Akihiro Ohira - Academia.edu (original) (raw)

Papers by Akihiro Ohira

Research paper thumbnail of Effect of Elevated Temperatures on the States of Water and Their Correlation with the Proton Conductivity of Nafion

ACS Omega, 2018

For the first time, we report the effects of elevated temperatures, from 80 to 100°C, on the chan... more For the first time, we report the effects of elevated temperatures, from 80 to 100°C, on the changes in the states of water and ion−water channels and their correlation with the proton conductivity of Nafion NR212, which was investigated using a Fourier transform infrared spectroscopy study. Experimentally, three types of water aggregates, protonated water (H + (H 2 O) n), nonprotonated hydrogen (H)-bonded water (H 2 O•••H 2 O), and non-Hbonded water, were found in Nafion, and the existence of those three types of water was confirmed through ab initio molecular dynamics simulation. We found that the proton conductivity of Nafion increased for up to 80°C, but from 80 to 100°C, the conductivity did not increase; rather, all of those elevated temperatures showed identical conductivity values. The proton conductivities at lower relative humidities (RHs) (up to 50%) remained nearly identical for all elevated temperatures (80, 90, and 100°C); however, from 60% RH (over λ = 4), the conductivity remarkably jumped for all elevated temperatures. The results indicated that the amount of randomly arranged water gradually increased and created more H-bonded water networks in Nafion at above 60% RH. From the deconvolution of the O− H bending band, it was found that the volume fraction f i (i=each deconvoluted band) of H-bonded water for elevated temperatures (>80−100°C) increased remarkably higher than for 60°C.

Research paper thumbnail of A DFT Study on the Dissociation Property of Sulfonic Acids with Different Neighboring Pendants in Polymer Electrolyte Membranes

Proceedings of Computational Science Workshop 2014 (CSW2014), 2015

The proton dissociation property of four model compounds of polymer electrolyte membranes, M1-M4,... more The proton dissociation property of four model compounds of polymer electrolyte membranes, M1-M4, has been studied based on density functional theory. These four model compounds have the same proton donor group, sulfonic acid, while differ by types of neighboring pendants, non-fluorinated and fluorinated. We find that the protons in the fluorinated model compounds can be dissociated when hydrated by 3 water molecules, comparable to Nafion, while for those non-fluorinated compounds, the protons can be dissociated only hydrated by 4 water molecules. The results indicate that the neighboring pendants have a significant effect on the proton dissociation property of the model compounds. The electron-withdrawing group involved in the neighboring pendants can improve the proton dissociation property of the compounds, which would be meaningful for finding a novel polymer electrolyte membrane with good conductivity.

Research paper thumbnail of 二次元空間における半屈曲性ケイ素高分子の配向・構造相転移

Research paper thumbnail of Crosslinked Sulfonated Polyphenylsulfone (CSPPSU) Membranes for Elevated-Temperature PEM Water Electrolysis

Membranes

In order to reduce the burden on the environment, there is a need to develop non-fluorinated elec... more In order to reduce the burden on the environment, there is a need to develop non-fluorinated electrolyte membranes as alternatives to fluorinated electrolyte membranes, and water electrolysis using hydrocarbon-based electrolyte membranes has been studied in recent years. In this paper, for the first time, we report elevated-temperature water electrolysis properties of crosslinked sulfonated polyphenylsulfone (CSPPSU) membranes prepared by sulfonation and crosslinking of hydrocarbon-based PPSU engineering plastics. The sulfone groups of the CSPPSU membrane in water were stable at 85 °C (3600 h) and 150 °C (2184 h). In addition, the polymer structure of the CSPPSU membrane was stable during small-angle X-ray scattering (SAXS) measurements from room temperature to 180 °C. A current density of 456 mA/cm2 was obtained at 150 °C and 1.8 V in water electrolysis using the CSPPSU membrane and IrO2/Ti as the catalytic electrode for oxygen evolution. The stability of the CSPPSU membrane at ele...

