Nb2O5 Nanowires Research Articles

Surface Nitriding Enables Improved Intercalation Pseudocapacitance of T−Nb2O5 for Lithium‐Ion Batteries

AbstractThe low electrical conductivity limits the application of T−Nb2O5 as anode materials for practical applications. The large‐grain T−Nb2O5 nanowires with nitrogen doping are obtained by simple hydrothermal and annealing treatments. After nitriding with ammonia, an amorphous layer of NbON as an intermediate is formed and then the new crystalline NbN is generated with the deepening of the nitriding degree, causing homogeneous pores on the surface of the T−Nb2O5 and thus increasing the specific surface area. Meanwhile, the formation of the nitriding layer enhances the electrical conductivity, inducing a pseudo‐capacitance mechanism. Therefore, the N−T−Nb2O5 nanowire demonstrates superior electrochemical performance. Specifically, the 45N−T−Nb2O5 nanowires delivered a first reversible specific capacity of 238.33 mAh g−1 at 0.1 C, higher than of theoretical capacity (201.6 mAh g−1). However, the excessive nitride will be completely converted into NbN, reducing the initial lithium storage of the material due to the lack of a lithium storage site, which has not been previously discussed. Besides, at the high rate of 100 C, with the deepening of nitride degree of the T−Nb2O5, the higher the rate performance. Therefore, to find the balance between the high rate performance and the initial lithium storage amount, the nitride degree should be strictly controlled.

Rapid Growth of Niobium Oxide Nanowires by Joule Resistive Heating

Joule heating of niobium (Nb) metal wires by running a high electric current density through them has been used to grow Nb2O5 nanowires. The formation of a micrometric oxide layer on the Nb wires has also been observed. The size and density of the nanowires are related to the current values applied, as well as the thickness of the oxide layer formed. Characterization of both nanowires and oxide layer has been performed using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis, and micro-Raman spectroscopy. It has been observed that this method allows the growth of Nb2O5 nanowires in times as short as tens of seconds.

One-pot synthesis of Ru/Nb2O5@Nb2C ternary photocatalysts for water splitting by harnessing hydrothermal redox reactions

MXenes, 2D transition metal carbides/nitrides, have been demonstrated as promising platform for fabricating novel composites with interesting photo-/electrochemical properties. It is desirable to gain insights into the reactivity of MXenes, enabling the controllable transformation of MXenes. Here, a one-pot hydrothermal synthesis method of MXene-based photocatalyst is validated by harnessing the reducibility of Nb2CTx MXene. The origin of reducibility of Nb2CTx during the hydrothermal oxidation process was demonstrated as the active hydrogen produced from the water splitting in the presence of Nb2CTx, which reduced Ru3+ in situ to Ru nanoparticles on Nb2O5 nanowires derived from Nb2CTx. Compared with the traditional photo-deposition method, the chemical valance of the noble metal Ru/Pt obtained by the one-pot synthesis method was closer to the metal state, which reduced the charge transfer resistance by 82.5%. It led to the photocatalytic hydrogen production of 10.11 mmol·h−1·g−1 with 41.25% apparent quantum yield at 313 nm.

Architecturing aligned orthorhombic Nb2O5 nanowires toward sodium-ion hybrid capacitor and Lithium–Sulfur battery applications

In recent years, orthorhombic Nb2O5 (T-Nb2O5) has been considered as a promising anode material for sodium-ion hybrid capacitors (SICs) due to its fast ion storage properties. Moreover, the T-Nb2O5 has a strong adsorption effect with sulfur species, which shows merits for efficient management of polysulfides in lithium–sulfur (Li–S) batteries. Herein, we in target prepared T-Nb2O5 nanowires (T-Nb2O5 NWs) and systematically analyzed the electrochemical performances with regards to SICs and Li–S batteries. The resulting T-Nb2O5 NWs//activated carbon SICs delivered a high energy density (106.2 Wh kg−1) and power density (4976 W kg−1). Thus-derived flexible SICs manifested excellent performances upon deformation, which was applicable for fast-charging wearable electronic sensors. Meanwhile, Li–S batteries incorporating T-Nb2O5/graphene/sulfur cathode offered a discharge capacity of 1300 and 917.1 mAh g−1 at 0.2 and 1C, respectively.

Interface structures in Al-Nb2O5 nanocomposites processed by high-pressure torsion at room temperature

Extremely thin Nb2O5 nanowires and Al powder were successfully consolidated at room temperature by using high-pressure torsion (HPT), producing a novel metal matrix nanocomposite with exceptional mechanical properties. It is shown that minor additions of Nb2O5 increase sharply the hardness of commercially pure Al. For instance, hardness of over 180 Hv was developed at the edge of samples with 10% nanowires and processed through 10 turns of HPT. This is markedly higher than any other value reported for pure aluminum matrix composites having this level of reinforcement phase. A detailed characterization of the interface structure using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) revealed a pronounced grain refinement of the Al matrix at the nanoscale and the occurrence of the aluminothermic reduction of the part of Nb2O5. The latter led to: (i) the formation of Al2O3 nanolayer at the Al/Nb2O5 interface and (ii) the nanosegregation of metallic Nb (with few atomic layers) along grain boundaries and dislocations. The pronounced increase in hardness is attributed to the formation of this interface nanostructure.

