Properties Of Polymer Electrolyte Membranes Research Articles

Mechanism of Ionomer Film Formation via Solution Drying.

Film formation via the drying of ionomer solutions is a crucial process that has a strong influence on the morphology and transport properties of polymer electrolyte membranes and thin films. However, the microscopic mechanism of this process remains unclear. Here, we elucidate this mechanism using a coarse-grained model based on all-atom molecular dynamics that accurately reproduces small-angle X-ray scattering spectra. In dilute ionomer solutions, ionomers form rod-like bundles with diameters of 1.5-2 nm. As the water solvent evaporates, these bundles gradually aggregate and connect to each other, while maintaining their diameter. Finally, the remaining water forms nanosized clusters surrounded by the surfaces of the bundles with hydrophilic sulfonate groups.

Ratcheting assessment of the catalyst layer in polymer electrolyte membrane fuel cells considering thermal-mechanical-humidity cycling

The properties of polymer electrolyte membrane fuel cells (PEMFCs) are highly affected by the catalyst layer (CL). However, the cyclic swelling and shrinking of the ionomer caused by the change of temperature and relative humidity (RH) combined with external random mechanical loads may lead to electrochemical activity degradation through cyclic plasticity accumulation. In this study, a theoretical model to assess the ratcheting limit of the CL for PEFMCs subjected to thermal-mechanical-humidity cycling is developed based on linear matching method (LMM). The influences of embedded depth of Pt/C particle, cyclic temperature or RH modes, as well as the random reaction force are considered by the proposed method. The ratcheting limits of CL are achieved under various thermal-mechanical-humidity cycling and verified by step-by-step simulation. Moreover, a simplified prediction model is established to evaluate the ratcheting limits under the combined temperature and RH cycling. It is of interest that the ratcheting limit under the pure normal force is almost 3 time of that under the pure tangential force under the same thermal-humidity cycling. Furthermore, the accumulated plastic strain occurs near the junction area causing the debonding of Pt/C particle from the ionomer under thermal-mechanical-humidity cycling, which agrees well with the microscopic observation. Based on ratcheting assessment results obtained by the proposed method, the reliability and durability of PEMFCs can be improved by increasing the affinity between Pt/C and ionomer, decreasing the size of gas pore and inhibiting the tangential force in the CL.

Parametric study on geometric and material properties of polymer electrolyte membrane fuel cell with free vibration analysis

The mechanical aspect of understanding the dynamic behaviour is very important in stack assembly of fuel cell configuration. Designing such configuration would be very useful to tune the system accordingly to avoid catastrophic failure due to resonance. The dynamic analysis of a polymer electrolyte membrane fuel cell (PEMFC) is performed to understand its response during complex loading nature. The stack assembly of bipolar plate, gas diffusion electrolyte (GDE) and membrane are modelled and analysed using Mindilin plate element with finite element method (FEM). The parametric study on thickness, density and young's modulus and its influence on dominant modes of natural frequencies are analysed with a 5%–20% range of variations. It is observed that the bipolar plate's thickness plays a vital role in the vibration behaviour of the PEMFC.

Influences of Flow Channel on Electrochemical Characteristics of Polymer Electrolyte Fuel Cells Humidified with NaCl Contained H2O

In this study, the effects of flow field types on the electrochemical properties of polymer electrolyte membrane fuel cells (PEMFCs) humidified with NaCl solution are systematically investigated. The parallel flow field and serpentine flow field were used to investigate the PEMFCs. Long-term stability was evaluated for 20 h using chronoamperometry. Fuel cells with both parallel and serpentine flow fields showed a decrease in performance because of the NaCl solution. Interestingly, the PEMFC with the serpentine flow field showed significantly more severe degradation during long-term stability evaluation compared to the fuel cell with the parallel flow field. Electrochemical impedance spectroscopy analysis showed that a significant increase in faradaic resistance caused the degradation of the performance. After long-term stability examinations, regenerations of fuel cells were performed with deionized water at a constant voltage (0.4 V). After the regeneration, the performance of the fuel cells with the serpentine flow field was improved more (52.96%) than the PEMFC with the parallel flow field (1.22%).