Research paper thumbnail of Water Electrolysis Using a Porous IrO2/Ti/IrO2 Catalyst Electrode and Nafion Membranes at Elevated Temperatures

Membranes

Porous IrO2/Ti/IrO2 catalyst electrodes were obtained by coating IrO2 on both sides of three type... more Porous IrO2/Ti/IrO2 catalyst electrodes were obtained by coating IrO2 on both sides of three types of porous Ti powder sheets (sample 1, sample 2, and sample 3) using different surface treatment methods, and a hydrogen evolution catalyst electrode was obtained by coating Pt/C on carbon gas diffusion layers. A Nafion115 membrane was used as an electrolyte for the membrane electrode assemblies (MEA). Water electrolysis was investigated at cell temperatures up to 150 °C, and the electrical characteristics of the three types of porous IrO2/Ti/IrO2 catalyst electrodes were investigated. The sheet resistance of sample 1 was higher than those of samples 2 and 3, although during water electrolysis, a high current density was observed due to the nanostructure of the IrO2 catalyst. In addition, the structural stabilities of Nafion and Aquivion membranes up to 150 °C were investigated by using small angle X-ray scattering (SAXS). The polymer structures of Nafion and Aquivion membranes were sta...

Research paper thumbnail of Application of high‐performance hydrocarbon‐type sulfonated polyethersulfone for vanadium redox‐flow battery

International Journal of Energy Research

Research paper thumbnail of Chemically Crosslinked Sulfonated Polyphenylsulfone (CSPPSU) Membranes for PEM Fuel Cells

Membranes

Sulfonated polyphenylsulfone (SPPSU) with a high ion exchange capacity (IEC) was synthesized usin... more Sulfonated polyphenylsulfone (SPPSU) with a high ion exchange capacity (IEC) was synthesized using commercially available polyphenylsulfone (PPSU), and a large-area (16 × 18 cm2) crosslinked sulfonated polyphenylsulfone (CSPPSU) membrane was prepared. In addition, we developed an activation process in which the membrane was treated with alkaline and acidic solutions to remove sulfur dioxide (SO2), which forms as a byproduct during heat treatment. CSPPSU membranes obtained using this activation method had high thermal, mechanical and chemical stabilities. In I-ViR free studies for fuel cell evaluation, high performances similar to those using Nafion were obtained. In addition, from the hydrogen (H2) gas crossover characteristics, the durability is much better than that of a Nafion212 membrane. In the studies evaluating the long-term stabilities by using a constant current method, a stability of 4000 h was obtained for the first time. These results indicate that the CSPPSU membrane ob...

Research paper thumbnail of Differences in the oxygen permeation behavior of perfluorinated and hydrocarbon-type polymer electrolyte membranes at elevated temperatures

European Polymer Journal

ABSTRACT Differences in the oxygen permeation behavior of perfluorinated and hydrocarbon (HC)-typ... more ABSTRACT Differences in the oxygen permeation behavior of perfluorinated and hydrocarbon (HC)-type polymer electrolyte membranes (PEMs) were systematically investigated at 80 and 90 °C under controlled relative humidity. We evaluated oxygen permeability under different humidity conditions, using dry–wet and wet–wet configurations, which correspond to the dry H2–wet (humidified) O2, and wet H2–wet O2 conditions, respectively. For perfluorinated PEMs, permeation behavior was significantly dependent on the growth of ionic-water channel networks, and an unusual depression of permeability at 90 °C and 70% RH (wet–wet) compared to that at 80 °C under the same humidity conditions was also observed due to slight stiffening of the membrane. For HC-type PEMs, on the other hand, the permeation behavior was likely to depend on the free volume inside the membrane, which undergoes a large dimensional change with swelling. The gas permeation behavior and gas diffusion pathways of perfluorinated and HC-type PEMs are essentially different because of differences in the structural changes between the membranes.

Research paper thumbnail of Self-organization of a-cyclodextrin on Au(111) surfaces induced by potential controlled adsorption

J Electroanal Chem, 1999

Potential-induced self-organization of α-cyclodextrin (CyD) on Au(111) surfaces in sodium perchlo... more Potential-induced self-organization of α-cyclodextrin (CyD) on Au(111) surfaces in sodium perchlorate has been investigated by using in-situ scanning tunneling microscopy (STM). Near the open circuit potential (approximately +0.0 V vs. SCE), the CyD molecule adsorbs randomly on bare Au(111) surfaces and the desorption of CyD from Au surfaces is observed at negative potentials less than −0.40 V. On the other hand, it was found that the CyD molecules formed an ordered array with a cylindrical structure on the Au(111) surface in the potential region from −0.20 to −0.15 V. The cylindrical structure in which the cavities of CyD face sideways proved that the structure of the adlayer is formed not by simple epitaxy but by self-organization of the molecules.

