Search

Novel fluorocarbon–hydrocarbon hybrid block copolymer electrolytes were synthesized. The block copolymer electrolytes consist of poly(perfluoropropyl sulfonimide) (PC3SI) as a perfluorinated hydrophilic segment and poly(ether ether sulfone) as a hydrocarbon hydrophobic segment. The sulfonimide group of poly(perfluoropropyl sulfonimide) has superacidity, very low equivalent weight (EW = 293 g/equiv), and a proton conductivity of 1.2 × 10–2 S/cm under dry conditions and 25 °C, although soluble in water. The proton conductivity of the block copolymer was 1.7 × 10–3 S/cm at 20% relative humidity and 25 °C, which is three times as high as that of Nafion 112.

This paper proposes an in-situ method to estimate cation contamination level in Polymer Electrolyte Membrane Fuel Cells (PEMFCs). Results of experiments and theoretical analysis revealed that the dimensionless peak height in imaginary part of the electrochemical impedance spectroscopy (EIS) at low frequency under H2-H2 condition is proportional to cation contamination level, independent of platinum loading, catalyst layer structure, gas diffusion layer thickness, ion exchange capacity of the PEM, and PEM thickness. From the dimensionless peak height, cation contamination level can be estimated without destruction of cells.

The effect of side-chain structures in perfluoro-sulfonic acid ionomers on the adsorption of the terminal sulfonate moiety on the surface of Pt is investigated with voltammetry and surface-enhanced infrared absorption spectroscopy (SEIRAS). Analyses with low-molecular-weight model anions with and without an ether group in the perfluoro-alkyl chain indicate that the anions are adsorbed on Pt through one or two oxygen atom(s) of the terminal sulfonate group and that the oxygen atom of the ether group also interacts with the Pt surface, leading to stronger adsorption of the anions with an ether group. On the basis of the results obtained with the model anions, the adsorption of the terminal sulfonate moieties in perfluorinated sulfonic acid ionomers and its effect on oxygen reduction reaction (ORR) is discussed. It is shown that the ionomers having longer side chains more strongly block ORR due to the flexibility of the side chains.

For improving the efficiency and reducing Pt use in polymer electrolyte fuel cells, it is essential to improve the catalytic activity per Pt mass for oxygen reduction reaction (ORR) in the cathode. In addition, recent studies have demonstrated that a high surface area of the catalyst per Pt mass is necessary for reducing the oxygen transport resistance in the catalyst layer. Alloying inner cores of nanoparticles by introducing base metals and reducing particle sizes are established methods to increase the mass activity and the surface area, respectively. Both the methods are, however, disadvantageous for the catalyst durability. Thus, the activity, durability, and power density are generally in trade-off relations. A promising method for solving this problem is to change the properties of the surrounding rather than the catalyst itself. Ionomers adsorbed on Pt catalyst have been confirmed to inhibit ORR and oxygen permeation to the interface [1, 2]. In other words, both the reaction and permeation can be promoted without deteriorating the catalyst durability by mitigating the ionomer adsorption. We have indeed shown that the ionomer adsorption can be suppressed by modifying the molecular structure of ionomer [3]. The ionomer adsorption can be suppressed also by inserting a sub-nanometer thin porous carbon layer between the Pt surface and ionomer. The inserted carbon layer has been also shown to suppress the catalyst degradation during potential cycles [4]. In this talk, we first summarize our analytical works on Pt/ionomer interfaces, focusing on the mechanisms of the adsorption of anionic moieties in ionomers and its effect on ORR. Then, we discuss the effectiveness of various approaches for mitigating ionomer adsorption, as well as their limitations. The future direction of cathode catalyst developments is also discussed. [1] Subbaraman et al., ChemPhysChem 11, 2825 (2010). [2] Jinnouchi et al., Electrochim. Acta, 188, 767 (2016) [3] Kodama et al., ACS Catal. 8 694 (2018). [4] Yamada et al., J. Electrochem. Soc., in press.