Effects of Humidification with NaCl Solution Mist on Electrochemical Characteristics of Polymer Electrolyte Membrane Fuel Cells

This study examined the effects of mist generated from NaCl solution on the electrochemical properties of polymer electrolyte membrane fuel cells. Mist-containing Na+ and Cl- ions were generated using a custom-made mist generator. The current density-voltage-power density curves and electrochemical impedance spectroscopy of fuel cells were systematically achieved. Furthermore, long-term stability experiments were carried out using chronoamperometry mode for 20 h with deionized water and NaCl solution. After the chronoamperometry measurement, the regeneration of fuel cells was performed with deionized water. The effects of regeneration methods on the performance of the fuel cell were evaluated. Due to the internally produced H2O, constant voltage regeneration was more effective than open circuit voltage regeneration.

Nanophase-Segregated Structures and Transport in Aquivion Membrane for Polymer Electrolyte Membrane Fuel Cell

In this study, molecular dynamic simulation method was employed to study the structure and transport properties of Aquivion in comparison to Nafion. From experimental and computational work, there is a general consensus that the favored properties of Polymer electrolyte membrane (PEM) system are a result of nano-phase segregation of hydrophilic clusters in a hydrophobic matrix. Aquivion has a similar chemical structure to Nafion with hydrophobic backbone and hydrophilic sulfonate group. As such, we investigate the structure formed by Aquivion, to check for the desired nanophase segregation, when simulated in conditions similar to fuel cell conditions of temperature and humidity. We also characterize water diffusion and proton transport in this segregated structure, and compared them with hydrated Nafion membrane system.

Investigating the Influence of Humidity on Liquid Water Transport Mechanisms in Fuel Cell Gas Diffusion Layers Using Operando X-Ray Computed Tomography

The intermittent nature of many renewable energy sources, such as solar and wind, presents the need to acquire on-demand renewable energy either through energy storage or energy production methods. The polymer electrolyte membrane (PEM) fuel cell is quickly becoming an attractive solution as it can produce high power densities under a rapid change in load while producing zero local carbon emissions [1] and is ideal for large-scale applications, such as automotive [2]. However, barriers to their widespread implementation are attributed to the high costs associated with mass transport losses at high current density operation due to inefficiencies in liquid water management in the gas diffusion layer (GDL) [3][4]. Understanding the relationship between liquid water distributions in the cathode GDL and transport properties of PEM fuel cells under varying operating conditions can lead to improved GDL configurations for improved performance. Previously, studies have been conducted to characterize the effect of operating temperature on liquid water pathways in GDLs by using 3D imaging techniques on operando PEM fuel cells [5]. High-speed, high-resolution 3D imaging techniques, such as computed tomography (CT), enable the visualization of dynamic pore-scale effects and are advantageous in elucidating transport mechanisms in the GDL.In this work, the effect of operating relative humidity on the formation of liquid water pathways in the GDL will be explored by imaging an operando PEM fuel cell with synchrotron X-ray CT. To date, a custom PEM fuel cell has been developed in-house which features a novel design with two rotary unions on either side of the cell. The rotary unions enable continuous rotation of the cell during imaging, and thus are central to achieving high temporal resolution for visualizing the development of preferential water pathways. High spatial resolution (pixel resolution of 1.44 microns per pixel [6]) is also obtained with the synchrotron beam, which allows for the visualization of liquid water in individual pores at the microscale in the GDL. Visualizing water in the micropores of the GDL can help us further understand water transport mechanisms within the complex structure of the GDL to ultimately develop methods to expel excess water efficiently. In the next steps of this research, we will use the results from electrochemical testing and the reconstructed images of the fuel cell to draw important conclusions about the relationship between liquid water distributions in the GDL and fuel cell performance. As well, the effect that operating relative humidity has on this relationship will be determined. The aim of this work is to inform optimal design for GDL materials for improved PEM fuel cell performance, which will ultimately accelerate their utilization on a global scale as a reliable and sustainable energy source.[1] P. Shrestha, CH. Lee, K. F. Fahy, M. Balakrishnan, N. Ge, and A. Bazylak, “Formation of Liquid Water Pathways in PEM Fuel Cells: A 3-D Pore-Scale Perspective,” Journal of The Electrochemical Society, vol. 167, no. 5, p. 054516, Jan. 2020, doi: 10.1149/1945-7111/ab7a0b.[2] S. Park, J. W. Lee, and B. N. Popov, “A review of gas diffusion layer in PEM fuel cells: Materials and designs,” International Journal of Hydrogen Energy, vol. 37, no. 7, pp. 5850– 5865, Apr. 2012, doi: 10.1016/J.IJHYDENE.2011.12.148.[3] Y. Nagai et al., “Improving water management in fuel cells through microporous layer modifications: Fast operando tomographic imaging of liquid water,” Journal of Power Sources, vol. 435, p. 226809, Sep. 2019, doi: 10.1016/J.JPOWSOUR.2019.226809.[4] U. U. Ince et al., “3D classification of polymer electrolyte membrane fuel cell materials from in situ X-ray tomographic datasets,” International Journal of Hydrogen Energy, vol. 45, no. 21, pp. 12161–12169, Apr. 2020, doi: 10.1016/J.IJHYDENE.2020.02.136.[5] Hong Xu, Shinya Nagashima, Hai P. Nguyen, Keisuke Kishita, Federica Marone, Felix N. Büchi, Jens Eller, Temperature dependent water transport mechanism in gas diffusion layers revealed by subsecond operando X-ray tomographic microscopy, Journal of Power Sources, Volume 490, 2021, 229492, ISSN 0378-7753, https://doi.org/10.1016/j.jpowsour.2021.229492.[6] Canadian Light Source, “Detectors,” BMIT. [Online]. Available: https://bmit.lightsource.ca/tech-info/detectors/. [Accessed: 05-Apr-2022].

