The dynamic and kinetic evolution of supported metal particles in the presence of reactants is decisive in shaping the nature of the catalytic active sites and the deactivation process. Ostwald ripening of FeO/Pt(111)...The dynamic and kinetic evolution of supported metal particles in the presence of reactants is decisive in shaping the nature of the catalytic active sites and the deactivation process. Ostwald ripening of FeO/Pt(111) supported Au particles in the presence of carbon monoxide is addressed here by firstprinciples kinetics. It is found that CO stabilizes the ripening monomer(Au atom) by forming favorable Au carbonyls with lower total activation energy, and corresponding phase diagram at wide range of temperature and CO pressures is constructed. Evolution of particle number, dispersion and particle size distribution of supported Au particles are explored. Great influence of CO promotion on ripening kinetics is revealed and explored in details, and mbar range of CO can lower the onset temperature of ripening by a few hundred kelvins. The present work reveals the crucial role of the metal-reactant complexes formed under reaction conditions on ripening of metal catalysts.展开更多
This study explores the thin-layer convective solar drying of Marrubium vulgare L.leaves under conditions typical of sun-rich semi-arid climates.Drying experiments were conducted at three inlet-air temperatures(40℃,5...This study explores the thin-layer convective solar drying of Marrubium vulgare L.leaves under conditions typical of sun-rich semi-arid climates.Drying experiments were conducted at three inlet-air temperatures(40℃,50℃,60℃)and two air velocities(1.5 and 2.5 m·s^(-1))using an indirect solar dryer with auxiliary temperature control.Moisture-ratio data were fitted with eight widely used thin-layer models and evaluated using correlation coefficient(r),root-mean-square error(RMSE),and Akaike information criterion(AIC).A complementary heattransfer analysis based on Reynolds and Prandtl numbers with appropriate Nusselt correlations was used to relate flow regime to drying performance,and an energy balance quantified the relative contributions of solar and auxiliary heat.The logarithmic model consistently achieved the lowest RMSE/AIC with r>0.99 across all conditions.Higher temperature and air velocity significantly reduced drying time during the decreasing-rate period,with no constantrate stage observed.On average,solar input supplied the large majority of the thermal demand,while the auxiliary heater compensated short irradiance drops to maintain setpoints.These findings provide a reproducible dataset and a modelling benchmark for M.vulgare leaves,and they support energy-aware design of hybrid solar dryers formedicinal plants in sun-rich regions.展开更多
This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy, metal impurity, impurity vacancy complex in LiNH2, a promising material for hydrogen storage. It f...This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy, metal impurity, impurity vacancy complex in LiNH2, a promising material for hydrogen storage. It finds easy formation of H vacancy in the form of impurity-vacancy complex, and the rate-limiting step to the H diffusion. Based on the analysis of the density of states, it finds that the improvement of the dehydrogenating kinetics of LiNH2 by Ti catalysts and Mg substitution is due to the weak bonding of N-H and the new system metal-like, which makes H atom diffuse easily. The mulliken overlap population analysis shows that H vacancy leads to the H local diffusion, whereas impurity-vacancy complexes result from H nonlocal diffusion, which plays a dominant role in the process of dehydrogenation reaction of LiNH2.展开更多
Suppressing sintering of supported particles is of importance for the study and application of metal-TiO_(2)system.Theoretical study of Ostwald ripening of TiO_(2)(110)-supported Pd particles would be helpful to exten...Suppressing sintering of supported particles is of importance for the study and application of metal-TiO_(2)system.Theoretical study of Ostwald ripening of TiO_(2)(110)-supported Pd particles would be helpful to extend the understanding of the sintering.In this paper,based on density functional theory(DFT),the surface energy of Pd and the total activation energy(the sum of formation energy and diffusion barrier)of TiO2-supported Pd were calculated.Since the total activation energy is mainly contributed from the formation energy,it is indicated that the ripening of Pd particles would be in the interface control limit.Subsequently,the calculated surface energy and total activation energy were used to simulate Ostwald ripening of TiO_(2)(l 10)-supported Pd particles.As a result,in comparison with larger particles,smaller particles would worsen the performance of ripening-resistance according to its lower onset temperature and shorter half-life time.The differences on ripeningresistance among different size particles could be mitigated along with the increase of temperature.Moreover,it is verified that the monodispersity can improve ripening resistance especially for the smaller particles.However,the different performances of the ripening originating from difference of the relative standard deviation are more obvious at higher temperature than lower temperature.This temperature effect for the relative standard deviation is the inverse of that for the initial main particle size.It is indicated that the influence of dispersity of TiO_(2)(l 10)-supported Pd particles on ripening may be more sensitive at higher temperature.In this contribution,we extend the first principle kinetics to elaborate the ripening of Pd on TiO_(2)(l 10).It is expected that the information from first principle kinetics would be helpful to the study in experiments.展开更多
The mechanical and thermodynamic properties of W-Ti alloys(including W_(15)Ti_(1),W_(14)Ti_(2),W_(12)Ti_(4) and W_(8)Ti_(8) alloys)were investigated by the first-principles approach based on density functional theory....The mechanical and thermodynamic properties of W-Ti alloys(including W_(15)Ti_(1),W_(14)Ti_(2),W_(12)Ti_(4) and W_(8)Ti_(8) alloys)were investigated by the first-principles approach based on density functional theory.The results indicate that W-Ti alloys except W_(8)Ti_(8) are thermodynamically stable.The modulus and hardness of W-Ti alloys are smaller than those of pure tungsten and gradually decrease with increasing Ti concentration.However,their B/G ratios and Poisson's ratios exceed those of pure tungsten,suggesting that the introduction of Ti decreases the mechanical strength while enhancing the ductility of W-Ti alloys.The thermal expansion coefficients for W-Ti alloys all surpass those of pure tungsten,indicating that the introduction of titanium exacerbates the thermal expansion behavior of W-Ti alloys.Nevertheless,elevated pressure has the capacity to suppress the thermal expansion tendencies in titanium-doped tungsten alloys.This study offers theoretical insights for the design of nuclear materials by exploring the mechanical and thermodynamic properties of W-Ti alloys.展开更多
