Adsorption of Ag on M-doped graphene:First principle calculations

Graphene is an ideal reinforcing phase for a high-performance composite filler,which is of great theoretical and practical significance for improving the wettability and reliability of the filler.However,the poor adsorption characteristics between graphene and the silver base filler significantly affect the application of graphene filler in the brazing field.It is a great challenge to improve the adsorption characteristics between a graphene and silver base filler.To solve this issue,the adsorption characteristic between graphene and silver was studied with first principle calculation.The effects of Ga,Mo,and W on the adsorption properties of graphene were explored.There are three possible adsorbed sites,the hollow site(H),the bridge site(B),and the top site(T).Based on this research,the top site is the most preferentially adsorbed site for Ag atoms,and there is a strong interaction between graphene and Ag atoms.Metal element doping enhances local hybridization between C or metal atoms and Ag.Furthermore,compared with other doped structures(Ga and Mo),W atom doping is the most stable adsorption structure and can also improve effective adsorption characteristic performance between graphene and Ag.

Structural,phonon,elastic,thermodynamic and electronic properties of Mg-X(X=La,Nd,Sm)intermetallics:The first principles study

We show the results of first-principles calculations of structural,phonon,elastic,thermal and electronic properties of the Mg-X inter-metallics in their respective ground state phase and meta-stable phases at equilibrium geometry and the studied pressure range.Phonon dispersion spectra for these compounds were investigated by using the linear response technique.The phonon spectra do not show any abnormality in their respective ground state phase.The respective ground states phases of the studied system remain stable within the studied pressure range.Electronic and thermodynamic properties were derived by analysis of the electronic structures and quasi-harmonic approximation.The mixed bonding character of the Mg-X intermetallics is revealed by Mg-X bonds,and it leads the metallic nature.Most of the contribution originated from X ions d like states at Fermi level compared to that of Mg ion in these intermetallics.In this work,we also predicted the melting temperature of these intermetallics and evaluated the Debye temperature by using elastic constants.

First-principles study of magnetism of 3d transition metals and nitrogen co-doped monolayer MoS2

The electronic structures and magnetic properties of diverse transition metal (TM=Fe, Co, and Ni) and nitrogen (N) co-doped monolayer MoS2 are investigated by using density functional theory. The results show that the intrinsic MoS2 does not have magnetism initially, but doped with TM (TM=Fe, Co, and Ni) the MoS2 possesses an obvious magnetism distinctly. The magnetic moment mainly comes from unpaired Mo:4d orbitals and the d orbitals of the dopants, as well as the S:3p states. However, the doping system exhibits certain half-metallic properties, so we select N atoms in the V family as a dopant to adjust its half-metal characteristics. The results show that the (Fe, N) co-doped MoS2 can be a satisfactory material for applications in spintronic devices. On this basis, the most stable geometry of the (2Fe-N) co-doped MoS2 system is determined by considering the different configurations of the positions of the two Fe atoms. It is found that the ferromagnetic mechanism of the (2Fe-N) co-doped MoS2 system is caused by the bond spin polarization mechanism of the Fe-Mo-Fe coupling chain. Our results verify that the (Fe, N) co-doped single-layer MoS2 has the conditions required to become a dilute magnetic semiconductor.

Hollow sphere of heterojunction(NiCu)S/NC as advanced anode for sodium-ion battery

