Competitive Redox Chemistries in Vanadium Niobium Oxide for Ultrafast and Durable Lithium Storage

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.

Electrochemical Study on the Change in Valency of Niobium Oxide in the MnO-SiO_2-Nb_2O_5 System

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.

Electrochemical performance of aluminum niobium oxide as anode for lithium-ion batteries

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.

Depositing the PtNi nanoparticles on niobium oxide to enhance the activity and CO-tolerance for alkaline methanol electrooxidation

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.

Niobium Tungsten Oxide in a Green Water‑in‑Salt Electrolyte Enables Ultra‑Stable Aqueous Lithium‑Ion Capacitors

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.

Doping sites modulation of T-Nb_(2)O_(5) to achieve ultrafast lithium storage

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).

Preparation of gold nanoparticles supported on Nb_2O_5 by deposition precipitation and deposition reduction methods and their catalytic activity for CO oxidation

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.

Design of phase interface and defect in niobium-nickel oxide for ultrafast Li-ion storage

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.

Regulating the synergy coefficient of composite materials for alleviating self-discharge of supercapacitors

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.

Mössbauer Spectroscopic Characterization of Fe Occupation of Columns in the Nb28O70 Structure

In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb28O70 with small amounts of transition metal oxides (TM;in this case Fe2O3) or rare-earth oxides3, 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 Nb28O70 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 Fe3+ 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.

Mössbauer Spectroscopic Characterization of Fe Occupation of Columns in the Nb28O70 Structure

In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb28O70 with small amounts of transition metal oxides (TM;in this case Fe2O3) or rare-earth oxides3, 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 Nb28O70 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 Fe3+ 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.

Lithium-ion diffusion path of tetragonal tungsten bronze(TTB)phase Nb_(18)W_(16)O_(93)

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.

Fibonacci Stoichiometry and Superb Performance of Nb16W5O55 and Related Super-Battery Materials

In this contribution, two important crystallographic concepts for the formation of a series of block structures associated with channeling have been compared: chemical twinning and crystallographic shear. Twin planes respectively shear planes besides formed channels serve as a sink for charge carriers or, when the oxidation state of metal ions can be reduced, as a reservoir for intercalated lithium. In this way, Wadsley-Roth shear phases such as niobium tungsten oxide exhibit channels for ultra-fast lithium-ion diffusion. They are in focus as anode material for super-batteries, superb in terms of energy respectively power density, charging time, cycle life and safety. It should be noted that the transition metal to oxygen ratio TM/O = 21/55 of the title compound is a Fibonacci number quotient. Also, the crystal lattice can be traced back to Fibonacci geometry. When replacing only 0.0213 tungsten atoms in the formula with less expensive titanium, a TM/O ratio of 0.381966 =ϕ2 can be adapted besides an average valence electron concentration of 2⋅ϕ-2, where represents the most irrational number of the golden mean. The additional disorder caused by even such small titanium replacement and accompanied oxygen vacancies could fasten up the already high lithium diffusion further. Ultrasonic treatment may be applied besides thermal cycling to prepare phase-pure of the highest electrochemical performance. A replacement of oxygen by some fluorine atoms is an obvious synthesis possibility, but the higher binding energy expected between lithium and fluorine in contrast to oxygen may rather hinder than promote lithium diffusion.

New Superionic Memory Devices Can Provide Clues to the Human Memory Structure and to Consciousness

Since the work of Penrose and Hameroff the possibility is discussed that the location of human memory and consciousness could be connected with tubulin microtubules. If one would use superionic nano-materials rolled up to microtubules with an electrolyte inside the formed channels mediating fast ionic exchange of protons respectively lithium ions, it seems to be possible to write into such materials whole image arrays (pictures) under the action of the complex electromagnetic spectrum that composes these images. The same material and architecture may be recommended for super-computers. Especially microtubules with a protofilament number of 13 are the most important to note. We connected such microtubules before with Fibonacci nets composed of 13 sub-cells that were helically rolled up to deliver suitable channels. Our recent Fibonacci analysis of Wadsley-Roth shear phases such as niobium tungsten oxide , exhibiting channels for ultra-fast lithium-ion diffusion, suggests to use these materials, besides super-battery main application, in form of nanorods or microtubules as effectively working superionic memory devices for computers that work ultra-fast with the complex effectiveness of human brains. Finally, we pose the question, whether dark matter, ever connected with ultrafast movement of ordinary matter, may be responsible for synchronization between interactions of human brains and consciousness.

