查看更多>>摘要：High-entropy alloys(HEAs)have attracted extensive attention ascribed to their unique physical and chemical properties induced by the cocktail effect.However,their oxidation behaviors,in particular at nanoscale,are still lack because of multi-element complexity,which could also be completely differ-ent from the bulk counterparts.In this work,we synthesized FeCoNiTiCu five-element HEA nanopar-ticles(NPs)with uniform elemental distribution by arc-discharging approach,and further investigated their oxidation behaviors at 250 ℃,and 350 ℃.The morphology,structure and element distribution of NPs were analyzed by transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS)and electron energy loss spectroscopy(EELS).The surface oxidation in FeCoNiTiCu NPs during the high-temperature process can induce nanoscale pores at core/shell interfaces by Kirkendall effect,and even the eventual coalescence into a single cavity.Additionally,the oxidation states of NPs with diameters(d)varying from 60 to 350 nm were analyzed in detail,revealing two typical configurations:hollow(d＜150 nm)and yolk-shell structures(d＞150 nm).The experimental results were complemented by first-principles calculations to investigate the diffusion behaviors of five elements,evidencing that the surface oxidation strongly alters the surface segregation preferences:(1)in the initial stage,Cu and Ni appear to prefer segregating on the surface,while Co,Ti and Fe tend to stay in the bulk;(2)in the oxidation process,Cu prefers to stay in the center,while Ti segregates to the surface ascribed to the reduced po-tential energies.The study gives new insights into oxidation of nanoscale HEA,and also provides a way for fabrication of high-entropy oxides with controllable architectures.
查看更多>>摘要：Photocatalysis is a green and environmentally-friendly process that utilizes the ubiquitous intermittent sunlight.To date,an emerging S-scheme heterojunction across the intimately coupled heterojunction materials is proposed to surpass the efficiency of conventional Ⅱ-type and Z-type photocatalysis.Further-more,S-scheme heterojunction photocatalysts with greatly improved photocatalytic performance have gained significant attention due to their fast charge carriers separation along with strong redox ability and stability,since its proposal in 2019.Herein,a timely and comprehensive review is highly desired to cover the state-of-the-art advances.Driven by this idea,the review conveys the recent progress and provides new insights into further developments.Unlike the conventional method,in this review,we im-plement a quantification model to outline current trends in S-scheme heterojunctions research as well as their correlations.The overview begins with the fundamentals of four basic photocatalytic mechanisms,followed by its design principles.Afterward,diverse characterization techniques used in the S-scheme heterojunctions are systematically summarized along with the modification strategies to boost photocat-alytic performances.Additionally,the internal reaction mechanism and emerging applications have been reviewed,including water conversion,CO2 remediation,wastewater treatment,H202 production,N2 fix-ation,etc.To sum up the review,we present several current challenges and future prospects of the S-scheme heterojunctions photocatalysts,aiming to provide indispensable platforms for the future smart design of photocatalysts.
查看更多>>摘要：Magnetic metal absorbers exhibit remarkable microwave absorption capacity.However,their practical application is severely limited due to their susceptibility to corrosion,particularly in marine environ-ments.To address this challenge,we propose a novel approach involving the modification and control of FeCo/rGO microwave absorbers using rare earth lanthanum(La).This strategy aims to achieve both high-performance microwave absorption and enhanced resistance to marine corrosion.In this study,we employ a La2O3 modifying control strategy to refine the FeCo magnetic particles and coat them with CoFe2O4 on the surface,leveraging the pinning effect of in situ generated La2O3.This process enhances the interface polarization of the absorbers,thereby improving their electromagnetic performance and ma-rine corrosion resistance.Consequently,the La2O3 modified FeCo@rGO composites exhibit broadband ab-sorption,covering a wide frequency range of 6.11 GHz at 1.55 mm.Notably,the electromagnetic proper-ties of the La2O3 modified FeCo@rGO absorbers remain stable even after prolonged exposure to a 3.5 wt％NaCI solution,simulating marine conditions,for at least 15 days.Furthermore,we perform first-principle calculations on FeCo and FeCo-O to validate the corrosion resistance of the La2O3 modified FeCo@rGO composites at the atomic level.This comprehensive investigation explores the control of rare earth lan-thanum modification on the size of magnetic metal particles,enabling efficient electromagnetic wave absorption and marine corrosion resistance.The results of this study provide a novel and facile strategy for the control of microwave absorbers,offering promising prospects for future research and development in this field.
