Synthesis and characterization of sulfonated polyimides bearing sulfonated aromatic pendant group for DMFC applications

A novel side-chain-type sulfonated aromatic diamine, 5-[1,1-bis(4-aminophenyl)-2,2,2- trifluoroethyl]-2-(4-sulfophenoxy)benzenesulfonic acid (BABSA) was synthesized and characterized. Two series of sulfonated polymides (SPI-N and SPI-B) were prepared from 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) or 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BNTDA), sulfonated diamine BABSA and various non-sulfonated aromatic diamines. The resulting sulfonated polyimide (SPI) membranes exhibited good dimensional stability with isotropic swelling of 7-22% and high thermal stability with desulfonation temperature of 283-330 °C. These membranes also displayed excellent oxidation stability and good water stability. The SPI membranes exhibited better permselectivity than Nafion 115 membrane due to their much lower methanol permeability. The ratios of proton conductivity to methanol permeability (Ф) for the SPI membranes were almost two to three times of that for Nafion 115. The SPI-N membranes exhibited excellent conducting performance with the proton conductivity higher than Nafion 115 as the temperature over 40 °C, which attributed to their good hydrophobic/hydrophilic microphase separation structure.     

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.     

Morphology of sulfonated polyarylenethioethersulfone random copolymer series as proton exchange fuel cells membranes by small angle neutron scattering

Sulfonated polyarylenethioethersulfone (SPTES) copolymers with high proton conductivity (100-215 mS/cm at 65 °C, 85% relative humidity) are promising potential proton exchange membrane (PEM) for fuel cells. Small angle neutron scattering (SANS) of the hydrated SPTES copolymer membranes at 25 °C exhibit a nanostructure which can be approximated by correlated polydisperse spherical aggregates containing water molecules with liquid-like ordering (Percus Yevick approximation) and large scale water pockets. The ionic domain radius and the volume packing density of the aggregates present in the hydrated SPTES copolymer membranes at 25 °C increased with increasing degree of sulfonation. SPTES-80 with highest degree of sulfonation (71.6%) showed a Guinier plateau at the very low q range (q < 1 × 10⁻⁴ 1/Å) indicating presence of isolated large scale morphology (R_g = 1.3 ± 0.18 micron). The radius of spherical ionic aggregates present in the hydrated SPTES-50 and SPTES-60 copolymer membranes increased with increasing temperature to 55 °C, but the large scale morphology changed to a fractal network. Further increase of the sulfonation degree to 63.3% and 71.6% (SPTES-70 and SPTES-80) resulted in a substantial morphology change of the spherical aggregates to an irregular bicontinuous hydrophobic/hydrophilic morphology for the hydrated SPTES-70 and SPTES-80 copolymer membranes at 55 °C. Presence of ionic maxima followed by a power law decay of −4 for SPTES-70 and SPTES-80 copolymer membranes was attributed to the bicontinuous phase morphology at high degree of sulfonation and elevated temperature (55 °C). The disruption of the larger scale fractal morphology was characterized by significant decrease in the intermediate scattering intensity. Hydrophobic and hydrophilic domains were separated distinctly by sulfonic groups at the interface showing as power law decay of −4 for all hydrated SPTES copolymers.     

Characterization and fuel cell performance analysis of polyvinylalcohol–mordenite mixed-matrix membranes for direct methanol fuel cell use

Polyvinylalcohol–mordenite (PVA–MOR) mixed matrix membranes were synthesized for direct methanol fuel cell (DMFC) use. For the structural and the morphological characterization, Scanning Electron Microscopy and Thermal Gravimetric Analysis methods were used. Zeolite distribution within the polymer matrix was found to be homogeneous. An impedance spectroscope was used to measure the proton conductivity. In order to obtain information about methanol permeation characteristics, swelling tests and a series of pervaporation experiments were carried out. 60–40 wt% PVA–MOR membranes were found to give the optimum transport properties. Proton conductivity of these membranes was found to be slightly lower than that of Nafion117™ whereas their methanol permeability was at least two orders of magnitude lower than Nafion117™. DMFC performance of the PVA–MOR membranes was also measured. The inferior DMFC performance of PVA–MOR membranes was linked to drying in the fuel cell medium and the consequent proton conductivity loss. Their performance was improved by adding a dilute solution of sulfuric acid into the feed methanol solution. Future studies on the improvement of the proton conductivity of PVA–MOR membranes, especially via sulfonation of the polymer matrix, can overcome the low-performance problem associated with insufficient proton conductivity.     