The electric field effect on the nanostructure, transport, mechanical, and thermal properties of polymer electrolyte membrane

The electric field effect on the nanostructure, transport, mechanical, and thermal properties of polymer electrolyte membrane

Energy Harvesting of Ionic Polymer-Metal Composites Based on Microcellular Foamed Nafion in Aqueous Environment

The purpose of this study was to determine how to improve the energy-harvesting properties of polymer electrolyte membranes by varying their porosity. We achieved this by applying microcellular foaming process (MCP) to Nafion-based ionic polymer–metal composites (IPMCs). We manufactured an IPMC by forming a Pt electrode through an electroless plating method on the Nafion film, to which porosity was imparted by varying the foaming ratio and inducing deformation by vibrating the specimen using a prototype device that we developed ourselves. We attempted to harvest energy via fluid flow that occurred owing to displacement movement. When the Nafion film was foamed at a temperature of 140 °C or higher, it was observed that cells with size of approximately 1 µm or more were formed, and when the saturation temperature was lowered, a denser and larger number of cells were formed. Moreover, the cells formed on the electrolyte membrane allowed the retention of more water. Water retention generated charges contributed to the operational stability of IPMC. This was attributed to the difference in the amount of charge generated by changing only the internal morphology of the electrolyte membrane, without changing the substrate or the electrode material.

Nanometer-Scale Water Dynamics in Nafion Polymer Electrolyte Membranes: Influence of Molecular Hydrophobicity and Water Content Revisited.

The ionic conductivity of polymer electrolyte membranes (PEMs) is an essential parameter for their device applications. In water-swollen PEMs, protons and other ions are transferred through hydrophilic channels of a few nanometers in diameter at most. Thus, optimizing the chemical and physical properties of the channels can enhance the conductivity of PEMs. However, the factors controlling the conductivity have not been completely clarified. Here, we report that measurements taken near the channel walls by a special nuclear magnetic resonance technique with ≤1 nm spatial resolution showed the largest water diffusivity when ∼80% of hydrophilic sulfonic acid groups were blocked, but the proton conductivity was low. The water diffusivity was much less affected by differences in water content. Our results provide a concept for changing the properties of PEMs and a challenge to implement the improved diffusivity in a way that enhances net ion conductivity.

