In-plane Swelling Research Articles

Polycarbazole-based anion exchange membranes containing flexible side-chain linked piperidine pendants for alkaline fuel cells

In recent years, advancements in anion exchange membranes (AEMs) have notably enhanced the overall performance of anion exchange membrane fuel cells (AEMFCs). However, issues like limited alkali stability and low ionic conductivity of AEMs have become apparent. In this study, focusing on molecular design, a series of polycarbazole-based AEMs with flexible side chains, named PCP-n (where ‘n’ denotes the molar ratio of the newly synthesized monomer BHC in carbazole derivatives), were developed. The integration of long flexible side chains fosters chain movement and the clustering of piperidine cations, leading to distinct hydrophilic/hydrophobic nanoscale phase separation within the PCP-n membranes. Moreover, the PCP-n membranes demonstrate effective water management capabilities, with the PCP-90 membrane displaying a 32 % water uptake and an in-plane swelling ratio below 20 % at 80 °C. The introduction of an ether-free main chain based on carbazole derivatives along with the highly stable piperidine cationic group endows the PCP-n membranes with exceptional alkali resistance. Following a 1500-h immersion in 2 M KOH at 80 °C, the PCP-90 membrane successfully retains 79.92 % of its original ionic conductivity. Given its substantial thermal stability and mechanical strength, the PCP-90 membrane underwent testing in membrane electrode assembly and single-cell performance, achieving a notable peak power density of 275.64 mW cm−2 and an open-circuit voltage of 0.98 V. Overall, the impressive comprehensive performance of the PCP-n membranes suggests a promising future for their application.

Anisotropic polyphenylene-based anion-exchange membranes with flexible side-chains via click reaction for high-performance water electrolysis

Anion-exchange membrane water electrolysis (AEMWE) represents a promising and cost-effective electrochemical energy conversion system for green hydrogen production owing to its utilization of earth-abundant metals for various cell components (catalysts, porous transport layers, bipolar plates) and the zero-gap design. However, the lack of high-performance anion-exchange membranes (AEMs) has hampered the advancement of AEMWE technology. Here, by using colon coupling and click reactions, the ether-free polyphenylene-based AEMs (QPPBTF-TMA-w) with flexible side-chains containing triazole linkers. The QPPBTF-TMA-w membranes stand out for their lower activation energy for hydroxide conduction which is attributed to the well-structured ion-conducting channels via distinct phase separation facilitated by the triazole linker, which optimizes hydrophilicity and ensures efficient ion transport within the membrane. In addition, the QPPBTF-TMA-w membranes exhibit unique anisotropic swelling and ion-conduction behaviors, such as lower in-plane swelling and higher through-plane conductivity, which are advantageous for practical cell applications. Therefore, despite having a modest ion exchange capacity (IEC) value of 2.0, the QPPBTF-TMA-w membrane delivers high-performance in anion-exchange membrane water electrolysis (AEMWE), achieving 6.4 A/cm2 at 2.0 V at 70 °C using a 1.0 M KOH solution.

Anisotropic Deformation in a Polymer Slab Subjected to Fluid Adsorption.

Nanoporous adsorbents can mechanically swell or shrink once upon the accumulation of guest fluid molecules at their internal surfaces or in their cavities. Existing theories in this field attribute such sorption-induced swelling to a tensile force, while shrinkage is always associated with a contractive force. In this study, however, we propose that the sorption-induced deformation of a porous architecture is not solely dictated by the stress conditions but can also be largely influenced by its mechanical anisotropy. In more detail, the sorption-induced deformation of a polymeric slab is investigated using a hybrid molecular dynamics and Monte Carlo algorithm. When subjected to water loading, the slab is found to swell along its normal direction and display an overall positive volumetric strain. Moreover, the surface roughness is enhanced as a response to the surface energy decrease induced by the water covering the slab external surface. Unexpectedly, the in-plane deformation of the slab material seems to be highly constrained, so that it is far below its normal counterpart. This anisotropy is enhanced when the slab thickness decreases. With a thickness of around 1.35 nm, an in-plane shrinkage is observed throughout the entire hygroscopic range. A theoretical analysis based on a poromechanical model suggests that the anisotropic mechanical properties, which are common for a slab material, are the essence of the constrained in-plane swelling or even shrinkage under the isotropic sorption-induced tensile forces. This study, unveiling overlooked mechanisms of sorption-induced shrinkage in mechanically anisotropic materials, provides new insights into this field.