In this work,silicon-carbon hybrid materials were adopted as an example to illustrate the novel strategy to in situ construct heterostructure with adjustable microstructure.Based on the temperature-dependent thermodyn...In this work,silicon-carbon hybrid materials were adopted as an example to illustrate the novel strategy to in situ construct heterostructure with adjustable microstructure.Based on the temperature-dependent thermodynamics and kinetics of reaction between Si and C,the processes for Si nanocrystals growth and C decoration were coupled at different zones of plasma flame according to its temperature and velocity fields by theoretical modeling,aiming to intentionally suppress the formation of undesirable carbide,and enable adjusting the microstructure of each counterpart separately in transient process.As a result,well-controlled Si/C nanocomposites,including nanospheres and nanowires with core-shell structures,were achieved,and this continuous and in-flight route is also potential for large-scale production.Further investigation on the electrochemical properties highlights the advantage of as proposed strategy to efficiently construct heterostructures with superior performance for various applications.展开更多
Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH_(2).Herein,the sulfur doped Ti_(3)C_(2)(S-Ti_(3)C_(2))was successfully prepared by heat treatment ...Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH_(2).Herein,the sulfur doped Ti_(3)C_(2)(S-Ti_(3)C_(2))was successfully prepared by heat treatment of Ti_(3)C_(2)MXene under Ar/H_(2)S atmosphere to facilitate the hydrogen release and uptake from MgH_(2).The S-Ti_(3)C_(2)exhibited pleasant catalytic effect on the hydriding/dehydriding kinetics and cyclic stability of MgH_(2).The addition of 5 wt%S-Ti_(3)C_(2)into MgH_(2)resulted in a reduction of 114℃in the starting dehydriding temperature compared to pure MgH_(2).MgH_(2)+5 wt%S-Ti_(3)C_(2)sample could quickly release 6.6 wt%hydrogen in 17 min at 220℃,and 6.8 wt%H_(2)was absorbed in 25 min at 200℃.Cyclic testing revealed that MgH_(2)+5 wt%S-Ti_(3)C_(2)system achieved a reversible hydrogen capacity of 6.5 wt%.Characterization analysis demonstrated that Ti-species(Ti0,Ti^(2+),Ti-S,and Ti^(3+))as active species significantly lowered the dehydrogenation temperature and promoted the re-/dehydrogenation kinetics of MgH_(2),and sulfur doping can effectively improve the stability of Ti0 and Ti^(3+),contributing to the improvement of cyclic stability of MgH_(2).This study provides strategy for the construction of catalysts for hydrogen storage materials.展开更多
This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that ...This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.展开更多
Constructing silicon(Si)-based composite electrodes that possess high energy density,long cycle life,and fast charging capability simultaneously is critical for the development of high performance lithium-ion batterie...Constructing silicon(Si)-based composite electrodes that possess high energy density,long cycle life,and fast charging capability simultaneously is critical for the development of high performance lithium-ion batteries for mitigating range anxiety and slow charging issues in new energy vehicles.Herein,a thick silicon/carbon composite electrode with vertically aligned channels in the thickness direction(VC-SC)is constructed by employing a bubble formation method.Both experimental characterizations and theoretical simulations confirm that the obtained vertical channel structure can effectively address the problem of sluggish ion transport caused by high tortuosity in conventional thick electrodes,conspicuously enhance reaction kinetics,reduce polarization and side reactions,mitigate stress,increase the utilization of active materials,and promote cycling stability of the thick electrode.Consequently,when paired with LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)(NCM622),the VC-SC||NCM622 pouch type full cell(~6.0 mAh cm^(-2))exhibits significantly improved rate performance and capacity retention compared with the SC||NCM622 full cell with the conventional silicon/carbon composite electrode without channels(SC)as the anode.The assembled VC-SC||NCM622 pouch full cell with a high energy density of 490.3 Wh kg^(-1)also reveals a remarkable fast charging capability at a high current density of 2.0 mA cm^(-2),with a capacity retention of 72.0%after 500 cycles.展开更多
Single-atom catalysts have been applied in many processes recently.The difference of their kinetic behavior compared to the traditional heterogeneous catalysts has not been extensively discussed yet.Herein a complete ...Single-atom catalysts have been applied in many processes recently.The difference of their kinetic behavior compared to the traditional heterogeneous catalysts has not been extensively discussed yet.Herein a complete catalytic cycle of CH4 combustion assuming to be confined at isolated single sites of the Co3O4(110)surface is computationally compared with that on multi sites.The macroscopic kinetic behaviors of CH4 combustion on Co3O4(110)is systematically and quantitatively compared between those on the single site and multi sites utilizing kinetic Monte Carlo simulations upon the energetic information from the PBE+U calculation and statistic mechanics.The key factors governing the kinetics of CH4 combustion are disclosed for both the catalytic cycles respectively following the single-site and multi-site mechanisms.It is found that cooperation of multi active sites can promote the activity of complete CH4 combustions substantially in comparison to separated single-site catalyst whereas the confinement of active sites could regulate the selectivity of CH4 oxidation.The quantitative understanding of catalytic mechanism paves the way to improve the activity and selectivity for CH4 oxidation.展开更多
Hydrogen-enriched ironmaking presents a promising approach to mitigate coke consumption and carbon emission in blast furnace(BF)operations.This work investigated the relationship between the structural features of cok...Hydrogen-enriched ironmaking presents a promising approach to mitigate coke consumption and carbon emission in blast furnace(BF)operations.This work investigated the relationship between the structural features of cokes and their reactivity towards solution loss(SL),especially under hydrogen-enriched atmospheres.Six cokes were characterized,and their SL behaviors were examined under varying atmospheres to elucidate the effects of hydrogen enrichment.The results indicate that an increase in fixed carbon content leads to a decrease in the coke reactivity index(CRI)and an increase in coke strength after reaction(CSR),in the CO_(2) atmosphere,the CSR of coke increases from 35.76%−62.83%,while in the 90CO_(2)/10H_(2) atmosphere,the CSR of coke increases from 65.67%−84.09%.There is a good linear relationship between CRI and microcrystalline structure parameters of coke.Cokes with larger crystalline size,lower amorphous content,and smaller optical texture index(OTI)values show enhanced resistance to degradation and maintain structural integrity in BF.Kinetic analysis performed with the shifted-modified-random pore model(S-MRPM)reveals that alterations in pore structure and intrinsic mineral composition significantly influence the reaction rate.The introduction of a small amount of water vapor raises SL rates,whereas a minor addition of hydrogen(<10%)decelerates SL due to its incomplete conversion to water vapor and the reduced partial pressure of the gasifying agent.Thermodynamic calculations also indicate that the introduced hydrogen does not convert into the same fraction of water vapor.The shift from chemical reaction control to gas diffusion control as the rate-determining step with rising temperatures during SL process was confirmed,and the introduction of hydrogen does not notably alter SL behavior.This result demonstrated that introducing a small amount of hydrogen(<10%)can mitigate SL rates,thereby enhancing coke strength and reducing coke consumption and carbon emissions.展开更多
