Niobium pentoxide(Nb_(2)O_(5))anodes have gained increasing attentions for high-power lithium-ion batteries owing to the outstanding rate capability and high safety.However,Nb2O5 anode suffers poor cycle stability eve...Niobium pentoxide(Nb_(2)O_(5))anodes have gained increasing attentions for high-power lithium-ion batteries owing to the outstanding rate capability and high safety.However,Nb2O5 anode suffers poor cycle stability even after modified and the unrevealed mechanisms have restricted the practical applications.Herein,the over-reduction of Nb5+has been demonstrated to be the critical reason for the capacity loss for the first time.Besides,an effective competitive redox strategy has been developed to solve the rapid capacity decay of Nb_(2)O_(5),which can be achieved by the incorporation of vanadium to form a new rutile VNbO_(4)anode.The highly reversible V^(3+)/V^(2+)redox couple in VNbO_(4)can effectively inhibit the over-reduction of Nb^(5+).Besides,the electron migration from V^(3+)to Nb5+can greatly increase the intrinsic electronic conductivity for VNbO4.As a result,VNbO4 anode delivers a high capacity of 206.1 mAh g^(−1)at 0.1 A g^(−1),as well as remarkable cycle performance with a retention of 93.4%after 2000 cycles at 1.0 A g^(−1).In addition,the assembled lithium-ion capacitor demonstrates a high energy density of 44 Wh kg^(−1)at 5.8 kW kg^(−1).In summary,our work provides a new insight into the design of ultra-fast and durable anodes.展开更多
AlNbO_4,as lithium-ion batteries（LIBs） anode,has a high theoretical capacity of 291.5 m Ah g^-1.Here,AlNbO_4 anode materials were synthesized through a simple solid-state method.The structure,morphology and electroc...AlNbO_4,as lithium-ion batteries（LIBs） anode,has a high theoretical capacity of 291.5 m Ah g^-1.Here,AlNbO_4 anode materials were synthesized through a simple solid-state method.The structure,morphology and electrochemical performances of AlNbO4 anode were systematically investigated.The results show that AlNbO4 is monoclinic with C2/m space group.The scanning electron microscopy（SEM） and transmission electron microscopy（TEM） characterizations reveal the AlNbO_4 particles with the size of 100 nm^–2 lm.As a lithium-ion batteries anode,AlNbO4 delivers a high reversible capacity and good rate capability.The discharge capacity is as high as 151.0 m Ah g^-1 after 50 charge and discharge cycles at 0.1 C corresponding to capacity retention of 90.7 %.When the current density increases to 5.0C,AlNbO4 anode displays reversible discharge capacity of 73.6 m Ah g^-1 at the50 th cycle.展开更多
Change in valency of Nb-oxide in MnO-SiO_2-Nb_2O_5 system was studied with the electrochemical method using ZrO_2 as the solid electrolyte.Thermodynamic analysis has shown that the only possible reaction that could ta...Change in valency of Nb-oxide in MnO-SiO_2-Nb_2O_5 system was studied with the electrochemical method using ZrO_2 as the solid electrolyte.Thermodynamic analysis has shown that the only possible reaction that could take place at the working elec- trode is:2(Nb_2O_5)=2(Nb_2O_4)+O_2 with the a_0 values experimentally evaluated,values of a Nb_2O:/a Nb_2O:were calculated and isoactivity-ratio curves drawn in MnO-SiO_2-Nb_2O_5 triangles at 1418 and 1585K.The simultaneous existence of tetra-and penta-valent Nb mineral constituents in industrial Nb-bearing slags was thus verified experimentally.展开更多
Niobium pentoxide(Nb2O5)has attracted much attention in lithium batteries due to its advantages of high operating voltage,large theoretical capacity,environmental friendliness and cost-effectiveness.However,the intrin...Niobium pentoxide(Nb2O5)has attracted much attention in lithium batteries due to its advantages of high operating voltage,large theoretical capacity,environmental friendliness and cost-effectiveness.However,the intrinsic poor electrical conductivity,sluggish kinetics,and large volume changes hinder its electrochemical performance at high power density,making it away from the requirements for practical applications.In this research work,we regulate the electron transport of niobium-nickel oxide(NiNbO)anode material with enhanced structural stability at high power density by constructing the two-phase boundaries between niobium pentoxide(Nb2O5)and nickel niobate(NiNb2O6)through simple solid phase reaction.In addition,the presence of lattice defects in NiNbO-F further speeds up the transport of Li+and promotes the electrochemical reaction kinetics more effectively.The two-phase boundaries and defect modulated anode material displays high Li+diffusion coefficient of 1.63×10^(−10) cm^(2) s^(−1),pretty high initial discharge capacity of 222.8 mAh g^(−1) at 1 C,extraordinary high rate performance(66.7 mAh g^(−1))at an ultrahigh rate(100 C)and ultra-long cycling stability under high rate of 25 C(83.4 mAh g^(−1) after 2000 cycles)with only 0.016%attenuation per cycle.These results demonstrate an effective approach for developing electrode materials that greatly improve rate performance and durability.展开更多
Direct methanol fuel cells have the advantages of simple system,convenient operation,high conversion rate and low carbon emission,which are considered as the environmental and friendly energy conversion devices.How-ev...Direct methanol fuel cells have the advantages of simple system,convenient operation,high conversion rate and low carbon emission,which are considered as the environmental and friendly energy conversion devices.How-ever,the low activity,CO-tolerance and high cost of anode catalysts restrict the large-scale commercial appli-cations.Therefore,it is of great practical significance to design and construct the anodic catalysts with high activity,stability and low cost for methanol oxidation reaction.In this work,the PtM/Nb_(2)O_(5)-C(M=Co,Sn,Ni)catalysts are synthesized by the ethylene glycol solvothermal method using transition metal oxide Nb_(2)O_(5)as the support.The catalytic performance of different catalysts is further evaluated for alkaline MOR.The results show that the introduction of Ni(existing in Ni^(2+)and Ni^(3+))has the most obvious improvement for alkaline MOR performance.By adjusting the doped ratio of Pt:Ni,it is shown that PtNi/Nb_(2)O_(5)-C has the highest mass activity(3877.9 mA-mg_(pt)^(-1)),12 times that of the commercial Pt/C catalyst.CV,LSV,Tafel and EIS analyses show that PtNi/Nb_(2)O_(5)-C has the lowest onset potential and charge transfer resistance,and the fastest electrocatalytic oxidation rate of methanol.CA tests show that the electrochemical stability is also significantly improved with the introduction of Nb_(2)O_(5)and Ni.Combined with the structural characterization and electrochemical tests,it is found that the evident electronic effect among Pt and Ni,Nb_(2)O_(5)and the hydroxyl brought from Ni species are mainly ascribed for enhancing the activity,CO resistance and stability of PtNi/Nb_(2)O_(5)-C.展开更多
