Jun-ichi Hamagami

Preparation of Li4Ti5O12 and LiCoO2 thin film electrodes from precursors obtained by sol–gel method

Thin films of Li4Ti5O12 and LiCoO2 were prepared from precursors obtained by a sol–gel process using poly(vinylpyrrolidone) (PVP) followed by a heat treatment at 600–800 °C. Both thin films were characterized with X-ray diffraction method and cyclic voltammetry (CV). The Li4Ti5O12 and LiCoO2 thin films have spinel structure and layered rock salt structure, respectively. Their crystallinity was comparable with those for highly crystallized samples. The thickness of both films was about 1 μm after three times of the sol–gel process followed by the heat treatment. An orientation of the thin films was observed. The electrochemical characteristics for both films were comparable with those for standard powder samples.

Development of Particle Assembling Technology by Using Micro-Electrophoretic Deposition Process

A novel particle assembling technique using a local electric fie ld has been investigated by electrophoretic deposition technique using a very small counter ele ct od (microelectrode), this is so-called μ-EPD process. Polystyrene (PS) or silica spherical particle s with uniform diameter were used as a dispersed particle in a suspension. A micrometersiz dots and its patterning can be successfully formed onto a desired position of an indium-tin oxide-coat ed glass substrate by using this μ-EPD process. By optimizing the μ-EPD process parameter, the obtained dot consisted of three-dimensionally ordered spherical particles.

High temperature pH sensing and O2− conduction properties of electrophoretically fabricated ceria composites

Abstract Sm 2 O 3 -doped ceria (SC) ceramics, in which an yttria-stabilized zirconia (YSZ) thin layer of 2 μm in thickness was inserted, was fabricated by the electrophoretic lamination method followed by sintering. The pH sensing properties of the SC/YSZ/SC composite ceramics were examined: the result indicated an approximate Nernstian response of −65.3 mV/pH and the response time of within 50 s at 353 K. The electrolytic properties of SC/YSZ/SC composites were also studied using solid oxide fuel cells (SOFCs) and oxygen sensors.

3D Particle Assembly in Micro-Scale by Using Electrophoretic Micro-Fabrication Technique

A novel micro-fabrication technique for particle assembly has been performed by an electrophoretic deposition (EPD) method using a local electric field in a colloidal suspension generated by a microelectrode. This unique EPD technique was called a “μ-EPD process”. Monodispersed polystyrene microspheres with diameters of 204, 290, and 320 nm were used in this study. A 50 μm Pt wire embedded into a polytetrafluoroethylene tube and an ITO glass slide were employed as the micro-counter electrode and the substrate, respectively. A slow deposition rate in the μ-EPD process was preferable to form a high quality micro-deposit consisting of a three-dimensional periodic polystyrene array. Under the optimized μ-EPD conditions, three-dimensionally ordered polystyrene particles were deposited in front of the micro-counter electrode. This micro-deposit constructed from polystyrene particles with a close-packed structure showed a characteristic optical absorption peak due to Bragg’s law.

Micropattern of Colloidal Crystal by Using Electrophoretic Deposition Process with Three-Electrode System

A novel micropatterning process for a particle assembly has been performed by using an electrophoretic deposition (EPD) method with a local electric field in a colloidal suspension generated by a three-electrode system. Monodisperse silica colloidal spheres with a diameter of 300 nm were used to fabricate micropattern of colloidal crystal. An interdigitated gold-microarray electrode with a 10 μm of width and a gold plate electrode were used as the working and the counter electrodes, respectively. After optimization of the EPD processing parameters, a micropattern was constructed from silica colloidal spheres. It had a relatively close-packed structure formed onto the interdigitated microarray electrode. This micropattern showed a characteristic optical reflectance peak due to Bragg’s law.

Micropatterning of Monodisperse Spherical Particles by Electrophoretic Deposition Process Using Interdigitated Microarray Electrode

Micrometer wire consisting of microbeads was successfully fabricated onto a patterned conductive electrode substrate by an electrophoretic deposition (EPD) process with precise control of electric field distribution generated in the colloidal suspension. Monodisperse polystyrene microspheres with 320 nm in diameter and an interdigitated microarray Au electrode having 10 μm in width and 5 μm in spacing were used in this EPD system. A micropattern of polystyrene particles with two dimensional arrays was formed onto the patterned electrode by the EPD process with two electrode system using an electrostatic interaction between the electrodes and the charged particles in the suspension.

Influence of Catalyst Loading Method on Titania-Based Optical Hydrogen Gas Sensing Properties

We reported that titania ceramic coating loaded with palladium catalyst worked as an optical hydrogen gas sensor at room temperature. The palladium metal of this sensor worked as a catalyst not only for room-temperature operation but also for high selectivity to hydrogen gas. Precise control of metal/ceramic interface between the titania and the palladium was very important in order to improve the sensor performance such as sensitivity, response time, recovery time. Influence of a difference in palladium-catalyst loading method (photodeposition and sputtering) on the optical hydrogen gas sensing properties for the titania-based sensor was investigated. It was found that the catalytic loading process significantly affected the optical hydrogen characteristics of the titania-based coating.

Low-Temperature Processing and Optical Hydrogen Gas Sensing Property of Pd-Loaded Titania Coating onto Flexible Plastic Substrate

Transparent titania coating was formed onto a flexible polycarbonate plastic substrate by low-temperature fabrication process below 100 °C consisting of a sol-gel technique and a hot water treatment method. The titania coating with high transparency showed a good photocatalytic activity under ultraviolet (UV) light irradiation. Palladium metal acts as a catalyst for dissociative adsorption of hydrogen gas at room temperature under an atmospheric pressure. The palladium catalyst was deposited on the photocatalytic titania coating by a photodeposition process at room temperature under UV-light irradiation. The flexible polycarbonate plastic sheet with semitransparent palladium-deposited titania coating works as an optically readable hydrogen gas sensor which can operate at room temperature.

Low Temperature Preparation and Optical Hydrogen Response of Pd/Titania Composite Film

Photocatalytic titania coatings loaded with palladium catalyst were prepared onto soda-lime glass substrates by using a low temperature synthesis for application of optical hydrogen gas sensor. Titania coatings were formed on the glass substrate by a sol-gel spin-coating process followed by a hot water treatment at 55°C. Metallic palladium nanoparticles were deposited onto the titania coatings, which obtained with addition of poly(ethylene glycol) (PEG) and without PEG after the hot water treatment, by means of a photodeposition technique at room temperature using UV-light irradiation. The whole fabrication process was carried out under atmospheric pressure. The Pd-photodeposited titania coating obtained with addition of PEG after hot water treatment showed higher hydrogen sensing properties than that obtained without PEG.

Enhancement on Proton Conductivity of Three-Dimensionally Ordered Macroporous Silica Membrane by Surface Sulfonation

A new proton-conducting membrane was prepared consisting of uniformly macroporous silica matrix and a proton-conducting gel polymer, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). Three-dimensionally ordered macroporous silica membrane was fabricated by use of a colloidal template method with mono-dispersed polystyrene beads. Surface sulfonation of the pores in the silica matrix was performed by using 1,3-propanesultone. The sulfonated silica matrix exhibited about 400 times higher proton conductivity than unmodified one. The proton conductivity of the composite membrane was also successfully enhanced by using the sulfonated silica matrix.