查看更多>>摘要：The poor wear and corrosion resistance of aluminum alloys has led to the easy failure of surface perfor-mance.In this work,composite coatings of TiC/martensitic stainless steel(TiC/MSS)on aluminum alloy are fabricated by a novel approach of circular oscillating laser for enhanced surface performance of alu-minum alloys.The oscillation of laser leads to dense microstructure,and nano/micro scale TiC particles are formed simultaneously.The structure of coatings transforms from dendritic to ring-like with the ad-dition of TiC,and the hardness of the substrate is increased by 4.5-7.8 times.The main wear form of coatings is adhesive wear.The refinement of microstructure and formation of multi-scale TiC have given rise to an increase in the resistance of the coating to plastic deformation,which reduces the degree of adhesion and improves wear resistance.Besides,the barrier effect of TiC particles to the electrolyte solu-tion in the passive film gives rise to the drop in corrosion current density.The Cr-rich stacking faults can provide nucleation sites for the formation and growth of passive films with high continuity and stability,thereby improving the corrosion resistance of the coatings.The superior anticorrosion and wear resis-tance properties of the composite coatings in this work have emphasized the merits of oscillating laser in fabricating high-performance coatings and would enlighten the design of more advanced composite coatings.
查看更多>>摘要：Herein,we focused on the development of the V4C3 MXene composite bimetallic selenide heterostruc-ture(V4C3@CuSe2/CoSe2)as a cathode material for aluminum batteries.This heterostructure was pre-pared through a Lewis melt salt etching and selenization process.By capitalizing on the synergistic effect between the bimetallic selenide and V4C3 MXene,V4C3@CuSe2/CoSe2 exhibited rapid charge transfer and demonstrated superior discharge specific capacity compared to V4C3 composite monometallic selenide.Furthermore,the incorporation of V4C3 improved the material's stability during charging/discharging.The initial discharge specific capacity of V4C3@CuSe2/CoSe2 reached an impressive 809 mAh g-1 at 1 Ag-1.Even after nearly 3000 cycles,it retained a substantial capacity of 169.1 mAh g-1.Ex-situ XPS analysis confirmed the reversible valence transitions of Cu,Co,and Se elements as the main energy storage reac-tions taking place in the cathode material.Density functional theory analysis provided further insights,revealing that the strong metallic behavior of the heterostructure stemmed from the charge rearrange-ment facilitated by the bimetallic selenide structure and the optimization of the energy level structure.Additionally,the presence of the bimetallic selenide structure significantly improved the adsorption ef-ficiency of[AlCl4]-.Overall,this research contributes to the advancement of rechargeable aluminum ion batteries and presents a promising avenue for future developments in composite metal selenide struc-tures and MXene-based materials.
查看更多>>摘要：Strain engineering of two-dimensional(2D)material interfaces represents a powerful strategy for enhanc-ing the electrocatalytic activity of water splitting.However,maintaining catalytic stability under various harsh conditions by introducing interface strain remains a great challenge.The catalyst developed and evaluated herein comprised Ir clusters dispersed on 2D NiO nanosheets(NSs)derived from metal organic frameworks(lr@NiO/CBDc),which displays a high activity and stability under all pH conditions,and even a change of only 1％in the applied voltage is observed after continuous electrocatalytic operation for over 1800 h under alkaline conditions.Through combined experimental and computational studies,we found that the introduced interfacial strain contributes to the outstanding structural stability of the Ir@NiO/CBDC catalyst,arising from its increased Ir and Ni vacancy formation energies,and hence suppressing its leach-ing.Moreover,strain also enhances the kinetically sluggish electrocatalytic water splitting reaction by op-timizing its electronic structure and coordination environment.This work highlights the effects of strain on catalyst stability and provides new insights for designing widely applicable electrocatalysts.
