Mechanical and hydration properties of Nafion®/ceramic nanocomposite membranes produced by mechanical attrition

A solid state method of Nafion®/ceramic nanocomposite membrane preparation is described. A nanocomposite powder from Nafion pellets and a zirconium phosphate ceramic is formed by mechanical milling. The nanoparticles are then consolidated into membrane form by mechanical pressing. Cross‐sectional analysis by scanning electron microscopy indicates that the ceramic particles exist in agglomerates that are evenly dispersed across the membrane. Dynamic mechanical analysis and tensile testing found the membranes to be mechanically equivalent, and in some cases superior, to a commercial extruded membrane. Increasing ceramic content is accompanied by an increase in modulus and shift in the alpha peak to higher temperature. Maximum water uptake of the membranes, as measured by thermal gravimetric analysis, is double that of values reported for the commercial membrane, and complete dehydration is postponed to higher temperature. The proton conductivity of fully hydrated membranes, measured by the 4‐probe method at 60°C in water, is comparable with that of the extruded membrane. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

致密超细球形氧化铝制备性能良好的陶瓷超滤膜

热等离子体制备的超细球形氧化铝具有表面致密光滑、分散性好等特点,本工作以超细球形氧化铝为原料,通过浸渍提拉烧结法,制备了孔径分布窄、渗透通量高的陶瓷超滤膜,研究了烧结温度对陶瓷膜微孔结构的演化、孔径分布和渗透通量的影响。随后对1250℃下烧结的陶瓷膜进行了纳米硅水分散液过滤处理,采用不同堵塞模型分析了陶瓷膜过滤纳米硅水分散液的膜污染过程。结果表明,通过调节烧结温度调控陶瓷膜的微孔结构,当烧结温度为1250℃时,陶瓷膜的孔径分布较窄,孔径大小为25?65 nm,渗透通量为986.4 L/(m2?h)。超细球形氧化铝粒径分布较窄及表面致密光滑有助于1250℃下烧结形成均匀的烧结颈,提供了陶瓷膜较窄的孔径分布。对1250℃下烧结的陶瓷膜进行了纳米硅水分散液过滤处理后其浊度下降为0.231 NTU,浊度去除率达99.96%。采用不同堵塞模型分析了陶瓷膜过滤纳米硅水分散液的膜污染过程,结果表明,纳米硅水分散液的堵塞模型是滤饼过滤,属于可逆污染。     

Partially Sulfonated Poly(1,4‐phenylene ether‐ether‐sulfone) and Poly(vinylidene fluoride) Blend Membranes for Fuel Cells

Blend membranes based on high conductive sulfonated poly(1,4‐phenylene ether‐ether‐sulfone) (SPEES) and poly(vinylidene fluoride) (PVDF) having excellent chemical stability were prepared and characterized for direct methanol fuel cells. The effects of PVDF content on the proton conductivity, water uptake, and chemical stability of SPEES/PVDF blend membranes were investigated. The morphology, miscibility, thermal, and mechanical properties of blend membranes were also studied by means of scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) measurements. The blend membrane containing 90 wt.% SPEES (degree of sulfonation – DS = 72%) and 10 wt.% PVDF (M_w = 180,000) exhibits optimum properties among various SPEES72/PVDF membranes. Addition of PVDF enhanced resistance of the SPEES membrane against peroxide radicals and methanol significantly without deterioration of its proton conductivity. It's proton conductivity at 80 °C and 100% relative humidity is higher than Nafion 115 while it's methanol permeability is only half of that of Nafion 115 at 80 °C. The direct methanol fuel cell performance of the SPEES membranes was better than that of Nafion 115 membrane at 80 °C.     

