Poly(vinyl alcohol)/Cu(II) complex anion exchange membranes prepared using chemical fiber for direct methanol fuel cells

PVA/Cu (II) complex anion exchange membranes (AEMs) were prepared for direct methanol fuel cells. The complex was for the first time used as membrane material of AEMs. Glutaraldehyde as a crosslinking agent was introduced to control water uptake and swelling of the membranes. The membranes with thickness of 1 μm were fabricated using chemical fibers based on the solution surface tension. The complex membranes show good ionic conductivity and low methanol permeability in the magnitude of 10^?2 S · cm^?1 and 10^?7 cm^?2 · S^?1, respectively. This is a facile, efficient, green, and fast way to prepare new AEMs for direct methanol fuel cells. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1172‐1178, 2013     

A Unique Cross-Linking Strategy to Prepare Poly(Vinyl Alcohol)-Based Anion Conducting Membrane for Fuel Cell Applications

Anion conducting polymer electrolyte membrane (PVA/KOH/CHDMG) was prepared by cross-linking of poly(vinyl alcohol) (PVA) with 1,4-cyclohexanedimethanol diglycidyl ether (CHDMG) in the presence of KOH. FTIR, FESEM, and DSC-TGA techniques were used for the structural, morphological and thermal characterization of the membrane. The effect of cross-linking on the water uptake, thermomechanical characteristics, ionic conductivity, and chemical stability of the membranes was studied with respect to CHDMG contents. The membrane ionic conductivity at room temperature was 2.2–4.7 × 10^?3 S.cm^?1. Further, the membrane exhibited good mechanical attributes and chemical stability. Thus, these low cost membranes exhibited good prospect for application in alkaline fuel cell.     

Hybrid anion exchange membranes with adjustable ion transport channels designed by compounding SEBS and homo-polystyrene

Hybrid anion exchange membranes (AEMs) were prepared via chemically functionalizing and crosslinking poly(styrene-b-[ethylene-co-butylene]-b-styrene) (SEBS) copolymers and low molecular weight homo-polystyrene (hPS). Via sequential chloromethylation, crosslinking, quaternization, and alkalization, a series of hPS/SEBS AEMs were obtained with varying content of hPS. Systematic structural, morphological, mechanical, absorption, and transport measurements reveal that these properties depend on the total PS content in the membranes. Particularly, increasing total PS content causes (a) PS domains in the AEMs transition the cylindrical morphology to lamella-like morphology with comparable correlation length; (b) Young's modulus, water uptake, swelling ratio, ionic exchange capacity and ionic conductivity of the AEMs, and T_g of PS phase increase. In addition, the alkaline stability of the hPS/SEBS AEMs is also improved by addition of hPS. These findings suggest that the proposed method can develop high performance SEBS AEMs that are suitable for fuel cell applications.     

Preparation of KOH‐doped PVA/PSSA Solid Polymer Electrolyte for DMFC: The Influence of TiO2 and PVP on Performance of Membranes

The development of low cost alkaline anion solid exchange membranes requires high ionic conductivity, low liquid uptake, strong mechanical properties and chemical stability. PVA/PSSA blends cross‐linked with glutaraldehyde and decorated with titanium dioxide nanoparticles introduce advantages relative to the pristine membrane of PVA and PVA/PVP membranes due to their improved electrical response and low methanol uptake/ swelling ratio allowing their use in alkaline direct methanol fuel cells.     

New highly proton-conducting membrane poly(vinylpyrrolidone)(PVP) modified poly(vinyl alcohol)/2-acrylamido-2-methyl-1-propanesulfonic acid (PVA-PAMPS) for low temperature direct methanol fuel cells (DMFCs)