Nafion/Analcime and Nafion/Faujasite composite membranes for polymer electrolyte membrane fuel cells

The Nafion/zeolite composite membranes were synthesized for polymer electrolyte fuel cells (PEMFCs) by adding zeolite in the matrix of Nafion polymer. Two kinds of zeolites, Analcime and Faujasite, having different Si/Al ratio were used. The physico-chemical properties of the composite membranes such as water uptake, ion-exchange capacity, hydrogen permeability, and proton conductivity were determined. The fabricated composite membranes showed the significant improvement of all tested properties compared to that of pure Nafion membrane. The maximum proton conductivity of 0.4373 S cm⁻¹ was obtained from Nafion/Analcime (15%) at 80 °C which was 6.8 times of pure Nafion (0.0642 S cm⁻¹ at 80 °C). Conclusively, Analcime exhibited higher improvement than Faujasite.     

Mass transport of direct methanol fuel cell species in sulfonated poly(ether ether ketone) membranes

Homogeneous membranes based on sulfonated poly(ether ether ketone) (sPEEK) with different sulfonation degrees (SD) were prepared and characterized. In order to perform a critical analysis of the SD effect on the polymer barrier and mass transport properties towards direct methanol fuel cell species, proton conductivity, water/methanol pervaporation and nitrogen/oxygen/carbon dioxide pressure rise method experiments are proposed. This procedure allows the evaluation of the individual permeability coefficients in hydrated sPEEK membranes with different sulfonation degrees. Nafion^® 112 was used as reference material. DMFC tests were also performed at 50 °C. It was observed that the proton conductivity and the permeability towards water, methanol, oxygen and carbon dioxide increase with the sPEEK sulfonation degree. In contrast, the SD seems to not affect the nitrogen permeability coefficient. In terms of selectivity, it was observed that the carbon dioxide/oxygen selectivity increases with the sPEEK SD. In contrast, the nitrogen/oxygen selectivity decreases. In terms of barrier properties for preventing the DMFC reactants loss, the polymer electrolyte membrane based on the sulfonated poly(ether ether ketone) with SD lower or equal to 71%, although having slightly lower proton conductivity, presented much better characteristics for fuel cell applications compared with the well known Nafion^® 112. In terms of the DMFC tests of the studied membranes at low temperature, the sPEEK membrane with SD = 71% showed to have similar performance, or even better, as that of Nafion^® 112. However, the highest DMFC overall efficiency was achieved using sPEEK membrane with SD = 52%.     

Enhanced thermo-oxidative stability of sulfophenylated poly(ether sulfone)s

Monophenylated poly(ether sulfone)s (Ph-PES) and diphenylated poly(ether sulfone)s (DiPh-PES), were synthesized as starting materials for the preparation of sulfonated polymers with well-defined chemical structure. Mild post-polymerization sulfonation conditions led to sulfonated Ph-PES (Ph-SPES) bearing acid groups on both the pendant phenyl group and the backbone, and sulfonated DiPh-PES (DiPh-SPES) bearing acid groups only on the two pendant phenyl groups. Both series of polymers had excellent mechanical properties, high glass transition temperatures, good thermal and oxidative stability, as well as good dimensional stability. It is interesting to note that exclusively pendant-phenyl-sulfonated (bis-sulfophenylated) DiPh-SPES copolymers possessed obviously better thermal and oxidative stability compared with the corresponding pendant-phenyl-sulfonated/main-chain-sulfonated Ph-SPES copolymers. The methanol permeability values of the membranes were in the range of 7.0 × 10⁻⁷-9.4 × 10⁻⁸ cm²/s at 30 °C, which is several times lower than that of Nafion 117. DiPh-SPES-50 and Ph-SPES-40 also exhibited high proton conductivity (approximately 0.13 S/cm at 100 °C).     

