Similar Ion Exchange Capacity Research Articles

Synthesis and Properties of Fluorenyl-Containing Multiblock Sulfonated Poly(Arylene Ether Sulfone) Membranes for Fuel Cell Applications

A series of novel multiblock copolymers containing rigid hydrophilic/soft hydrophobic blocks were synthesized and evaluated for use as proton exchange membranes (PEMs). The multiblock copolymers were prepared by a coupling reaction between phenoxide-terminated sulfonated poly(arylene ether sulfone) oligomer (OSO) and fluorine-terminated poly(arylene ether sulfone) oligomer (FNO). All copolymers produced tough, flexible and transparent membranes by casting from DMSO solution. The resulting membranes displayed good water stability and enhanced proton conductivities comparable to that of the corresponding random ones with similar ion exchange capacity (IEC) values. They also showed slight anisotropic swelling behavior, while isotropic behavior for the random ones. The results revealed that these multiblock copolymers were potential candidates for PEM materials.

Cross-linked tri-side chains poly(arylene ether ketone)s containing pendant alkylsulfonic acid groups for proton exchange membranes

In order to enhance the ion exchange capacity (IEC) in the proton exchange membrane materials, a novel sulfonated poly(arylene ether ketone) (SQNPAEK) containing tri-side chains in one unit is synthesized by direct polymerization. The SQNPAEK membrane shows excellent proton conductivity up to 0.102 S cm −1 at 80 °C, which are superior to previous side-chain-type and main-chain-type sulfonated polymer membranes at similar IEC. Cross-linked membranes are then obtained by a heating reaction at 190 °C, using 4,4′-diglycidyl (3,3′,5,5′-tetramethylbiphenyl) epoxy resin (TMBP) as the cross-linker. As expected, the water uptake and the methanol permeability of the cross-linked membranes decrease with increasing the content of TMBP. Compared to Nafion 117, the cross-linked membranes show comparable proton conductivities and much higher selectivities, which are in the range of 5.18 × 10 5–1.46 × 10 6 S s −1 cm 3. Other properties of the cross-linked membranes, such as mechanical properties, thermal properties, are also investigated. All the results indicated that the cross-linked membranes based on SQNPAEKs and TMBP are promising candidate for direct methanol fuel cells.

Understanding properties of copoly(arylene ether nitrile)s high-performance polymer electrolyte membranes for fuel cells from molecular dynamics simulations

Sulfonated poly(arylene ether ether nitrile) (m-SPAEEN) copolymers are reported to have the property of reduced water uptake compared with other hydrocarbon membranes, such as sulfonated polysulfones or polyketones, with similar ion exchange capacity. It is believed that this difference is largely due to the nitrile group. In this study, to investigate the effect of the nitrile group on properties of polymer electrolyte membranes for fuel cell applications, we carried out a series of molecular dynamics (MD) simulations. We compared the results of MD simulations for m-SPAEEN and sulfonated poly(arylene ether sulfone)s (BPSH). We found that water molecules hydrate not only the sulfonate (SO3 −) groups of m-SPAEEN but also other hydrophilic functional groups in the copolymers. Results showed that hydration around the nitrile group in m-SPAEEN and around the sulfone (SO2) group in BPSH differs in features related to water uptake: The former exhibits uptake of fewer water molecules than does the latter. This difference in hydration features causes m-SPAEEN to have a relatively low water-uptake level compared with BPSH.

Densely Sulfophenylated Segmented Copoly(arylene ether sulfone) Proton Exchange Membranes

Segmented copoly(arylene ether sulfone) membranes having densely sulfonated pendent phenyl blocks were synthesized by the coupling reaction of phenoxide-terminated oligomers with bis(4-hydroxyphenyl) sulfone and decafluorobiphenyl (DFBP), followed by postpolymerization sulfonation of the blocks containing pendent phenyl substituents. The coupling reaction was conducted at relatively low temperature by utilizing highly reactive DFBP to prevent any possible trans-etherification that would randomize the hydrophilic–hydrophobic sequences. Segmented copolymer molecular weights were reasonably high, as determined by viscosity measurements. Postsulfonation occurred selectively on the pendent phenyl substituent to yield hydrophilic blocks that were highly sulfonated in regular sequence on the linked phenyl rings. The resulting polymers gave transparent, flexible, and tough membranes by solution casting. Morphological observation by transmission electron microscopy (TEM) and atomic force microscopy (AFM) showed that the high local concentration and regular sequence of pendent sulfonic acid groups within the hydrophilic blocks enhanced nanophase separation between the hydrophobic and hydrophilic blocks. A comparison of copolymers with similar ion exchange capacities (IECs) indicated that proton conductivity and water uptake were strongly influenced by the hydrophilic block sequence lengths. Proton conductivity and water uptake increased with increasing block length, even at low relative humidity (RH). The ionomer membrane with X20Y20 (X and Y refer to the number of hydrophilic and hydrophobic repeat units, respectively) and 1.82 mequiv/g of IEC had a proton conductivity of 3.6 × 10–2 S/cm at 80 °C and 50% RH, which is comparable to that of perfluorinated ionomer (Nafion) membrane (4.0 × 10–2 S/cm).

