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.     

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.     

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.     

Preparation of Nafion/sulfonated poly(phenylsilsesquioxane) nanocomposite as high temperature proton exchange membranes

Nafion/sulfonated poly(phenylmethyl silsesquioxane) (sPPSQ) composite membranes are fabricated using homogeneous dispersive mixing and a solvent casting method for direct dimethyl ether fuel cell (DDMEFC) applications operated above 100 °C. The inorganic conducting filler, sPPSQ significantly affects the characteristics in the nanocomposite membranes by functionalization with an organic sulfonic acid to PPSQ. Moreover, sPPSQ content plays an important role in membrane properties such as microstructure, proton conductivity, fuel crossover, and single cell performance test. With increasing sPPSQ content in the nanocomposite membrane, the proton conductivity increased and fuel crossover decreased. However, in a higher temperature range above 110 °C, Nafion/sPPSQ 5 wt.% composite membrane has the highest proton conductivity. Also, the DME permeability for the composite membrane with higher sPPSQ content increased sharply. The excessive sPPSQ content caused a large aggregation of inorganic fillers, leading to the deterioration of membrane properties. In this study, the optimal sPPSQ content for maximizing the DDMEFC performance was 5 wt.%. Our nanocomposite membranes demonstrated proton conductivities as high as 1.57 × 10⁻¹ S/cm at 120 °C, which is higher than that of Nafion. The cell performances were compared to Nafion/sPPSQ composite membrane with Nafion 115, and the composite membrane with sPPSQ yielded better cell performance than Nafion 115 at temperatures ranging from 100 to 120 °C and at pressures from 1 to 2 bar.     

Self-assembled polyelectrolyte multilayered films on Nafion with lowered methanol cross-over for DMFC applications

The paper is concerned with the deposition of self-assembled polyelectrolyte multilayer on Nafion membrane by layer-by-layer (LbL) technique with lowered methanol cross-over for direct methanol fuel cell (DMFC) applications. The formation of self-assembled multilayered film on Nafion was characterized by UV–vis spectroscopy and it was found that the polyelectrolyte layers growth on the Nafion surface regularly. Furthermore, the proton conductivity and methanol cross-over measurements were carried out for characterization of the LbL self-assembled composite membranes. The results showed that the concentration and pH of the polyelectrolytes significantly affect the proton conductivity and methanol barrier properties of the composite membranes. 10⁻¹ monomol polyelectrolyte concentration and pH 1.8 was found to be optimum deposition conditions considering proton conductivity and methanol permeation properties of the LbL self-assembled composite membranes. The methanol permeability of the 10 bi-layers of PAH1.8/PSS1.8 deposited LbL self-assembly composite membrane was significantly suppressed and found to be 4.41 × 10⁻⁷ cm²/s while the proton conductivity value is in acceptable range for fuel cell applications.     

Preparation of alkaline anion exchange membranes based on functional poly(ether-imide) polymers for potential fuel cell applications

A novel poly(ether-imide)-based alkaline anion exchange membrane with no free base has been prepared and characterized for its ionic conductivity in water, which is a critical metric of its applicability in a liquid-fed direct methanol fuel cell. The poly(ether-imide)-based membranes were prepared by chloromethylation, quaternization and alkalization of commercial poly(ether-imide) and the derivatives were characterized by NMR. The chemical and thermal stabilities were investigated by measuring changes of ionic conductivities when the membranes were placed in various alkaline concentrations and temperatures for 24 h. The membranes were stable at all concentrations of KOH at room temperature, but not at elevated temperatures. The membranes were stable in 1.0 M KOH solution up to 80 °C without losing membrane integrity. The measured conductivity of the formed membrane ranged from 2.28 to 3.51 × 10⁻³ S/cm at room temperature. This preliminary study indicates that functionalized poly(ether-imide) has suitable conductivity suggesting that it can be used as an alkaline anion exchange membrane in fuel cell applications.     

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.     