Research paper thumbnail of Development of the Glial Cells in the Rat Retina

Acta Histochemica Et Cytochemica, 1985

Research paper thumbnail of Theoretical studies on the degradation of hydrocarbon copolymer ionomers used in fuel cells

Journal of Membrane Science, 2015

ABSTRACT Details on the degradation mechanism of hydrocarbon ionomers for polymer electrolyte mem... more ABSTRACT Details on the degradation mechanism of hydrocarbon ionomers for polymer electrolyte membrane fuel cells (PEFCs) have been investigated using density functional theory (DFT). Two model compounds of a hydrocarbon ionomer were selected to investigate the nature of the degradation, where the compounds selected represented the general features of available hydrocarbon polymer electrolyte membranes (PEMs). The results show that two degradation reactions are energetically favorable, indicating two possible weak sites in the hydrocarbon PEMs susceptible to OH or H radical attack. One site has an aryl sulfonated bond and a sulfonate group, and the other site has an aryl ether bond. The alkane chains in the PEMs were calculated to be relatively stable against radical attack. In addition, we found that in contrast to the degradation of perfluorinated PEMs, hydrocarbon PEMs are relatively robust against H radical attack.

Research paper thumbnail of Preparation and Characterization of SPEEK/Silicotunstic Acid/Acid Functionalized Polysilsesquioxane Hybrid Composite Membranes for PEM Fuel Cells

ECS Transactions, 2013

We described the synthesis and properties of SPEEK/inorganic fillers (silicotunstic acid/acid fun... more We described the synthesis and properties of SPEEK/inorganic fillers (silicotunstic acid/acid functionalized polysilsesquioxane hybrid)composite membranes with the goal of increasing the proton conductivity. The membranes were characterized to determine the thermal stability, water uptake as well as proton conductivity. The flexible, tough, and transparent free-standing membranes were successfully obtained by the solution casting method. The results showed that the composited membranes possess excellent thermal stability as well as high proton conductivity over a wide range of relative humidity (30-95%RH). Therefore, these materials proved to be promising materials for use in fuel cell application as polymer electrolyte membranes.

Research paper thumbnail of Proton Dynamics in a Polymer Electrolyte Membrane, Sulfonated Polyether Sulfone (SPES): A Computational Study

ECS Transactions, 2009

The nature of proton dynamics in highly hydrated sulfonated polyethersulfone (SPES) (λ = 67.5) ha... more The nature of proton dynamics in highly hydrated sulfonated polyethersulfone (SPES) (λ = 67.5) has been studied theoretically by means of quantum chemical calculations and first-principles molecular dynamics (MD) simulations. Comparison of results on SPES with those on Nafion shows that, in highly hydrated case, the nature of proton dynamics in both membranes is very similar, exhibiting remarkable contribution of the Grötthuss type proton transport.

Research paper thumbnail of 1H and 19F FFC-NMR of Catalyst Layer Materials for Polymer Electrolyte Membrane Fuel Cells

1 H and 19 F spin lattice relaxation rates of catalyst layer materials (CLM) of polymer electroly... more 1 H and 19 F spin lattice relaxation rates of catalyst layer materials (CLM) of polymer electrolyte membrane fuel cells were measured by the fast field cycling (FFC) method. In contrast to ionomer membranes, 1 H relaxation rates of adsorbed water in both platinum-Ketjen black (Pt-KB) catalyst powder and CLM were strongly dependent on Larmor frequency approximated by a power law due to the strong surface interaction of adsorbed water. The difference in the frequency dependence in the Pt-KB and the CLM was attributed to higher acidity of the CLM.

Research paper thumbnail of Dispersion of Rod-like Particles of Nafion in Salt-Free Water/1-Propanol and Water/Ethanol Solutions

The journal of physical chemistry. B, Jan 10, 2014

The dispersion of perfluorinated sulfonic acid ionomers in catalyst inks is an important factor c... more The dispersion of perfluorinated sulfonic acid ionomers in catalyst inks is an important factor controlling the performance of catalyst layers in membrane electrode assemblies of proton exchange membrane fuel cells (PEMFCs). The effect of water/alcohol composition on the dispersion of H-Nafion in water/1-propanol and water/ethanol solutions was studied by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and (19)F nuclear magnetic resonance ((19)F NMR) spectroscopy. Hydrodynamic radii calculated from DLS decay profiles and the radii and interparticle distance of rod-like particles derived from SAXS profiles showed almost the same dependence on alcohol concentration. 1-Propanol was more effective than ethanol to induce changes in the characteristic lengths of the rod-like particles. The motional narrowing in the (19)F NMR spectra by addition of 1-propanol indicates selective solvation of the rod-like particles. We suppose this might have decreased their radii and i...

