Toyoshima, Ryo

写真a

Affiliation

Faculty of Science and Technology, Department of Chemistry (Yagami)

Position

Research Associate/Assistant Professor/Instructor

 

Papers 【 Display / hide

  • Origin of the High Selectivity of the Pt-Rh Thin-Film H<inf>2</inf>Gas Sensor Studied by Operando Ambient-Pressure X-ray Photoelectron Spectroscopy at Working Conditions

    Toyoshima R., Tanaka T., Kato T., Uchida K., Kondoh H.

    Journal of Physical Chemistry Letters (Journal of Physical Chemistry Letters)  13 ( 36 ) 8546 - 8552 2022.09

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    The Pt-Rh thin-film sensors exhibit excellent sensitivity and selectivity for H2 gas detection. Here, we studied the mechanism of highly selective detection of H2 by the Pt-Rh thin-film sensors with ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) measurements at working conditions, which were paralleled with electric resistivity measurements. The elemental composition and chemical state of surface Pt and Rh drastically change depending on the background gas environments, which directly link to the sensor response. It is revealed that surface segregated Pt atoms accelerate dissociative adsorption of H2, resulting in a reduction of the sensor surface and then a decrease of electric resistivity of the film, whereas a thin oxidized Rh layer blocks dissociation of the other reducing agent, that is, NH3. This is supported from the adsorption energetics obtained by the density functional theory (DFT) calculations.

  • Substrate Effect of Ir and Rh on Surface ReO<inf>x</inf>Species under a Hydrogen Atmosphere Studied by NAP-XPS

    Chen J., Kawai J., Ozawa K., Toyoshima R., Tomishige K., Kondoh H.

    Journal of Physical Chemistry C (Journal of Physical Chemistry C)  126 ( 28 ) 11544 - 11552 2022.07

    ISSN  19327447

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    The substrate effect of M-Re (M is a noble metal) bifunctional catalysts for C-O hydrogenolysis has been studied by using single-crystal substrates including Ir(111) and Rh(111) with in situ near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS). Compared with Ir-Re and Rh-Re nanoparticle systems reported in the literature, the single crystals Ir(111) and Rh(111) have shown a more significant substrate effect in determining the surface Re species under a H2 atmosphere at elevated temperatures. It has been found that the hydrogen dissociation and spillover efficiency as the intrinsic property of the noble metals significantly impacts the surface species. A surface that supplies hydrogen more efficiently results in a lower overall oxidation state of Re. Most importantly, the chemical environment of OH species is also closely related to the hydrogen spillover; that is, the more efficient hydrogen spillover, the lower is the oxidation state of Re(-OH). Because the Re-OH sites are commonly considered as the active sites for terminal binding of the reactant molecules, the noble-metal substrates are expected to impact the binding strength of the adsorbate species and hence the overall catalytic activity by tuning the acidity of the Re-OH sites.

  • XPS and HAXPES analyses for pre-sputtered InP surface and InP/Pt interface

    Saito Y., Uemura S., Kagiyama T., Toyoshima R.

    Japanese Journal of Applied Physics (Japanese Journal of Applied Physics)  61 ( 3 )  2022.03

    ISSN  00214922

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    The state of the pre-sputtered indium phosphide (InP) surface was analyzed by X-ray photoelectron spectroscopy, employing synchrotron-based relatively low-energy X-ray. It was found that the pre-sputtering treatment induced the phosphorus vaporization and made the surface composition In-rich, which was thought to promote oxidation of InP surface in atmosphere. The state of the interface between InP and Pt was also investigated nondestructively, by using hard X-ray photoemission spectroscopy. As a result, it was demonstrated that the interfacial layer was composed of the native oxide (In-O, P-O) and metallic state (In-Pt or In-In, P-P) and that the pre-sputtering treatment increased significantly the amount of the P-O, In-Pt or In-In, and P-P. From a simplified calculation, assuming a Pt/In-Pt/In-P layer stacking structure and neglecting the In-O and P-O components, the thickness of the interfacial layer was estimated to be approximately 3.0 nm.

  • A newly designed compact CEY-XAFS cell in the soft X-ray region and its application to surface XAFS measurements under ambient-pressure conditions without photoinduced side effects

    Shimizu H., Toyoshima R., Isegawa K., Mase K., Nakamura J., Kondoh H.

    Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics)  24 ( 5 ) 2988 - 2996 2022.02

    ISSN  14639076

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    We report a newly designed compact cell to measure XAFS spectra with the conversion electron yield (CEY) method in the soft X-ray region under ambient-pressure gas conditions. Secondary electrons generated from the gas and sample by collision of X-ray-absorption-induced Auger electrons are collected by a positively biased collector electrode to obtain XAFS spectra. It was confirmed that this cell is applicable to soft X-ray surface XAFS measurements for different types of materials such as insulating organic materials and metal oxides under 1 bar gas conditions. During the measurements, photoinduced side effects were observed; i.e. photoinduced degradation of organic materials and photoinduced reduction/oxidation of metal oxides. We found that these photoinduced side effects can be sufficiently suppressed by controlling the measuring conditions. The presented measuring approach will enable surface XAFS spectra to be obtained in the soft X-ray region for various types of functional materials under ambient-pressure working conditions. This journal is

  • Ligand effects on surface oxide at RhPd(100) alloy surfaces: A density functional theory calculation study

    Shirahata N., Toyoshima R., Yoshida M., Ueda K., Mase K., Mun B.S., Kondoh H.

    Surface Science (Surface Science)  716 2022.02

    ISSN  00396028

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    Density functional theory calculations were applied to a study on ligand effects on a Pd surface oxide formed on RhPd(100) alloy surfaces. It was found that chemical composition of the topmost layer of alloy significantly influences on the electronic structure of the Pd surface oxide. Such interlayer ligand effects are originating from the Rh−O and Pd−O interactions between the topmost layer of alloy and the Pd surface oxide. These effects give rise to substantial changes in binding energies of adsorbates and could change catalytic activity depending on atomic fraction of the Rh−Pd alloy.

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Papers, etc., Registered in KOARA 【 Display / hide

 

Courses Taught 【 Display / hide

  • LABORATORY IN SCIENCE

    2022

  • LABORATORIES IN CHEMISTRY 1

    2022

  • LABORATORY IN SCIENCE

    2021

  • LABORATORIES IN CHEMISTRY 1

    2021

  • LABORATORY IN SCIENCE

    2020

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