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. II. Characterization of sulfonated graft copolymer membranes

PFA‐g‐polystyrene sulfonic acid membranes were prepared by simultaneous radiation‐induced graft copolymerization of styrene onto poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA) film followed by sulfonation. The membrane physico‐chemical properties such as swelling behavior, ion exchange capacity, hydration number, and ionic conductivity were studied as a function of the degree of grafting. Thermal as well as chemical stability of the membranes was also investigated. The membrane properties were found to be mainly dependent upon the degree of grafting. The water uptake, ion exchange capacity, hydration number, and ionic conductivity of the membranes were increased, whereas the chemical stability decreased as the degree of grafting increased. The membranes showed reasonable physico‐chemical properties compared to Nafion 117 membranes. However, their chemical stability has to be further improved to make them acceptable for practical use in electrochemical applications. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1–11, 2000     

Recast Nafion‐117 thin film from water solution

Perfluorosulfonated ionomer (PFSI) dispersions in various solvents, usually mixtures of organic compounds and water, were used to prepare the membrane‐electrode system in polymer electrolyte membrane fuel cells (PEMFC), the aim being to increase performance by improving the triple contact of graphite (electron conducting material), Pt (hydrogen dissociation catalyst) and ionomeric membrane (proton conducting). When using PFSI dispersions in water‐organic solvent mixture, care must be taken not to poison the Pt catalyst through organic decomposition products, a consequence of the thermal treatment of the electrode‐polymer system bonded with PFSI dispersion. In the present study some procedures for preparing Nafion water dispersion, starting from a Nafion‐117 membrane, are described. The morphological characteristics of the prepared dispersions were compared with Nafion commercial dispersion (NCD). Moreover, membranes with a thickness of 5–20 μm were prepared and characterised, using both the obtained and the NCD dispersions. The obtained data showed that Nafion water dispersion, which can be used to prepare the membrane/electrode system, results in thin membranes that absorb more water than NCD membranes, and have equal and/or higher proton conduction than the NCD.     

Nafion®—titania nanocomposite proton exchange membranes

Proton exchange membranes consisting of Nafion^® and crystallized titania nanoparticles have been developed to improve water‐retention and proton conductivity at elevated temperature and low relative humidity. The anatase‐type titania nanoparticles were synthesized in situ in Nafion solution through sol–gel process and the size of the formed titiania nanoparticles is in the range of 3–6 nm. The formed nanoparticles are well‐dispersed in Nafion solution at the titania concentration of 5 wt %. The glass transition temperature of the formed Nafion‐titania composite membrane is about 20^oC higher than that of plain Nafion membrane. At elevated temperature (above 100°C), the Nafion‐titania nanocomposite membrane shows higher water uptake ability and improved proton conductivity compared to pure Nafion membrane. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Water in different poly(styrene sulfonic acid)‐grafted fluoropolymers

We investigated the water present in a series of radiation‐grafted fluoropolymers with similar poly(styrene sulfonic acid) (PSSA) contents with the aim of determining the influence of the initial fluoropolymer. Radiation‐grafted membranes were compared with Nafion 117 and 105. Sorption curves and differential scanning calorimetry thermograms showed that all the membranes contained the same number of water molecules tightly bound to the sulfonic acid groups; this water did not freeze. In radiation‐grafted membranes, the content of freezing water absorbed from the liquid‐phase water varied according to the swelling abilities of the membrane, which were dependent on the initial fluoropolymer. Larger pores accompanied high water uptakes and high conductivity. The amount of water absorbed from the vapor phase was similar for all radiation‐grafted membranes with similar PSSA contents, irrespective of matrix material. Nafion membranes had higher conductivities at intermediate hydration levels, and the relaxation times measured by NMR were longer than for the radiation‐grafted materials. This suggests that the channels for water and proton conduction are different in the two types of materials. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 33–42, 2002     

Electrospinning preparation of a graphene oxide nanohybrid proton‐exchange membrane for fuel cells