Electro chemical properties of porous PVdF-HFP membranes prepared with different nonsolvents

Porous poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) membranes were prepared by solvent–nonsolvent evaporation technique. Morphology and porosity of the membranes were varied with different nonsolvents and had an effect on electrochemical properties. The porous membranes were functionalized with different liquid electrolyte solutions such as p-toluene sulfonic acid/phosphoric acid/sulfuric acid. Maximum electrolyte uptake and minimal electrolyte leakage were tailored by the optimized porosity of the membranes. Thermal behavior obtained in this study ensures the complete evaporation of nonsolvents and ensures its thermal stability. The pTSA-activated PVdF-HFP/THF membrane exhibited high ionic conductivity of about 27.27 mS/cm and a lower methanol permeability in the range of 9.7 × 10⁻⁸ cm²/s. High compatibility between pTSA solution and porous PVdF-HFP polymer electrolyte membrane enhances its electro chemical behavior than that of conventional liquid electrolytes.     

Surface redox polymerized SPEEK–MO2–PANI (M = Si, Zr and Ti) composite polyelectrolyte membranes impervious to methanol

We reported sulfonated poly(ether ether ketone) (SPEEK, 61% degree of sulfonation)–metal oxides (MO₂:SiO₂, TiO₂ and ZrO₂)–polyaniline composite membranes. Metal oxides were incorporated into the swelled SPEEK membrane by sol–gel method and cured by thermal treatment. SPEEK–metal oxide membranes surfaces were modified with polyaniline (PANI) by a redox polymerization process. It was observed that water retention capacity of membrane was increased and methanol permeability was reduced due to synergetic effect of metal oxides and surface modification with polyaniline. These composite membranes showed extremely low methanol permeability (1.9–1.3 × 10⁻⁷ cm² s⁻¹), which was lower than till reported values either for SPEEK–metal oxide or SPEEK/PANI membranes. Relatively high selectivity parameter (SP) values at 343 K of these membranes, especially S–SiO₂–PANI and S–TiO₂–PANI, indicated their great advantages over Nafion117 (N117) membrane for targeting on moderate temperature applications due to the synergetic effect of MO₂ and PANI in SPEEK matrix. S–TiO₂–PANI and N117 showed comparable cell performance in direct methanol fuel cell (DMFC).     

Proton and methanol transport behavior of SPEEK/TPA/MCM-41 composite membranes for fuel cell application

This paper reports proton and methanol transport behavior of composite membranes prepared for use in the direct methanol fuel cell (DMFC). The composite membranes were prepared by embedding various proportions (10–30 wt.%) of inorganic proton conducting material (tungstophosphoric acid (TPA)/MCM-41) into sulfonated poly(ether ether ketone) (SPEEK) polymer matrix. The results indicate that the proton conductivity of the membranes increases with increasing loading of solid proton conducting material. The highest conductivity value of 2.75 mS/cm was obtained for the SPEEK composite membrane containing 30 wt.% solid proton conducting material (50 wt.% TPA in MCM-41). The methanol permeability and crossover flux were also found to increase with increasing loading of the solid proton conducting material. Lowest permeability value of 5.7 × 10⁻⁹ cm² s⁻¹ was obtained for composite membrane with 10 wt.% of the solid proton conducting material (40 wt.% TPA in MCM-41). However, all the composite membranes showed higher selectivity (ratio between the proton conductivity and the methanol permeability) compared to the pure SPEEK membrane. In addition, the membranes are thermally stable up to 160 °C. Thus, these membranes have potential to be considered for use in direct methanol fuel cell.     