Aqueous hybrid supercapacitors are attracting increasing attention due to their potential low cost,high safety and eco-friendliness.However,the narrow operating potential window of aqueous electrolyte and the lack of ...Aqueous hybrid supercapacitors are attracting increasing attention due to their potential low cost,high safety and eco-friendliness.However,the narrow operating potential window of aqueous electrolyte and the lack of suitable negative electrode materials seriously hinder its future applications.Here,we explore high concentrated lithium acetate with high ionic conductivity of 65.5 mS cm−1 as a green“water-in-salt”electrolyte,providing wide voltage window up to 2.8 V.It facilitates the reversible function of niobium tungsten oxide,Nb18W16O93,that otherwise only operations in organic electrolytes previously.The Nb18W16O93 with lithium-ion intercalation pseudocapacitive behavior exhibits excellent rate performance,high areal capacity,and ultra-long cycling stability.An aqueous lithium-ion hybrid capacitor is developed by using Nb18W16O93 as negative electrode combined with graphene as positive electrode in lithium acetate-based“water-in-salt”electrolyte,delivering a high energy density of 41.9 W kg−1,high power density of 20,000 W kg−1 and unexceptionable stability of 50,000 cycles.展开更多
Niobium oxide as the promoter was doped in the V/WTi catalyst for the selective catalytic reduction（SCR）of NO.The results showed that the addition of Nb2O5could improve the SCR activity at low temperatures and the 6...Niobium oxide as the promoter was doped in the V/WTi catalyst for the selective catalytic reduction（SCR）of NO.The results showed that the addition of Nb2O5could improve the SCR activity at low temperatures and the 6 wt.%additive was an appropriate dosage.The enhanced reaction activity of adsorbed ammonia species and the improved dispersion of vanadium oxide might be the reasons for the elevation of SCR activity at low temperatures.The resistances to SO2of 3V6Nb/WTi catalyst at different temperatures were investigated.FTIR spectrum and TG-FTIR result indicated that the deposition of ammonium sulfate species was the main deactivation reason at low temperatures,which still exhibited the reactivity with NO above 200℃ on the catalyst surface.There was a synergistic effect among NH3,H2O and SO2that NH3and H2O both accelerated the catalyst deactivation in the presence of SO2at 175℃.The thermal treatment at 400℃ could regenerate the deactivated catalyst and get SCR activity recovered.The particle and monolith catalysts both kept stable NOxconversion at 225℃ with high concentration of H2O and SO2during the long time tests.展开更多
The NbO electrode materials were successfully synthesized by high-temperature solid-phase method using Nb powders and Nb2O5 powders as raw materials. The crystalline structure, morphology, and electrochemical properti...The NbO electrode materials were successfully synthesized by high-temperature solid-phase method using Nb powders and Nb2O5 powders as raw materials. The crystalline structure, morphology, and electrochemical properties of the obtained materials were characterized by X-ray diffi＇action （XRD）, scanning electron microscopy （SEM）, dynamic light scattering instrument （DLSA）, half- cell charge-discharge tests, and cyclic voltammetry （CV）. The reaction mechanism of lithium with NbO was inves- tigated by ex-situ XRD studies. The results show that material average Li storage voltage is nearly located at 1.6 V, and the lithium intercalation into NbO remains a single-phase process. For the first discharge, a capacity of 355 mAh·g^-1 is obtained at a current rate of 0.1C, and 293 mAh·g^-1is maintained after 50 cycles, whereas a capacity of 416 mAh·g^-1 is obtained at a current rate of 0.1C alter ball milling. And 380 mAh·g^-1 reversible capacity remains for the ball milling sample.展开更多
Heteroatoms doping has been regarded as a promising route to modulate the physiochemical properties of electrode materials,in which the doping sites greatly influence the electrochemical performances.However,very few ...Heteroatoms doping has been regarded as a promising route to modulate the physiochemical properties of electrode materials,in which the doping sites greatly influence the electrochemical performances.However,very few reports focus on enhancing the lithium storage performances of Nb_(2)O_(5) via heteroatoms doping,yet the effect of different doping sites remains unclear.Herein,nitrogen doping has been proposed to improve the fast-charging capability of orthorhombic Nb_(2)O_(5)(T-Nb_(2)O_(5))via a urea-assisted annealing process.Experimental data and theoretical calculation demonstrate that the N doping sites in T-Nb_(2)O_(5) can be tuned by the heating rate,in which substitutional N can increase the spacing of the Li^(+)transport layer as well as reduce the band gap,while interstitial N can provide an electron-rich environment for Li^(+)transport layer and then reduce the Li^(+)diffusion barrier.Arising from the synergistic effect of N doping at different sites,the N-doped T-Nb_(2)O_(5) without carbon coating delivers impressive rate performance(104.6 mA h g^(-1) at 25 C)as well as enhanced cycle stability with a retention of 70.5%over1000 cycles at 5 C.In addition,the assembled lithium ion capacitor exhibits a high energy density of46.6 Wh kg^(-1) even at high power density of 8.4 kW kg^(-1).展开更多