Hydrogen desorption kinetics and characteristics,residual hydrogen content and activation energy of TC21 alloy were investigated by the constant volume method.Results show that hydrogen desorption temperature and init...Hydrogen desorption kinetics and characteristics,residual hydrogen content and activation energy of TC21 alloy were investigated by the constant volume method.Results show that hydrogen desorption temperature and initial hydrogen pressure affect hydrogen desorption characteristics of TC21 alloy.The hydrogen desorption process is mainly dominated by nucleation and growth process(kt=[-ln(1-α)]^(2/3)),chemical reaction process(kt=(1-α)^(-1/2))and three-dimensional diffusion process(kt=[1-(1-α)^(1/3)]^(1/2))when the hydrogenated TC21 alloy is dehydrogenated at temperatures of 700-940°C.When the hydrogenated TC21 alloy releases hydrogen,the following relationship exists among the rate constants of each process:k(chemical reaction process)>k(nucleation and growth process)>k(three-dimensional diffusion process).The residual hydrogen content of the hydrogenated TC21 alloy after hydrogen desorption decreases gradually with the increase in hydrogen desorption temperature,and increases gradually with the increase in the initial hydrogen pressure.The activation energy of TC21 alloy in the process of hydrogen desorption is about 26.663 kJ/mol.展开更多
Accurately determining the Flade potential(E_(Flade))is of significant importance in the design of novel corrosion-resisting alloys.However,due to the complex nature of the E_(Flade)influenced by several factors inclu...Accurately determining the Flade potential(E_(Flade))is of significant importance in the design of novel corrosion-resisting alloys.However,due to the complex nature of the E_(Flade)influenced by several factors including compositions of the alloys and corrosive solutions,there is currently a lack of truly predictive ab initio model.Here,we established the critical potential condition required for passivation in acidic solutions containing chloride ions(Cl^(-))by developing an ab initio model that incorporates the potential drop from the metal electrode to the solution,considering tunneling of electrons at metal/film interface,breakdown of the film,and electrochemical adsorption reactions at film/solution interface.These parameters were derived from the work function of the alloy substrate and passivation film,the band gap of the passivation film,and the Gibbs free energy of adsorption on the passivation film,all of which can be obtainable from first-principles calculations.This theoretical model has been successfully validated for alloyed stainless steel,exhibiting a remarkable agreement with experimental results.Importantly,enabled by the model,we have identified several alloying elements(i.e.,Ta,W,Os,and Ir)that can effec-tively lower the EFlade of the stainless steel.This work constitutes an important step forward in modeling complex passivation behaviors from first-principles,providing a useful tool for the design of corrosion-resisting alloys.展开更多
Based on first-principles calculation framework,the surface model,anodic dissolution,cathodic oxygen absorption reaction,and other related electrochemical corrosion models of Fe-Ce system were constructed,and the infl...Based on first-principles calculation framework,the surface model,anodic dissolution,cathodic oxygen absorption reaction,and other related electrochemical corrosion models of Fe-Ce system were constructed,and the influencing mechanism Ce doping on the corrosion resistance of Fe-Ce system in the Cl medium environment was analyzed.The results show that Ce doping on the first surface and subsurface inhibits the ionization of Fe atoms and greatly promotes the repassivation process of Fe matrix.Ce doping on the first layer is conducive to preventing the detachment of surface Fe atoms from Fe matrix and delaying the occurrence of corrosion.Ce atoms in the subsurface effectively increase the difficulty of Fe atoms detaching from the matrix at high Cl concentrations.When O diffusion is the controlling link of oxygen absorption reaction,Ce doping has no effects on the reaction rate of cathodic oxygen absorption.Ce doping enhances the electrochemical stability of Fe(100)1and reduces the anodic dissolution rate of Fe matrix,thereby improving its corrosion resistance.展开更多
The vacuum reactive wetting and brazing of Er_(2)Si_(2)O_(7)/MoSi_(2) coatings were investigated using a (CoFeNiCrMn)_(88)Nb_(12) high-entropy alloy (HEA) brazing filler. The microstructural evolution and wettability ...The vacuum reactive wetting and brazing of Er_(2)Si_(2)O_(7)/MoSi_(2) coatings were investigated using a (CoFeNiCrMn)_(88)Nb_(12) high-entropy alloy (HEA) brazing filler. The microstructural evolution and wettability of the HEA filler were analyzed, with particular attention to the surface energy, interfacial stability, and electronic properties of the HEA filler/rare earth silicate coating system, as determined by density functional theory (DFT). As Nb diffused into the interface and the ErNbO_(4) phase formed, the wetting angle gradually decreased to 23.12° The effective wetting and spreading of the HEA brazing filler on the rare earth silicate coating surface are strongly correlated with the formation of the ErNbO_(4) phase at the interface. Furthermore, DFT calculations reveal that the interfacial bonding energy between the BCC' and FCC' phases and the ErNbO_(4) phase, after the wetting reaction, is significantly higher than the bonding energy between the initial filler and Er_(2)Si_(2)O_(7). This finding suggests that the formation of the ErNbO_(4) phase improves the wetting and spreading behavior of the filler.展开更多