In situ polymerization: A novel route for thermally stable proton-conductive membranes

In this paper, a new solvent-free route for preparing proton-conductive membranes is proposed. Flexible and fiber-supported polymer electrolyte membranes, as potential proton exchange membranes, were readily obtained by in situ polymerization of a homogenous solution that consisted of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO, polymer)–monomer mixtures of styrene (ST) and divinylbenzene (DVB), which was pre-cast onto SEFAR PETEX fibers. Factors such as the components of the casting solution and the sulfonation time, were fully investigated. The membrane structure and components were confirmed by FTIR-ATR spectra and SEM-EDXA images, and the thermal stability was examined via TGA and DrTGA. The membrane exhibited a proton conductivity of about 0.07 S/cm at 100% humidity and at room temperature, which is close to that of Nafion 117 at identical conditions (around 0.08 S/cm), whereas its thickness (about 120 μm) was less than that of Nafion 117. The tensile strength and the elongation at the break of the membrane were 31.2 MPa and 71%, respectively, which are several times higher than those of Nafion (about 6.16 MPa tensile strength and 36% elongation ratio). The dimensional change ratio of the membrane between the wet and dry states was below 3%, which is much lower than that of Nafion 117. The membrane showed a high thermal stability up to 400 °C. The method can be applied to other compatible systems of (aromatic) polymers and (aromatic) monomers.     

SPEEK/PES-C、SPEEK/SPES-C共混质子交换膜研究

通过在磺化聚醚醚酮(SPEEK,DS=61.68%)中分别混入酚酞型聚醚砜(PES-C)、磺化酚酞型聚醚砜(SPES-C,DS=53.7%)制备出SPEEK/PES-C、SPEEK/SPES-C共混质子交换膜.结果表明,共混的两种聚合物之间均具有较好的相容性.PES-C、SPES-C的混入能有效降低膜的溶胀及甲醇透过,且随着共混量的增加,这种作用越趋明显.纯SPEEK膜在75℃左右溶解,而SPEEK/PES-C(30wt%)、SPEEK/SPES-C(30wt%)共混膜在80℃时溶胀度仅为22.5%、26.32%.在室温至80℃范围内,纯SPEEK及共混膜的甲醇透过系数都在10-7cm2.s-1数量级上,远小于Nafion115膜.在饱和湿度下,温度大于90℃时,SPEEK/PES-C(20wt%)共混膜电导率超过Nafion115膜;温度大于110℃时,SPEEK/SPES-C(30wt%)共混膜电导率与Nafion115膜相当,达到0.11S.cm-1.高电导率,低透醇系数以及明显提高了的可使用温度表明该类共混膜有望在DMFC中使用.     

DMFC用PES/SPEEK共混阻醇质子交换膜

将磺化聚醚醚酮(SPEEK, 磺化度DS为68.3%)和聚醚砜(PES)两种聚合物共混制得PES/SPEEK共混膜. DSC研究表明两种聚合物之间具有较好的相容性, 因而共混膜均匀致密, 未发生大尺度相分离. PES的混入能有效降低膜的溶胀度及甲醇透过系数. 纯SPEEK 膜40 ℃时在1 mol•L−1甲醇水溶液中溶胀度达到160%, 45 ℃时就完全溶解, 而含30%(w)PES的共混膜在80 ℃时的溶胀度仅有15%. 室温下含20%−30%(w)PES的共混膜的甲醇透过系数为1×10−7 cm2•s−1左右, 比Nafion 115膜的透过系数小一个数量级. 尽管80 ℃下30%(w)PES/SPEEK共混膜的电导率与Nafion 115膜相当, 但由于共混膜的厚度比Nafion 115膜小1/3左右, 膜电阻较小, 因而其电池性能比Nafion 115膜的好.     

