Imidazolium functionalized poly(vinyl alcohol) membranes for direct methanol alkaline fuel cell applications

In this study, imidazolium functionalized poly(vinyl alcohol) (PVA) was synthesized by acetalization and direct quaternization reaction. Afterwards, composite anion exchange membranes based on imidazolium‐ and quaternary ammonium‐ functionalized PVA were used for direct methanol alkaline fuel cell applications. ¹H NMR and Fourier transform infrared spectroscopy data indicated that imidazole functionalized PVA was successfully synthesized. Inductively coupled plasma mass spectrometry data demonstrated that the imidazolium structure was efficiently obtained by direct quaternization of the imidazole group. Composite anion exchange membranes were fabricated by application of the functionalized PVA solution on the surface of porous polycarbonate (PC) membranes. Fuel cell related properties of all prepared membranes were investigated systematically. The imidazolium functionalized composite membrane (PVA‐Im/PC) exhibited higher ionic conductivity (7.8 mS cm^?1 at 30 °C) despite a lower water uptake and ion exchange capacity value compared to that of quaternary ammonium. In addition, PVA‐Im/PC showed the lowest methanol permeation rate and the highest membrane selectivity as well as high alkaline and oxidative stability. Dynamic mechanical analysis results reveal that both composite membranes were mechanically resistant up to 10⁷ Pa at 140 °C. The superior performance of imidazolium functionalized PVA composite membrane compared to quaternary ammonium functionalized membrane makes it a promising candidate for direct methanol alkaline fuel cell applications. © 2020 Society of Chemical Industry     

Nanocomposite polyvinyl alcohol fibers for medical applications

It was investigated how the HAp and SiO₂ nanoadditives introduced into the material of fibers made from polyvinyl alcohol (PVA) affects the structure, sorption, and strength properties of those fibers. The conditions of the fibers' production were selected with the aim of obtaining the nanocomposite PVA fibers which would be soluble in water and in body fluids. These fibers are intended to be used for the production of a biocomposite with another biodegradable polymer. The determination was made of the effect of two different deformations applied at the fiber production stage on the structure and properties of the fibers. Using the WAXS method, the supramolecular structure of the fibers was determined. Nanocomposite PVA fibers obtained in this work have an oriented crystalline structure with a rather low level of crystallinity, reaching 40%, and a relatively high orientation index of crystallites: 0.48–0.54. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Branched poly(biphenylene-co-sulfone)ether ion exchange membranes containing perfluorocyclobutane groups for fuel cell applications

A series of branched poly(biphenylene-co-sulfone) ion exchange membranes containing perfluorocyclobutane groups were prepared for fuel cells. Two bifunctional trifluorovinyloxy-terminated monomers (sulfonable 4,4′-bis(trifluorovinyloxy)biphenyl and insulfonable 4,4′-sulfonyl-bis(trifluorovinyloxy)biphenyl) and a trifunctional trifluorovinyloxy-terminated branching agent (1,1,1-tris(4′-trifluorovinyloxyphenyl)ethane) were synthesized and terpolymerized via thermal [2π + 2π] cyclodimerization to obtain partially fluorinated and branched polymers containing 0–5 mol% of the branching agent. They were then postsulfonated by chlorosulfonic acid at room temperature, cast as membranes, and characterized to evaluate their electrochemical properties for fuel cell applications. As the branching agent content was increased, their polydispersity values highly increased, indicating they became highly branched. It was confirmed that higher branching agent content also increased the ion exchange capacity, water uptake, and proton conductivity of the branched ion exchange membranes containing perfluorocyclobutane groups. This indicates that their electrochemical properties can be easily controlled by the degree of branching. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48373.     

