Sulfonated poly(fluorene-co-sulfone)ether membranes containing perfluorocyclobutane groups for fuel cell applications

A new class of sulfonated poly(fluorene-co-sulfone)ether membranes containing perfluorocyclobutane (PFCB) groups were synthesized and characterized in terms of their electrochemical properties as proton exchange membranes for fuel cells. Two monomers, 9,9-bis(4-trifluorovinyloxyphenyl)fluorene and 4,4′-sulfonyl-bis(trifluorovinyloxy)biphenyl were synthesized and statistically copolymerized by thermal [2π + 2π] cycloaddition to yield a series of polymers containing 0–60 mol% of fluorenyl content (PFS-X). The copolymers were then sulfonated using chlorosulfonic acid to afford five kinds of ionomers with different sulfonation levels (SPFS-X), which were cast into membranes and analyzed in terms of electrochemical properties. It was found that the ion exchange capacity (IEC), water uptake, proton conductivity and methanol permeability values of SPFS-X increased with the increment of the sulfonated fluorenyl content. The proton conductivities of SPFS-50 and -60 with high IECs and water uptake values were higher than those of Nafion-115 between 25 and 80 °C. The methanol permeability of SPFS-X was considerably lower than that of Nafion-115.     

Development and Characterization of Highly Conducting Nonfluorinated Di and Triblock Copolymers for Polymer Electrolyte Membranes

To achieve stable polymer electrolyte membranes (PEMs) with efficient ionic nano-channels, novel fully aromatic AB or ABA copolymers composed of poly(fluorenyl ether sulfone biphenyl)s (PFESBs) and poly(arylene ether sulfone)s (PAESs) were synthesized via polymerization and post-sulfonation methods, and were explored as fuel cell membranes. The structural analysis of synthesized copolymers and the corresponding membranes were ascertained by gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and ¹H nuclear magnetic resonance (NMR) techniques. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis showed that the prepared membranes were thermally stable, so that elevated temperature fuel cell operation would be possible. High hydrophilic and hydrophobic nano-phase separation and obvious ionic aggregate block morphology was observed in both triblock and diblock copolymers in atomic force microscopy (AFM) phase images, which may be highly related to their proton transport ability. A sulfonated AB diblock copolymer membrane with an ion-exchange capacity (IEC) of 2.06 meq g^?1 has a maximum proton conductivity of 184 mS cm^?1, which is higher than that of a perfluorosulfonic acid membrane under the same measurement conditions.     

Sulfonated polybenzimidazoles: Proton conduction and acid–base crosslinking

A 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     

High performance direct methanol fuel cells based on acid–base blend membranes containing benzotriazole

Novel acid–base blend membranes consisting of acidic sulfophenylated poly(ether ether ketone ketone) (Ph-SPEEKK) and various amounts of basic polysulfone tethered with 5-amino-benzotriazole (PSf-BTraz) have been prepared and characterized. The blend membranes show higher proton conductivity and lower liquid uptake and dimensional swelling compared to plain Ph-SPEEKK and sulfonated poly(ether ether ketone) (SPEEK) membranes. The Ph-SPEEKK/PSf-BTraz blend membranes with optimized basic polymer contents exhibit lower methanol crossover and higher performance with improved stability in direct methanol fuel cells (DMFC) at various methanol concentrations (1–10 M) than plain Ph-SPEEK and Nafion-115 membranes.     

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.     

Synthesis and properties of poly(ether ether ketone)-block-sulfonated polybutadiene copolymers for PEM applications

A novel series of sulfonated block copolymers were successfully synthesized by the condensation of modified poly(ether ether ketone) (PEEK) and polybutadiene (PB), followed by the selective post-sulfonation of PB blocks using acetyl sulfate as the sulfonating reagent. The sulfonic acid groups were only attached onto PB segments due to the high reactivity of double bonds to sulfonating reagent. The degree of sulfonation was controlled by changing the feed ratio of sulfonating reagent to block copolymer. PEEK-b-sPB could be easily cast into flexible and transparent membranes. The obtained membranes exhibited good thermal stability and satisfied mechanical properties. Tensile test showed the incorporation of sulfonate groups into PB blocks resulted in an increase in tensile strength and a decrease in elongation at break. TEM images revealed the existence of ionic spherical domains with the average sizes of 50-100 nm. Some of these small domains further aggregated to form large hydrophilic regions. The proton conductivity values were measured in the range of 10⁻² S/cm in water and increased with increasing IEC and temperature.     

