Improvement of electrochemical performances of sulfonated poly(arylene ether sulfone) via incorporation of sulfonated poly(arylene ether benzimidazole)

In the present study, modified acid–base blend membranes were fabricated via incorporation of sulfonated poly(arylene ether benzimidazole) (SPAEBI) into sulfonated poly(arylene ether sulfone) (SPAES). These membranes had excellent methanol-barrier properties in addition to an ability to compensate for the loss of proton conductivity that typically occurs in general acid–base blend system. To fabricate the membranes, SPAEBIs, which served as amphiphilic polymers with different degrees of sulfonation (0–50 mol%), were synthesized by polycondensation and added to SPAES. It resulted in the formation of acid–amphiphilic complexes such as [PAES-SO₃]⁻⁺[H-SPAEBI] through the ionic crosslinking, which prevented SO₃H groups in the complex from transporting free protons in an aqueous medium, contributing to a reduction of ion exchange capacity values and water uptake in the blend membranes, and leading to lower methanol permeability in a water–methanol mixture. Unfortunately, the ionic bonding formation was accompanied by a decrease of bound water content and proton conductivity, although the latter problem was solved to some extent by the incorporation of additional SO₃H groups in SPAEBI. In the SPAES–SPAEBI blend membranes, enhancement of proton conductivity and methanol-barrier property was prominent at temperatures over 90 °C. The direct methanol fuel cell (DMFC) performance, which was based on SPAES–SPAEBI-50–5, was 1.2 times higher than that of Nafion^® 117 under the same operating condition.     

Composite membranes based on a sulfonated poly(arylene ether sulfone) and proton-conducting hybrid silica particles for high temperature PEMFCs

The organic-inorganic composite membranes are prepared by inserting poly(styrene sulfonate)-grafted silica particles into a polymer matrix of sulfonated poly(arylene ether sulfone) copolymer. The first step consisted in using atom transfer radical polymerization method to prepare surface-modified silica particles grafted with sodium 4-styrenesulfonate, referred to as PSS-g-SiO₂. Ion exchange capacities up to 2.4 meq/g are obtained for these modified silica particles. In a second step, a sulfonated poly(arylene ether sulfone) copolymer is synthesized via nucleophilic step polymerization of sulfonated 4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone and phenolphthalin monomers in the presence of potassium carbonate. The copolymer is blended with various amounts of silica particles to form organic-inorganic composite membranes. Esterification reaction is carried out between silica particles and the sulfonated polymer chains by thermal treatment in the presence of sodium hypophosphite, which catalyzed the esterification reaction. The water uptake, proton conductivity, and thermal decomposition temperature of the membranes are measured. All composite membranes show better water uptake and proton conductivity than the unmodified membrane. Moreover, the membranes are tested in a commercial single cell at 80 °C and 120 °C in humidified H₂/air under different relative humidity conditions. The composite membrane containing 10%(w/w) of PSS-g-SiO₂ particles, which have ester bonds between polymer chains and silica particles, showed the best performance of 690 mA cm⁻² at 0.6 V, 120 °C and 30 %RH, even higher than the commercial Nafion^® 112 membrane.     

Synthesis and properties of novel HMS-based sulfonated poly(arylene ether sulfone)/silica nano-composite membranes for DMFC applications

Novel 4,4′-dihydroxy-α-methylstilbene (HMS)-based sulfonated poly(arylene ether sulfone) with sulfonic acid composition ranging from 10 to 40 mol% was synthesized via nucleophilic step polymerization of 4,4′-dihydroxy-α-methylstilbene, 4,4′-dichloro-3,3′-disulfonic acid diphenylsulfone and 4,4′-dichlorodiphenylsulfone and blended with silica sol to form organic/inorganic nano-composite membranes. The organic/inorganic nano-composite copolymers produced show a high glass transition temperature and thermal decomposition temperatures from 318 to 451 °C. The copolymers present appropriate toughness during the membrane process. The equilibrium water uptake and proton conductivity of the obtained organic/inorganic nano-composite membranes were measured as functions of temperature, degree of sulfonation and silica content. In general, the water uptake increased from 8 to 37 wt.%, and the proton conductivity of the organic/inorganic nano-composite membranes increased from 0.003 to 0.110 S cm⁻¹ as the degree of sulfonation increased from 10 to 40 mol%, the silica content increased from 3 to 10 wt.%, and the temperature increased from 30 to 80 °C. The single cell performance of the 40 mol% organic/inorganic nano-composite membrane with various silica contents ranged from 11 to 13 mW cm⁻² at 80 °C, and the power density was higher than Nafion^® 117. Including the thermal properties, swelling, conductivity and single cell performance, the nano-composite membranes are able to satisfy the requirements of proton exchange membranes for direct methanol fuel cells (DMFC).     