Metal sulfide is considered as a potential anode for sodium-ion batteries(SIBs),due to the high theoretical capacity,strong thermodynamic stability and low-cost.However,their cycle capacity and rate performance are limited by the excessive expansion rate and low intrinsic conductivity.Herein,heterogeneous hollow sphere NiS-Cu_(9)S_(5)/NC(labeled as(NiCu)S/NC)based on Oswald ripening mechanism was prepared through a simple and feasible methodology.From a structural perspective,the hollow structure provides an expansion buffer and raises the electrochemical active area.In terms of electron/ion during the cycles,Na^(+)storage mechanism is optimized by NiS/Cu_(9)S_(5)heterogeneous interface,which increases the storage sites and shortens the migration path of Na^(+).The formation of built-in electric field strengthens the electron/ion mobility.Based on the first principle calculations,it is further proved the formation of heterogeneous interfaces and the direction of electron flow.As the anode for SIBs,the synthesized(NiCu)S/NC delivers high reverse capacity(559.2 mA h g^(-1)at 0.5 A g^(-1)),outstanding rate performance(185.3 mA h g^(-1)at 15 A g^(-1)),long-durable stability(342.6 mA h g^(-1)at 4 A g^(-1)after 1500cycles,150.0 m A h g^(-1)at 10 A g^(-1)after 20,000 cycles with 0.0025%average attenuation rate).The matching cathode electrode Na_(3)V_(2)(PO_(4))_(3)/C is assembled with(NiCu)S/NC for the full-battery that achieves high energy density(253.7 W h kg^(-1))and reverse capacity(288.7 mA h g^(-1)).The present work provides a distinctive strategy for constructing electrodes with excellent capacity and stability for SIBs.

High CO_(2) absorption capacity of metal-based ionic liquids: A molecular dynamics study

The absorption of CO_(2)is of importance in carbon capture,utilization,and storage technology for greenhouse gas control.In the present work,we clarified the mechanism of how metal-based ionic liquids (MBILs),Bmim[XCl_(n)]_(m)(X is the metal atom),enhance the CO_(2)absorption capacity of ILs via performing molecular dynamics simulations.The sparse hydrogen bond interaction network constructed by CO_(2)and MBILs was identified through the radial distribution function and interaction energy of CO_(2)-ion pairs,which increase the absorption capacity of CO_(2)in MBILs.Then,the dynamical properties including residence time and self-diffusion coefficient confirmed that MBILs could also promote the diffusion process of CO_(2)in ILs.That's to say,the MBILs can enhance the CO_(2)absorption capacity and the diffusive ability simultaneously.Based on the analysis of structural,energetic and dynamical properties,the CO_(2)absorption capacity of MBILs increases in the order Cl^-→[ZnCl_(4)]^(2-)→[CuCl_(4)]^(2-)→[CrCl_(4)]^-→[FeCl_(4)]^-,revealing the fact that the short metal–Cl bond length and small anion volume could facilitate the performance of CO_(2)absorbing process.These findings show that the metal–Cl bond length and effective volume of the anion can be the effective factors to regulate the CO_(2)absorption process,which can also shed light on the rational molecular design of MBILs for CO_(2)capture and other key chemical engineering processes,such as IL-based gas sensors,nano-electrical devices and so on.

Approaching High-Performance Lithium Storage Materials by Constructing Hierarchical CoNiO_(2)@CeO_(2)Nanosheets

In this work,the hierarchical CoNiO_(2)@CeO_(2)nanosheet composites were successfully prepared by a one-step hydrothermal process with a subsequent annealing process for the first time.The CeO_(2)nanoparticles successfully deposit on the surface of CoNiO_(2)nanosheet,and benefit the improvement of electrical contact between CoNiO_(2)and CeO_(2).CeO_(2)modification improve the reversibility of insertion/extraction of Li-ions and electrochemical reaction activity,and promotes the transport of Li-ions.Benefited of the unique architecture and component,the CoNiO_(2)@CeO_(2)nanosheet composites show high-reversible capacities,excellent cycling stability and good rate capability.The CoNiO_(2)@CeO_(2)(5.0 wt%)shows a charge/discharge capacity of 867.1/843.2 m Ah g^(-1)after 600 cycles at 1 A g^(-1),but the pristine CoNiO_(2)@CeO_(2)nanosheet only delivers a charge/discharge capacity of 516.9/517.6 m Ah g^(-1)after 500 cycles.The first-principles calculation reveals that valid interfaces between CeO_(2)and NiCoO_(2)can be formed,and the formation process of the interfaces is exothermic.The strong interfacial interaction resulting in an excellent structure stability and thus a cycling stability of the CoNiO_(2)@CeO_(2)material.This work provides an effective strategy to develop highperformance anode materials for advanced a lithium-ion battery,and the CoNiO_(2)@CeO_(2)nanosheet shows a sizeable potential as an anode material for next generation of high-energy Li-ion batteries.