The Membranes with Modified Surface to Stabilize Water Balance of Fuel Cell under Low Humidity Conditions: A Model Study

The problem of water management in a fuel cell with a polymer electrolyte membrane (PEM) under low humidity conditions is most acute. The addition of adsorbents to a membrane improves the water-holding properties of PEMs. A stationary one-dimensional computer model is developed to analyze the distribution of water in the layers of membrane electrode assembly. An ionomer layer modified with an adsorbent is taken into account to increase the concentration of water in the membrane. The spatial distribution of the concentration of water in the catalytic layer and PEM for a standard membrane and a membrane containing a surface modified layer is obtained. The best distribution of water in the membrane is achieved through the addition of a layer with a threefold increase in water capacity from the side adjacent to a cathode catalytic layer.

Polymer Electrolyte Membranes

Polymer electrolyte membranes (PEM) with good properties are essential for the improvement of electrochemical operations. The increase in properties of polymer electrolyte membranes will develop the performance of polymer electrolyte membranes in the fuel cells. The importance of polymer electrolyte membranes is increasing recently due to its activity and simplicity in energy associated applications like automobiles and various portable applications. PEM has various properties like proton conductivity, chemical stability, mechanical properties, thermal stability and so on. These properties are enhanced and influenced by various factors like morphology, the molecular weight of the membranes, chemical structures, cross linkages etc. The present chapter attempts to summarize about the properties of polymer electrolyte membrane involved in the different types of electrochemical utilizations. Keywords: Polymer electrolyte membrane, fuel cells, morphology, proton conductivity, chemical structure.

Thermal Stability and Morphology Analysis of Polymer Electrolyte Membranes Prepared from Cellulose Acetate-LiClO<sub>4</sub>

Polymer electrolyte membranes of cellulose acetate-LiClO4 were prepared from the cellulose acetate with various ratios of lithium perchlorate in tetrahydrofuran (THF) as solvent. The properties of polymer electrolyte membranes with various ratios of lithium perchlorate were studied by Thermogravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM). The obtained TGA curves showed that these membranes were degraded thermally in three steps, which were attributed to dehydration, the main thermal degradation of the cellulose acetate chains, and the carbonization of the product to form ash. The thermal stability of the membrane decreased with the increase in LiClO4 content. The initial temperatures of the main degradation process decreased gradually from 330 °C in pure cellulose acetate membrane to 258 °C in cellulose acetate membrane containing 25% lithium perchlorate. The morphology of the membranes transformed from dense to the more porous membrane along with the increase in lithium perchlorate ratios on membranes.

Recent advances in additive‐enhanced polymer electrolyte membrane properties in fuel cell applications: An overview

Recent advances in additive‐enhanced polymer electrolyte membrane properties in fuel cell applications: An overview

Kajian Struktur dan Morfologi Grafin Oksida Bersulfonat yang Disediakan dengan Pelopor Berbeza

In this study, graphene oxide (GO) as nano sized filler to improve the properties of polymer electrolyte membrane was synthesized via the modified Hummers method. Hummers is the most common method used to synthesize GO. The GO is produced by exfoliation of graphite oxide under sonication method. Dispersion by sonication method shows mechanical disruption that breaks apart the graphite flakes which is then sterically stabilized in the base solution. The as-synthesized GO will be sulfonated using different precursors, namely (3-mercaptopropyl)trimethoxysilane (MPTMS), butane sultone (BS) and sulfanilic acid (SA). The structure and morphology of GO and sulfonated GO (SGO) were investigated in details by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FTIR analysis confirmed the presence of several functional groups such as hydroxyl, epoxy, carbonyl, carboxyl and sulfonic acid group. The obtained SEM and TEM images indicated, that the morphology of GO dispersion is folded, multilayered and crumpled with some wrinkles. The morphology of SGO showed a folded, thicker and overlap surface compared with GO sheets. Based on TEM image, the addition of sulfonic acid group into the GO network reveals the black spot on the sheets surface. This SGO will act as a potential base material for the application of solid acid catalyst, water purification as well as a composite in membrane fabrication.