Nanoparticulate gold catalysts supported on niobium oxides （Nb2O5） were prepared by different deposition methods. The deposition precipitation （DP） method, DP method with urea, deposition reduction （DR） method a...Nanoparticulate gold catalysts supported on niobium oxides （Nb2O5） were prepared by different deposition methods. The deposition precipitation （DP） method, DP method with urea, deposition reduction （DR） method and one‐pot method were used to prepare a 1 wt%Au/Nb2O5 catalyst. Lay‐ered‐type Nb2O5 synthesized by a hydrothermal method （Nb2O5（HT）） was the most suitable as a support among various types of Nb2O5 including commercially available Nb2O5 samples. It appeared that the large BET surface area of Nb2O5（HT） enabled the dispersion of gold as nanoparticles （NPs）. Gold NPs with a mean diameter of about 5 nm were deposited by both the DP method and DR method on Nb2O5（HT） under an optimized condition. The temperature for 50%CO conversion for Au/Nb2O5（HT） prepared by the DR method was 73 ＆#176;C. Without deposition of gold, Nb2O5（HT） showed no catalytic activity for CO oxidation even at 250 ＆#176;C. Therefore, the enhancement of the activity by deposition of gold was remarkable. This simple Au/Nb2O5 catalyst will expand the types of gold catalysts to acidic supports, giving rise to new applications.展开更多
We report the fabrication of highly ordered Nb_(2)O_(5)nanochannel film(Nb_(2)O_(5)-NCF)onto niobium foil by an anodization method.After thermal treatment,the obtained Nb_(2)O_(5)-NCF with rich oxygen vacancies exhibi...We report the fabrication of highly ordered Nb_(2)O_(5)nanochannel film(Nb_(2)O_(5)-NCF)onto niobium foil by an anodization method.After thermal treatment,the obtained Nb_(2)O_(5)-NCF with rich oxygen vacancies exhibits electrochemical N_(2)reduction reaction(NRR)activity with an NH3 yield rate of 2.52×10^(-10)mol cm^(-2)s^(-1)and a faradaic efficiency of 9.81%at-0.4 V(vs.RHE)in 0.1 mol/L Na2SO4 electrolyte(pH 3.2).During electrocatalytic NRR,the Nb_(2)O_(5)-NCF takes place electrochromism(EC),along with a crystalline phase transformation from pseudo hexagonal phase to hexagonal phase owing to H+insertion.This results in the reduced NRR activity due to the decrease of oxygen vacancies of hexagonal phase Nb_(2)O_(5),which can be readily regenerated by low-temperature thermal treatment or applying an anodic potential,showing superior recycling reproducibility.展开更多
Herein,a series of niobium oxide supported cerium nanotubes(Ce NTs)catalysts with different loading amount of Nb_(2)O_(5)(0–10 wt.%)were prepared and used for selective catalytic reduction of NOxwith NH_(3)(NH_(3)-SC...Herein,a series of niobium oxide supported cerium nanotubes(Ce NTs)catalysts with different loading amount of Nb_(2)O_(5)(0–10 wt.%)were prepared and used for selective catalytic reduction of NOxwith NH_(3)(NH_(3)-SCR)in the presence of CH_(2)Cl_(2).Commercial V_(2)O_(5)-WO_(3)-TiO_(2) catalyst was also prepared for comparison.The physcial properties and chemical properties of the Nb_(2)O_(5) loaded cerium nanotubes catalysts were investigated by X-ray diffractometer,Transmission electron microscope,Brunauer-Emmett-Teller specific surface area,H_(2)-temperature programmed reduction,NH_(3)-temperature programmed desorption and Xray photoelectron spectroscopy.The experiment results showed that the loading amount of Nb_(2)O_(5) had a significant effect on the catalytic performance of the catalysts.10 wt.%Nb-Ce NTs catalyst presented the best NH_(3)-SCR performance and degradation efficiency of CH_(2)Cl_(2) among the prepared catalysts,due to its superior redox capability,abundant surface oxygen species and acid sites,the interaction between Nb and Ce,higher ratio of Nb^(4+)/(Nb^(5+)+Nb^(4+))and Ce^(3+)/(Ce^(3+)+Ce^(4+)),as well as the special tubular structure of cerium nanotube.This study may provide a practical approach for the design and synthesis of SCR catalysts for the simultaneously removal NOxand chlorinated volatile organic compounds(CVOCs)emitted from the stationary industrial sources.展开更多
Selective cleavage of robust C−C bonds to harvest value-added aromatic oxygenates is an intriguing but challenging task in lignin depolymerization.Photocatalysis is a promising technology with the advantages of mild r...Selective cleavage of robust C−C bonds to harvest value-added aromatic oxygenates is an intriguing but challenging task in lignin depolymerization.Photocatalysis is a promising technology with the advantages of mild reaction conditions and strong sustainability.Herein,we show a novel urchin-like Nb_(2)O_(5)hollow microsphere(U-Nb_(2)O_(5)HM),prepared by one-pot hydrothermal method,are highly active and selective for C_(α)−C_(β)bond cleavage of ligninβ-O-4 model compounds under mild conditions,achieving 94%substrate conversion and 96%C−C bond cleavage selectivity.Systematic experimental studies and density functional theory(DFT)calculations revealed that the superior performance of U-Nb_(2)O_(5)HMs arises from more exposed active sites,more efficient free charge separation and the active(001)facet,which facilitates the activation of Cβ−H bond of lignin models and generate key Cβradical intermediates by photogenerated holes,further inducing the C_(α)−C_(β)bond cleavage to produce aromatic oxygenates.This work could provide some suggestions for the fabrication of hierarchical photocatalysts in the lignin depolymerization system.展开更多
TiNb_(2)O_(7) is an advanced anode material for high-energy density lithium-ion batteries(LIBs) due to its considerable specific capacity and satisfactory safety.However,its rate capability is limited by its poor ioni...TiNb_(2)O_(7) is an advanced anode material for high-energy density lithium-ion batteries(LIBs) due to its considerable specific capacity and satisfactory safety.However,its rate capability is limited by its poor ionic conductivity and electronic conductivity.To solve this problem,TiNb_(2)O_(7) with W^(6+) doping was synthesized by a convenient solid-state method.The doping of W^(6+) will lead to arranging cation mixing and charge compensation.The cation rearrangement creates a new Li-conductive environment for lithiation,resulting in a low-energy barrier and the fast Li^(+)storage/diffusion.The results show that the Li^(+)diffusion coefficient of W_(0.06)Ti_(0.91)Nb_(2)O_(7) is increased by 9.96 times greater than that of TiNb_(2)O_(7).Besides,as the calculation proves,due to the partial reduction of the Nb^(5+)and Ti^(4+) caused by charge compensation,W^(6+)doping results in low charge transfer resistance and excellent electronic conductivity.Moreover,W^(6+) doping accounts for a high pseudocapacitive contribution.At the scan rate of 1 mV·s^(-1),the pseudocapacitive contribution for TiNb_(2)O_(7) is 78%,while that for W_(0.06)Ti_(0.91)Nb_(2)O_(7) increases to 83%.The reversible specific capacity of W_(0.06)Ti_(0.91)Nb_(2)O_(7) after 600 cycles is maintained at 148.90mAh·g^(-1) with a loss of only 16.37% at 10.0C.Also,it delivers a commendable capacity of 161.99 mAh·g^(-1) at20.0C.Even at 30.0C,it still retains a satisfactory capacity of 147.22 mAh·g^(-1),much higher than TiNb_(2)O_(7)(97.49mAh·g^(-1)).Our present study provides ideas for the development of electrode materials for lithium-ion batteries.展开更多