Direct laser patterning of two-dimensional lateral transition metal disulfide-oxide-disulfide heterostructures for ultrasensitive sensors

Two-dimensional(2D)heterostructures based on the combination of transition metal dichalcogenides(TMDs)and transition metal oxides(TMOs)have aroused growing attention due to their integrated merits of both components and multiple functionalities.However,nondestructive approaches of constructing TMD-TMO heterostructures are still very limited.Here,we develop a novel type of lateral TMD-TMO heterostructure(NbS2-Nb2O5-NbS2)using a simple lithography-free,direct laser-patterning technique.The perfect contact of an ultrathin TMO channel(Nb2O5)with two metallic TMDs(NbS2)electrodes guarantee strong electrical signals in a two-terminal sensor.Distinct from sensing mechanisms in separate TMOs or TMDs,this sensor works based on the modulation of surface conduction of the ultrathin TMO(Nb2O5)channel through an adsorbed layer of water molecules.The sensor thus exhibits high selectivity and ultrahigh sensitivity for room-temperature detection of NH3(ΔR/R=80%at 50 ppm),superior to the reported NH3 sensors based on 2D materials,and a positive temperature coefficient of resistance as high as 15%–20%/℃.Bending-invariant performance and high reliability are also demonstrated in flexible versions of sensors.Our work provides a new strategy of lithography-free processing of novel TMD-TMO heterostructures towards high-performance sensors,showing great potential in the applications of future portable and wearable electronics.

Nb_(2)O_(5) nanocrystals decorated graphene composites as anode materials for high-performance dual-ion batteries

Niobium oxide(Nb_(2)O_(5))is a promising material in photocatalytic,solar cell,electronic like electron field emitters,and especially lithium-ion batteries(LIBs)because of its adjustable morphologies,controllable crystal type,stable structure,and environmental friendliness.However,its low electrical conductivity lowers the rate performance and limits the practical applications in LIBs.Herein,we present a one-step solid-state synthesis of orthogonal Nb_(2)O_(5) nanocrystals/graphene composites(Nb_(2)O_(5)/G)as high-performance anode materials in LIBs.Benefiting from the nanoscale crystalline structure Nb_(2)O_(5) and highly-conductive graphene substrate,the as-prepared Nb_(2)O_(5)/G exhibits excellent electrochemical performances.Impressively,a reversible structural phase transition between orthogonal Nb_(2)O_(5) and tetragonal Li1-xNbO_(2)(0<x<1)was verified by ex-situ transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).After coupling with graphite cathode based on PF6-intercalation/deintercalation mechanisms,Nb_(2)O_(5)/G||graphite dual-ion batteries(DIBs)full cell delivers good electrochemical performance in terms of cyclic performance and rate capability.We believe this work can provide a clear route towards developing advanced transition metal oxide/graphene composite anode and a comprehension of its electrochemical reaction mechanism.

NH3-SCR performance and the resistance to SO2 for Nb doped vanadium based catalyst at low temperatures

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.

Anode material NbO for Li-ion battery and its electrochemical properties

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.

Narrow-bandgap Nb_2O_5 nanowires with enclosed pores as high-performance photocatalyst

Porous niobium oxide nanowires synthesized via a solvothermal method exhibited decreased bandgap,en- hanced light absorption and reduced charge-recombination rate.The porous Nb2O5 nanowires showed increased performance for the photocatalytic H2 evolution and photo- degradation of rhodamine B,as compared to their solid counterparts,which could be ascribed to the peculiar porous nanostructure.

Highly ordered Nb_(2)O_(5)nanochannel film with rich oxygen vacancies for electrocatalytic N2 reduction:Inactivation and regeneration of electrode

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.