The effect of spatial confinement of Nafion in porous membranes on macroscopic properties of the membrane

Polyelectrolytes were incorporated into porous reinforcing materials to study the properties of ionomers in confined spaces and to determine the effect of the porous material on the behaviour of the membranes. Nafion^® was imbibed into porous polypropylene (Celgard^®), ultra-high-molecular weight polyethylene (Daramic^®), and polytetrafluoroethylene (PTFE) films. Through the use of reinforcing materials, it is possible to prepare membranes that are thinner, but stronger than pure ionomer membranes. Thin reinforced membranes have advantages such as lower areal resistance (as low as 0.14 Ω cm² for 57 μm CG3501 + Nafion^® compared to 0.34 Ω cm² for 89 μm cast Nafion^®) and lower dimensional changes due to swelling (as low as a 4% change in length and width for WDM + Nafion^® compared to 13% for cast Nafion^®). Using reinforcing materials results in a reduction in important membrane properties compared to bulk Nafion^®, such as proton conductivity (as low as 0.016 S cm⁻¹ for CG3401 + Nafion^® compared to 0.076 S cm⁻¹ for cast Nafion^®), effective proton mobility (as low as 3.2 × 10⁻⁴ cm² V⁻¹ s⁻¹ CG3401 + Nafion^® compared to 7.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ for cast Nafion^®), and water vapour permeance (as low as 0.036 g h⁻¹ Pa⁻¹ m⁻² for WDM + Nafion^® compared to 0.056 g h⁻¹ Pa⁻¹ m⁻² for cast Nafion^®). By normalizing the membrane properties with respect to ionomer content, it was possible to examine the properties of the Nafion^® inside the pores of the membranes. The proton conductivity (as low as 0.032 S cm⁻¹ for CG3401 + Nafion^®), effective proton mobility (as low as 3.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ for CG3401 + Nafion^®), and water vapour permeability (as low as 2.7 × 10⁻⁶ g h⁻¹ Pa⁻¹ m⁻¹ for PTFE MP 0.1 + Nafion^®) of the ionomer in the membrane are also diminished compared to bulk Nafion^® due to decreased connectivity of the ionomer and a restriction in macromolecular motions caused by the pore walls. A series of porous materials with increasing pore were also examined. As the pore size of the PTFE MP materials increased from 0.1 μm to 10 μm, the proton conductivity (0.022 S cm⁻¹ to 0.041 S cm⁻¹), effective proton mobility ((4.1 to 5.6) × 10⁻⁴ cm² V⁻¹ s⁻¹), and water vapour permeability ((2.4 to 4.3) × 10⁻⁶ g h⁻¹ Pa⁻¹ m⁻¹) of the reinforced membranes improved with increasing pore size and the properties of the ionomer inside the membranes approached the value of bulk Nafion^®.     

一种新型的用于质子交换膜燃料电池的磺化聚醚醚酮酮

以发烟硫酸和4,4-二(4-氟苯甲酰基)苯[1,4-bi(4-fluorobenzoyl)benzene]为原料,通过磺化反应,制得磺化二氟三苯二酮[1,4-bi(3-sodiumsulfonate-4-fluorobenzoyl)benzene].利用亲核缩聚反应,调整磺化单体和非磺化单体的比例,与酚酞进行聚合,制取了具有不同磺化度的聚醚醚酮酮,并对聚合物的结构进行了表征.结果表明,此系列磺化聚醚醚酮酮的膜制品具有良好的离子交换特性,可望应用于燃料电池膜.     

磺化侧苯基杂萘联苯聚醚酮酮的合成与性能

以4-(3-苯基-4-羟基苯基)-2,3-二氮杂萘-1-酮(DHPZ-P)、 4-(4-羟基苯基)-2,3-二氮杂萘-1-酮(DHPZ)和1,4-二(4'-氟苯甲酰基)苯(BFBB)为原料, 经溶液亲核取代缩聚反应, 通过调节DHPZ-P和DHPZ的比例, 合成了一系列侧苯基杂萘联苯聚醚酮酮(PPEKK-P), 然后以浓硫酸为磺化剂, 制备出一系列磺化侧苯基杂萘联苯聚醚酮酮(SPPEKK-P). 利用傅里叶变换红外光谱(FTIR)和氢核磁共振谱(¹H NMR)对聚合物结构进行表征, 结果表明, 磺酸基团引入到聚合物链的侧苯基上. 采用溶液浇铸法制备SPPEKK-P质子交换膜. SPPEKK-P膜的吸水率、 溶胀率和质子传导率均随离子交换容量(IEC)的增加而增加, 且具有较好的耐氧化性. IEC最高的SPPEKK-P-100膜的质子传导率在95℃能达到7.44×10^-2 S/cm, 且甲醇渗透系数为5.57×10^-8 cm²/s, 阻醇性能优于Nafion117膜.     