Niobium oxide nanowire-deposited carbon fiber（CF） samples were prepared using a hydrothermal method with amorphous Nb2O5·nH2O as precursor. The physical properties of the samples were characterized by means of ...Niobium oxide nanowire-deposited carbon fiber（CF） samples were prepared using a hydrothermal method with amorphous Nb2O5·nH2O as precursor. The physical properties of the samples were characterized by means of numerous techniques, including X-ray diffraction（XRD）, energy-dispersive spectroscopy（EDS）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, selected-area electron diffraction（SAED）, UV–visible spectroscopy（UV–vis）, N2 adsorption–desorption, Fourier transform infrared spectroscopy（FT-IR）, and X-ray photoelectron spectroscopy. The efficiency for the removal of Cr（VI） was determined.Parameters such as pH value and initial Cr（VI） concentration could influence the Cr（VI） removal efficiency or adsorption capacity of the Nb2O5/carbon fiber sample obtained after hydrothermal treatment at 160°C for 14 hr. The maximal Cr（VI） adsorption capacity of the Nb2O5 nanowire/CF sample was 115 mg/g. This Nb2O5/CF sample also showed excellent photocatalytic activity and stability for the reduction of Cr（Ⅵ） under UV-light irradiation： the Cr（VI） removal efficiency reached 99.9% after UV-light irradiation for 1 hr and there was no significant decrease in photocatalytic performance after the use of the sample for 10 repeated cycles. Such excellent Cr（VI） adsorption capacity and photocatalytic performance was related to its high surface area,abundant surface hydroxyl groups, and good UV-light absorption ability.展开更多
Supercapacitor is an efficient energy storage device,yet its wider application is still limited by self-discharge.Currently,various composite materials have been reported to have improved inhibition on self-discharge,...Supercapacitor is an efficient energy storage device,yet its wider application is still limited by self-discharge.Currently,various composite materials have been reported to have improved inhibition on self-discharge,while the evaluation of the synergistic effect in composite materials is challenging.Herein,pairs of intercalation type pseudocapacitive niobium oxides are pre-lithiated and coupled to construct conjugatedly configured supercapacitors,within which the cathode and anode experience identical reaction environment with single type of charge carrier,thus providing ideal platform to quantify the synergistic effect of composite materials on the self-discharge process.By using titanium dioxide as the stabilizer,we have compared how the modes of forming composite would influence the selfdischarge performance of the active composite materials with similar ratio of the constituent materials.Specifically,core@shell Nb_(2)O_(5)@TiO_(2) composite using TiO_(2) as the shell shows significantly higher synergy coefficient(μ=0.61,defined as the value that evaluates the synergistic effect between composite materials,and can be quantified using the overall performance of the composite,performance of individual component as well as the ratio of the component.) than other control group samples,which corresponds to the highest retained energy of 63% at 100 h.This work is expected to provide a general method for quantifying the synergistic effect and guide the design of composite materials with specific mode of forming the composite.展开更多
In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition met...In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.展开更多
In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition met...In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.展开更多
Anode materials of lithium-ion batteries(LIBs)endowed with high-rate performance and fast charging capability are crucial for future energy storage systems.Here,Mo_(8.7)Nb_(6.1)O_(x)@NCs(nitrogen-doped carbon nanotube...Anode materials of lithium-ion batteries(LIBs)endowed with high-rate performance and fast charging capability are crucial for future energy storage systems.Here,Mo_(8.7)Nb_(6.1)O_(x)@NCs(nitrogen-doped carbon nanotubes,NCs)egg-nest structure synthesized by an in-situ solvothermal method is reported.The Mo_(8.7)Nb_(6.1)O_(x)@NCs egg-nest exhibits high embedding potential,high pseudocapacitance contribution rate(87.5%),and low charge transfer resistance.The electrochemical results show that Mo_(8.7)Nb_(6.1)O_(x)@NCs demonstrates excellent rate performance(reversible capacity of 196.8 mAh·Ag^(-1)at 10 A·Ag^(-1),and full charging only takes 1.1 min)and excellent cycle stability(reversible capacity of 513 mAh·Ag^(-1)at 0.5 A·Ag^(-1)combined with a capacity loss of only 5.4%after 100 cycles),outperforming the state-of-the-art literature.The full cell is assembled with Mo_(8.7)Nb_(6.1)O_(x)@NCs as the anode and LiFeP04 as the cathode,which can provide a remarkably high energy density of 731.9 Wh·kg^(-1),indicating its excellent prospect for practical applications.展开更多
By taking tetragonal tungsten bronze(TTB)phase Nb_(18)W_(16)O_(93)as an example,an improved solid-state sintering method at lower temperature of 1000℃for 36 h was proposed via applying nanoscale raw materials.XRD,SEM...By taking tetragonal tungsten bronze(TTB)phase Nb_(18)W_(16)O_(93)as an example,an improved solid-state sintering method at lower temperature of 1000℃for 36 h was proposed via applying nanoscale raw materials.XRD,SEM and XPS confirm that the expected sample was produced.GITT results show that the lithium-ion diffusion coefficient of Nb_(18)W_(16)O_(93)(10−12 cm^(2)/s)is higher than that of the conventional titanium-based anode,ensuring a relatively superior electrochemical performance.The lithium-ion diffusion mechanism was thoroughly revealed by using density functional theory simulation.There are three diffusion paths in TTB phase,among which the interlayer diffusion with the smallest diffusion barrier(0.46 eV)has more advantages than other typical anodes(such as graphite,0.56 eV).The relatively smaller lithium-ion diffusion barrier makes TTB phase Nb_(18)W_(16)O_(93)become a potential highspecific-power anode material.展开更多
基金support from National Natural Science Foundation of China(51874142)Tip-top Scientific and Technical Innovative Youth Talents of Guangdong Special Support Program(2019TQ05L903)Young Elite Scientists Sponsorship Program by CAST(2019QNRC001).