The adsorption properties of a magnesium porphyrin(MgP)molecule on Au(111)surface covered with up to three lay-ers of sodium chloride(NaCl)were investigated by means of first-principles calculations.The most stable ad...The adsorption properties of a magnesium porphyrin(MgP)molecule on Au(111)surface covered with up to three lay-ers of sodium chloride(NaCl)were investigated by means of first-principles calculations.The most stable adsorption configuration of MgP on the NaCl/Au(111)heterosurfaces was found to be at the Cl-top site with a 20°angle between the[110]lattice direction of NaCl and the Mg–N bond of the molecule.Compared with MgP molecule adsorbed on bare Au(111),the inclusion of NaCl lay-ers can lead to a significant decrease in the adsorption energy of the MgP molecule.The exis-tence of NaCl layers also reduced the charge transfer between the molecule and the surface.For heterosurfaces with two or three monolayers of NaCl,the charge transfer was almost com-pletely suppressed.The obtained partial density of states(PDOS)showed that hybridization between the electronic structures of the adsorbed MgP molecule and the metal surface can be significantly suppressed when NaCl layers were added.For the heterosurface with three lay-ers of NaCl,the PDOS around the Fermi level was almost identical with that of the free molecule,suggesting the electronic structure of the MgP molecule was nicely preserved.Influ-ence of the NaCl layers on the electronic structure of the MgP molecule was mainly found for molecular orbitals(MOs)away from the Fermi level as a result of the large band gap of the NaCl layers.展开更多
Control of hyperfine interaction strength of shallow donors in Si is one of the central issues in realizing Kane quantum computers.First-principles calculations on the hyperfine Stark shift of shallow donors are chall...Control of hyperfine interaction strength of shallow donors in Si is one of the central issues in realizing Kane quantum computers.First-principles calculations on the hyperfine Stark shift of shallow donors are challenging since large supercells are needed to accommodate the delocalized donor wave functions.In this work,we investigated the hyperfine Stark shift and its strain tunability for shallow donors P and As in Si using the potential patching method based on first-principles density functional theory calculations.The good agreement between our calculations and experimental results confirms that the potential patching method is a feasible and accurate first-principles approach for studying wave-function-related properties of shallow impurities,such as the Stark shift parameter.It is further shown that the application of strain expands the range of hyperfine Stark shift and helps improve the response of shallow donor based qubit gates.The results could be useful for developing quantum computing architectures based on shallow donors in Si.展开更多
Ni-Mn-Ti Heusler alloys have great potential for elastocaloric refrigeration due to the colossal caloric effect and good mechanical properties. However, theoretical calculations on the characterization of the elastoca...Ni-Mn-Ti Heusler alloys have great potential for elastocaloric refrigeration due to the colossal caloric effect and good mechanical properties. However, theoretical calculations on the characterization of the elastocaloric effect are rare. An important parameter to evaluate the elastocaloric effect is the transformation entropy change, whose main source is the vibrational entropy change (ΔS_(vib)). Unfortunately, the widely used quasiharmonic approximation method fails in the prediction of the vibrational entropy for high-temperature austenite due to its dynamical instability at 0 K. To solve this problem, the temperature dependent effective potential method was used considering the temperature and anharmonic effect. Sc, V, and Zr doping at the Ti sites in B2 disordered Ni_(8)Mn_(5)Ti_(3) were studied about phase stability, martensitic transformation, and elastocaloric properties. The results revealed the austenitic structures of all the doping systems exhibit antiferromagnetic coupling characteristics at 300 K due to the temperature effect. Sc and Zr doping at the Ti sites decreased the ΔS_(vib) value, whereas V doping at the Ti site increased the ΔS_(vib) value. Further analysis proved the important evaluation criterion that the ΔS_(vib) value increases with the tetragonal distortion ratio and volume change, which has important guiding significance for improving the elastocaloric effect. Besides, the calculations of elastic constants presented all the doping systems maintain outstanding ductility evaluated from the B/G ratio. This work provides an effective strategy for designing excellent elastocaloric material with large vibrational entropy change and good mechanical properties.展开更多
Solute segregation at grain boundaries(GBs)can significantly influence GB cohesion.In this work,the segregation energies of solutes(Zn,Al,Ag,Ca,and Gd)were first investigated at six symmetrical tilt GBs rotating aroun...Solute segregation at grain boundaries(GBs)can significantly influence GB cohesion.In this work,the segregation energies of solutes(Zn,Al,Ag,Ca,and Gd)were first investigated at six symmetrical tilt GBs rotating around[0001]axis of Mg,to uncover the impact of GB characteristics on solute segregation behavior.The results reveal that solute segregation propensity is closely related to the local geometric environment of GB sites,but has little correlation with intrinsic GB properties(such as GB misorientation and GB energy).Furthermore,relationships between GB site characteristics and solute segregation tendencies were established.Ca-like solutes tend to occupy GB sites with larger Voronoi volumes(V),while Zn-like solutes prefer GB sites with smaller V as well as smaller shortest bond lengths(SBL).Based on this finding,we further evaluated the segregation capacities of 26 solutes at their most energetically stable segregation sites and their impact on GB cohesion.A descriptor that can effectively capture the strengthening/embrittling potency of segregated solutes on GBs was proposed by performing the crystal orbital Hamilton population(COHP)analyses.It was found that the discrepancies in bond strength between GBs and free surface dominate the solute-strengthening behavior.Finally,a first-principles“design map”regarding the segregation energies and strengthening energies was provided,which offers a database for designing Mg alloys with high fracture toughness.展开更多
基金supported by the National Key R&D Program of China(2017YB0602205)the National Natural Science Foundation of China(91645202)the Chinese Academy of Sciences(QYZDJSSW-SLH054)
文摘The dynamic and kinetic evolution of supported metal particles in the presence of reactants is decisive in shaping the nature of the catalytic active sites and the deactivation process. Ostwald ripening of FeO/Pt(111) supported Au particles in the presence of carbon monoxide is addressed here by firstprinciples kinetics. It is found that CO stabilizes the ripening monomer(Au atom) by forming favorable Au carbonyls with lower total activation energy, and corresponding phase diagram at wide range of temperature and CO pressures is constructed. Evolution of particle number, dispersion and particle size distribution of supported Au particles are explored. Great influence of CO promotion on ripening kinetics is revealed and explored in details, and mbar range of CO can lower the onset temperature of ripening by a few hundred kelvins. The present work reveals the crucial role of the metal-reactant complexes formed under reaction conditions on ripening of metal catalysts.