Sulfonated poly(arylene ether sulfone) as a methanol-barrier layer in multilayer membranes for direct methanol fuel cells

Novel poly(arylene ether sulfone) copolymers containing different amount of pendant sulfonic acid groups have been synthesized by an aromatic substitution polymerization reaction. The properties of the synthesized sulfonated poly(diphenylsulfone-diphenol) (SDPS-DP) copolymers depend on the sulfonic acid group content in the copolymers. Although all the copolymers show good thermal stability, low liquid uptake, and low methanol crossover, they exhibit lower proton conductivity than Nafion or sulfonated poly(ether ether ketone) (SPEEK). Taking advantage of the low methanol crossover, multilayer membranes consisting of the SDPS-DP copolymer as a methanol-barrier center layer and SPEEK as the proton-conducting outer layers have been fabricated and characterized. The SPEEK/SDPS-DP-60/SPEEK multilayer membranes with an optimized center layer thickness are found to exhibit better performance and higher power density in DMFC than plain SPEEK and Nafion 115 membranes.     

Sulfonated poly(arylene ether sulfone)/disulfonated silsesquioxane hybrid proton conductors for proton exchange membrane fuel cell application

Fuel cell operating at high temperature and low humidity conditions is in urgent demand. Low glass transition temperature, high cost, and high humidity dependence of commercial membranes such as Nafion, however, are major obstacles to commercialization. Sulfonated poly (arylene ether sulfone) is a promising polymer that may show a breakthrough in this respect as it shows high thermal stability and mechanical strength while maintaining performance and cost competitiveness. Its relatively high dependence on humidity levels, however, is still an obstacle that needs to be tackled. The incorporation of silsesquioxane particles with disulfonated naphthol (NSi) functionalization is designed to increase the number of proton conducting moieties in the polymer matrix thus aiding proton transport. The incorporation of NSi has drastically improved performance especially at lower humidity conditions. Although current density of 5 wt.% NSi hybrid membrane shows a 2.0% increase in performance at 80°C/100 R.H.% that at 120 °C/30 R.H.% shows a 200% rise in current density at 0.7 V compared to that of pristine membranes. In addition, the evenly distributed silsesquioxane particles physically reduce fuel crossover values by 33.4%.     

Quinoxaline-based crosslinked membranes of sulfonated poly(arylene ether sulfone)s for fuel cell applications

A series of crosslinkable sulfonated poly(arylene ether sulfone)s (SPAESs) were synthesized by copolymerization of 4,4′-biphenol with 2,6-difluorobenzil and 3,3′-disulfonated-4,4′-difluorodiphenyl sulfone disodium salt. Quinoxaline-based crosslinked SPAESs were prepared via the cyclocondensation reaction of benzil moieties in polymer chain with 3,3′-diaminobenzidine to form quinoxaline groups acting as covalent and acid-base ionic crosslinking. The uncrosslinked and crosslinked SPAES membranes showed high mechanical properties and the isotropic membrane swelling, while the later became insoluble in tested polar aprotic solvents. The crosslinking significantly improved the membrane performance, i.e., the crosslinked membranes had the lower membrane dimensional change, lower methanol permeability and higher oxidative stability than the corresponding precursor membranes, with keeping the reasonably high proton conductivity. The crosslinked membrane (CS1-2) with measured ion exchange capacity of 1.53 mequiv. g⁻¹ showed a reasonably high proton conductivity of 107 mS/cm with water uptake of 48 wt.% at 80 °C, and exhibited a low methanol permeability of 2.3 × 10⁻⁷ cm² s⁻¹ for 32 wt.% methanol solution at 25 °C. The crosslinked SPAES membranes have potential for PEFC and DMFCs.     

