To achieve high-performance proton-exchange membranes (PEMs), understanding of the polymer structure/property relationship is crucial. In particular, the structure of water clusters (number, size, interdomain distance, interconnectivity, etc.) and hydrophobic domains dominates important membrane properties, such as proton conductivity and mechanical strength, which can be adjusted by the monomer sequence in the polymer chains. In the present paper, we have prepared three sulfonated polyphenylene-based copolymers (SPP-MP, SPP-BP, and SPP-QP) whose main chain components were the same but their sequence differed by the use of different hydrophobic monomers (monophenylene,-MP; biphenylene,-BP; and quinquephenylene,-QP, respectively). Careful investigation of the proton nuclear magnetic resonance (1H NMR) spectra suggested that the randomness of the hydrophilic component (sulfophenylene unit) was dominated by the hydrophobic component: 51% for-MP, 32% for-BP, and 19% for-QP, respectively. Transmission electron microscopy (TEM) observation of the three polyphenylene ionomer membranes revealed that the lower randomness of the hydrophilic component caused a larger hydrophilic domain size in their phase-separated morphology under dry conditions. Small-angle X-ray scattering (SAXS) measurements suggested that SPP-QP, with the lowest randomness of the hydrophilic component, possessed the most pronounced periodic structure under humidified conditions. The connectivity of water clusters, estimated by the small-angle neutron scattering (SANS) measurements, was in the order SPP-QP > SPP-MP > SPP-BP with a minor humidity dependence. The proton conductivity and elongation at break increased with increasing connectivity of the water clusters or decreasing randomness of the hydrophilic component. These results suggest that the sequence of the hydrophobic component strongly affected the hydrophilic component, and accordingly, the membrane morphology and properties.

Proton exchange membrane fuel cells (PEMFCs) are promising clean energy conversion devices in residential, transportation, and portable applications. Currently, a high-pressure tank is the state-of-the-art mode of hydrogen storage; however, the energy cost, safety, and portability (or volumetric hydrogen storage capacity) presents a major barrier to the widespread dissemination of PEMFCs. Here we show an ‘all-polymer type’ rechargeable PEMFC (RCFC) that contains a hydrogen-storable polymer (HSP), which is a solid-state organic hydride, as the hydrogen storage media. Use of a gas impermeable SPP-QP (a polyphenylene-based PEM) enhances the operable time, reaching up to ca. 10.2 s mg , which is more than a factor of two longer than that (3.90 s mg ) for a Nafion NRE-212 membrane cell. The RCFCs are cycleable, at least up to 50 cycles. The features of this RCFC system, including safety, ease of handling, and light weight, suggest applications in mobile, light-weight hydrogen-based energy devices. HSP HSP −1 −1

Anion-conductive ionomers are used for electrolyte membranes in membrane-electrode assemblies and for binders in catalyst layers in anion exchange membrane fuel cells (AEMFCs). The conformations of these ionomers as well as their water distribution are important for designing new efficient/durable anion-conductive ionomers for AEMFCs. For a deeper understanding of the distribution of deuterium oxide (D2O) as a function of depth, neutron reflectometry (NR) was carried out on thin films of an anion exchange ionomer, BAF-QAF, with a thickness of approximately 60 nm formed on a thermally formed SiO2 film on Si(100) and on a 20 nm Pt layer deposited on the SiO2 film at a temperature of 60 °C and relative humidities of 0, 50, 70, and 90%. Clear NR modulation was obtained under each condition. The NR data were fit very well with a three-sublayered model parallel to the substrate with different densities of BAF-QAF and D2O. The influence of the SiO2 and Pt substrates was observed not only at the BAF-QAF/substrate interface but also on the entire thin film. The D2O absorption/desorption behavior in each sublayer differed in the BAF-QAF films cast on SiO2 and Pt. The BAF-QAF/SiO2 interface was rather hydrophilic, while the BAF-QAF/Pt interface was very hydrophobic.

Novel anion conductive aromatic copolymers containing hexafluoroisopropylidene groups as the hydrophobic component and fluorenyl groups substituted with pendant hexyltrimethylammonium groups as the hydrophilic component were synthesized and characterized. Precursor copolymers, BAF-AF, were synthesized by a nickel(0) promoted polycondensation reaction and had a high molecular weight (M-n = 10-12 kDa, M-w = 77-115 kDa). Quaternization of BAF-AF using dimethyl sulfate gave tough and bendable thin BAF-QAF membranes having the ion exchange capacity (IEC) from 1.3 to 2.4 mequiv g(-1) by solution casting. The morphology of BAF-QAFs was investigated by TEM images and SAXS profiles, and a nanoscale fine phase-separated structure was confirmed. The BAF-QAF membrane with IEC of 2.4 mequiv g(-1) showed a superior OH- conductivity (134 mS cm(-1) at 80 degrees C) in water. The membranes retained high conductivity under strongly alkaline conditions (similar to 4 M KOH at 80 degrees C) for 1000 h. An H-2/O-2 anion alkaline fuel cell using the BAF-QAF membrane and binder achieved the maximum power density of 319 mW cm(-2) at 702 mA cm(-2) at 60 degrees C and 100% RH. Hexafluoroisopropylidene groups contributed to improving membrane properties as anion exchange membranes for alkaline fuel cells.

Structures of polymer electrolyte membranes and binders and the distribution of water inside are important for designing new ion-conductive ionomers for polymer electrolyte fuel cells. Neutron reflectometry (NR) was carried out on a Nafion (R) film with a thickness of 100 nm formed on native SiO2 surface on Si(100) for understanding the in-plane water distribution. The temperature was set at 80 degrees C and the relative humidity at 30, 50, 65, and 80% for NR measurements, simulating the conditions for the power generation. Clear NR modulation was obtained under each condition. NR data were fit very well with a 4-layer model parallel to the substrate with different densities of Nafion and water. At the interface between the Nafion film and the Si substrate, a 1 nm water-rich layer was observed under all conditions. The water concentration increased with humidity at all 4 layers, but the thickness increased mainly at the bulk layer. (C) 2019 The Japan Society of Applied Physics

The structures of polymer electrolyte membranes and catalyst layer binders and the distribution of water therein are important for designing new ion-conductive ionomers for polymer electrolyte fuel cells. To aid the understanding of the in-plane water distribution, neutron reflectometry (NR) was carried out on a Nafion (R) film with a thickness of 150 nm formed on a 20-nm Pt layer deposited on Si(100) with a native SiO2 layer. By means of ambient pressure X-ray absorption spectroscopy at room temperature in air, the Pt substrate was found to be metallic. For NR, the temperature was set at 80 degrees C and the relative humidity at 30, 50 and 80%, simulating the conditions for power generation. Clear NR modulation was obtained under each condition. NR data were fit very well with a 3-sublayered model parallel to the substrate with different densities of Nafion and water. The influence of the Pt substrate was observed not only at the Nafion/Pt interface, but also on the thin-film structure. The water uptake in a Nafion film on Pt also differed from that on SiO2. At 80 degrees C, the surface of the Pt substrate was proposed to be oxidized, and the Nafion/Pt interface was found to contain water, in contrast to the interface observed at room temperature. (C) The Electrochemical Society of Japan, All rights reserved.

Novel anion-conductive polymers containing perfluoroalkyl and ammonium-functionalized fluorene groups were synthesized and characterized. The quaternized polymers synthesized using a dimethylaminated fluorene monomer had a well-defined chemical structure in which each fluorenyl group was substituted with two ammonium groups at specific positions. The resulting polymers had a high molecular weight (Mn = 8.9-13.8 kDa, Mw = 13.7-24.5 kDa) to provide bendable thin membranes with the ion-exchange capacity (IEC) ranging from 0.7 to 1.9 mequiv g-1 by solution casting. Both transmission electron microscopy images and small-angle X-ray scattering patterns suggested that the polymer membranes possessed a nanoscale phase-separated morphology based on the hydrophilic/hydrophobic differences in the polymer components. Unlike typical anion-exchange membranes found in the literature, hydroxide ion conductivity of the membranes did not increase with increasing IEC because of their high swelling capability in water. The membrane with IEC = 1.2 mequiv g-1 showed balanced properties of high hydroxide ion conductivity (81 mS cm-1 at 80 °C in water) and mechanical strength (>100% elongation and 14 MPa maximum stress at 80 °C, 60% relative humidity). The polymer main chains were stable in 4 M KOH for 1000 h, whereas the trimethylbenzyl-type ammonium groups degraded under the conditions to cause loss in the hydroxide ion conductivity. An H2/O2 fuel cell with the membrane with IEC = 1.2 mequiv g-1 exhibited a maximum power density of 242 mW cm-2 at 580 mA cm-2 current density.

For improving the alkaline stability and other properties of aromatic semiblock copolymer [QPE-bl-11a(C1)] membranes containing benzyltrimethylammonium groups, several novel hydrophilic monomers with different side-chain lengths and substitution positions were designed and synthesized for the polymerization. The pendant-type preaminated copolymers PE-bl-11s were quaternized using iodomethane to obtain the target QPE-bl-11s with well-defined chemical structure. In TEM analyses, QPE-bl-11a(C3) and QPE-bl-11a(C5) membranes with propyl and pentyl side-chains, respectively, showed more developed phase-separated morphology with greater hydrophilic domains (ca. 10-20 nm in width) than that of the C1 equivalent. The phase separation was more distinct and larger for the QPE-bl-11a membranes linked with p-phenylene groups in the hydrophilic part than for the QPE-bl-11b membranes with m-phenylene groups. In particular, QPE-bl-11b(C5) membrane exhibited considerably smaller hydrophilic/hydrophobic domains compared to those of the other membranes. After the alkaline stability test in 1 M KOH aqueous solution at 60 °C for 1000 h, the remaining conductivity was better as increasing the side-chain length: 34% for QPE-bl-11a(C1), 54% for QPE-bl-11a(C3), and 72% for QPE-bl-11a(C5) at 60 °C. The results suggest that the pendant alkyl chains could improve the alkaline stability and the main-chain bond position could improve morphology, water utilization, and mechanical properties of QPE-bl-11 membranes. An H2/O2 fuel cell with QPE-bl-11 membrane showed 139 mW cm-2 of the maximum power density at 0.28 A cm-2 of the current density.

