查看更多>>摘要：The insensitivity of semiconductors to visible and infrared light is a key constraint on the utilization of light energy in photocatalytic reactions.Constructing photocatalysts with full-spectrum absorption through surface engineering is an effective approach to fully harnessing light energy in semiconductor materials.Herein,a novel stable Ti3C2Tx MXene/CdS heterojunction catalyst is obtained by in-situ epitax-ial growth of two-dimensional(2D)CdS nanosheets on 2D MXene interface via a solvothermal method.The exceptional light absorption properties of MXene confer outstanding full-spectrum driven photocat-alytic hydrogen evolution capability upon the heterogeneous catalyst.The unique 2D/2D structure effec-tively mitigated the recombination of photogenerated carriers,enhancing the photocatalytic performance of the catalyst.Moreover,the composite catalyst exhibits a significantly higher surface temperature of 80.4 ℃ under visible light irradiation at an intensity of 0.1 W/cm2,which is 1.84 times higher than that of CdS.Under irradiation of visible and near infrared light,the composite catalyst with photothermal ef-fect demonstrates a remarkable hydrogen evolution rate of 65.4 mmol g-1 h-1,which is 7.2 times higher than that of CdS catalyst.This study introduces a novel approach for constructing full-spectrum absorp-tion catalysts and expands the application of the photothermal effect in photocatalytic hydrogen evolution research.
查看更多>>摘要：The all-optical wavelength conversion using cascaded four-wave mixing(FWM)phenomena with graphene oxide(GO)and a highly nonlinear fiber(HNLF)device is demonstrated experimentally.GO has a strong third-order nonlinear effect and is an excellent nonlinear optical material for nonlinear optical wavelength conversion.The group velocity matching of pump and signal,HNLF,and GO amplification promote the cascaded nonlinear frequency mixing process.From the experimental and analytical results,the maximum spacing between signal and pump is 21 nm,and specifically,the order of cascaded FWM light increases from order 1 to order 2 with increasing GO,and the first-order FWM conversion effi-ciency increases to a maximum of-14.5 dB.To the best of our knowledge,this is the first time that cascaded FWM-based all-optical wavelength conversion in HNLF-GO with wide wavelength selectivity is investigated with combined pump and signal light.Our findings not only provide an effective method for achieving all-optical wavelength conversion in cascaded FWM but also offer the possibility of fabricating high-performance nonlinear optical devices.
查看更多>>摘要：Carbon nanofibers(CNFs)with high specific surface area show great potential for sodium storage as a hard carbon material.Herein,CNFs anchored with Ni nanoparticles(CNFs/Ni)were prepared through chemical vapor deposition and impregnation reduction methods,in situ growing on the three-dimensional porous copper current collector(3DP-Cu).The coupling effect of high-spin state Ni nanopar-ticles leads to the increase of defect density and the expansion of lattice spacing of CNFs.Meanwhile,the 3DP-Cu ensures a high loading capacity of CNFs and short ion/electron transport channels.As an integral binder-free anode,the 3DP-Cu/CNFs/Ni exhibits excellent electrochemical performance,which demon-strates a high specific capacity with 298.5 mAh g-1 at 1000 mA g-1 after 1500 cycles,and a high power density with 200 mAh g-1 over 1000 cycles at 5000 mA g-1.Density functional theory calculation re-sults show that the high-spin state Ni regulates the electronic structure of CNFs,which significantly re-duces the adsorption energy for Na+(-2.7 Ev)and thus enables high-rate capability.The regulation of the electronic structure of carbon materials by high-spin state metal provides a new strategy for developing high-power carbonaceous anode materials for sodium-ion batteries.
查看更多>>摘要：Heat treatment plays an important role in tailoring the mechanical properties of powder-metallurgy(PM)titanium alloys.However,only limited work about the rapid heat treatment(RHT)of PM titanium alloys has been reported.In this work,RHT was applied to PM Ti-5Al-5Mo-5V-1Cr-1Fe alloy after hot rolling to study the evolution of its mechanical properties and the influence of residual pores on its properties.Through hot rolling and annealing,a fine and uniform α+β structure with few residual pores is ob-tained.During RHT,the primary α dissolves gradually and completes in the β region,and the β grains then grow,resulting in the continuous decrease in elongation after aging.Moreover,the tensile strength first increases and then decreases with increasing RHT temperature,owing to the increase in volume fraction of secondary α in α+β region and the β grain growth in β region.In contrast to the RHT of cast-and-wrought titanium,the negative influence of residual pores lowers the RHT temperature for obtaining the highest tensile strength to a temperature below the β-transus temperature.Despite the negative influence of the residual pores,retained primary α and fine β grains with fine secondary αinside contribute to achieving a good strength/ductility balance(1570 MPa and 6.1％,respectively).Addi-tionally,although at higher cycles to failure,the negative influence of residual pores increases as it affects the crack initiation zone at the subsurface,the good resistance of secondary α to fatigue crack propaga-tion still enhances the fatigue strength considerably(about 300 MPa).This work suggests a cost-effective strategy to produce titanium alloys with high performance.