Sulfonated poly(arylene ether sulfone) membranes blended with hydrophobic polymers for direct methanol fuel cell applications

In this paper, proton exchange membranes for direct methanol fuel cells were prepared by blending sulfonated poly(arylene ether sulfone) with poly (vinylidene fluoride-co-hecafluoropropylene)(PVdF-HFP) and polyethersulfone (PES) to decrease methanol permeability while maintaining high proton conductivity. The content of the second polymer, such as PES and PVdF, in the blend membranes was controlled at 10–40 wt% based on SPAES. In order to investigate the effects of the second polymer content in the blended membranes, parameters of the prepared membranes related to fuel cell performance were characterized, including their morphology, mechanical properties, methanol permeability, and proton conductivity. Surface roughness of the blend membrane was increased by the introduction of a hydrophobic polymer. Mechanical properties of the PES/SPAES blend membrane were improved owing to interaction between the sulfonic acid groups in SPAES and PES. However, the tensile strength of the PVdF/SPAES blend membrane was decreased by due to the poor compatibility of SPAES and PVdF. The methanol permeability in the blended membranes decreased with increasing content of PES and PVdF. The SPAES/PES blend membranes exhibited good proton conductivity and lower methanol permeability than the SPAES membrane. The SVdF15 blend membrane showed the highest selectivity due to the absence of methanol crossover and a small decrease of proton conductivity. These blend membranes are suitable for DMFC applications.     

Cross-linked miscible blend membranes of sulfonated poly(arylene ether sulfone) and sulfonated polyimide for polymer electrolyte fuel cell applications

Cross-linked miscible blend (CMB) membranes were prepared from sulfonated poly(arylene ether sulfone) (SPAES) and sulfonated polynaphthalimide (SPI). They were transparent and insoluble in solvents. They showed the intermediate properties between SPAES and SPI concerning mechanical strength, water uptake, membrane swelling and proton conductivity. As for membrane swelling and proton conductivity, SPAES was almost isotropic, whereas SPI was highly anisotropic. CMB membranes were moderately anisotropic and had the advantages of the smaller in-plane membrane swelling and the larger through-plane conductivity compared to SPAES and SPI, respectively. Polymer electrolyte fuel cell performance of CMB2 membrane with an equal weight ratio of SPAES/SPI and an ion exchange capacity (IEC) of 1.74 meq g⁻¹ was investigated, compared to SPI membrane (R1) with a slightly higher IEC of 1.86 meq g⁻¹. At 90 °C, 0.1 MPa and relatively high humidification of 82/68% RH or 0.2 MPa and low humidification of 50-30% RH, CMB2 showed the reasonably high cell performances. At 110 °C and 50-33% RH, the cell performance was fairly high only at a high pressure of 0.3 MPa, but low at 0.2-0.15 MPa. At these conditions, the cell performance was better for CMB2 than for R1 due to the more effective back-diffusion of water formed at cathode into membrane. CMB2 showed the fairly high PEFC durability at 110 °C.     

Synthesis and characterization of crosslinked sulfonated poly(arylene ether sulfone) membranes for high temperature PEMFC applications

Sulfonated poly(arylene ether sulfone) copolymers containing carboxyl groups are prepared by an aromatic substitution polymerization reaction using phenolphthalin, 3,3′-disulfonated-4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone and 4,4′-bisphenol A as polymer electrolyte membranes for the development of high temperature polymer electrolyte membrane fuel cells. Thin, ductile films are fabricated by the solution casting method, which resulted in membranes with a thickness of approximately 50 μm. Hydroquinone is used to crosslink the prepared copolymer in the presence of the catalyst, sodium hypophosphite. The synthesized copolymers and membranes are characterized by ¹H NMR, FT-IR, TGA, ion exchange capacity, water uptake and proton conductivity measurements. The water uptake and proton conductivity of the membranes are decreased with increasing the degree of crosslinking which is determined by phenolphthalin content in the copolymer (0-15 mol%). The prepared membranes are tested in a 9 cm² commercial single cell at 80 °C and 120 °C in humidified H₂/air under different relative humidity conditions. The uncrosslinked membrane is found to perform better than the crosslinked membranes at 80 °C; however, the crosslinked membranes perform better at 120 °C. The crosslinked membrane containing 10 mol% of phenolphthalin (CPS-PP10) shows the best performance of 600 mA cm⁻² at 0.6 V and better performance than the commercial Nafion^® 112 (540 mA cm⁻² at 0.6 V) at 120 °C and 30 % RH.     