For higher performances of anion exchange membrane (AEM) fuel cells, understanding the phase-separated structures inside AEMs is essential, as well as those at the catalyst layer/membrane interfaces. The AEMs based on quaternized aromatic semi-block copolymers with different ion exchange capacities (IECs) were systematically investigated. With IECs of 1.23 and 1.95 mequiv g−1, the water uptakes at room temperature were 37% and 98%, and the anion conductivities 23.6 and 71.4 mS cm−1, respectively. The increases were not proportional to the IEC. Images obtained by transmission electron microscopy in vacuum were similar with both IEC values, but the development of a clear phase separation in humidified nitrogen was observed in the profiles only with 1.95 mequiv g−1obtained by small-angle X-ray scattering. At the temperature of 40 °C and the relative humidity (RH) of 30%, the average currents observed at the tip apex by current-sensing atomic force microscopy were &lt
0.5 and 10 pA with 1.23 and 1.95 mequiv g−1, respectively, and those at 70% RH were 10 and 15 pA, respectively. The humidity gave a larger influence on the bulk structure with 1.95 mequiv g−1, whereas a larger influence on the surface conductivity with 1.23 mequiv g−1.

In this research, copolymerization reaction of sulfonated dichlorobenzene and dichloro-Terminated aromatic oligomer was investigated for the preparation of sulfonated copolymers as proton conductive membranes. We found that a versatile synthetic method without using costly Ni(0) catalyst, where NiBr2 could be reduced to Ni(0) with Zn in situ during the copolymerization reaction, was applicable. The resulting copolymer had comparable molecular weight and proton conductivity to those of the copolymers prepared by the previous method using Ni(0).

A novel series of ammonium-containing copolymers (QPAF-4) were designed and synthesized as anion exchange membranes for alkaline fuel cell applications. The copolymers were prepared via a nickel promoted polycondensation reaction with high molecular weights (M-w = 72.7-276.4 kDa as precursors) and were composed of perfluoroalkylene and fluorenyl groups with pendant ammonium groups. The QPAF-4 membrane with optimized copolymer composition and ion exchange capacity exhibited high hydroxide ion conductivity (86.2 mS cm(-1) in water at 80 degrees C) and excellent mechanical properties (large elongation at break = 269%). A severe alkaline stability test of the QPAF-4 membranes in 1 M KOH at 80 degrees C for 1000 h and the post-test analyses of the H-1 NMR spectra, solubility, and mechanical properties revealed minor, or no, changes in the chemical structure and properties. Alkaline fuel cells using the QPAF-4 membrane were operated using hydrazine as a fuel and oxygen or air as oxidant to achieve the high maximum power density of 515 mW cm(-2). The durability of the membrane was also confirmed in the operating fuel cell at a constant current density for longer than 1000 h.

The chemical durabilities of two proton-conducting hydrocarbon polymer electrolyte membranes, sulfonated benzophenone poly(arylene ether ketone) (SPK) semiblocic copolymer and sulfonated phenylene poly(arylene ether ketone) (SPP) semiblocic copolymer are evaluated under accelerated open circuit voltage (OCV) conditions in a polymer electrolyte fuel cell (PEFC). Post-test characterization of the membrane electrodes assemblies (MEAs) is carried out via gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy. These results are compared with those of the initial MEAs. The SPP cell shows the highest OCV at 1000 h, and, in the post-test analysis, the SPP membrane retains up to 80% of the original molecular weight, based on the GPC results, and 90% of the hydrophilic structure, based on the NMR results. The hydrophilic structure of the SPP membrane is more stable after the durability evaluation than that of the SPK. From these results, the SPP membrane, with its simple hydrophilic structure, which does not include ketone groups, is seen to be significantly more resistant to radical attack. This structure leads to high chemical durability and thus impedes the chemical decomposition of the membrane. (C) 2017 The Author(s). Published by Elsevier B.V.

We report synthesis and properties of a novel series of ammonium-functionalized perfluoroalkylene/aromatic copolymers. In particular, the effect of number and position of ammonium groups on the properties of the copolymer thin membranes was investigated. Fluorenylidene biphenylene groups were used as a scaffold for the ammonium groups. By controlling the chloromethylation reaction conditions, the ammonium groups could be introduced up to 4.0 per fluorenylidene biphenylene unit, resulting in the ion exchange capacity (IEC) of the resulting copolymers ranging from 1.0 to 1.8 meq g(-1). The copolymers provided bendable and transparent membranes by solution casting. The membranes exhibited phase-separated morphology based on the hydrophilic/hydrophobic differences in the copolymer components. A copolymer membrane with IEC = 1.0 meq g(-1) showed high hydroxide ion conductivity (ca. 70mS cm(-1)) at 80 degrees C in water and good alkaline stability in 1M KOH aq. over 1000 h at 60 degrees C. The membrane showed only minor degradation after the long-term alkaline stability test.

Proton exchange membrane fuel cells (PEMFCs) are promising devices for clean power generation in automotive, stationary, and portable applications. Perfluorosulfonic acid (PFSA) ionomers (for example, Nafion) have been the benchmark PEMs; however, several problems, including high gas permeability, low thermal stability, high production cost, and environmental incompatibility, limit thewidespread dissemination of PEMFCs. It is believed that fluorine-free PEMs can potentially address all of these issues; however, none of these membranes have simultaneously met the criteria for both high performance (for example, proton conductivity) and durability (for example, mechanical and chemical stability). We present a polyphenylene-based PEM (SPP-QP) that fulfills the required properties for fuel cell applications. The newly designed PEM exhibits very high proton conductivity, excellent membrane flexibility, low gas permeability, and extremely high stability, with negligible degradation even under accelerated degradation conditions, which has never been achieved with existing fluorine-free PEMs. The polyphenylene PEM also exhibits reasonably high fuel cell performance, with excellent durability under practical conditions. This new PEM extends the limits of existing fluorine-free proton-conductive materials and will help to realize the next generation of PEMFCs via cost reduction as well as the performance improvement compared to the present PFSA-based PEMFC systems.

The recent progress of our research on proton exchange membranes (PEMs) for fuel cell applications is reviewed. In particular, we focus on fluorine-free sulfonated aromatic polymers as alternatives to the benchmark perfluorosulfonic acid ionomer (e.g., Nafion) PEMs. Most fluorine-free sulfonated aromatic polymers require improved proton conductivity (at high temperatures and low humidity) and chemical and mechanical stability. To address these issues, a wide range of molecular structures and their sequences were investigated. First, the effect of molecular structure on the membrane properties of sulfonated multiblock copoly(arylene ether)s is discussed. We emphasize that phosphine oxide moieties might improve chemical stability; however, aromatic ether linkages in the hydrophilic block are not suitable because oxidative degradation and excess water swelling followed by mechanical failure is essentially inevitable. We then developed a novel polymer synthetic method, an intrapolymer Heck reaction, to ladderize aromatic ether linkages in the hydrophilic block. The ladderized rigid hydrophilic structure is an effective molecular design for balancing proton conductivity and mechanical stability. We then discuss two types of segmented copolymers based on the rigid hydrophilic structural design via a Ni-mediated coupling reaction; the hydrophilic structures are sulfonated phenylene and sulfonated benzophenone. We found that the traditional multiblock structure as well as any additional polar groups (e.g., ether, sulfone, ketone) in the hydrophilic sections are not necessary for improving the membrane properties that are important for fuel cell applications, such as proton conductivity and chemical and mechanical stability. The results indicate that fluorine-free aromatic PEMs are a potentially applicable class of ionomers for the next generation of proton exchange membrane fuel cells.

For enhancing hydroxide ion conductivity, alkaline stability, and fuel cell performance of quaternaized aromatic/perfluoroaklyl copolymer (QPAF) membranes, ammonium groups attached to the polymer backbone have been investigated. The ammonium groups included dimethyl-butylamine (DMBA), dimethylhexylamine (DMHA), and 1,2dimethylimidazole (DMIm) groups in comparison to the trimethylammonium (TMA) group. DMBA turned to be the optimum ammonium group for QPAF membranes in terms of its high hydroxide ion conductivity based on well-connected and larger phase-separated morphology than that of QPAF-TMA with similar ion exchange capacity (IEC) value. QPAF-DMBA (IEC = 1.33 mequiv g(-1)) exhibited the highest hydroxide ion conductivity among the tested membranes up to 152 mS cm(-2) in water at 80 degrees C, which was 1.6 times higher than that of QPAFTMA (95 mS cm(-1)). In addition, QPAF-DMBA exhibited reasonable alkaline stability in 1 M KOH at 60 degrees C for 1000 h. The remaining conductivity was 44 mS cm(-1) (58%) for QPAF-DMBA, while that for QPAF-TMA was 1.0 mS cm(-1) (1%). QPAFDMBA (IEC = 1.09 mequiv g(-1)) exhibited excellent stability in 1 M KOH at 80 degrees C without change in the ion conductivity (22 mS cm(-1)) for 500 h. The post-test membranes exhibited a minor degradation in QPAF-DMBA as suggested by FT-IR spectra and DMA analyses. An H-2/O-2 fuel cell was operated with the QPAF-DMBA membrane to achieve the maximum power density of 167 mW cm(-2) at the current density of 0.42 A cm(-2), which was higher than that (138 mW cm(-2)) for QPAF-TMA membrane under the same operating conditions.

Synthesis and properties of a series of ammonium-containing terpolymers (QPAF-3) as anion conductive membranes are reported. The QPAF-3s composed of perfluoroalkylene, alkylene, and ammonium-functionalized phenylene groups without heteroatom linkages in the main chain were synthesized via nickel-mediated polycondensation reaction, followed by chloromethylation, quaternization, and ion exchange reactions. Self-standing, bendable membranes were obtained by solution casting. The QPAF-3 membrane with optimized terpolymer composition and ion exchange capacity (1.46 meq g(-1)) showed high hydroxide ion conductivity (123 mS cm(-1) in water at 80 degrees C). The alkaline stability test in 1 M KOH for 1000 h at 80 degrees C and the posttest analysis with IR spectra and tensile strength suggested that ammoniumgroups were likely to be decomposed while the polymer main chain was chemically more robust. The presence of the alkylene groups in the terpolymers lowered solubility, glass transition temperature, and elongation property of the resulting membranes. (C) 2017 Wiley Periodicals, Inc.

A novel series of anion conductive polymers, quaternized poly(phenylene alkylene)s (QPAs), were synthesized and characterized. Because of the unique main chain structure composed of alkylene and ammonium-functionalized fluorene groups, QPA thin membranes exhibited high ion conductivity and good chemical and mechanical stabilities.