Cathode catalyst layers for polymer electrolyte fuel cells (PEFC) with ionomer nanofiber scaffoldings (iNFS-CL) are fabricated by the electrospinning method, and their performances and elemental properties are comprehensively investigated. The cells with the iNFS-CLs exhibit higher performances than those with conventional cathode catalyst layers over the humidity range of 30%–165%RH. The higher robustness against the change in humidity is ascribed to improved oxygen and water transport properties by continuous pores in the catalyst layer. In addition, the fabrication method could reduce the ionomer densities near the catalyst surfaces, and as a result, catalyst poisonings by anionic groups from the ionomer are suppressed. Thus, the iNFS-CL structure is promising for improving the efficiency and power density of the PEFCs.

Introduction In catalyst layers of polymer electrolyte membrane fuel cells (PEMFC), a solid polymer electrolyte, called “ionomer” to be distinguishable from the electrolyte membrane, is used to form electrochemical interfaces on catalyst surfaces. Recent studies, however, showed that a perfluorinated sulfonic acid polymer (e.g. Nafion), which is almost exclusively used for the ionomer, blocks active sites on Pt catalyst and, therefore, slows down the kinetics of oxygen reduction reaction (ORR) [1]. A plausible poisoning species is the sulfonic anion of the polymer molecule, the adsorption of which on Pt (111) surface is clearly seen in the cyclic voltammogram (CV) [1-3]. It is, therefore, expected to be effective for improving the ORR performance to use an ionomer with a functional group that is less adsorptive to Pt surface. Recently, Shinohara et al. developed a novel ionomer having two sulfonimide acid groups in its side chain ended with a hydrophobic group, instead of a sulfonic acid group, NBC4 (Fig. 1), which has higher protonic conductivity and O2 permeability than Nafion [4]. The new side chain likely has a stronger steric effect for anion adsorption, and NBC4 is expected to be lesspoisoning and have improved properties not only for the proton conduction and O2 transport but also for ORR kinetics. These expectations are examined experimentally in the present study.

Since the inventions in 1980s of the basic structure, i.e. a layered structure of a perfluorosulfonic acid membrane and gas diffusion electrodes including Pt on carbon and an ionomer, significant advancement has been achieved and finally, commercial products are now in the market for automobile and stationary applications. In this talk, key technologies established in this period were quickly reviewed and present status and issues were presented as well as on-going trends to address the issues. A part of this study was financially supported by the New Energy and Industrial Technology Development Organization.

The present study was undertaken to investigate the function of protease-activated receptor (PAR) in endometriotic lesions using a mouse model of endometriosis. Unilateral ovariectomy (uOVX) was performed on female nude mice followed by intraperitoneal transplantation of a suspension mixture of immortalized human endometrial epithelial cells (EM-1) and stromal cells (EtsT-499). Endometriosis-like lesions were observed mostly around the dissection site after transplantation. The expression of interleukin (IL)-6 and cyclooxygenase-2 in the lesions was enhanced in uOVX mice compared to non-uOVX animals. In non-uOVX mice, IL-6 mRNA levels were higher in lesions formed with cells that were pretreated with PAR1/2 agonists (thrombin, 10 U/ml and PAR2-activating peptide, 30 μM) compared to untreated, intact cells. Peritoneal IL-6 concentrations were also increased in the PAR1/2 agonists–treated group. IL-6 expression induced by PAR activation was blocked by the treatment of cells with serine protease inhibitors. In cultured endometrial cells, simultaneous treatment with PAR1 and PAR2 agonists significantly increased the expression of IL-6. These results suggest that peritoneal bleeding may accelerate IL-6 expression in endometriotic lesions in part through the activation of PAR. Keywords:: endometriosis, endometrial cell, interleukin (IL)-6, protease-activated receptor (PAR), thrombin