Solvent processible, high-performance partially fluorinated copoly(arylene ether) alkaline ionomers for alkaline electrodes

A solvent processable, low water uptake, partially fluorinated copoly(arylene ether) functionalized with pendant quaternary ammonium groups (QAPAE) was synthesized and uses as the ionomer in alkaline electrodes on fuel cells. The quaternized polymers containing fluorinated biphenyl groups were synthesized via chloromethylation of copoly(arylene ether) followed by amination with trimethylamine. The resulting ionomers were very soluble in polar, aprotic solvents. Highly aminated ionomers had conductivities approaching 10mScm−1 at room temperature. Compared to previous ionomers based on quaternized poly(arylene ether sulfone) (QAPSF) with similar ion exchange capacity (IEC), the water uptake of QAPAE was significantly less due to the hydrophobic octafluoro-biphenyl groups in the backbone. The performance of the fuel cell electrodes made with the QAPAE ionomers was evaluated as the cathode on a hybrid AEM/PEM fuel cell. The QAPAE alkaline ionomer electrode with IEC=1.22meqg−1 had superior performance to the electrodes prepared with QAPSF, IEC=1.21meqg−1 at 25 and 60°C in a H2/O2 fuel cell. The peak power densities at 60°C were 315mWcm−2 for QAPAE electrodes and 215mWcm−2 for QAPSF electrodes.

Sulfonated multiblock copolynaphthalimides for polymer electrolyte fuel cell application

Sulfonated multiblock copolynaphthalimides (multiblock co-SPIs) were prepared by two-pot polymerization method from 1,4,5,8-naphthalenetetracarboxylic dianhydride, sulfonated diamine of 4,4′-bis(4-aminophenoxy)-3,3′-bis(4-sulfophenyl)biphenyl (BAPSPB) and nonsulfonated diamine of 4,4′-diaminophenyl hexafluoropropane. The multiblock co-SPI (BA1) with hydrophilic/hydrophobic block length of 20/10 and ion exchange capacity (IEC) of 1.67 meq g −1 exhibited larger water uptake, larger in-plane and through-plane proton conductivity ( σ ∥ and σ ⊥ , respectively) than the random co-SPI with the similar IEC. The multiblock co-SPI (BA2) with the longer block length of 20/20 exhibited the large σ ∥ and σ ⊥ comparable to those of BA1, in spite of the smaller IEC of 1.35 meq g −1. Both the multiblock and random co-SPIs showed the moderate anisotropic proton conductivity ( σ ⊥/ σ //≒ 0.70) as well as anisotropic membrane swelling with about three times larger through-plane swelling than in-plane swelling. The TEM observation revealed that BA2 had an isotropic and inhomogeneous morphology with indistinct microphase-separated structure, whereas the random co-SPIs had a homogeneous morphology. The behavior of BAPSPB-based multiblock co-SPI membranes were quite different from that of the multiblock co-SPIs based on 2,2′-bis(4-sulfophenoxy)benzidine, which was due to the presence of two flexible ether bonds in BAPSPB moiety of the main chain. Even under the low humidification of 27/27% RH at 90 °C and 0.2 MPa, BA2 exhibited the fairly high PEFC performance; namely, cell voltage of 0.67 V at load current density of 0.5 A cm −2 and maximum output of 0.51 W cm −2, which were much larger than those of BA1 and the random co-SPI (RA1) with IEC of 1.84 meq g −1, and have the high potential as PEM for PEFC applications.