Strain and interfacial engineering to accelerate hydrogen evolution reaction of two-dimensional phosphorus carbide

Hydrogen,regarded as a promising energy carrier to alleviate the current energy crisis,can be generated from hydrogen evolution reaction(HER),whereas its efficiency is impeded by the activity of catalysts.Herein,effective strategies,such as strain and interfacial engineering,are imposed to tune the catalysis performance of novel two-dimensional(2D)phosphorus carbide(PC)layers using first-principle calculations.The findings show that P site in pristine monolayer PC(ML-PC)exhibits higher HER performance than C site.Intriguingly,constructing bilayer PC sheet(BL-PC)can change the coordinate configuration of P atom to form 3-coordination-P atom(3-co-P)and 4-coordination-P atom(4-co-P),and the original activity of 3-co-P site is higher than the 4-co-P site.When an external compressive strain is applied,the activity of the 4-co-P site is enhanced whereas the external strain can barely affect that of 3-co-P site.Interestingly,the graphene substrate enhances the overall activity of the BL-PC because the graphene substrate optimizes the?GH*value of 4-co-P site,although it can barely affect the HER activity of 3-co-P site and ML-PC.The desirable properties render 2 D PC-based material promising candidates for HER catalysts and shed light on the wide utilization in electrocatalysis.

Theoretical investigation on radiation tolerance of M(n＋1)AXn phases

Ternary M_(n+1)AX_n phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, M_(n+1)AX_n materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different M_(n+1)AX_n(MAX) phases in terms of electronic structure, including the density of states(DOS) and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds,thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between M_(n+1)AC_n and M_(n+1)AN_n due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti_3AlC_2 to Ti_2AlC (Ti_3AlC_2 and Ti_2AlC have the same chemical elements), can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other M_(n+1)AX_n phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors.

Stability and optoelectronic property of low-dimensional organic tin bromide perovskites

The toxicity and degradation of hybrid lead-halide perovskites hinder their extensive applications.It is thus of great importance to explore non-toxic alternative materials with excellent stability and optoelectronic property.We investigate the atomic structures and optoelectronic properties of non-toxic organic tin bromide perovskites(OTBP)with one/zerodimensional(1D/0D)structures by first-principles calculations.The calculated atomic structures show that the 1D/0D OTBPs are stable and the structure of inorganic octahedra in 0D is higher order than that in 1D.Moreover,the origination of exceptional purity emitting light in experiments is explained based on the calculated electronic structure.

Can HHe^(+)exist at high pressure:Exploration of high pressure induced HF–He compounds

HHe^(+)is considered as the strongest acid and most powerful proton donor known to human.Whether HHe^(+)exists at planetary high pressure environment is a quite important problem in physics,chemistry and planetary sciences.Here,using the ab initio evolutionary algorithm USPEX package,we searched HF–He system,which was reported as the most possible candidate to contain HHe^(+).The calculation proved HHe^(+)cannot form at pressure<1000 GPa,due to a conflict between the covalent component in symmetric hydrogen bond and ionic HHe^(+).Although He atoms have no chemical bonding with other elements,they can supply a chemical pressure,leading to two new phases He2(HF)4 and He(HF).With coplanar(HF)_(4)rings,He_(2)(HF)_(4)have an aromaticity-like electronic behavior while He(HF)has a new type of chiral HF chain.The formation of He_(2)(HF)_(4)and He(HF)prove that the chemical pressure from He,on par with external pressure,have ability to control the structural and electronic configuration and induce some new familiars of compounds include H and He elements which are fundamental planetary materials in giant planets.