4-Aminopyridine grafted sulfonated poly(arylene ether ketone sulfone) proton exchange membrane with high relative selectivity for fuel cells

A series of sulfonated poly(arylene ether ketone sulfone)s polymer having a degree of sulfonation of 80% and a carboxyl group in the side chain (C-SPAEKS) were prepared by polycondensation. The 4-aminopyridine grafted sulfonated poly(arylene ether ketone sulfone)s polymer membranes (SPPs) were prepared by amidation reaction with the carboxyl group to immobilize 4-aminopyridine on the side chain. The ¹H NMR results and Fourier transform infrared of SPP membranes demonstrated the successful grafting of the 4-aminopyridine. Proton conductivity, water absorption, swelling ratio, and thermal stability of different proportions of SPP membranes were investigated under the different conditions. With the increase of pyridine grafting content, the methanol permeability coefficient of the membrane decreased significantly from 8.17 × 10⁻⁷ cm²s⁻¹ to 8.92 × 10⁻⁸ cm²s⁻¹ at 25 °C. And, the proton conductivity and relative selectivity of the membrane were positively correlated with the grafted pyridine content. Among them, the SPP-4 membrane exhibited the highest proton conductivity of 0.088 Scm⁻¹ at 100 °C. The relative selectivity increased from 4.73 × 10⁴ S scm⁻³ to 9.84 × 10⁴ S scm⁻³.     

Novel modification method to prepare crosslinked sulfonated poly(ether ether ketone)/silica hybrid membranes for fuel cells

Crosslinked organic-inorganic hybrid membranes are prepared from hydroxyl-functionalized sulfonated poly(ether ether ketone) (SPEEK) and various amounts of silica with the aims to improve dimensional stability and methanol resistance. The partially hydroxyl-functionalized SPEEK is prepared by the reduction of some benzophenone moieties of SPEEK into the corresponding benzhydrol moieties which is then reacted with (3-isocyanatopropyl)triethoxysilane (ICPTES) to get a side chained polymer bearing triethoxysilyl groups. These groups are subsequently co-hydrolyzed with tetraethoxysilane (TEOS) and allow the membrane to form a crosslinked network via a sol-gel process. The obtained hybrid membranes with covalent bonds between organic and inorganic phases exhibit much lower methanol swelling ratio and water uptake. With the increase of silica content, the methanol permeability coefficient of the hybrid membranes decreases at first and then increased. At silica content of about 6 wt.%, the methanol permeability coefficient reaches a minimum of 7.15 × 10⁻⁷ cm² s⁻¹, a 5-fold decrease compared with that of the pristine SPEEK. Despite the fact that the proton conductivity is decreased to some extent as a result of introduction of the silica, the hybrid membranes with silica content of 4-8 wt.% shows higher selectivity than Nafion117.     

Crosslinked sulfonated poly(arylene ether sulfone) membranes for fuel cell application

A series of sulfonated poly(arylene ether sulfone) with photocrosslinkable moieties is successfully synthesized by direct copolymerization of 3,3′-disulfonated 4,4′-difluorodiphenyl sulfone (SDFDPS) and 4,4′-difluorodiphenyl sulfone (DFDPS) with 4,4′-biphenol (BP) and 1,3-bis-(4-hydroxyphenyl) propenone (BHPP). The content of crosslinkable moieties in the polymer repeat unit is controlled from 0 to 10 mol% by changing the monomer feed ratio of BHPP to BP. The polymer membranes can be crosslinked by irradiating UV with a wavelength of 365 nm. From FT-IR analysis, it can be identified that UV crosslinking mainly occurs due to the combination reaction of radicals that occurs in conjunction with the breaking of the carbon–carbon double bonds (–CH = CH-) of the chalcone moieties in the backbone. Consequently, a new bond is created to form cyclobutane. The crosslinked membranes show less water uptake, a lower level of methanol permeability, and good thermal and mechanical properties compared to pristine (non-crosslinked) membranes while maintaining a reasonable level of proton conductivity. Finally, the fuel cell performance of the crosslinked membranes is comparable to that of the Nafion 115 membrane, demonstrating that these membranes are promising candidates for use as polymer electrolyte membranes in DMFCs.     