One of the fundamental hurdles for further commercialization of fuel cell vehicles (FCV) using polymer electrolyte membrane fuel cells (PEMFC) is their upper limitation of operating temperature. Operating temperature of current PEMFC is much lower than that of internal-combustion engines and it makes FCV require huge radiators for high power operation. Raising operating temperature is beneficial for downsizing and cost reduction for FCV system because it downsizes not only cooling system but also PEMFC stack. One of the root causes of this limitation is the decrease in proton conductivity of the membrane during long term operation. In order to avoid the decrease in proton conductivity, reducing the contamination of metal cations in the membrane is an effective way. Metal cations, which contaminate into the membrane during operation, reduce the proton conductivity of the membrane due to decrease in the proton path in the membrane. Proton conductivity loss by contamination of metal cations is critical for the high temperature performance. In order to reduce cation contamination into the membrane, it is necessary to understand its mechanism. An in-situ measurement for the amount of metal cations should be helpful to understand the phenomena. For this reason, we propose an in-situ quantitative measurement for cation contamination ratio in PEMFC. Electrochemical impedance spectroscopy (EIS) was adapted to the measurement because cation transport inside the membrane was expected to be detectable with EIS. Experimental results showed that EIS spectrum under a certain condition reflects metal cation contamination ratio strongly, which was proposed to be an indicator of cation contamination ratio. The mechanism of EIS spectrum change is explained theoretically by a numerical simulation using a simple model of cation and water transport. Detail of the measurement will be shown in the conference. Therefore this EIS measurement is proposed for the analysis of metal cation contamination mechanisms in PEMFC. Further study will elucidate the impact of catalyst layer, membrane and metal cation species against the EIS spectrum.

Vanadium silyl complexes of the type Cp(dmpe)VSiHRR′ are formed by reaction of Cp(dmpe)VMe (1) with RR′SiH2 (2, R, R′ = Ph; 3, R = Mes, R′ = H) in benzene at room temperature with concomitant relea...

Reaction of 9-bromo-9,10-dihydro-9-silaphenanthrene (6) with lithium diisopropylamide (LDA) in THF at room temperature afforded kinetically stabilized 9-silaphenanthrene 1a bearing an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt). 9-Silaphenanthrene 1a was isolated as pale yellow crystals, and the structure of 1a was completely determined by spectroscopic and X-ray crystallographic analyses. The 1H and 13C NMR chemical shifts corresponding to the 9-silaphenanthrene ring of 1a were observed in a typical aromatic region, while the central silicon atom showed the characteristic signal at 86.9 ppm in the 29Si NMR in C6D6. The 9-silaphenanthrene ring of 1a showed completely planar geometry, indicating that 9-silaphenanthrene has a delocalized 14π-electron system as an aromatic compound. In spite of its high thermal stability, 1a still has high reactivity at the 9,10-position toward small reagents such as H2O.

Synthesis of the first neutral η6-silabenzene complexes [M(η6-C5H5SiTbt)(CO)3] (M = Cr (2), Mo (3); Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl) was achieved by the ligand exchange reactions of [M(CH3CN)3(CO)3] (M = Cr, Mo) with the kinetically stabilized silabenzene 1. X-ray crystallographic analysis of 2 revealed that the η6-coordinated silabenzene rings of the complexes have almost planar geometries with delocalized π-electron structures. The structures of η6-silabenzene complexes 2 and 3 were fully characterized by NMR, UV/vis, and IR spectroscopic analysis. All the 1H, 13C, and 29Si NMR chemical shifts of the SiC5H5 rings of 2 and 3 were shifted to upper field relative to those for silabenzene 1, due to the π-coordination of the silabenzene ring to the metal center. The carbonyl stretching frequencies of 2 and 3 were observed in a region of lower wavenumber as compared to those of the corresponding group 6 metal complexes of benzene. In the UV/vis spectra of 2 and 3, the absorption maxima were ...

