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The adjacent chemical microenvironment of single metal atoms in heterogeneous catalysis is crucial to their chemical activity for various catalytic processes. Here, based on first-principles calculations, 25 single transition metal atom catalysts coordinated to sulfur species embedded in graphene (TM-S

Two-dimensional (2D) metal-organic frameworks (MOFs) with room-temperature magnetism are highly desirable but challenging due to the weak superexchange interaction between metal atoms. For this purpose, strengthening the hybridization between metal ion and organic linkage presents an experiment-feasible chemical solution to enhance the Curie temperature. Here, we report three 2D Cr(II) aromatic heterocyclic MOF magnets with enhanced Curie temperature by bridging Cr(II) ions with pyrazine, 1,4-diphosphinine, and 1,4-diarsenin linkers, i.e., Cr(pyz)

Single-atom catalysts (SACs) are one of the most promising candidates for catalyzing various electrochemical reactions, due to their maximum atom utilizations and unique electronic structures.

The spin and valence states of active sites have a direct and crucial bearing on the activity of transition-metal-based catalysts. However, modulating spin and valence states based on the synergistic...

The exploration of two-dimensional (2D) semiconductors with intrinsic room-temperature magnetism for use in nanoscale spintronic devices is of particular interest. Recently, the ferromagnetic CrX3 monolayer (X = Br, I) has received growing attention, but low critical temperature hinders its practical applications in spintronics. Here, using first-principles calculations, we report 2D Cr2X3S3 (X = Br, I) Janus semiconductors with room-temperature magnetism by replacing one layer of halogon atoms with sulfur atoms in CrX3 monolayer. Our results demonstrate that Cr2Br3S3 and Cr2I3S3 Janus crystals are ferrimagnetic semiconductors, that maintain their magnetic order, with a direct bandgap of 1.19 and 0.61 eV and high critical temperature of 387 and 447 K, respectively. The residual unpaired p electrons on the S anions lead to a strong direct-exchange interaction between the Cr and S atoms. Moreover, their room-temperature magnetism is robust under biaxial strain, while the bandgap can be remarkably modulated with strain. The novel magnetic properties in 2D Cr2X3S3 Janus magnetic semiconductors give them promising applications in spintronics.

Interfacial polarons have been demonstrated to play important roles in heterostructures containing polar substrates. However, most of polarons found so far are diffusive large polarons; the discovery and investigation of small polarons at interfaces are scarce. Herein, we report the emergence of interfacial polarons in monolayer SnSe2 epitaxially grown on Nb-doped SrTiO3 (STO) surface using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). ARPES spectra taken on this heterointerface reveal a nearly flat in-gap band correlated with a significant charge modulation in real space as observed with STM. An interfacial polaronic model is proposed to ascribe this in-gap band to the formation of self-trapped small polarons induced by charge accumulation and electron-phonon coupling at the van der Waals interface of SnSe2 and STO. Such a mechanism to form interfacial polaron is expected to generally exist in similar van der Waals heterojunctions consisting of layered 2D materials and polar substrates.

It is still a great challenge to explore hydrogen evolution reaction (HER) electrocatalysts with both lower overpotential and higher stability in acidic electrolytes. In this work, an efficient HER catalyst, Ru@COF-1, is prepared by complexation of triazine-cored sp

Metal–support interaction is of great significance for catalysis as it can induce charge transfer between metal and support, tame electronic structure of supported metals, impact adsorption energy of reaction intermediates, and eventually change the catalytic performance. Here, we report the metal size-dependent charge transfer reversal, that is, electrons transfer from platinum single atoms to sulfur-doped carbons and the carbon supports conversely donate electrons to Pt when their size is expanded to ~1.5 nm cluster. The electron-enriched Pt nanoclusters are far more active than electron-deficient Pt single atoms for catalyzing hydrogen evolution reaction, exhibiting only 11 mV overpotential at 10 mA cm−2 and a high mass activity of 26.1 A mg−1 at 20 mV, which is 38 times greater than that of commercial Pt/C. Our work manifests that the manipulation of metal size-dependent charge transfer between metal and support opens new avenues for developing high-active catalysts., The charge transfer between metal and support is significant for catalysis, but little attention has been focused on charge transfer tuned by metal size. Here, authors report a metal size-dependent reversal of charge transfer between metal and carbon support in hydrogen evolution electrocatalysts.