Efficient synthesis of niobium pentoxide nanowires and application in ethanolysis of furfuryl alcohol.

Nb2O5 nanowires with high specific surface area and crystallinity were prepared by using ammonium oxalate and an acetic acid solvent system. The nanomaterial was applied in ethanolysis of furfuryl alcohol (FA), and the yield of the product, 2-(ethoxymethyl)furan (FEE), achieved was up to 79.6%. Compared to mesoporous Nb2O5 materials and other porous materials, the residence time of FEE on the surface of the catalyst is shorter, and the yield of ethyl levulinate (EL) is lower. Furthermore, a high temperature calcination treatment can change the acid sites and acidity type distribution on the nanowire surface. By XRD, NH3-TPD, IR, and TG-DTA determination methods, it was found that the weak and medium-strong acid sites on the surface of Nb2O5 nanowires were reduced after a 300 °C treatment, and the amount of strong acid was relatively higher. According to the catalytic performance test data and acidity determination, it was concluded that more weak acid and medium-strong acid sites improve the conversion of furfuryl alcohol to FEE, and the strong acid sites promote further conversion of FEE to EL.

Narrow-bandgap Nb2O5 nanowires with enclosed pores as high-performance photocatalyst

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

Highly bonded T-Nb2O5/rGO nanohybrids for 4 V quasi-solid state asymmetric supercapacitors with improved electrochemical performance

T-Nb2O5/reduced graphene oxide nanohybrids were fabricated via the hydrothermal attachment of Nb2O5 nanowires to dispersed graphene oxide nanosheets followed by a high-temperature phase transformation. Electrochemical measurements showed that the nanohybrid anodes possessed enhanced reversible capacity and superior cycling stability compared to those of a pristine T-Nb2O5 nanowire electrode. Owing to the strong bonds between graphene nanosheets and T-Nb2O5 nanowires, the nanohybrids achieved an initial capacity of 227 mAh·g−1. Additionally, non-aqueous asymmetric supercapacitors (ASCs) were fabricated with the synthesized nanohybrids as the anode and activated carbon as the cathode. The 3 V Li-ion ASC with a LiPF6-based organic electrolyte achieved an energy density of 45.1 Wh·kg−1 at 715.2 W·kg−1. The working potential could be further enhanced to 4 V when a polymer ionogel separator (PVDF-HFP/LiTFSI/EMIMBF4) and formulated ionic liquid electrolyte were employed. Such a quasi-solid state ASC could operate at 60 °C and delivered a maximum energy density of 70 Wh·kg−1 at 1 kW·kg−1.

Morphology Control of Energy-Gap-Engineered Nb2O5 Nanowires and the Regioselective Growth of CdS for Efficient Carrier Transfer Across an Oxide-Sulphide Nanointerface

Semiconductor nanowires with both nano- and micrometre dimensions have been used as effective materials for artificial photosynthesis; however, a single synthesis approach to provide rational control over the macroscopic morphology, which can allow for the high-throughput screening of photocatalytic performance, and carrier transfer between oxide and sulphide nanostructures has been poorly known. Our recent findings indicate that a single parameter, Nb foil thickness, in a vapor-phase synthesis method can alter the macroscopic morphology of resulting Nb2O5 nanowires. Thick Nb foil results in a free-standing Nb2O5 film, whereas a thinner foil leads to fragmentation to give a powder. During the synthesis process, a Rh dopant was provided through metal-organic chemical vapor deposition to reduce the Nb2O5 energy gap. Upon irradiation with visible light (λ > 440 nm), the free-standing nanowire film [Nb2O5:Rh-NW(F)] showed photoanodic current with a Faradaic efficiency of 99% for O2 evolution. Under identical irradiation conditions, the powdered counterpart [Nb2O5:Rh-NW(P)] showed activity for O2 evolution in the presence of an electron acceptor. The poor water-reduction ability was greatly enhanced by the Au-catalysed vapor-liquid-solid (VLS) growth of H2-evolving CdS onto the reduction sites of Nb2O5:Rh-NW(P) [Au/CdS/Nb2O5:Rh-NW(P)].

Nb2O5 nanowires in-situ grown on carbon fiber: A high-efficiency material for the photocatalytic reduction of Cr(VI)

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 14hr. The maximal Cr(VI) adsorption capacity of the Nb2O5 nanowire/CF sample was 115mg/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 1hr 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.