Proton‐exchange membrane (PEM) is a core component of fuel cells that provides a channel for proton migration and transport. Prevailing PEMs fabricated using well‐established casting techniques have several limitations such as low proton conductivity, high fuel permeability, and poor stability. To overcome these shortcomings, this article introduces a graphene oxide (GO)‐based nanohybrid Nafion nanofiber membrane prepared using a facile electrospinning technique. On the one hand, electrospinning nanofibers provide efficient transport paths for protons, which tremendously enhance the proton conductivity. On the other hand, GO doping in PEM improves the self‐humidification, stabilities (mechanical, thermal, and chemical), and proton conductivity and reduces the fuel permeability. In this research, nanofiber membranes were obtained from Nafion solutions containing 0, 0.1, and 0.2 wt % GO via electrospinning. The morphology, structure, mechanical properties, proton conductivity, water uptake, and swelling properties of the membranes were studied. The results demonstrated that the comprehensive performance of PEM was significantly improved. The new findings may promote the wide application of PEM fuel cells. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46443.     

Carbon Nanotubes Based Nafion Composite Membranes for Fuel Cell Applications

Carbon nanotubes (CNTs) containing Nafion composite membranes were prepared via melt‐blending at 250 °C. Using three different types of CNTs such as pure CNTs (pCNTs), oxidised CNTs (oCNTs) and amine functionalised CNTs (fCNTs); the effect of CNTs surface oxidation as well as functionalisation in composite membranes was investigated by focussing on three aspects: thermo‐mechanical stability, thermal degradation and proton conductivity. The oCNTs‐containing Nafion composite membrane exhibited concurrent improvement in most of the properties as compared to that of pure Nafion or other CNTs‐containing Nafion composite membranes.     

PWA/silica doped sulfonated poly(ether sulfone) composite membranes for direct methanol fuel cells

A novel sulfonated poly(ether sulfone) (SPES)/phosphotungstic acid (PWA)/silica composite membranes for direct methanol fuel cells (DMFCs) application were prepared. The structure and performance of the obtained membranes were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), water uptake, proton conductivity, and methanol permeability. Compared to a pure SPES membrane, PWA and SiO₂ doped membranes had a higher thermal stability and glass transition temperature (T_g) as revealed by TGA‐FTIR and DSC. The morphology of the composite membranes indicated that SiO₂ and PWA were uniformly distributed throughout the SPES matrix. Proper PWA and silica loadings in the composite membranes showed high proton conductivity and sufficient methanol permeability. The selectivity (the ratio of proton conductivity to methanol permeability) of the SPES‐P‐S 15% composite membrane was almost five times than that of Nafion 112 membrane. This excellent selectivity of SPES/PWA/silica composite membranes indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and testing of Nafion/titanium dioxide nanocomposite membrane electrode assembly by ultrasonic coating technique

Membrane electrode assemblies with Nafion/nanosize titanium dioxide (TiO₂) composite membranes were manufactured with a novel ultrasonic‐spray technique (UST) and tested in proton exchange membrane fuel cell (PEMFC). The structures of the membranes were investigated by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and thermogravimetric analysis. The composite membranes gained good thermal resistance with insertion of TiO₂. The SEM and XRD techniques have proved the uniform and homogeneous distribution of TiO₂ and the consequent enhancement of crystalline character of these membranes. The existence of nanometer size TiO₂ has improved the thermal resistance, water uptake, and proton conductivity of composite membranes. Gas diffusion electrodes were fabricated by UST. Catalyst loading was 0.4 (mg Pt) cm^?2 for both anode and cathode sides. The membranes were tested in a single cell with a 5 cm² active area operating at the temperature range of 70°C to 110°C and in humidified under 50% relative humidity (RH) conditions. Single PEMFC tests performed at different operating temperatures indicated that Nafion/TiO₂ composite membrane is more stable and also performed better than Nafion membranes. The results show that Nafion/TiO₂ is a promising membrane material for possible use in PEMFC at higher temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40541.     