Fully Aromatic Block Copolymers for Fuel Cell Membranes with Densely Sulfonated Nanophase Domains

Two multiblock copoly(arylene ether sulfone)s with similar block lengths and ion exchange capacities (IECs) were prepared by a coupling reaction between a non-sulfonated precursor block and a highly sulfonated precursor block containing either fully disulfonated diarylsulfone or fully tetrasulfonated tetraaryldisulfone segments. The latter two precursor blocks were sulfonated via lithiation-sulfination reactions whereby the sulfonic acid groups were exclusively placed in ortho positions to the many sulfone bridges, giving these blocks IECs of 4.1 and 4.6 meq·g⁻¹, respectively. Copolymer membranes with IECs of 1.4 meq·g⁻¹ displayed well-connected hydrophilic nanophase domains and had decomposition temperatures at, or above, 300 °C under air. The copolymer with the tetrasulfonated tetraaryldisulfone segments showed a proton conductivity of 0.13 S·cm⁻¹ at 80 °C under fully humidified conditions, and surpassed that of a perfluorosulfonic acid membrane (NRE212) by a factor of 5 at -20 °C over time.

Synthesis and characterization of poly(arylene ether ketone)s bearing pendant sulfonic acid groups for proton exchange membrane materials

AbstractA bisphenol monomer (2,5‐dimethoxy)phenylhydroquinone was prepared and further polymerized to obtain poly(arylene ether ketone) copolymers containing methoxy groups. After demethylation and sulfobutylation, a series of novel poly(arylene ether ketone)s bearing pendant sulfonic acid group (SPAEKs) with different sulfonation content were obtained. The chemical structures of all the copolymers were analyzed by 1H NMR and 13C NMR spectra. Flexible and tough membranes with reasonably good mechanical properties were prepared. The resulting side‐chain‐type SPAEK membranes showed good dimensional stability, and their water uptake and swelling ratio were lower than those of conventional main‐chain‐type SPAEK membranes with similar ion exchange capacity. Proton conductivities of these side‐chain‐type sulfonated copolymers were higher than 0.01 S/cm and increased gradually with increasing temperature. Their methanol permeability values were in the range of 1.97 × 10−7–5.81 × 10−7 cm2/s, which were much lower than that of Nafion 117. A combination of suitable proton conductivities, low water uptake, low swelling ratio, and high methanol resistance for these side‐chain‐type SPAEK films indicated that they may be good candidate material for proton exchange membrane in fuel cell applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Preparation and Characterization of an Oxidized MWCNT-Reinforced Nafion<SUP>®</SUP> Nanocomposite Membrane for Direct Methanol Fuel Cell

Oxidized multiwalled carbon nanotube (MWCNT) reinforced Nafion ® nanocomposite membranes were prepared toward the use a polymer electrolyte membrane (PEM) for direct methanol fuel cells. To reduce methanol crossover through Nafion ® membrane, the oxidized MWCNTs were prepared and added into the Nafion ® membrane in the range of 0.5―3 wt%. The oxidized MWCNTs were prepared by treatment with 60% nitric acid at 120 ° C for 12 h and characterized by scanning electron microscope and Raman spectroscopy. Well-aligned structures with low entanglement were observed in the oxidized MWCNTs. The portion of amorphous carbon structure in the oxidized MWCNTs was increased by the oxidation reaction. The oxidized MWCNT reinforced Nafion ® nanocomposite membranes were prepared by a solution casting method on a hot plate. Thermal stability was enhanced by adding MWCNT into Nafion ® membranes. While MWCNT-reinforced Nafion ® nanocomposite membranes exhibited similar ion exchange capacity to that of Nafion ® , the methanol uptake was reduced about 14 wt%.

Sulfonated polybenzimidazoles: Proton conduction and acid–base crosslinking

AbstractA series of soluble, benzimidazole‐based polymers containing sulfonic acid groups (SuPBI) has been synthesized. SuPBI membranes resist extensive swelling in water but are poor proton conductors. When blended with high ion exchange capacity (IEC) sulfonated poly(ether ether ketone) (SPEEK), a polymer that has high proton conductivity but poor mechanical integrity, ionic crosslinks form reducing the extent of swelling. The effect of sulfonation of PBI on crosslinking in these blends was gauged through comparison with nonsulfonated analogs. Sulfonic acid groups present in SuPBI compensate for acid groups involved in crosslinking, thereby increasing IEC and proton conductivity of the membrane. When water uptake and proton conductivity were compared to the IEC of blends containing either sulfonated or nonsulfonated PBI, no noticeable distinction between PBI types could be made. Comparisons were also made between these blends and pure SPEEK membranes of similar IEC. Blend membranes exhibit slightly lower maximum proton conductivity than pure SPEEK membranes (60 vs. 75 mS cm−1) but had significantly enhanced dimensional stability upon immersion in water, especially at elevated temperature (80 °C). Elevated temperature measurements in humid environments show increased proton conductivity of the SuPBI membranes when compared with SPEEK‐only membranes of similar IEC (c.f. 55 for the blend vs. 42 mS cm−1 for SPEEK at 80 °C, 90% relative humidity). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3640–3650, 2010