Poly(arylene ether) ionomers containing sulfofluorenyl groups: Effect of electron-withdrawing groups on the properties

For polymer electrolyte membrane fuel membrane cell (PEMFC) applications, the effect of electron-withdrawing groups on the properties of sulfonated poly(arylene ether) (SPE) ionomer membranes was investigated. A series of poly(arylene ether)s containing fluorenyl groups and electron-withdrawing groups (sulfone, nitrile, or fluorine) was synthesized, which were sulfonated with chlorosulfonic acid using a flow reactor to obtain the title ionomers. The ionomers had high molecular weight (M_n > 77 kDa, M_w > 238 kDa) and gave tough, ductile membranes by solution casting. The ion exchange capacity (IEC) of the membranes ranged from 1.6 to 3.5 mequiv/g as determined by titration. The electron-withdrawing groups did not appear to affect the thermal properties (decomposition temperature higher than 200 °C). The presence of nitrile groups, especially at positions meta to the ether linkages, improved the oxidative stability of the SPE membranes, while it led to a deterioration of the hydrolytic stability. The perfluorinated biphenylene groups were effective in providing high mechanical strength with reasonable dimensional change, probably due to a somewhat decreased water absorbability. The SPE membrane containing sulfone groups showed the highest proton conductivity (10⁻³-10⁻¹ S/cm) at 20-93% RH (relative humidity) and 80 °C. The nitrile-containing SPE membrane showed smaller apparent activation energies for oxygen and hydrogen permeability and is thus considered to be a possible candidate for applications in PEMFCs.     

Synthesis of sulfonated aromatic poly(ether amide)s and their application to proton exchange membrane fuel cells

A series of wholly aromatic sulfonated poly(ether amide)s (SPEAs) containing a sulfonic acid group on the dicarbonyl aromatic ring were prepared via a polycondensation reaction of sulfonated terephthalic acid (STA), terephthalic acid (TA), and aromatic diamine monomers. The degree of sulfonation was readily controlled by adjusting the monomer feed ratio of STA and TA in the polymerization process, and randomly sulfonated polymers with an ion exchange capacity (IEC) of 1.0–1.8 mequiv/g were prepared using this protocol. The chemical structures of randomly sulfonated polymers were characterized using NMR and FT‐IR spectroscopies. Gel permeation chromatography analysis of SPEAs indicated the formation of high‐molecular‐weight sulfonated polymer. Tough and flexible SPEA membranes were obtained from solution of N,N‐dimethylacetamide, and thermogravimetric analysis of these membranes showed a high degree of thermal stability. Compared with previously reported sulfonated aromatic polyamides, these new SPEAs showed a significantly lower water uptake of 10–30%. In proton conductivity measurements, ODA‐SPEA‐70 (IEC = 1.80 mequiv/g), which was obtained from polycondensation of 4,4′‐oxydianiline and 70 mol % STA, showed a comparable proton conductivity (105 mS/cm) to that of Nafion 117 at 80 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 485–496, 2009     

磺化聚芳醚砜/磺化聚酰亚胺复合质子交换膜的制备与性能研究

利用溶液浇铸法制备了一系列双磺化型磺化聚芳醚砜/磺化聚酰亚胺(SPAES/SPI)复合质子交换膜.扫描电子显微镜(SEM)结果显示复合膜不存在明显的相分离,表明二者具有很好的相容性.由于SPI的引入,复合膜在甲醇中稳定性较纯SPAES具有大幅的提高,比Nafion112低得多的甲醇吸收率表明了这些复合膜具有比后者更低的甲醇透过率.复合膜显示了与单组分膜相类似的高温分解稳定性,磺酸基团的分解温度达到了290℃以上.复合膜显示出远高于纯SPAES膜的尺寸稳定性能,在130℃高温中200h处理后,所有的复合膜均保持了高的机械性能,而此时纯SPAES膜已经溶解于水中.而且由于两种磺化聚合物间的复合,复合膜维持了较高的IEC水平,显示了较高的质子导电率,在80%相对湿度时的质子导电率与Nafion112相近,而在水中的质子导电率均高于Nafion112.     

Characterizations and stability of polyimide-phosphotungstic acid composite electrolyte membranes for fuel cell

Organic-inorganic composite membranes from partially aliphatic sulfonated polyimides and heteropolyacids (HPAs) were synthesized. A series of composite membranes with varying amounts of heteropolyacid were prepared by altering the weight ratio of polyimide and HPA. The partially aliphatic sulfonated polyimides are synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,4′-diaminobiphenyl 2,2′-disulfonic acid as the sulfonated diamine, and decamethylenediamine as the aliphatic diamine. The incorporation of HPA is confirmed by FT-IR analyses. When appropriately embedded in a hydrophilic polymer matrix, the hydrated HPAs are expected to endow the composite membrane with their high proton conductivity, while retaining the desirable mechanical properties of the polymer film. These composite membranes were evaluated for thermal stability, ion exchange capacity, water uptake and proton conductivity. Also the extraction of HPA from the polyimide membranes and their stability in water were determined. Though water uptake and IEC decreased with increase in HPA content, the proton conductivity of the composite membranes increased with increase in HPA weight content. This study shows that partially aliphatic sulfonated polyimide composite membranes with HPA can be a viable substitute for Nafion^® for fuel cells which show good conductivity comparable to Nafion^®117 at temperatures nearing 100 °C, keeping in mind that polyimides have good thermal stability and low cost.     