Synthesis of highly sulfonated poly(arylene ether sulfone)s with sulfonated triptycene pendants for proton exchange membranes

A series of poly(aryl ether sulfone)s containing triptycene groups PES-x-TPD (x refers to molar percentage of TPD) were firstly synthesized through nucleophilic aromatic substitution polycondensation by using 2,5-triptycenediol (TPD), bis(4-hydroxyphenyl) sulfone (BHPS) and 4,4′-difluorodiphenyl sulfone (DFDPS). The sulfonation of copolymers was conducted at room temperature by using a mild sulfonating reagent (98% H₂SO₄), and the degree of sulfonation was readily and accurately controlled by adjusting the ratio of TPD and BHPS. The structures of PES-x-TPD and SPES-x-TPD were characterized by IR, ¹H NMR and ¹³C NMR spectra. These ionomers generally showed high thermal stability and mechanical strength at low humidity regardless of high IEC value. Meanwhile, it is noteworthy that these novel SPES-x-TPD membranes with high IEC value achieved high proton conductivity in a wide range of humidity at 80 °C. For example, SPES-60-TPD with the highest IEC value 2.86 mmol/g displays the conductivity of 2.5 × 10⁻¹ S/cm which is much higher than that of the perfluorinated Nafion membrane (1.1 × 10⁻¹ S/cm) at 80 °C and 94% RH. At 80 °C and 34% RH, SPES-60-TPD displays the conductivity of 4.5 × 10⁻³ S/cm which is also higher than that of the Nafion membrane (3.0 × 10⁻³ S/cm). Microscopic analyses revealed that well-de?ned phase separated structures and uniform ionic pathway was formed for SPES-45-TPD membrane with the IEC of 2.29 mmol/g. Moreover, a H₂/O₂ fuel cell using the SPES-55-TPD (IEC = 2.68 mmol/g) also showed better performance than that of Nafion 117 at 40 °C and 30% RH.     

Nafion-clay nanocomposite membranes: Morphology and properties

A series of Nafion-clay nanocomposite membranes were synthesized and characterized. To minimize any adverse effects on ionic conductivity the clay nanoparticles were H⁺ exchanged prior to mixing with Nafion. Well-dispersed, mechanically robust, free-standing nanocomposite membranes were prepared by casting from a water suspension at 180 °C under pressure. SAXS profiles reveal a preferential orientation of Nafion aggregates parallel to the membrane surface, or normal plane. This preferred orientation is induced by the platy nature of the clay nanoparticles, which tend to align parallel to the surface of the membrane. The nanocomposite membranes show dramatically reduced methanol permeability, while maintaining high levels of proton conductivity. The hybrid films are much stiffer and can withstand much higher temperatures compared to pure Nafion. The superior thermomechanical, electrochemical and barrier properties of the nanocomposite membranes are of significant interest for direct methanol fuel cell applications.     

Sulfonated poly(ether sulfone)/phosphotungstic acid/attapulgite composite membranes for direct methanol fuel cells

Novel composite sulfonated poly(ether sulfone)(SPES)/phosphotungstic acid (PWA)/attapulgite (AT) membranes were investigated for direct methanol fuel cells (DMFCs). Physical–chemical properties of the composite membranes were characterized by FTIR, DSC, TGA, SEM‐EDX, water uptake, tensile test, proton conductivity, and methanol permeability. Compared with a pure SPES membrane, PWA, and AT doping in the membrane led to a higher thermal stability and glass transition temperature (T_g) as revealed by TGA and DSC. Tensile test indicated that lower AT content (3%) in the composite can significantly increase the tensile strength, while higher AT loading demonstrated a smaller contribution on strength. Proper PWA and AT loadings in the composite membranes can increase the proton conductivity and lower the methanol cross‐over. The proton conductivity of the SPES‐P‐A 10% composite membrane reached 60% of the Nafion 112 membrane conductivity at room temperature while the methanol permeability was only one‐fourth of that of Nafion 112 membrane. This excellent performances of SPES/PWA/AT composite membranes could indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Proton conducting membranes based on sulfonated poly(ether ether ketone)/TiO2 nanocomposites for a direct methanol fuel cell

This paper presents an evaluation of the effects of titanium dioxide nanoparticles in sulfonated poly(ether ether ketone) (SPEEK) with a sulfonation degree of 57%. A series of inorganic/organic hybrid membranes was prepared with a systematic variation of titanium dioxide nanoparticle content. Their water uptake, methanol permeability and proton conductivity as a function of temperature were investigated. The results obtained show that the inorganic oxide network decreases the proton conductivity and water swelling. It is also found that increasing the inorganic oxide content leads to a decrease of methanol permeability. In terms of morphology, the membranes are homogeneous and exhibit good adhesion between inorganic domains and the polymer matrix. The proton conductivity and fuel cell performances of the nanocomposite membranes showed very good prospective in direct methanol fuel cell usages. The properties of the composite membranes are compared with those of standard Nafion membranes. Copyright © 2006 Society of Chemical Industry     