Assembling p orbital ferromagnetic half-metallicity and a topological element, such as a Dirac point at the Fermi level, in a single nanomaterial is of particular interest for long-distance, high-speed, and spin-coherent transportation in nanoscale spintronic devices. On the basis of the tight-binding model, we present an orbital design of a two-dimensional (2D) anionogenic Dirac half-metal (ADHM) by patterning cations with empty d orbitals and anions with partially filled p-type orbitals into a kagome lattice. Our first-principles calculations show that 2D transition-metal peroxides h-TM2(O2)3 (TMO3, TM = Ti, Zr, Hf), containing group IVB transition-metal cations [TM]4+ bridged with dioxygen anions [O2]8/3- in a kagome structure, are stable ADHMs with a Curie temperature over 103 K. The 2/3 filled π* orbitals of dioxygen anions are ferromagnetically coupled, leading to p orbital ferromagnetism and a half-metallic Dirac point right at the Fermi level with a Fermi velocity reaching 2.84 × 105 m/s. We proposed that 2D h-TM2(O2)3 crystals may be extracted from ABO3 bulk materials containing 2D TMO3 layers.

The exploration of two-dimensional (2D) semiconductors with intrinsic room-temperature magnetism for use in nanoscale spintronic devices is of particular interest. Recently, the ferromagnetic CrX

Photocatalysis may provide an intriguing approach to nitrogen fixation, which relies on the transfer of photoexcited electrons to the ultrastable N≡N bond. Upon N2 chemisorption at active sites (e.g., surface defects), the N2 molecules have yet to receive energetic electrons toward efficient activation and dissociation, often forming a bottleneck. Herein, we report that the bottleneck can be well tackled by refining the defect states in photocatalysts via doping. As a proof of concept, W18O49 ultrathin nanowires are employed as a model material for subtle Mo doping, in which the coordinatively unsaturated (CUS) metal atoms with oxygen defects serve as the sites for N2 chemisorption and electron transfer. The doped low-valence Mo species play multiple roles in facilitating N2 activation and dissociation by refining the defect states of W18O49: (1) polarizing the chemisorbed N2 molecules and facilitating the electron transfer from CUS sites to N2 adsorbates, which enables the N≡N bond to be more feasible fo...

The development of two-dimensional (2D) transitional metal based crystals with nontrivial electronic and magnetic properties is important both for fundamental research and practical applications in nanotechnology. Here, we report two 2D transitional metal dihydride (MH2, M = Mo, W) crystals on the basis of first-principles calculations and the concept of hydrogen substitution of sulphur in MoS2 and WS2. In 2D MH2 crystals, metal atoms are coordinated with hydrogen atoms in either trigonal prismatic (H-MH2) or octahedral (T-MH2) configurations, where T-MH2 is more energetically stable than H-MH2. All 2D MH2 crystals are metallic, and in particular, T-MH2 is ferromagnetic with an anisotropic spin-polarized Fermi Dirac cone and high Curie temperature of about 658 K. The calculated Fermi velocities vary from 0.21 × 105 to 6.02 × 105 m s−1. Our results further demonstrate that hydrogen substitution of sulphur in MoS2 and WS2 is thermodynamically favorable, and their lattice dynamic stabilities are confirmed by both phonon spectrum calculations and Born–Oppenheimer molecular dynamic simulations at temperatures up to 800 K. These novel properties endow the 2D MH2 crystals with great potential in spintronics applications.