The mechanical durability of sulfonated poly (phenylene) (SPP) membrane, used for polymer electrolyte fuel cells (PEFCs), is evaluated by the United States Department of Energy (USDOE) stress protocol involving wet-dry cycling, and the degradation is analyzed specifically by comparing with sulfonated poly(arylene ether ketone) (SPK) membrane. Initially, the SPP membrane exhibits 2-fold higher stiffness and 50% lower dimensional change ratio than the SPK membrane. In durability cycling, the SPP membrane lasts more than 20,000 wet-dry cycles without mechanical failure, which is more than 5-fold better durability than that for the SPK membrane. Higher mechanical strength and lower dimensional change can reduce both irreversible membrane deformation and mechanical stress attributed to the membrane swelling and shrinking. In post-test analyses, the SPP membrane is found to rupture in the peripheral region of the membrane electrode assemblies. The SPP membrane maintains only 10% of the elongation at break in the peripheral region but 50% in the electrode region, compared with the pristine condition. It is most likely that the membrane deteriorates in the peripheral region due to stress concentration by cell compression and membrane deformation during wet-dry cycling. (185 words) (C) The Author(s) 2017. Published by ECS. All rights reserved.

A decomposition mechanism of H2O2 by triphenylphosphine oxide (TPPO) is presented. TPPO is often incorporated in proton-exchange membrane electrolytes as a moiety to inhibit the H2O2-induced degradation of the membranes. However, it has not been revealed how TPPO decreases the concentration of free H2O2 in the membranes. Following the experimental X-ray structures, the TPPO dimer capturing two H2O2 molecules was used as the calculation model. The vibrational spectrum calculations for various hydration numbers show that this model correctly reproduces the spectral peaks of TPPO capturing H2O2. On the basis of this model, the H2O2 decomposition mechanism by the TPPO dimer was searched. It was consequently found that this reaction proceeds through three steps: (1) Hydrogen transfer from H2O2 to the P=O bond of TPPO, (2) Hydrogen transfer from the -OOH group to the -OH group, and (3) O-O bond formation between O2 groups. The calculated vibrational spectra for the reactants and intermediates indicated that the first and second steps are activated by vibrational excitations. Moreover, the third step giving low barrier heights is considered to proceed through two reaction paths: directly producing the O2 molecule or going through an HOOOH intermediate. Interestingly, this reaction mechanism was found to use the violation of the octet rule for the P=O double bond, resulting in the strong H2O2 binding of TPPO.

A collaborative experimental and theoretical study on the dependence of the infrared (IR) spectrum of hydrated Nafion,electrolyte membrane on the hydration number is investigated in great detail. Experimental time-resolved attenuated total reflection Fourier transform IR spectroscopic results show that Nafion membrane has a unique IR peak intensity dependence on the hydration number. Calculated IR spectra indicate that this unique IR peak intensity dependence is correctly reproduced not for the singly hydrated Nafion but for the doubly hydrated Nafion. This result strongly supports the relay mechanism of the proton conductance, in which protonated water dusters are relayed by the side chains through the doubly hydrated sulfonic acid groups under low humidity conditions.

Anion conductivity at the surfaces of two anion-exchange membranes (AEMs), quaternized ammonium poly(arylene ether) multiblock copolymer(QPE-bl-3) and quaternized ammonium poly(arylene perfluoro-alkylene) copolymer (QPAF-1), synthesized by our group was investigated using current-sensing atomic force microscopy under purified air at various relative humidities. The anion-conducting spots were distributed inhomogeneously on the surface Of QPE-bl-3, and the total areas of the anion-conducting spots and the current at each spot increased with humidity. The anion-conductive areas on QPAF-1 were found on the entire surface even at a low humidity. Distribution of the anion-conducting spots on the membrane was found to directly affect the performance of an AEM fuel cell.

Proton-conducting membranes are key materials in polymer electrolyte fuel cells. In addition to high proton conductivity and durability, a membrane must also support good electrocatalytic performance of the catalyst layer at the membrane electrode interface. We herein propose an effective molecular approach to the design of high-performance proton-conducting membranes designed for fuel cell applications. Our new copolymer (SPAF) is a simple combination of perfluoroalkylene and sulfonated phenylene groups. Because this ionomer membrane exhibits a well-controlled finely phase-separated morphology, based on the distinct hydrophilic hydrophobic differences along with the polymer chain, it functions well in an operating fuel cell with good durability under practical conditions. The advantages of this ionomer, unlike typical perfluorosulfonic acid ionomers (e.g., Nafion), include easy synthesis and versatility in molecular structure, enabling the fine-tuning of membrane properties.

The properties of anion-exchange membranes composed of fluorinated block copoly(arylene ether)s, QPE-b1-3, were investigated. QPE-b1-3 membranes exhibited high chemical stability under accelerated testing conditions. Reasonably high fuel cell performance was obtained with QPE-b1-3, hydrazine hydrate as a fuel, and non-platinum catalysts.

The introduction of sulfonated triphenylphosphine oxide moieties improved the oxidative stability of aromatic block copolymer membranes, while other factors such as water affinity also played an important role in determining the membrane properties.

A series of anion exchange membranes (QPE-bl-9) based on a partially fluorinated hydrophobic segment and oligophenylene as scaffolds for ammonium cations were synthesized to evaluate the effect of the various ammonium groups derived from trimethyl amine (TMA), dimethyl hexyl amine (DMHA), methyl imidazole (MIm), dimethyl imidazole (DMIm), tributyl amine (TBA), and dicyclohexyl methyl amine (DCHMA) on the membrane properties. QPE-bl-9 membranes were well characterized by H-1 NMR spectroscopy, in which all the peaks were assigned to the supposed structure. The TEM images of QPE-bl-9-TMA, -MIm, -DMIm and -DMHA membranes showed small hydrophilic/hydrophobic phase separated morphology (hydrophilic domains 1-3 nm). QPE-bl-9-TMA (1.6 mequiv. g(-1)) exhibited the highest hydroxide ion conductivity (101 mS cm(-1) at 80 degrees C) among the tested membranes, followed by QPE-bl-9-DMHA (62 mS cm(-1)) and QPE-bl-9-DMIm (62 mS cm(-1)). The alkaline stability of the membranes was tested in 1 M KOH at 60 degrees C for 1000 h. QPE-bl-9-TMA exhibited the highest retention of the conductivity (58%), which was higher than that of the Tokuyama A201 anion exchange membrane (29%). The post stability test IR analyses suggested that the major degradation mechanism of the QPE-bl-9 membranes in alkaline solution involved the decomposition of the ammonium groups. The QPE-bl-9 membranes retained their mechanical stability after the stability test, as proved by DMA analyses.

We developed a new FTIR system with two polarizers in its optics in order to conduct polarization-modulated measurements. Polarization characteristics were examined for the Kretschmann polarization-modulated attenuated total reflectance (ATR) configuration by the use of gold-sputtered films of 10-100 nm thickness on Ge and ZnSe prisms. The marked increase of the polarization characteristics for Au film thicknesses below 30-40 nm is closely associated with a large reflectivity decrease of the p-polarized radiation. A cast film of sulfonated block poly(arylene ether sulfone ketone) membrane was formed on the Au film, and the interfacial spectra were acquired by the use of the ATR FTIR system. The interfacial spectra resemble those of the ATR spectra of the bulk membrane but exhibited strong dependence of the intensity and line shape of the vibrational modes on the Au thickness. The dependence is closely associated with a change of the polarization characteristics of the interface. Electromagnetic as well as chemical effects were concluded to be responsible for the band anomalies and enhancement.

A rigid, planar dibenzofuran in the hydrophobic parts provided sulfonated aromatic block copolymer with improved membrane properties, i.e., well-developed phase separation, effective water uptake, high proton conductivity, and moderate mechanical strength at wide range of humidity.

To improve the performances of fuel cells at low humidity, we have prepared composite electrolyte membranes by incorporating SiO2 nanoparticles into poly(arylene ether sulfone ketone) (SPESK) membrane. SiO2 particles were able to be dispersed in SPESK highly uniformly on the nanometer scale by the use of a commercial SiO2-dimethylacetamide sol. The SiO2/SPESK cell exhibited improved I-E performance at 53% relative humidity (RH) and 80 degrees C. It was found that such an improvement was due to the reduction of the ohmic resistance and the oxygentransport overpotential at high current densities, probably because the SiO2 nanoparticles promoted the backdiffusion of water generated at the cathode catalyst layer toward the anode. Both the ohmic resistance and the oxygen-transport overpotential were reduced further by using a thin (ca. 12 mu m) SiO2/SPESK membrane, resulting in remarkably high performances at 53% RH and 30% RH. (C) The Electrochemical Society of Japan, All rights reserved.

We have utilized rn-terphenyl (MTP) moiety as a component of hydrophobic blocks for sulfonated multiblock poly(arylene ether) copolymers. For this purpose, bisphenol-type MTP monomer was polymerized with bis(4-fluorophenyl)sullone to obtain hydroxyl-terminated hydrophobic oligomers, which were copolymerized with sulfonated hydrophilic blocks to obtain the targeted multiblock copolymers. The block copolymers possessed high apparent molecular weight (M-w=74-180 kDa) and gave bendable membranes by solution casting. Transmission electron microscopic (TEM) images revealed that the membranes exhibited hydrophilic/hydrophobic phase separated morphology with distinct interfaces. The domain sizes were dependent on the compositions of the multiblock copolymers, indicating the sequenced structure is responsible for the morphology. The introduction of MTP moieties in the hydrophobic blocks resulted in the membrane with the higher ion exchange capacity (IEC) value (2.13 meq/g) and higher proton conductivity (ca. 320 mS/cm at 80 degrees C and 90% relative humidity) than that of the previous polymers sharing the same hydrophilic but different hydrophobic (p biphenyl, BP) moieties (1.69 meq/g, ca. 200 mS/cm under the same conditions, respectively). In contrast, humidity dependence of dynamic mechanical properties in MTP membranes was similar to BE membranes, suggesting the introduction of MTP moieties in the hydrophobic segments has minor impact on the mechanical stability and its dependence on the humidity. (C) 2014 Elsevier B.V. All rights reserved.

A novel & series of ammonium-containing copoIymers (QPAFs) were synthesized as anion exchange membranes for aIkaIine fueI cell appEications. The precursor copoIymers (A/l = 28.3-90.1 kDa) composed of perfluoroaIkyIene and phenyIene groups were obtained by a nick& promoted poIycondensation reaction. ChIoromethyEation and quaternization reactions of the precursors provided thin and ductlle QPAF membranes with ion exchange capacity (IEC) ranging from 0.79 to 1.74 meq g-1. The QPAF membranes exhibited a phase-separated morphoIogy based on the hydrophiIic/hydrophobic differences in the main chain structure. The QPAF membrane with an optimized copoIymer composition and IEC = 1.26 meq g(-1) showed high hydroxide ion conductivity (95.5 mS cm(-1) in water at 80 degrees C), excellent mechanicaI properties (Large eIongation at break (218%)), and reasonabIe aIkaIine stabiIity at 80 degrees C. An aIkaIine fueI cell using the QPAF as the membrane and eIectrode binder achieved the maximum power density of 139 mW cm-2 at a current density of 420 mA cm(-2).