SYNTHESIS OF CELLULOSE ACETATE FROM OIL PALM EMPTY FRUIT BUNCH AND ITS PROPERTIES AS POLYMER ELECTROLYTE MEMBRANES ON LITHIUM ION BATTERY

Biodegradable polymer electrolyte utilization on lithium ion battery is increasingly considered to prevent any waste. This study was conducted to synthesis cellulose acetate from oil palm empty fruit bunch and its properties as polymer electrolyte membranes on lithium ion battery. This study was done by extracting cellulose from oil palm empty fruit bunch. That cellulose was acetylated become cellulose acetate and characterized its functional group. Further, polymer electrolyte was synthesized with composition 25/60/15(%b/b) (SAS/PEO/LiClO4). The properties of polymer electrolyte membranes were characterized by analysis thermal properties, ionic conductivity and mechanical properties. Based on functional group data, synthetic cellulose acetate had similar the main functional group with commercial cellulose acetate. Synthetic cellulose acetate contained 27% acetyl with 1,4 substitution degree. Analysis thermal properties showed that the decomposition of SAS/PEO/LiClO4 polymer electrolyte membranes was started above 260oC. The ionic conductivity 10,81 x 10-4 S/cm of these polymer electrolyte membranes was 10,81 x 10-4 S/cm. Analysis of mechanic properties were 0,05 MPa stress, 14,23 MPa elongation and 0,35 MPa Modulus Young. SAS/PEO/LiClO4 polymer electrolyte membranes had higher ionic conductivity than SAK/PEO/LiClO4 polymer electrolyte membranes. However, SAS/PEO/LiClO4 polymer electrolyte membranes had lower thermal and mechanic properties than SAK/PEO/LiClO4 polymer electrolyte membranes.

Rugged catalyst layer supported on a Nafion fiber mat for enhancing mass transport of polymer electrolyte membrane fuel cells

In this study, a new rugged catalyst layer (CL) structure is derived from a Nafion fiber mat to enhance the mass transport properties of polymer electrolyte membrane fuel cell. Nafion fiber mat is fabricated on a membrane surface by electrospinning technique and then a catalyst ink is sprayed on the fiber-coated membranes. With the Nafion fiber mat with 3.0 μm fiber diameter, a rugged CL supported on the fiber mat is formed, dictating the structural feature of the Nafion fiber mat. The resulting CL, which features an expanded outer CL surface, exhibits 21% improved power performance at 0.4 V under high humidity operation due to the increase of gas and water transport properties. These results demonstrate that Nafion fiber mat can be as an effective and scalable scaffold for the development of advanced CL.

Structure and electrical properties of polymer electrolyte membrane for fuel cell application

In this study to investigate the Polymer Electrolyte Membrane or Proton Exchange Membrane (PEM) that were synthesized by using acrilonitrile butadiene styrene (ABS). In order to enhance ability as a proton conductive polymer membrane as electrolyte, amorphous and crystalline silica ( 3 % and 5 %) were added to the initial mixture of ABS to inhibit relatively high proton conductivity. The structural and morphological characterization of samples was done by X-ray powder diffractometer, FTIR and scanning electron microscopy. Electrical properties were determined by LCR-meter (HIOKI 3522-50LCR HiTESTER). The structure analysis shows that the ABS amorphous phase with the unsmoth surface. The electrical conductivity of Polymer Electrolyte Membrane is 4,21 x10-3 S/cm of ABS with 5 % amorphous silica.

Performance Improvement By Introduction of Macropore Structure in Membrane Electrolyte Assembly Using Mechanical Properties of Polymer Electrolyte Membrane

We have introduced macropores that help improve mass transfer of fuel cell electrode by using simple mechanical method. Polymers generally have elastic and inelastic regions when strain is applied. Nafion®, which is commonly used as a proton conductive membrane for polymer electrolyte membrane fuel cell (PEMFC), has a relatively large inelastic region compared to the elastic region. When an electrode is applied to Nafion® membrane and strain of inelastic region is applied, the macropores are formed due to the difference in elastic modulus between the membrane and the electrode. The electrochemical performance of MEAs with macropores at various strain ratios was evaluated. We have discussed the cause of performance improvement and durability was also confirmed. Furthermore, research into MEAs that contain shape-controlled macropores is being studied as a replacement for randomly formed macropores.

