Superior catalyst supports are crucial to developing advanced electrocatalysts toward heterogeneous catalytic reactions.Herein,we systematically investigate the role of transition metal‐functionalized N‐doped carbon...Superior catalyst supports are crucial to developing advanced electrocatalysts toward heterogeneous catalytic reactions.Herein,we systematically investigate the role of transition metal‐functionalized N‐doped carbon nanosheets(M‐N‐C,M=Mn,Fe,Co,Ni,Cu,Mo,and Ag)as the multifunctional electrocatalyst supports toward hydrogen evolution/oxidation reactions(HER/HOR)in alkaline media.The results demonstrate that all the M‐N‐C nanosheets,except Cu‐N‐C and Ag‐N‐C,can promote the alkaline HER/HOR electrocatalytic activity of Pt by accelerating the sluggish Volmer step,among which Mn plays a more significant role.Analyses reveal that the promotion effect of M‐N‐C support is closely associated with the electronegativity of the metal dopants and the relative filling degree of their d‐orbitals.For one,the metal dopant in M‐N‐C with smaller electronegativity would provide more electrons to oxygen and hence tune the electronic structure of Pt via the M‐O‐Pt bonds at the interface.For another,the transition metal in M‐N4 moieties with more empty d orbitals would hybridize with O 2p orbitals more strongly that promotes the adsorption of water/hydroxyl species.The results demonstrate the conceptual significance of multifunctional supports and would inspire the future development of advanced electrocatalysts.展开更多
THz time-domain spectroscopy(THz-TDS)is used to study the THz-optical properties of a single crystal bismuth ferrite BiFeO3(BFO).It can be found that the anisotropy of BiFeO3 is strongly dependent on the temperature.A...THz time-domain spectroscopy(THz-TDS)is used to study the THz-optical properties of a single crystal bismuth ferrite BiFeO3(BFO).It can be found that the anisotropy of BiFeO3 is strongly dependent on the temperature.A giant birefringence up to around 3.6 is observed at 1 THz.The presence of a spatially modulated cycloidal antiferromagnetic structure leads to spin cycloid resonances(SCR)ψandΦ,corresponding to the out-of-plane and in-plane modes of the spin cycloid,respectively.We distinguish the SCR with respect to their response to orthogonal polarizations of the electric fields of the incident THz beam.In addition,we observe a resonance appearing below 140 K,which might be interpreted as an electromagnon mode and related to a spin reorientation transition.Our present observations present that the temperature and polarization,as the external control parameters,can be used to modulate the THz optical properties of BFO single crystal.展开更多
The rapidly advancing energy storage performance of dielectric ceramics capacitors has garnered significant interest for applications in fast charge/discharge and high-power electronic techniques.Exploring the excepti...The rapidly advancing energy storage performance of dielectric ceramics capacitors has garnered significant interest for applications in fast charge/discharge and high-power electronic techniques.Exploring the exceptional electrical properties in harsh environments can further promote their practical applications.Defect carriers can be excited under luminance irradiation,thereby leading to degradation of energy storage performance.Herein,a synergic optimization strategy is proposed to enhance energy storage properties and luminance resistance of(K_(0.5)Na_(0.5))NbO_(3)-base(KNN)ceramics.First,the introduction of Bi(Zn0.5Ti0.5)O_(3) solid solution and La3+ions disrupts the long-range polar orders and enhances super paraelectric relaxation characteristics.Additionally,doping La3+ions can increase the band gap and reduce oxygen vacancy concentration,resulting in excellent luminance resistance.Finally,the viscous polymer process is employed to suppress the grain growth and promote chemical homogeneity.As a result,ultrahigh recoverable energy storage density(Wrec)of 8.11 J/cm3 and high efficiency(η)of 80.98%are achieved under an electric field of 568 kV/cm.Moreover,the variations in Wrec andηare only 12.45%and 1.75%,respectively,under 500 W xenon lamp irradiation compared to the performance under a dark environment.These findings hold great potential in facilitating the practical application of dielectric ceramic capacitors in luminance irradiation environments.展开更多