文摘This study explores the thin-layer convective solar drying of Marrubium vulgare L.leaves under conditions typical of sun-rich semi-arid climates.Drying experiments were conducted at three inlet-air temperatures(40℃,50℃,60℃)and two air velocities(1.5 and 2.5 m·s^(-1))using an indirect solar dryer with auxiliary temperature control.Moisture-ratio data were fitted with eight widely used thin-layer models and evaluated using correlation coefficient(r),root-mean-square error(RMSE),and Akaike information criterion(AIC).A complementary heattransfer analysis based on Reynolds and Prandtl numbers with appropriate Nusselt correlations was used to relate flow regime to drying performance,and an energy balance quantified the relative contributions of solar and auxiliary heat.The logarithmic model consistently achieved the lowest RMSE/AIC with r>0.99 across all conditions.Higher temperature and air velocity significantly reduced drying time during the decreasing-rate period,with no constantrate stage observed.On average,solar input supplied the large majority of the thermal demand,while the auxiliary heater compensated short irradiance drops to maintain setpoints.These findings provide a reproducible dataset and a modelling benchmark for M.vulgare leaves,and they support energy-aware design of hybrid solar dryers formedicinal plants in sun-rich regions.
基金supported by the National High Technology Research and Development Program of China (Grant No. 2009AA05Z105)the Natural Science Foundation of Liaoning Province of China (Grant No. 20102173)
文摘This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy, metal impurity, impurity vacancy complex in LiNH2, a promising material for hydrogen storage. It finds easy formation of H vacancy in the form of impurity-vacancy complex, and the rate-limiting step to the H diffusion. Based on the analysis of the density of states, it finds that the improvement of the dehydrogenating kinetics of LiNH2 by Ti catalysts and Mg substitution is due to the weak bonding of N-H and the new system metal-like, which makes H atom diffuse easily. The mulliken overlap population analysis shows that H vacancy leads to the H local diffusion, whereas impurity-vacancy complexes result from H nonlocal diffusion, which plays a dominant role in the process of dehydrogenation reaction of LiNH2.
基金Key Project of Chinese National Development Programs(No.2018YFB0406602)the National Natural Science Foundation of China(Grant No.61774065).
文摘Suppressing sintering of supported particles is of importance for the study and application of metal-TiO_(2)system.Theoretical study of Ostwald ripening of TiO_(2)(110)-supported Pd particles would be helpful to extend the understanding of the sintering.In this paper,based on density functional theory(DFT),the surface energy of Pd and the total activation energy(the sum of formation energy and diffusion barrier)of TiO2-supported Pd were calculated.Since the total activation energy is mainly contributed from the formation energy,it is indicated that the ripening of Pd particles would be in the interface control limit.Subsequently,the calculated surface energy and total activation energy were used to simulate Ostwald ripening of TiO_(2)(l 10)-supported Pd particles.As a result,in comparison with larger particles,smaller particles would worsen the performance of ripening-resistance according to its lower onset temperature and shorter half-life time.The differences on ripeningresistance among different size particles could be mitigated along with the increase of temperature.Moreover,it is verified that the monodispersity can improve ripening resistance especially for the smaller particles.However,the different performances of the ripening originating from difference of the relative standard deviation are more obvious at higher temperature than lower temperature.This temperature effect for the relative standard deviation is the inverse of that for the initial main particle size.It is indicated that the influence of dispersity of TiO_(2)(l 10)-supported Pd particles on ripening may be more sensitive at higher temperature.In this contribution,we extend the first principle kinetics to elaborate the ripening of Pd on TiO_(2)(l 10).It is expected that the information from first principle kinetics would be helpful to the study in experiments.
基金Funded by National Key R&D Program of China(No.2021YFB3802300)the National Natural Science Foundation of China(No.52171045)the Joint Fund(No.8091B022108)。
文摘The mechanical and thermodynamic properties of W-Ti alloys(including W_(15)Ti_(1),W_(14)Ti_(2),W_(12)Ti_(4) and W_(8)Ti_(8) alloys)were investigated by the first-principles approach based on density functional theory.The results indicate that W-Ti alloys except W_(8)Ti_(8) are thermodynamically stable.The modulus and hardness of W-Ti alloys are smaller than those of pure tungsten and gradually decrease with increasing Ti concentration.However,their B/G ratios and Poisson's ratios exceed those of pure tungsten,suggesting that the introduction of Ti decreases the mechanical strength while enhancing the ductility of W-Ti alloys.The thermal expansion coefficients for W-Ti alloys all surpass those of pure tungsten,indicating that the introduction of titanium exacerbates the thermal expansion behavior of W-Ti alloys.Nevertheless,elevated pressure has the capacity to suppress the thermal expansion tendencies in titanium-doped tungsten alloys.This study offers theoretical insights for the design of nuclear materials by exploring the mechanical and thermodynamic properties of W-Ti alloys.
基金financially supported by the National Natural Science Foundation of China(No.52174342)Beijing Natural Sci-ence Foundation(No.2232044)Beijing Municipal Education Commission Research Plan General Project(No.KM202410005009).