The effects of in situ amorphous graphite coating on ablation behavior of SiC fiber reinforced SiBCN ceramics in an oxyacetylene flame are explored. The ablation products for both the monoliths and composites are similar, comprising amorphous SiO2 and cristobalite. The ablation resistance stems from formation of dense, passivating oxide scale of B2O3 containing amorphous SiO2. In different ablation stages, the ablation rates are synergistically controlled by various mechanisms. Interfacial structure and degradation of SiC fibers both deteriorate ablation resistance. The crystallization of SiC fibers leading to strength reduction is the main reason for poorer performance vs monoliths.

SiBCN ceramics were prepared using various volumes of graphene platelets (GPLs) as nanofiller. The effects of the nanofiller on microstructure, and oxidation and thermal shock resistance of as-sintered ceramics were investigated. The phase composition and microstructures were very similar for all investigated ceramics consisting primarily of β-SiC, BNC and small amounts of α-SiC with relatively homogeneously distributed 5–10 nm thick GPLs in the matrix. For SiBCN ceramics incorporating graphene as nanofiller, a porous oxide layer forms at 1500 °C and the oxidation behavior shows a linear kinetics by thickness measurement method. Gas evolution during heating lead to a passive oxidation behavior and weight loss. Graphene reinforced SiBCN ceramics exhibit thermal shock resistance superior to monoliths of the same material. The graphene distributed in SiBCN matrix can dissipate the energy of crack growth and acts as a stopper to cracks. The toughening mechanisms offered by graphene, including pull-out and bridging appear to aid in ameliorating thermal shock effects. Furthermore, the existence of a dense oxide surface layer retards oxygen diffusion into the inner matrix and heals surface pores and cracks, which also contributes to thermal shock resistance.

Photocatalysis may provide an intriguing approach to nitrogen fixation, which relies on the transfer of photoexcited electrons to the ultrastable N≡N bond. Upon N

Three types of molecular regular tessellations, i.e., hexagonal, square and triangular tessellations, were constructed on Cu(111) by using 4,4′-dihydroxydiphenyl as the precursor through molecular assembly. These tessellations are stabilized by multiple intermolecular hydrogen bonds and the proportion of each tessellation can be tuned by thermal treatment.

Engineering material structures at the atomic level is a promising way to tune the physicochemical properties of materials and optimize their performance in various potential applications. Here, we show that the lithiation-induced amorphization of layered crystalline Pd3P2S8 activates this otherwise electrochemically inert material as a highly efficient hydrogen evolution catalyst. Electrochemical lithiation of the layered Pd3P2S8 crystal results in the formation of amorphous lithium-incorporated palladium phosphosulfide nanodots with abundant vacancies. The structure change during the lithiation-induced amorphization process is investigated in detail. The amorphous lithium-incorporated palladium phosphosulfide nanodots exhibit excellent electrocatalytic activity towards the hydrogen evolution reaction with an onset potential of −52 mV, a Tafel slope of 29 mV dec−1 and outstanding long-term stability. Experimental and theoretical investigations reveal that the tuning of morphology and structure of Pd3P2S8 (for example, dimension decrease, crystallinity loss, vacancy formation and lithium incorporation) contribute to the activation of its intrinsically inert electrocatalytic property. This work provides a unique way for structure tuning of a material to effectively manipulate its catalytic properties and functionalities. The structural modification of inactive materials to effectively engineer active catalysts is very attractive. Here, layered crystalline Pd3P2S8 is transformed by electrochemical lithiation into amorphous Li-incorporated nanodots. This process turns the inert parent material into a highly active and stable hydrogen-evolving catalyst.

The superplasticity and diffusion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at different temperatures and various initial strain rates using the tensile speed mutation method; m readied its maximum value 0.53 at an inititil strain rate of 1×10−4s−1 at 1253K. The diffusion bonding parameters, including the bonding temperature T, pressure p, and time t, affected the mechanism of joints. When the bonded specimen with 25μm thick nickel foil interlayer was tensile at room temperature, the shear fracture of the joints with nickel foil interlayer took place at the IN718 part. Microstructure study was carried out with the bonded samples. The microstructure shows an excellent bonding at the interfaces. The optimum parameters for the diffusion bonding are: T=1273-1323K, p=20-30MPa, t=45-60min.