Highly-conductive proton exchange membrane of sulfonated poly(biphenyl alkylene) copolymers for H2/O2 fuel cell with 2.62 W cm-2 power density

Ether-free proton exchange membranes (PEMs) based on aromatic polymers are considered as potential alternatives to perfluorosulfonic acid (PFSA) PEMs due to their low cost, less reactant crossing, exceptional chemical stability and outstanding thermal stability. Herein, a series of high-performance sulfonated poly(biphenyl alkylene) (BPSA-PT-x) membranes with full carbon chain backbones were synthesized to investigate the effect of different ratios of hydrophobic components on membrane properties. Among the prepared membranes, the BPSA-PT-10 % PEM with the highest proton conductivity (311 mS cm-1 at 80 °C water) possessed excellent dimensional stability (in-plane swelling rate ≤19.7 %, through-plane swelling rate ≤24.9 %), mechanical properties (elongation at break: 89.8 % in wet state), thermal stability (glass transition temperature >450 °C) and low H2 crossover (1.80 mA cm-2). Further, the assembled H2/O2 fuel cell based on BPSA-PT-10 % PEM exhibited competitive performance with a peak power density of 2.62 W cm-2. The developed poly(biphenyl alkylene)-based PEMs should have potential applications in hydrogen energy field.

Enhancement in the alkaline stability of poly(arylene ether ketone)-typed anion-exchange membranes via phenylene piperidinium blocks

In alkaline environments, the cationic groups and polymeric backbones of conventional poly(arylene ether ketone)-typed anion-exchange membranes (AEMs) tend to degrade. Herein, we report poly(phenylene piperidinium-co-arylene ether ketone)s (QPPPiAEK-x) with enhanced alkaline stability as potential AEM candidates. Specifically, a diphenyl piperidine precursor was synthesized and subjected to Ni(0)-catalyzed coupling polymerization with poly(arylene ether ketone) oligomers and followed by classic Menshutkin reaction. Membranes with an ion exchange capacity ranging from 1.85 to 2.24 meq g-1 showed high water uptakes (97.7%–159.2%) and high OH- conductivities at 80 °C (73.4–82.2 mS cm-1) but moderate swelling behaviors (i.e., in-plane swelling ratios of 28.0%–35.8%, and through-plane swelling ratios of 28.4%–56.2%). Morphological studies confirmed the presence of hydrophilic–hydrophobic microphase separation (ionic domain sizes of 17.9–22.3 nm) in all membranes, which was ascribed to the high feed content of phenylene piperidinium blocks. The H2/O2 single-cell test revealed the highest power output (187.7 mW cm-2) for the QPPPiAEK-2.0 membrane at 60 °C and 100% relative humidity. During the stability test, all membranes exhibited adequate ion conduction abilities. The most durable membrane retained 69.6% of its initial conductivity after 936 h in a 1 M NaOH solution at 80 °C. Results of ex-situ nuclear magnetic resonance spectroscopy revealed that approximately 9.7%–20.6% of cationic decomposition was the main degradation pathway for the QPPPiAEK-x ionomers, whereas 2.6%–4.4% accounted for the cleavage of backbones. Our study provides a promising methodology for fabricating alkali-stable AEMs for fuel cell applications.

Sorption-Deformation Interplay in Hierarchical Porous Polymeric Structures Composed of a Slit Pore in an Amorphous Matrix.