The performance of polymer electrolyte fuel cells (PEFCs) is strongly affected by interfaces between the catalyst and ionomer in the cathode catalyst layer. While searching and synthesizing new catalysts have been major strategies for improving the catalytic activity for oxygen reduction reaction (ORR) until recently, modifying the other side of the interface, i.e.the ionomer, is becoming another big challenge because recent studies have revealed its significance on both the activity and oxygen transport. One of the most important properties of ionomers is the strength of the interaction between the anionic groups and Pt surface as already confirmed for real and model catalysts [1 - 3], and therefore, detailed understandings of the adsorption mechanisms of the anionic groups on Pt is essential for developing desirable ionomers. Figure 1 shows the cyclic voltammograms and ORR Tafel plots in 0.1 M HClO4 for Pt (111) surfaces bare and coated with Nafion® film, which was confirmed to be uniform by scanning electron microscopy. The results indicate that ORR activity is suppressed significantly (by over 80%) by the ionomer, while the coverage of the sulfonate moieties adsorbed on the Pt surface is estimated to be small (0.08 ML) from the adsorption peak in the CV by assuming that the adsorption is a one-electron-transfer process (-SO3 – + Pt → -SO3 – Pt + e-). To further investigate the effect of ionomers, low-molecular-weight sulfonic acids were employed as model compounds for the side-chains of ionomers, and the interface was analyzed by in-situ surface enhanced infrared absorption spectroscopy (SEIRAS). Figure 2a shows the SEIRA spectrum of perfluoro-(2-ethoxyethane) sulfonic acid (PESA, C2F5OC2F4SO3H) adsorbed on polycrystalline Pt film. The spectrum reveals the presence of strong bands due to the asymmetric stretching modes of SO3 -and the absence of them due to the asymmetric stretching mode of COC. These observations and the surface selection rule in SEIRAS suggest that the perfluoroalkyl chain is almost parallel to the surface as depicted in Fig. 2b. The orientation of the molecule is presumably determined by the interaction between the ether group and surface and can elucidate the significant ORR suppression by the small coverage with the sulfonate; not only the sulfonate moiety but also the perfluoroalkyl chain blocks Pt sites for ORR. In the meeting, further analytical results as well as promising strategies for suppressing the catalyst poisoning with ionomers will be discussed. References [1] K. Shinozaki, J.W. Zack, S. Pylypenko, B.S. Pivovar, S.S. Kocha, J. Electrochem. Soc., 162F1384-F1396 (2015). [2] R. Subbaraman, D. Strmcnik, V. Stamenkovic, N.M. Markovic, Journal of Physical Chemistry C, 114 8414-8422 (2010). [3] K. Kodama, A. Shinohara, N. Hasegawa, K. Shinozaki, R. Jinnouchi, T. Suzuki, T. Hatanaka and Y. Morimoto, J. Electrochem. Soc. 161, F649 (2014). Figure 1

The first 1-silanaphthalene, 4, was successfully synthesized by taking advantage of an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)-methyl]phenyl (Tbt), and the aromaticity of 4 was discussed on the basis of its 1 H, 1 3 C, and 2 9 Si NMR, Raman, and UV/vis spectra together with theoretical calculations. In contrast to the thermal stability of the Tbt-substituted 2-silanaphthalene 2, 1-Tbt-1-silanaphthalene (4) undergoes a ready [2 + 4] dimerization reaction in solution even at room temperature, despite its stability in the solid state.

The first stable 9-silaanthracene, 5, bearing an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt), was successfully synthesized by the reaction of the corresponding silyl triflate, 7, with a 1.0 M amount of lithium diisopropylamide. The aromaticity of 5 is discussed on the basis of the NMR, UV/vis, and Raman spectra, X-ray structural analysis, and theoretical calculations.

Double hydrosilylation of arylacetylenes with trichlorosilane catalyzed first by platinum and second by a chiral monophosphine−palladium complex generated the corresponding 1,2-bis(silyl)-1-arylethanes, the oxidation of which with hydrogen peroxide gave 1-aryl-1,2-diols of high enantiomeric purity (94−98% ee) in high yields.

Reactions of Cp*(dmpe)Mo(eta(3)-CH(2)Ph) with organogermanes (RR'GeH(2)) afforded germylene complexes Cp*(dmpe)Mo(H)GeRR' (RR' = Ph(2) (2), Et(2) (3), (Mes)H (4), ((t)Bu)H (5)). Compound 2 does not possess an intramolecular H...Ge interaction of the type exhibited by its silicon analogue and by 3. The existence of such interactions appears to depend on the steric properties of substituents on the Ge (or Si) atom. For comparison, a silylene complex was prepared by reaction of 9-silafluorene with 1, to give Cp*(dmpe)Mo(H)Si(C(12)H(8)), which on the basis of NMR spectroscopy does not possess a significant Si...H interaction.