Anisotropy management on microstructure and mechanical property in 3D printing of silica-based ceramic cores

Ceramic core is an essential component in the precise casting of hollow turbine blades, and the investigation on 3D printing of silica-based ceramic cores is crucial to the development of aviation industry; however, they are suffered from difficulty in high-temperature strength and structural anisotropy. In present work, silica-based ceramic cores were prepared via DLP stereolithography 3D printing, and the anisotropy management on microstructures and properties were explored based on the particle size of fused silica powders. In 3D printed ceramic cores with coarse powders, significant anisotropy was displayed exhibiting multilayer structure with large gaps in horizontal printing and uniform porous microstructure in the vertical direction, which was further explained by the particle deposition in printing. With finer silica powders, the uniformity in the microstructures was highly improved, attributed to the enhanced particle dispersion in ceramic slurries and promoted interlayer particle rearrangement during sintering. To evaluate the anisotropy in mechanical property, the ratio of vertical strength to horizontal strength (σ_V/σ_H) was proposed, which rose from 0.48 to 0.86 as the particle size decreased from 35 µm to 5 µm, suggesting enhanced mechanical uniformity. While the average particle size of silica powders was 5 µm, the flexure strengths of ceramic cores in different directions were up to 18.5 MPa and 16.3 MPa at 1540 °C with σ_V/σ_H ratio of 0.88, which well satisfied the demands for the casting of turbine blades. This work inspires new guidance on the anisotropy management in ceramic cores prepared by 3D printing, and provides new technology for fabrication of silica-based ceramic cores with superior high temperature mechanical properties.     

Anisotropic membranes from electrospun mats of sulfonated/nonsulfonated poly (ether ketone)s containing ion-rich paths as proton exchange membranes

Anisotropic proton exchange membranes composed of five layers with different contents of ionic groups across the membrane were prepared by simultaneous electrospinning of sulfonated and nonsulfonated poly(ether ketone) (PEK)s. To prepare nonporous and defect- free membranes from electrospun mats, nonsulfonated fibers as hydrophobic part of the membrane were melted by hot-pressing so that covered sulfonated fibers (hydrophilic part). Prepared membranes showed better thermal and dimensional stability compared to Nafion 115. Proton conductivity of membranes was comparable with Nafion especially at higher temperatures. Water uptake of prepared membranes and mechanical strength of them were in an acceptable range. The results showed that the difference between sulfonated PEK fibers in surface and center of the membranes affect proton conductivity and mechanical properties of the membranes.     

New hyperbranched polymers for membranes of high‐temperature polymer electrolyte membrane fuel cells: Determination of the crystal structure and free‐volume size

The key requirements for a membrane in polymer electrolyte membrane fuel cells are a high ion conductivity, mechanical strength, and barrier properties. We reported earlier on two new promising hyperbranched polymers: poly(benzimidazole‐co‐aniline) (PBIANI), with a uniform rectangular net structure, and poly(benzimidazole‐co‐benzene) (PBIB), with a honeycomb structure. Both polymers exhibit a high ion conductivity and mechanical strength and have proven themselves suitable for the membranes of high‐temperature polymer electrolyte membrane fuel cells. In this article, we deal with the determination of crystal structure and free‐volume cell/microvoid size of these two polymers. Both PBIANI and PBIB had the same d‐spacing (3.5 Å). However, the percentage of crystallinity was higher and the crystallite size was larger for PBIB. The kinetic diameters of hydrogen (2.89 Å), oxygen (3.46 Å), water (2.60 Å), and methanol (～ 4.00 Å) were much larger than the free‐volume cell/microvoid diameters of PBIANI (1.81 Å) and PBIB (1.96 Å) but much smaller than those of Nafion 115 (6.54 Å) and polybenzimidazole (PBI) (～ 6.00 Å). The very small free‐volume sizes of PBIANI and PBIB ensured good barrier properties against hydrogen, oxygen, water, and methanol, unlike those of Nafion‐ and PBI‐type membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characterization of random and multiblock copolymers of highly sulfonated poly(arylene ether sulfone) for a proton‐exchange membrane