不同磺化度下的磺化聚醚醚酮对全钒储能液流电池性质影响的研究

本文报道了采用浓硫酸作为磺化剂,成功合成了不同磺化度下的聚醚醚酮(PEEK)膜,并深入研究了磺化条件包括磺化时间和磺化剂的用量对所获薄膜性能的影响,获得了在不同磺化度（DS）下SPPEK膜的离子交换容,含水率,机械性能,质子电导率等参数,特别测定了在全钒液流电池工作条件下钒离子(Ⅳ)渗透率,首次为该类液流储能电池使用价廉质优的质子交换膜提供了基础实验数据。室温条件下的实验结果如下：1）磺化12小时后,膜的磺化度46%,含水量为28%,钒离子(Ⅳ)选择性最佳（钒离子渗透率为1.2×10-7 cm2/min-1,是Nafion117 (2.9×10-6 cm2/min-1)的1/24）,其质子电导率只有0.02 S/cm;2）磺化96小时其磺化度达79%的膜,质子电导率达0.16 S/cm,是Nafion117 (0.10S/cm) 的1.6倍, 但其机械性能最差;3）与Nafion117膜相比,磺化在36到48小时的SPPEK膜其机械力学性能好,薄膜的钒离子渗透率、离子交换容IEC、质子导电率和含水率高,且对钒离子的选择性佳,尤其价格仅为Nafion膜的1/13,是理想的Nafion膜的代替物,可望直接应用于全钒氧化还原液流（VRB）电池中。本文还讨论了磺化时间和不同磺化剂量对膜的性质的影响。     

Sulfonated poly(ether ether ketone)–silica membranes doped with phosphotungstic acid. Morphology and proton conductivity

Sulfonated poly(ether ether ketone) (SPEEK)–silica membranes doped with phosphotungstic acid (PWA) are presented. The silica is generated in situ via the water free sol–gel process of polyethoxysiloxane (PEOS), a liquid hyperbranched inorganic polymer of low viscosity. At 100 °C and 90% RH the membrane prepared with PEOS (silica content = 20 wt%) shows two times higher conductivity than the pure SPEEK. The addition of small amounts of PWA (2 wt% of the total solid content) introduced in the early stage of membrane preparation brings to a further increase in conductivity (more than three times the pure SPEEK). During membrane formation PWA and the sulfonic acid groups of SPEEK act as catalysts in the conversion of PEOS in silica. Once the membranes are formed, PWA is incorporated in the silica network and acts as proton conductivity enhancer. The correlation between morphology and proton conductivity allows establishing the optimal doping level and preparation procedure. The morphology is studied by transmission electron microscopy (TEM) while the proton conductivity is measured by impedance spectroscopy (IS). The direct methanol fuel cell performance is also investigated.     

Improving anion exchange membranes for DMAFCs by inter-crosslinking CPPO/BPPO blends

New anion exchange membranes are prepared by heat-treating the blend base membranes of chloroacetylated poly(2,6-dimethyl-1,4-phenyleneoxide)(CPPO)/bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO). A partially inter-crosslinked structure can be formed therein via a Friedel–Crafts reaction without adding any crosslinking reagent or catalyst. FT-IR and NMR analyses are used to confirm this inter-crosslinking structure and quantify the crosslinking distribution. Physical properties, such as toughness and thermal stability, are enhanced remarkably due to this heat treatment. Furthermore, the final membranes exhibit a high hydroxyl conductivity (up to 0.032 S cm⁻¹ at 25 °C) and extremely low methanol permeability (1.26–1.04 × 10⁻⁷ cm² s⁻¹), which match the requirements for application in low temperature direct methanol alkaline fuel cells (DMAFCs).     

Preliminary evaluation of sulfonated poly(ether ether ketone)/monoethanolamine/adipic acid composite membranes for direct methanol fuel cell applications

A series of sulfonated poly(ether ether ketone)/monoethanolamine/adipic acid (SPEEK/MEA/AA) composite membranes are prepared and investigated to assess their possibility as proton exchange membranes in direct methanol fuel cells (DMFCs). A preliminary evaluation shows that introducing MEA and AA into SPEEK matrix decreases the thermal stability of membrane. However, the degradation temperatures are still above 260 °C, satisfying the requirement for fuel cell operation. Compared with the pure SPEEK membrane, the composite membranes exhibit not only lower water uptake and swelling ratios but also better mechanical property and oxidative stability. Noticeably, the methanol diffusion coefficient of the composite membranes decrease significantly from 3.15 × 10^?6 to 0.76 × 10^?6 cm²/s with increasing MEA and AA content, accompanied by only a small sacrifice in proton conductivity. Although both the methanol diffusion coefficient and the proton conductivity of composite membranes are lower than those of pure SPEEK and Nafion® 117 membranes, their selectivity (conductivity/methanol diffusion coefficient) are higher. In addition, the composite membranes show excellent stability in aqueous methanol solution. The good thermal and chemical stability, low swelling ratio, excellent mechanical property, low methanol diffusion coefficient, and high selectivity make the use of these composite membranes in DMFCs quite attractive. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2871–2879, 2007     