文摘In this work,silicon-carbon hybrid materials were adopted as an example to illustrate the novel strategy to in situ construct heterostructure with adjustable microstructure.Based on the temperature-dependent thermodynamics and kinetics of reaction between Si and C,the processes for Si nanocrystals growth and C decoration were coupled at different zones of plasma flame according to its temperature and velocity fields by theoretical modeling,aiming to intentionally suppress the formation of undesirable carbide,and enable adjusting the microstructure of each counterpart separately in transient process.As a result,well-controlled Si/C nanocomposites,including nanospheres and nanowires with core-shell structures,were achieved,and this continuous and in-flight route is also potential for large-scale production.Further investigation on the electrochemical properties highlights the advantage of as proposed strategy to efficiently construct heterostructures with superior performance for various applications.
基金supported by the National Natural Science Foundation of China(U22A20120,52071135,51871090,U1804135,and 52301269)the Natural Science Foundation of Hebei Province for Innovation Groups Program(C2022203003)Fundamental Research Funds for the Universities of Henan Province(NSFRF220201).
文摘Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH_(2).Herein,the sulfur doped Ti_(3)C_(2)(S-Ti_(3)C_(2))was successfully prepared by heat treatment of Ti_(3)C_(2)MXene under Ar/H_(2)S atmosphere to facilitate the hydrogen release and uptake from MgH_(2).The S-Ti_(3)C_(2)exhibited pleasant catalytic effect on the hydriding/dehydriding kinetics and cyclic stability of MgH_(2).The addition of 5 wt%S-Ti_(3)C_(2)into MgH_(2)resulted in a reduction of 114℃in the starting dehydriding temperature compared to pure MgH_(2).MgH_(2)+5 wt%S-Ti_(3)C_(2)sample could quickly release 6.6 wt%hydrogen in 17 min at 220℃,and 6.8 wt%H_(2)was absorbed in 25 min at 200℃.Cyclic testing revealed that MgH_(2)+5 wt%S-Ti_(3)C_(2)system achieved a reversible hydrogen capacity of 6.5 wt%.Characterization analysis demonstrated that Ti-species(Ti0,Ti^(2+),Ti-S,and Ti^(3+))as active species significantly lowered the dehydrogenation temperature and promoted the re-/dehydrogenation kinetics of MgH_(2),and sulfur doping can effectively improve the stability of Ti0 and Ti^(3+),contributing to the improvement of cyclic stability of MgH_(2).This study provides strategy for the construction of catalysts for hydrogen storage materials.
基金supported by the National Natural Science Foundation of China(No.52271089)the financial support from the C hina Postdoctoral Science Foundation(No.2023M732192)。
文摘This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.
基金National Key R&D Program of China,Grant/Award Number:2023YFB2503900National Natural Science Foundation of China,Grant/Award Number:12172143Shenzhen Science and Technology Program,Grant/Award Numbers:JCYJ20220818100418040,JCYJ20220530160816038。
文摘Constructing silicon(Si)-based composite electrodes that possess high energy density,long cycle life,and fast charging capability simultaneously is critical for the development of high performance lithium-ion batteries for mitigating range anxiety and slow charging issues in new energy vehicles.Herein,a thick silicon/carbon composite electrode with vertically aligned channels in the thickness direction(VC-SC)is constructed by employing a bubble formation method.Both experimental characterizations and theoretical simulations confirm that the obtained vertical channel structure can effectively address the problem of sluggish ion transport caused by high tortuosity in conventional thick electrodes,conspicuously enhance reaction kinetics,reduce polarization and side reactions,mitigate stress,increase the utilization of active materials,and promote cycling stability of the thick electrode.Consequently,when paired with LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)(NCM622),the VC-SC||NCM622 pouch type full cell(~6.0 mAh cm^(-2))exhibits significantly improved rate performance and capacity retention compared with the SC||NCM622 full cell with the conventional silicon/carbon composite electrode without channels(SC)as the anode.The assembled VC-SC||NCM622 pouch full cell with a high energy density of 490.3 Wh kg^(-1)also reveals a remarkable fast charging capability at a high current density of 2.0 mA cm^(-2),with a capacity retention of 72.0%after 500 cycles.
文摘Single-atom catalysts have been applied in many processes recently.The difference of their kinetic behavior compared to the traditional heterogeneous catalysts has not been extensively discussed yet.Herein a complete catalytic cycle of CH4 combustion assuming to be confined at isolated single sites of the Co3O4(110)surface is computationally compared with that on multi sites.The macroscopic kinetic behaviors of CH4 combustion on Co3O4(110)is systematically and quantitatively compared between those on the single site and multi sites utilizing kinetic Monte Carlo simulations upon the energetic information from the PBE+U calculation and statistic mechanics.The key factors governing the kinetics of CH4 combustion are disclosed for both the catalytic cycles respectively following the single-site and multi-site mechanisms.It is found that cooperation of multi active sites can promote the activity of complete CH4 combustions substantially in comparison to separated single-site catalyst whereas the confinement of active sites could regulate the selectivity of CH4 oxidation.The quantitative understanding of catalytic mechanism paves the way to improve the activity and selectivity for CH4 oxidation.
基金supported by National Natural Science Foundation of China(22178002,22178001)Natural Science Foundation of Anhui Province(2308085Y19)Excellent Youth Research Project of Anhui Provincial Department of Education(2022AH030045).