Prevailing absorbents like wood-derived porous scaffolds or polymeric aerogels are normally featured with hierarchical porous structures. In former molecular simulation studies, sorption, deformation, and coupled sorption-deformation have been studied for single-scale materials, but scarcely for materials where micropores (<2 nm) and mesopores (2-50 nm) coexist. The present work, dealing with a mesoscopic slit pore between two slabs of microporous amorphous cellulose (AC), aims at modeling sorption-deformation interplay in hierarchical porous cellulosic structures inspired by polymeric modern adsorbents. Specifically, the atomic system is modeled by a hybrid workflow combining molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The results clarify the multiple sorption/deformation mechanisms in porous materials with different slit-pore sizes, including water filling in micropores, surface covering at the solid-air interface, and subsequent capillary condensation in mesopores. In particular, before the onset of capillary condensation, the sorption behavior of the AC matrix in the hybrid system is almost the same as that of bulk AC, in which sorption and deformation enhance each other through sorption-induced swelling and additional sorption in the newly created voids. Upon capillary condensation, the interaction between the micropores and the mesopore emerges. Water molecules in the mesopore exert a negative hydrostatic pressure perpendicular to the slab surface on the matrices, resulting in an increase in porosity and water content, a decrease in distance between the centers of mass (COMs) of the slabs, and thus a thinning of the slit pore. As described by Bangham's Law, the surface area of the rough slit-pore slab increases proportionally to the surface energy variation during surface covering. For a system composed of a compliant polymer like AC, however, the surface area enlargement does not result in an in-plane swelling as expected but instead in an in-plane shrinkage along with an increase in local roughness or irregularity (an accordion effect).

Flexible All-in-one Quasi-Solid-State Batteries Enabled by Low-water-content Hydrogel Films.

The high conductivities and good mechanical properties of hydrogel electrolyte films are critical for energy storage devices with high flexibility, fast redox kinetics, and long life. Herein, a low water content (6.63wt%) hydrogel film is prepared, and a favorable environment is created, with an electrochemical stability window of 2.26V and a high ionic conductivity of 2.6mScm-1 . The hydrogel film exhibits good folding ability, low in-plane swelling, and anti-freezing abilities. These properties are benefitted by immobilizing free water molecules on the abundant oxygenic groups of polymer fibers in the hydrogel film, offering a unique 3D channel to allow Li+ to quickly transport along the polymer network. Therefore, the hydrogel film-based all-in-one flexible cell exhibits stable cycling performance with a retention of 81.8% of the initial capacity after 500 cycles at room temperature and 66.2% of capacity retention at -30°C. Furthermore, the full cell with high cathode loading (≈21mgcm-2 ) exhibits a high areal capacity of 2.5mAhcm-2 (≈119mAhg-1 ). The overall merits of flexible all-in-one quasi-solid-state batteries demonstrate high potential to be used for power wearable electronics.

Mechanical Properties and Swelling Behaviors of Ultrathin Chemically Cross-Linked Polybutadiene Films

With the advancement of nanoscience and nanotechnology, understanding the unique mechanical properties of ultrathin polymer films is becoming increasingly important. We report the mechanical properties and swelling behaviors of ultrathin chemically cross-linked polybutadiene films. Upon reducing the film thickness, the Young’s modulus increased, and an unusual stress-relaxation behavior was observed. After stress relaxation, the fully relaxed modulus was significantly higher than that expected from the amount of added cross-linker and the entanglement degree. The out-of-plane swelling of the ultrathin films prepared on a substrate was comparable to that in the bulk, whereas the in-plane swelling of films floating on water was significantly suppressed. Such suppression of the in-plane deformation may be attributed to the effects of interface-induced orientations of the chains and the chain segments trapped at the interfaces acting as pseudo-cross-linking points. This study contributes to an understanding of the physical properties of ultrathin cross-linked elastomer films.