Preparation and properties of Nafion/hollow silica spheres composite membranes

In present work, hollow silica spheres (HSS)/Nafion^® composite membranes were prepared by solution casting. The thermal properties, water retention, swelling behavior and proton conductivity of the composite membranes were explored. It was found that HSS dispersed well at micrometer scale in the obtained composite membranes by SEM and TEM observation. Thermal properties of composite membranes were improved than that of recast Nafion^® membrane. Compared with the recast Nafion^® membrane, the composite membranes showed higher water uptake and lower swelling degree at the temperature range from 40 to 100 °C. At the same HSS loading, the smaller the diameter of HSS in composite membranes, the more the water uptake, however, the swelling degree of composite membranes was increased. The proton conductivity of the composite membrane with 3–5 wt.% HSS (120 and 250 nm) increased distinctively at above 60 °C, reached the optimal value at 100 °C, and decreased slowly when the temperature exceeded 100 °C.     

Characterization and performance of proton exchange membranes for direct methanol fuel cell: Blending of sulfonated poly(ether ether ketone) with charged surface modifying macromolecule

Modification of sulfonated poly(ether ether ketone) (SPEEK) membrane was attempted by blending charged surface modifying macromolecule (cSMM). The modified membrane was tested for direct methanol fuel cell (DMFC) application; i.e. a SPEEK/cSMM blend membrane was compared to a SPEEK membrane and a Nafion 112 membrane for the thermal and mechanical stability, methanol permeability, and proton conductivity. Thermal and mechanical stability of the blended membrane were slightly reduced from the SPEEK membrane but still higher than the Nafion 112 membrane. The blend membrane was found to be promising for DMFC applications because of its lower methanol diffusivity (2.75 × 10⁻⁷ cm² s⁻¹) and higher proton conductivity (6.4 × 10⁻³ S cm⁻¹), than the SPEEK membrane. A plausible explanation was given for the favorable effect of cSMM blending.     

Preparation and properties of UV irradiation-induced crosslinked sulfonated poly(ether ether ketone) proton exchange membranes

The crosslinkable sulfonated poly(ether ether ketone)s (SPEEKs) were synthesized by nucleophilic substitution reaction of diallyl bisphenol A, tert-butylhydroquinone, 4,4′-difluorobenzophenone and sodium 5,5′-carbonylbis(2-fluorobenzene-sulfonate). The SPEEKs with high intrinsic viscosity showed good solubility and could be cast into flexible and transparent membranes. The SPEEK membranes containing benzophenone (BP) and triethylamine (TEA) photo-initiator system were treated by UV light to promote crosslinking. The experimental results revealed that the crosslinked membrane with 10 min irradiation time showed the most potential as proton exchange membrane for direct methanol fuel cell applications. When the irradiation time increased from 0 to 10 min, the water uptake decreased from 29.1 to 26.1%, and the tensile modulus and the tensile strength enhanced sharply from 0.80 to 1.44 GPa and from 40.3 to 63.4 MPa, respectively. In addition, the methanol diffusion coefficient reduced sharply from 1.70 × 10⁻⁶ to 7.42 × 10⁻⁷ cm²/s with only slight sacrifice in the proton conductivity, which made the crosslinked membrane with 10 min irradiation time possess the highest selectivity.     

Synthesis and characterization of novel sulfonated naphthalenic polyimides as proton conductive membrane for DMFC applications

To prepare proton conductive membrane for direct methanol fuel cells (DMFC), a novel sulfonated aromatic diamine monomer, 1,4-bis(4-amino-2-sulfonic acid-phenoxy)-benzene (DSBAPB) was synthesized and characterized by ¹H NMR and FT-IR. Then a series of sulfonated polyimides (SPIs) were prepared from DSBAPB with 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) and a non-sulfonated diamine, 4,4′-oxydianiline (ODA) via one-step high-temperature polymerization method. The sulfonation degree of the SPIs can be controlled by changing the mole ratio of sulfonated monomer to non-sulfonated monomer. The obtained SPI membranes exhibit desirable proton conductivity ranged from 7.9 × 10⁻³ to 7.2 × 10⁻² S cm⁻¹ and low methanol permeability of less than 2.85 × 10⁻⁷ cm² s⁻¹. Furthermore, the hydrolysis stability of the obtained SPIs is better than the BDSA based SPIs caused by the flexible structure.     