Sulfonated titania submicrospheres-doped sulfonated poly(ether ether ketone) hybrid membranes with enhanced proton conductivity and reduced methanol permeability

Sulfonated titania submicrospheres (TiO₂-SO₃H) prepared through a facile chelation method are incorporated into sulfonated poly(ether ether ketone) (SPEEK) to fabricate organic-inorganic hybrid membranes with enhanced proton conductivity and reduced methanol permeability for potential use in direct methanol fuel cells (DMFCs). The pristine titania submicrospheres (TiO₂) with a uniform particle size are synthesized through a modified sol-gel method and sulfonated using 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt as the sulfonation reagent. The sulfonation process is confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). The hybrid membranes are systematically characterized in terms of thermal property, mechanical property, ionic exchange capacity (IEC), swelling behavior, and microstructural features. The methanol barrier property and the proton conductivity of the SPEEK/TiO₂-SO₃H hybrid membranes are evaluated. The presence of the fillers reduces methanol crossover through the membrane. Compared with the unsulfonated TiO₂-doped membranes, the TiO₂-SO₃H-doped ones exhibit higher proton conductivity due to the additional sulfonic acid groups on the surface of TiO₂. The hybrid membrane doped with 15 wt.% TiO₂-SO₃H submicrospheres exhibits an acceptable proton conductivity of 0.053 S cm⁻¹ and a reduced methanol permeability of 4.19 × 10⁻⁷ cm² s⁻¹.     

A facile,effective thermal crosslinking to balance stability and proton conduction for proton exchange membranes based on blend sulfonated poly(ether ether ketone)/sulfonated poly(arylene ether sulfone)

The development of hydrocarbon polymer electrolyte membranes with high proton conductivities and good stability as alternatives to perfluorosulfonic acid membranes is an ongoing research effort. A facile and effective thermal crosslinking method was carried out on the blended sulfonated poly (ether ether ketone)/poly (aryl ether sulfone) (SPEEK/SPAES) system. Two SPEEK polymers with ion exchange capacities (IECs) of 1.6 and 2.0 mmol g^?1 and one SPAES polymer (2.0 mmol g^?1) were selected to create different blends. The effect of thermal crosslinking on the fundamental properties of the membranes, especially their physicochemical stability and electrochemical performance, were investigated in detail. The homogeneous and flexible thermally-crosslinked SPEEK/SPAES membranes displayed excellent mechanical toughness (27–46 Mpa), suitable water uptake (<60%), high dimensional stability (swelling ratio < 15%) and large proton conductivity (>120 mS cm^?1) at 80 °C. The thermal crosslinking membranes also show significantly enhanced hydrolytic (<2.5%) and oxidative stability (<2%). Fuel cell with t-SPEEK/SPAES (1:2:2) membrane achieves a power density of 665 mW cm^?2 at 80 °C.     

Sulfonated poly(ether ether ketone) membranes with sulfonated graphene oxide fillers for direct methanol fuel cells

Sulfonated organosilane functionalized graphene oxides (SSi-GO) synthesized through the grafting of graphene oxide (GO) with 3-mercaptopropyl trimethoxysilane and subsequent oxidation have been used as a filler in sulfonated poly(ether ether ketone) (SPEEK) membranes. The incorporation of SSi-GOs greatly increases the ion-exchange capacity (IEC), water uptake, and proton conductivity of the membrane. With well-controlled contents of SSi-GOs, the composite membranes exhibit higher proton conductivity and lower methanol permeability than Nafion^® 112 and Nafion^® 115, making them particularly attractive as proton exchange membranes (PEMs) for direct methanol fuel cells (DMFC). The composite membrane with optimal SSi-GOs content exhibit over 38 and 17% higher power densities, respectively, than Nafion^® 112 and Nafion^® 115 membranes in DMFCs, offering the possibilities to reduce the DMFC membrane cost significantly while keeping high-performance.     

Sulfonated poly(arylene ether)s based proton exchange membranes for fuel cells

During the past decade proton exchange membrane fuel cells (PEMFCs) as one kind of the potential clean energy sources for electric vehicles and portable electronic devices are attracting more and more attentions. Although Nafion® membranes are considered as the benchmark of proton exchange membranes (PEMs), the drawbacks of Nafion® membranes restrict the commercialization in the practical application of PEMFCs. As of today, the attention is to focus on developing both high-performance and low-cost PEMs to replace Nafion® membranes. In all of these PEMs, sulfonated poly(arylene ether ketone)s (SPAEKs) and sulfonated poly(arylene ether sulfone)s (SPAESs) are the most promising candidates due to their excellent performance and low price. In this review, the efforts of SPAEK and SPAES membranes are classified and introduced according to the chemical compositions, the microstructures and configurations, as well as the composites with polymers and/or inorganic fillers. Specifically, several perspectives related to the modification and composition of SPAESs and SPAEKs are proposed, aiming to provide the development progress and the promising research directions in this field.     