Research paper thumbnail of Synthesis of Hydrocarbon Ionomer Materials and Evaluations of MEA

ECS Transactions, 2013

We synthesized a new sulfonated phenylene block copolymer (S-PPBP-PES) by a Ni(0) coupling reacti... more We synthesized a new sulfonated phenylene block copolymer (S-PPBP-PES) by a Ni(0) coupling reaction. Membrane electrode assemblies (MEAs) were fabricated with the S-PPBP-PES ionomer and a Nafion 112 membrane. Five alcohols (methanol, ethanol, 1-propanol, 2-propanol, or mixed propanol) were used as the dispersion solvent for catalyst ink, and the effect of solvents on the fuel cell performance was investigated. These MEAs prepared with mixed propanol exhibited the highest power density among them due to the larger electrochemically active area and smooth surfaces of the catalytic layer compared with others.

Research paper thumbnail of Synthesis and Proton Exchange Membrane Application of Aromatic Diblock Copolymer Electrolytes

ECS Transactions, 2013

A poly(p-phenylene)-based diblock copolymer P2-P1 was synthesized with a hydrophilic monomer, 2,5... more A poly(p-phenylene)-based diblock copolymer P2-P1 was synthesized with a hydrophilic monomer, 2,5-dibromo-1,4-di [4-(2,2-dimetylpropoxysulfonyl)phenyl]butoxybenzene, and a hydrophobic monomer, 2,5-dibromo-1,4-dihexyloxybenzene, via a catalyst transfer polycondensation. Deprotection of the neopentyl groups using diethylamine hydrobromide and subsequent acidic hydrolysis provided a sulfonated diblock copolymer SP2-P1. The diblcok copolymer SP2-P1 showed similar hydration numbers to the random copolymer SP2-ran-P1 in the rage of 30-90% RH at 80 ºC. The proton conductivity of the SP2-P1 was higher than that of SP2-ran-P1 membranes at 80 ºC despite of the lower IEC and the comparable hydration numbers.

Research paper thumbnail of PFG-NMR and SANS Studies in Cation Exchange Membranes Based on Sulfonated Polyphenylene Multiblock Copolymers

ECS Transactions, 2013

not Available.

Research paper thumbnail of Free volume and permeabilities of O-2 and H-2 in Nafion membranes for polymer electrolyte fuel cells

Polymer, 2008

The mechanism of gas permeation in Nafion membranes for polymer electrolyte fuel cells has been i... more The mechanism of gas permeation in Nafion membranes for polymer electrolyte fuel cells has been investigated from the viewpoint of free volume. Three different samples, a membrane with ionic exchange capacity (IEC) ¼ 0.92 meq/g, and recast samples with IEC ¼ 0.92 and 1.00 meq/g were used after drying. Free volume was quantified using the positron annihilation lifetime (PAL) technique and gas permeabilities were measured for O 2 and H 2 as functions of temperature and relative humidity. Good linear correlations between the logarithm of the permeabilities at different temperatures and reciprocal free volume indicate that gas permeation in dry Nafion is governed by the free volume. Nevertheless permeabilities are much smaller than the corresponding flexible chain polymer with a similar free volume size due to stiff chains of the perfluoroethylene backbone. In highly hydrated Nafion above 60% relative humidity, where the O 2 permeability varies oppositely to the free volume, gas permeation proved to be controlled by the gradual increase in overall flexibility of the Nafion-water system.

Research paper thumbnail of A study on structural property of ionomer as a model for catalyst layer: Relationship between thickness and proton conduction for ionomer thin film on different substrate

ECS Transactions, 2012

To study the property of proton conduction for electrolyte thin film inside catalyst layer, model... more To study the property of proton conduction for electrolyte thin film inside catalyst layer, model ionomer thin films were prepared on different surfaces such as carbon and platinum substrates. An atomic force microscopy coupled with electrochemical technique (e-AFM) demonstrated that proton conduction reduced with film thickness, and abruptly decreased when film thickness was less than 10 nm for both carbon and platinum substrate. This indicates that number of active proton conductive pathway and/or connectivity of proton path network change with film thickness, and is though that the morphology of thin film is essentially different from that of a bulk membrane.