Characterization of sulfonated poly(styrene-co-pyrrolidone) pore-filling membranes for fuel cell applications

Pore-filling membranes using three monomers, i.e., styrene, N-vinyl pyrrolidone (VP), and divinylbenzene (DVB), are prepared for polymer electrolyte fuel cell (PEFC) applications. A porous polyethylene (PE) film substrate is used to enhance the dimensional stability of the prepared membranes. The proton conductivity and the water uptake of the styrene/VP/DVB membranes are similar to those of the styrene/DVB membranes, even though their ion exchange capacity is slightly lesser than that of the styrene/DVB membranes. Furthermore, the thermal stability of the styrene/VP/DVB membranes is higher than that of the styrene/DVB membranes, and, for the same DVB content, the membranes containing VP exhibit better oxidative stability. VP increases the membrane’s water-absorbing ability due to its intrinsic hydrophilic property and decreases weak α-hydrogen derived from the sulfonated styrene. Finally, the membrane-electrode assembly (MEA) using the 80/10/10 (Styrene/VP/DVB in weight percentage) membrane shows better performance than that using the 90/0/10 membrane.     

Inter-lamellar crystallization in poly(tetramethylene oxide)

High molecular weight poly(tetramethylene oxide) crystallizes isothermally from the bulk to a final crystallinity level of approximately 50%. Further crystallization can be induced in this material by cooling. This effect has been studied by differential scanning calorimetry (d.s.c.) and small angle X-ray scattering (SAXS). The additional crystalline material has a lower melting point than the original and its presence causes a pronounced decrease in the small angle spacing (correlation function maximum). The propensity to crystallize further at low temperatures decreases with increasing secondary crystallization under the original isothermal conditions. Additional crystallinity can also be induced, without temperature change, by cleaving chains by prolonged exposure to an X-ray source. These facts are explained in terms of the additional crystallinity occurring by growth of new thin lamellae between the original isothermally grown lamellae. The new lamellae grow preferentially in the thicker amorphous regions, which are reduced in size and number by secondary crystallization. The radiation damage effects indicate that amorphous chain constraint as well as available space is an important factor inhibiting crystallization between preformed lamellae.     

Random sulfonated poly(arylene ether sulfone) and sulfonated poly(arylene ether ketone) membranes for fuel cell applications

In this study, sulfonated poly(arylene ether sulfone) (SPAES) and sulfonated poly(arylene ether ketone) (SPAEK) were randomly synthesized, employing a presulfonation process. This presulfonation process resulted in a more controlled and reproducible sulfonation level. The respective polymers were prepared using 2,2-Bis(4-hydroxyphenyl) propane at 50% molar ratio, which also provided some membrane elasticity. The resulting polymers, each had 25% of the block containing the sulfonic domains (SPAES A 25 and SPAEK A 25). Better conductive membranes were achieved for the random sulfone polymers than for the random ketone polymers, with values, respectively, of 0.24 and 0.07 S cm⁻¹ at 80°C. The lower proton conductivity from the ketone-based polymer was compensated with very low methanol permeability (0.25 × 10⁻⁶ cm² s⁻¹) and outstanding oxidative stability. The selectivity of both polymer membranes exceeded the reported values for the state-of-the-art Nafion® 117 and other commercially available options. Both polymer membranes, with their unique combination of ionic domains, elastomeric blocks, and resulting morphology, could be viable candidates for fuel cell applications.     

Electrospinning of poly(vinyl alcohol) and poly(4‐styrenesulfonic acid) for fuel cell applications

Electrospun fibers of poly(vinyl alcohol) (PVA) and PVA/poly(4‐styrenesulfonic acid) (PSSA) were obtained. By varying PVA to PSSA weight ratios, various fiber sizes and shapes were observed. The fiber diameters ranged from 176 to 766 nm, and the largest fibers were obtained from 15 wt % aqueous PVA solution. The effect of solution viscosity on fiber morphology was discussed. The presence of PSSA in electrospun fibers was confirmed by Fourier Transform Infrared spectroscopy. The PVA fibers were thermally stable up to 250°C, and the PVA/PSSA fibers were stable up to approximately 150°C. The water stability of the fibers was improved by heat‐treatment at 120°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Hydrogels based on poly(ethylene oxide) and poly(tetramethylene oxide) or poly(dimethyl siloxane). II. Physical properties and bacterial adhesion