Random and multiblock copolymers of sulfonated poly(arylene ether sulfone) (SPAES) were synthesized and characterized to compare the differences in the properties of proton‐exchange membranes made with random and multiblock SPAES copolymers. Atomic force microscopy observations and small‐angle X‐ray scattering measurements suggested the presence of nanoscale, clusterlike structures in the multiblock SPAES copolymers but not in the random SPAES copolymers. Proton‐exchange membranes were prepared from random and multiblock copolymers with various ion‐exchange capacities (IECs). The water uptake, proton conductivity, and methanol permeability of the SPAES membranes depended on the IECs of the random and multiblock SPAES copolymers. At the same IEC, the multiblock SPAES copolymers exhibited higher performances with respect to proton conductivity and proton/methanol permeation selectivity than the random SPAES copolymers. The higher performances of the multiblock SPAES copolymers were thought to be due to their clusterlike structure, which was similar to the ionic cluster of a Nafion membrane. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of electrolytes of Li salts,EMIMBF4, and mixed phases on electrochemical and physical properties of Nafion membrane

Electrolyte‐soaked Nafion is commonly used as an ionic polymer in soft actuators. Here, a multitechnique investigation was applied to correlate the electrochemical behavior of Nafion membranes with their microstructures and nanostructures as a function of electrolyte type. The influence of electrolytes of Li salts with different counteranions on the Nafion membranes was investigated in terms of hydration level, structure (using X‐ray diffraction and small angle X‐ray scattering), stress–strain characteristics, and electrochemical behavior (by cyclic voltammetery and electrochemical impedance spectroscopy). The effects of using ionic liquid (IL), as the electrolyte, addition of different supporting solvent and the addition of Li⁺ ions to water‐free IL‐soaked membranes on the structural and electrochemical properties of Nafion were examined. The nano‐ and microstructure of the Nafion changed considerably as a function of the identity of the electrolyte solution. The electrochemical behavior of the IL‐soaked samples was compared with that of the water‐soaked Li⁺‐exchanged Nafion. It was seen that the ionic conductivity of the Nafion membranes was reduced significantly when water was replaced by pure IL. Using the supporting solvents increased the conductivity of IL‐soaked Nafion membranes dramatically. The presence of a small amount of Li⁺ ions together with the IL ions caused a significant decrease in charge transfer resistance and increases in double layer capacitance and in ionic conductivity over that of the water‐free sample and also over water‐soaked Li⁺‐exchanged Nafion. These findings can be useful to improve the knowledge on Nafion's microstructure and also to improve the electromechanical behavior of Nafion‐based ionic polymer–metal composites actuators. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45239.     

Novel grafted nafion membranes for proton‐exchange membrane fuel cell applications

Novel poly(glycidyl methacrylate)‐grafted Nafion–phosphoric acid membranes for direct‐oxidation methanol fuel cells were prepared with a potassium persulfate chemical initiation system for the first time. The introduced epoxy groups were converted to amine groups through a reaction with ethylenediamine, which consequently doped with phosphoric acid ( PO₃H) groups. The latter significantly contributed to enhancing the ion‐exchange capacity, mechanical properties, and thermal stability. Factors affecting the modification steps were studied. Changes in the chemical and morphological structure were verified through Fourier transform infrared spectroscopy, TGA, and scanning electron microscopy characterization. Various grafting percentages (GP%'s) up to 32.31% were obtained. As a result, the thickness of the grafted membranes increased. Furthermore, the methanol permeability of the modified membranes was reduced with increasing grafted polymer content compared with that of the Nafion membrane. An 83.64% reduction in the methanol permeability was obtained with a polymer grafted content of 18.27%. Finally, the efficiency factor for all of the modified Nafion membranes was enhanced compared with that of Nafion. A fourfold improvement was obtained with membranes with a GP% of 18.27% as a maximum value. Such promising results nominate the used technique as a one for the improvement of Nafion membrane efficiency. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of PES on the morphology and properties of proton conducting blends with sulfonated poly(ether ether ketone)