Synthesis and characterization of multiblock copolymers based on hydrophilic disulfonated poly(arylene ether sulfone) and hydrophobic partially fluorinated poly(arylene ether ketone) for fuel cell applications

AbstractSulfonated fluorinated multiblock copolymers based on high performance polymers were synthesized and evaluated for use as proton exchange membranes (PEMs). The multiblock copolymers consist of fully disulfonated poly(arylene ether sulfone) and partially fluorinated poly(arylene ether ketone) as hydrophilic and hydrophobic segments, respectively. Synthesis of the multiblock copolymers was achieved by a condensation coupling reaction between controlled molecular weight hydrophilic and hydrophobic oligomers. The coupling reaction could be conducted at relatively low temperatures (e.g., 105 °C) by utilizing highly reactive hexafluorobenzene (HFB) as a linkage group. The low coupling reaction temperature could prevent a possible trans‐etherification, which can randomize the hydrophilic‐hydrophobic sequences. Tough ductile membranes were prepared by solution casting and their membrane properties were evaluated. With similar ion exchange capacities (IECs), proton conductivity and water uptake were strongly influenced by the hydrophilic and hydrophobic block sequence lengths. Conductivity and water uptake increased with increasing block length by developing nanophase separated morphologies. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments revealed that the connectivity of the hydrophilic segments was enhanced by increasing the block length. The systematic synthesis and characterization of the copolymers are reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 214–222, 2010

Sulfonated poly(ether sulfone)s with binaphthyl units as proton exchange membranes for fuel cell application

AbstractSulfonated poly(ether sulfone)s containing binaphthyl units (BNSHs) were successfully prepared for fuel cell application. BNSHs, which have very simple structures, were easily synthesized by postsulfonation of poly(1,1′‐dinaphthyl ether phenyl sulfone)s and gave tough, flexible, and transparent membranes by solvent casting. The BNSH membranes showed low water uptake compared to a typical sulfonated poly(ether ether sulfone) (BPSH‐40) membrane with a similar ion exchange capacity (IEC) value and water insolubility, even with a high IEC values of 3.19 mequiv/g because of their rigid and bulky structures. The BNSH‐100 membrane (IEC = 3.19 mequiv/g) exhibited excellent proton conductivity, which was comparable to or even higher than that of Nafion 117, over a range of 30–95% relative humidity (RH). The excellent proton conductivity, especially under low RH conditions, suggests that the BNSH‐100 membrane has excellent proton paths because of its high IEC value, and water insolubility due to the high hydrophobicity of the binaphthyl structure. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5827–5834, 2009

Preparation and Properties of Cross‐linked Sulphonated Poly(sulphide sulphone) Membranes for Fuel Cell Applications

AbstractA series of cross‐linked sulphonated poly(sulphide sulphone) (SPSSF) membranes have been prepared via a polyphosphoric‐acid‐catalysed condensation reaction at 180 °C for a period of time (1.5–5.0 h) and the resulting cross‐linking bonds are the highly stable sulphonyl groups. The cross‐linking density could be controlled by regulating the reaction time. Cross‐linking caused significant enhancement in the mechanical properties and large reduction in both water uptake (WU) and methanol permeability. The SPSSF‐60 membrane (the numeral 60 refers to the degree of sulphonation), e.g. had a tensile strength increased from 16 to 27 MPa (wet membranes) after cross‐linking for 5 h, while the WU substantially decreased from 320 to 58 wt.‐% and the methanol permeability decreased from 1.9 × 10–6 to 2.7 × 10–7 cm2 s–1 (30 °C). Single cell test on hydrogen/oxygen revealed that the cross‐linked SPSSF‐50 (1.5 h) membrane displayed higher open circuit voltage (OCV, 1.02 V), higher maximum output power density (1.32 W cm–2) and significantly slower OCV decay rate than the uncross‐linked SPSSF‐40 membrane under the same operating conditions despite their similar ion exchange capacities. The cross‐linked SPSSF‐60 (5.0 h) and SPSSF‐50 (1.5 h) membranes showed significantly better fuel cell performance than Nafion 212.

