Syo Matsumura

Hydrogen storage in Pd nanocrystals covered with a metal–organic framework

Hydrogen is an essential component in many industrial processes. As a result of the recent increase in the development of shale gas, steam reforming of shale gas has received considerable attention as a major source of H2, and the more efficient use of hydrogen is strongly demanded. Palladium is well known as a hydrogen-storage metal and an effective catalyst for reactions related to hydrogen in a variety of industrial processes. Here, we present remarkably enhanced capacity and speed of hydrogen storage in Pd nanocrystals covered with the metal-organic framework (MOF) HKUST-1 (copper(II) 1,3,5-benzenetricarboxylate). The Pd nanocrystals covered with the MOF have twice the storage capacity of the bare Pd nanocrystals. The significantly enhanced hydrogen storage capacity was confirmed by hydrogen pressure-composition isotherms and solid-state deuterium nuclear magnetic resonance measurements. The speed of hydrogen absorption in the Pd nanocrystals is also enhanced by the MOF coating.

Discovery of Face-Centered-Cubic Ruthenium Nanoparticles: Facile Size-Controlled Synthesis Using the Chemical Reduction Method

We report the first discovery of pure face-centered-cubic (fcc) Ru nanoparticles. Although the fcc structure does not exist in the bulk Ru phase diagram, fcc Ru was obtained at room temperature because of the nanosize effect. We succeeded in separately synthesizing uniformly sized nanoparticles of both fcc and hcp Ru having diameters of 2-5.5 nm by simple chemical reduction methods with different metal precursors. The prepared fcc and hcp nanoparticles were both supported on γ-Al2O3, and their catalytic activities in CO oxidation were investigated and found to depend on their structure and size.

Solid Solution Alloy Nanoparticles of Immiscible Pd and Ru Elements Neighboring on Rh: Changeover of the Thermodynamic Behavior for Hydrogen Storage and Enhanced CO-Oxidizing Ability

Pd(x)Ru(1-x) solid solution alloy nanoparticles were successfully synthesized over the whole composition range through a chemical reduction method, although Ru and Pd are immiscible at the atomic level in the bulk state. From the XRD measurement, it was found that the dominant structure of Pd(x)Ru(1-x) changes from fcc to hcp with increasing Ru content. The structures of Pd(x)Ru(1-x) nanoparticles in the Pd composition range of 30-70% consisted of both solid solution fcc and hcp structures, and both phases coexist in a single particle. In addition, the reaction of hydrogen with the Pd(x)Ru(1-x) nanoparticles changed from exothermic to endothermic as the Ru content increased. Furthermore, the prepared Pd(x)Ru(1-x) nanoparticles demonstrated enhanced CO-oxidizing catalytic activity; Pd0.5Ru0.5 nanoparticles exhibit the highest catalytic activity. This activity is much higher than that of the practically used CO-oxidizing catalyst Ru and that of the neighboring Rh, between Ru and Pd.

Radiation-induced defect clusters in fully stabilized zirconia irradiated with ions and/or electrons

Abstract Microstructure evolution of yttria-stabilized cubic zirconia (YSZ), ZrO 2 –13 mol% Y 2 O 3 , was investigated through transmission electron microscopy under irradiation with electrons and/or ions. Anomalous formation of large defect clusters was found under electron irradiation subsequent to ion irradiation, such as 300 keV O + , 100 keV He + and 4 keV Ar + ions. Such defect clusters were not formed solely with ion irradiation. The extended defect clusters possess strong black/black lobes contrast, and are observed preferentially around a focused electron beam at or near dislocations at temperature less than 520 K. The defect clusters were transformed into dislocation network when they reached a critical diameter of about 1.0–1.5 μm, and processes of nucleation, growth and transformation were repeated under electron irradiation. The defect clusters are assumed to be oxygen platelets induced through selective displacements of oxygen ions in YSZ with electron irradiation. An important role of the accumulation of electric charges due to the selective displacements in YSZ is also discussed.