As an essential energy-stored device,the inorganic dielectric film capacitor plays an irreplaceable role in high-energy pulse power technology area.In this work,propelled by the challenge of overcoming the bottlenecks...As an essential energy-stored device,the inorganic dielectric film capacitor plays an irreplaceable role in high-energy pulse power technology area.In this work,propelled by the challenge of overcoming the bottlenecks of inflexibility and inferior energy storage density of the pure BiFeO3 films,the mica with high bendability and thermal stability is adopted as substrate,and the relaxor ferroelectric(Sr_(0.7)Bi_(0.2))TiO_(3) is introduced to form solid solution to introduce relaxor behavior.The subsequently fabricated 0.3Bi(Fe_(0.95)Mn_(0.05))O_(3)-0.7(Sr_(0.7)Bi_(0.2))TiO_(3)(BFMO-SBT)thin film capacitor exhibits a high recoverable energy storage density(W_(rec)=61 J cm^(-3))and a high efficiency(η=75%)combined with a fast discharging rate(23.5 μs)due to the large polarization difference(ΔP=59.4 μC cm^(-2)),high breakdown strength(E_(b)=3000 kV cm^(-1)),and the strong relaxor dispersion(γ=1.78).Of particular importance is the capacitor presents excellent stability of energy storage performance,including a wide working temperature window of -50-200℃,fatigue endurance of 108 cycles,and frequency range of 500 Hz-20 kHz.Furthermore,there are no obviously deteriorations on energy storage capability under various bending states and after 104 times of mechanical bending cycles.All these results indicate that BFMO-SBT on mica film capacitor has potential application in the future flexible electronics.展开更多
The oxygen evolution reaction(OER)with its intractably high overpotentials is the rate-limiting step in many devices,including rechargeable metal-air batteries,water electrolysis systems and solar fuel devices.Corresp...The oxygen evolution reaction(OER)with its intractably high overpotentials is the rate-limiting step in many devices,including rechargeable metal-air batteries,water electrolysis systems and solar fuel devices.Correspondingly,spin state transitions from spin singlet OH^(-)/H_(2)O reactants to spin triplet O_(2)product have not yet received enough attention.In view of this,this article will discuss electron behaviours during OER by taking into consideration of spin attribute.The main conclusion is that,regardless of the possible adopted mechanisms(the adsorbate evolution mechanism or the lattice oxygen mechanism),the underlying rationale of OER is that three in four electrons being extracted from adsorbates should be in the same spin direction before O=O formation,superimposing high requirements on the spin structure of electrocatalysts.Therefore,upon fully understanding of the OER mechanism with considerations of spin,the awareness of the coupling between spin,charge,orbital and lattice parameters is necessary in the optimization of geometric and electronic structures in transition metal systems.Based on this,this article will discuss the possible dependency of OER efficiency on the electrocatalyst spin configuration,and the relevance of well-recognized factors with spin,including the crystal field,coordination,oxidation,bonding,the e_(g) electron number,conductivity and magnetism.It is hoped that this article will clarify the underlying physics of OER to provide rational guidance for more effective design of energy conversion electrocatalysts.展开更多
Oxygen vacancy is one of the pivotal factors for tuning/creating various oxide properties.Understanding the behavior of oxygen vacancies is of paramount importance.In this study,we identify a metastable oxygen vacancy...Oxygen vacancy is one of the pivotal factors for tuning/creating various oxide properties.Understanding the behavior of oxygen vacancies is of paramount importance.In this study,we identify a metastable oxygen vacancy ordering state other than the well-known Magnéli phases in TiO2 crystals from both experimental and theoretical studies.The oxygen vacancy ordering is found to be a zigzag chain along the[001]direction in the(110)plane occurring in a wide temperature range of 200–500℃.This metastable ordering state leads to a first-order phase transition accompanied by significant enhancement of dielectric permittivity and a memristive effect featuring a low driving electric field.Our results can improve oxide properties by engineering oxygen vacancies.展开更多