A new type of chemically cross-linked polymer blend membranes consisting of poly(vinyl alcohol) (PVA), 2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS) and poly(vinylpyrrolidone) (PVP) have been prepared and evaluated as proton conducting polymer electrolytes. The proton conductivity (σ) of the membranes was investigated as a function of cross-linking time, blending composition, water content and ion exchange capacity (IEC). Membranes were also characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), and the differential scanning calorimetry (DSC). Membrane swelling decreased with cross-linking time, accompanied by an improvement in mechanical properties and a small decrease in proton conductivity due to the reduced water absorption. The membranes attained 0.088 S cm⁻¹ of the proton conductivity and 1.63 mequiv g⁻¹ of IEC at 25±2 °C for a polymer composition PVA-PAMPS-PVP being 1:1:0.5 in mass, and a methanol permeability of 6.1×10⁻⁷ cm² s⁻¹, which showed a comparable proton conductivity to Nafion 117, but only one third of Nafion 117 methanol permeability under the same measuring conditions. The membranes displayed a relatively high oxidative durability without weight loss of the membranes (e.g. 100 h in 3% H₂O₂ solution and 20 h in 10% H₂O₂ solution at 60 °C). PVP, as a modifier, was found to play a crucial role in improving the above membrane performances.     

Alkaline blend polymer electrolytes based on polyvinyl alcohol (PVA)/tetraethyl ammonium chloride (TEAC)

Alkaline blend polymer electrolytes based on PVA/TEAC were obtained by a solution casting technique. Tetraethyl ammonium chloride (TEAC) was added to PVA polymer matrix to form an alkaline blend polymer electrolyte exhibiting excellent ionic transport and mechanical properties. The ionic conductivity of the alkaline PVA/TEAC blend polymer electrolyte was found to be of the order of 10⁻² S cm⁻¹ at ambient temperature when the blend ratio of PVA:TEAC varied from 1:0.2 to 1:2. The characteristic properties of alkaline PVA/TEAC blend polymer electrolytes were examined using DSC, TGA, XRD, SEM, EA, stress–strain tests and AC impedance spectroscopy. The ionic transport properties for the blend polymer electrolytes were measured using Hittorf’s method. It was found that the anionic transport numbers (t ⁻) were between 0.82 and 0.99; the membranes are highly dependent on the types of alkali metal salts and the chemical composition of the polymer blend. The ionic transport and mechanical properties were greatly improved at the expense of the ionic conductivity. In this work we demonstrate that alkaline blend polymer electrolyte can be tailored with a blend technique to achieve specific characteristic properties for battery applications.     

离子交换容量可控自交联型阴离子交换膜的制备

以N-溴代丁二酰亚胺(NBS)为溴化试剂,对十氟二唑与四甲基双酚A(TM-BPA)聚合的聚合物主链进行溴化,随后以N-乙烯基咪唑作为双功能化试剂进行功能化,制备了含有双功能化试剂的氟化聚二唑芳醚阴离子交换膜。其中,功能化试剂(作为离子交换的功能基传导离子及作为膜内分子的交联点)改善膜物理性质。制备的阴离子交换膜在80℃下的离子传导率为9.02×10-2 S·cm-1,甲醇渗透率为1.89×10-7 cm2·s-1(20℃),在碱性燃料电池中具有应用潜力。     

Surface Cross-Linked Poly (Vinyl Alcohol) Hydrogel for Colon Targeted Drug Release

A series of surface cross-linked PVA hydrogels (previously bulk cross-linked with maleic anhydride) were prepared for different cross-linker (glutaraldehyde) concentration. FTIR-ATR study revealed the cross-linking reaction. Surface cross-linking results in contraction of pores and increase in hydrophobicity, pore tortuosity around the surface of the membrane. As a result swelling, drug release decreases with increasing glutaraldehyde concentration. After surface cross-linking swelling of the hydrogels in simulated gastric fluid (SGF) further decreased to attain half of the value as observed for only bulk cross-linked membranes. Surface cross-linking has improved the colon-targeted release characteristics of the drugs from the PVA hydrogels.     