Modification of proton conductive polymer membranes with phosphonated polysilsesquioxanes

New hybrid membranes for fuel cell applications based on sulfonated poly(ether ether ketone) (SPEEK) and phosphonated polysilsesquioxanes were synthesized. The impedance spectroscopy measurements show an increase of the proton conductivity for all studied composites, in comparison to plain SPEEK. For hybrid membranes containing 20 wt% of polysilsesquioxane with 80 mol% of phosphonated units the conductivities can reach values that are similar to Nafion 117^® at 100% RH. The best results of proton conductivity (142 mS/cm) were obtained for composites with 40 wt% of the same polysilsesquioxane at 120 °C also at 100% RH.     

Physicochemical characterization of ion-exchange membranes in water-methanol mixtures

A complete physicochemical characterization of two ion-exchange membranes—CM2 and Nafion^®117—used in electrodialysis and in direct methanol fuel cells (DMFC) has been carried out. For each membrane, in different methanol-water mixtures—0%, 20%, 40%, 60%, 80% and 100%—and at different temperatures (25.0; 40.0 et 55.0 °C), we have measured the variations of the geometrical dimensions, the proton electrical conductivity, the swelling rate and the amount of methanol in the membrane. The FTIR analysis of Nafion^®117 was performed at different methanol contents of the external solution.The results show that the CM2 membrane presents the best geometrical stability, and the lowest conductivity at any methanol content. At high methanol contents, Nafion^®117 is 10 times more conductive than the CM2 membrane. It was found that the methanol is absorbed more by Nafion^®117, and its effect is more noticeable on the microstructure of this membrane, under standard conditions. The high methanol permeability of these membranes, particularly of the Nafion^®117, induces bad cell efficiencies and lifetimes.     

用于燃料电池质子交换膜材料的磺化聚芳醚酮砜的合成与性能研究

以叔丁基对苯二酚(TBHQ)为双酚单体,1,4-二(4′-氟苯甲酰基)苯,3,3′-二磺酸钠基-4,4′-二氧二苯砜(SDCDPS)为原料,采用亲核缩聚反应,通过调整磺化单体和非磺化单体的比例与叔丁基对苯二酚共聚,合成了一系列具有不同磺化度的聚芳醚酮砜.通过红外光谱(FTIR),TGA,DSC等分析方法对其结构及性能进行了表征.并用TEM对其内部形态进行了研究,建立了结构与性能之间的关系.通过对膜进行综合性能评价发现,磺化度为0.8的磺化聚芳醚酮砜膜的质子传导率在80℃时达到了0.061 S/cm接近了Nafion 117,而且其甲醇渗透系数为3.4×10-7cm2/s远低于Nafion 117,在质子交换膜燃料电池(PEMFC)和直接甲醇燃料(DMFC)电池中表现出了好的应用前景.     

Synthesis and characterization of poly(aryl ether ketone) ionomers with sulfonic acid groups on pendant aliphatic chains for proton-exchange membrane fuel cells

A series of parent poly(aryl ether ketone)s bearing different content of unsaturated pendant propenyl groups were synthesized via nucleophilic substitution polymerization from 3,3′-diallyl-4,4′-dihydroxybiphenyl, 9,9′-bis(4-hydroxyphenyl) fluorene and 4,4′-difluorobenzophenone. The polymers with pendant aliphatic sulfonic acid groups were further synthesized by free radical thiol-ene coupling reactions between 3-mercapto-1-propanesulfonic sodium and the parent propenyl functional copolymers. The resulting sulfonated polymers with high inherent viscosity (1.83-4.69 dL/g) were soluble in polar organic solvents and can form flexible and transparent membranes by casting from their solutions. The copolymers with different ion exchange capacity could be conveniently synthesized by varying the monomers ratios. Transmission electron microscopy (TEM) was used to examine the microstructures of the membrane and the results revealed that significant hydrophilic/hydrophobic microphase separation with spherical, uniform-sized (5-10 nm) and well-dispersed hydrophilic domains was afforded. The proton conductivities of the as-prepared membranes and the state-of-the-art Nafion 117 membrane in fully hydrated state were investigated. The results revealed that the proton conductivity of the synthesized membranes increased more remarkably than that of Nafion 117 membrane with increasing temperature. The membrane with 1.69 mequiv/g of IEC had a conductivity of 2.5 × 10⁻² Scm⁻¹ at 100 °C. The membranes also possessed excellent mechanical properties, good thermal, oxidative, hydrolytic and dimensional stabilities.     