(1-x)(0.8Bi_(1/2)Na_(1/2)TiO3-0.2Bi_(1/2)K_(1/2)TiO3)-xBi(Ni_(2/3)Nb_(1/3))O3(BNKT-xBNN)solid solution ceramics were fabricated by high temperature solid-state reaction method.All the compositions possess relaxor ferr...(1-x)(0.8Bi_(1/2)Na_(1/2)TiO3-0.2Bi_(1/2)K_(1/2)TiO3)-xBi(Ni_(2/3)Nb_(1/3))O3(BNKT-xBNN)solid solution ceramics were fabricated by high temperature solid-state reaction method.All the compositions possess relaxor ferroelectric features,among which the ergodic BNKT-0.02BNN exhibits large repeatable electrostrain value Suni¼0.51%at electric field of 65 kV/cm,with high piezoelectric stain coefficient d33*of 890 pm/V at 45 kV/cm,while the non-ergodic compositions present unrepeatable large strain response.Based on the electric field-composition phase diagram,the repeatability of strain response in ergodic compositions can be attributed to the reversible electric-field-induced phase transition.In addition,the effects of BNN contents on the macroscopic strain properties are explored by analyzing the existing states of the polar regions with corresponding thermal evolutions and electric-field-induced phase transitions.This research is expected to guide the design of lead free relaxor ferroelectric materials with desired electrostrain properties.展开更多
Among the lead-free compositions identified as potential capacitor materials, BiScO_(3)-BaTiO_(3) (BS-BT)relaxor dielectrics exhibit good energy storage performance. In this research, 0.4BS-0.6BT is consideredas the p...Among the lead-free compositions identified as potential capacitor materials, BiScO_(3)-BaTiO_(3) (BS-BT)relaxor dielectrics exhibit good energy storage performance. In this research, 0.4BS-0.6BT is consideredas the parent composition, with NaNbO_(3) (NN) addition intended to substitute the A and B site cations.The NN modified BS-BT ceramics exhibit excellent temperature stability in terms of their dielectricproperties, with the room-temperature dielectric constant on the order of 500e1 000 and variation lessthan 10% up to 400 C. In addition, NN has a high band-gap energy leading to increased breakdownstrength and energy storage properties in modified compositions. The highest breakdown strength wasachieved for 0.4BS-0.55BT-0.05NN, being on the order of 430 kV/cm, and a high energy density of 4.6 J/cm3 with high energy efficiency of 90% was simultaneously achieved. Of particular importance is that thevariation of the energy density was below 5% due to the temperature-insensitive dielectric constant,while ~90% energy efficiency was retained over the temperature range of 25e160 C. The improvedtemperature stability with NN addition makes this composition promising for high temperaturecapacitor and dielectric energy storage applications.展开更多
Two-dimensional(2D)van der Waals(vdW)materials provide the versatile playground to stack two or more vdW layers for creation of superior materials with desired properties.Here we theoretically adopt a twisted stack-en...Two-dimensional(2D)van der Waals(vdW)materials provide the versatile playground to stack two or more vdW layers for creation of superior materials with desired properties.Here we theoretically adopt a twisted stack-engineering of two LaBr_(2)monolayers to break space inversion symmetry for ferroelectricity and ultimately multiferroism.The enhancement and reversal of electric polarization are accompanied with the transition from interlayer ferromagnetic and antiferromagnetic orderings,demonstrating an effective magnetoelectric coupling effect with a mechanism dissimilar to that of the conventional multiferroics.Magnetization dynamics simulations show that such magnetic phase transition can excite topologically protected bimeron,and the skyrmion Hall effect can be suppressed by bilayer-bimeron stabilized in both ferromagnetic and antiferromagnetic configurations.Moreover,in the small-angle twisted moirésuperlattice,the uniform polarization will evolve into a staggered domain structure,accompanied with the appearance of bimeron,which forms a significant discrepancy with the non-twisted stack-engineered multiferroic LaBr_(2)bilayer.This work provides a strategy for 2D multiferroic materials by twisted stack engineering of magnetic single layers.展开更多