Research paper thumbnail of Effect of Elevated Temperatures on the States of Water and Their Correlation with the Proton Conductivity of Nafion

ACS Omega, 2018

For the first time, we report the effects of elevated temperatures, from 80 to 100°C, on the chan... more For the first time, we report the effects of elevated temperatures, from 80 to 100°C, on the changes in the states of water and ion−water channels and their correlation with the proton conductivity of Nafion NR212, which was investigated using a Fourier transform infrared spectroscopy study. Experimentally, three types of water aggregates, protonated water (H + (H 2 O) n), nonprotonated hydrogen (H)-bonded water (H 2 O•••H 2 O), and non-Hbonded water, were found in Nafion, and the existence of those three types of water was confirmed through ab initio molecular dynamics simulation. We found that the proton conductivity of Nafion increased for up to 80°C, but from 80 to 100°C, the conductivity did not increase; rather, all of those elevated temperatures showed identical conductivity values. The proton conductivities at lower relative humidities (RHs) (up to 50%) remained nearly identical for all elevated temperatures (80, 90, and 100°C); however, from 60% RH (over λ = 4), the conductivity remarkably jumped for all elevated temperatures. The results indicated that the amount of randomly arranged water gradually increased and created more H-bonded water networks in Nafion at above 60% RH. From the deconvolution of the O− H bending band, it was found that the volume fraction f i (i=each deconvoluted band) of H-bonded water for elevated temperatures (>80−100°C) increased remarkably higher than for 60°C.

Research paper thumbnail of A DFT Study on the Dissociation Property of Sulfonic Acids with Different Neighboring Pendants in Polymer Electrolyte Membranes

Proceedings of Computational Science Workshop 2014 (CSW2014), 2015

The proton dissociation property of four model compounds of polymer electrolyte membranes, M1-M4,... more The proton dissociation property of four model compounds of polymer electrolyte membranes, M1-M4, has been studied based on density functional theory. These four model compounds have the same proton donor group, sulfonic acid, while differ by types of neighboring pendants, non-fluorinated and fluorinated. We find that the protons in the fluorinated model compounds can be dissociated when hydrated by 3 water molecules, comparable to Nafion, while for those non-fluorinated compounds, the protons can be dissociated only hydrated by 4 water molecules. The results indicate that the neighboring pendants have a significant effect on the proton dissociation property of the model compounds. The electron-withdrawing group involved in the neighboring pendants can improve the proton dissociation property of the compounds, which would be meaningful for finding a novel polymer electrolyte membrane with good conductivity.

Research paper thumbnail of 二次元空間における半屈曲性ケイ素高分子の配向・構造相転移

Research paper thumbnail of Crosslinked Sulfonated Polyphenylsulfone (CSPPSU) Membranes for Elevated-Temperature PEM Water Electrolysis

Membranes

In order to reduce the burden on the environment, there is a need to develop non-fluorinated elec... more In order to reduce the burden on the environment, there is a need to develop non-fluorinated electrolyte membranes as alternatives to fluorinated electrolyte membranes, and water electrolysis using hydrocarbon-based electrolyte membranes has been studied in recent years. In this paper, for the first time, we report elevated-temperature water electrolysis properties of crosslinked sulfonated polyphenylsulfone (CSPPSU) membranes prepared by sulfonation and crosslinking of hydrocarbon-based PPSU engineering plastics. The sulfone groups of the CSPPSU membrane in water were stable at 85 °C (3600 h) and 150 °C (2184 h). In addition, the polymer structure of the CSPPSU membrane was stable during small-angle X-ray scattering (SAXS) measurements from room temperature to 180 °C. A current density of 456 mA/cm2 was obtained at 150 °C and 1.8 V in water electrolysis using the CSPPSU membrane and IrO2/Ti as the catalytic electrode for oxygen evolution. The stability of the CSPPSU membrane at ele...

