Influence of Ag Clusters on the Electronic Structures of β‑Ga₂O₃ Photocatalyst Surfaces

In order to understand the photocatalytic carbon dioxide reduction over Ag-loaded β-Ga2O3 photocatalysts, first principles calculations based on density functional theory were performed on the surface model of a Ag cluster-adsorbed β-Ga2O3 system. The stable adsorption structures of Agn (n = 1 to 4) clusters on the β-Ga2O3 (100) surface were determined. In the electronic structure analysis, the valence states of all Ag clusters mixed with the top of the O 2p valence band of Ga2O3, leading the Fermi level of Agn/β-Ga2O3 to shift to the bottom of the conduction band. It was also revealed that the unoccupied states of Agn clusters overlapped with the Ga unoccupied states, and occupied electronic states of Ag clusters were formed in the band gap. These calculation results corresponded to the experimental ones obtained in our previous study, i.e., small Ag clusters had strong interaction with the Ga2O3 surface, enhancing the electron transfer between the Ag clusters and the Ga2O3 surface. That is, excited electrons toward Agn clusters or the perimeter of Ag-Ga2O3 should be the important key to promote photocatalytic CO2 reduction

Lithium Lanthanum Titanate Single Crystals: Dependence of Lithium-Ion Conductivity on Crystal Domain Orientation

Lithium lanthanum titanate La2/3‑xLi3xTiO3 (LLTO) has the potential to exhibit the highest Li-ion conductivity among oxide-based electrolytes because of the fast Li-ion diffusion derived from its crystal structure. Herein, bulk Li-ion conductivity of up to σbulk = 4.0 × 10–3 S/cm at 300 K, which is approximately three to four times higher than that of LLTO polycrystals, was demonstrated using LLTO single crystals, and their dependence on crystal domain orientation was examined. A change in the activation energy, which was previously obscured because of random crystal orientation, was observed at approximately 260 K. Furthermore, electron microscopy analysis indicated that the ionic conductivity of LLTOs remained higher because the region with the highest ionic conductivity was tilted away from the ideal conduction orientation. The results reported herein provide the highest conductivity in LLTO and important insights into their crystal structures, enabling higher conductivity in novel oxide-based electrolyte design

Anion Redox in an Amorphous Titanium Polysulfide

Amorphous transition-metal polysulfides are promising positive electrode materials for next-generation rechargeable lithium-ion batteries because of their high theoretical capacities. In this study, sulfur anion redox during lithiation of amorphous TiS4 (a-TiS4) was investigated by using experimental and theoretical methods. It was found that a-TiS4 has a variety of sulfur valence states such as S2–, S–, and Sδ−. The S2– species became the main component in the Li4TiS4 composition, indicating that sulfur is a redox-active element up to this composition. The simulated a-TiS4 structure changed gradually by lithium accommodation to form a-Li4TiS4: S–S bonds in the disulfide units and polysulfide chains were broken. Bader charge analysis suggested that the average S valency decreased drastically. Moreover, deep lithiation of a-TiS4 provided a conversion reaction to metallic Ti and Li2S, with a high practical capacity of ∼1000 mAh g–1 when a lower cutoff voltage was applied

Epitaxial Growth of LiMn₂O₄ Thin Films by Chemical Solution Deposition for Multilayer Lithium-Ion Batteries

Cathodic LiMn₂O₄ films on various single-crystal substrates for use in thin-film Li-ion batteries prepared using a chemical solution deposition method are reported. Transmission electron microscopy is utilized to characterize the microstructures of the films. The results show that the film/substrate lattice misfit can affect significantly the quality of epitaxially grown grains of LiMn₂O₄. Using state-of-the-art high-angle annular dark-field imaging, the degree of coherency and lattice distortion at interfaces between LiMn₂O₄ and Au-coated and uncoated Al₂O₃ (0001) single-crystal substrates are examined at the atomic scale. When the lattice misfit is sufficiently small, fully coherent LiMn₂O₄/Au heterointerfaces form, although lattice strain to a distance of up to around 10 nm from the interface changes the symmetry of spinel LiMn₂O₄ from cubic to tetragonal. Such an interface in the LiMn₂O₄/Au/Al₂O₃ system facilitates high-quality epitaxial film growth to thicknesses of a couple hundred nanometers

On the Structural Origin of the Catalytic Properties of Inherently Strained Ultrasmall Decahedral Gold Nanoparticles