Synthesis and properties of sulfonated poly(arylene ether ketone sulfone) containing amino groups/functional titania inorganic particles hybrid membranes for fuel cells

In this work, the organic-inorganic hybrid membranes were prepared. The synthesis and properties of the hybrid membranes were investigated. The sulfonated poly(arylene ether ketone sulfone) containing amino groups (Am-SPAEKS) was synthesized by nucleophilic polycondensation. The sol-gel method was used to prepared functional titania inorganic particles (L-TiO₂). The ¹H NMR and FT-IR were performed to verified the structure of Am-SPAEKS and L-TiO₂. The organic-inorganic hybrid membranes showed both good thermal stabilities and mechanical properties than that of Am-SPAEKS. The L-Am-15% membrane exhibited the highest Young's modulus (2262.71 MPa) and Yield stress (62.09 MPa). The distribution of L-TiO₂ particles was revealed by SEM. Compared to Am-SPAEKS, the hybrid membranes showed higher proton conductivities. The L-Am-15% exhibited the highest proton conductivity of 0.0879 S cm⁻¹ at 90 °C. The results indicate that the organic-inorganic hybrid membranes have potential for application in proton exchange membrane fuel cells.     

Synthesis and characterization of sulfonated poly(arylene ether ketone ketone sulfone) membranes for application in proton exchange membrane fuel cells

A series of sulfonated poly(arylene ether ketone ketone sulfone) (SPAEKKS) copolymers were synthesized by nucleophilic polycondensation. The copolymers exhibit good thermal and oxidative stabilities, all the SPAEKKS copolymers can be cast into tough membranes. Ionic exchange capacities (IEC), water uptake properties, thermal stabilities, methanol diffusion coefficients and proton conductivities were thoroughly studied. Also the microstructures of the membranes were investigated by TEM. The proton conductivity of the SPAEKKS-4 membrane is close to that of Nafion-117 at 80 °C. The methanol diffusion coefficient of the membrane is much lower than that of Nafion-117 under the same testing conditions. The SPAEKKS membranes are promising in proton exchange membranes fuel cell (PEMFC) application.     

Alkyl chain modified sulfonated poly(ether sulfone) for fuel cell applications

A new alkyl chain modified sulfonated poly(ether sulfone) (mPES) was synthesized and formed into membranes. The MEAs were tested in the PEMFC and evaluated systematically in the DMFC by varying the methanol concentration from 0.5 to 5.0 M at 60 °C and 70 °C. The synthesized mPES copolymer has been characterized by nuclear magnetic resonance spectroscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. The proton conductivity of the resulting membrane is higher than the threshold value of 10⁻² S cm⁻¹ at room temperature for practical PEM fuel cells. The membrane is insoluble in boiling water, thermally stable until 250 °C and shows low methanol permeability. In the H₂/air PEMFC at 70 °C, a current density of 600 mA cm⁻² leads to a potential of 637 mV and 658 mV for 50 μm thick mPES 60 and Nafion NRE 212, respectively. In the DMFC, mPES 60's methanol crossover current density is 4 times lower than that for Nafion NRE 212, leading to higher OCV values and peak power densities. Among all investigated conditions and materials, the highest peak power density of 120 mW cm⁻² was obtained with an mPES 60 based MEA at 70 °C and a methanol feed of 2 M.     

Nafion/nitrated sulfonated poly(ether ether ketone) membranes for direct methanol fuel cells

Sulfonated poly(ether ether ketone)s (SPEEKs) are substituted on the main chain of the polymer by nitro groups and blended with Nafion^® to attain composite membranes. The sulfonation, nitration and blending are achieved with a simple, inexpensive process, and the blended membranes containing the nitrated SPEEKs reveal a liquid-liquid phase separation. The blended membranes have a lower water uptake compared to recast Nafion^®, and the methanol permeability is reduced significantly to 4.29 × 10⁻⁷-5.34 × 10⁻⁷ cm² s⁻¹ for various contents of nitrated SPEEK for S63N17, and 4.72 × 10⁻⁷-7.11 × 10⁻⁷ cm² s⁻¹ for S63N38, with a maximum proton conductivity of ∼0.085 S cm⁻¹. This study examines the single-cell performance at 80 °C of Nafion^®/nitrated SPEEK membranes with various contents of nitrated SPEEK and a degree of nitration of 23-25 mW cm⁻² for S63N17 and 24-29 mW cm⁻² for S63N38. Both the power density and open circuit voltage are higher than those of Nafion^® 115 and recast Nafion^®.