查看更多>>摘要：Carbon hollow microspheres as microwave absorption materials(MAMs)are of great significance in the research focuses owing to their lightweight,good impedance matching,and modifiable dielectric proper-ties.However,it is still a huge challenge to distinguish the contribution of dielectric attenuation between carbon intrinsic feature and hollow structure due to the lack of appropriate model materials.Then,the inadequate analysis of effective dielectric attenuation resulted in the construction of carbon hollow mi-crospheres semiempirical and often lacked precise modification of microstructure.Herein,a series of car-bon hollow microspheres with controllable graphitization and thickness of shell derived from phenolic resin coated on polystyrene microspheres that fully decomposed were synthesized,which is free of the impact of template residue.The carbon fragments ground from hollow microspheres exhibit the same broadband response as hollow microspheres,with effective bandwidth(RL＜-10 dB)of 7.6 GHz,while their electromagnetic wave loss mechanisms are distinct.The high dielectric loss of carbon fragments with the same intrinsic characteristics as carbon hollow microspheres is mainly caused by dipole po-larization relaxation and enhancement of electrical conductivity ascribed to overlapping between carbon sheets.For the hollow structure,in addition to dipole polarization relaxation attributed to carbon intrin-sic feature,the effective dielectric loss is also comprised of the interfacial polarization in advantage due to the effective heterogeneous interface between air and carbon shell.This work provides a simplified model to clarify the effect of carbon intrinsic feature and microstructure on the dielectric loss of carbon hollow microspheres.
查看更多>>摘要：As-hot-rolled medium-entropy alloys(MEAs)with unevenly distributed grain sizes of face-centered cubic grains exhibit better yield strength without uniform elongation loss compared to cold-rolled and an-nealed ones.Successive operation of dynamic recrystallization(DRX)during several hot rolling passes leads to a wide range of grain sizes from submicrons to tens of micrometers due to the grain growth after nucleation:early recrystallized grains are coarser than recently recrystallized ones.Not only the grain size but internal dislocation density of the recently recrystallized grain is low.During the tensile deformation of the hot-rolled MEAs at-196 ℃,dislocation pile-ups in the relatively soft and fine DRX grains enhance yield stress and hetero-deformation-induced strain hardening.Thanks to the enhanced yield stress of the as-hot-rolled MEAs,stress-induced martensitic transformation easily occurs.Notably,partially DRXed MEAs hot-rolled at 800 ℃ have lower yield stress than fully DRXed ones,hot-rolled at 900 and 1000 ℃.This is attributed to the softening effect of the stress-induced body-centered cubic martensitic transformation in unrecrystallized coarse grains prior to the yielding,which lowers the yield stress of the partially DRXed ones.After yielding,the martensitic transformation facilitates strain hard-ening and early necking is precluded.This study presents a fresh outlook on the uneven distribution of grain sizes by hot rolling beneficial to mechanical responses of uniform elongation of～45％despite the as-rolled states with an advantage of simplified thermo-mechanical processes.
查看更多>>摘要：This study aimed to investigate the erosion behavior and mechanism of a newly developed 25Cr3Mo2WNiV steel with a chrome coating using promoted ignition combustion tests.The erosion threshold pressure and temperature of the chrome-coated 25Cr3Mo2WNiV steel were determined to be 0.2 MPa and 254.3 K higher than those of traditional chrome-coated 30SiMn2MoV steel.Furthermore,Kirkendall voids and inter-diffusion between the Cr coating and matrix were first observed before ero-sion.The improved erosion resistance of the chrome-coated 25Cr3Mo2WNiV steel was attributed to the suppression of the Kirkendall effect,which minimized heat generation at the Cr/matrix interface by pre-venting oxygen diffusion and reducing oxygen affinity.
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