查看更多>>摘要：The practical applications of lithium-sulfur(Li-S)batteries are hampered by the sluggish redox kinetics and polysulfides shuttle in the cyclic process,which leads to a series of problems including the loss of active materials and poor cycling efficiency.In this paper,the pore structures of carbon nanosheets based electrocatalysts were precisely controlled by regulating the content of water-soluble KCl template.The relationship between pore structures and Li-S electrochemical behavior was studied,which demonstrates a key influence of pore structure in polysulfides phase conversions.In the liquid-sloid redox reaction of polysulfides,the micropores and small mesopores(d＜20 nm)exhibited little impact,while the meso-pores(d＞20 nm)and macropores played a decisive role.As a typical exhibition,the nickel-embedded carbon nanosheets(Ni-CNS)with a high content of large mesopores and macropores can aid Li-S batteries in exhibiting stable cycling performance(760.1 mAh g-1 at 1 C after 300 cycles)and superior rate capac-ity(847.8 mAh g-1 at 2 C).Furthermore,even with high sulfur loading(8 mg cm-2)and low electrolyte(E/S is around 6 μL mg-1),the high area capacity of 7.7 mAh cm-2 at 0.05 C could be achieved.This work can provide a guideline for the design of the pore structure of carbon-based electrocatalysts toward high-efficiency sulfur species redox reactions,and afford a general,controllable,and simple approach to constructing high performance Li-S batteries.
查看更多>>摘要：Increasing the utilization efficiency of photogenerated electrons is highly recognized as one of the ef-ficient approaches to boost the photocatalytic CO2 conversion efficiency.Herein,ZIF-67-derived porous carbon(PC)material was employed for the construction of PC@ultrafine Bi12O17Br2 nanotubes(PC@BOB NTs)composites through a facile solvothermal synthesis in order to optimize the use of excited elec-trons in the BOB NTs.Photoelectrochemical characterization results revealed that the introduction of PC material achieved a faster charge separation rate in the PC@BOB composites,ensuring more photogener-ated electrons participate in the CO2 adsorption and activation process.Moreover,the pore structures of ZIF-67-derived PC material provided abundant confined spaces for the enrichment of CO2 molecules.Af-ter 5 h of Xenon lamp irradiation,PC@BOB composites exhibited obviously increased photocatalytic CO2 reduction activity in the pure water.When the addition amount of PC was 5 wt％,the PC@BOB-2 com-posite showed the highest CO evolution rate of 359.70 μmol/g,which was 2.95 times higher than that of the pure BOB NTs.This work provides some independent insights into the applications of Metal-Organic Framework(MOF)-derived hierarchical porous structures to strengthen the CO2 enrichment,as well as the excited charge utilization efficiency,thus achieving a high solar-to-fuel conversion efficiency.
查看更多>>摘要：The microstructure and microsegregation of atomized powder,which depend on their sizes,are of great importance to the mechanical properties of the consolidated bulk materials.Therefore,it is necessary to reveal the relationship between particle size and powder attributes.The effects of particle size on the so-lidification characterization of the atomized Ni-based superalloy powders were studied via finite element simulation.Based on the simulations,a model was developed to predict the microsegregation and mi-crostructure of atomized powders with different sizes and study the influence of thermal history on the powder attributes during the atomization processes.The radiation heat transfer and temperature gradi-ent within the rapid solidification alloy powders were taken into account in this model.For validating the accuracy of the model,the predictions of the present model were compared with the microsegregation and microstructure of the specific size powder close to the screen mesh size.The results showed that mi-crostructure depended primarily on the temperature gradient within the powder,while the solidification rate had a more significant effect on the microsegregation.The model predicted microstructure features in agreement with the experiment,and for microsegregation,the deviations of prediction for most ele-ments were less than 10％.This work provides a new model to precisely predict the microsegregation and microstructure of the atomized alloy powders and sets a foundation to control the powder features for various engineering applications.