To investigate the effects of polymer chemistry and topology on physical properties and bacterial adhesion, various hydrogels composed of short hydrophilic [poly(ethylene oxide) (PEO)] and hydrophobic blocks were synthesized by polycondensation reactions. Differential scanning calorimetry and X‐ray diffraction analysis confirmed that all of the hydrogels were strongly phase‐separated due to incompatibility between PEO and hydrophobic blocks such as poly(tetramethylene oxide) (PTMO) and poly(dimethyl siloxane) (PDMS). The crystallization of PEO in the hydrogels was enhanced by the incorporation of longer PEO chains, the adoption of PDMS as a hydrophobic block, and the grafting of monomethoxy poly(ethylene oxide) (MPEO). Compared to Pellethane, the control polymer, the hydrogels exhibited higher Young's moduli and elongations at break, which was attributed to the crystalline domains of PEO and the flexible characteristics of the hydrophobic blocks. The mechanical properties of the hydrogels, however, significantly deteriorated when they were hydrated in distilled water; this was primarily ascribed to the disappearance of PEO crystallity. The water capacity of hydrogels at 37°C in phosphate‐buffered saline (PBS) (pH = 7.4) was dominantly dependant on PEO content, which also influenced the thermonegative swelling behavior. From the bacterial adhesion tests, it was evident that both S. epidermidis and E. coli adhered to Pellethane much greater than to the hydrogels, regardless of the preadsorption of albumin. Better resistance to bacterial adhesion was observed in hydrogels with longer PEO chains, with PTMO as a hydrophobic block, and with MPEO grafts. The least bacterial adhesion for both species was achieved on MPEO_2k–PTMO, a hydrogel with MPEO grafts. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1505–1514, 2003     

Synthesis and characterization of poly(vinyl alcohol)‐based membranes for direct methanol fuel cell

Membranes made of poly(vinyl alcohol) (PVA) and its ionic blends with sodium alginate (SA) and chitosan were synthesized and characterized for their ion-exchange capacity (IEC) and swelling index values to investigate their applicability in direct methanol fuel cells (DMFCs). These membranes were assessed for their intermolecular interactions, thermal stabilities, and mechanical strengths with Fourier transform infrared spectroscopy, X-ray diffraction methods, differential scanning calorimetry, thermogravimetric analysis, and tensile testing, respectively. Methanol permeability and proton conductivity were also estimated and compared to that of Nafion 117. In addition to being effective methanol barriers, the membranes had a considerably high IEC and thermal and mechanical stabilities. The addition of small amounts of anionic polymer was particularly instrumental in the significant reduction of methanol permeability from 8.1 × 10⁻⁸ cm²/s for PVA to 6.9 × 10⁻⁸ cm²/s for the PVA–SA blend, which rendered the blend more suitable for a DMFC. Low methanol permeability, excellent physicomechanical properties, and above all, cost effectiveness could make the use of these blends in DMFCs quite attractive. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1154–1163, 2005     

Novel imidazole‐grafted hybrid anion exchange membranes based on poly(2,6‐dimethyl‐1,4‐phenylene oxide) for fuel cell applications

Novel organic–inorganic hybrid membranes, based on poly(2,6‐dimethyl‐1,4‐phenylene oxide), have been prepared through 1,2‐dimethylimidazole functional groups and double crosslinking agents including 3‐glycidyloxypropyltrimethoxysilane and tetraethyl orthosilicate by sol–gel process for the purpose of improving the conductivity and alkaline resistance. The structure of membranes was characterized using Fourier‐transform infrared spectra, ¹H NMR, and X‐ray diffraction. The physico‐chemical properties of all membranes were shown in ion exchange capacity, water uptake, stability, and conductivity. Membranes with OH^– conductivity up to 0.022 at 25 °C and 0.036 S cm^?1 at 80 °C. Promisingly, the chemical stability of the resulting membranes remains unchanged after storage in 2 mol dm^?3 KOH at 25 °C over at least 10 days. The tensile strength can be higher than 30 MPa, and the elongation at break (Eb) is in the range 6.68–10.84%. Hence, this hybrid membrane can be potentially applied in alkaline fuel cells. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46034.     