High efficiency direct methanol fuel cell based on poly(styrenesulfonic) acid (PSSA)-poly(vinylidene fluoride) (PVDF) composite membranes

semi-Interpenetrating polymer network (sIPN) composite membranes consisting of poly(styrenesuflonic) acid (PSSA) and poly(vinylidene fluoride) (PVDF) have been prepared and evaluated as proton exchange membrane electrolytes in direct methanol fuel cells (DMFCs). The membranes fabricated were evaluated in terms of their proton conductivity, methanol permeability, and their performance characteristics in direct methanol fuel cells (DMFCs). PSSA-PVDF membranes demonstrated decreased methanol crossover during operation of direct methanol fuel cells compared to state-of-art Nafion^®-H membranes, yielding improved efficiency. PSSA-PVDF membranes have been demonstrated to operate efficiently in 1 in. × 1 in. and 2 in. × 2 in. direct methanol fuel cells. Fuel cells operating with PSSA-PVDF membranes were observed to have dramatically lower crossover rates compared to Nafion^® 117 systems. Greater than 95% reduction in crossover was observed in some cases. These properties of PSSA-PVDF membranes resulted in improved fuel performance and fuel cell efficiencies for direct methanol fuel cells. It was also observed that the PSSA-PVDF membranes behave quite differently compared with Nafion^®-based systems in terms water management characteristics at the cathode. The best performance with the new membranes was observed with very low oxygen or air flow rates at the cathode which is in contrast to Nafion^®-based systems, which generally require higher flow rates due to excessive water accumulation at the cathode, resulting in flooding.     

Fluorene-containing block sulfonated poly(ether ether ketone) as proton-exchange membrane for PEM fuel cell application

A series of sulfonated block poly(ether ether ketone)s with different sulfonic acid group clusters were successfully synthesized by nucleophilic displacement condensation. Membranes were accordingly cast from their DMSO solutions, and fully characterized by determining the ion-exchange capacity, water uptake, proton conductivity, dimensional stabilities and mechanical properties. The experimental results showed that the main properties of the membrane can be tailored by changing the cluster size of sulfonic acid groups. The membrane of block-7c(40) has good mechanical, oxidative and dimensional stabilities together with high proton conductivity (5.09 × 10⁻² S cm⁻¹) at 80 °C under 100% relative humidity. The membranes also possess excellent thermal and dimensional stabilities. These polymers are potential and promising proton conducting membrane material for PEM full cell applications.     

Methanol permeability in sulfonated poly(etheretherketone) membranes: A comparison with Nafion membranes

Partially sulfonated poly(etheretherketone) (SPEEK) samples were prepared by modification of corresponding poly(etheretherketone) (PEEK) with concentrated sulfuric acid. Membranes cast from these materials were evaluated as polymer electrolytes for direct methanol fuel cells (DMFCs). SPEEK membranes were characterized by ¹H NMR, FT-IR and TGA. The transverse proton conductivities increased from 4.1 to 9.3 × 10⁻³ S/cm with the increase of the degree of sulfonation (DS) from 0.59 to 0.93. These values were comparable with that of Nafion 117 membrane (1.0 × 10⁻² S/cm) measured under the same condition. Nearly one order magnitude difference between transverse conductivity and longitudinal conductivity was found. The methanol permeabilities of the SPEEK membranes were all lower than that of Nafion 117 membrane. The effects of temperature and methanol concentration on the methanol permeability were also studied. In addition, the selectivities of the SPEEK membranes for protons and methanol were all higher than that of Nafion 117 membrane.     

Synthesis of novel crosslinked sulfonated poly(ether sulfone)s using bisazide and their properties for fuel cell application

Novel crosslinked sulfonated poly(ether sulfone)s (PESs) were prepared by thermal irradiation of the allyl-terminated telechelic sulfone polymers using a bisazide. The sulfonated polymers in different comonomer compositions were fully characterized by ¹H NMR, and the crosslinked structure was also verified by FT-IR spectroscopic analyses. Having both the uniform distribution of the hydrophilic conductive sites and controlled hydrophobic nature by minimized crosslinking over the rigid rod poly(ether sulfone) backbone, the crosslinked polymer membrane (PES-60) offered excellent proton conductivity of 0.79 S cm⁻¹ at 100 °C together with hydrolytic and oxidative stability. In addition, only 17% of methanol permeability of the Nafion^® was observed for the crosslinked PES-60.     