Preparation and characterization of fluorine-containing polybenzimidazole/imidazole hybrid membranes for proton exchange membrane fuel cells

Polybenzimidazole (PBI)/imidazole (Im) hybrid membranes were prepared from an organosoluble, fluorine-containing PBI with Im. The thermal decomposition of the PBI/Im hybrid membranes occurred at about 160 °C. The conductivities of the acid doped PBI/Im hybrid membranes increased with both the temperature and the Im content. The conductivity of acid doped PBI-40Im (molar ratio of Im/PBI = 40) reached 3.1 × 10⁻³ (S/cm) at 160 °C. The proton conductivities of PBI/Im hybrid membranes were over 2 × 10⁻³ (S/cm) at 90 °C and 90% relative humidity. The addition of Im could reduce the mechanical properties and methanol barrier ability of the PBI membranes.     

Naphthalene‐based poly(arylene ether ketone) copolymers containing sulfobutyl pendant groups for proton exchange membranes

A new monomer 1,5‐bis(4‐fluorobenzoyl)‐2,6‐dimethoxynaphthalene (DMNF) was prepared and further polymerized to form naphthalene‐based poly(arylene ether ketone) copolymers containing methoxy groups (MNPAEKs). The side‐chain‐type sulfonated naphthalene‐based poly(arylene ether ketone) copolymers (SNPAEKs) were obtained by demethylation and sulfobutylation. Flexible and tough membranes with reasonably high mechanical strength were prepared. The SNPAEKs membrane showed anisotropic membrane swelling with larger swelling in thickness than in plane. Transmission electron microscopy (TEM) analysis revealed clear nanophase separated structure of SNPAEKs membranes, which composed of hydrophilic side chain and hydrophobic main‐chain domains. Proton conductivities of copolymers increased gradually with increase in temperature. The highest conductivity of 0.179 S/cm was obtained for SNPAEK‐80 (IEC = 1.82 mequiv/g) at 80 °C, which is higher than that of Nafion117 (0.146 S/cm). The SNPAEKs membranes exhibit the methanol permeability in the range of 3.42 × 10^?8?4.49 × 10^?7 cm²/s, which are much lower than that of Nafion117. They could be the promising materials as alternative to Nafion membrane for direct methanol fuel cells applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47:5772–5783, 2009     

Sulfonated poly(ether ether ketone)/poly(vinylpyrrolidone) acid–base polymer blends for direct methanol fuel cell application

Acid–base polymer blends for polymer electrolyte membranes have been prepared by blending sulfonated poly(ether ether ketone) (SPEEK) with poly(vinylpyrrolidone) (PVP) to reduce methanol uptake and to decrease methanol permeability while maintaining high proton conductivity. The acid‐base interaction occurring on the sulfonic acid group and on the tertiary amide group was characterized by FTIR and DMA. As the composition of PVP lowered than 20 wt % in the blends, the acid–base interaction causes great reduction on methanol uptake and the methanol permeability; however, the proton conductivity is still high. In this work, membrane–electrode assemblies (MEAs) have been prepared for direct methanol fuel cell (DMFC) from both blend membrane and Nafion 117. DMFC single cell performance was also evaluated. Results confirmed that SPEEK (with the degree of sulfonation (DS) = 69%) blended with PVP (M_n = 1,300,000) with a ratio of 80/20 (w/w) exhibits higher open‐circuit voltages (OCV) and lower polarization loss than those of Nafion 117. These acid–base blends will be suitable for DMFC application. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 565–572, 2006