Nafion membranes reinforced by cellulose nanocrystals for fuel cell applications: aspect ratio and heat treatment effects on physical properties

This study explored the improvement of the physicochemical properties (mechanical resistance, water uptake, swelling, etc.) of Nafion membranes by cellulose nanocrystals (CNCs). These composite membranes were prepared from Ramie and Tunicate nanocrystals with respective aspect ratios of about 28 and 106. It was demonstrated that, regardless of the type of nanocrystals, increasing the cellulose weight content from 0 to 10 wt% increased the water uptake and the thickness swelling and decreased the in-plane swelling of the composite membranes during water immersion. The mechanical performances of the composite membranes (tensile strength, elongation at break and Young’s modulus) were also enhanced, with the best compromise for Tunicate nanocrystals found to be 5 wt%. The effect of thermal annealing up to 150 °C on the Nafion-Tunicate 5 wt% composite was tested and compared to that of pure Nafion. With thermal annealing, a small decrease in water uptake capacity, protonic conductivity, ion exchange capacity and hydration number was observed for both membranes. At the sub-molecular level, FTIR data suggest that the heat treatment of Nafion-Tunicate membranes induces cross-linking reactions between sulfonic groups of Nafion chains and surface functional groups of CNCs, leading for example to sulfonic ester links. The exothermic peak observed by DSC can assign an increase of the crystalline phase of Nafion chains and especially in the vicinity of CNCs. All cross-linkages led to an improvement in the mechanical resistance of the membranes when thermal annealing was below 130 °C.

Intrinsic swelling behavior of free-standing nanoporous ionomer-bound carbon films

Nanoporous ionomer-bound carbon films are frequently operated in the wet environments when they applied as electrode materials in advanced devices, such as polymer electrolyte membrane fuel cells, and electro-active polymer actuators. However, the intrinsic swelling behavior is still concealed because of the challenge in obtaining the film in free-standing form due to its inherent brittleness. Here, we report the pure swelling characteristic of the film under various temperature and humidity by attaining the free-standing film. Mismatched strain is adopted for the separation of the films from the coating substrates. The swelling strain of the free-standing films is measured in-situ by a digital image correlation method. Simultaneously, the electrical resistance is measured by a digital multimeter and it is correlated with the microstructural alteration caused by the swelling. Macroscopic swelling is discovered in contrast to the conventional knowledge that the electrode is dimensionally stable due to the absorption of ionomer's swelling into pore spaces. The nanoporous electrodes demonstrate in-plane swelling of 1–4% at 90 %RH depending on the weight fraction of ionomer. In spite of the macroscopic swelling, the ionomer 30 wt% containing electrode is electrically stable but the ionomer 80 wt% electrode shows 10 times increased electrical resistances. The correlated characteristics reveal that the film has a structural transition from decoupling to coupling between the macroscopic swelling and the electrical resistance depending on the ionomer's binding structure.

Anisotropic swelling of anisotropic elastic panels.

While isotropic in-plane swelling problems for thin elastic sheets have been studied extensively in recent years, many shape-programmable materials, including nematic solids and 3D-printed structures, are anisotropic, as are most industrial sheet materials. In this theoretical work, we consider central swelling and shrinkage of plates of aspect ratio and material properties relevant to the manufacture of engineered wood composite panels in which both in-plane swelling and material stiffness are highly orthotropic, leading to multiple separations in energy scales. With transverse swelling in the soft direction, and gradients in the stiff direction, the warped plates adopt two distinct types of configurations, axisymmetric and twisted, which we illustrate with toy models. We employ a two-parameter family of isometries to embed the metric programmed by the swelling, thus reducing the problem to one of minimizing bending energy alone. A simple argument is seen to closely predict averaged axisymmetric curvatures. While purely cylindrical shapes are unobtainable by pure in-plane swelling, they can be closely approximated in a highly anisotropic system. However, anisotropy can favor twisting, and breaks a degenerate soft deformation mode associated with minimal surfaces in isotropic materials. Bifurcations from axisymmetric to twisted shapes can be induced by anisotropy or by certain attributes of a central shrinkage profile. Finally, we note how our findings indicate practical limitations on the diagnosis of moisture inhomogeneities in manufactured panels by observation of warped conformations, due to the sensitivity of the qualitative response to specifics of the profile.