Research paper thumbnail of Water Electrolysis Using a Porous IrO2/Ti/IrO2 Catalyst Electrode and Nafion Membranes at Elevated Temperatures

Membranes

Porous IrO2/Ti/IrO2 catalyst electrodes were obtained by coating IrO2 on both sides of three type... more Porous IrO2/Ti/IrO2 catalyst electrodes were obtained by coating IrO2 on both sides of three types of porous Ti powder sheets (sample 1, sample 2, and sample 3) using different surface treatment methods, and a hydrogen evolution catalyst electrode was obtained by coating Pt/C on carbon gas diffusion layers. A Nafion115 membrane was used as an electrolyte for the membrane electrode assemblies (MEA). Water electrolysis was investigated at cell temperatures up to 150 °C, and the electrical characteristics of the three types of porous IrO2/Ti/IrO2 catalyst electrodes were investigated. The sheet resistance of sample 1 was higher than those of samples 2 and 3, although during water electrolysis, a high current density was observed due to the nanostructure of the IrO2 catalyst. In addition, the structural stabilities of Nafion and Aquivion membranes up to 150 °C were investigated by using small angle X-ray scattering (SAXS). The polymer structures of Nafion and Aquivion membranes were sta...

Research paper thumbnail of Application of high‐performance hydrocarbon‐type sulfonated polyethersulfone for vanadium redox‐flow battery

International Journal of Energy Research

Research paper thumbnail of Chemically Crosslinked Sulfonated Polyphenylsulfone (CSPPSU) Membranes for PEM Fuel Cells

Membranes

Sulfonated polyphenylsulfone (SPPSU) with a high ion exchange capacity (IEC) was synthesized usin... more Sulfonated polyphenylsulfone (SPPSU) with a high ion exchange capacity (IEC) was synthesized using commercially available polyphenylsulfone (PPSU), and a large-area (16 × 18 cm2) crosslinked sulfonated polyphenylsulfone (CSPPSU) membrane was prepared. In addition, we developed an activation process in which the membrane was treated with alkaline and acidic solutions to remove sulfur dioxide (SO2), which forms as a byproduct during heat treatment. CSPPSU membranes obtained using this activation method had high thermal, mechanical and chemical stabilities. In I-ViR free studies for fuel cell evaluation, high performances similar to those using Nafion were obtained. In addition, from the hydrogen (H2) gas crossover characteristics, the durability is much better than that of a Nafion212 membrane. In the studies evaluating the long-term stabilities by using a constant current method, a stability of 4000 h was obtained for the first time. These results indicate that the CSPPSU membrane ob...

Research paper thumbnail of Differences in the oxygen permeation behavior of perfluorinated and hydrocarbon-type polymer electrolyte membranes at elevated temperatures

European Polymer Journal

ABSTRACT Differences in the oxygen permeation behavior of perfluorinated and hydrocarbon (HC)-typ... more ABSTRACT Differences in the oxygen permeation behavior of perfluorinated and hydrocarbon (HC)-type polymer electrolyte membranes (PEMs) were systematically investigated at 80 and 90 °C under controlled relative humidity. We evaluated oxygen permeability under different humidity conditions, using dry–wet and wet–wet configurations, which correspond to the dry H2–wet (humidified) O2, and wet H2–wet O2 conditions, respectively. For perfluorinated PEMs, permeation behavior was significantly dependent on the growth of ionic-water channel networks, and an unusual depression of permeability at 90 °C and 70% RH (wet–wet) compared to that at 80 °C under the same humidity conditions was also observed due to slight stiffening of the membrane. For HC-type PEMs, on the other hand, the permeation behavior was likely to depend on the free volume inside the membrane, which undergoes a large dimensional change with swelling. The gas permeation behavior and gas diffusion pathways of perfluorinated and HC-type PEMs are essentially different because of differences in the structural changes between the membranes.

Research paper thumbnail of Self-organization of a-cyclodextrin on Au(111) surfaces induced by potential controlled adsorption

J Electroanal Chem, 1999

Potential-induced self-organization of α-cyclodextrin (CyD) on Au(111) surfaces in sodium perchlo... more Potential-induced self-organization of α-cyclodextrin (CyD) on Au(111) surfaces in sodium perchlorate has been investigated by using in-situ scanning tunneling microscopy (STM). Near the open circuit potential (approximately +0.0 V vs. SCE), the CyD molecule adsorbs randomly on bare Au(111) surfaces and the desorption of CyD from Au surfaces is observed at negative potentials less than −0.40 V. On the other hand, it was found that the CyD molecules formed an ordered array with a cylindrical structure on the Au(111) surface in the potential region from −0.20 to −0.15 V. The cylindrical structure in which the cavities of CyD face sideways proved that the structure of the adlayer is formed not by simple epitaxy but by self-organization of the molecules.

