 450 and 23 Barrer for the other two gases respectively. Additionally, when tested at higher pressures of up to 10 bar under humid conditions, the membrane properties remained largely unchanged, thus confirming the overall stability and durability of Aquivion® E87-12S in acid environments.

Molecular Dynamics Study of Adsorption Phenomenon of Aromatic Hydrocarbon Ionomer in Catalytic Layer of Polymer Electrolyte Fuel Cell

In response to the current global energy crisis and environmental problems, fuel cells are an optional solution. Among them, polymer electrolyte fuel cell (PEFC) has high expectations because of its low operating temperature and suitability for applications in households and mobility devices. Since PEFC requires the use of proton exchange membranes, the transmission efficiency and durability of the exchange membrane is a major concern. To improve the proton transport efficiency, which is generally required, a catalytic layer is integrated into the PEFC. The catalyst layer of PEFC generally contains platinum catalyst covered with the ionomer membrane. Proton conductivity increases with ionomer thickness, while oxygen permeability decreases with ionomer thickness. Therefore, in order to improve the power generation efficiency of PEFC, it is important to design the catalyst layer. In addition, the fluorinated ionomer membrane material (such as Nafion) used for PEFC has good proton conductivity and chemical stability, but the synthesis cost is relatively high. As a consequence, new materials such as composite materials and non-fluorine-based materials have received a lot of attention in recent years. In this study, we focus on a new ionomer material of aromatic hydrocarbon (named SPP-BP) and elucidate the adsorption state of the ionomer on the platinum surface on a nanoscale using molecular dynamics (MD) simulations. Then, the structural properties and water diffusion characteristics of the ionomers of new material (SPP-BP) and conventional Nafion were analyzed based on the MD simulation results.The degree of polymerization (m, p, s) of the monomers were given as 20, 5, and 23 (molecular weight 7.38 kDa), respectively, based on the reported experimental values of SPP-BP. For the polymer composition, molecular models of a random type (r-type), which shows a randomness of monomers, were used. A molecular model of Nafion was also created as the conventional fluorinated membrane materials for comparison with the SPP-BP. The platinum surface was built with a three layers of platinum atoms in a face-centered cubic lattice structure. Regarding the calculation potentials, the DREIDING forcefield was used for the interactions with the molecules. While for the intermolecular potential, the Spohr potential was used for Pt-H2O and Pt-H3O+ interactions, and the others were applied with the Lennard Jones (LJ). The parameters of those potentials were based on the previous studies.In the ionomer membrane, water content is an important indicator that affects the transfer of protons and substances. Based on the water absorption results obtained in the experiment, the water content of SPP-BP was calculated to be between 1.8 and 7.2. Therefore, the water content during the MD simulation was used 3, 5, and 7. The computational size was 55.5 Å × 52.9 Å in the transverse direction of the ionomer membrane (X and Y directions), and the thickness of the membrane adsorbed on the platinum surface was about 50-60 Å. A vacuum region of about 40 Å was set at the top of the system. To calculate the diffusion coefficient and the cluster character of water, multiple simulations with different initial structure were considered. Furthermore, in order to compare to the Nafion, the number of polymers and the computational size was adjusted for containing the same water content.Based on the simulation results, the density distribution of water, hydrophilic sulfo groups, and main body of polymer was analyzed. By the analysis of density distribution, the structure of the ionomer at the interface-vacuum, near the Pt surface and inside was studied. In addition, the orientation of the sulfo group of SPP-BP and Nafion near the Pt surface was analyzed. Besides, the water cluster characteristics and water diffusion properties of the ionomers of SPP-BP and Nafion were also investigated.Acknowledgements: This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan through the fund for ECCEED'30 Projects (No. JPNP20003). Numerical simulations were performed on the Supercomputer system "AFI-NITY" at the Advanced Fluid Information Research Center, Institute of Fluid Science, Tohoku University.

(Invited) Novel Ionomers and Ionomer Membranes for Fuel Cells and Redox-Flow Batteries

In this contribution the development of new nonfluorinated and partially fluorinated polymeric platsforms containing perfluoroaromatic building blocks, and their modification with phosphonic and/or sulfonic acid groups and/or anion-exchange groups and/or flexible alkane side chains by nucleophilic aromatic substitution of F or via other synthesis routes is described. The prepared polymers were, where appropriate, blended among each other or with basic high-performance commercial polymers such as polybenzimidazoles or self-synthesized novel basic aromatic polymers to further improve their membrane properties by ionic cross-linking. Moreover, composite membranes consisting of ion-conductive or non-conductive electrospun fiber mats which were filled with PFSA dispersions were synthesized and optimized. The synthesized ionomers and ionomer (blend) membranes were characterized in terms of composition via NMR and FTIR, molecular weight by size exclusion chromatography (SEC), thermal stability via TGA-FTIR-GC-MS coupling and via DSC, and mechanical properties via stress-strain tests and DMA, morphology via electron microscopy, and conductivity via impedance spectroscopy. The (blend) membranes were then applied in fuel cells (low-T and high-T, H2 and direct alcohol fuel cells), and in redox-flow batteries, yielding good performance in these applications.