Shape-Dependent Hydrogen-Storage Properties in Pd Nanocrystals: Which Does Hydrogen Prefer, Octahedron (111) or Cube (100)?

Pd octahedrons and cubes enclosed by {111} and {100} facets, respectively, have been synthesized for investigation of the shape effect on hydrogen-absorption properties. Hydrogen-storage properties were investigated using in situ powder X-ray diffraction, in situ solid-state (2)H NMR and hydrogen pressure-composition isotherm measurements. With these measurements, it was found that the exposed facets do not affect hydrogen-storage capacity; however, they significantly affect the absorption speed, with octahedral nanocrystals showing the faster response. The heat of adsorption of hydrogen and the hydrogen diffusion pathway were suggested to be dominant factors for hydrogen-absorption speed. Furthermore, in situ solid-state (2)H NMR detected for the first time the state of (2)H in a solid-solution (Pd + H) phase of Pd nanocrystals at rt.

High-angle triple-axis specimen holder for three-dimensional diffraction contrast imaging in transmission electron microscopy.

Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt-rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90° ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils.

Nanosize-Induced Drastic Drop in Equilibrium Hydrogen Pressure for Hydride Formation and Structural Stabilization in Pd–Rh Solid-Solution Alloys

We have synthesized and characterized homogeneous solid-solution alloy nanoparticles of Pd and Rh, which are immiscible with each other in the equilibrium bulk state at around room temperature. The Pd-Rh alloy nanoparticles can absorb hydrogen at ambient pressure and the hydrogen pressure of Pd-Rh alloys for hydrogen storage is dramatically decreased by more than 4 orders of magnitude from the corresponding pressure in the metastable bulk state. The solid-solution state is still maintained in the nanoparticles even after hydrogen absorption/desorption, in contrast to the metastable bulks which are separated into Pd and Rh during the process.

Detection of photons emitted from single erbium atoms in energy-dispersive X-ray spectroscopy

Researchers use energy-dispersive X-ray spectroscopy to detect X-ray emission from a single erbium atom. Although the measured intensities are relatively weak, the work may allow single-atom X-ray spectra to be obtained from other atomic species.

Concurrent ordering and phase separation in the vicinity of the metastable critical point of order-disorder transition in Fe-Si alloys

Abstract Transmission electron microscopy was employed in study of microstructural change due to phase separation from B2 to (B2+D03) in Fe-base binary alloys with 12.4 and 13.8 at.% Si, which were annealed at temperatures around the critical line of metastable order–disorder transition between B2 and D03 expected within the miscibility gap. Dark-field images have shown that fine fluctuations of the degree of order appear in the early stage and then gradually fade away with development of phase separation in the following stage. These fluctuations are regarded as due to the thermal dissipation effect pronounced around the critical temperature of metastable order–disorder transition. It suggests that the critical point retains attributes of the second-order transition even inside the two-phase field, and it plays a role as the limit of metastability and instability for quenched B2 phase against phase separation into (B2+D03). Besides, a roughening transition of 〈100〉/2 antiphase boundaries has been recognized in D03 phase in Fe–14.6 at.%Si at a temperature 1024 K slightly lower than the critical point of equilibrium B2–D03 order–disorder transition around 1030 K. The antiphase boundaries wander through the D03 matrix in the narrow temperature range between the two transitions, contrary to faceted orientation to {100} at lower temperature.

Stability of ordered phases under irradiation

The present paper reviews recent results of experiments and modelling on phase changes of L1 2 ordered alloys under energetic particle irradiation. The temperature dependence of the various processes are discussed for the single phase Ni 3 Al as well as for the precipitated phase in a disordered solid solution. Treated are the size of the cascade-induced disordered zones, the ordering efficiency by point defect migration, the disordering kinetics for overlapping cascade damage and the disordering and dissolution of γ precipitates in a Ni base alloy.