Robust three‐dimensionally printed polypropylene/highly sulfonated polysulfone composites for potential applications in fuel cells

Advanced ion-conducting composites were prepared by ionomer synthesis, fused deposition modeling (FDM) 3D-printing, surface modification, and pore-filling. The cost-effective, mechanically robust, and inert microporous substrates of polypropylene were made by FDM printing. Three infill contents of 30, 50, and 70 vol% of polypropylene were designed. A synthesized highly sulfonated hydroquinone-based polysulfone, with 80% degree of sulfonation (DS), was used as the pore material. Nucleophilic aromatic substitution on difluorodiphenyl sulfone was used to synthesize the highly sulfonated ionomer. Pore-filling of the designed printed substrate was done via 10 w/v% of the ionomer solution. Oxygen plasma treatment was applied to enhance the compatibility of the substrate and the pore material's interfaces. Modification of porous substrate was confirmed by alteration of surface polar characteristics and roughness from contact angle measurements and atomic force microscopy, respectively. Confinement of highly sulfonated ionomer by the robust structure resulted in the preparation of electrolyte with controlled water uptake, no in-plane swelling, high conductivity (up to 0.417 S/cm at 60°C under 100% relative humidity), and current density of about 836 mA.cm−2 at 60°C under 100% relative humidity. Regarding the presence of commodity polypropylene in the structure, the performance was good, compared to commercial Nafion membrane, with a cell current density of about 1120 mA.cm−2.

Lithium-Ion Exchange Polymer Membranes Limit Migration of Dissolved Polysulfide Species in Li-S Batteries

Conventional lithium-ion (Li-ion) batteries dominate development efforts in electrical vehicles due to their high open circuit voltage, desirable power density, and long cycle life. Despite these advantages, state-of-the-art Li-ion batteries barely meet the energy requirement of EV-based power trains due low energy density (180-200 Wh/kg cell) and high cost. Lithium sulfur (Li-S) batteries are promising for EV applications because they address both these barriers. Li-S batteries exploit a redox couple described by the reaction below, which has an open circuit potential of 2.2 V with respect to Li+/Li: 16 Li+ + S8 + 16e-→ 8 Li2S Assuming full conversion, the theoretical energy density and specific capacity of Li-S batteries is 2500 Wh/kg S and 1675 mAh/g S, respectively.1 In addition, sulfur, the key active cathode material is significantly less expensive than conventional transition metal oxide cathodes used in Li-ion batteries. However, Li-S batteries have not gained acceptance for practical applications because of their poor cycle life. This limitation originates from polysulfide diffusion from the cathode through the electrolyte to the anode which causes parasitic side-reactions and limits capacity and cycle retention. Our work aims to overcome the challenges of polysulfide diffusion by incorporating lithium-ion exchange (LIE) ionomers as polysulfide blocking barriers in Li-S cells. When exposed to electrolyte solvent, these LIE membranes provide a physical barrier that limits polysulfide diffusion, while also delivering high Li+ ion conductivity through swelling in electrolyte solvent. The LIE ionomers can be applied in a variety of ways including as: binders in the electrode formulation, coatings applied directly to the electrode surface, and as freestanding polymer electrolyte membranes. We have also developed a porous, dimensionally stable membrane (DSM) which can be impregnated with LIE ionomers to improve mechanically stability by limiting in-plane (X-Y direction) swelling. This general approach of incorporating LIE ionomers into Li-S cells has achieved improvements in discharge capacity, cycle life, coulombic efficiency, and energy density.