A study of linear versus angled rigid rod polymers for proton conducting membranes using sulfonated polyimides

Linear and angled monomers were incorporated into the main chain of a polyimide in order to investigate the effect of kinked versus linear polymers on membrane properties such as water uptake and proton conductivity. Polymers prepared using linear 4,4′-sulfonyldianiline, SPI1, and using angled 3,4′-sulfonyldianiline, SPI2, were cast into membranes possessing ion exchange capacities that varied from 0.79 to 2.75 meq g⁻¹. Membranes are thermally stable up to 300 °C under air. Proton conductivity of both membranes increases with temperature to values of 0.1-0.2 S cm⁻¹. The conductivity of angled, SPI2 membranes is greater than those prepared from SPI1 for a given IEC but water uptakes are lower. These differences are attributed to increased entanglements of the angled polymers, which limits the degree of swelling and increases the proton concentration. These results may be important in the design of proton conducting membranes from other rigid polyarylenes.     

Crosslinking of sulphonated poly (ether ether ketone) using aromatic bis(hydroxymethyl) compound

2,6-Bis(hydroxymethyl)-4-methyl phenol and 1,4-bis(hydroxymethyl) benzene have been used as crosslinkers in sulphonated poly (ether ether ketone) (SPEEK DS 65%, IEC 1.84 mequiv./g) for the preparation of proton exchange membranes (PEMs). Crosslinking of SPEEK has been achieved by thermally activated bridging of the polymer chain with the hydroxymethyl group of crosslinker through condensation reaction with sulphonic acid group. The physico-chemical properties of uncrosslinked and crosslinked membrane were evaluated in terms of ion exchange capacity (IEC), water uptake, ionic conductivity and mechanical properties. The crosslinked membrane showed controlled swelling, ionic conductivity of 25–50 mS/cm at 80 °C and good mechanical properties. The chemical stability of the crosslinked membranes was studied by Fenton's test. The % loss in weight and changes in physico-chemical properties of the treated membranes were determined.     

The stability of semi-interpenetrating polymer networks based on sulfonated polyimide and poly(ethylene glycol) diacrylate for fuel cell applications

A series of the semi-interpenetrating polymer network (semi-IPN) membranes based on sulfonated polyimide and poly(ethylene glycol) diacrylate were prepared and characterized comparing with pure sulfonated polyimide membrane and commercially available membrane, Nafion^® 117. The proton conductivity increased with the increase of poly(ethylene glycol) diacrylate contents in spite of the decrease in ion exchange capacity which is a key factor to improve the proton conductivity. The water stability of semi-IPN membranes containing poly(ethylene glycol) diacrylate is higher than the pure sulfonated polyimide membrane. Morphological structure showed that amorphous nature of the films also increased with the poly(ethylene glycol) diacrylate contents, which could make a crosslink, so that the crystallinity of polyimide could disappear. Semi-IPN membranes based on sulfonated polyimide and poly(ethylene glycol) diacrylate, which show good conductivity comparable to Nafion^® 117 in the range of 20-50% content of poly(ethylene glycol) diacrylate, could be promising proton conducting membranes in fuel cell application.     

Synthesis, polymerization and conducting properties of an ionic liquid-type anionic monomer

The synthesis of a new ionic liquid-type monomer has been performed by association of a methacrylate polymerizable group, a polar tri(ethylene oxide) (TEO) spacer, a trifluoromethane sulfonic (TFSI⁻) anion and a free imidazolium (EMIm⁺) cation. The ionic liquid monomer (ILM) has demonstrated a good thermal stability and a high ionic conductivity around 2.1 × 10⁻³ S cm⁻¹ at 20 °C. The corresponding homopolymer has shown an ionic conductivity closely related to the monomer (6.5 × 10⁻⁴ S cm⁻¹ at 20 °C), which confirms the ILM as a valuable monomer for the formation of polymeric ionic liquid (PIL) materials.     

Zirconium meta-sulfonphenyl phosphonic acid-incorporated Nafion membranes for reduction of methanol permeability

Zirconium meta-sulfonphenyl phosphonic acid (Zr-msPPA)/Nafion^® composite membranes were prepared to reduce methanol permeability of the Nafion^® 117 membrane in direct methanol fuel cell (DMFC) applications. Zr-msPPA crystalline nano proton conductors were synthesized inside the membranes via the reaction of zirconium chloride octahydrate and meta-sulfonphenyl phosphonic acid that had been soaked prior. Synthesis of the Zr-msPPA in the membranes was identified from a series of chemical and physical structure characterizations using FTIR, NMR, EDS, and XRD spectroscopy. The thermal stability of the composite membranes was enhanced by addition of the Zr-msPPA, with considerable reduction in methanol permeability with increasing Zr-msPPA content, as the Zr-msPPA nano conductors acted as crystalline barriers to methanol permeation. The ion conductivity also decreased with increasing Zr-msPPA content, but its effect was not as strong as with methanol permeation given the innate, high conductivity of Zr-msPPA.