Kyushu University · Engineering
Professor Katsuro Hayashi's research lab specializes in advanced oxide materials for energy conversion and storage, with a focus on ion-conducting ceramics, defect chemistry in complex oxides, and reactive oxygen species in nanostructured frameworks. The lab investigates the fundamental behavior of charged species—such as O⁻, O₂⁻, OH⁻, and H⁻—in materials like C12A7 (mayenite) and NASICON, combining experimental techniques with ab initio calculations to understand their electronic structure and reactivity. Key research directions include solid-state ionics, oxygen radical generation under high pO₂, and the development of robust solid electrolytes for all-solid-state batteries, particularly with sodium metal anodes. The lab also explores aqueous Na–air cells and interfacial phenomena in battery systems to enable high-energy-density, cost-effective energy storage solutions.
Figures are computed from collected data and may differ slightly.
Extremely high concentrations (>1020 cm-3) of active oxygenic radicals, O- and O2-, have been created in the zeolitic crystal, 12CaO.7Al2O3 (C12A7), which can accommodate anions in its cavities. An increase in oxygen pressure and a decrease in water vapor pressure at high temperature enhance the formation of the radicals. The oxidation of Pt is observed on the surface of the material as a result of reaction with the active oxygens.
The true oxidation state of formally 'H(-)' ions incorporated in an oxide host is frequently discussed in connection with chemical shifts of (1)H nuclear magnetic resonance spectroscopy, as they can exhibit values typically attributed to H(+). Here we systematically investigate the link between geometrical structure and chemical shift of H(-) ions in an oxide host, mayenite, with a combination of experimental and ab initio approaches, in an attempt to resolve this issue. We demonstrate that the
An aqueous (mixed aqueous/aprotic) Na-air cell is fabricated and its discharge properties are examined experimentally. This design is attractive because Na is not only more abundant and cheaper than Li, but also potentially advantageous for enhancing cell output. The theoretical energy density of the aqueous Na-air cell exceeds that of a Li one under conditions where precipitation of hydroxides in the aqueous electrolyte is not allowed. Na3Zr2Si2PO12 (NASICON) ceramics, which has a Na+ ion condu
We have examined the thermodynamics and kinetics of hydroxide (OH-) ions that formed in cages of 12 CaO x 7 Al2O3 (C12A7) with nanoporous structures. It is confirmed using thermogravimetric-evolved gas analyses (TG-EGA) that hydration in C12A7 is mediated by a reaction between an oxide (O2-) ion in the cage and an H2O molecule in the atmosphere to form two OH- ions in the cages. To simply and exactly quantify the OH- content from infrared absorption measurements of OH-stretching band, we propose
The effects of oxygen partial pressure (pO2) up to 400 atm on the generation of active oxygen radicals in 12CaO·7Al2O3 (C12A7) was examined using a hot isostatic pressing technique. Concentrations of superoxide (O2-) and oxygen anion radicals (O-), which were analyzed from a combination of electron paramagnetic spin resonance (EPR) and Raman spectroscopy, increased with pO2. The total concentration of the radicals reached 1.7 × 1021 cm3, which is comparable to the theoretical maximum, confirmed
A robust ceramic solid electrolyte with high ionic conductivity is a key component for all-solid-state batteries (ASSBs). In terms of the demand for high-energy-density storage, researchers have been tackling various challenges to use metal anodes, where a fundamental understanding on the metal/solid electrolyte interface is of particular importance. The Na+ superionic conductor, so-called NASICON, has high potential for application to ASSBs with a Na anode due to its high Na+ ion conductivity a
Journal Article The Enzyme-substrate Complex in a Muramidase Catalyzed Reaction: I. Difference Spectrum of Complex Get access KATSUYA HAYASHI, KATSUYA HAYASHI Laboratory of Biochemistry, Faculty of Agriculture, Kyushu UniversityFukuoka Search for other works by this author on: Oxford Academic PubMed Google Scholar TAIJI IMOTO, TAIJI IMOTO Laboratory of Biochemistry, Faculty of Agriculture, Kyushu UniversityFukuoka Search for other works by this author on: Oxford Academic PubMed Google Scholar MA
The positive temperature coefficient of resistivity (PTCR) effect is directly measured in single grain boundaries in 0.1‐mol%‐Nb‐doped BaTiO 3 with 1 mm coarse grains. The PTCR effect largely depends on grain boundary structure. Random grain boundaries exhibit the PTCR effect as in polycrystalline samples, but the PTCR effect does not appear in highly coherent boundaries such as small‐angle boundaries, twin boundaries, and coincidence site lattice (CSL) boundaries with low Σ values. For Σ= 3 bou
A novel nanoporous material 12CaO.7Al2O3 (C12A7) offers a possibility of incorporating large concentrations (>1021 cm-3) of a wide range of extraframework anions inside its nanopores. We have investigated, both experimentally and theoretically, optical absorption associated with several types of such anions, including F-, OH-, O-, O2-, O2-, and O22-, and assigned their optical absorption bands. It is demonstrated that the chemical identity and concentration of extraframework anions can be contro
The 12CaO.7Al2O3 (C12A7) crystal with a nanoporous lattice framework exhibits high electrical conductivity with an activation energy of approximately 1.5 eV when equilibrated in a hydrogen atmosphere above approximately 800 degrees C. The high conductivity is preserved in a quenched state below approximately 600 degrees C with a reduced activation energy of approximately 0.8 eV. Such complex behavior in electrical conductivity is associated with incorporation of hydride ions (H-) in cages of the
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