Electrospun tri-layer membranes for H2/Air fuel cells

Dual nanofiber electrospinning was used to fabricate a series of multi-layer fuel cell membranes with high proton conductivity and low in-plane water swelling, using 825 EW perfluorosulfonic acid (PFSA) ionomer and polyamide-imide (PAI). The relative flow rates of the two polymer solutions were adjusted during electrospinning to create multiple layers with different PFSA/PAI weight ratios. After electrospinning, fiber mats were transformed into dense membranes with a total thickness of 20 µm by heating and compaction, where each layer had the same composite morphology: a PFSA ionomer matrix with an embedded network of reinforcing PAI fibers. Tri-layer films were fabricated with surface layers composed of 95 wt% PFSA and 5 wt% PAI and an inner (reinforcing) layer that was enriched in PAI (25–60 wt% PAI), with either a uniform PFSA/PAI composition or with a symmetric PFSA/PAI compositional gradient. The thickness of the inner layer (uniform or gradient composition) was adjusted so that the effective/average composition of the entire membrane was 80 wt% PFSA and 20 wt% PAI. As compared to a single layer membrane with a uniform distribution of PAI fibers in a PFSA matrix, the tri-layer membrane structures exhibited dramatically less in-plane swelling (5–6% vs. 11%) with no loss in proton conductivity. For a slightly different system, with alternating layers of neat PFSA and 70/30 PFSA/PAI, increasing the number of layers from 3 to 5, 7, or 9 had no effect on proton conductivity (because the overall membrane composition was held constant) and did not further reduce the membrane in-plane swelling.

Adamantammonium as a novel functional group for anion exchange membranes with excellent comprehensive performances

In the pursuit of alkali stable cation as functional group for anion exchange membranes (AEMs), a novel adamantammonium (AdA) cation, which replacing methyl group of conventional trimethylammonium by an adamantyl group, was synthesized and investigated. 1H NMR spectroscopy was employed to quantify the extent of decomposition and the results showed that > 99% adamantammonium remaining after 7 days immersion in 2 M NaOH (in D2O) at 80 °C. The AdA functionalized benzyl type poly(2,6-dimethyl phenylene oxide) polyelectrolytes, PPO-AdAs, were further prepared and characterized the AEM properties. Not only the chemical durability of these new PPO-AdA membranes, interestingly, but the conductivity and dimensional stability (water uptake and in-plane swelling) are superior to the benzylmethylammonium-benchmark PPO-based AEM (PPO-TMA). With the similar IEC values, the water uptake of PPO-AdA-41 sample is much lower than PPO-TMA-28, however, the conductivity of the former (15.7 mS cm-1, chloride conductivity at 50 °C) is higher than the latter (13.3 mS cm-1). Overall, the results of this study offer a base-stable cation, adamantammonium, and the corresponding adamantammonium-based AEMs for fuel cell applications with the advantages of chemical stability, enhanced conductivity and excellent dimensional stability as well as facial functionalization technique.

Combining control of branching and sulfonation in one-pot synthesis of random sulfonated polyarylethersulfones: effects on thermal stability and water retention

In functional polymers with tunable hydrophilic behaviour like sulfonated polyarylethersulfone (SPES) high ionic conductance can be obtained directly by increasing the concentration of sulfonic moieties along the macromolecular chain. This, however, often comes to the cost of excessive water sorption, which can lead to membrane rupture and consequent device failure. To overcome this drawback, and to reconcile high hydrophilicity with the high mechanical properties of aromatic polymers, we propose the use of SPES copolymers with a low degree of branching. A series of branched SPES was synthesized using homogeneous (one-pot) copolymerization by replacing an amount up to 0.9% mol of the difunctional monomer 4,4′-dihydroxydiphenyl with the trifunctional 1,3,5-trihydroxybenzene (THB). The polymers were characterized by 1H-NMR spectroscopy, intrinsic viscosity, water sorption measurements, thermogravimetric analysis and differential scanning calorimetry. Like linear SPES, branched SPES is totally amorphous and soluble in polar aprotic solvents, lending itself to easy fabrication of membranes and coatings. Besides reducing the water sorption and in-plane swelling of SPES membranes upon equilibration in liquid, branching also improves the retention of water in swollen membranes.