Stable anion exchange membranes derived from fluorinated poly(aryl ethers) with quaternized fluorene units for fuel cell applications

A series of fluorinated poly(aryl ethers) containing benzyltrimethyl quaternary ammonium functionalized fluorene units (QPFAE) are synthesized via condensation polymerization, chloromethylation, and quaternization. Ionomer structure and the ion exchange capacity are confirmed by ¹H‐nuclear magnetic resonance spectroscopy. Other characterization techniques such as Fourier transform infrared spectroscopy, atomic force microscopy, thermogravimetric analysis, gel permeation chromatography, electrochemical impedance spectroscopy, Fenton, water‐swelling, and hydrolytic aging tests are used to evaluate the physicochemical properties of the as‐prepared QPFAE membranes. For the QPFAE membranes with ion exchange capacity of 0.95–1.94 mmol/g, they displayed low water uptake and methanol permeability (4.59–26.1 × 10⁻⁸ cm²/s at 25 °C), fairly good dimensional stability, high mechanical toughness, as well as fine thermal‐oxidative‐hydrolytic stability and ion conductivity at least 10 mS/cm. The membranes also showed clear hydrophilic/hydrophobic phase‐separation morphology. Furthermore, the QPFAE membranes could endure harsh basic conditions (1–4 mol/L NaOH solution) at 60 and 80 °C at least 240 h, keeping rather high mechanical toughness and ion conduction capability during the aging test. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46301.     

Pervaporation membranes based on imide‐containing poly(amic acid) and poly(phenylene oxide)

Three imide‐containing poly(amic acids) were synthesized and used for homogeneous and composite membrane preparation. The transport properties of composite membranes consisting of an imide‐containing poly(amic acid) top layer on an asymmetric porous poly(phenylene oxide) support were studied in the pervaporation of aqueous solutions of organic liquids (ethanol, isopropanol, acetone, and ethylacetate) and organic/organic mixtures (ethylacetate/ethanol, methanol/cyclohexane). For most of the aqueous/organic mixtures, the composite membranes exhibited dehydration properties. Dilute aqueous solutions of ethylacetate were an exception. In these solutions, the composite membranes exhibited organophilic properties, high permeability, and selectivity with respect to ethylacetate. In the pervaporation of methanol/cyclohexane mixtures, methanol was removed with very high selectivity. To account for specific features of pervaporation on the composite membranes, the sorption and transport properties of homogeneous membranes prepared from polymers comprising the composite membrane [imide‐containing poly(amic acids) and poly(phenylene oxide)] were studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2361–2368, 2003     

Nanocomposite polymer electrolytes containing silica nanoparticles: Comparison between poly(ethylene glycol) and poly(ethylene oxide) dimethyl ether

Nanocomposite polymer electrolytes consisting of low molecular weight poly(ethylene oxide) (PEO), iodine salt MI (M = K⁺, imidazolium⁺), and fumed silica nanoparticles have been prepared and characterized. The effect of terminal group in PEO, i.e., hydroxyl (? OH) and methyl (CH₃) using poly(ethylene glycol) (PEG) and PEO dimethyl ether (PEODME), respectively, was investigated on the interactions, structures, and ionic conductivities of polymer electrolytes. Wide angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), and complex viscositymeasurements clearly showed that the gelation of PEG electrolytes occurred more effectively than that of PEODME electrolytes. It was attributed to the fact that the hydroxyl groups of PEG participated in the hydrogen‐bonding interaction between silica nanoparticles, and consequently helped to accelerate the gelation reaction, as confirmed by FTIR spectroscopy. Because of its interaction, the ionic conductivities of PEG electrolytes (maximum value ～ 6.9 × 10^?4 S/cm) were lower than that of PEODME electrolytes (2.3 × 10^?3 S/cm). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Formalized poly(vinyl alcohol) membranes for reverse osmosis