聚苯并咪唑/改性聚环氧氯丙烷阴离子交换膜的性能

通过缩聚法制备了含氟聚苯并咪唑(FPBI),以1–甲基咪唑和聚环氧氯丙烷为原料,制备了咪唑盐修饰的聚环氧氯丙烷(Im PECH),并通过溶液浇铸法制备了FPBI/Im PECH复合膜。系统地研究了复合膜中Im PECH含量的不同对复合膜的力学性能、热稳定性、离子电导率、离子交换容量(IEC)、吸水率、溶胀度等性能的影响。研究结果表明,随着Im PECH含量的增加,复合膜的吸水率、溶胀度、IEC、离子电导率逐渐增加,依然能够保持良好的力学性能和热稳定性。FPBI/Im PECH复合膜在80℃下最高电导率达到55.74 m S/cm,并展示了优异的耐碱性,该复合阴离子交换膜有望在碱性阴离子交换膜燃料电池中得到应用。     

Alkaline solid polymer electrolyte membranes based on structurally modified PVA/PVP with improved alkali stability

Novel alkaline solid polymer electrolyte membranes that can conduct anions (OH⁻) have been prepared from poly(vinyl alcohol)/poly(vinylpyrrolidone) (PVA/PVP) by blending and chemical cross-linking, followed by doping in aqueous KOH solution. The physicochemical properties of these membranes have been studied in detail by FTIR, TG, and SEM analyses. The ionic conductivity was found to be greatly dependent on the concentration of KOH and the interpenetrated PVP in the PVA matrix. A maximum conductivity of up to 0.53 S cm⁻¹ at room temperature was achieved for PVA/PVP in a mass ratio of 1:0.5 after doping in 8 m aqueous KOH solution. The membrane showed perfect alkaline stability without losing its integrity even upon exposure to 10 m KOH solution at up to 120 °C. Scanning electron micrographs revealed a highly ordered microvoid structure uniformly dispersed on the membrane surface with a pore size of ca. 200 nm after heat-curing, which imparted the membrane with good liquid electrolyte (KOH) retention ability. FTIR spectra showed that these high ionic conductivities may be attributed to the presence of excess free KOH in the polymer matrix in addition to KOH bound to the polymer. Almost constant, highly stable, ionic conductivity while maintaining mechanical integrity was retained at room temperature for more than one month.     

燃料电池用纳米改性聚苯并咪唑阴离子交换膜的制备

以环氧氯丙烷和1–甲基咪唑为原料制备新型离子液体(IL),以IL为原料对氧化石墨烯(GO)进行表面修饰制备离子液体功能化氧化石墨烯(IL–GO),以IL–GO为添加剂制备基于含氟聚苯并咪唑(FPBI)复合膜。研究了IL–GO的含量对复合膜的热稳定性、力学强度、离子电导率、离子交换容量(IEC)、吸水率、溶胀度和耐碱性等性能的影响。研究结果表明,复合膜的IEC、离子电导率和拉伸性能都随着IL–GO含量的增加而增大,当IL–GO含量为30%时其拉伸应力和拉伸弹性模量分别达到77.5 MPa和1.95 GPa,在80℃下,其最大离子电导率可达72.3 m S/cm,然而复合膜的热稳定性并没随着IL–GO含量的增加而改变。FPBI/IL–GO复合膜具有良好的稳定性,该系列阴离子交换膜有望在碱性阴离子交换膜燃料电池中得到应用。     

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     

Studies On The Crosslinking Of Poly (Vinyl Alcohol)

This paper is concerned with the cross-linking of poly(vinyl alcohol) (PVA) using maleic acid as the cross-linker. The curative (maleic acid) dose and the curing temperature and time were varied between 2.5 and 60% (w/w), 120 and 160 °C and 30 and 120 min, respectively. From a thorough swelling study in both hot and cold water (percentage swelling, gel content, swelling ratio, etc-) the optimum curative dose and curing conditions have been evaluated. The molecular weight between the cross-links exhibited a sharp fall up to a maleic acid dose of 20% (w/w). A comparative evaluation of maleic acid cross-linked and heat-treated PVA films has been done. Better heat stability for maleic acid cross-linked PVA was observed from thermogravimetric analysis. A shift in glass transition temperature was observed for both heat-treated and maleic acid treated PVA compared with the virgin one. IR spectroscopic study indicated the presence of an ester linkage and an olefinic double bond in maleic acid treated and heat-treated PVA films, respectively. Maleic acid cross-linked PVA is quite stable in different polar and nonpolar solvents. A definite structural pattern has been observed in maleic acid cross-linked PVA films through scanning electron microscopy.     

