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Inoue H.,University of Tokyo | Masuno A.,University of Tokyo | Ishibashi K.,Canon ANELVA Corporation | Tawarayama H.,Frontier Technologies Corporation | And 5 more authors.
Materials Characterization | Year: 2013

Silica glass substrates with very flat surfaces were exposed to atomic hydrogen at different temperatures and durations. An atomic force microscope was used to measure root-mean-square (RMS) roughness and two-dimensional power spectral density (PSD). In the treatment with atomic hydrogen up to 900 C, there was no significant change in the surface. By the treatment at 1000 C, the changes in the RMS roughness and the PSD curves were observed. It was suggested that these changes were caused by etching due to reactions of atomic hydrogen with surface silica. By analysis based on the k-correlation model, it was found that the spatial frequency of the asperities became higher with an increase of the treatment time. Furthermore, the data showed that atomic hydrogen can flatten silica glass surfaces by controlling heat-treatment conditions. © 2013 Elsevier Inc.


Ishiyama T.,Osaka University | Ishiyama T.,Japan National Institute of Advanced Industrial Science and Technology | Yamaguchi T.,Osaka University | Nishii J.,Hokkaido University | And 5 more authors.
Physical Chemistry Chemical Physics | Year: 2015

Structural changes of 35NaO1/2-1WO3-8NbO5/2-5LaO3/2-51PO5/2 glass (1W-glass) before and after the electrochemical substitution of sodium ions with protons by alkali-proton substitution (APS) are studied by Raman and 31P magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopies. The glass before APS consists of (PO3-)8.6(P2O74-) chains on average and the terminal Q1 units (-O-PO33-) are bound to MO6 octahedra (M denotes niobium or tungsten) through P-O-M bonds. Some non-bridging oxygens (NBOs) in the MO6 octahedra are present in addition to the bridging oxygens (BOs) in P-O-M bonds. APS induces fragmentation of the phosphate chains because the average chain length decreases to (PO3-)3.7(P2O74-) after APS, despite the total number of modifier cations of sodium and lanthanum ions and protons being unaffected by APS. This fragmentation is induced by some of the NBOs in the MO6 octahedra before APS, changing to BOs of the newly formed M-O-P bonds after APS, because of the preferential formation of P-OH bonds over M-OH ones in the present glass. We show that APS under the conditions used here is not a simple substitution of sodium ions with protons, but it is accompanied by the structural relaxation of the glass to stabilize the injected protons. This journal is © the Owner Societies.


Kawaguchi K.,Hokkaido University | Yamaguchi T.,Osaka University | Omata T.,Osaka University | Yamashita T.,Frontier Technologies Corporation | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2015

Electrochemical substitution of sodium ions with protons (alkali-proton substitution; APS), and the injection of proton carriers was applied to sodium lanthanum phosphate glasses. A clear and homogeneous material was obtained for a glass of composition 25NaO1/2-8LaO3/2-66PO5/2-1GeO2 following APS, with a resulting proton conductivity of 4 × 10-6 S cm-1 at 250 °C. The glass underwent phase separation and crystallization at temperatures > 255 °C, forming a highly hygroscopic and proton conducting H3PO4 phase in addition to LaP5O14 and other unidentified phases. A glass of composition 25NaO1/2-8LaO3/2-67PO5/2 underwent phase separation and crystallization during APS, forming both H3PO4 and LaP5O14 phases. Sodium lanthanum phosphate glasses are prone to phase separation and crystallization during APS unlike the previously reported NaO1/2-WO3-NbO5/2-LaO3/2-PO5/2 glasses. The phase separation was explained by a reduction in viscosity following APS and the introduction of protons, which exhibit high field strength. Thus, phase separation and crystallization of glasses during APS was difficult to avoid. An approach to suppress phase separation is discussed. © the Owner Societies 2015.