A new mechanism for reactivity of multiply twinned gold nanoparticles resulting from their inherently strained structure provides a further explanation of the surprising catalytic activity of small gold nanoparticles. Atomic defect structural studies of surface strains and quantitative analysis of atomic column displacements in the decahedral structure observed by aberration corrected transmission electron microscopy reveal an average expansion of surface nearest neighbor distances of 5.6%, with many strained by more than 10%. Density functional theory calculations of the resulting modified gold <i>d-</i>band states predict significantly enhanced activity for carbon monoxide oxidation. The new insights have important implications for the applications of nanoparticles in chemical process technology, including for heterogeneous catalysis

Hydride Conductivity in an Anion-Ordered Fluorite Structure LnHO with an Enlarged Bottleneck

We report on the hydride (H–) conductivity in fluorite-type LnHO oxyhydrides (Ln = lanthanide) using samples prepared under high pressure. It is found that, despite its “stoichiometric” composition, the anion-ordered phase (Ln = La, Nd) exhibits hydride conductivity (e.g., 2.3 × 10–5 S cm–1 for NdHO at 300 °C), while the anion-disordered one (Ln = Gd, Er) is an ionic insulator. The systematic structural analysis combined with computational calculations has revealed the indirect interstitial mechanism, where H– anions migrate between the tetrahedral and octahedral sites through a triangular Ln3 bottleneck expanded by the anion order, with a critical bottleneck radius of 1.18 Å. This study may offer a general guide for the design and control of suitable anion diffusion pathways for oxyhydrides and more generally mixed-anion compounds

On the Structural Origin of the Catalytic Properties of Inherently Strained Ultrasmall Decahedral Gold Nanoparticles

A new mechanism for reactivity of multiply twinned gold nanoparticles resulting from their inherently strained structure provides a further explanation of the surprising catalytic activity of small gold nanoparticles. Atomic defect structural studies of surface strains and quantitative analysis of atomic column displacements in the decahedral structure observed by aberration corrected transmission electron microscopy reveal an average expansion of surface nearest neighbor distances of 5.6%, with many strained by more than 10%. Density functional theory calculations of the resulting modified gold <i>d-</i>band states predict significantly enhanced activity for carbon monoxide oxidation. The new insights have important implications for the applications of nanoparticles in chemical process technology, including for heterogeneous catalysis

Crystalline Grain Interior Configuration Affects Lithium Migration Kinetics in Li-Rich Layered Oxide

The electrode kinetics of Li-ion batteries, which are important for battery utilization in electric vehicles, are affected by the grain size, crystal orientation, and surface structure of electrode materials. However, the kinetic influences of the grain interior structure and element segregation are poorly understood, especially for Li-rich layered oxides with complex crystalline structures and unclear electrochemical phenomena. In this work, cross-sectional thin transmission electron microscopy specimens are “anatomized” from pristine Li1.2Mn0.567Ni0.167Co0.067O2 powders using a new argon ion slicer technique. Utilizing advanced microscopy techniques, the interior configuration of a single grain, multiple monocrystal-like domains, and nickel-segregated domain boundaries are clearly revealed; furthermore, a randomly distributed atomic-resolution Li2MnO3-like with an intergrown LiTMO2 (TM = transitional metals) “twin domain” is demonstrated to exist in each domain. Further theoretical calculations based on the Li2MnO3-like crystal domain boundary model reveal that Li+ migration in the Li2MnO3-like structure with domain boundaries is sluggish, especially when the nickel is segregated in domain boundaries. Our work uncovers the complex configuration of the crystalline grain interior and provides a conceptual advance in our understanding of the electrochemical performance of several compounds for Li-ion batteries

Ba₂ScHO₃: H^– Conductive Layered Oxyhydride with H^– Site Selectivity

Hydride (H–) conduction is a new frontier related to hydrogen transport in solids. Here, a new H– conductive oxyhydride Ba2ScHO3 was successfully synthesized using a high-pressure technique. Powder X-ray and neutron diffraction experiments investigated the fact that Ba2ScHO3 adopts a K2NiF4-type structure with H– ions preferentially occupying the apical sites, as supported by theoretical calculations. Electrochemical impedance spectra showed that Ba2ScHO3 exhibited H– conduction and a conductivity of 5.2 × 10–6 S cm–1 at 300 °C. This value is much higher than that of BaScO2H, which has an ideal perovskite structure, suggesting the advantage of layered structures for H– conduction. Tuning site selectivity of H– ions in layered oxyhydrides might be a promising strategy for designing fast H– conductors applicable for novel electrochemical devices