A novel series of poly(arylene ether sulfone ketone) multiblock copolymers containing sulfonic acid and bromine groups in the hydrophilic blocks were synthesized and characterized. The copolymers were high molecular weight (M-n = 21-98 kDa, M-w = 234-357 kDa) and provided bendable and transparent membranes by solution casting. The bromine groups caused slight decrease in the proton conductivity at low humidity, however, were effective in improving the mechanical properties as confirmed by dynamic mechanical analyses and tensile tests.

A sulfonated polybenzophenone/polyimide block copolymer membrane exhibited high proton conductivity, good dimensional and mechanical stabilities, and low gas permeability, which are attractive for fuel cell applications.

The synthesis and properties of anion conductive aromatic copolymers containing oligophenylene moieties as a scaffold for quaternized ammonium groups are reported. Our new hydrophilic components consist of a chemically robust oligophenylene main chain modified with a high density of ionic groups. A partially fluorinated oligo(arylene ether) was employed as a hydrophobic block. The targeted copolymers (QPE-bl-9) were synthesized via nickel-mediated coupling polymerization, followed by chloromethylation, quaternization, and ion exchange reactions. QPE-bl-9 provided tough, bendable membranes by solution casting. The resulting membrane with the highest ion exchange capacity (IEC = 2.0 mequiv g(-1)) exhibited high hydroxide ion conductivity (138 mS cm(-1)) in water at 80 degrees C. Reasonable alkaline stability of QPE-bl-9 membrane was confirmed in 1 M KOH aqueous solution for 1000 h at 40 degrees C. A noble metal-free fuel cell with QPE-bl-9 used as the membrane and electrode binder was successfully operated. A maximum power density of 510 mW cm(-2) was achieved at a current density of 1.20 A cm(-2) with hydrazine as the fuel and O-2 as the xidant.

The important roles of Ni in electrocatalytic reactions such as hydrazine oxidation are limited largely by high oxidation states because of its intrinsically high oxophilicity. Here, we report the synthesis and properties of highly metallic Ni nanoparticles (NPs) on carbon black supports. We discovered that the heat treatment of as-prepared Ni NPs with an average particle size of 5.8 nm produced highly metallic Ni NPs covered with thin carbon shells, with negligible particle coarsening. The carbon shells were formed by the segregation of carbons in the Ni lattice to the surface of the Ni NPs, leaving highly metallic Ni NPs. X-ray photoelectron spectroscopic analyses revealed that the atomic ratio of metallic Ni increased from 19.2 to 71.7% as a result of the heat treatment. The NPs exhibited higher electrocatalytic activities toward the hydrazine oxidation reaction in alkaline solution, as compared to those of the as-prepared Ni NPs and commercial Ni powders.

A novel series of aromatic block copolymers composed of fluorinated phenylene and biphenylene groups and diphenyl ether (QPE-bl-5) or diphenyl sulfide (QPE-bl-6) groups as a scaffold for quaternized ammonium groups is reported. The block copolymers were synthesized via aromatic nucleophilic substitution polycondensation, chloromethylation, quaternization, and ion exchange reactions. The block copolymers were soluble in organic solvents and provided thin and bendable membranes by solution casting. The membranes exhibited well-developed phase-separated morphology based on the hydrophilic/hydrophobic block copolymer structure. The membranes exhibited mechanical stability as confirmed by DMA (dynamic mechanical analyses) and low gas and hydrazine permeability. The QPE-bl-5 membrane with the highest ion exchange capacity (IEC = 2.1 mequiv g(-1)) exhibited high hydroxide ion conductivity (62 mS cm(-1)) in water at 80 degrees C. A noble metal-free fuel cell was fabricated with the QPE-bl-5 as the membrane and electrode binder. The fuel cell operated with hydrazine as a fuel exhibited a maximum power density of 176 mW cm(-2) at a current density of 451 mA cm(-2).

A double-layer ionomer membrane, thin-layer Nafion (perfluorinated sulfonic acid polymer) on a sulfonated aromatic block copolymer (SPK-bl-1), was prepared for improving fuel cell performance. Each component of the double-layer membrane showed similar phase-separated morphologies to those of the original membranes. A fuel cell with the double-layer membrane exhibited lower ohmic resistance and higher cathode performance than those with the original SPK-bl-1 membrane despite their comparable water uptake and proton conductivity. Detailed electrochemical analyses of fuel cell data suggested that the thin Nafion interlayer contributed to improving the interfacial contact between the SPK-bl-1 membrane and the cathode catalyst layer and to mitigating excessive drying of the membrane. The results provide new insight on designing high-performance fuel cells with nonfluorinated ionomer membranes such as sulfonated aromatic polymers.

We have developed new composite membranes of sulfonated polyimide containing triazole-groups (SPI-8) as a matrix ionomer and SiO2 nanoparticles. The incorporation of SiO2 nanoparticles remarkably improved the fuel cell performances during low humidity operation at 53% RH and 80 degrees C. Among the cells with SPI-8 membranes with uniformly dispersed SiO2 from 0 to 15 wt%, the single cell with 10 wt% SiO2/SPI-8 was found to exhibit the highest I - E performance, with the highest mass activity at 0.85 V and the smallest oxygen-transport overpotential (O-2-gain) as well as the lowest ohmic resistance. This strongly indicates that SiO2 nanoparticles were able to promote the back-diffusion of water produced in the cathode catalyst layer to the anode catalyst layer, maintaining high Water content in the membrane during the operation. It was found that the cell with a bilayer SPI-8 membrane having 10 wt% SiO2 in the anode-side layer and 3 wt% SiO2 in the cathode-side layer exhibited performance superior to that with a uniform dispersion of 10 wt%SiO2, especially in the higher current density region at low RH, which can be ascribed with certainty to the fact that the concentration gradient of SiO2 in the SPI-8 led to enhancement of the back-diffusion of water through the membrane (C) 2014 Elsevier Ltd. All rights reserved.

Proton conductive spots on the membrane surface of sulfonated poly(arylene ketone) multiblock copolymer were investigated by current-sensing atomic force microscopy (CS-AFM) under the hydrogen atmosphere with changing relative humidity, temperature, and bias voltage. The bright spots, where the hydrophilic clusters should be effectively connected inside the membrane, were distributed rather inhomogeneously on the surface at low temperature and humidity but became more homogeneous at higher temperature and humidity. The average diameter of the spots was approximately 10 nm at 40% RH, which increased to 13 nm at 70% RH. The total area of the proton conducting spots, as well as current at each spot, on the membrane surface increased at high humidity and temperature. In addition, the diameter of the proton-conductive spots and the ratio of proton-conductive area on the membrane surface continuously increased with increasing the bias voltage. This increase of the conducting area and the current should be related to the change of the bulk ionic conductivity. (C) The Electrochemical Society of Japan, All rights reserved.

By using a current-sensing atomic force microscope (CS-AFM) under a hydrogen atmosphere, microscopic proton-conductive areas on the membrane surface of sulfonated poly(arylene ether sulfone ketone) block copolymer were investigated. With increasing the bias voltage during the CS-AFM scans, the number and the diameter of proton-conductive spots on the membrane surface continuously increased. Both reversible/irreversible changes in the proton-conductive area on the surface were found. The reversible change indicates that the proton-conductive paths are dynamically rearranged during the power generation in a polymer electrolyte fuel cell. The irreversible change might be related to the enhancement of the performance of the membrane electrode assemblies after being "conditioned" prior to the operation. (C) 2013 Elsevier B.V. All rights reserved.

Five kinds of ammonium groups functionalized partially fluorinated poly(arylene ether) block copolymer membranes were prepared for investigating the structure-property relationship as anion exchange membranes (AEMs). Consequently, the pyridine (PYR)-modified membrane showed the highest alkaline and hydrazine stability in terms of the conductivity, water uptake, and dry weight. The chloromethylated precursor block copolymers were reacted with amines, such as trimethylamine, N-butyldimethylamine, 1-methylimidazole, 1,2-dimethylimidazole, and PYR to provide the target quaternized poly(arylene ether)s. The structures of the polymers, as well as model compounds and oligomers were well characterized by H-1 NMR spectra. The obtained AEMs were subjected to water uptake and hydroxide ion conductivity measurements and stabilities in aqueous alkaline and hydrazine media. The pyridinium-functionalized quaternized polymers membrane showed the highest alkaline and hydrazine stability with minor losses in the conductivity, water uptake, and dry weight. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 383-389

A novel polymer synthetic method, the intrapolymer Heck reaction, provided ladder-type ionomer membranes with excellent proton conductivity (221 mS cm(-1) at 80 degrees C and 90% relative humidity) and mechanical strength over a wide range of humidity (ca. 0-90% relative humidity) at 80 degrees C.

The introduction of triphenylphosphine oxide moiety into the hydrophilic segments of aromatic multiblock copolymers provided outstanding oxidative stability and high proton conductivity. Our designed multiblock copolymers are composed of highly sulfonated phenylene ether phosphine oxide ketone units as hydrophilic blocks and phenylene ether biphenylene sulfone units as hydrophobic blocks. High molecular weight block copolymers (Mw = 204-309 kDa and Mn = 72-94 kDa) with different copolymer compositions (number of repeat unit in the hydrophobic blocks, X = 30, and that of hydrophilic blocks, Y = 4, 6, or 8) were synthesized, resulting in self-standing, transparent, and bendable membranes by solution-casting. The block copolymer membranes exhibited well-developed hydrophilic/hydrophobic phase separation, high proton conductivity, and excellent oxidative stability due to the highly sulfonated hydrophilic blocks, which contained phenylene rings with sulfonic acid groups and electron-withdrawing phosphine oxide or ketone groups. © 2013 American Chemical Society.

Synthesis and properties of aromatic block copolymers containing fluorinated phenylene and biphenylene groups and ammonium-substituted fluorene groups are reported. High-molecular-weight poly(arylene ether) block copolymers were prepared from the corresponding telechelic oligomers and were chloromethylated. Quaternization reaction of the chloromethylated precursors with trimethylamine provided the title ammonium-substituted block copolymers (QPE-b1-4). The QPE-b1-4 membrane with the highest ion-exchange capacity (IEC = 1.3 mequiv g(-1)) showed high hydroxide ion conductivity (45 mS cm(-1)) at 80 degrees C due to its phase-separated morphology with interconnected ion-transporting pathway. The accelerated stability test in aqueous KOH solution containing hydrazine revealed that the ammonium groups decomposed to certain extent while the polymer main chains were rather robust to maintain the self-supporting membranes.