Ishiyama T.,Osaka University | Suzuki S.,Osaka University | Nishii J.,Hokkaido University | Yamashita T.,Frontier Technologies Corporation | And 2 more authors.
Solid State Ionics | Year: 2014

High concentrations of proton carriers (5.0 × 1021 cm - 3) were injected into tungsten phosphate glass (8WO 3-35NaO1/2-8NbO5/2-5LaO3/2-44PO 5/2) by electrochemical substitution of sodium ions with protons at 345 °C. The electromotive force of a hydrogen concentration cell that used the substituted glass as a solid electrolyte indicated a mixed conduction of protons and electrons in the glass with a mean proton transport number of 0.8 at 300 °C. The partial conductivity of the protons was 8.0 × 10 - 4 Scm- 1. The fuel cell generated electricity at a maximum power density of 1.3 mWcm- 2, even though its open circuit voltage was only 0.77 V because of the electronic contribution to the conductivity. Methods to increase the proton conductivity for improving fuel cell performance are discussed. © 2013 Elsevier B.V. All rights reserved.


Yamaguchi T.,Osaka University | Ishiyama T.,Osaka University | Sakuragi K.,Osaka University | Nishii J.,Hokkaido University | And 3 more authors.
Solid State Ionics | Year: 2015

We investigated electrochemical substitution involving the electrochemical oxidation of hydrogen with proton injection into an oxide glass. This was accompanied by the electrochemical reduction of sodium ions and the discharge of metallic sodium out of the glass. This is referred to as the alkali-proton substitution technique and we applied it to a sodium-containing phosphate glass. The thermal stability of the 1WO3-35NaO1/2-8NbO5/2-5LaO3/2-51PO5/2 glass that previously deformed at > 250 °C improved to 350 °C after alkali-proton substitution technique by the introduction of AlO3/2 and/or YO3/2. However, the mobility of the proton carriers decreased by 1/20-1/50 by the introduction of AlO3/2 and/or YO3/2 while the thermal stability improved. Based on infrared absorption spectra the reduced mobility can be attributed to the increase in protons that are tightly bound to oxygen by weak hydrogen bondings. © 2015 Elsevier B.V. All rights reserved.


Yamaguchi T.,Osaka University | Ishiyama T.,Osaka University | Ishiyama T.,Japan National Institute of Advanced Industrial Science and Technology | Sakuragi K.,Osaka University | And 6 more authors.
Solid State Ionics | Year: 2016

Using Raman and 31P magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopies, we studied the structural changes in 35NaO1/2-1WO3-8NbO5/2-5LaO3/2-51PO5/2 glass upon introducing Al2O3 and/or Y2O3 in order to understand the reduced mobility of proton carriers in glasses with Al2O3 and/or Y2O3 in which proton carriers were injected by alkali-proton substitution (APS). The Raman and 31P MAS-NMR spectra showed that phosphate chains were shortened by the Al2O3 and/or Y2O3 introduced into 1W glass. This structural change increased the fraction of protons bound to oxygen atoms in the terminal PO4 (i.e., the Q1 unit) of the phosphate chains. Because the protons bound to terminal Q1 units in phosphate chains tightly bind to oxygen atoms, as opposed to the protons bound to inner Q2 units in phosphate chains, we attributed the reduced mobility of proton carriers upon introducing AlO3/2 and/or YO3/2 into 1W glass to the shortening of phosphate chains. From these results we propose that to obtain a highly proton-conducting glass after APS, the glass must have a composition of O/P <3.5 and thus a sufficiently high fraction of Q2 units. © 2016 Elsevier B.V.