文摘Superior catalyst supports are crucial to developing advanced electrocatalysts toward heterogeneous catalytic reactions.Herein,we systematically investigate the role of transition metal‐functionalized N‐doped carbon nanosheets(M‐N‐C,M=Mn,Fe,Co,Ni,Cu,Mo,and Ag)as the multifunctional electrocatalyst supports toward hydrogen evolution/oxidation reactions(HER/HOR)in alkaline media.The results demonstrate that all the M‐N‐C nanosheets,except Cu‐N‐C and Ag‐N‐C,can promote the alkaline HER/HOR electrocatalytic activity of Pt by accelerating the sluggish Volmer step,among which Mn plays a more significant role.Analyses reveal that the promotion effect of M‐N‐C support is closely associated with the electronegativity of the metal dopants and the relative filling degree of their d‐orbitals.For one,the metal dopant in M‐N‐C with smaller electronegativity would provide more electrons to oxygen and hence tune the electronic structure of Pt via the M‐O‐Pt bonds at the interface.For another,the transition metal in M‐N4 moieties with more empty d orbitals would hybridize with O 2p orbitals more strongly that promotes the adsorption of water/hydroxyl species.The results demonstrate the conceptual significance of multifunctional supports and would inspire the future development of advanced electrocatalysts.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61975110,11674213,61735010,and 11604202)the 111 Project,China(Grant No.D18014)+3 种基金the International Joint Lab Program supported by Science and Technology Commission Shanghai Municipality,China(Grant No.17590750300)the Key Project supported by Science and Technology Commission Shanghai Municipality,China(Grant No.YDZX20193100004960)Science and Technology Commission of Shanghai Municipality,China(Shanghai Rising-Star Program 18QA1401700)Shanghai Educational Development Foundation,China(Chen Guang Project 16CG45).
文摘THz time-domain spectroscopy(THz-TDS)is used to study the THz-optical properties of a single crystal bismuth ferrite BiFeO3(BFO).It can be found that the anisotropy of BiFeO3 is strongly dependent on the temperature.A giant birefringence up to around 3.6 is observed at 1 THz.The presence of a spatially modulated cycloidal antiferromagnetic structure leads to spin cycloid resonances(SCR)ψandΦ,corresponding to the out-of-plane and in-plane modes of the spin cycloid,respectively.We distinguish the SCR with respect to their response to orthogonal polarizations of the electric fields of the incident THz beam.In addition,we observe a resonance appearing below 140 K,which might be interpreted as an electromagnon mode and related to a spin reorientation transition.Our present observations present that the temperature and polarization,as the external control parameters,can be used to modulate the THz optical properties of BFO single crystal.
基金supported by the National Natural Science Foundation of China(Grant Nos.52072150 and 51972146)Shandong Province Key Fundamental Research Program(Grant No.ZR2022ZD39).
文摘The rapidly advancing energy storage performance of dielectric ceramics capacitors has garnered significant interest for applications in fast charge/discharge and high-power electronic techniques.Exploring the exceptional electrical properties in harsh environments can further promote their practical applications.Defect carriers can be excited under luminance irradiation,thereby leading to degradation of energy storage performance.Herein,a synergic optimization strategy is proposed to enhance energy storage properties and luminance resistance of(K_(0.5)Na_(0.5))NbO_(3)-base(KNN)ceramics.First,the introduction of Bi(Zn0.5Ti0.5)O_(3) solid solution and La3+ions disrupts the long-range polar orders and enhances super paraelectric relaxation characteristics.Additionally,doping La3+ions can increase the band gap and reduce oxygen vacancy concentration,resulting in excellent luminance resistance.Finally,the viscous polymer process is employed to suppress the grain growth and promote chemical homogeneity.As a result,ultrahigh recoverable energy storage density(Wrec)of 8.11 J/cm3 and high efficiency(η)of 80.98%are achieved under an electric field of 568 kV/cm.Moreover,the variations in Wrec andηare only 12.45%and 1.75%,respectively,under 500 W xenon lamp irradiation compared to the performance under a dark environment.These findings hold great potential in facilitating the practical application of dielectric ceramic capacitors in luminance irradiation environments.
基金supported by the National Natural Science Foundation of China(Nos.51972144,51632003,51702120,U1806221 and 51761145023)the Taishan Scholars Program,the Case-by-Case Project for Top Outstanding Talents of Jinan+3 种基金the Project of“20 Items of University”of Jinan(2019GXRC017)the Key Research and Development Program of Shandong Province(2019GGX102015)the Shandong provincial key research and development plan(Grant No.2016JMRH0103)the Australian Research Council for providing support(DP190100150).