The proton-conductive spots on the membrane surface of sulfonated poly(arylene ether) multiblock copolymer were successfully imaged by current-sensing atomic force microscopy under hydrogen atmosphere at various temperatures and humidities. These spots should be connected to the proton-conductive paths inside the membrane. The average diameter of the spots was approximately 12 nm, consistent with the size of hydrophilic domains observed by transmission electron microscopy. The size of the proton-conducting spots was almost unchanged regardless of the temperature and humidity, whereas the number of the spots increased at higher humidity; the total area of the proton-conducting spots increased accordingly on the membrane surface. This increase in the conducting area at high humidity should be related to the bulk ionic conductivity measured by impedance spectroscopy.

We have conducted combined time-resolved ATR-FTIR and proton conductivity measurements of a sulfonated block poly(arylene ether sulfone ketone) membrane, to be called a SPE-bl-1 membrane hereafter, during the hydration/dehydration cycle at room temperature. The result was discussed in comparison with the Nafion NRE211 membrane. Dissociation of the sulfonic acid groups and conductivity change were interpreted in terms of different states of water in the membrane characterized by delta(HOH) bands at 1705 and 1637 cm(-1), respectively. The former is assigned to hydrated protons produced by the dissociation followed by hydration. Proton conductivity increases significantly, over 0.1-0.2 S cm(-1), after the dissociation is completed at the initial stage of hydration, which is common to both membranes. The 1637 cm(-1) band contains contributions from the water in the proton conduction channels as well as some water which is hydrogen bonded to the polar groups in the SPE-bl-1 membrane such as ether (COC), sulfonyl (O=S=O), and carbonyl (C=O). The presence of the latter water lowers the effectiveness of the water in promoting proton conduction in the membrane. It is concluded that incomplete dissociation of the sulfonic acid groups coupled by the lower effectiveness is contributing to the lower proton conductivity of SPE-bl-1 than Nafion NRE211 at low hydration levels.

We have designed and synthesized a new bistriazole compound, 3,3'-(1,3-phenylene)bis[4-phenyl-5-(4-fluorophenyl)-4H-1,2,4-triazole], as a comonomer for a series of sulfonated block poly(arylene ether) copolymers. The bistriazole was successfully synthesized from isophthalic dihydrazide and 4-fluorobenzoyl chloride via bisoxadiazole. The bistriazole monomer was polymerized with 4,4'-biphenol or 4,4'-dihydroxydiphenyl ether to obtain hydroxyl-terminated hydrophobic oligomers, which were copolymerized with sulfonated oligomers to obtain the title block copolymers. The block copolymers were high-molecular-weight (M-w = 91-500 kDa) and provided tough and bendable membranes by solution casting. Because of the sequenced block copolymer structures, the membranes exhibited hydrophilic/hydrophobic phase-separated morphology as confirmed by scanning transmission electron microscopic (STEM) images. The membranes showed proton conductivity under humidified conditions; the highest proton conductivity was 6 x 10(-2) S cm(-1) at 95% relative humidity (RH) and 80 degrees C. The membranes were mechanically stable with high storage moduli (ca. 10(9) Pa) and loss moduli (ca. 10(8) Pa). These mechanical properties were independent on the ion exchange capacity (IEC) of the membranes. The triazole groups were effective in improving the mechanical and oxidative stability of the sulfonated poly(arylene ether) block copolymer membranes.

A sulfonated aromatic block copolymer (SABC), consisting of hydrophobic and hydrophilic blocks, was analyzed by heteronuclear single-quantum correlation (HSQC), heteronuclear multiple-bond correlation (HMBC) and HSQC total correlation spectroscopy (HSQC-TOCSY). Because of its complicated chemical structure with five different phenylene rings, 12 types of H-1 signals and 24 types of C-13 signals were observed in a narrow chemical shift range (7.0-8.0 p p.m. for H-1 and 118-162 p.p.m. for C-13). To improve the H-1 signal separation, the temperature conditions for the H-1 nuclear magnetic resonance (NMR) experiments were optimized. Moreover, H-1 and C-13 NMR signal assignments for the hydrophobic blocks were performed using HSQC and HMBC, with reference to the assignments of a model oligomer. For the hydrophilic blocks, furthermore, HSQC-TOCSY techniques were applied. As a result of these studies, complete H-1 and C-13 NMR signal assignments were made for the SABC. The ion-exchange capacity (IEC) and the copolymerization composition were calculated using the H-1 NMR assignments for the SABC, and the IEC value obtained in this way was consistent with that obtained via titration. Polymer Journal (2012) 44, 845-849; doi:10.1038/pj.2012.125; published online 20 June 2012

Sulfonated polybenzophenone/poly(arylene ether) block copolymers were designed and synthesized via Ni-mediated coupling polymerization. The block copolymers were obtained as high-molecular-weight (M-n = 70-110 kDa, M-W = 150-230 kDa) with low polydispersity index (M-W/M-n = 2.0-2.3). The block copolymer membranes showed well-developed hydrophilic/hydrophobic phase separation and high proton conductivity and low gas permeability. The membrane showed better fuel cell performance and durability compared with those with Nafion, state-of-the-art proton conducting membrane.

An aromatic proton conductive polymer, sulfonated polyimide copolymer membrane, was tested in humidity cycling under the conditions simulating fuel cell operation. The membrane was exposed periodically (every 2 min) to dry (nominal 0% relative humidity) and wet (100% relative humidity) at 80 C, similar to the United States Department of Energy (US DOE) protocol for proton exchange membrane fuel cells. The membrane was durable for 10,000 cycles without mechanical failure. Post-test analyses by H-1 NMR spectra and gel permeation chromatography (GPC) revealed that the membrane was hydrolyzed to some extent during the cycling test while mechanical properties and gas impermeability were only slightly deteriorated. (C) 2011 Elsevier B.V. All rights reserved.

A new series of poly(arylene ether sulfone) multiblock copolymers were synthesized by polycondensation of linear and rigid hydrophobic and densely sulfonated hydrophilic oligomers. Thin membranes were prepared therefrom by solution casting and their properties were compared with those of Nation and other poly(arylene ether sulfone) multiblock copolymers containing perfluorinated biphenylene moieties. The membranes showed good water affinity, high proton conductivity, low hydrogen and oxygen permeability, high mechanical strength, and reasonable oxidative stability. These properties are attractive as an electrolyte for polymer electrolyte membrane fuel cells. It was found that the perfluofinated biphenylene moieties as connecting groups for hydrophilic and hydrophobic blocks affected only slightly the properties of poly(arylene ether sulfone) multiblock copolymer membranes.

Sulfonated polyimide (SPI-8) ionomers were used as binders in the catalyst layers, and their fuel cell performance was evaluated. SPI-8 ionomers functioned well in the anode with only minor overpotential even at low humidity (50% relative humidity (RH)). In contrast, the cathode performance was significantly dependent on the content and molecular weight of the ionomers and humidity of the supplied gases. Higher molecular weight of the ionomer caused larger potential drop at high current density at 80 and 100% RH since oxygen supply and/or water discharge became insufficient due to higher water uptake (swelling) of the ionomer. Similar results were obtained at higher ionomer content, because of the increase of thickness in the catalyst layer. The mass transport was improved with decreasing humidity, however, proton conductivity became lower. While the maximum values of j(@0.70) (v) for all membrane electrode assemblies (MBAs) were ca. 0.35 A/cm(2), each electrode could have the different appropriate operating conditions The results suggest that the parameters such as oxygen supply, proton conductivity, and water uptake and discharge need to be carefully optimized in, the catalyst layers for achieving reasonable cathode performance with hydrocarbon ionomers.

The effect of platinum loading on cathode performance in hydrogen/oxygen fuel cells was investigated using perfluorosulfonic acid (Nafion), sulfonated polyimide (SPI-8) and sulfonated poly(phenylene ether ether ketone) (SPEEK) ionomers as the electrode binder. By lowering the platinum loading, the cathode polarization decreased for MEAs using SPI-8 and SPEEK binders at high humidity (90-100% RH (relative humidity)) due to an improvement of mass transport (oxygen supply and/or water discharge) in the catalyst layer. In contrast, at humidity lower than 80% RH, the effect of platinum loading on the cathode performance differed between these two hydrocarbon (HC) ionomers. When SPI-8 was used as the binder, the cathode polarization increased when lowering the platinum loading due to an increase of activation overpotential. When SPEEK was used as the binder, the effect of platinum loading on the cathode performance was smaller. Such differences can be ascribed to the specific adsorbability of these hydrocarbon binders on the platinum catalyst at low humidity. These results point to crucial factors in achieving higher performance at low platinum loadings and low humidity using HC binders.

Synthesis and properties of aromatic block copolymers composed of highly sulfonated phenylene ether sulfone ketone units as hydrophilic blocks and phenylene ether biphenyene sulfone units as hydrophobic blocks are reported. High molecular weight block copolymers 4 (M-w = 275-362 kDa and M-n = 76-144 kDa) with different compositions (number of repeat unit in the hydrophobic blocks (X) = 15, 30, or 60, and that of hydrophilic blocks (Y) = 4, 8, or 12) were synthesized. Transparent and bendable membranes were obtained by casting from the solution of 4. Due to the rigid rod-like structure of the hydrophilic blocks, the nanophase-separated morphology was not as distinct as that of the conventional sulfonated aromatic block copolymer membranes. Highly sulfonated hydrophilic blocks, which contained phenylene rings with sulfonic acid groups and electron-withdrawing sulfone or ketone groups, contributed to the high proton conductivity and improved oxidative stability of 4 membranes. The 4 (X60Y12) membrane with low IEC (1.18 mequiv g(-1)) showed comparable or higher conductivity than that of Nafion at >80% relative humidity (RH).

A versatile synthetic method of superacid-modified poly(arylene ether sulfone)s via post-bromination has been developed. Three kinds of high molecular weight poly(arylene ether sulfone)s, in which differences lie in the main chain structures, were synthesized and brominated. Careful control of the reaction conditions enabled selective and quantitative bromination of the polymers. The bromo groups were converted to superacid groups via Ullmann coupling reaction to obtain the title ionomers (FSPE-1a, 1b, and 1c). The chemical structure and the ion exchange capacity (IEC) of the FSPE-1s were characterized by H-1 and F-19 NMR spectra. Tough, flexible, and transparent membranes with IEC ranging from 0.87 to 1.09 meq g(-1) were obtained by solution casting. The FSPE-1 membranes showed comparable properties (chemical stability, phase-separated morphology, water absorbability, and proton conductivity,) to those of our previous version of the superacid-modified poly(arylene ether sulfone) (FSPE) synthesized from brominated monomers (pre-bromination method). The advantages of the post-bromination method have been proven by significant improvement in the mechanical strength of the FSPE-1 membranes since it could provide superacid-modified aromatic ionomers with much higher molecular weight.