Ishiyama T.,Osaka University | Suzuki S.,Osaka University | Nishii J.,Hokkaido University | Yamashita T.,Frontier Technologies Corporation | And 2 more authors.
Journal of the Electrochemical Society | Year: 2013

A novel technique was developed to inject proton carriers into phosphate glass. Sodium ions in the sodium tungsten phosphate glass were electrochemically substituted with protons. A glass plate with a deposited Pd anode was placed on the molten tin cathode and heated at a temperature below glass transition temperature under DC-bias in hydrogen containing atmosphere. Protons were injected from the palladium anode and substituted the sodium ions in the glass. The sodium ions migrated to the cathode and discharged to the molten tin cathode by capturing an electron from the external circuit. The atomic sodium dissolved into the cathode and reacted with CO2 impurities in the atmosphere resulting deposition of sodium carbonate on the tin cathode surface. After almost all of the sodium ions were discharged from the glass, the proton concentration in the glass reached 4.3 × 1021 cm-3. The proton conductivity was found to be 1 × 10-3 Scm-1 at 350°C. The injected protons were stable at temperatures below 400°C. The glass obtained by this technique behaves as a mixed conductor of protons and electrons with a proton transport number of 0.30. A possible means to suppress the electronic conductivity was discussed. © 2013 The Electrochemical Society. All rights reserved.


Ishiyama T.,Osaka University | Nishii J.,Hokkaido University | Yamashita T.,Frontier Technologies Corporation | Kawazoe H.,Frontier Technologies Corporation | Omata T.,Osaka University
Journal of Materials Chemistry A | Year: 2014

Electrochemical substitution involving electrochemical oxidation of hydrogen and proton injection into oxide glass accompanied by electrochemical reduction of alkali ions and discharge of metallic alkali out of the glass has recently been proposed as a proton injection technique. Herein, this electrochemical substitution technique was applied to phosphate glass with a composition of WO3-35NaO1/2-8NbO5/2-5LaO 3/2-51PO5/2 (1W-glass). Temporal evolution of the substitution of sodium ions with protons was studied using a range of techniques. The concentration depth profiles of sodium ions and protons were mirror images of each other and the amount of injected protons quantitatively agreed with that of the decrease of sodium ions. The concentration of W 5+ ions formed after substitution was only 3 ppm of the amount of injected protons, so reduction of W6+ ions in glass is not essential for proton injection. Raman spectra of the glasses indicated that the glass network structure did not change during electrochemical substitution; therefore, the protons substitute sodium ions not only quantitatively but also structurally. The glass after substitution attained a high proton concentration of 4.6-6.6 × 1021 cm-3 and pure proton conduction with a conductivity of 4.0 × 10-4 S cm-1 at 250 °C. A test fuel cell using electrochemically substituted 1W-glass as a solid electrolyte generated a maximum power density of 0.35 mW cm-2 operating at 250 °C. © 2014 The Royal Society of Chemistry.


Oliva I.,University of Tokyo | Masuno A.,University of Tokyo | Inoue H.,University of Tokyo | Tawarayama H.,Frontier Technologies Corporation | Kawazoe H.,Frontier Technologies Corporation
Solid State Ionics | Year: 2012

Glasses of the 45xMO 1/2-45(1-x)WO 3-25NbO 5/2-30PO 5/2 (M = Na or K, 0.5 ≤ x ≤ 1.0) system possessing carriers such as electrons, protons, and alkali ions were prepared. Well-oxidized glasses with almost no electrons or protons as carriers exhibited alkali ionic conductivity in the all compositions considered here. The glasses were colored by heat treatment under H 2 atmosphere. The treated glasses with lower alkali content showed a remarkable increase in electrical conductivity, whereas those with higher alkali content showed almost no change compared to the well-oxidized state. It was found that there was a strong correlation between the increase in electrical conductivity due to heat treatment under H 2 atmosphere and the hydrogen absorption capacity of the glasses. The increase in conductivity of the glasses with lower alkali content was owing to the change of the major carrier from alkali ions to electrons or protons generated by hydrogen absorption. The composition dependence of the electrical conductivity of the treated glasses reached the minimum at the composition where the contributions of ion and electron or proton conductions became almost equivalent. Mixed conduction was realized in the glass exhibiting minimum conductivity. © 2011 Elsevier B.V. All rights reserved.


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