Magnetic anisotropy in 5d transition metal-porphyrin molecules

Single molecule magnets(SMMs) with large magnetic anisotropy energy(MAE) have great potential applications in magnetic recording.Using the first-principles calculations,we investigate the MAE of 5 d transition metal-porphyrin-based SMMs by using the PBE and PBE+U with different U values,respectively.The results indicate that W-P,Re-P,Os-P,and Ir-P possess the considerably large MAE among 5 d TM-P SMMs.Furthermore,the MAE of 5 d TM-P can be facilely manipulated by tensile strain.The reduction of the absolute value of MAE for Ir-P molecule caused by tensile strain makes it easier to implement the writing operation.The decreasing of the occupation number of minority-spin channels of Ir-d_(x^(2)-y^(2)) orbital leads the MAE to decrease when the tensile strain increases.

Facile preparation of hierarchical Ni@Mn-doped NiO hybrids for efficient and durable oxygen evolution reaction

Exploring highly efficient and non-noble-metal-based electrocatalysts for oxygen evolution reaction(OER)is of great importance not only for water splitting but also for rechargeable metal-air batteries and fuel cells.Herein,we describe a simple strategy to prepare hierarchical Ni@Mn-doped Ni O hybrids using flower-like Ni-Mn layered double hydroxides(Ni Mn-LDHs)as a precursor.After calcination at 400℃for an hour under N_(2)atmosphere,the flower-like Ni Mn-LDHs transform to porous microspheres consisting of nanoparticles,in which Ni cores are encapsulated by Mn-doped NiO shells(denoted as Ni@MnNi O-400).Benefiting to this unique porous,core-shell structures and element doping,the as-prepared Ni@Mn-NiO-400 hybrid shows a low overpotential of 178 mV at the current density of 10 mA/cm^(2)and Tafel slope of 52.7 m V/dec in 1 mol/L KOH solution.More significantly,the Ni@Mn-Ni O-400 hybrid also demonstrates superior stability of 98.6%after 50 h continuously testing,much higher than pristine Ni MnLDHs and commercial IrO_(2)catalyst.In addition,theoretical simulation shows that Ni core and Mn doping greatly affect the electronic states and electronic structure of Ni O.As a result,Ni@Mn-doped Ni O hybrid possesses an optimal adsorption activity towards oxygen species than Ni O and undoped Ni@Ni O hybrid.Considering the compositional and structural flexibility of LDHs,this work may offer a simple method to prepare other non-noble metal-based electrocatalysts for OER.

New insights into the mechanism of localised corrosion induced by TiN-containing inclusions in high strength low alloy steel

This work investigated the chemical and electrochemical mechanisms of localised corrosion triggered by CaS·xMgO·y Al_(2)O_(3)·TiN complex inclusions in high strength low alloy steel(HSLAS)under a simulated marine environment.Special focus was given to the role of the TiN portion of the inclusion on the initiation and growth of the corrosion pits.The thermodynamic process of pitting initiation was investigated by Gibbs free energy,Pourbaix diagram and first principle calculation.Localised corrosion is mainly induced by inclusions and triggered by dissolution of adjacent distorted matrix.Chemical dissolution of CaS portion in CaS·xMgO·y Al_(2)O_(3)·TiN complex inclusion creates an acidic aggressive environment that accelerates the further dissolution of inclusion and matrix.Galvanic coupling effect between TiN inclusion and matrix is directly verified.TiN covered with a TiOfilm acts as the cathodic phase in galvanic corrosion,although it has a lower Volta potential than the matrix.This is an unusual correlation with the scanning Kelvin probe force microscopy result,which has been explained for this special system.

Enhanced electrical transport performance through cation site doping in Y-doped Mg_(3.2)Sb_(2)

Mg_(3)Sb_(2)-based alloys are promising thermoelectric materials through n-type doping in Mg-rich growth conditions to overcome their intrinsic p-type behavior.First principle calculations are employed to investigate the dopant formation energy and electronic structures of Y-doped Mg_(3)Sb_(2).Results indicate that the Y atom is more favorable for substitution at the cation site.Simultaneously,the flattened band structure and increased density of state near the Fermi level of Y-doped Mg_(3)Sb_(2) indicate an enhanced electronic transport performance.The carrier concentration rises to 5.31×10^(19) cm^(-3) at room temperature,resulting in a significant increased power factor for Mg_(3.17)Y_(0.03)Sb_(2).The available optimization of electrical transport contributes to excellent thermoelectric performance,and a peak ZT~0.83 at 773 K was achieved for Y concentration x=0.03 in Mg_(3.2-x)Y_(x)Sb_(2).This work provides an alternative measure for optimizing the thermoelectric performance of n-type Mg_(3)Sb_(2) alloys by cation site doping.