Novel side-chain-type sulfonated poly(arylene ether ketone) with pendant sulfoalkyl groups for direct methanol fuel cells

Abstract Novel side-chain-type sulfonated poly(arylene ether ketone) with pendant sulfoalkyl groups (SPAEK-xx) were synthesized by post-sulfonation method. Their structures were confirmed by FT-IR and NMR spectra. The all obtained membranes had excellent thermal stability and mechanical properties. The side-chain-type SPAEK films showed good dimensional stability, and their water uptake and swelling ratio were lower than those of the main-chain-type SPAEK with similar ion exchange capacity (IEC) value. It should be noted that the most highly sulfonated copolymer, SPAEK-100 (DS = 1.0) with IEC of 1.54 meq./g, showed proton conductivity of 0.083 S/cm and water swelling ratio of only 9.74% at 80 °C. Moreover, the methanol permeability of SPAEK-100 membrane was 3.95 × 10 −7 cm 2 /s, which was much lower than 23.80 × 10 −7 cm 2 /s of Nafion 117.

Effect of the Hydrophobic Component on the Properties of Sulfonated Poly(arylene ether sulfone)s

Four kinds of sulfonated poly(arylene ether sulfone)s containing hydrophobic component of different size was synthesized by the copolymerization of disodium 3,3′-disulfo-4,4′-difluorophenyl sulfone and 4,4′-difluorophenyl sulfone with 2,2-bis(2-hydroxy-5-biphenylyl)propane (SPE1), 4,4′-dihydroxytetraphenylmethane (SPE2), 9,9-bis(4-hydroxyphenyl)fluorene (SPE3), or 2,7-dihydroxynaphthalene (SPE4) under nucleophilic aromatic substitution conditions. The copolymer composition was set at 45−70 mol % of 3,3′-disulfo-4,4′-difluorophenyl sulfone in order to achieve similar ion exchange capacity (ca. 2.0 mequiv/g) for all the sulfonated copolymers SPE1−4. The copolymers were of high molecular weight (Mn = 150−220 kDa, Mw = 310−695 kDa) to give tough and flexible membranes by solution casting. STEM observation revealed that small hydrophobic components (SPE3 and SPE4) induced larger water cluster than bulky hydrophobic ones (SPE1 and SPE2). The small hydrophobic components induced high proton conductivities and pr...

Preparation of organic/inorganic composite membranes using two types of polymer matrix via a sol–gel process

Organic/inorganic composite membranes were prepared using two different polymers. BPO 4 particles were introduced into polymers via an in situ sol–gel process. Pre-/post-sulfonated polymers were used to prepare composite membranes as matrix. Pre-sulfonated poly(aryl ether ketone) (SPAEK-6F) copolymer was synthesized via nucleophilic aromatic substitution. Degree of sulfonation was adjusted by the percentage of sulfonated monomer. Post-sulfonated poly(ether ether ketone) (SPEEK) was prepared using concentrated sulfuric acid as sulfonation agent. The membranes were characterized in terms of the ion-exchange capacity (IEC), proton conductivity, water uptake, AFM, SEM and their thermal properties. The SPAEK-6F plain membranes showed higher proton conductivity than that of the SPEEK plain membranes at similar water uptake or IEC due to their structural difference. SEM images of the composite membranes showed that the BPO 4 particles were homogenously dispersed in the polymer matrices and BPO 4 particle size was greatly influenced by polymer matrix. The SPAEK-6F/BPO 4 composite membranes had much smaller BPO 4 particle size than the SPEEK/BPO 4 composite membranes due to well dispersion of BPO 4 sol-like particulates in SPAEK-6F polymer solutions forming more hydrophobic/hydrophilic nanophase than SPEEK polymer solutions. The latter containing a few micrometer-scale BPO 4 particles showed higher proton conductivity than the former containing hundreds nanometer-scale BPO 4 particles at similar water uptake due to the increase in freezable water and effect of particle size.

