Tetsu Ohsuna

Organic Dicarboxylate Negative Electrode Materials with Remarkably Small Strain for High-Voltage Bipolar Batteries†

As advanced negative electrodes for powerful and useful high-voltage bipolar batteries, an intercalated metal-organic framework (iMOF), 2,6-naphthalene dicarboxylate dilithium, is described which has an organic-inorganic layered structure of π-stacked naphthalene and tetrahedral LiO4 units. The material shows a reversible two-electron-transfer Li intercalation at a flat potential of 0.8u2005V with a small polarization. Detailed crystal structure analysis during Li intercalation shows the layered framework to be maintained and its volume change is only 0.33%. The material possesses two-dimensional pathways for efficient electron and Li(+) transport formed by Li-doped naphthalene packing and tetrahedral LiO3C network. A cell with a high potential operating LiNi(0.5)Mn(1.5)O4 spinel positive and the proposed negative electrodes exhibited favorable cycle performance (96% capacity retention after 100 cycles), high specific energy (300u2005Whu2009kg(-1)), and high specific power (5u2005kWu2009kg(-1)). An 8u2005V bipolar cell was also constructed by connecting only two cells in series.

A periodic mesoporous organosilica-based donor-acceptor system for photocatalytic hydrogen evolution.

A new solid-sate donor-acceptor system based on periodic mesoporous organosilica (PMO) has been constructed. Viologen (Vio) was covalently attached to the framework of a biphenyl (Bp)-bridged PMO. The diffuse reflectance spectrum showed the formation of charge-transfer (CT) complexes of Bp in the framework with Vio in the mesochannels. The transient absorption spectra upon excitation of the CT complexes displayed two absorption bands due to radical cations of Bp and Vio species, which indicated electron transfer from Bp to Vio. The absorption bands slowly decayed with a half-decay period of approximately 10 mus but maintained the spectral shape, thereby suggesting persistent charge separation followed by recombination. To utilize the charge separation for photocatalysis, Vio-Bp-PMO was loaded with platinum and its photocatalytic performance was tested. The catalyst successfully evolved hydrogen with excitation of the CT complexes in the presence of a sacrificial agent. In contrast, reference catalysts without either Bp-PMO or Vio gave no or little hydrogen generation, respectively. In addition, a homogeneous solution system of Bp molecules, methylviologen, and colloidal platinum also evolved no hydrogen, possibly due to a weaker electron-donating feature of molecular Bp than that of densely packed Bp in Bp-PMO. These results indicated that densely packed Bp and Vio are essential for hydrogen evolution in this system and demonstrated the potential of PMO as the basis for donor-acceptor systems suitable for photocatalysis.

Crystal-like periodic mesoporous organosilica bearing pyridine units within the framework

Periodic mesoporous organosilica with densely packed pyridine units within the framework and crystal-like molecular-scale periodicity was synthesized. The framework pyridines were chemically active and fully accessible for protonation and Cu(2+) adsorption.

Monolayer-to-bilayer transformation of silicenes and their structural analysis

Silicene, a two-dimensional honeycomb network of silicon atoms like graphene, holds great potential as a key material in the next generation of electronics; however, its use in more demanding applications is prevented because of its instability under ambient conditions. Here we report three types of bilayer silicenes that form after treating calcium-intercalated monolayer silicene (CaSi2) with a BF4− -based ionic liquid. The bilayer silicenes that are obtained are sandwiched between planar crystals of CaF2 and/or CaSi2, with one of the bilayer silicenes being a new allotrope of silicon, containing four-, five- and six-membered sp3 silicon rings. The number of unsaturated silicon bonds in the structure is reduced compared with monolayer silicene. Additionally, the bandgap opens to 1.08u2009eV and is indirect; this is in contrast to monolayer silicene which is a zero-gap semiconductor.