文摘Niobium pentoxide(Nb_(2)O_(5))anodes have gained increasing attentions for high-power lithium-ion batteries owing to the outstanding rate capability and high safety.However,Nb2O5 anode suffers poor cycle stability even after modified and the unrevealed mechanisms have restricted the practical applications.Herein,the over-reduction of Nb5+has been demonstrated to be the critical reason for the capacity loss for the first time.Besides,an effective competitive redox strategy has been developed to solve the rapid capacity decay of Nb_(2)O_(5),which can be achieved by the incorporation of vanadium to form a new rutile VNbO_(4)anode.The highly reversible V^(3+)/V^(2+)redox couple in VNbO_(4)can effectively inhibit the over-reduction of Nb^(5+).Besides,the electron migration from V^(3+)to Nb5+can greatly increase the intrinsic electronic conductivity for VNbO4.As a result,VNbO4 anode delivers a high capacity of 206.1 mAh g^(−1)at 0.1 A g^(−1),as well as remarkable cycle performance with a retention of 93.4%after 2000 cycles at 1.0 A g^(−1).In addition,the assembled lithium-ion capacitor demonstrates a high energy density of 44 Wh kg^(−1)at 5.8 kW kg^(−1).In summary,our work provides a new insight into the design of ultra-fast and durable anodes.
基金financially supported by the National Natural Science Foundation of China (No.51271036)
文摘AlNbO_4,as lithium-ion batteries（LIBs） anode,has a high theoretical capacity of 291.5 m Ah g^-1.Here,AlNbO_4 anode materials were synthesized through a simple solid-state method.The structure,morphology and electrochemical performances of AlNbO4 anode were systematically investigated.The results show that AlNbO4 is monoclinic with C2/m space group.The scanning electron microscopy（SEM） and transmission electron microscopy（TEM） characterizations reveal the AlNbO_4 particles with the size of 100 nm^–2 lm.As a lithium-ion batteries anode,AlNbO4 delivers a high reversible capacity and good rate capability.The discharge capacity is as high as 151.0 m Ah g^-1 after 50 charge and discharge cycles at 0.1 C corresponding to capacity retention of 90.7 %.When the current density increases to 5.0C,AlNbO4 anode displays reversible discharge capacity of 73.6 m Ah g^-1 at the50 th cycle.
文摘Change in valency of Nb-oxide in MnO-SiO_2-Nb_2O_5 system was studied with the electrochemical method using ZrO_2 as the solid electrolyte.Thermodynamic analysis has shown that the only possible reaction that could take place at the working elec- trode is:2(Nb_2O_5)=2(Nb_2O_4)+O_2 with the a_0 values experimentally evaluated,values of a Nb_2O:/a Nb_2O:were calculated and isoactivity-ratio curves drawn in MnO-SiO_2-Nb_2O_5 triangles at 1418 and 1585K.The simultaneous existence of tetra-and penta-valent Nb mineral constituents in industrial Nb-bearing slags was thus verified experimentally.
基金supported by the National Natural Science Foundation of China(Nos.52002119 and 52102346)the National Key R&D Program of China(No.2021YFB3400800)the Startup Funds from the Henan University of Science and Technology(Nos.13480095,13480096,13554031 and 13554032).
文摘Niobium pentoxide(Nb2O5)has attracted much attention in lithium batteries due to its advantages of high operating voltage,large theoretical capacity,environmental friendliness and cost-effectiveness.However,the intrinsic poor electrical conductivity,sluggish kinetics,and large volume changes hinder its electrochemical performance at high power density,making it away from the requirements for practical applications.In this research work,we regulate the electron transport of niobium-nickel oxide(NiNbO)anode material with enhanced structural stability at high power density by constructing the two-phase boundaries between niobium pentoxide(Nb2O5)and nickel niobate(NiNb2O6)through simple solid phase reaction.In addition,the presence of lattice defects in NiNbO-F further speeds up the transport of Li+and promotes the electrochemical reaction kinetics more effectively.The two-phase boundaries and defect modulated anode material displays high Li+diffusion coefficient of 1.63×10^(−10) cm^(2) s^(−1),pretty high initial discharge capacity of 222.8 mAh g^(−1) at 1 C,extraordinary high rate performance(66.7 mAh g^(−1))at an ultrahigh rate(100 C)and ultra-long cycling stability under high rate of 25 C(83.4 mAh g^(−1) after 2000 cycles)with only 0.016%attenuation per cycle.These results demonstrate an effective approach for developing electrode materials that greatly improve rate performance and durability.
基金National Natural Science Foundation of China(22075225,21706203,22038011 and 22005236)Natural Science Basic Research Plan in Shaanxi Province of China(2022JZ-07)+1 种基金State Key Laboratory of Clean and Efficient Coal Utilization,Taiyuan University of Technology(MJNYSKL202308)Key Research and Development Program in Shaanxi Province(2022QCY-LL-16).
文摘Direct methanol fuel cells have the advantages of simple system,convenient operation,high conversion rate and low carbon emission,which are considered as the environmental and friendly energy conversion devices.How-ever,the low activity,CO-tolerance and high cost of anode catalysts restrict the large-scale commercial appli-cations.Therefore,it is of great practical significance to design and construct the anodic catalysts with high activity,stability and low cost for methanol oxidation reaction.In this work,the PtM/Nb_(2)O_(5)-C(M=Co,Sn,Ni)catalysts are synthesized by the ethylene glycol solvothermal method using transition metal oxide Nb_(2)O_(5)as the support.The catalytic performance of different catalysts is further evaluated for alkaline MOR.The results show that the introduction of Ni(existing in Ni^(2+)and Ni^(3+))has the most obvious improvement for alkaline MOR performance.By adjusting the doped ratio of Pt:Ni,it is shown that PtNi/Nb_(2)O_(5)-C has the highest mass activity(3877.9 mA-mg_(pt)^(-1)),12 times that of the commercial Pt/C catalyst.CV,LSV,Tafel and EIS analyses show that PtNi/Nb_(2)O_(5)-C has the lowest onset potential and charge transfer resistance,and the fastest electrocatalytic oxidation rate of methanol.CA tests show that the electrochemical stability is also significantly improved with the introduction of Nb_(2)O_(5)and Ni.Combined with the structural characterization and electrochemical tests,it is found that the evident electronic effect among Pt and Ni,Nb_(2)O_(5)and the hydroxyl brought from Ni species are mainly ascribed for enhancing the activity,CO resistance and stability of PtNi/Nb_(2)O_(5)-C.