文摘Hydrogen-enriched ironmaking presents a promising approach to mitigate coke consumption and carbon emission in blast furnace(BF)operations.This work investigated the relationship between the structural features of cokes and their reactivity towards solution loss(SL),especially under hydrogen-enriched atmospheres.Six cokes were characterized,and their SL behaviors were examined under varying atmospheres to elucidate the effects of hydrogen enrichment.The results indicate that an increase in fixed carbon content leads to a decrease in the coke reactivity index(CRI)and an increase in coke strength after reaction(CSR),in the CO_(2) atmosphere,the CSR of coke increases from 35.76%−62.83%,while in the 90CO_(2)/10H_(2) atmosphere,the CSR of coke increases from 65.67%−84.09%.There is a good linear relationship between CRI and microcrystalline structure parameters of coke.Cokes with larger crystalline size,lower amorphous content,and smaller optical texture index(OTI)values show enhanced resistance to degradation and maintain structural integrity in BF.Kinetic analysis performed with the shifted-modified-random pore model(S-MRPM)reveals that alterations in pore structure and intrinsic mineral composition significantly influence the reaction rate.The introduction of a small amount of water vapor raises SL rates,whereas a minor addition of hydrogen(<10%)decelerates SL due to its incomplete conversion to water vapor and the reduced partial pressure of the gasifying agent.Thermodynamic calculations also indicate that the introduced hydrogen does not convert into the same fraction of water vapor.The shift from chemical reaction control to gas diffusion control as the rate-determining step with rising temperatures during SL process was confirmed,and the introduction of hydrogen does not notably alter SL behavior.This result demonstrated that introducing a small amount of hydrogen(<10%)can mitigate SL rates,thereby enhancing coke strength and reducing coke consumption and carbon emissions.
基金National Natural Science Foundation of China(52275328,51875157)。
文摘Hydrogen desorption kinetics and characteristics,residual hydrogen content and activation energy of TC21 alloy were investigated by the constant volume method.Results show that hydrogen desorption temperature and initial hydrogen pressure affect hydrogen desorption characteristics of TC21 alloy.The hydrogen desorption process is mainly dominated by nucleation and growth process(kt=[-ln(1-α)]^(2/3)),chemical reaction process(kt=(1-α)^(-1/2))and three-dimensional diffusion process(kt=[1-(1-α)^(1/3)]^(1/2))when the hydrogenated TC21 alloy is dehydrogenated at temperatures of 700-940°C.When the hydrogenated TC21 alloy releases hydrogen,the following relationship exists among the rate constants of each process:k(chemical reaction process)>k(nucleation and growth process)>k(three-dimensional diffusion process).The residual hydrogen content of the hydrogenated TC21 alloy after hydrogen desorption decreases gradually with the increase in hydrogen desorption temperature,and increases gradually with the increase in the initial hydrogen pressure.The activation energy of TC21 alloy in the process of hydrogen desorption is about 26.663 kJ/mol.
基金supported by the Natural Science Foundation Project of Liaoning province(Nos.2023-MS-017 and 2022-MS-005)the National Science and Technology Major Project(No.J2019-VI-0019-0134)+2 种基金the National Natural Science Foundation of China(Nos.52201028 and 52188101)the Project funded by China Postdoctoral Science Foundation(No.2021M700153)the Special Projects of the Central Government in Guidance of Local Science and Technology Development(No.2024010859-JH6/1006).
文摘Accurately determining the Flade potential(E_(Flade))is of significant importance in the design of novel corrosion-resisting alloys.However,due to the complex nature of the E_(Flade)influenced by several factors including compositions of the alloys and corrosive solutions,there is currently a lack of truly predictive ab initio model.Here,we established the critical potential condition required for passivation in acidic solutions containing chloride ions(Cl^(-))by developing an ab initio model that incorporates the potential drop from the metal electrode to the solution,considering tunneling of electrons at metal/film interface,breakdown of the film,and electrochemical adsorption reactions at film/solution interface.These parameters were derived from the work function of the alloy substrate and passivation film,the band gap of the passivation film,and the Gibbs free energy of adsorption on the passivation film,all of which can be obtainable from first-principles calculations.This theoretical model has been successfully validated for alloyed stainless steel,exhibiting a remarkable agreement with experimental results.Importantly,enabled by the model,we have identified several alloying elements(i.e.,Ta,W,Os,and Ir)that can effec-tively lower the EFlade of the stainless steel.This work constitutes an important step forward in modeling complex passivation behaviors from first-principles,providing a useful tool for the design of corrosion-resisting alloys.
基金Project supported by the National Natural Science Foundation of China(52364044,52204364)Scientific Research Special Project for First-Class Disciplines of Education Department of Inner Mongolia Autonomous Region(YLXKZX-NKD-001,YLXKZX-NKD-011)Basic Scientific Research Business Expenses of Colleges and Universities of Inner Mongolia Autonomous Region(2023QNJS011)。
文摘Based on first-principles calculation framework,the surface model,anodic dissolution,cathodic oxygen absorption reaction,and other related electrochemical corrosion models of Fe-Ce system were constructed,and the influencing mechanism Ce doping on the corrosion resistance of Fe-Ce system in the Cl medium environment was analyzed.The results show that Ce doping on the first surface and subsurface inhibits the ionization of Fe atoms and greatly promotes the repassivation process of Fe matrix.Ce doping on the first layer is conducive to preventing the detachment of surface Fe atoms from Fe matrix and delaying the occurrence of corrosion.Ce atoms in the subsurface effectively increase the difficulty of Fe atoms detaching from the matrix at high Cl concentrations.When O diffusion is the controlling link of oxygen absorption reaction,Ce doping has no effects on the reaction rate of cathodic oxygen absorption.Ce doping enhances the electrochemical stability of Fe(100)1and reduces the anodic dissolution rate of Fe matrix,thereby improving its corrosion resistance.
基金support from the National Natural Science Foundation of China(No.52374402)the National Key Research and Development Program(No.2022YFB3402200)+2 种基金the National Science and Technology Major Project(No.J2022-VII-0003-0045)the Project of Key areas of innovation team in Shaanxi Province(No.2024RS-CXTD-20)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX2024055).