Novel polymeric systems for lithium ion batteries gel electrolytes: II. Hybrid cross-linked poly(fluorosilicone-ethyleneoxide)

Cross-linked, self-supporting, membranes for lithium ion battery gel electrolytes were obtained by cross-linking a mixture of polyfluorosilicone (PFSi) and polysilicone containing ethylene oxide (EO) units [P(Si-EO)]. The membranes were also reinforced with nanosized silica. The two polymer precursors were synthesized with functional groups capable to form inter-molecular cross-linking, thus obtaining three-dimensional, polymer matrices. The precursors were dissolved in a common solvent and cross-linked to obtain free-standing PFSi/P(Si-EO):SiO₂ composite films. The latter were undergone to swelling processes in (non-aqueous, aprotic, lithium salt containing) electrolytic solutions to obtain gel-type polymer electrolytes. The properties of the swelled PFSi/P(Si-EO):SiO₂ samples were evaluated as a function of the electrolytic solutions and the dipping time. The PFSi/P(Si-EO):SiO₂ membranes exhibited large swelling properties, high ionic conductivity and good electrochemical stability.     

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     

Preparation and characterization of hydroxyl ion-conducting interpenetrating polymer network based on PVA and PEI

Novel interpenetrating polymer networks (IPNs) and semi-interpenetrating polymeric networks (sIPNs) based on polyethyleneimine (PEI) and poly(vinyl alcohol) (PVA) have been prepared via crosslinking reactions with respective crosslinking agent, 1,4-dibromobutane and glutaraldehyde (GA). IPNs, sIPNs and PEI/PVA blend membranes are characterized in detail by Fourier transform Infrared attenuated total reflection (FTIR-ATR) spectroscopy, mechanical properties, water uptake, swelling ratio, field emission scanning electron microscope (FE-SEM), hydroxide ion (OH^?) conductivity. Moderate water uptake and swelling ratio are obtained by the IPN derived from PEI:PVA (1:1), achieving 78.4 and 36.8 %, respectively. And the IPN also shows an acceptable OH^? conductivity of 4.87 mS/cm at 80 °C.     

Designing advanced alkaline polymer electrolytes for fuel cell applications

Although the polymer electrolyte fuel cell (PEFC) is a superior power source for electric vehicles, the high cost of this technology has served as the primary barrier to the large-scale commercialization. Over the last decade, researchers have pursued lower-cost next-generation materials for fuel cells, and alkaline polymer electrolytes (APEs) have emerged as an enabling material for platinum-free fuel cells. To fulfill the requirements of fuel cell applications, the APE must be as conductive and stable as its acidic counterpart, such as Nafion. This benchmark has proved challenging for APEs because the conductivity of OH(-) is intrinsically lower than that of H(+), and the stability of the cationic functional group in APEs, typically quaternary ammonia (-NR(3)(+)), is usually lower than that of the sulfonic functional group (-SO(3)(-)) in acidic polymer electrolytes. To improve the ionic conductivity, APEs are often designed to be of high ion-exchange capacity (IEC). This modification has caused unfavorable changes in the materials: these high IEC APEs absorb excessive amounts of water, leading to significant swelling and a decline in mechanical strength of the membrane. Cross-linking the polymer chains does not completely solve the problem because stable ionomer solutions would not be available for PEFC assembly. In this Account, we report our recent progress in the development of advanced APEs, which are highly resistant to swelling and show conductivities comparable with Nafion at typical temperatures for fuel-cell operation. We have proposed two strategies for improving the performance of APEs: self-cross-linking and self-aggregating designs. The self-cross-linking design builds on conventional cross-linking methods and works for APEs with high IEC. The self-aggregating design improves the effective mobility of OH(-) and boosts the ionic conductivity of APEs with low IEC. For APEs with high IEC, cross-linking is necessary to restrict the swelling of the membrane. In our self-cross-linking design, a short-range cross-linker, tertiary amino groups, is grafted onto the quaternary ammonia polysulfone (QAPS) so that the cross-linking process can only occur during membrane casting. Thus, we obtain both the stable ionomer solution and the cross-linked membrane. The self-cross-linked QAPS (xQAPS) possesses a tight-binding structure and is highly resistant to swelling: even at 80 °C, the membrane swells by less than 3%. For APEs with low IEC, the key is to design efficient OH(-) conducting channels. In our self-aggregating design, long alkyl side-chains are attached to the QAPS. Based on both the transmission electron microscopy (TEM) observations and the molecular dynamics (MD) simulations, these added hydrophobic groups effectively drive the microscopic phase separation of the hydrophilic and hydrophobic domains and produce enlarged and aggregated ionic channels. The ionic conductivity of the self-aggregated QAPS (aQAPS) is three-fold higher than that of the conventional QAPS and is comparable to that of Nafion at elevated temperatures (e.g., greater than 0.1 S/cm at 80 °C).     