Investigation of sulfonated poly(ether ether ketone sulfone)/heteropolyacid composite membranes for high temperature fuel cell applications

The sulfonated poly(ether ether ketone sulfone) (SPEEKS)/heteropolyacid (HPA) composite membranes with different HPA content in SPEEKS copolymers matrix with different degree of sulfonation (DS) were investigated for high temperature proton exchange membrane fuel cells. Composite membranes were characterized by Fourier transfer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR band shifts suggested that the sulfonic acid groups on the copolymer backbone strongly interact with HPA particles. SEM pictures showed that the HPA particles were uniformly distributed throughout the SPEEKS membranes matrix and particle sizes decreased with the increment of copolymers' DS. The holes were not found in SPEEKS‐4/HPA30 (consisting of 70% SPEEKS copolymers with DS = 0.8 and 30% HPA) composite membrane after composite membranes were treated with boiling water for 24 h. Thermal stabilities of the composite membranes were better than those of pure sulfonated copolymers membranes. Although the composite membranes possessed lower water uptake, it exhibited higher proton conductivity for SPEEKS‐4/HPA30 especially at high temperature (above 100 °C). Its proton conductivity linearly increased from 0.068 S/cm at 25 °C to 0.095 S/cm at 120 °C, which was higher than 0.06 S/cm of Nafion 117. In contrast, proton conductivity of pure SPEEKS‐4 membrane only increased from 0.062 S/cm at 25 °C to 0.078 S/cm at 80 °C. At 120 °C, proton conductivity decreased to poor 0.073 S/cm. The result indicated that composite membranes exhibited high proton conductivity at high temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1967–1978, 2006     

含羧基交联型质子交换膜的制备及其性能

合成了一种含酯基的磺化聚合物,利用后水解的方法得到了含有羧基侧基的聚合物;将磺化聚合物与聚乙烯醇通过溶液共混,热处理后得到交联型的共混膜材料。 研究结果表明,膜材料的玻璃化转变温度(Tg)有明显的上升,证明了交联反应的发生;同时,膜的吸水率和溶胀率有一定的下降,力学性能和热稳定性也有一定的提升。 通过共价交联的方法,制备了综合性能优异的磺化聚芳醚质子交换膜材料。 在100 ℃,交联膜的质子传导率为0.072~0.065 S/cm,吸水率为51%~89%,溶胀率为19%~30%。     

Synthesis and properties of novel sulfonated polyimides containing phthalazinone moieties for PEMFC

A novel sulfonated diamine, 1,2-dihydro-2-(3-sulfonic-4-aminophenyl)-4-[4-(3-sulfonic-4-aminophenoxy)-phenyl]-phthalazin-1-one(S-DHPZDA), was successfully synthesized and two series of six-membered sulfonated polyimides (SPIs) were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), S-DHPZDA, and nonsulfonated diamines DHPZDA or 4,4′-diaminodiphenyl ether (ODA). The chemical structure of the S-DHPZDA and the SPIs were characterized by ¹H NMR and FT-IR. Tough, brownish and transparent membranes were cast from SPIs’ solution in NMP. The water uptake, swelling ratio, chemical and thermal stability, hydrolytic and oxidative stability as well as proton conductivity of these new polymers were investigated systematically. Compared with Nafions, the obtained SPI membranes have onset decomposed temperatures of these two series SPIs were above 318 °C and decomposed temperature of main chain were 565 °C and excellent dimension stabilities on similar IECs. Introduction of phthalazinone moieties had improved the copolyimides’ solubility in polar aprotic organic solvents like m-cresol, NMP, DMSO, DMF etc. The SPIs had high proton conductivity (σ) in the order of magnitude of 10⁻³ to 10⁻² S cm⁻¹ depending on the degree of sulfonation (DS) of the polymers.     

侧链结构对磺化聚芳醚性能及微观形貌的影响

比较了3种主链结构相同而侧链结构不同的磺化聚芳醚(SPAE)材料的性能. 分析了侧链结构对聚合物的吸水、 溶胀及质子传导行为的影响. 结果表明, 在相同的离子交换容量(IEC)条件下, 具有柔顺脂肪族侧链的聚芳醚材料具有较高的质子传导率. 其原因是由于柔顺的脂肪族侧链比刚性的芳香族侧链更易运动, 有利于侧链末端磺酸基团的聚集, 进而形成离子簇. 3种聚合物微观形貌的分析结果表明, 含柔顺侧链结构的聚合物薄膜具有更大的质子传输通道, 其结果与聚合物的宏观吸水和传导现象相吻合.     