Inhibiting the Swelling Behavior of Nafion Membranes for PEM Water Electrolysis

Nafion is a commercially available perfluorosulphonate (PFSA) polymer electrolyte membrane (PEM) commonly used in both PEM fuel cells and electrolyzers. Catalyst coated membranes (CCMs) are prepared by hot-pressing the catalyst layers on a hot and dry Nafion film[1]. In the electrolyser, the dry CCMs get in contact with liquid water, which swells the membrane. Because the CCM is clamped in the cell, this leads to formation of folds and wrinkles. Furthermore, when the membrane shows stronger in-plane swelling than the catalyst layer, this swelling can also lead to membrane-electrode delamination and formation of electrode cracks. Therefore, the large in-plane swelling of Nafion membranes is an unwanted feature. In this work, a facile and economical approach was developed to inhibit the in-plane swelling behavior of Nafion membranes. When first swollen on a fixed metal frame and afterwards dried in a fixed geometry, the Nafion film will memorize the wet shape and show reduced area swelling upon rehydration, providing outstanding benefits for CCM fabrication[2]. We expect that when using Nafion membranes with inhibited swelling behavior for CCM fabrication, the life time of PEM water electrolyzers shall be remarkably increased. [1] M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 4901-4934 (2013) [2] S. Hink, D. Henkensmeier, J. H. Jang, H.‐J. Kim, J. Han, S.‐W. Nam, Macromol. Chem. Phys. 2015, DOI: 10.1002/macp.201500063.

Reduced In-Plane Swelling of Nafion by a Biaxial Modification Process

Reduced In-Plane Swelling of Nafion by a Biaxial Modification Process

Guanidine functionalized radiation induced grafted anion-exchange membranes for solid alkaline fuel cells

Alkaline anion-exchange membranes (AAEMs) for solid alkaline fuel cells (SAFC) application were successfully prepared by radiation induced grafting of Vinyl benzyl chloride onto ultra-high molecular weight polyethylene powder (UHMWPE), followed by film fabrication by melt pressing and quaternization with a Guanidine derivative, 1,1,3,3-tetramethyl-2-n-butylguanidine (TMBG). The chemical structures of the resulting AAEMs were examined by Fourier transform infrared, which showed that the grafted membranes were successfully functionalized by modified guanidine. The performance of the AEMs, including ion exchange capacity, water uptake, in-plane swelling, methanol uptake, methanol permeability, and hydroxide ion conductivity were investigated. Thermal analysis showed that the Guanidine-based AAEMs comprises better thermal stability. The AAEMs membrane exhibited a maximum ionic conductivity of 27.7 mS cm−1 at 90 °C. Methanol permeability is found to be in the order of 10−9 cm2 s−1, which is significantly lower than that of Nafion®. The membranes have useful properties as an anion exchange membranes suitable for alkaline fuel cells.

Static friction force between catalyst layer and micro porous layer and its effect on deformations of membrane electrode assemblies under swelling

Membrane electrode assemblies (MEAs) composed of a Nafion membrane and heat-transferred catalyst layers (CLs) were employed in this study. The deformation of MEAs between micro porous layers (MPLs)/gas diffusion layers (GDLs) was investigated in response to humidity cycles. The MEA deformed into wrinkle shapes at lower contact pressures and exhibited bulge deformation at higher contact pressures. Wrinkles were generated by large in-plane swelling after buckling when swelling could not be restricted by the friction force from MPLs. Next, the static friction coefficient between the MEA and MPL was measured, and a friction mechanism was investigated. The static friction coefficient was 0.43 at the contact pressure of 0.22 MPa between the MEA and MPL and increased with the increase in the contact pressure. The surface observation of the MPL after the friction test indicated that a static friction was generated by the contact of the convex MPL and flat CL surface. The static friction force and swelling force were calculated to investigate the effect of the static friction force on the MEA deformation. The static friction force, which was more than 12% of the swelling force, could prevent wrinkles in 33 μm thick MEA.