Germanene, a single-atom-thick germanium nanosheet in a honeycomb lattice, was proposed to be a Dirac fermion material beyond graphene. We performed scanning tunneling microscopy and in situ Raman ...spectroscopy studies combined with first-principles calculations on the atomic structures and the electronic and phonon properties of germanene on Au(111). The low-buckled 1 × 1 germanene honeycomb lattice was determined to exist in an unexpected rectangular √7 × √7 superstructure. Through in situ Raman measurements, distinctive vibrational phonon modes were discovered in √7 × √7 germanene, revealing the special coupling between the Dirac fermion and lattice vibrations, namely, electron–phonon coupling (EPC). The significant enhancement of EPC is correlated with the tensile strain, which is evoked by the singular buckled structure of √7 × √7 germanene on the Au(111) substrate. Our results present clear evidence for the existence of epitaxial germanene and elucidate the exotic properties of germanene on Au(111).
Ground-state structures of supported C clusters, C N (N = 16, ..., 26), on four selected transition metal surfaces Rh(111), Ru(0001), Ni(111), and Cu(111) are systematically explored by ab initio ...calculations. It is found that the core–shell structured C21, which is a fraction of C60 possessing three isolated pentagons and C 3v symmetry, is a very stable magic cluster on all these metal surfaces. Comparison with experimental scanning tunneling microscopy images, dI/dV curves, and cluster heights proves that C21 is the experimentally observed dominating C precursor in graphene chemical vapor deposition (CVD) growth. The exceptional stability of the C21 cluster is attributed to its high symmetry, core–shell geometry, and strong binding between edge C atoms and the metal surfaces. Besides, the high barrier of two C21 clusters’ dimerization explains its temperature-dependent behavior in graphene CVD growth.
Direct conversion of carbon dioxide (CO2) to high-energy fuels and high-value chemicals is a fascinating sustainable strategy. For most of the current electrocatalysts for CO2 reduction, however, ...multi-carbon products are inhibited by large overpotentials and low selectivity. Herein, we exploit dispersed 3d transition metal dimers as spatially confined dual reaction centers for selective reduction of CO2 to liquid fuels. Various nitrogenated holey carbon monolayers are shown to be promising templates to stabilize these metal dimers and dictate their electronic structures, allowing precise control of the catalytic activity and product selectivity. By comprehensive first-principles calculations, we screen the suitable transition metal dimers that universally have high activity for ethanol (C2H5OH). Furthermore, remarkable selectivity for C2H5OH against other C1 and C2 products is found for Fe2 dimer anchored on C2N monolayer. The role of electronic coupling between the metal dimer and the carbon substrates is thoroughly elucidated.
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•Dual metal centers provide an exclusive pathway for CO2 reduction to C2 products•Activity and selectivity are modulatable by the metal-support interaction•Fe2 dimer anchored on C2N leads to remarkable selectivity for ethanol
Catalysis; Atomic Electronic Structure; Energy Sustainability; Numerical Method in Materials Science
Ab initio total energy calculations are used to determine the elastic properties of TiZrVNb, TiZrNbMo and TiZrVNbMo high-entropy alloys in the body centered cubic (bcc) crystallographic phase. ...Calculations are performed using the Vienna Ab initio Simulation Package and the Exact Muffin-Tin Orbitals methods, and the compositional disorder is treated within the frameworks of the special quasi-random structures technique and the coherent potential approximation, respectively. Special emphasis is given to the effect of local lattice distortion and trends against composition. Significant distortion can be observed in the relaxed cells, which result in an overlap of the first and second nearest neighbor (NN) shells represented in the histograms. When going from the four-component alloys TiZrVNb and TiZrNbMo to the five-component TiZrVNbMo, the changes in the elastic parameters follow the expected trends, except that of C44 which decreases upon adding equiatomic Mo to TiZrVNb despite of the large shear elastic constant of elemental Mo. Although the rule of mixtures turns out to be a useful tool to estimate the elastic properties of the present HEAs, to capture the more delicate alloying effects one needs to resort to ab initio results.
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•The influence of local lattice distortion is significant on the mixing energy and negligible on the elastic properties of HEAs.•Local lattice distortion may lead to overlap of the first and second nearest neighbor shell in bcc HEAs.•Alloying shows unexpected trends highlighting the importance of complex chemical interactions between constituents.•The rule of mixtures can estimate first-levelly the values of the lattice parameters and elastic constants of HEAs.
Water electrolysis shows great promise for the low-cost mass production of high-purity hydrogen. The relatively high dissociation energy of water, however, often results in rather sluggish kinetics ...of the hydrogen evolution reaction (HER) in alkaline conditions, even for the case of state-of-the-art Pt-based electrocatalysts. Here, we show the high efficiency of the hybrids of PtRu nanoclusters (NCs) and black phosphorus (BP) nanosheets in HER. Our PtRu NCs/BP electrocatalysts demonstrate a HER activity of 88.5 mA cm–2 at −70 mV in 1 M KOH, which is higher than that of commercial Pt/C by 1 order of magnitude. The observed extraordinarily high HER activity of the PtRu NCs/BP hybrids is interpreted in the framework of density functional theory. Theoretical modeling indicates that the electronic interaction between BP and PtRu NCs speeds up the dissociation of water and optimizes the adsorption strength for H* species, giving rise to the remarkably high HER activity of the PtRu NCs/BP hybrids.