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.     

New Composite Proton-Conducting Membranes Based on Nafion and Cross-Linked Sulfonated Polystyrene

New composite membranes based on commercial perfluorinated Nafion-115 membrane and cross-linked sulfonated polystyrene were synthesized and investigated. The membranes were prepared by radical polymerization of styrene in the presence of a cross-linking agent divinylbenzene in Nafion polymer matrix and subsequent sulfonation of formed polystyrene. The membranes containing approximately 5 and 10 wt % of cross-linked polystyrene with ion-exchange capacity of 1.1 to 1.3 mg-eq/g were obtained. Modification with sulfonated polystyrene leads to an increase in the moisture content and proton conductivity of membranes in the humidity range of 15 to 100 RH.     

Sulfonated poly(fluorenyl ether ketone) membrane prepared via direct polymerization for PEM fuel cell application

Sulfonated poly(fluorenyl ether ketone)s with inherent viscosity ranging from 0.68 to 0.93 dL/g were directly synthesized by aromatic nucleophilic polycondensation of bisphenol fluorene with various ratios of sulfonated difluorobenzophenone to difluorobenzophenone. The synthesized polymers were characterized by ¹H NMR method and elemental analysis. The polymers were tested to be soluble in dipolar aprotic solvents such as DMAc, DMF and DMSO and can be readily cast into tough films. These films showed highly thermal degradation temperature, glass transition temperature and excellent water affinity as well as excellent proton conductivity. The polymers showed a promising proton membrane material for PEM fuel cell application.     

Polymer blend membranes of sulfonated poly(arylene ether ketone) for direct methanol fuel cell

The blend membranes of sulfonated poly(arylene ether ketone) (sPAEK) (IEC = 1.0 mequiv./g)/Nafion^® and the blend membranes of sPAEK (IEC = 1.0 mequiv./g)/sPAEK (IEC = 1.7 mequiv./g) were prepared. sPAEK with low IEC was introduced to reduce the methanol permeability through the membrane. Morphology, water uptake, proton conductivity and methanol permeability of the blend membranes were investigated by SEM, AFM, AC impedance spectroscopy and permeability measuring instrument. The cross-sections of blend membranes showed phase-separated morphologies. The effect of phase-separated morphology on the properties of blend membranes was investigated. The properties like water uptake, proton conductivity, and methanol permeability of sPAEK/Nafion^® blend membranes showed similar values with sPAEK and properties of sPAEK/sPAEK blend membranes showed intermediate values of two polymers due to the difference in morphology of the blend membranes. sPAEK/sPAEK blend membranes showed relatively high proton conductivity and lowered methanol permeability compared to Nafion^®. sPAEK/sPAEK blend membranes could be a competent substitution for Nafion^®.     

后磺化法精确可控合成主链型磺化聚苯喹喔啉及其质子交换膜性能研究

以不同摩尔比的4,4′-双(4-(2-苯基乙二酮基)苯氧基联苯、4,4′-双(2-苯基乙二酮基)二苯醚与3,3′,4,4′-四氨基联苯共聚制备聚喹喔啉,经后磺化法得到一系列磺化度可控的磺化聚苯基喹喔啉(SPPQ).模型化合物确认,磺酸基团精确接入电子云密度较高的含醚键的联苯片段的2,2′-位上,证明通过单体分子结构设计与后磺化法结合,可使磺酸基团在温和条件下,按预想接入到聚合物主链上,达到磺化度和磺化位置精确可控的目的. SPPQ的相对黏度均在3.8 dL/g以上.通过溶液涂膜法制备的主链型磺化聚苯基喹喔啉质子交换膜(SPPQ PEM)的吸水率都低于39%,尺寸变化率为2.1%~13%,且随着IEC和温度的提高而线性增加.如,80℃下,IEC高达2.21 meq/g的SPPQ-5的膜面和膜厚方向的尺寸变化率仅为11%和13%,具有良好的形状维持能力.热重分析表明,SPPQ PEM在320℃左右脱去磺酸基团,550℃左右发生聚合物主链降解,具有良好的热稳定性. Fenton试剂测试表明,SPPQ PEM开始破碎的时间随IEC的增加而缩短,在20℃时,IEC较低的SPPQ-1 (1.29 meq/g)破碎时间可达151 h,而IEC较高的SPPQ-5(2.21 meq/g)破碎时间缩短至81 h. PEM的质子传导率随温度和IEC的增加而显著提高,最高可达64 mS/cm,由于磺酸基团和喹喔啉酸碱对的形成以及吸水率偏低的原因,这一数值远低于Nafion.     

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.