查看更多>>摘要：Recently,Lee et al.claimed the experimental discovery of room-temperature ambient-pressure super-conductivity in a Cu-doped lead-apatite(LK-99)(arXiv:2307.12008,arXiv:2307.12037).Remarkably,the claimed superconductivity can persist up to 400 K at ambient pressure.Despite the experimental im-plication,the electronic structure of LK-99 has not yet been studied.Here,we investigate the electronic structures of LK-99 and its parent compound using first-principles calculations,aiming to elucidate the doping effects of Cu.Our results reveal that the parent compound Pb10(PO4)6O is an insulator,while Cu doping induces an insulator-metal transition and thus volume contraction.The band structures of LK-99 around the Fermi level are featured by a half-filled flat band and a fully-occupied flat band.These two very flat bands arise from both the 2p orbitals of 1/4-occupied O atoms and the hybridization of the 3d orbitals of Cu with the 2p orbitals of its nearest-neighboring O atoms.Interestingly,we observe four van Hove singularities on these two flat bands.Furthermore,we show that the flat band structures can be tuned by including electronic correlation effects or by doping different elements.We find that among the considered doping elements(Ni,Cu,Zn,Ag,and Au),both Ni and Zn doping result in the gap opening,whereas Au exhibits doping effects more similar to Cu than Ag.Our work establishes a foundation for fu-ture studies to investigate the role of unique electronic structures of LK-99 in its claimed superconducting properties.
查看更多>>摘要：The commercial viability of thermoelectric(TE)devices relies heavily on two factors:cost reduction and efficiency enhancement.In this study,we first produce p-type Cu12Sb4S16-x(x=0,3,4)using a low-temperature bottom-up approach and demonstrate Cu12Sb4S13 to show the best TE performance among the three tested compositions.Subsequently,the TE energy conversion efficiency of Cu12Sb4S13 is further enhanced by optimizing its electronic band structure through the incorporation of small amounts of tel-lurium.At an optimal Te content of 5 mol％,more than a twofold increase in the TE figure of merit(zT)is obtained.To gain insight into the mechanism of improvement on the transport properties of the mate-rial,we compare the interphase transport mechanism by incorporating nanodomains of different metals(Ag and Cu)into the Cu12Sb4S13 matrix.The improved electrical conductivity obtained with Cu12Sb4S13-Te nanocomposites is attributed to a charge flooding of the Cu12Sb4S13 surface.In contrast,excessive down-ward band-bending at the interphases of Ag/Cu metal-semiconductor drastically reduces the electrical conductivity.Besides,a weighted mobility(μw)analysis shows a dominant thermal activation of carri-ers in Cu12Sb4S13-Te nanocomposites.In this material,a strong decrease in lattice thermal conductivity is also found,which is associated with a phonon-carrier scattering mechanism.Our work shows the impor-tance of proper band-engineering in TE nanocomposites to decouple electrical and thermal transport to enhance TE performance,and the efficacy of μw for electrical and thermal transport analysis.
查看更多>>摘要：Ni47Ti44Nb9 shape memory alloy(SMA)is a promising material in the aerospace field due to its wide transformation hysteresis.The application of shape memory effect depends on multistep thermomechan-ical loading,viz.,low-temperature deformation and subsequent heating to recovery.Low-temperature deformation prestrain plays a pivotal role in shape memory properties tailoring of SMA components.However,microstructure evolution and deformation mechanisms of Ni47Ti44Nb9 SMA subjected to vari-ous prestrain levels are still unclear.To this end,microstructure evolution and shape memory behaviors of Ni47Ti44Nb9 alloy subjected to multistep thermomechanical loading with prestrain levels of 8％-16％at-28 ℃(Ms+30 ℃)were investigated.The results demonstrate that the stress-strain curve of the specimen exhibits four distinct stages at a maximal prestrain of 16％.Whereas stage Ⅱ and stage Ⅲ end at prestrains of～8％and～12％,respectively.In stage Ⅱ,the stress-induced martensitic transformation is accompanied by the dislocation slip of the NiTi matrix and β-Nb inclusions.In stage Ⅲ,in addition to the higher density of dislocations and further growth of stress-induced martensite variants(SIMVs),(00 1)compound twins are introduced as a result of the(0 0 1)deformation twinning in stress-induced martensite.More{2 0-1｝ martensite twins are gradually introduced in stage Ⅳ.Correspondingly,after subsequent unloading and heating,a higher density of {1 1 4｝ austenite twins form in the specimen with a larger prestrain of 16％.With increasing prestrain from 8％to 16％,the recoverable strainεreT upon heating increases first and then decreases.The εreT obtains a maximum of 7.03％at 10％prestrain and de-creases to 6.17％at 16％prestrain.The increase of εreT can be attributed to the formation of new SIMVs,the further growth of existing SIMVs,and the recoverable(0 0 1)compound twins.While the decrease of εreT is mainly associated with the irrecoverable strain by ｛2 0-1｝ martensite twins.The effect of β-Nb inclusions on the evolution of SIMVs is also found herein that deformed β-Nb inclusions can significantly hinder the growth and recoverability of adjacent stress-induced martensite.
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