Catalytic Activity of Pt/TaB2(0001) for the Oxygen Reduction Reaction

Proton-exchange-membrane fuel cells (PEMFCs) are a promising power source for automobiles. For their wide application, however, there still remain several problems. 2] One problem is the limited mass activity (reaction rate per mass) of cathode electrocatalysts for the oxygen reduction reaction (ORR). Bulk Pt has a high specific activity (reaction rate per surface area), and the specific activity can be further increased by alloying the subsurfaces with several nonprecious metals, such as Fe, Co, Ni, Cu, Sc, or Y, or by replacing subsurfaces with Pd. However, the specific areas (surface area per mass of the precious metal) of bulk materials are small, and therefore, the mass activities (specific activity multiplied by specific area) are also small. To increase the mass activity, the specific surface area should be increased by decreasing the catalyst size to the nanometer scale. Although Pt nanoparticles supported on carbon (Pt/C) are used practically in PEMFCs, the mass activity is not sufficiently high because the decrease in the size of the catalyst leads to a decrease in the specific activity as a result of the so-called particle-size effect. 9, 10] To avoid the particlesize effect, the specific surface area must be increased while maintaining the extended bulklike surface morphology. This new approach was employed by the company 3M in the development of nanostructured thin-film (NSTF) catalysts, in which Pt films with a thickness of a few tens of nanometers are deposited on organic nanostructured whiskerlike supports. The discovery of these new electrocatalysts inspired a number of studies on the fabrication of electrocatalysts with an extended Pt surface and high specific surface area with the aim of further increasing the mass activity. Herein, we show that a high mass activity of 1890 Ag , which is six times as high as that of Pt/C (299 Ag ), can be attained by the use of an epitaxial Pt thin film with a thickness of 1.5 nm on a TaB2(0001) single-crystal substrate. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images of the Pt/TaB2 structure at the 10 10 TaB2 incidence and the 2 1 10 TaB2 incidence are shown in Figure 1. TaB2(0001) was selected because of its strong bonding with Pt, as shown by our DFT calculations, which indicated a cohesive energy of the Pt monolayer on TaB2(0001) terminated with Ta of 6.47 eV, which is much larger than that of a Pt monolayer on a graphene sheet (3.76 eV) or on Pt(111) (5.06 eV). We deposited Pt on the cleaned TaB2(0001) substrate and carried out CO annealing to obtain a flat and uniform Pt surface. Figure 2a shows the cyclic voltammogram (CV) recorded during CO annealing. In the anodic scan of the first cycle, the oxidation current appeared at approximately 0.5 V and then gradually increased (preignition potential region). This oxidation current disappeared in following cycles. The oxidation current in the preignition region is due to CO oxidation at the sites of Pt adatoms and adislands; thus, the disappearance of this current suggests the elimination of the Pt adatoms and adislands. Figure 2b shows the voltammogram for CO stripping in an argon-purged solution. The electrochemical surface area (ECSA) was estimated from the charge of 420 mC cm 2 required for CO oxidation to be 0.21 cm, which corresponds to a roughness factor (ECSA/ geometrical surface area) of 1.06. The ORR activity of the Pt/ TaB2(0001) alloy was evaluated by linear sweep voltammetry with a rotating disk electrode (measurement at 1600 rpm) under oxygen-saturated conditions (Figure 2c). The current on Pt/TaB2(0001) was corrected to compensate for the geometrical conditions of the working electrode (see Figure S1 in the Supporting Information for details). The specific activity of Pt/TaB2(0001) (kinetic current at 0.9 V) was 4961 mAcm , which is more than twice that observed for polycrystalline Pt (1400 mAcm ) and Pt(111) (1867 mAcm ). The mass activity of Pt/TaB2(0001) was 1890 Ag , which is almost six times that of Pt/C (299 Ag ). The CVs recorded under argon-saturated conditions are shown in Figure 2d. The shape of the CV of Pt/ TaB2(0001) is more similar to that of polycrystalline Pt than to Figure 1. HAADF-STEM images of the epitaxial Pt thin film on the TaB2(0001) single-crystal substrate as observed for: a) 10 10 1⁄2 TaB2 incidence; b) 2 1 10 1⁄2 TaB2 incidence.

Mapping of Heterogeneous Chemical States of Lithium in a LiNiO2-Based Active Material by Electron Energy-Loss Spectroscopy

It is difficult to analyze the local concentrations and chemical states of lithium in lithium-ion secondary battery electrodes by microanalysis techniques based on transmission electron microscopy because the core excitation spectra of transition metals invariably overlap with the absorption/emission spectra of Li-K. We propose a promising analysis method that enables the spatial distribution of lithium with different chemical states from the original phase in a LiNiO 2 -based positive electrode to be visualized. It employs a suite of spectrum imaging techniques including scanning transmission electron microscopy, electron energy-loss spectroscopy, and multivariate curve resolution. This method is successfully applied to a cross-sectioned positive electrode.

Light‐Harvesting Photocatalysis for Water Oxidation Using Mesoporous Organosilica

An organic-based photocatalysis system for water oxidation, with visible-light harvesting antennae, was constructed using periodic mesoporous organosilica (PMO). PMO containing acridone groups in the framework (Acd-PMO), a visible-light harvesting antenna, was supported with [Ru(II)(bpy)3(2+)] complex (bpy = 2,2-bipyridyl) coupled with iridium oxide (IrO(x)) particles in the mesochannels as photosensitizer and catalyst, respectively. Acd-PMO absorbed visible light and funneled the light energy into the Ru complex in the mesochannels through excitation energy transfer. The excited state of Ru complex is oxidatively quenched by a sacrificial oxidant (Na2S2O8) to form Ru(3+) species. The Ru(3+) species extracts an electron from IrO(x) to oxidize water for oxygen production. The reaction quantum yield was 0.34u2009%, which was improved to 0.68 or 1.2u2009% by the modifications of PMO. A unique sequence of reactions mimicking natural photosystemu2005II, 1)u2005light-harvesting, 2)u2005charge separation, and 3)u2005oxygen generation, were realized for the first time by using the light-harvesting PMO.

Mesoporous organosilica nanotubes containing a chelating ligand in their walls

We report the synthesis of organosilica nanotubes containing 2,2′-bipyridine chelating ligands within their walls, employing a single-micelle-templating method. These nanotubes have an average pore diameter of 7.8 nm and lengths of several hundred nanometers. UV-vis absorption spectra and scanning transmission electron microscopy observations of immobilized nanotubes with an iridium complex on the bipyridine ligands showed that the 2,2′-bipyridine groups were homogeneously distributed in the benzene-silica walls. The iridium complex, thus, immobilized on the nanotubes exhibited efficient catalytic activity for water oxidation using Ce4+, due to the ready access of reactants to the active sites in the nanotubes.

Synthesis of Iron silicide-based composite particulates and their performance for lithium-ion battery negative electrode

We have fabricated the composite particulate aggregates, of which Iron silicides, Ca-Si compound and Si are tightly compounded, and evaluated their performance for the lithium-ion battery negative electrode. The particulates are prepared by the solid-state reaction between the layered CaSi2 and FeCl2 using our proposed `Solid-State Exfoliation Reaction (SSER) route. The Ca-Si compound is the material that was expected to have similar crystal structure to the layered CaSi2. The co-existing Iron silicides are the materials with well-known phases (FeSi and Fe3Si), however, they are fine particles. The fabricated composite particulates show a capacity per volume, at first cycle, ~ 6 times larger than that of the artificial graphite, MCF. The particulates with larger amount of Ca-Si compound and Si phases show higher capacity. It is suggested that fine particles of the Ca-Si compound and Si would work as the Li ion storage sites leading to such an excellent capacity values.