Development of alternate materials to Nafion, based on ionically conducting polymers and their blends is important for the wider applications of proton exchange membrane fuel cells. In this work, blends of sulfonated poly(ether ether ketone) (SPEEK) with poly(ether sulfone) (PES) are investigated. SPEEK with various ion exchange capacity (IEC) was prepared and blended with PES, which is nonionic and hydrophobic in nature. A comparative study of the water uptake, proton conductivity, and thermo‐mechanical characteristics of SPEEK and the blend membranes as a function of the IEC is presented. Addition of PES decreases the water uptake and conductivity of SPEEK. Chemical and thermal stability and mechanical properties of the membrane improve with the addition of PES. The effect of water content on the thermo‐mechanical properties of membranes was also studied. The morphology of blend membranes was studied using SEM to understand the microstructure and miscibility of the components. On the basis of the results, a plausible microstructure of the blends is presented, and is shown to be useful in understanding the variation of different properties with blending. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Separation of bovine serum albumin (BSA) using γ‐Al2O3–clay composite ultrafiltration membrane

BACKGROUND: Ceramic membranes have received more attention than polymeric membranes for the separation and purification of bio‐products owing to their superior chemical, mechanical and thermal properties. Commercially available ceramic membranes are too expensive. This could be overcome by fabricating membranes using low‐cost raw materials. The aim of this work is to fabricate a low‐cost γ‐Al₂O₃–clay composite membrane and evaluate its potential for the separation of bovine serum albumin (BSA) as a function of pH, feed concentration and applied pressure. To achieve this, the membrane support is prepared using low‐cost clay mixtures instead of very expensive alumina, zirconia and titania materials. The cost of the membrane can be further reduced by preparing a γ‐alumina surface layer on the clay support using boehmite sol synthesized from inexpensive aluminium chloride instead of expensive aluminium alkoxide using a dip‐coating technique. RESULTS: The pore size distribution of the γ‐Al₂O₃‐clay composite membrane varied from 5.4–13.6 nm. The membrane was prepared using stable boehmite sol of narrow particle size distribution and mean particle size 30.9 nm. Scanning electron microscopy confirmed that the surface of the γ‐Al₂O₃–clay composite membrane is defect‐free. The pure water permeability of the support and the composite membrane were found to be 4.838 × 10^?6 and 2.357 × 10^?7 m³ m^?2 s^?1 kPa^?1, respectively. The maximum rejection of BSA protein was found to be 95%. It was observed that the separation performance of the membrane in terms of flux and rejection strongly depends on the electrostatic interaction between the protein and charged membrane. CONCLUSION: The successively prepared γ‐Al₂O₃‐clay composite membrane proved to possess good potential for the separation of BSA with high yield and could be employed as a low cost alternate to expensive ceramic membranes. Copyright © 2009 Society of Chemical Industry     

Preparation of novel heterogeneous cation‐permeable membranes from blends of sulfonated poly(phenylene sulfide) and poly(ether sulfone)

Novel heterogeneous cation‐exchange membranes using poly (ether sulfone)(PES) as binder and sulfonated poly(phenylene sulfide) (SPPS) powder as polyelectrolyte were prepared by the solution casting‐immersion method. Compared with a conventional route for heterogeneous membrane, the steps of milling resin into fine powders and the pressing at high temperature are avoided, and thus permits a simple technique for the preparation of such membrane. The effect of the particle size and loading of SPPS resin on the properties of the membranes such as ion‐exchange capacity, water content, electrical resistance, transport number, diffusion coefficient of electrolytes, etc., have been studied. It is shown that the membrane fundamental properties are largely dependent on both the resin loading and the particle size of SPPS resin. By adjusting these two important parameters, one can obtain heterogeneous membrane with both good conductivity, selectivity, and proper water content for different industrial purposes such as electrodialysis, diffusional dialysis, etc. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 167–174, 2004