Montmorillonite‐reinforced sulfonated poly(phthalazinone ether sulfone ketone) nanocomposite proton exchange membranes for direct methanol fuel cells

To produce a composite membrane with high conductivity and low permeability, SPPESK with a degree of sulfonation of 101% was carefully selected for the preparation of montmorillonite (MMT)‐reinforced SPPESK using solution intercalation. The fundamental characteristics such as water uptake, swelling ratio, proton conductivity, methanol permeability, and mechanical properties of the composite membranes were studied. Water uptake is improved when organic MMT (OMMT) loading increase. The composite membranes with CTAB‐MMT loading of 4–0.5% show 0.143–0.150 S cm^?1 proton conductivity at 80°C, which approaches the value of Nafion112. In addition, methanol permeability was decreased to 6.29 × 10^?8 cm² s^?1 by the addition of 6 wt % OMMT. As a result, the SPPESK‐MMT composite membrane is a good candidate for use in direct methanol fuel cells. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39852.     

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.     

直接甲醇燃料电池用新型质子交换膜的研究

以聚醚醚酮(PEEK)为原料,浓硫酸为磺化剂制备了不同磺化度的磺化聚醚醚酮(SPEEK)膜,以及磺化聚醚醚酮与聚乙烯醇(PVA)、正硅酸乙酯(TEOS)、磷钨酸的复合膜.分别对膜的电导率、阻醇性能和吸水率进行了研究.随着SPEEK膜磺化度的增大,膜的电导率有所提高,然而甲醇渗透系数也增大,膜的机械强度明显降低.SPEEK膜的吸水率低于Nafion 115膜,而PVA膜的吸水率则过高.     

Studies of a high temperature proton exchange membrane based on incorporating an ionic liquid cation 1-butyl-3-methylimidazolium into a Nafion matrix

High temperature proton exchange membranes based on Nafion were prepared by incorporating the polymer with ionic liquid cation 1-butyl-3-methylimidazolium (BMIm) and doping with phosphoric acid (PA). We found that using the hydroxide form rather than the chloride form of BMIm incorporated more readily the BMIm cation into Nafion film. A mole ratio of about 2 of BMIm cation to Nafion repeat unit, i.e., λ_BMIm/Nafion, was reached with the hydroxide form BMIm. The incorporated BMIm cation enhanced the doping of phosphoric acid into Nafion. A proton conductivity of 10.9 mS cm⁻¹ and a tensile stress at break of 5.3 MPa were achieved, respectively, with a composite membrane of Nafion/2.3BMIm/5.2PA in molar ratio at 160 °C without humidification.     

Synthesis and characterization of sulfonated poly(ether sulfone ether ketone ketone) for proton exchange membranes

A series of sulfonated poly(ether sulfone ether ketone ketone) (SPESEKK) with different degree of sulfonation (DS) are prepared by the postsulfonation of PESEKK using chlorosulfonic acid as sulfonating agent and concentrated sulfuric acid as solvent. The chemical structures of the polymers are analyzed by the proton nuclear magnetic resonance. The thermal properties of the SPESEKK show that they are greatly influenced by the DS value and sulfonation time. The water uptake, proton conductivity, and Ion exchange capacity values increase as the sulfonation time increasing. The methanol permeability of the SPESEKK in the range of 7.02 × 10^?8 to 4.477 × 10^?7 cm² s^?1, is one or two orders of magnitude lower than that of Nafion 115. The morphology of the SPESEKK membranes is investigated by scanning electron microscope. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fluorinated naphthalene-based poly(arylene ether ketone)s containing pendant groups for direct methanol fuel cells