In situ confocal micro-Raman spectroscopy was used to probe the interior of the electrolyte membrane of a polymer electrolyte fuel cell (PEFC) at various temperatures (40-110 degrees C) and humidities (dry-90% RH). No changes in the Raman spectra for functional groups involved in the polymer were found under humidified and dry conditions, except for the sulfonic acid group. With increasing relative humidity, the band intensity for S-O stretching (nu(S-O)) in the latter increased, and the peak shifted toward lower wavenumber. By analyzing the Raman peaks, water distributions through the Nafion membrane thickness were successfully evaluated in the operating PEFC. It was found that the back-diffusion of water produced at the cathode to the anode, humidifying the membrane, was clearly detectable, and also the rate of water transport in the membrane increased with increasing cell temperature. (C) 2011 Elsevier Ltd. All rights reserved.

Random and multiblock sulfonated poly(arylene ether sulfone)s (SPEs) containing various azole groups such as oxadiazole and triazole were synthesized and characterized for fuel cell application. Successful preparation of SPE membranes depended on the structure of azole groups, which affected solubility of precursors and the resulting SPEs. Although oxadiazole groups were incorporated into hydrophobic component, they were found to be hydrophilic to give higher proton conductivity. Introduction of oxadiazole groups into random SPE gave comparable proton conductivity to that of Nafion NRE at >60% relative humidity at 80 degrees C. Block copolymer structure further increased the proton diffusion coefficient without increasing ion exchange capacity. Hydrolytic and oxidative stability of the SPE membranes was affected by both hydrophilic and hydrophobic components. Oxadiazole groups gave negative impact on hydrolytic and mechanical stability to the SPE membranes. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3863 3873, 2011

The stability of poly(arylene ether sulfone ketone) (SPESK) multiblock copolymer membranes having highly sulfonatecl hydrophilic blocks was tested in an operating fuel cell. The electrochemical properties and drain water were monitored during the test, followed by post-test analyses of the membrane. During a 2000-h fuel cell operation test at 80 degrees C and 53% RH (relative humidity) and with a constant current density (0.2 A cm(-2)), the cell voltage showed minor losses, with slight increases in the resistance. In the drain water, anions such as formate, acetate, and sulfate were observed. Post-test analyses of the chemical structure by NMR and IR spectra revealed that the sulfonated fluorenyl group with ether linkage was the most likely to have degraded during the long-term operation, producing these small molecules. The minor oxidative degradation only slightly affected the proton conductivity, water uptake, and phase-separated morphology.

Poly(arylene ether sulfone) multiblock copoly. were synthesized via oligomeric sulfonation. The successful oligomeric sulfonation enabled multiblock copolymer membranes with different hydrophobic block moiety (biphenyl and naphthalene units). High local concentration of sulfonic acid groups within the hydrophilic blocks enhanced the phase separation between hydrophilic and hydrophobic moiety. Rigid, nonpolar, and planar hydrophobic moiety such as naphthalene groups were effective in increasing proton conductivity and decreasing gas permeability. The multiblock copolymers with naphthalene hydrophobic units with IEC = 2.01 mequiv/g showed comparable proton conductivity to Nafion NRE 212 membrane (0.91 mequiv/g) at >40% RH. The longer blocks were found to increase a characteristic factor (ratio of the proton conductivity to the water volume fraction) as well as phase separation. The membrane showed relatively low oxidative stability under Fenton's test conditions due to higher water uptake and swelling. However, low gas permeability could compensate this drawback for fuel cell applications.

We have conducted combined time-resolved attenuated total reflection Fourier transform infrared (ATR-FTIR) and proton conductivity measurements of Nafion NRE211 membrane during hydration/dehydration cycles at room temperature. Conductivity change was interpreted in terms of different states of water in the membrane based on its delta(HOH) vibrational spectra. It was found that hydration of a dry membrane leads first to complete dissociation of the sulfonic acid groups to liberate hydrated protons, which are isolated from each other and have delta(HOH) vibrational frequency around 1740 cm(-1). The initial hydration is not accompanied by a significant increase of the proton conductivity. Further hydration gives rise to a rapid increase of the conductivity in proportion to intensity of a new delta(HOH) band around 1630 cm(-1). This was interpreted in terms of formation of channels of weakly hydrogen-bonded water to combine the isolated hydrophilic domains containing hydrated protons and hydrated sulfonate ions produced during the initial stage of hydration. Upon dehydration, proton conductivity drops first very rapidly due to loss of the weakly hydrogen bonded water from the channels to leave hydrophilic domains isolated in the membrane. Dehydration of the protons proceeds very slowly after significant loss of the proton conductivity.

A luminescent PtTFP/PMSP polymer coating was prepared for the oxygen partial pressure visualization inside a PEFC. PMSP formed a smooth and tough coating as a highly oxygen-permeable matrix with a thickness of ca. 2 mu m in which the PtTFP was homogeneously dispersed. The coating displayed a strong red luminescence with significantly decreasing intensity upon increasing oxygen partial pressure. The sensitivity for the oxygen partial pressure was high and the analytical curve of the sensor polymer coating was undisturbed by external factors. The PtTFP/PMSP sensor was coated on the surface of a cathode gas diffusion layer on the air flow channel inside PEFC. The oxygen-pressure distribution in the air flow channel was successfully visualized while operating the PEFC.

Novel ionomers based on polybenzimidazole block sulfonated poly(arylene ether sulfone) show excellent thermal properties. The ionic aggregation of sulfonic acid groups leads to well-developed phase separated morphology and thus high proton conductivity at wide humidity range, up to 65 mS cm(-1) at 90% relative humidity.

A series of block copoly(arylene ether)s containing pendant superacid groups were synthesized, and their properties were investigated for fuel cell applications. Two series of telechelic oligomers, iodo-substituted oligo(arylene ether ketone)s and oligo(arylene ether sulfone)s, were synthesized. The degree of oligomerization and the end groups were controlled by changing the feed ratio of the monomers. The nucleophilic substitution polymerization of the two oligomers provided iodo-substituted precursor block copolymers. The iodo groups were converted to perfluorosulfonic acid groups via the Ullmann coupling reaction. The high degree of perfluorosulfonation (up to 83%) was achieved by optimizing the reaction conditions. Tough and bendable membranes were prepared by solution casting. The ionomer membranes exhibited characteristic hydrophilic/hydrophobic phase separation with large hydrophilic clusters (ca. 10 nm), which were different from that of our previous random copolymers with similar molecular structure. The block copolymer structure was found to be effective in improving the proton-conducting behavior of the superacid-modified poly(arylene ether) ionomer membranes without increasing the ion exchange capacity (IEC). The highest proton conductivity was 0.13 S/cm at 80 degrees C, 90% relative humidity, for the block copolymer ionomer membrane with IEC = 1.29 mequiv/g. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 452-464, 2011

Proton exchange membrane fuel cells (PEMFCs) are promising clean energy conversion devices in residential, transportation, and portable applications. Currently, a high-pressure tank is the state-of-the-art mode of hydrogen storage; however, the energy cost, safety, and portability (or volumetric hydrogen storage capacity) presents a major barrier to the widespread dissemination of PEMFCs. Here we show an ‘all-polymer type’ rechargeable PEMFC (RCFC) that contains a hydrogen-storable polymer (HSP), which is a solid-state organic hydride, as the hydrogen storage media. Use of a gas impermeable SPP-QP (a polyphenylene-based PEM) enhances the operable time, reaching up to ca. 10.2 s mg , which is more than a factor of two longer than that (3.90 s mg ) for a Nafion NRE-212 membrane cell. The RCFCs are cycleable, at least up to 50 cycles. The features of this RCFC system, including safety, ease of handling, and light weight, suggest applications in mobile, light-weight hydrogen-based energy devices. HSP HSP −1 −1

Poly(arylene ether)s containing superacid groups (FSPEs) were synthesized as proton conducting membranes for fuel cell applications. To obtain the title ionomers, a series of brominated poly(arylene ether)s were synthesized and perfluorosulfonated via Ullmann coupling. The chemical structure and the ion exchange capacity (IEC) of the FSPEs were characterized by H-1 and F-19 NMR spectra. Tough, flexible, and transparent membranes with the IEC ranging from 0.34 to 1.29 mequiv g(-1) were obtained by solution casting. The FSPE membranes did not show obvious glass transition behavior up to the decomposition temperature (180 degrees C). Microscopic analyses revealed homogeneous and well-connected ionic clusters for the high IEC membrane. Compared to conventional sulfonated poly(arylene ether) membranes, the FSPE membranes showed much higher proton conductivity. The highest proton conductivity of 0.07S cm(-1) was achieved at 80 degrees C and 86% relative humidity (RH) with the IEC = 1.29 mequiv g(-1) membrane. A fuel cell using the FSPE membrane showed comparable performance to that of a Nafion cell at 78% RH and 80 degrees C.

Poly(arylene ether sulfone ketone) (SPESK) multiblock copolymers having highly sulfonated hydrophilic blocks were synthesized and the fuel cell performance with the copolymers was investigated. A membrane electrode assembly (MEA) using an SPESK ionomer with an ion exchange capacity of 1.8 mequiv g(-1) as membrane and Nafion as the electrode binder showed comparable fuel cell performance and ohmic resistance to that using a Nafion NRE 211 membrane at 80 degrees C and 30% relative humidity (RH). A Nafion-free, all-SPESK MEA using SPESK as both the membrane and the binder was operable at 100 degrees C and 50% RH. The fuel cell performance was limited not only by the proton conductivity of the SPESK membrane but also by the low water flux through the membrane and specific adsorption of the ionomer on the platinum catalyst.