Incorporating pentagons and heptagons into the hexagonal networks of pristine carbon nanotubes （CNTs） can form various CNT-based nanostructures, as pentagons and heptagons will bend or twist the CNTs ...by introducing positive and negative curvature, respectively. Some typical so-made CNT-based nanostructures are reviewed in this article, including zero-dimensional toroidal CNTs, and one-dimensional kinked and coiled CNTs. Due to the presence of non-hexagonal rings and curved geometries, such nanostructures possess rather different structural, physical and chemical properties from their pristine CNT counterparts, which are reviewed comprehensively in this article. Additionally, their synthesis, modelling studies, and potential applications are discussed.
Clearances in the joints of real mechanisms are unavoidable due to assemblage, manufacturing errors, and wear. The dual-axis driving and positioning mechanism is one kind of space actuating mechanism ...for satellite antenna to implement precise guidance and positioning. However, in dynamics analysis and control of the satellite antenna system, it is usually assumed that the revolute joint in the satellite antenna system is perfect without clearances or imperfect with planar radial clearance. However, the axial clearance in an imperfect revolute joint is always ignored. In this work, the revolute joint is considered as a 3D spatial clearance joint with both the radial and axial clearances. A methodology for modeling the 3D revolute joint with clearances and its application in satellite antenna system is presented. The dynamics modeling and analysis of the satellite antenna system are investigated considering the 3D revolute clearance joint. Firstly, the mathematical model of the 3D revolute clearance joint is established, and the definitions of the radial and axial clearance are presented. Then, the potential contact modes, contact conditions, and contact detection of the 3D revolute clearance joint are analyzed. Further, the normal and tangential contact force models are established to describe the contact phenomenon and determine the contact forces in the 3D revolute clearance joint. Finally, a satellite antenna system considering the 3D revolute clearance joint with spatial motion is presented as the application example. Different case studies are presented to discuss the effects of the 3D revolute clearance joint. The results indicate that the 3D revolute clearance joint will lead to more severe effects on the dynamic characteristics of the satellite antenna system. Therefore, the effects of axial clearance on the satellite antenna system cannot be ignored in dynamics analysis and design of the satellite antenna system.
Based on the experimental observations, amorphous structural models of graphene oxides (GOs) were constructed and investigated by first-principles computations. Geometric structures, thermodynamic ...stabilities, and electron density of states of these amorphous GO models were examined and compared with the previously proposed ordered GO structures. The thermodynamically most favorable amorphous GO models always contain some locally ordered structures in the short range, due to a compromise of the formation of hydrogen bonds, the existence of dangling bonds, and the retention of the π bonds. Compared to the ordered counterparts, these amorphous GO structures possess good stability at low oxygen coverage. Varying the oxygen coverage and the ratio of epoxy and hydroxyl groups provides an efficient way to tune the electronic properties of the GO-based materials.
Abstract
Activation of
p
-block elements to replace the rare and precious transition metals for renewable energy applications is highly desirable. In this review, we go over recent experimental and ...theoretical progress on the low-dimensional non-metal materials for clean energy production, including carbon, silicon, oxide, boron, and phosphorus-based nanostructures, with the
p
-block elements serving as active sites. We aim to elucidate the mechanism for triggering activity in different kinds of non-metal systems, and extract general principles for controlling the
p
-orbital-mediated reactivity from a theoretical point of view. The perspectives and challenges for developing high-efficiency non-metal catalysts are provided in the end.
•CuTi-containing catalyst derived from hydrotalcite-like used for NOx removal.•Cu can be categorized into surface and bulk species of the CuTi-containing catalyst.•Surface Cu is active site, while ...bulk Cu possesses adsorption property.•Lewis acid sites actively contribute to the catalytic performance.•Nitrates, acetate and formate are evidenced as key intermediates for NOx removal.
A series of hydrotalcite-based CuxTi1 (x=2, 3, 4, 5)-mixed oxide catalysts have been synthesized by homogeneous precipitation and tested in the selective catalytic reduction (SCR) of NO by C3H6 in the presence of excess oxygen. Cu atoms can be categorized into surface and bulk species. The surface Cu species are the active sites while the bulk Cu species possess adsorption property for nitrogen species, and such bulk Cu species varies from CuxTiyOz to CuO with increasing Cu content. The Cu3Ti1 catalyst with the highest amount of surface copper and Lewis acid sites exhibits the best catalytic performance due to its improved electrophilicity of CuxTiyOz, which enhance the adsorption capability of nitrogen species. In situ infrared characterization revealed that nitrates in terms of bridging, bidentate and chelating species are reactive toward acetate and formate, and they are the key intermediates produced during the SCR of NO.
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