基金Shengyang Dong and Yi Wang contributed equally to this work.This work was supported by the National Natural Science Foundation of China(Nos.U1802256,51672128,51802154)the Key Research and Development Program in Jiangsu Province(BE2018122)+1 种基金Jiangsu Specially-Appointed Professors Program,the Fundamental Research Funds for the Central Universities(NE2016005)the Startup Foundation for Introducing Talent of NUIST(1441622001004).
文摘Aqueous hybrid supercapacitors are attracting increasing attention due to their potential low cost,high safety and eco-friendliness.However,the narrow operating potential window of aqueous electrolyte and the lack of suitable negative electrode materials seriously hinder its future applications.Here,we explore high concentrated lithium acetate with high ionic conductivity of 65.5 mS cm−1 as a green“water-in-salt”electrolyte,providing wide voltage window up to 2.8 V.It facilitates the reversible function of niobium tungsten oxide,Nb18W16O93,that otherwise only operations in organic electrolytes previously.The Nb18W16O93 with lithium-ion intercalation pseudocapacitive behavior exhibits excellent rate performance,high areal capacity,and ultra-long cycling stability.An aqueous lithium-ion hybrid capacitor is developed by using Nb18W16O93 as negative electrode combined with graphene as positive electrode in lithium acetate-based“water-in-salt”electrolyte,delivering a high energy density of 41.9 W kg−1,high power density of 20,000 W kg−1 and unexceptionable stability of 50,000 cycles.
基金supported by the Policy-induced Project of Jiangsu Province for the Industry-University-Research Cooperation (No. BY2015070-21)the project was also supported by National Science and Technology Ministry (No. 2015BAA05B01)the Natural Science Fund Program of Jiangsu Province (No. BK20150749)
文摘Niobium oxide as the promoter was doped in the V/WTi catalyst for the selective catalytic reduction（SCR）of NO.The results showed that the addition of Nb2O5could improve the SCR activity at low temperatures and the 6 wt.%additive was an appropriate dosage.The enhanced reaction activity of adsorbed ammonia species and the improved dispersion of vanadium oxide might be the reasons for the elevation of SCR activity at low temperatures.The resistances to SO2of 3V6Nb/WTi catalyst at different temperatures were investigated.FTIR spectrum and TG-FTIR result indicated that the deposition of ammonium sulfate species was the main deactivation reason at low temperatures,which still exhibited the reactivity with NO above 200℃ on the catalyst surface.There was a synergistic effect among NH3,H2O and SO2that NH3and H2O both accelerated the catalyst deactivation in the presence of SO2at 175℃.The thermal treatment at 400℃ could regenerate the deactivated catalyst and get SCR activity recovered.The particle and monolith catalysts both kept stable NOxconversion at 225℃ with high concentration of H2O and SO2during the long time tests.
基金financially supported by the National Science and Technology Support Project of China(No.2007BAE12B01)the Science and Technology Project of Changsha(No.k1201039-11)
文摘The NbO electrode materials were successfully synthesized by high-temperature solid-phase method using Nb powders and Nb2O5 powders as raw materials. The crystalline structure, morphology, and electrochemical properties of the obtained materials were characterized by X-ray diffi＇action （XRD）, scanning electron microscopy （SEM）, dynamic light scattering instrument （DLSA）, half- cell charge-discharge tests, and cyclic voltammetry （CV）. The reaction mechanism of lithium with NbO was inves- tigated by ex-situ XRD studies. The results show that material average Li storage voltage is nearly located at 1.6 V, and the lithium intercalation into NbO remains a single-phase process. For the first discharge, a capacity of 355 mAh·g^-1 is obtained at a current rate of 0.1C, and 293 mAh·g^-1is maintained after 50 cycles, whereas a capacity of 416 mAh·g^-1 is obtained at a current rate of 0.1C alter ball milling. And 380 mAh·g^-1 reversible capacity remains for the ball milling sample.
基金the financial support from National Natural Science Foundation of China(51874142)Tip-top Scientific and Technical Innovative Youth Talents of Guangdong Special Support Program(2019TQ05L903)Young Elite Scientists Sponsorship Program by CAST(2019QNRC001)。
文摘Heteroatoms doping has been regarded as a promising route to modulate the physiochemical properties of electrode materials,in which the doping sites greatly influence the electrochemical performances.However,very few reports focus on enhancing the lithium storage performances of Nb_(2)O_(5) via heteroatoms doping,yet the effect of different doping sites remains unclear.Herein,nitrogen doping has been proposed to improve the fast-charging capability of orthorhombic Nb_(2)O_(5)(T-Nb_(2)O_(5))via a urea-assisted annealing process.Experimental data and theoretical calculation demonstrate that the N doping sites in T-Nb_(2)O_(5) can be tuned by the heating rate,in which substitutional N can increase the spacing of the Li^(+)transport layer as well as reduce the band gap,while interstitial N can provide an electron-rich environment for Li^(+)transport layer and then reduce the Li^(+)diffusion barrier.Arising from the synergistic effect of N doping at different sites,the N-doped T-Nb_(2)O_(5) without carbon coating delivers impressive rate performance(104.6 mA h g^(-1) at 25 C)as well as enhanced cycle stability with a retention of 70.5%over1000 cycles at 5 C.In addition,the assembled lithium ion capacitor exhibits a high energy density of46.6 Wh kg^(-1) even at high power density of 8.4 kW kg^(-1).
文摘Nanoparticulate gold catalysts supported on niobium oxides （Nb2O5） were prepared by different deposition methods. The deposition precipitation （DP） method, DP method with urea, deposition reduction （DR） method and one‐pot method were used to prepare a 1 wt%Au/Nb2O5 catalyst. Lay‐ered‐type Nb2O5 synthesized by a hydrothermal method （Nb2O5（HT）） was the most suitable as a support among various types of Nb2O5 including commercially available Nb2O5 samples. It appeared that the large BET surface area of Nb2O5（HT） enabled the dispersion of gold as nanoparticles （NPs）. Gold NPs with a mean diameter of about 5 nm were deposited by both the DP method and DR method on Nb2O5（HT） under an optimized condition. The temperature for 50%CO conversion for Au/Nb2O5（HT） prepared by the DR method was 73 ＆#176;C. Without deposition of gold, Nb2O5（HT） showed no catalytic activity for CO oxidation even at 250 ＆#176;C. Therefore, the enhancement of the activity by deposition of gold was remarkable. This simple Au/Nb2O5 catalyst will expand the types of gold catalysts to acidic supports, giving rise to new applications.