Electrical properties of yttrium calcium oxyborate crystal annealed at high temperature and low oxygen partial pressure

The yttrium calcium oxyborate crystal(YCa_(4)O(BO_(3))_(3),YCOB)has been actively studied for hightemperature piezoelectric sensing applications.In this work,the stability of electric properties of YCOB crystal annealed in critical conditions(high-temperatures of 900-1100℃ with a low oxygen partial pressure of 4×10^(-6) atm for 24 h)was investigated and the recovery mechanism for the electrical resisitivity,dielectric permittivity and dielectric loss were studied,taking advantage of the X-ray photoelectron spectra and the first principle calculations.The electrical resistivity of the annealed YCOB crystal was slightly decreased when compared to the pristine counterpart,being(2-5)×10^(7) Ω·cm at 850
C.The dielectric permittivity and dielectric loss were found to increase after annealing,showing recoverable behaviours after thermal treatment above 650℃ in air.The calculated vacancy formation energy indicates that the oxygen vacancy is the dominant defects in YCOB.The formation of oxygen vacancy weakens the chemical bonding strength between B(Ca or Y)and O atoms,introduces extra donor levels in the band gap,which excites the electrons to conduction band more easily thus enhances the electrical conductivity and dielectric loss.The recovered electrical properties are believed to be associated with the reduced vacancy defects at elevated temperatures in air.

Construction and electrochemical mechanism investigation of hierarchical core-shell like composite as high performance anode for potassium ion batteries

Potassium-ion batteries(PIBs)are promising candidates for next-generation energy storage devices due to the earth abundance of potassium,low cost,and stable redox potentials.However,the lack of promising high-performance electrode materials for the intercalation/deintercalation of large potassium ions is a major challenge up to date.Herein,we report a novel uniform nickel selenide nanoparticles encapsulated in nitrogen-doped carbon(defined as“NiSe@NC”)as an anode for PIBs,which exhibits superior rate performance and cyclic stability.Benefiting from the unique hierarchical core-shell like nanostructure,the intrinsic properties of metal-selenium bonds,synergetic effect of different components,and a remarkable pseudocapacitance effect,the anode exhibits a very high reversible capacity of 438 mA·h·g^(-1)at 50 mA·g^(-1),an excellent rate capability,and remarkable cycling performance over 2,000 cycles.The electrochemical mechanism were investigated by the in-situ X-ray diffraction,ex-situ high-resolution transmission electron microscopy,selected area electron diffraction,and first principle calculations.In addition,NiSe@NC anode also shows high reversible capacity of 512 mA·h·g^(-1)at 100 mA·g^(-1)with 84%initial Coulombic efficiency,remarkable rate performance,and excellent cycling life for sodium ion batteries.We believe the proposed simple approach will pave a new way to synthesize suitable anode materials for secondary ion batteries.

Superior mechanical and thermal properties than diamond:Diamond/lonsdaleite biphasic structure

It has been found recently in experiments that diamond/lonsdaleite biphase could possess excellent thermal-mechanical properties,implying that the properties of carbon materials can be improved by reasonably designing their internal structures.The mechanism of the excellent performance arising from biphasic structure is still unknown and needs to be revealed.In this paper,we established a series of possible diamond/lonsdaleite biphasic structures and revealed the optimization mechanism of the biphasic structure using first principles calculations.It shows in our ab-initio molecular dynamics simulations that the lonsdaleite cannot exist stably at room temperature,which could explain why pure lonsdaleite can hardly be found or synthesized.Detailed analysis shows that partial slip would occur in the lonsdaleite region if the applied strain is sufficiently large,leading to the transition from biphasic phase to cubic phase.Then,further shear strain would be applied along the hard shear direction of the cubic structure,resulting in an ascent of stress.The results presented could offer an insight into the structural transformation at high temperature and large strain.