The permeation properties of formalized poly(vinyl alcohol) membranes are described. The interest of this work is centered on the properties relevant to desalination by reverse osmosis. These membranes, when properly prepared, showed reasonably high water permeability, high salt rejection, and stability in the presence of acids and alkalies.     

Characteristics of permeation and separation for propanol isomers through poly(vinyl alcohol) membranes containing cyclodextrin

Poly(vinyl alcohol) membranes containing cyclodextrin (CD–PVA membrane) were prepared and characteristics of permeation and separation for propanol (PrOH) isomers through the CD–PVA membranes were investigated by pervaporation and evapomeation. Evapomeation was more effective for the separation of PrOH isomers through the CD–PVA membrane than was pervaporation. The CD–PVA membrane more preferentially permeated n-PrOH than i-PrOH from their mixtures. In particular, the mixture of 10 wt % n-PrOH concentration was concentrated to about 45 wt % through the CD–PVA membrane. Both permeability and selectivity for n-PrOH were improved with an increase of CD content in the membrane. The results were supported by the fact that the affinity of CD for n-PrOH was stronger than that for i-PrOH. The permeation mechanism of PrOH isomers through the CD–PVA membrane is discussed based on the solution–diffusion theory. © 1994 John Wiley & Sons, Inc.     

Influence of silica content in sulfonated poly(arylene ether ether ketone ketone) (SPAEEKK) hybrid membranes on properties for fuel cell application

Sulfonated poly(arylene ether ether ketone ketone) (SPAEEKK) copolymer containing pendant sulfonic acid group (sulfonic acid content (SC) = 0.67) was synthesized from commercially available monomers such as sodium 6,7-dihydroxy-2-naphthalenesulfonate (DHNS), 1,3-bis(4-fluorobenzoyl)-benzene (BFBB), and hexafluorobisphenol A (6F-BPA). SPAEEKK/silica hybrid membranes were prepared using the sol-gel process under acidic conditions. The SPAEEKK/silica hybrid membranes were fabricated with different silica contents and the membranes were modified to achieve improved proton conductivity incorporating P-OH groups (H₃PO₄ treatment).The silica particles within the membranes were used for the purpose of blocking excessive methanol cross-over and for forming a pathway for proton transport due to water absorption onto the hydrophilic SiOH surface. The proton conductivities of H₃PO₄-doped membranes were somewhat higher than the un-doped (H₃PO₄-free) membranes due to increasing hydrophilicity of the membranes. The presence of silica particles within the organic polymer matrix, which decreases the ratio of free water to bound water due to the SiOH on the surface of silica derived from sol-gel reaction, results in hybrid membranes with reduced methanol permeability and improved proton conductivity.     

Glucose-responsive insulin release from poly(vinyl alcohol)-blended polyacrylamide membranes containing glucose oxidase

Glucose-sensitive membranes that can increase their permeability in the presence of glucose have been developed. Membranes are fabricated by free-radical polymerization of acrylamide and poly(vinyl alcohol) blends, containing glucose oxidase (GOD). The polymers are hydrogels, with water content in the range of 85–95%, depending on the pH or glucose concentration. The gluconic acid produced by an enzymatic reaction between glucose oxidase and glucose induces a decrease in pH value of the medium. This may causes the protonation of the amino groups in the membrane, resulting in an increase in water content of the polyamine membrane or which changes the solubility of insulin and the diffusional driving force. The in vitro retention of the enzyme activity by the membrane is also reported. It appears that the problem of membrane rupture may be alleviated by the blending of polyacrylamide (AA) with poly(vinyl alcohol) (PVA), since they have demonstrated an improved wet strength, without altering their insulin-transport properties. This preliminary report proposes the possibility of developing glucose-sensitive membranes for controlled delivery of insulin and also benefits from ongoing research on biosensors.     