文摘As an essential energy-stored device,the inorganic dielectric film capacitor plays an irreplaceable role in high-energy pulse power technology area.In this work,propelled by the challenge of overcoming the bottlenecks of inflexibility and inferior energy storage density of the pure BiFeO3 films,the mica with high bendability and thermal stability is adopted as substrate,and the relaxor ferroelectric(Sr_(0.7)Bi_(0.2))TiO_(3) is introduced to form solid solution to introduce relaxor behavior.The subsequently fabricated 0.3Bi(Fe_(0.95)Mn_(0.05))O_(3)-0.7(Sr_(0.7)Bi_(0.2))TiO_(3)(BFMO-SBT)thin film capacitor exhibits a high recoverable energy storage density(W_(rec)=61 J cm^(-3))and a high efficiency(η=75%)combined with a fast discharging rate(23.5 μs)due to the large polarization difference(ΔP=59.4 μC cm^(-2)),high breakdown strength(E_(b)=3000 kV cm^(-1)),and the strong relaxor dispersion(γ=1.78).Of particular importance is the capacitor presents excellent stability of energy storage performance,including a wide working temperature window of -50-200℃,fatigue endurance of 108 cycles,and frequency range of 500 Hz-20 kHz.Furthermore,there are no obviously deteriorations on energy storage capability under various bending states and after 104 times of mechanical bending cycles.All these results indicate that BFMO-SBT on mica film capacitor has potential application in the future flexible electronics.
基金supported by the Australia Research Council(DP190100150,DP170104116).We would like to thank Dr.Tania Sliver for her critical insights into this article.
文摘The oxygen evolution reaction(OER)with its intractably high overpotentials is the rate-limiting step in many devices,including rechargeable metal-air batteries,water electrolysis systems and solar fuel devices.Correspondingly,spin state transitions from spin singlet OH^(-)/H_(2)O reactants to spin triplet O_(2)product have not yet received enough attention.In view of this,this article will discuss electron behaviours during OER by taking into consideration of spin attribute.The main conclusion is that,regardless of the possible adopted mechanisms(the adsorbate evolution mechanism or the lattice oxygen mechanism),the underlying rationale of OER is that three in four electrons being extracted from adsorbates should be in the same spin direction before O=O formation,superimposing high requirements on the spin structure of electrocatalysts.Therefore,upon fully understanding of the OER mechanism with considerations of spin,the awareness of the coupling between spin,charge,orbital and lattice parameters is necessary in the optimization of geometric and electronic structures in transition metal systems.Based on this,this article will discuss the possible dependency of OER efficiency on the electrocatalyst spin configuration,and the relevance of well-recognized factors with spin,including the crystal field,coordination,oxidation,bonding,the e_(g) electron number,conductivity and magnetism.It is hoped that this article will clarify the underlying physics of OER to provide rational guidance for more effective design of energy conversion electrocatalysts.
基金supported by the National Natural Science Foundation of China(51872001,51572001,11404002,11404003,11474059,and 11674064)Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics(KF201803)+1 种基金the National Key Research and Development Program of China(2016YFA0300700)Australia Research Council,and the U.S.Department of Energy under Contract no.DE-AC02-05CH11231。
文摘Oxygen vacancy is one of the pivotal factors for tuning/creating various oxide properties.Understanding the behavior of oxygen vacancies is of paramount importance.In this study,we identify a metastable oxygen vacancy ordering state other than the well-known Magnéli phases in TiO2 crystals from both experimental and theoretical studies.The oxygen vacancy ordering is found to be a zigzag chain along the[001]direction in the(110)plane occurring in a wide temperature range of 200–500℃.This metastable ordering state leads to a first-order phase transition accompanied by significant enhancement of dielectric permittivity and a memristive effect featuring a low driving electric field.Our results can improve oxide properties by engineering oxygen vacancies.
基金supported by the National Natural Science Foundation of China(51672220,51902258,51972265)Fundamental Research Funds for the Central Universities(3102019GHXM002)+2 种基金State Key Laboratory of Solidification Processing Project(2019-TZ-04)of China,China Postdoctoral Science Foundation(2019M653729)Natural Science Foundation of Shaanxi Province(2019JQ-621)the Shaanxi Province Postdoctoral Science Foundation(2017BSHEDZZ07).