In catalyst layers of polymer electrolyte fuel cells, a solid polymer electrolyte, called “ionomer” for distinguishing it from the electrolyte membrane, is generally used to form good electrochemical interfaces on catalyst surfaces. However, model experiments using Pt single crystal electrodes covered with ionomer films suggested that sulfonate anion in perfluorinated sulfonic acid polymer (e.g. Nafion, with the side chain of OCF2CF(CF3)O(CF2)2SO3H) blocks active sites on Pt catalyst and therefore, slows down the kinetics of oxygen reduction reaction (ORR) [1]. Recently, the catalyst poisoning was found to be weakened by using an ionomer with different anionic structure (NBC4, having two sulfonimide acid groups in its side chain ended with a perfluorobutane, instead of a sulfonic acid group), as shown by broader and smaller anion-related peaks (0.4 – 0.6 V) in the cyclic voltammogram (CV) of Pt (111) coated with NBC4 (black dashed curve in Fig. 1a) than that with Nafion (gray solid curve in Fig. 1a) [2]. In the present study, we report that the anion adsorptivity can be also controlled even by changing the structures of perfluorinated side chain of sulfonic acid ionomer. In Fig. 1a, the black solid curve is the CV for a sulfonic acid ionomer with short side chains (Aquivion, with the side chain of O(CF2)2SO3H). Although the peaks due to the adsorption and desorption of sulfonate anion are sharp, the peak potentials are higher and the peak intensities are weaker than those for the Nafion-coated Pt. Thus ionomer with the shorter side chain is less adsorptive on Pt surface. Fig. 1b shows the CVs for a bare Pt (111) single crystal electrode in low-molecular-weight perfluoro-sulfonic acids of C4F9SO3H (nonafluorobutane sulfonic acid, NFBSA) and C2F5OC2F4SO3H (Perfluoro (2-ethoxyethane) sulfonic acid, PES). The CVs show reduction current due to residual oxygen and ill-defined features probably due to impurities. The Pt (111)-like Hupd plateaus are, however, seen between 0.07 – 0.4 V and anion-related peaks are observed (dashed circles). The potentials of the anion adsorption/desorption peaks are lower and the peak areas are larger for PES than for NFBSA. In addition, the surface enhanced infrared absorption (SEIRA) spectra for a Pt polycrystalline film in the electrolyte of NFBSA showed the band for adsorbed sulfate anion on Pt at 0.4 – 0.7 V (Fig. 2a, the shaded region at ca. 1100 cm-1) and therefore, the anion adsorption peak in the CV of Pt (111) may be not due to the adsorption of NFBSA anion itself, but due to the adsorption of sulfate anion as impurity, which was found to be contained with non-negligible concentration, -1in the SEIRA spectra can be ascribed to the orientations of NFBSA molecules to more IR-active states, not to their adsorptions on the Pt surface.) In contrast, because the SEIRA spectra for PES do not show the clear band due to adsorbed sulfate anion (Fig. 2b), the anion adsorption peak in the CV can be ascribed to the adsorption of PES anion itself. Therefore, presumably, the PES anion is much more adsorptive on Pt than NFBSA anion is, and the presence or absence of the ether group in the perfluoro-sulfonate anions affects the adsorptivity of the anions. References [1]R. Subbaraman et al., ChemPhysChem, 11(2010) 2825. [2]K. Kodama et al., J. Electrochem. Soc. 161(2014) F649. Figure 1

The first stable eta6-germabenzene complexes, that is, [M(CO)3(eta6-C5H5GeTbt)] {M=Cr (2), Mo (3), and W (4); Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}, have been synthesized by ligand-exchange reactions between [M(CO)3(CH3CN)3] (M=Cr, Mo, and W) and the kinetically stabilized germabenzene 1 and characterized by 1H and 13C NMR, IR, and UV/Vis spectroscopy. In the 1H and 13C NMR spectra of 2-4, all of the signals for the germabenzene rings were shifted upfield relative to their counterparts in the free germabenzene 1. X-ray crystallographic analysis of 2 and 4 revealed that the germabenzene ligand was nearly planar and was coordinated to the M(CO)3 group (M=Cr, W) in an eta6 fashion. The formation of complexes 2-4 from germabenzene 1 should be noted as the application of germaaromatics as 6pi-electron ligands toward complexation with Group 6 metals. On the other hand, treatment of 1 with [{RuCp*Cl}4] (Cp*=C5Me5) in THF afforded a novel eta5-germacyclohexadienido complex of ruthenium-[RuCp*{eta5-C5H5GeTbt(Cl)}] (9)-instead of the expected eta6-germabenzene-ruthenium cationic complex [RuCp*{eta6-C5H5GeTbt}]Cl (10). Crystallographic structural analysis of 9 showed that the five carbon atoms of the germacyclohexadienido ligand of 9 were coordinated to the Ru center in an eta5 fashion.