基金financially supported by the National Key Research and Development Program of China(No.2017YFA0207203)the Natural Science Foundation of China(No.51872292)。
文摘We report the fabrication of highly ordered Nb_(2)O_(5)nanochannel film(Nb_(2)O_(5)-NCF)onto niobium foil by an anodization method.After thermal treatment,the obtained Nb_(2)O_(5)-NCF with rich oxygen vacancies exhibits electrochemical N_(2)reduction reaction(NRR)activity with an NH3 yield rate of 2.52×10^(-10)mol cm^(-2)s^(-1)and a faradaic efficiency of 9.81%at-0.4 V(vs.RHE)in 0.1 mol/L Na2SO4 electrolyte(pH 3.2).During electrocatalytic NRR,the Nb_(2)O_(5)-NCF takes place electrochromism(EC),along with a crystalline phase transformation from pseudo hexagonal phase to hexagonal phase owing to H+insertion.This results in the reduced NRR activity due to the decrease of oxygen vacancies of hexagonal phase Nb_(2)O_(5),which can be readily regenerated by low-temperature thermal treatment or applying an anodic potential,showing superior recycling reproducibility.
基金financially supported by National Natural Science Foundation of China(Nos.52070168 and 51708492)National Key Research and Development Plan of China(No.2016YFC0204100)+1 种基金Zhejiang Provincial“151 Talents Programthe Program for Zhejiang Leading Team of S&T Innovation(No.2013TD07)。
文摘Herein,a series of niobium oxide supported cerium nanotubes(Ce NTs)catalysts with different loading amount of Nb_(2)O_(5)(0–10 wt.%)were prepared and used for selective catalytic reduction of NOxwith NH_(3)(NH_(3)-SCR)in the presence of CH_(2)Cl_(2).Commercial V_(2)O_(5)-WO_(3)-TiO_(2) catalyst was also prepared for comparison.The physcial properties and chemical properties of the Nb_(2)O_(5) loaded cerium nanotubes catalysts were investigated by X-ray diffractometer,Transmission electron microscope,Brunauer-Emmett-Teller specific surface area,H_(2)-temperature programmed reduction,NH_(3)-temperature programmed desorption and Xray photoelectron spectroscopy.The experiment results showed that the loading amount of Nb_(2)O_(5) had a significant effect on the catalytic performance of the catalysts.10 wt.%Nb-Ce NTs catalyst presented the best NH_(3)-SCR performance and degradation efficiency of CH_(2)Cl_(2) among the prepared catalysts,due to its superior redox capability,abundant surface oxygen species and acid sites,the interaction between Nb and Ce,higher ratio of Nb^(4+)/(Nb^(5+)+Nb^(4+))and Ce^(3+)/(Ce^(3+)+Ce^(4+)),as well as the special tubular structure of cerium nanotube.This study may provide a practical approach for the design and synthesis of SCR catalysts for the simultaneously removal NOxand chlorinated volatile organic compounds(CVOCs)emitted from the stationary industrial sources.
基金financially supported by the National Natural Science Foundation of China (No. 22008073)Shanghai Sailing Program (No. 20YF1410600)
文摘Selective cleavage of robust C−C bonds to harvest value-added aromatic oxygenates is an intriguing but challenging task in lignin depolymerization.Photocatalysis is a promising technology with the advantages of mild reaction conditions and strong sustainability.Herein,we show a novel urchin-like Nb_(2)O_(5)hollow microsphere(U-Nb_(2)O_(5)HM),prepared by one-pot hydrothermal method,are highly active and selective for C_(α)−C_(β)bond cleavage of ligninβ-O-4 model compounds under mild conditions,achieving 94%substrate conversion and 96%C−C bond cleavage selectivity.Systematic experimental studies and density functional theory(DFT)calculations revealed that the superior performance of U-Nb_(2)O_(5)HMs arises from more exposed active sites,more efficient free charge separation and the active(001)facet,which facilitates the activation of Cβ−H bond of lignin models and generate key Cβradical intermediates by photogenerated holes,further inducing the C_(α)−C_(β)bond cleavage to produce aromatic oxygenates.This work could provide some suggestions for the fabrication of hierarchical photocatalysts in the lignin depolymerization system.
基金financially supported by the National Natural Science Foundation of China (Nos. 52274299, 52004103 and 51974137)the Postdoctoral Science Foundation of China (Nos. 2021M691321 and 2020M671361)the Postdoctoral Science Foundation of Jiangsu Province (No. 2020Z090)。
文摘TiNb_(2)O_(7) is an advanced anode material for high-energy density lithium-ion batteries(LIBs) due to its considerable specific capacity and satisfactory safety.However,its rate capability is limited by its poor ionic conductivity and electronic conductivity.To solve this problem,TiNb_(2)O_(7) with W^(6+) doping was synthesized by a convenient solid-state method.The doping of W^(6+) will lead to arranging cation mixing and charge compensation.The cation rearrangement creates a new Li-conductive environment for lithiation,resulting in a low-energy barrier and the fast Li^(+)storage/diffusion.The results show that the Li^(+)diffusion coefficient of W_(0.06)Ti_(0.91)Nb_(2)O_(7) is increased by 9.96 times greater than that of TiNb_(2)O_(7).Besides,as the calculation proves,due to the partial reduction of the Nb^(5+)and Ti^(4+) caused by charge compensation,W^(6+)doping results in low charge transfer resistance and excellent electronic conductivity.Moreover,W^(6+) doping accounts for a high pseudocapacitive contribution.At the scan rate of 1 mV·s^(-1),the pseudocapacitive contribution for TiNb_(2)O_(7) is 78%,while that for W_(0.06)Ti_(0.91)Nb_(2)O_(7) increases to 83%.The reversible specific capacity of W_(0.06)Ti_(0.91)Nb_(2)O_(7) after 600 cycles is maintained at 148.90mAh·g^(-1) with a loss of only 16.37% at 10.0C.Also,it delivers a commendable capacity of 161.99 mAh·g^(-1) at20.0C.Even at 30.0C,it still retains a satisfactory capacity of 147.22 mAh·g^(-1),much higher than TiNb_(2)O_(7)(97.49mAh·g^(-1)).Our present study provides ideas for the development of electrode materials for lithium-ion batteries.