文摘(1-x)(0.8Bi_(1/2)Na_(1/2)TiO3-0.2Bi_(1/2)K_(1/2)TiO3)-xBi(Ni_(2/3)Nb_(1/3))O3(BNKT-xBNN)solid solution ceramics were fabricated by high temperature solid-state reaction method.All the compositions possess relaxor ferroelectric features,among which the ergodic BNKT-0.02BNN exhibits large repeatable electrostrain value Suni¼0.51%at electric field of 65 kV/cm,with high piezoelectric stain coefficient d33*of 890 pm/V at 45 kV/cm,while the non-ergodic compositions present unrepeatable large strain response.Based on the electric field-composition phase diagram,the repeatability of strain response in ergodic compositions can be attributed to the reversible electric-field-induced phase transition.In addition,the effects of BNN contents on the macroscopic strain properties are explored by analyzing the existing states of the polar regions with corresponding thermal evolutions and electric-field-induced phase transitions.This research is expected to guide the design of lead free relaxor ferroelectric materials with desired electrostrain properties.
文摘Among the lead-free compositions identified as potential capacitor materials, BiScO_(3)-BaTiO_(3) (BS-BT)relaxor dielectrics exhibit good energy storage performance. In this research, 0.4BS-0.6BT is consideredas the parent composition, with NaNbO_(3) (NN) addition intended to substitute the A and B site cations.The NN modified BS-BT ceramics exhibit excellent temperature stability in terms of their dielectricproperties, with the room-temperature dielectric constant on the order of 500e1 000 and variation lessthan 10% up to 400 C. In addition, NN has a high band-gap energy leading to increased breakdownstrength and energy storage properties in modified compositions. The highest breakdown strength wasachieved for 0.4BS-0.55BT-0.05NN, being on the order of 430 kV/cm, and a high energy density of 4.6 J/cm3 with high energy efficiency of 90% was simultaneously achieved. Of particular importance is that thevariation of the energy density was below 5% due to the temperature-insensitive dielectric constant,while ~90% energy efficiency was retained over the temperature range of 25e160 C. The improvedtemperature stability with NN addition makes this composition promising for high temperaturecapacitor and dielectric energy storage applications.
基金supported by the National Natural Science Foundation of China(U2032154)the Key Research and Development Program of Anhui(202004a05020072)+1 种基金Anhui Initiative in Quantum Information Technologies(AHY100000)Anhui Provincial Natural Science Foundation(1908085ME119)。
基金We acknowledge grants from the National Natural Science Foundation of China under research(Nos.52102238,51571083,and 11674083)Henan University(No.CX3040A0950115,CJ3050A0670499,CJ3050A0670524)+2 种基金H.L.acknowledges the support from the National Natural Science Foundation of China(Grant No.11804078)Henan University(Grant No.CJ3050A0240050)Z.X.C.thanks Australia Research Council for support(DP190100150).
文摘Two-dimensional(2D)van der Waals(vdW)materials provide the versatile playground to stack two or more vdW layers for creation of superior materials with desired properties.Here we theoretically adopt a twisted stack-engineering of two LaBr_(2)monolayers to break space inversion symmetry for ferroelectricity and ultimately multiferroism.The enhancement and reversal of electric polarization are accompanied with the transition from interlayer ferromagnetic and antiferromagnetic orderings,demonstrating an effective magnetoelectric coupling effect with a mechanism dissimilar to that of the conventional multiferroics.Magnetization dynamics simulations show that such magnetic phase transition can excite topologically protected bimeron,and the skyrmion Hall effect can be suppressed by bilayer-bimeron stabilized in both ferromagnetic and antiferromagnetic configurations.Moreover,in the small-angle twisted moirésuperlattice,the uniform polarization will evolve into a staggered domain structure,accompanied with the appearance of bimeron,which forms a significant discrepancy with the non-twisted stack-engineered multiferroic LaBr_(2)bilayer.This work provides a strategy for 2D multiferroic materials by twisted stack engineering of magnetic single layers.