Research paper thumbnail of Development of the Glial Cells in the Rat Retina

Acta Histochemica Et Cytochemica, 1985

Research paper thumbnail of Theoretical studies on the degradation of hydrocarbon copolymer ionomers used in fuel cells

Journal of Membrane Science, 2015

ABSTRACT Details on the degradation mechanism of hydrocarbon ionomers for polymer electrolyte mem... more ABSTRACT Details on the degradation mechanism of hydrocarbon ionomers for polymer electrolyte membrane fuel cells (PEFCs) have been investigated using density functional theory (DFT). Two model compounds of a hydrocarbon ionomer were selected to investigate the nature of the degradation, where the compounds selected represented the general features of available hydrocarbon polymer electrolyte membranes (PEMs). The results show that two degradation reactions are energetically favorable, indicating two possible weak sites in the hydrocarbon PEMs susceptible to OH or H radical attack. One site has an aryl sulfonated bond and a sulfonate group, and the other site has an aryl ether bond. The alkane chains in the PEMs were calculated to be relatively stable against radical attack. In addition, we found that in contrast to the degradation of perfluorinated PEMs, hydrocarbon PEMs are relatively robust against H radical attack.

Research paper thumbnail of Preparation and Characterization of SPEEK/Silicotunstic Acid/Acid Functionalized Polysilsesquioxane Hybrid Composite Membranes for PEM Fuel Cells

ECS Transactions, 2013

We described the synthesis and properties of SPEEK/inorganic fillers (silicotunstic acid/acid fun... more We described the synthesis and properties of SPEEK/inorganic fillers (silicotunstic acid/acid functionalized polysilsesquioxane hybrid)composite membranes with the goal of increasing the proton conductivity. The membranes were characterized to determine the thermal stability, water uptake as well as proton conductivity. The flexible, tough, and transparent free-standing membranes were successfully obtained by the solution casting method. The results showed that the composited membranes possess excellent thermal stability as well as high proton conductivity over a wide range of relative humidity (30-95%RH). Therefore, these materials proved to be promising materials for use in fuel cell application as polymer electrolyte membranes.

Research paper thumbnail of Proton Dynamics in a Polymer Electrolyte Membrane, Sulfonated Polyether Sulfone (SPES): A Computational Study

ECS Transactions, 2009

The nature of proton dynamics in highly hydrated sulfonated polyethersulfone (SPES) (λ = 67.5) ha... more The nature of proton dynamics in highly hydrated sulfonated polyethersulfone (SPES) (λ = 67.5) has been studied theoretically by means of quantum chemical calculations and first-principles molecular dynamics (MD) simulations. Comparison of results on SPES with those on Nafion shows that, in highly hydrated case, the nature of proton dynamics in both membranes is very similar, exhibiting remarkable contribution of the Grötthuss type proton transport.

Research paper thumbnail of 1H and 19F FFC-NMR of Catalyst Layer Materials for Polymer Electrolyte Membrane Fuel Cells

1 H and 19 F spin lattice relaxation rates of catalyst layer materials (CLM) of polymer electroly... more 1 H and 19 F spin lattice relaxation rates of catalyst layer materials (CLM) of polymer electrolyte membrane fuel cells were measured by the fast field cycling (FFC) method. In contrast to ionomer membranes, 1 H relaxation rates of adsorbed water in both platinum-Ketjen black (Pt-KB) catalyst powder and CLM were strongly dependent on Larmor frequency approximated by a power law due to the strong surface interaction of adsorbed water. The difference in the frequency dependence in the Pt-KB and the CLM was attributed to higher acidity of the CLM.

Research paper thumbnail of Dispersion of Rod-like Particles of Nafion in Salt-Free Water/1-Propanol and Water/Ethanol Solutions

The journal of physical chemistry. B, Jan 10, 2014

The dispersion of perfluorinated sulfonic acid ionomers in catalyst inks is an important factor c... more The dispersion of perfluorinated sulfonic acid ionomers in catalyst inks is an important factor controlling the performance of catalyst layers in membrane electrode assemblies of proton exchange membrane fuel cells (PEMFCs). The effect of water/alcohol composition on the dispersion of H-Nafion in water/1-propanol and water/ethanol solutions was studied by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and (19)F nuclear magnetic resonance ((19)F NMR) spectroscopy. Hydrodynamic radii calculated from DLS decay profiles and the radii and interparticle distance of rod-like particles derived from SAXS profiles showed almost the same dependence on alcohol concentration. 1-Propanol was more effective than ethanol to induce changes in the characteristic lengths of the rod-like particles. The motional narrowing in the (19)F NMR spectra by addition of 1-propanol indicates selective solvation of the rod-like particles. We suppose this might have decreased their radii and i...