Ionomer Dispersions in Water/Alcohol Solutions by Coarse-Grained Molecular Dynamics

The polymer electrolyte membrane (PEM) is one of the principal components for polymer electrolyte fuel cells. As the phase separation is considered one of the primary factors affecting its performance, the morphological properties of PEM have been studied experimentally and theoretically. Under good solvent conditions for the polymer backbone, where solvents dissolve the backbone chains, ionomers exhibit polyelectrolyte-type behavior, forming loose ionic aggregates. In sufficiently polar solvents, ionomer backbones undergo aggregation and phase separation. This process results in the formation of a solid PEM at high ionomer concentration. Perfluorosulfonic acid (PFSA) ionomers such as Nafion (developed by DuPont) are currently the principal electrolyte and separator materials adopted for use as PEMs. Chemically, Nafion is a random copolymer that consists of hydrophilic sulfonate groups and a hydrophobic polytetrafluoroethylene backbone, which together form microphase-separated higher-order structures. Under sufficiently hydrated conditions, PEMs exhibit high mechanical robustness, warranted by hydrophobic backbone segments, as well as good water retention and high proton conductivity, conferred by the high volumetric ion density. The characterization of the ionomer structures has been extensively studied using experimental measurements such as small-angle neutron scattering (SANS), wide-angle neutron scattering (WANS), small-angle X-ray scattering (SAXS), and nuclear magnetic resonance (NMR). They observed that hydrophobic backbones of Nafion form the cylindrical-like core of self-assembled ionomer structures while ionic groups are located at the periphery of this aggregates. Based on a combination of scattering and microscopy, the rod-like aggregates in well-hydrated PEMs were observed. The proton conductivity and mechanical strength of solution-cast membranes are correlated with the properties of ionomer dispersions in solutions. Theoretically, while most of studies have primarily focused on the solid membrane state with water volume fraction significantly below 50%, ionomer aggregations in solutions can also be an important phenomenon to understand the self-assembly behaviors of ionomers as key structure-forming elements in ionomer films. In this study, ionomer aggregations in water/alcohol solutions have been investigated using coarse-grained (CG) molecular dynamics simulations to understand the dependence of aggregation behaviors on the water and alcohol fractions. The use of CG models is a valuable tool to prove the time and length scales of systems beyond what is feasible with traditional all atom models. Our model has been developed based on the MARTINI force fields, which is in close connection with more detailed atomistic models in terms of thermodynamic data, in particular hydration/partitioning free energies. The whole CG model of Nafion copolymer, as shown in Fig. 1, includes a part of the atomistic level configuration of a Nafion chain. A three-monomer unit of polytetrafluoroethylene (PTFE) (-(CF2)3-) are coarse-grained as a spherical bead of diameter 0.47 nm, and one side chain is coarse-grained as two spherical beads. This model is comparable to the inter-distance of ~2 nm between side chains and a side chain length of ~1 nm in the Nafion ionomer with EW = 1100. To include the effect of polarization in water model, which is significant at the interfaces between water and other phases and in the vicinity of charged particles. The initial configurations were generated by randomly placing 15 ionomer chains in a box with periodic boundary condition in all directions. Water and 1-propanol CG beads were then added based on the water/1-propanol molar fractions. All the solutions were fixed at an ionomer concentration of 5 wt%. The equilibration of the systems was first carried out with NPT MD simulations at T = 300 K and P = 1 atm for 100 ns. The additional NPT ensemble for 50 ns was then performed for the production. The dependence of NPA content on the ionomer structures was studied by systematically changing the NPA content in the system. It was found that ionomers form the bundle-like structures with cylindrical shape as shown in Fig. 2, which are in general agreement with cylindrical-like structures found in experimental scattering measurements of Nafion solutions. The ionomer aggregation size was found to tend to be larger and more dispersive at higher NPA contents, although the ionomers aggregated into one cluster at all NPA contents. Figure 1