基金financially supported by the major Project of the national science and technology of China (No. SQ2017YFGX010248)the Beijing Natural Science Foundation (No. 2172011)
文摘Niobium oxide nanowire-deposited carbon fiber（CF） samples were prepared using a hydrothermal method with amorphous Nb2O5·nH2O as precursor. The physical properties of the samples were characterized by means of numerous techniques, including X-ray diffraction（XRD）, energy-dispersive spectroscopy（EDS）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, selected-area electron diffraction（SAED）, UV–visible spectroscopy（UV–vis）, N2 adsorption–desorption, Fourier transform infrared spectroscopy（FT-IR）, and X-ray photoelectron spectroscopy. The efficiency for the removal of Cr（VI） was determined.Parameters such as pH value and initial Cr（VI） concentration could influence the Cr（VI） removal efficiency or adsorption capacity of the Nb2O5/carbon fiber sample obtained after hydrothermal treatment at 160°C for 14 hr. The maximal Cr（VI） adsorption capacity of the Nb2O5 nanowire/CF sample was 115 mg/g. This Nb2O5/CF sample also showed excellent photocatalytic activity and stability for the reduction of Cr（Ⅵ） under UV-light irradiation： the Cr（VI） removal efficiency reached 99.9% after UV-light irradiation for 1 hr and there was no significant decrease in photocatalytic performance after the use of the sample for 10 repeated cycles. Such excellent Cr（VI） adsorption capacity and photocatalytic performance was related to its high surface area,abundant surface hydroxyl groups, and good UV-light absorption ability.
基金supported by the National Natural Science Foundation of China (52262030)the Natural Science Foundation of Guizhou Science and Technology Department (QKHJC-ZK[2021]YB257)。
文摘Supercapacitor is an efficient energy storage device,yet its wider application is still limited by self-discharge.Currently,various composite materials have been reported to have improved inhibition on self-discharge,while the evaluation of the synergistic effect in composite materials is challenging.Herein,pairs of intercalation type pseudocapacitive niobium oxides are pre-lithiated and coupled to construct conjugatedly configured supercapacitors,within which the cathode and anode experience identical reaction environment with single type of charge carrier,thus providing ideal platform to quantify the synergistic effect of composite materials on the self-discharge process.By using titanium dioxide as the stabilizer,we have compared how the modes of forming composite would influence the selfdischarge performance of the active composite materials with similar ratio of the constituent materials.Specifically,core@shell Nb_(2)O_(5)@TiO_(2) composite using TiO_(2) as the shell shows significantly higher synergy coefficient(μ=0.61,defined as the value that evaluates the synergistic effect between composite materials,and can be quantified using the overall performance of the composite,performance of individual component as well as the ratio of the component.) than other control group samples,which corresponds to the highest retained energy of 63% at 100 h.This work is expected to provide a general method for quantifying the synergistic effect and guide the design of composite materials with specific mode of forming the composite.
文摘In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.
文摘In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.
基金financially supported by the National Natural Science Foundation of China (Nos.22179077 and 51774251)Shanghai Science and Technology Commission’s "2020 Science and Technology Innovation Action Plan" (No. 20511104003)+2 种基金Natural Science Foundation in Shanghai (No. 21ZR1424200)Hebei Natural Science Foundation for Distinguished Young Scholars (No.B2017203313)the Scientific Research Foundation for the Returned Overseas Chinese Scholars (No. CG2014003002)
文摘Anode materials of lithium-ion batteries(LIBs)endowed with high-rate performance and fast charging capability are crucial for future energy storage systems.Here,Mo_(8.7)Nb_(6.1)O_(x)@NCs(nitrogen-doped carbon nanotubes,NCs)egg-nest structure synthesized by an in-situ solvothermal method is reported.The Mo_(8.7)Nb_(6.1)O_(x)@NCs egg-nest exhibits high embedding potential,high pseudocapacitance contribution rate(87.5%),and low charge transfer resistance.The electrochemical results show that Mo_(8.7)Nb_(6.1)O_(x)@NCs demonstrates excellent rate performance(reversible capacity of 196.8 mAh·Ag^(-1)at 10 A·Ag^(-1),and full charging only takes 1.1 min)and excellent cycle stability(reversible capacity of 513 mAh·Ag^(-1)at 0.5 A·Ag^(-1)combined with a capacity loss of only 5.4%after 100 cycles),outperforming the state-of-the-art literature.The full cell is assembled with Mo_(8.7)Nb_(6.1)O_(x)@NCs as the anode and LiFeP04 as the cathode,which can provide a remarkably high energy density of 731.9 Wh·kg^(-1),indicating its excellent prospect for practical applications.
基金the Key R&D Program of Shaanxi Province,China(No.2019ZDLGY04-05)the Natural Science Foundation of Shaanxi Province,China(No.2019JLZ-01)+1 种基金the Fundamental Research Funds for the Central Universities of China(Nos.19GH020302,3102019JC005,3102021ZD0401,3102021TS0406)the Science,Technology,and Innovation Commission of Shenzhen Municipality,China(No.JCYJ20180508151856806).
文摘By taking tetragonal tungsten bronze(TTB)phase Nb_(18)W_(16)O_(93)as an example,an improved solid-state sintering method at lower temperature of 1000℃for 36 h was proposed via applying nanoscale raw materials.XRD,SEM and XPS confirm that the expected sample was produced.GITT results show that the lithium-ion diffusion coefficient of Nb_(18)W_(16)O_(93)(10−12 cm^(2)/s)is higher than that of the conventional titanium-based anode,ensuring a relatively superior electrochemical performance.The lithium-ion diffusion mechanism was thoroughly revealed by using density functional theory simulation.There are three diffusion paths in TTB phase,among which the interlayer diffusion with the smallest diffusion barrier(0.46 eV)has more advantages than other typical anodes(such as graphite,0.56 eV).The relatively smaller lithium-ion diffusion barrier makes TTB phase Nb_(18)W_(16)O_(93)become a potential highspecific-power anode material.