Mechanistic evaluation of factors affecting compound loading into ion-exchange fibers

Donnan theory was applied to gain mechanistic understanding on the factors affecting drug loading process, compound-fiber affinity and subsequent release from fibrous ion-exchangers. Impact of initial loading solution concentration on fiber occupancy and loading efficiency of compounds were assessed experimentally and theoretically. Relative affinity towards the anion-exchange fibers was studied by dual loading of monovalent salicylic acid and either more lipophilic 3-isopropylsalicylic acid or divalent 5-hydroxyisophthalic acid. The effect of fiber framework on compound binding was evaluated separately for weakly and strongly basic fibers of similar ion-exchange capacities. The results revealed that loading into the ion-exchange fibers can be efficiently adjusted by the concentration of loading solution, leading to improved controllability of drug release from the fiber and minimised drug loss during the loading procedure. Ion-exchange fibers can be utilised successfully in simultaneous delivery of two ionic drugs, which offers a potential drug delivery system for synergistically active drugs. However, physicochemical characteristics of the drug (lipophilicity, valence) and framework of fibrous ion-exchanger affect the relative affinity of the drug towards the fiber, and should not be neglected when selecting appropriate ion-exchange fiber or optimising the external conditions during loading/release. Application of Donnan theory in modelling calculations supported precisely the experimental observations of compound loading (fiber occupancy and loading efficiency).

Synthesis and characterization of partially fluorinated hydrophobic–hydrophilic multiblock copolymers containing sulfonate groups for proton exchange membrane

A new hydrophobic–hydrophilic multiblock copolymer has been successfully synthesized based on the careful coupling of a fluorine terminated poly(arylene ether ketone) (6FK) hydrophobic oligomer and a phenoxide terminated disulfonated poly(arylene ether sulfone) (BPSH) hydrophilic oligomer. 19F and 1H NMR spectra were used to characterize the oligomers’ molecular weights and multiblock copolymer's structure. The comparison of the multiblock copolymer 13C NMR spectrum with that of the random copolymer showed that the transetherification side reaction was minimized in this synthesis. The morphologies of membranes were investigated by tapping mode atomic force microscopy (AFM), which showed that the multiblock membrane acidified by the high temperature method has sharp phase separation. Membrane properties like protonic conductivity, water uptake, and self-diffusion coefficient of water as a function of temperature and relative humidity (RH) were characterized for the multiblock copolymer and compared with ketone type random copolymers at similar ion exchange capacity value and Nafion ® controls. The multiblock copolymers are promising candidates for proton exchange membranes especially for applications at high temperatures and low relative humidity.

Sulfonated Poly(phthalazinones) Membranes For Direct Methanol Fuel Cell

Proton exchange membrane is one of the key parts of direct methanol fuel cell (DMFC). Sulfonated poly(phthalazinones) membranes were prepared and the feasibility of applying these membranes in DMFC was studied. The thermal degradation temperature of sulfonated poly(phthalazinone ether sulfone keton) (SPPESK) membrane was about 100 ℃ lower than that of sulfonated poly(phthalazinone ether keton) (SPPEK) and sulfonated poly(phthalazinone ether sulfone) (SPPES) membranes with similar ion-exchange capacity (IEC). These new membranes showed high proton conductivity and their methanol permeability was lower than that of Nafion membrane. DMFC performance of these new membranes was also investigated. The DMFCs with sulfonated poly(phthalazinones) membranes showed higher open circuit voltage than that using Nafion membrane as electrolyte. However, the DMFC performance of these new membranes was lower than that of Nafion membrane at high current density.

Comparative study on the preparation and properties of radiation‐grafted polymer electrolyte membranes based on fluoropolymer films

AbstractIn this study the fluoropolymers, poly(ethylene‐co‐tetrafluoroethylene) (ETFE) and poly(vinylidene fluoride) (PVDF) films, together with the radiation‐induced crosslinked polytetrafluoroethylene (cPTFE) film were compared on the basis of their preparation and properties of radiation‐grafted polymer electrolyte membranes. The polymer electrolyte membranes were prepared by radiation grafting of styrene into the base films and subsequent sulfonation. The proton conductivity and chemical stability of the three types of membranes with a similar ion exchange capacity (IEC) near 1.0 mmol/g were investigated and are discussed in detail. Although the ETFE‐based polymer electrolyte membrane was relatively more stable, its proton conductivity was lower than those of the PVDF‐ and cPTFE‐based membranes. On the other hand, the cPTFE‐based membrane showed a significantly higher proton conductivity, but its chemical stability was shorter than that of the ETFE‐based membrane. It is considered that the difference in the preparation and properties of the polymer electrolyte membranes was due to the difference in the degree of crystallinity as well as in the chemical structure of the fluoropolymer base films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1966–1972, 2007