Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Transparent conductors as solar energy materials: A panoramic review

The response of the worldwide scientific community to the discovery in 2008 of superconductivity at T c = 26 K in the Fe-based compound LaFeAsO1−x F x has been very enthusiastic. In short order, ot...

The puzzle of high temperature superconductivity in layered iron pnictides and chalcogenides

Over the past few decades, the design and development of advanced electrocatalysts for efficient energy conversion technologies have been subjects of extensive study. With the discovery of graphene, two-dimensional (2D) nanomaterials have emerged as some of the most promising candidates for heterogeneous electrocatalysts due to their unique physical, chemical, and electronic properties. Here, we review 2D-nanomaterial-based electrocatalysts for selected electrocatalytic processes. We first discuss the unique advances in 2D electrocatalysts based on different compositions and functions followed by specific design principles. Following this overview, we discuss various 2D electrocatalysts for electrocatalytic processes involved in the water cycle, carbon cycle, and nitrogen cycle from their fundamental conception to their functional application. We place a significant emphasis on different engineering strategies for 2D nanomaterials and the influence these strategies have on intrinsic material performance, ...

Emerging Two-Dimensional Nanomaterials for Electrocatalysis

Kamihara and coworkers' report of superconductivity at ${T}_{c}=26\text{ }\text{ }\mathrm{K}$ in fluorine-doped LaFeAsO inspired a worldwide effort to understand the nature of the superconductivity in this new class of compounds. These iron pnictide and chalcogenide (FePn/Ch) superconductors have Fe electrons at the Fermi surface, plus an unusual Fermiology that can change rapidly with doping, which lead to normal and superconducting state properties very different from those in standard electron-phonon coupled ``conventional'' superconductors. Clearly, superconductivity and magnetism or magnetic fluctuations are intimately related in the FePn/Ch, and even coexist in some. Open questions, including the superconducting nodal structure in a number of compounds, abound and are often dependent on improved sample quality for their solution. With ${T}_{c}$ values up to 56 K, the six distinct Fe-containing superconducting structures exhibit complex but often comparable behaviors. The search for correlations and explanations in this fascinating field of research would benefit from an organization of the large, seemingly disparate data set. This review provides an overview, using numerous references, with a focus on the materials and their superconductivity.

Superconductivity in iron compounds

We performed electrical resistivity measurements under high pressures for Ca(Fe1−xCox)AsF (x = 0.10, 0.15 and 0.20), in order to investigate the pressure effect on superconductivity in Ca(Fe1−xCox)AsF. All the compounds show an enhancement of the Tc. However, the Tc shows maximum values at low pressure region below 1 GPa, and the enhancement is less than 1 K, which is quite small compared with that in LaFeAsO1−xFx. These results indicate that the pressure effect on the superconductivity in Ca(Fe1−xCox)AsF is different from that in LaFeAsO1−xFx.

https://iopscience.iop.org/article/10.1088/1742-6596/200/1/012151/pdf

Pressure effect on iron-based superconductors Ca(Fe1?xCox)AsF

We report the emergence of superconductivity in Ca2InN consisting of a 2-dimensional (2D) array of zigzag indium chains embedded between Ca2N layers. A sudden drop of resistivity and a specific-heat (Cp) jump attributed to the superconducting transition were observed at 0.6 K. The Sommerfeld coefficient {\gamma}= 4.24 mJ/mol K2 and Debye temperature {\Theta}D = 322 K were determined from the Cp of the normal conducting state and the superconducting volume fraction was estimated to be ~80% from the Cp jump, assuming a BCS-type weak coupling. Density functional theory calculations demonstrated that the electronic bands near the Fermi level (EF) are mainly derived from In 5p orbitals with {\pi} and {\sigma} bonding states and the Fermi surface is composed of cylindrical parts, corresponding to the quasi-2D electronic state of the In chain array. By integrating the projected density of states of In-p component up to EF, a valence electron population of ~1.6 electrons/In was calculated, indicating that the partially anionic state of In. The In 3d binding energies observed in Ca2InN by x-ray photoemission spectroscopy were negatively shifted from that in In metal. The superconductivity of Ca2InN is associated with the p-p bonding states of the anionic In layer.

Superconductivity of Ca2InN with a layered structure embedding an anionic indium chain array

We have fabricated the F-doped LaFeAsO superconductors via three fabrication processes; (1) solid-state sintering, (2) high pressure (HP) synthesis and (3) crystallization from flux solution. Samples prepared by these processes have unique features depending on the process such as a large volume and uniformity of the sintered pellet, variety of the compositions in the high pressured pellet and potential of growing large single crystal using fluxes. In particular, the HP synthetic process has a unique advantage that the compositional variations in the compounds were realized by a large temperature gradient within a short reaction time.

Preparation of Fe-Oxipnictides Superconductors: Solid-State Sintering, High Pressure Synthesis and Flux Method

Transparent insulating oxide 12CaO·7Al2O3 (C12A7) is converted into electronic conductor by replacing the oxygen ions in the crystallographic cages with electrons. At the low electron concentration (Ne) <-1020 cm-3, C12A7 exhibits semiconductive properties due to hopping of localized electron. With increase of Ne, it becomes metallic state at a critical Ne-1×1021 cm-3. Fully oxygen-replaced C12A7 (C12A7: e-) may be regarded as a room-temperature-stable electride in which electrons serve as anions. Small work function of 2.4 eV comparable to that in metal potassium is a characteristic of C 12A7: e- and makes it a promising candidate for electron emitting source.

Stable Inorganic Electride C12A7: e-: Electronic Properties and Structure

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.

Satoru Matsuishi

Papers

Pressure effect on iron-based superconductors Ca(Fe1?xCox)AsF

Superconductivity of Ca2InN with a layered structure embedding an anionic indium chain array

Preparation of Fe-Oxipnictides Superconductors: Solid-State Sintering, High Pressure Synthesis and Flux Method

Stable Inorganic Electride C12A7: e-: Electronic Properties and Structure

Microporous Crystal 12CaO×7Al2O3 Encaging Abundant O‐ Radicals.