Photophysical and photochemical processes of 9-methyl- and 9-phenyl-9,10-dihydro-9-silaphenanthrene derivatives have been studied at room temperature and 77 K in comparison with the carbon analogue, 9,10-dihydrophenanthrene. These 9,10-dihydro-9-silaphenanthrene derivatives show smaller fluorescence quantum yield and remarkably larger Stokes shifts than those of the carbon analogue. In contrast, their phosphorescence quantum yields are two times larger than those of the carbon analogue, although the absolute value is not so large (approximately 0.1). Reaction products and intermediates produced by the 266 nm light photolysis have been studied, and it has been confirmed that 9-methyl- and 9-phenyl-9-silaphenanthrenes have been photochemically formed in methylcyclohexane at 77 K, in addition to the formation of radical cations of 9,10-dihydro-9-silaphenanthrene derivatives and the carbon-centered radical: 9-hydro-9-silaphenanthrenyl radical.

The first kinetically stabilized 1-silanaphthalenes bearing a 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt) group or a 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl (B...

Background: Various etiologies of myomatous erythrocytosis syndrome (erythrocytosis associated with a uterine leiomyoma), one of which is altered production of erythropoietin, have been proposed. We report a case of erythrocytosis associated with a large uterine leiomyoma in which erythropoietin activity and immunostaining for erythropoietin in the leiomyoma were found. Case: A 64-year-old woman, gravida 2, para 1, was referred to our department for treatment of a large uterine myoma and erythrocytosis with elevated levels of erythropoietin. Total abdominal hysterectomy with bilateral salpingo-oophorectomy was performed, and the results of the pathological examination confirmed the diagnosis of leiomyoma of the uterus, which weighed 920 g. The patient’s postoperative course was satisfactory, and the levels of hemoglobin and erythropoietin were normalized and remained within normal ranges. The level of erythropoietin in the uterine leiomyoma measured by radioimmunoassay was elevated (372 mU/wet gram), and specific immunostaining for erythropoietin was found in the cytoplasm of leiomyoma cells. The levels of erythropoietin extracted from uterine leiomyomas of other patients who did not have erythrocytosis (control patients, n = 5) were lower (65 ± 15.3 mU/wet gram), but specific immunostaining for erythropoietin was also found in the cytoplasm of leiomyoma cells from those patients. Conclusions: Our case was typical of myomatous erythrocytosis syndrome in which uterine leiomyoma was proved to produce erythropoietin. Our results also suggest that erythropoietin is produced in uterine leiomyomas of patients with and without erythrocytosis. Leiomyoma of the uterus may affect the production of erythropoietin and may develop into myomatous erythrocytosis syndrome when the level of erythropoietin exceeds the normal range.

Double hydrosilylation of arylacetylenes with trichlorosilane catalyzed first by platinum and second by a chiral monophosphine−palladium complex generated the corresponding 1,2-bis(silyl)-1-arylethanes, the oxidation of which with hydrogen peroxide gave 1-aryl-1,2-diols of high enantiomeric purity (94−98% ee) in high yields.

A kinetically stabilized 9-silaanthracene (1) underwent unique photochemical and thermal reactions to afford 9,10-Dewar-9-silaanthracene 2a and the head-to-tail [4 + 4] dimer 3, respectively. The structure of 2a was confirmed by 1H, 13C, and 29Si NMR spectra, and the kinetic parameters for the thermal reversion of 2a to 1 were obtained by the measurement of UV/vis spectra. The dimer 3 was thermally stable, and the molecular structure of 3 was determined by X-ray crystallographic analysis. It was experimentally demonstrated for the first time that 9-silaanthracene, as well as anthracene, can afford either the Dewar isomer or [4 + 4] dimer, depending on the reaction conditions.