A novel series of naphthalene-based poly(arylene ether ketone) copolymers containing methoxy groups and hexafluoroisopropylidene diphenyl moieties (6F-MNPAEKs) were successfully synthesized by aromatic nucleophilic polycondensation. Chain-type fluorinated and sulfonated naphthalene-based poly(arylene ether ketone) copolymers (6F-SNPAEKs) were subsequently synthesized by demethylation and sulfobutylation. The chemical structures of 6F-SNPAEKs were confirmed by ¹H NMR. The 6F-SNPAEKs in acid form showed excellent thermal stability at elevated temperatures. The 6F-SNPAEK membranes were easily obtained by solution casting and properties for fuel cells were investigated in detail. The water uptake, swelling ratio and proton conductivity increased with degree of sulfonation (DS) and temperature. 6F-SNPAEK-90 showed the highest conductivity of 0.181 S cm^?1 at 80 °C. The methanol permeability of the membranes was in the range of 0.238–6.49 × 10^?7 cm² s^?1, compared to 1.55 × 10^?6 cm² s^?1 for Nafion 117. The membranes also showed excellent mechanical properties: the elongation at break was greater than 15%. These results indicate that the 6F-SNPAEK membranes are a promising candidate for use in direct methanol fuel cell (DMFC) applications.     

Synthesis and properties of sulfonated copoly(p-phenylene)s containing aliphatic alkyl pendant for fuel cell applications

A series of novel copoly(p-phenylene)s (PPs) containing an alkyl pendant were successfully synthesized via Ni(0)-catalyzed coupling polymerization. Sulfonated copolymers (SPPs) were achieved by postsulfonation from concentrated H₂SO₄. SPPs showed good solubility in polar aprotic solvents and gave flexible, tough, and transparent free-standing films by solvent casting. The ion exchange capacities (IECs) of the membranes ranged from 2.50 to 2.65 meq/g. All SPP membranes displayed proton conductivity similar to or higher than that of Nafion, especially at high relative humidity (>70% RH) (SPP-1: 0.271 Scm⁻¹, SPP-2: 0.284 Scm⁻¹, SPP-3: 0.212 S cm⁻¹, Nafion: 0.127 Scm⁻¹; at 80 °C and 95% RH). They also exhibited acceptable water uptake in the range of 52-56 vol% at 80 °C with little dimensional change. The gas permeability of the SPP membranes was much lower than that of Nafion 112. Therefore, these materials are promising for fuel cell application.     

Novel triazole functional sol-gel derived inorganic-organic hybrid networks as anhydrous proton conducting membranes

In this work, novel inorganic-organic hybrid networks were prepared to obtain anhydrous proton conducting membranes for fuel cells. 3-glycidoxypropyl trimethoxy silane (GPTMS) was functionalized with 1H-1,2,4-triazole (Tri) and 3-aminotriazole (ATri) via ring opening of the epoxide ring and then sol-gel polymerization was performed to produce triazole containing silane networks abbreviated as Si-Tri and Si-ATri. In addition during sol-gel process trifluoromethane sulfonic acid (TA) was introduced into the matrix with several stoichometric ratios. Fourier transform infrared spectroscopy (FT-IR) confirmed the tethering of the Tri and ATri into the silane compound and the sol-gel reaction. Thermogravimetry analysis (TGA) showed that the membranes are thermally stable up to 200 °C. Differential scanning calorimeter (DSC) verified the softening effect of the dopant. The morphology of the membranes was analyzed with SEM images. The proton conductivity of these novel silane networks were studied by dielectric-impedance spectroscopy. Although proton conductivity of these membrane electrolytes depends on the acid ratio, the membrane without dopant produced a proton conductivity of 8.7 × 10⁻⁵ S/cm at 150 °C in dry state. The conductivity isotherms show Vogel-Tamman-Fulcher (VTF) behavior which implies the coupling of the charge carriers with the segmental motion of the polymer chains. A maximum proton conductivity of 8.9 × 10⁻⁴ S/cm was obtained for the sample Si-TriTA1 in the anhydrous condition.     

Modification of Nafion membranes with ternary composite materials for direct methanol fuel cells

Composite membranes for direct methanol fuel cells (DMFCs) were prepared by using Nafion115 membrane modification with polyvinyl alcohol (PVA), polyimide (PI) and 8-trimethoxysilylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS). The performance of the composite membranes was evaluated in terms of water sorption, dimensional stability, thermal stability, proton conductivity, methanol permeability and cell performance. The proton conductivity was slightly decreased by 1-3% compared with Nafion115, which still kept the high proton conduction of Nafion115. The methanol permeability of Nafion/PI-PVA-TSPS composite membranes was remarkably reduced by 35-55% compared with Nafion115. The power density of DMFCs with Nafion/PI-PVA-TSPS composite membranes reached to 100 mW/cm², exceeding that with Nafion115 (68m W/cm²).