文摘The vacuum reactive wetting and brazing of Er_(2)Si_(2)O_(7)/MoSi_(2) coatings were investigated using a (CoFeNiCrMn)_(88)Nb_(12) high-entropy alloy (HEA) brazing filler. The microstructural evolution and wettability of the HEA filler were analyzed, with particular attention to the surface energy, interfacial stability, and electronic properties of the HEA filler/rare earth silicate coating system, as determined by density functional theory (DFT). As Nb diffused into the interface and the ErNbO_(4) phase formed, the wetting angle gradually decreased to 23.12° The effective wetting and spreading of the HEA brazing filler on the rare earth silicate coating surface are strongly correlated with the formation of the ErNbO_(4) phase at the interface. Furthermore, DFT calculations reveal that the interfacial bonding energy between the BCC' and FCC' phases and the ErNbO_(4) phase, after the wetting reaction, is significantly higher than the bonding energy between the initial filler and Er_(2)Si_(2)O_(7). This finding suggests that the formation of the ErNbO_(4) phase improves the wetting and spreading behavior of the filler.
基金supported by the National Natural Science Foundation of China(No.22373084,No.62201494)Hebei Natural Science Foundation(B2022203007)the Cultivation Project for Basic Research and Innovation of Yanshan University(2024LGZD002).
文摘The adsorption properties of a magnesium porphyrin(MgP)molecule on Au(111)surface covered with up to three lay-ers of sodium chloride(NaCl)were investigated by means of first-principles calculations.The most stable adsorption configuration of MgP on the NaCl/Au(111)heterosurfaces was found to be at the Cl-top site with a 20°angle between the[110]lattice direction of NaCl and the Mg–N bond of the molecule.Compared with MgP molecule adsorbed on bare Au(111),the inclusion of NaCl lay-ers can lead to a significant decrease in the adsorption energy of the MgP molecule.The exis-tence of NaCl layers also reduced the charge transfer between the molecule and the surface.For heterosurfaces with two or three monolayers of NaCl,the charge transfer was almost com-pletely suppressed.The obtained partial density of states(PDOS)showed that hybridization between the electronic structures of the adsorbed MgP molecule and the metal surface can be significantly suppressed when NaCl layers were added.For the heterosurface with three lay-ers of NaCl,the PDOS around the Fermi level was almost identical with that of the free molecule,suggesting the electronic structure of the MgP molecule was nicely preserved.Influ-ence of the NaCl layers on the electronic structure of the MgP molecule was mainly found for molecular orbitals(MOs)away from the Fermi level as a result of the large band gap of the NaCl layers.
基金supported by the National Natural Science Foun-dation of China(Grant Nos.12393831 and 12088101).
文摘Control of hyperfine interaction strength of shallow donors in Si is one of the central issues in realizing Kane quantum computers.First-principles calculations on the hyperfine Stark shift of shallow donors are challenging since large supercells are needed to accommodate the delocalized donor wave functions.In this work,we investigated the hyperfine Stark shift and its strain tunability for shallow donors P and As in Si using the potential patching method based on first-principles density functional theory calculations.The good agreement between our calculations and experimental results confirms that the potential patching method is a feasible and accurate first-principles approach for studying wave-function-related properties of shallow impurities,such as the Stark shift parameter.It is further shown that the application of strain expands the range of hyperfine Stark shift and helps improve the response of shallow donor based qubit gates.The results could be useful for developing quantum computing architectures based on shallow donors in Si.
基金supported by the National Natural Science Foundation of China(Nos.52271172,and 51971085).
文摘Ni-Mn-Ti Heusler alloys have great potential for elastocaloric refrigeration due to the colossal caloric effect and good mechanical properties. However, theoretical calculations on the characterization of the elastocaloric effect are rare. An important parameter to evaluate the elastocaloric effect is the transformation entropy change, whose main source is the vibrational entropy change (ΔS_(vib)). Unfortunately, the widely used quasiharmonic approximation method fails in the prediction of the vibrational entropy for high-temperature austenite due to its dynamical instability at 0 K. To solve this problem, the temperature dependent effective potential method was used considering the temperature and anharmonic effect. Sc, V, and Zr doping at the Ti sites in B2 disordered Ni_(8)Mn_(5)Ti_(3) were studied about phase stability, martensitic transformation, and elastocaloric properties. The results revealed the austenitic structures of all the doping systems exhibit antiferromagnetic coupling characteristics at 300 K due to the temperature effect. Sc and Zr doping at the Ti sites decreased the ΔS_(vib) value, whereas V doping at the Ti site increased the ΔS_(vib) value. Further analysis proved the important evaluation criterion that the ΔS_(vib) value increases with the tetragonal distortion ratio and volume change, which has important guiding significance for improving the elastocaloric effect. Besides, the calculations of elastic constants presented all the doping systems maintain outstanding ductility evaluated from the B/G ratio. This work provides an effective strategy for designing excellent elastocaloric material with large vibrational entropy change and good mechanical properties.
基金supported by the National Natural Science Foundation of China(Nos.52222409 and U24A20104)the National Key Research and Development Program(No.2024YFB3408900)+1 种基金Partial financial support came from the Fundamental Research Funds for the Central Universities,JLUsupported by the High Performance Computing Center of Jilin University,China.
文摘Solute segregation at grain boundaries(GBs)can significantly influence GB cohesion.In this work,the segregation energies of solutes(Zn,Al,Ag,Ca,and Gd)were first investigated at six symmetrical tilt GBs rotating around[0001]axis of Mg,to uncover the impact of GB characteristics on solute segregation behavior.The results reveal that solute segregation propensity is closely related to the local geometric environment of GB sites,but has little correlation with intrinsic GB properties(such as GB misorientation and GB energy).Furthermore,relationships between GB site characteristics and solute segregation tendencies were established.Ca-like solutes tend to occupy GB sites with larger Voronoi volumes(V),while Zn-like solutes prefer GB sites with smaller V as well as smaller shortest bond lengths(SBL).Based on this finding,we further evaluated the segregation capacities of 26 solutes at their most energetically stable segregation sites and their impact on GB cohesion.A descriptor that can effectively capture the strengthening/embrittling potency of segregated solutes on GBs was proposed by performing the crystal orbital Hamilton population(COHP)analyses.It was found that the discrepancies in bond strength between GBs and free surface dominate the solute-strengthening behavior.Finally,a first-principles“design map”regarding the segregation energies and strengthening energies was provided,which offers a database for designing Mg alloys with high fracture toughness.
