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Yoshihiro Yamazaki Last modified date:2020.06.22

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Field of Specialization
Materials Science
Total Priod of education and research career in the foreign country
Outline Activities
Yoshihiro Yamazaki's researches in Advanced Functional Inorganic Materials Research Division focus on the multiple length scale ion, electron and electronic-hole transport characterization in metal oxides aiming for efficient solar-fuel and energy conversions. One of ultimate challenges in materials science is to activate a useful materials fuction for a specific application. In particular, the production of efficient solar fuel in conjunction with inorganic materials makes use of unlimited solar energy even at night. A challenge is to unravel critical material and architectural paramters, in a wide range from sub-nanometer to macroscopic scale, that activate such energy functions.
We combine materials synthesis, electrochemical spectroscopy, mass-spectroscopy, thermogravimetry and in-situ high-temperature solid-state NMR, and correlate them to energy functions in inorganic materials. The research topics include novel catalytic oxides for solar-driven thermochemical fuel production and proton transport in proton-conducting oxide.
Research Interests
  • Our work focuses on the electrochemical characterization of transport in oxides, with the twin objectives of understanding the ionic-electronic defect behaviors and of transforming that understanding into materials development for energy applications. We would like to understand the structure-property relationships, how inorganic materials electrochemically functions, in multiple length scale from sub-nanometer to millimeter, aiming for the drastic enhancement of solar-fuel and energy conversion efficiency and kinetics. Our ultimate goal is, based on materials electrochemistry, to activate any energy functions in oxides.
    keyword : advanced functional inorganic materials, metal oxide, point defect, solar-driven thermochemical water splitting catalyst, proton-conducting solid oxide fuel cell electrolyte
Academic Activities
1. Shunta Nishioka, Junji Hyodo, Junie Jhon M. Vequizo, Shunsuke Yamashita, Hiromu Kumagai, Koji Kimoto, Akira Yamakata, Yoshihiro Yamazaki, and Kazuhiko Maeda, Homogeneous Electron Doping into Nonstoichiometric Strontium Titanate Improves Its Photocatalytic Activity for Hydrogen and Oxygen Evolution, ACS Catalysis, 8, 7190-7200, 2018.06, Water splitting using a semiconductor photocatalyst has been extensively studied as a means of solar-to-hydrogen energy conversion. Powder-based semiconductor photocatalysts, in particular, have tremendous potential in cost mitigation due to system simplicity and scalability. The control and implementation of powder-based photocatalysts are, in reality, quite complex. The identification of the semiconductor–photocatalytic activity relationship and its limiting factor has not been fully solved in any powder-based semiconductor photocatalyst. In this work, we present systematic and quantitative evaluation of photocatalytic hydrogen and oxygen evolution using a model strontium titanate powder/aqueous solution interface in a half reaction. The electron density was controlled from 1016 to 1020 cm–3 throughout the strontium titanate powder by charge compensation with oxygen nonstoichiometry (the amount of oxygen vacancy) while maintaining its crystallinity, chemical composition, powder morphology, and the crystal and electronic structure of the surface. The photocatalytic activity of hydrogen evolution from aqueous methanol solution was stable and enhanced by 40-fold by the electron doping. The enhancement was correlated well with increased Δabsorbance, an indication of prolonged lifetime of photoexcited electrons, observed by transient absorption spectroscopy. Photocatalytic activity of oxygen evolution from aqueous silver nitrate solution was also enhanced by 3-fold by the electron doping. Linear correlation was found between the photocatalytic activity and the degree of surface band bending, ΔΦ, above 1.38 V. The band bending, potential downhill for electronic holes, enlarges the total flux of photoexcited holes toward the surface, which drives the oxygen evolution reaction..
2. C.K. Yang, Y.Yamazaki, A. Aydin, S.M. Haile, Thermodynamic and kinetic assessments of strontium-doped lanthanum manganites for thermochemical water splitting, J. Mater. Chem. A, 2, 13612-13623, 2014.07.
3. Y.Yamazaki, F. Blanc, Y. Okuyama, L. Buannic, J.C. Lucio-Vega, C.P. Grey, S.M. Haile, Proton trapping in yttrium-doped barium zirconate, Nature Materials, 12, 647-651, 2013.07.
4. Y.Yamazaki, R. Hernandez-Sanchez, S.M. Haile, Cation non-stoichiometry in yttrium-doped barium zirconate: phase behavior, microstructure and proton conductivity, J. Mater. Chem, 20, 8158-8166, 2010.08.
5. Y.Yamazaki, R. Hernandez-Sanchez, S.M. Haile, High total proton conductivity in large-grained yttrium-doped barium zirconate, Chem. Mater, 21, 2755-2762, 2009.05.
6. Y.Yamazaki, P. Babilo, S.M. Haile, Defect chemistry of yttrium-doped barium zirconate: A thermodynamic analysis of water uptake, Chem. Mater, 20, 6352-6357, 2008.09.
1. Y.Yamazaki, Proton trapping in proton-conducting oxide, 17th International Conference on Solid State Protonic Conductors, 2014.09.
2. Y.Yamazaki, Proton diffusion in solid oxide fuel cell electrolytes, International Conference on Diffusion in Materials, 2014.08.
3. Y.Yamazaki, F. Blanc, Y. Okuyama, L. Buannic, C.P. Grey, S.M. Haile, Proton trapping: a guide for proton conducting oxide electrolyte development, International Workshop on Protonic Ceramic Fuel Cells Status & Prospects (PPCC2013 – Prospects Protonic Ceramic Cells), 2013.07.
4. Y.Yamazaki, Novel perovskite catalysts for thermochemical water splitting, The 19th International Conference on Solid State Ionics, 2013.06.