A new series of sulfonated polyimide (SPI) copolymers containing NH, OH, or COOH groups were synthesized by the polycondensation of 1,4,5,8-naphthalnetetracarboxylic dianhydride, 3,3'-bis(sulfopropoxy)-4,4'-diaminobiphenyl, and 3-(4-aminophenyl)-5-(3-aminophenyl)-1H-1,2,4-triazole (SPI-8-m), 3,5-bis(4-aminophenyl)-1H-1,2,4-triazole (SPI-8-p), 3,6-diaminocarbazole (SPI-9), 3,5-diamino-1H-1,2,4-triazole (SPI-10), bis(3-aminopropyl)-amine (SPI-11), 2,6-diaminopurine (SPI-12), 2,4-diamino-6-hydroxyprymidine (SPI-13), or 3,5-bis(4-aminophenoxy)benzoic acid (SPI-14). The obtained SPIs were soluble in polar organic solvents and gave tough and flexible membranes by solution casting. The SPI membranes having NH and COOH groups showed high thermal (decomposition temperature approximate to 1200 degrees C) and mechanical (maximum stress >22 MPa) stability. Introducing NH groups, especially triazole and carbazole groups, was effective in improving proton conductive properties of SPI membranes at low humidity. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2846 2854, 2010

A series of poly(arylene ether)s containing pendant superacid groups on fluorenyl groups were synthesized and their properties were investigated for fuel cell applications. Poly(arylene ether)s containing iodo groups were synthesized by the polymerization of 2,7-diiodo-9,9-bis(4-hydroxyphenyl)fluorene with difluorinated compounds such as decafluorobiphenyl, bis(4-fluorophenyl)sulfone, and bis(4-fluorophenyl)ketone, under nucleophilic substitution conditions. The iodo groups on the fluorenyl groups were converted to perfluorosulfonic acid groups via the Ullmann coupling reaction. The degree of perfluorosulfonation was controlled to be up to 92%, which corresponds to an ion exchange capacity (IEC) of 1.52 meq/g. The ionomers yielded flexible, ductile membranes by solution casting. The ionomer membranes exhibited a characteristic hydrophilic/hydrophobic phase separation, with small interconnected hydrophilic clusters (2-3 nm), which is similar to that of the benchmark perfluorinated membrane (Nafion). The aromatic ionomers containing superacid groups showed much higher proton conductivities than those of the conventional sulfonated aromatic ionomers with similar main chain structures. Fuel cell performance with the superacidic ionomer membranes was also tested.

The performances of gas diffusion electrodes (GDEs) containing Pt/C catalyst (48 wt.% and 68 wt.%-Pt) and sulfonated poly (arylene ether) (SPAE) ionomer (ion exchange capacity, IEC = 1.8 and 2.5 meq g(-1)) as a proton-conducting binder (SPAE-GDE) were examined in a PEFC at 80 degrees C and relative humidities (RH) from 60% to 100%. Based on our analyses in Part 1, we have succeeded in improving the cathode performance over the whole range of current densities examined by using a high Pt-loading for the catalyst (68 wt.%-Pt/C), in place of the previously used 48 wt.% one, for the reduction of thickness of the catalyst layer, which enabled us to increase the O(2) gas diffusion rate and to suppress the adsorption of the SPAE binder on the Pt surface via an effective utilization of generated water. The performance, especially at low RH, was improved further by employing an SPAE binder with a lower IEC, 1.8 meq g(-1) [SPAE(1.8)]. It was demonstrated by cyclic voltammetry that the specific adsorption of the sulfonate or organic moiety on the Pt surface was indeed suppressed for the case of SPAE(1.8). Hence, for the SPAE-GDEs, the use of a high Pt-loading catalyst, together with a binder with an appropriate IEC, is very important. (C) 2010 Elsevier Ltd. All rights reserved.

Poly(arylene ether sulfone ketone) (SPESK) multiblock copolymer membranes having highly sulfonated hydrophilic blocks were synthesized. The degree of polymerization of hydrophobic blocks (X) was controlled to be 15, 30, and 60 and that of hydrophilic blocks ( Y) to be 4, 8, 12, and 16. Morphological observation by scanning transmission microscopy (STEM) and small-angle X-ray scattering (SAXS) showed that high local concentration of sulfonic acid groups within the hydrophilic blocks enhanced phase separation between the hydrophobic and hydrophilic blocks. Rodlike hydrophilic aggregates were found to be interconnected very well, which resulted in high proton conductivity even at low relative humidity (RH). The ionomer membrane with X30 Y8 and 1.86 mequiv/g of ion exchange capacity (IEC) showed 0.03 S/cm at 80 degrees C and 40% RH, which was a comparable or higher proton conductivity than that of the state-of-the-art perfluorinated ionomer (Nation) membrane. The longer blocks induced higher proton conductivity; however, excessively long block length offset mechanical properties. Low hydrogen and oxygen permeability was also observed.

Gas diffusion electrodes (GDEs) containing Pt/C catalyst and sulfonated poly (arylene ether) (SPAE) ionomer as a proton conducting binder (SPAE-GDE) were prepared. The cathode performances were evaluated in a PEFC at 80 degrees C and relative humidities (RH) from 60 to 100%. The value of the electrochemical active surface area (ECA) of 65 m(2) g(-1) for the SPAE-GDE. which was measured by cyclic voltammetry at 100%-RH and 40 degrees C, was nearly the same as that for a Nafion-GDE. In contrast, the RH-dependencies of the performance indices (Such as mass activity at 0.9 V, Tafel slope, or current density at 0.7 V) at the SPAE-GDE were very large and distinct from those for the conventional Nafion-GDE. With decreasing RH, the mass activity at the Nafion-GDE decreased monotonically, whereas that at the SPAE-GDE reached a maximum at 88%-RH and decreased steeply below 78%-RH. predominantly due to a strong adsorption of functional groups, probably sulfonate groups, in the SPAE on the Pt catalyst surface. However, at 88-100%-RH, the concentration polarization became significant for current densities j > 0.1 A cm(-2) due to excessive swelling of the SPAE ionomer. Strategies to improve the performance of SPAE-GDEs have been elucidated. (C) 2009 Elsevier Ltd. All rights reserved.

A series of sulfonated poly(arylene ether sulfone)s (SPES) block copolymers containing fluorenyl groups were synthesized. Bis(4-fluorophenyl)sulfone (FPS) and 2,2-bis(4-hydroxy-3,5-dimethylpheny)propane were used-as comonomers for hydrophobic blocks, whereas FPS and 9,9-bis(4-hydroxyphenyl)fluorene were used as hydrophilic blocks. Sulfonation with chlorosulfonic acid gave sulfonated block copolymers with molecular Weight (M(w)) higher than 150 kDa. Proton conductivity of the SPE block copolymer with the ion exchange capacity (IEC) = 2.20 mequiv/g was 0.14 S/cm [80% relative humidity (RH)] and 0;02 S/cm (40% RH) at 80 degrees C, which is higher or comparable to that of a perfluorinated ionomer (Nafion) membrane. The longer hydrophilic and hydrophobic blocks resulted in higher water uptake and higher proton conductivity; Scanning transmission electron microscopy observation revealed that phase separation of the SPE block copolymers was more pronounced than that of the SPE random copolymers. The SPE block copolymer membranes showed higher mechanical properties than those of the random ones. With these properties, the SPE block copolymer membranes seem promising for fuel-cell applications.

We have investigated the oxygen reduction reaction (ORR) at the interface of Pt nanoparticles dispersed on carbon black (Pt/CB) with a sulfonated polyimide ionomer layer (SPI-8). The electrochemical experiments were carried out in air-saturated 0.1 M HClO(4) aqueous solution at 25 degrees C via the rotating ring disk electrode technique. Slow-sweep (5 mV s(-1)) hydrodynamic voltammetry yielded accurate estimates of the activity of the Pt catalysts under steady state conditions. It was found that the ORR was purely kinetically controlled provided that the polyimide ionomer layer covering the Pt/CB catalysts was thinner than 0.05 mu m (threshold thickness) for higher potentials. When thicker than 0.05 mu m, the oxygen diffusion limitation through the ionomer was non-negligible for potentials lower than 0.8 V vs the reversible hydrogen electrode, RHE. The threshold thickness was approximately half of that for a similar perfluorinated ionomer(Nafion)-coated Pt/CB (Nafion-PUCB) electrode. The hydrogen peroxide yield, P(H(2)O(2)), was lower than 0.6% of the overall ORR current in the 0.7-+0.8 V vs RHE range for the SPI-8-Pt/CB electrodes, which was somewhat lower than that for the Nafion-Pt/CB ones. In particular, P(H(2)O(2)) was negligibly low (<0.2%) when the polyimide ionomer layer was thinner than 0.05 mu m. The low P(H(2)O(2)) is favorable for fuel cell applications, since hydrogen peroxide is regarded as one of the major factors responsible for the degradation of fuel cell constituent materials such as the ionomer binder in the catalyst layers, the ionomer membrane itself, and the carbon support.

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 (M(n) = 150-220 kDa; M(w) = 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 proton diffusion coefficients as well as low water swelling. SPE4 membrane showed the highest proton conductivity at 50-80 degrees C and 10-90% RH among the four SPEs membranes. The smaller hydrophobic component was also effective in terms of gas permeation and mechanical properties for fuel cell applications.

Aromatic polymers containing perfluorosulfonic acid groups show well-developed and interconnected ionic clusters, and thus high proton conductivity at wide humidity range.

Poly(arylene ether sulfone)s (SPEs) block copolymers containing fluorenyl groups were synthesized for fuel cell applications. Post-sulfonation of the polymers by chlorosulfonic acid gave sulfonated block copolymers having highly sulfonated hydrophilic block. SPE block copolymer membrane with the ion exchange capacity (IEC) = 2.20 meq/g showed proton conductivity, 0.14 S/cm (80% RH) and 0.02 S/cm (40% RH) at 80 degrees C, which is higher or comparable to that of perfluorinated ionomer (Nafion (R)) membrane. STEM observation of Ag-stained membranes revealed that phase separation of the SPE block copolymers was more developed than that of the SPE random copolymers. Long-term hydrolytic stability of these membranes has been confirmed.

For polymer electrolyte membrane fuel 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 degrees 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 degrees 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. (C) 2008 Elsevier Ltd. All rights reserved.

A series of sulfonated polyimide (SPI) copolymers containing methyl, methoxy, or fluorine groups were synthesized to elucidate the substituents effect on their proton conducting properties as well as thermal, hydrolytic, and oxidative stability for polymer electrolyte membrane fuel cell applications. SPIs of high molecular weight (M-w > 200 kDa, M-n > 80 kDa) along with the ion exchange capacity (IEC) varying between 1.34 and 1.91 mequiv/g were obtained, which gave tough, ductile, and flexible membranes by solution, casting. The thermal properties of the SPIs were dominated by the electronic structure of the sulfonated aromatic rings. The electron-donating methyl groups lowered the thermal decomposition temperature. The hydrolytic and oxidative stability was roughly in the order of IEC (the higher IEC membranes were less stable). Fluorine groups, either as -F or -CF3, had negative effect on the hydrolytic and oxidative stability. In the water uptake and proton conductivity, hydrophobic components are rather more influential than the substituents. It was found out that the SPI(5, 8, 0.7) containing bis(phenoxy)biphenylene sulfone moieties as a rigid hydrophobic component showed the best balanced properties in terms of the stability and the proton conductivity for its rather low IEC. (c) 2008 Wiley Periodicals, Inc.