Comb-shaped block poly(arylene ether sulfone ketone)s for anion exchange membranes

A well-designed architecture is presented here to construct high-performance anion exchange membranes (AEMs). A series of quaternized fluorene-containing block poly(arylene ether sulfone ketone)s (QFPESK-m-n) is synthesized as the main chains, and grafted with comb-shaped C8 long alkyl chains for the AEMs. By varying the hydrophilic segment’ length, there has been a significant change in the microstructure as well as phase separation morphology of the membranes, as confirmed by atomic force microscopy. Hence the as-prepared AEMs with moderate ion exchange capacities (IECs) show enhanced hydroxide conductivities in the range of 28.8―94.7 mS⋅cm⁻¹ from 30 to 80°C. Furthermore, based on the block backbones and hydrophobic comb-shaped alkyl chains, the AEMs show low-level swelling ratios of 4.3% to 9.2% at 30°C and from 6.2% to 13.2% at 80°C, and superior ratios of conductivity to swelling. In addition, the QFPESK-m-n AEMs also depict acceptable mechanical properties, good thermal stability and an optimizable alkaline stability.     

燃料电池用阴离子交换膜分子结构研究进展

阴离子交换膜（AEMs）作为燃料电池的核心部件,其发展得到了普遍关注。然而,AEMs中聚合物骨架和阳离子基团无序的直接相连的结构导致了膜在应用过程中存在离子电导率低、碱稳定性差和机械性能不足等问题,因此对连接二者的分子结构进行设计,开发综合性能优异的AEMs很有必要。本文介绍了AEMs选择性透过的基本机理,并从不同的分子结构出发,总结了近年来应用较为广泛的嵌段结构、接枝结构、交联结构、局部高密度结构以及由局部高密度结构与其他三种结构组成的复合结构AEMs的研究进展;从离子电导率、碱稳定性、机械性能以及吸水率等方面对AEMs的性能提升进行了归纳,重点关注AEMs离子电导率和吸水率的权衡问题,并从分子结构及其组合使用的角度对燃料电池用AEMs的未来发展方向进行了展望。     

Preparation of water‐swollen hydrogel membranes for gas separation

Water‐swollen hydrogel (WSH) membranes for gas separation were prepared by the dip‐coating of asymmetric porous polyetherimide (PEI) membrane supports with poly(vinyl alcohol) (PVA)–glutaraldehyde (GA), followed by the crosslinking of the active layer by a solution method. Crosslinked PVA/GA film of different blend compositions (PVA/GA = 1/0.04, 0.06, 0.08, 0.10, 0.12 mol %) were characterized by differential scanning calorimetry (DSC) and their water‐swelling ratio. The swelling behavior of PVA/GA films of different blend compositions was dependent on the crosslinking density and chemical functional groups created by the reaction between PVA and GA, such as the acetal group, ether linkage, and unreacted pendent aldehydes in PVA. The permeation performances of the membranes swollen by the water vapor contained in a feed gas were investigated. The behavior of gas permeation through a WSH membrane was parallel to the swelling behavior of the PVA/GA film in water. The permeation rate of carbon dioxide through the WSH membranes was 10⁵ (cm³ cm^?2 s^?1 cmHg) and a CO₂/N₂ separation factor was about 80 at room temperature. The effect of the additive (potassium bicarbonate, KHCO₃) and catalyst (sodium arsenite, NaASO₂) on the permeation of gases through these WSH membranes was also studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1785–1791, 2001