Silicone-containing polymer blend electrolyte membranes for fuel cell applications

Polymer electrolyte membranes are developed from blends of chemically durable silicone-containing epoxy (Si-Epoxy) and proton conducting sulfonic polyimide (SPI). A charge-transfer (CT) complex is formed between electron-donating dihydroxynaphthalene units in Si-Epoxy, and electron-accepting naphthalenediimide units in SPI, as confirmed via X-ray diffraction and visible spectroscopy. The blend membranes show comparable mechanical strength to Nafion 211, but the elongation to break is much lower, indicating better resistance to deformation under strain stress, attributed to CT complex formation. The chemical durability of the blend membranes was much higher than pure SPI according to Fenton's test, also attributed to CT complex formation. Meanwhile, the proton conductivity is dependent on the sulfonic acid content of the SPI, which in turn affects the fuel cell performance. The maximum proton conductivity was measured to be 23.1 mS cm⁻¹ at 80°C and 90 %RH for a 1:1 blend, and the membranes were successfully incorporated into PEFCs.     

Organic-inorganic nanocomposite polymer electrolyte membranes for fuel cell applications

Organic-inorganic nanocomposite polymer electrolyte membrane (PEM) contains nano-sized inorganic building blocks in organic polymer by molecular level of hybridization. This architecture has opened the possibility to combine in a single solid both the attractive properties of a mechanically and thermally stable inorganic backbone and the specific chemical reactivity, dielectric, ductility, flexibility, and processability of the organic polymer. The state-of-the-art of polymer electrolyte membrane fuel cell technology is based on perfluoro sulfonic acid membranes, which have some key issues and shortcomings such as: water management, CO poisoning, hydrogen reformate and fuel crossover. Organic-inorganic nanocomposite PEM show excellent potential for solving these problems and have attracted a lot of attention during the last ten years. Disparate characteristics (e.g., solubility and thermal stability) of the two components, provide potential barriers towards convenient membrane preparation strategies, but recent research demonstrates relatively simple processes for developing highly efficient nanocomposite PEMs. Objectives for the development of organic-inorganic nanocomposite PEM reported in the literature include several modifications: (1) improving the self-humidification of the membrane; (2) reducing the electro-osmotic drag and fuel crossover; (3) improving the mechanical and thermal strengths without deteriorating proton conductivity; (4) enhancing the proton conductivity by introducing solid inorganic proton conductors; and (5) achieving slow drying PEMs with high water retention capability. Research carried out during the last decade on this topic can be divided into four categories: (i) doping inorganic proton conductors in PEMs; (ii) nanocomposites by sol-gel method; (iii) covalently bonded inorganic segments with organic polymer chains; and (iv) acid-base PEM nanocomposites. The purpose here is to summarize the state-of-the-art in the development of organic-inorganic nanocomposite PEMs for fuel cell applications.     

Structure-property behavior of new hybrid materials incorporating oligomeric poly(tetramethylene oxide) with inorganic silicates by a sol-gel process

Novel transparent hybrid materials incorporating triethoxysilane endcapped poly(tetramethylene oxide) with tetramethoxysilane have been successfully prepared by a sol-gel process. The molecular weight of PTMO has been varied to study its effect on the structure-property behavior of these hybrid materials. Mechanical properties and dynamic mechanical behavior have been measured; small angle X-ray scattering (SAXS) has been utilized to obtain structural information. Based on the experimental results, a simplified morphological model has been suggested to describe these new hybrid systems.