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Kōtō-ku, Japan

Takada K.,Japan National Institute of Materials Science | Ohta N.,Japan National Institute of Materials Science | Ohta N.,Catalyst Research Group | Zhang L.,Japan National Institute of Materials Science | And 8 more authors.
Solid State Ionics | Year: 2012

The effects of surface coating on electrode properties of LiMn 2O 4 in a sulfide solid electrolyte were investigated. The surface coating with LiNbO 3 reduced the electrode resistance by two orders of magnitude. Changes in the electrode properties were very similar to those observed for the corresponding LiCoO 2 electrodes, which strongly suggest that the space-charge layer formed at the high-voltage cathode/sulfide electrolyte interface is rate-determining and must be controlled to improve the rate capability. © 2012 Elsevier B.V. Source

Ohta N.,Catalyst Research Group | Ohta N.,Japan National Institute of Materials Science | Nomura K.,Catalyst Research Group | Yagi I.,Catalyst Research Group | Yagi I.,Hokkaido University
Journal of Physical Chemistry C | Year: 2012

Surface-enhanced infrared absorption spectroscopy was applied to the in situ observations of the surface intermediates during the oxygen reduction reaction (ORR) on quasi-Au(111) thin-film electrode surfaces in contact with 0.5 M perchloric acid aqueous solutions. The spectroscopy revealed the presence of adsorbed molecular oxygen (O 2(ads)) and hydrogen superoxide (HO 2(ads)) during the reaction. These species are not present on the surfaces exposed to the solutions containing no dissolved O 2. In addition, coupled to the onset of the reaction current for the ORR, the surface coverages of the O 2(ads) and the HO 2(ads) showed an abrupt decrease and increase, respectively. These results constitute the first spectroscopic evidence of the proton-coupled one-electron electroreduction of the O 2(ads) to form the HO 2(ads), which has been postulated to occur during the ORR on Au surfaces in acidic media. In addition, the spectroscopy provided for the first time detailed information regarding the structure of the ionic and molecular species formed on the electrode surface in which the O 2(ads) is present; that is, the O 2 hydrated with water molecules is preferentially adsorbed onto the surfaces over the perchlorate anions. © 2012 American Chemical Society. Source

Ohta N.,Catalyst Research Group | Nomura K.,Catalyst Research Group | Yagi I.,Catalyst Research Group | Yagi I.,Japan National Institute of Advanced Industrial Science and Technology
Langmuir | Year: 2010

Surface-enhanced infrared absorption (SEIRA)-active Au/Ti bilayer films sputter deposited on Si substrates have been prepared by an electrochemical annealing (ECA) treatment for the first time. The application of Au/Ti bilayer films on Si substrates to the spectroscopic technique is a promising alternative to the conventional technique using directly deposited Au films on Si substrates, offering excellent adhesive durability of the deposited metal films. However, Au/Ti bilayer films have never been selected for the spectroscopy technique because the films in the as-prepared state exhibit relatively smooth surface morphology: the excitation of the localized surface plasmon is vital to achieving SEIRA enhancements but could hardly be observed on the smooth morphology. It is shown by ex situ scanning tunneling microscopy measurements that the unfavorable smooth morphology of the as-prepared Au/Ti bilayer films can be modified by the ECA treatment to a reasonably rough, island-structure morphology similar to that of the conventional SEIRA-active Au films. In situ infrared absorption spectroscopy of adsorbed sulfate anions has been conducted on the Au/Ti bilayer film both before and after ECA treatment. The spectroscopy measurements demonstrate that the SEIRA activity of the film after being subjected to the treatment is significantly improved so that the technique could detect adsorbates on the film electrodes even with the submonolayer coverage. As an additional benefit, the ECA treatment has brought about a substantial increase in the fraction of Au(111) domains on the polycrystalline Au film surfaces. Accordingly, this approach enables us to prepare SEIRA-active Au films having sufficient adhesion to the Si substrates as well as the highly preferred (111) orientation. © 2010 American Chemical Society. Source

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