Research paper thumbnail of Synthesis of Hydrocarbon Ionomer Materials and Evaluations of MEA

ECS Transactions, 2013

We synthesized a new sulfonated phenylene block copolymer (S-PPBP-PES) by a Ni(0) coupling reacti... more We synthesized a new sulfonated phenylene block copolymer (S-PPBP-PES) by a Ni(0) coupling reaction. Membrane electrode assemblies (MEAs) were fabricated with the S-PPBP-PES ionomer and a Nafion 112 membrane. Five alcohols (methanol, ethanol, 1-propanol, 2-propanol, or mixed propanol) were used as the dispersion solvent for catalyst ink, and the effect of solvents on the fuel cell performance was investigated. These MEAs prepared with mixed propanol exhibited the highest power density among them due to the larger electrochemically active area and smooth surfaces of the catalytic layer compared with others.

Research paper thumbnail of Synthesis and Proton Exchange Membrane Application of Aromatic Diblock Copolymer Electrolytes

ECS Transactions, 2013

A poly(p-phenylene)-based diblock copolymer P2-P1 was synthesized with a hydrophilic monomer, 2,5... more A poly(p-phenylene)-based diblock copolymer P2-P1 was synthesized with a hydrophilic monomer, 2,5-dibromo-1,4-di [4-(2,2-dimetylpropoxysulfonyl)phenyl]butoxybenzene, and a hydrophobic monomer, 2,5-dibromo-1,4-dihexyloxybenzene, via a catalyst transfer polycondensation. Deprotection of the neopentyl groups using diethylamine hydrobromide and subsequent acidic hydrolysis provided a sulfonated diblock copolymer SP2-P1. The diblcok copolymer SP2-P1 showed similar hydration numbers to the random copolymer SP2-ran-P1 in the rage of 30-90% RH at 80 ºC. The proton conductivity of the SP2-P1 was higher than that of SP2-ran-P1 membranes at 80 ºC despite of the lower IEC and the comparable hydration numbers.

Research paper thumbnail of PFG-NMR and SANS Studies in Cation Exchange Membranes Based on Sulfonated Polyphenylene Multiblock Copolymers

ECS Transactions, 2013

not Available.

Research paper thumbnail of Free volume and permeabilities of O-2 and H-2 in Nafion membranes for polymer electrolyte fuel cells

Polymer, 2008

The mechanism of gas permeation in Nafion membranes for polymer electrolyte fuel cells has been i... more The mechanism of gas permeation in Nafion membranes for polymer electrolyte fuel cells has been investigated from the viewpoint of free volume. Three different samples, a membrane with ionic exchange capacity (IEC) ¼ 0.92 meq/g, and recast samples with IEC ¼ 0.92 and 1.00 meq/g were used after drying. Free volume was quantified using the positron annihilation lifetime (PAL) technique and gas permeabilities were measured for O 2 and H 2 as functions of temperature and relative humidity. Good linear correlations between the logarithm of the permeabilities at different temperatures and reciprocal free volume indicate that gas permeation in dry Nafion is governed by the free volume. Nevertheless permeabilities are much smaller than the corresponding flexible chain polymer with a similar free volume size due to stiff chains of the perfluoroethylene backbone. In highly hydrated Nafion above 60% relative humidity, where the O 2 permeability varies oppositely to the free volume, gas permeation proved to be controlled by the gradual increase in overall flexibility of the Nafion-water system.

Research paper thumbnail of A study on structural property of ionomer as a model for catalyst layer: Relationship between thickness and proton conduction for ionomer thin film on different substrate

ECS Transactions, 2012

To study the property of proton conduction for electrolyte thin film inside catalyst layer, model... more To study the property of proton conduction for electrolyte thin film inside catalyst layer, model ionomer thin films were prepared on different surfaces such as carbon and platinum substrates. An atomic force microscopy coupled with electrochemical technique (e-AFM) demonstrated that proton conduction reduced with film thickness, and abruptly decreased when film thickness was less than 10 nm for both carbon and platinum substrate. This indicates that number of active proton conductive pathway and/or connectivity of proton path network change with film thickness, and is though that the morphology of thin film is essentially different from that of a bulk membrane.