In recent years, the concept of entropy stabilization of crystal structures in oxide systems has led to an increased research activity in the field of "high entropy oxides". These compounds comprise ...the incorporation of multiple metal cations into single-phase crystal structures and interactions among the various metal cations leading to interesting novel and unexpected properties. Here, we report on the reversible lithium storage properties of the high entropy oxides, the underlying mechanisms governing these properties, and the influence of entropy stabilization on the electrochemical behavior. It is found that the stabilization effect of entropy brings significant benefits for the storage capacity retention of high entropy oxides and greatly improves the cycling stability. Additionally, it is observed that the electrochemical behavior of the high entropy oxides depends on each of the metal cations present, thus providing the opportunity to tailor the electrochemical properties by simply changing the elemental composition.
Rechargeable magnesium batteries are one of the most promising candidates for next-generation battery technologies. Despite recent significant progress in the development of efficient electrolytes, ...an on-going challenge for realization of rechargeable magnesium batteries remains to overcome the sluggish kinetics caused by the strong interaction between double charged magnesium-ions and the intercalation host. Herein, we report that a magnesium battery chemistry with fast intercalation kinetics in the layered molybdenum disulfide structures can be enabled by using solvated magnesium-ions (Mg(DME)
). Our study demonstrates that the high charge density of magnesium-ion may be mitigated through dimethoxyethane solvation, which avoids the sluggish desolvation process at the cathode-electrolyte interfaces and reduces the trapping force of the cathode lattice to the cations, facilitating magnesium-ion diffusion. The concept of using solvation effect could be a general and effective route to tackle the sluggish intercalation kinetics of magnesium-ions, which can potentially be extended to other host structures.
High entropy oxides (HEOs) with chemically disordered multi-cation structure attract intensive interest as negative electrode materials for battery applications. The outstanding electrochemical ...performance has been attributed to the high-entropy stabilization and the so-called 'cocktail effect'. However, the configurational entropy of the HEO, which is thermodynamically only metastable at room-temperature, is insufficient to drive the structural reversibility during conversion-type battery reaction, and the 'cocktail effect' has not been explained thus far. This work unveils the multi-cations synergy of the HEO Mg
Co
Ni
Cu
Zn
O at atomic and nanoscale during electrochemical reaction and explains the 'cocktail effect'. The more electronegative elements form an electrochemically inert 3-dimensional metallic nano-network enabling electron transport. The electrochemical inactive cation stabilizes an oxide nanophase, which is semi-coherent with the metallic phase and accommodates Li
ions. This self-assembled nanostructure enables stable cycling of micron-sized particles, which bypasses the need for nanoscale pre-modification required for conventional metal oxides in battery applications. This demonstrates elemental diversity is the key for optimizing multi-cation electrode materials.
Size-selective precipitation was used to successfully separate colloidally stable allylbenzene-capped silicon nanocrystals into several visible emitting monodisperse fractions traversing the quantum ...size effect range of 1-5 nm. This enabled the measurement of the absolute quantum yield and lifetime of photoluminescence of allylbenzene-capped silicon nanocrystals as a function of size. The absolute quantum yield and lifetime are found to monotonically decrease with decreasing nanocrystal size, which implies that nonradiative vibrational and surface defect effects overwhelm spatial confinement effects that favor radiative relaxation. Visible emission absolute quantum yields as high as 43% speak well for the development of "green" silicon nanocrystal color-tunable light emitting diodes that can potentially match the performance of their toxic heavy metal chalcogenide counterparts.
Density changes between sheared zones and their surrounding amorphous matrix as a result of plastic deformation in a cold-rolled metallic glass (melt-spun Al88Y7Fe5) were determined using high-angle ...annular dark-field (HAADF) detector intensities supplemented by electron-energy loss spectroscopy (EELS), energy-dispersive X-ray (EDX) and nano-beam diffraction analyses. Sheared zones or shear bands were observed as regions of bright or dark contrast arising from a higher or lower density relative to the matrix. Moreover, abrupt contrast changes from bright to dark and vice versa were found within individual shear bands. We associate the decrease in density mainly with an enhanced free volume in the shear bands and the increase in density with concomitant changes of the mass. This interpretation is further supported by changes in the zero loss and Plasmon signal originating from such sites. The limits of this new approach are discussed.
•We describe a novel approach for measuring densities in shear bands of metallic glasses.•The linear relation of the dark-field intensity I/I0 and the mass thickness ρt was used.•Individual shear bands showed abrupt contrast changes from bright to dark and vice versa.•Density changes ranging from about −10% to +6% were found for such shear bands.•Mixtures of amorphous/medium range ordered domains were found within the shear bands.
Characterizing heterogeneous nanostructured amorphous materials is a challenging topic, because of difficulty to solve disordered atomic arrangement in nanometer scale. We developed a new ...transmission electron microscopy (TEM) method to enable phase analysis and mapping of heterogeneous amorphous structures. That is to combine scanning TEM (STEM) diffraction mapping, radial distribution function (RDF) analysis, and hyperspectral analysis. This method was applied to an amorphous zirconium oxide and zirconium iron multilayer system, and showed extreme sensitivity to small atomic packing variations. This approach helps to understand local structure variations in glassy composite materials and provides new insights to correlate structure and properties of glasses.
•A method for phase mapping of nanostructured amorphous materials was developed.•The phase mapping is purely based on structural information.•The method combines STEM diffraction with radial distribution function analysis.•The method was applied on an amorphous multilayer for demonstrating its sensitivity.
Abstract
Two-dimensional (2D) materials are of considerable interest for catalyzing the heterogeneous conversion of CO
2
to synthetic fuels. In this regard, 2D siloxene nanosheets, have escaped ...thorough exploration, despite being composed of earth-abundant elements. Herein we demonstrate the remarkable catalytic activity, selectivity, and stability of a nickel@siloxene nanocomposite; it is found that this promising catalytic performance is highly sensitive to the location of the nickel component, being on either the interior or the exterior of adjacent siloxene nanosheets. Control over the location of nickel is achieved by employing the terminal groups of siloxene and varying the solvent used during its nucleation and growth, which ultimately determines the distinct reaction intermediates and pathways for the catalytic CO
2
methanation. Significantly, a CO
2
methanation rate of 100 mmol g
Ni
−1
h
−1
is achieved with over 90% selectivity when nickel resides specifically between the sheets of siloxene.
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