A series of sulfonated polyimide copolymers containing 1H-1,2,4-triazole groups in the main chains were synthesized as proton-conducting membranes for fuel cell applications. Polycondensation of triazole-containing dianiline, acid-functionalized benzidine, and naphthalenetetracarboxylic dianhydride gave the title polyimide ionomers. The ionomers were high molecular weight (M-w > 100 kDa, M-n > 20 kDa) to give tough and flexible membranes by Solution casting. The ion exchange capacity (IEC) of the membranes ranged from 1.10 to 2.68 mequiv/g as confirmed by H-1 NMR analyses and titration. Comparison with the other polyimide ionomer membranes revealed that introducing triazole groups caused better thermal stability (decomposition temperature of ca. 200 degrees C), comparable hydrolytic and oxidative stability, and better mechanical properties. Although NH groups did not function as ion exchange sites, the triazole-containing membrane,; showed slightly higher proton conductivity. The highest proton conductivity (0.3 S/cm at 88% RH) was obtained for the high IEC (2.68 mequiv/g) ionomer membrane. The ionomer membranes showed low hydrogen and oxygen permeability under dry and wet conditions.

A series of sulfonated poly(arylene ether sulfone)s (SPEs) containing fluorenyl groups as bulky components were synthesized and characterized for fuel cell applications. Introduction of disodium 3,3'-disulfo-4,4'-difluorophenyl sulfone (SFPS) monomer gave ionomers with high acidity and accordingly high proton conductivity as well as high proton diffusion coefficient (D,) at low humidity. The membrane of SPE60 (where the number denotes mole percentage of the component containing sulfonic acid groups; IEC (ion exchange capacity) = 1.68 mequiv./g) exhibited high proton conductivity of 4.6 x 10(-3) S/cm at 40% RH and 80 degrees C, which is one order of magnitude higher than that (6 x 10(-4) S/cm) of our previous SPE (SPE-1, IEC = 1.58 mequiv./g). D, of SPE60 membrane was ca. 4 times higher than that of the SPE-1 membrane at low water volume fraction. SPE membranes showed good oxidative and hydrolytic stability as well as favorable thermal and mechanical properties. Small-angle X-ray scattering analyses showed that the phase separation of SPE membranes was much less developed than that of the perfluorinated Nafion membrane which accounts for lower hydrogen and oxygen permeability of the former membranes. (C) 2007 Elsevier B.V. All rights reserved.

Poly(arylene ether sulfone)-based ionomers containing sulfofluorenyl groups have been synthesized for applications to polymer electrolyte membrane fuel cells (PEMFCs). In order to achieve high proton conductivity and chemical, mechanical, and dimensional stability, the molecular structure of the ionomers has been optimized. Tough, flexible, and transparent membranes were obtained from a series of modified ionomers containing methyl groups with the ion-exchange capacity (IEC) ranging from 1.32 to 3.26 meq/g. Isopropylidene tetramethylbiphenylene moieties were more effective than the methyl-substituted fluorenyl groups in giving a high-IEC ionomer membrane with substantial stability to hydrolysis and oxidation. Dimensional stability was significantly improved for the methyl-substituted ionomer membranes compared to that of the non-methylated ones. This new ionomer membrane showed comparable proton conductivity to that of the perfluorinated ionomer membrane (Nafion 112) under a wide range of conditions (80-120 degrees C and 20-93% relative humidity (RH)). The highest proton conductivity of 0.3 S/cm was obtained at 80 degrees C and 93% RH. Although there is a decline of proton conductivity with time, after 10 000 h the proton conductivities were still at acceptable levels for fuel cell operation. The membranes retained their strength, flexibility, and high molecular weight after 10 000 h. Microscopic analyses revealed well-connected ionic clusters for the high-IEC membrane. A fuel cell operated using the polyether ionomer membrane showed better performance than that of Nafion at a low humidity of 20% RH and high temperature of 90 degrees C. Unlike the other hydrocarbon ionomers, the present membrane showed a lower resistance than expected from its conductivity, indicating superior water-holding capability at high temperature and low humidity.

In order to improve the stability and the proton conductivity of sulfonated polyimide ionomer membranes, effect of cross-linking has been investigated. The cross-linking moieties have been introduced into the ionomer structure by applying 2 mol% of trifunctional monomer in the polymerization reaction. Tough, flexible, and processable membranes were obtained by solution casting. Among the three cross-linking agents investigated, tris(aminoethyl)amine (TE) was the most effective to improve the membrane properties. Having high ion exchange capacity (2.33 meq/g), the cross-linked SPI-5TE showed good stability to the oxidative and hydrolytic degradation, superior mechanical strength, and high proton conductivity at low humidity conditions. Low methanol permeation of the cross-linked SPI-5TE membrane than the uncross-linked SPI-5 and Nafion 112 membranes has been confirmed.

A series of branched and cross-linked poly (arylene ether sulfone) ionomers containing sulfofluorenyl groups, 2b-e were synthesized in order to investigate the effect of these chemical modifications on the properties. Ionomers 2b-e gave a flexible, ductile, and transparent membrane by casting from DMAc solution. The branching and cross-linking were effective to improve the dimensional stability under wet conditions without losing their high thermal, oxidative, and hydrolytic stability. The cross-linked ionomer 2e (IEC=2.63 meq.g(-1)) membrane showed high proton conductivity of 0.2 S.cm(-1) at 87% RH and 0.02 S.cm(-1) at 57% RH. The branched ionomer 2b membrane was durable in proton conductivity for almost 2 months without any chemical degradation.

Sulfonated polyimide (SPI) membranes have been evaluated as electrolyte membranes in direct methanol fuel cells (DMFCs). The membrane-electrode assembly (MEA) was made by hot-pressing the membrane, an anode and a cathode, catalyzed with PtRu/CB (PtRu dispersed on carbon black) and Pt/CB bound with Nafion((R)) ionomer, respectively. The performance of the cell based on SPI was compared with that of Nafion((R)) 112 in various operation conditions such as cell temperature (T(cell)), cathode relative humidity (RH), and methanol concentration (C(MeOH)). The methanol crossover at the cell based on SPI was a half of Nafion((R)) 112, resulting in the improved cell efficiency. Advantage of the use of SPI became much distinctive from the conventional Nafion((R)) 112 when the DMFC was operated at a higher Tee or a higher C(MeOH). (c) 2005 Elsevier Ltd. All rights reserved.

Proton conducting membranes are key materials in polymer electrolyte fuel cells (PEFCs). Perfluorinated ionomers have been state-of-the-art for decades, but challenges remain for the high temperature operation of fuel cells. We present herein our approaches toward durable and high temperature-operable ionomer membranes using non-fluorinated aromatic polyimide copolymers combined with aliphatic building blocks.

A series of novel polyimide electrolyte copolymers (SPPI-X) containing fluorenyl and sulfopropoxy groups were synthesized. The copolymer composition (X: molar percentage of the fluorenyl groups) was set from 0-60 mol% so that the ion exchange capacity of the electrolyte membrane ranged from 1.3 to 2.9 meq g(-1). Tough and flexible membranes, with the typical polyimide brown colour, were obtained by casting from the polymer solution. The SPPI membranes are thermally stable up to 220 T without glass transition, melting, and decomposition under a dry nitrogen atmosphere. Sulfopropoxy groups are effective at improving oxidative stability in Fenton's reagent since the main polymer chains are separated from sulfonic acid groups and are less susceptible to hydrophilic attack by the oxidative radical species. A high mechanical strength, with 53 MPa of the maximum stress at break and 15% of strain, was confirmed for SPPI-30 membrane. The proton conductivity of the SPPI membranes was higher than 0.1 S cm(-1) at temperatures from 40 to 120 degrees C. The long term proton conductivity stability (ca. 1,000 h) was also confirmed at 120 degrees C, to prove the possible availability of the membrane materials for high temperature PEFC applications.

A series of sulfonated polyimide copolymers (FSPIH-X; X refers to molar percentage of his(trifluoromethyl)biphenylene content) with X from 0 to 60 mol % were synthesized, of which electrolyte properties were investigated and compared to those of the perfluorinated ionomer (Nafion 112). FSPIH-X membranes are thermally stable with no glass transition temperature observed below the decomposition temperature (280 degreesC). Oxidative stability of the membranes is improved with an increase in the content of trifluoromethyl substituents in the copolymer structure. FSPIH-60 endured for more than 9 h in Fenton's reagent at 80 degreesC. Bis(trifluoromethyl)biphenylene groups with the molecular size of 6.1 Angstrom make each polymer chain separate and produce space to hold water molecules despite their hydrophobic property so that the maximum water uptake was observed for FSPIH-20. Unlike the fluorene groups containing polyimides (SPIH-X), a strong water confinement effect was not obtained for FSPIH-X. The optimum composition of bis(trifluoromethyl)biphenylene groups was 30 mol %, and the FSPIH-30 membrane showed higher proton conductivity than 0.2 S cm(-1) at 30-140 degreesC. A direct methanol fuel cell (DMFC) using FSPIH-30 membrane has revealed that the methanol crossover through the membrane equivalent to the current density of methanol oxidation at cathode (j(CH3OH)) is 64 mA/cm(2) and merely 30% of that of Nafion 112 at open-circuit potential. A terminal voltage of 0.38 V was obtained at 200 mA/cm(2) by the operation at 80 and 90 degreesC with supplying dry and humidified oxygen.

Novel sulfonated polyimide copolymers as electrolytes for high-temperature fuel cell applications are reported. A series of sulfonated polyimide copolymers (SPIH-X; X refers to molar percentage of fluorenyl content) containing 0-60 mol % of fluorenyl groups as hydrophobic component were synthesized, of which electrolyte properties were investigated and compared to those of the perfluorinated ionomer (Nafion 112). High-molecular-weight copolymers with good film-forming capability were obtained. Thermal stability with decomposition temperature of ca. 280 degreesC and no glass transition temperature was confirmed for the copolymers. SPIH shows unique water uptake behavior with the maximum value of 57 wt % at X = 30. Water molecules absorbed in the electrolyte membrane with this specific composition do not evaporate easily so that the high proton conductivity of 1.67 S cm(-1) was obtained at 120 degreesC and 100% RH. The branching and cross-linking of SPIH-30 were carried out by applying 2 mol % of trifunctional monomer (melamine) in the polymerization and by electron beam irradiation upon the membrane. The branching and cross-linking are effective to improve oxidative stability and mechanical strength. Although the proton conductivity decreases slightly by the branching and cross-linking, it still remains at the comparable level to that of Nafion 112.