Flexible Nb2O5 nanowires/graphene film electrode for high-performance hybrid Li-ion supercapacitors

Abstract The hybrid Li-ion electrochemical supercapacitor (Li-HSC) combining the battery-like anode with capacitive cathode is a promising energy storage device boasting large energy and power densities. Orthorhombic Nb2O5 is a good anode material in Li-HSCs because of its large pseudocapacitive Li-ion intercalation capacity. Herein, we report a high-performance, binder-free and flexible anode consisting of long Nb2O5 nanowires and graphene (L-Nb2O5 NWs/rGO). The paper-like L-Nb2O5 NWs/rGO film electrode has a large mass loading of Nb2O5 of 93.5 wt% as well as short solid-state ion diffusion length, and enhanced conductivity (5.1 S cm−1). The hybrid L-Nb2O5 NWs/rGO paper electrode shows a high reversible specific capacity of 160 mA h g−1 at a current density of 0.2 A g−1, superior rate capability with capacitance retention of 60% when the current density increases from 0.2 to 5 A g−1, as well as excellent cycle stability. The Li-HSC device based on the L-Nb2O5/rGO anode and the cathode of biomass-derived carbon nanosheets delivers an energy density of 106 Wh kg−1 at 580 W kg−1 and 32 Wh kg−1 at a large power density of 14 kW kg−1. Moreover, the Li-HSC device exhibits excellent cycling performance without obvious capacitance decay after 1000 cycles.

Application of Nb2O5nanowire supported Pd nanoparticles in reduction of nitro-aromatic compounds as efficient and stable catalysts

A facile soft chemistry route was described to prepare a composite material of Nb2O5 nanowires modified with Pd nanoparticles having an average diameter of 7.9 nm. The Pd/w-Nb2O5 catalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), Brunauer–Emmett–Teller (BET) and X-ray photoelectron spectroscopy (XPS) techniques. In comparison with Pd/s-Nb2O5 and Pd/Al2O3, the Pd/w-Nb2O5 had a more substantial catalysis effect on the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) under ambient conditions. The results showed that the conversion rate of 4-NP (20 mg L−1, 100 mL) was about 98.3% after 4 min using 10 mg of the catalyst, Moreover, after the catalyst had been reused 10 times, the conversion rate still remained 85.3%. The significant enhancement in the catalysis activity can be ascribed to acidity and morphology of the catalyst support Nb2O5.

Synthesis of niobium oxide nanowires by polyethylenimine as template at varying pH values

Nb2O5 nanowires were synthesized by a hydrothermal method using polyethylenimine as a soft template. The results indicated that the pH value greatly affected the Nb2O5 nanowires.

Diameter-dependent photocatalytic performance of niobium pentoxide nanowires

Thermal reactions of a niobium oxo-oxalate complex, (NH4)3[NbO(Ox)3]·H2O, with ternary amines having more than two methylene chain units as structure directing solvents led to self-assemblies suitable for one dimensional growth to afford amorphous niobium oxide nanowires whose diameters depended on methylene chain lengths in the amines. These nanowires were crystallized at 773 K to obtain the TT phase of Nb2O5 whilst maintaining the same structure as before calcination. There was almost no difference in crystallinities, BET surface areas, and growth directions among the Nb2O5 nanowires. PtCl6(2-) was reduced by photogenerated electrons in the conduction band of the Nb2O5 nanowires following UV light irradiation (λ > 300 nm) in the presence of an electron donor. Metallic Pt nanoparticles were selectively deposited on a short axis plane of the nanowires prepared with tridodecylamine, whereas the others had the Pt nanoparticles throughout the surfaces. This indicated that photogenerated electrons moved along the nanowire growth direction associated with transfer of holes to the nanowire sidewall. The anisotropic carrier transport afforded the highest activity for photocatalytic H2 evolution reactions under UV light irradiation (λ > 300 nm).

Nb2O5 nanowire photoanode sensitized by a composition-tuned CdSxSe1−x shell

Nb2O5 nanowires (NWs) were grown by the thermal oxidation of Nb foils. The thermal chemical vapor transport of CdS/CdSe powders produces Nb2O5–CdSxSe1−x core–shell NWs with complete composition tuning. In the alloy composition, CdSe-like and CdS-like phases exist in the outer and inner regions of the shell, respectively, forming unique multi-shell structures. As x increases, the thickness of the CdSe-like outer shell decreases, while that of the CdS-like inner shell increases. We fabricated photoelectrochemical (PEC) cells using the as-grown Nb2O5–CdSxSe1−x NWs and measured their photocurrents and hydrogen generation rates under AM 1.5G irradiation. The PEC cells showed excellent photoconversion efficiency, which is comparable to that of TiO2–CdSxSe1−x NWs. It indicates that the present Nb2O5 NW promises an excellent photoanode of solar cell devices. The multi-shell structures increase the PEC performance by producing novel band alignment for efficient electron–hole separation following enhanced visible-range photon absorption.

Fast and highly-sensitive hydrogen sensing of Nb2O5 nanowires at room temperature

The single-crystalline Nb2O5 nanowires with tetragonal phase structures were synthesized through thermal oxidation process. The Nb2O5 nanowires were grown along [001] orientation and formed a layer of free-standing nanowire membrane. A pair of platinum electrodes was deposited on the surface of the nanowire layer to fabricate a Pt/Nb2O5 nanowire hydrogen sensor. The Pt/Nb2O5 nanowire hydrogen sensor exhibited fast, highly-sensitive and selective hydrogen response at room temperature, which may be attributed to the hydrogen induced interface and surface effects together with the high specific surface area of the Nb2O5 nanowires.

Synthesis of metal oxide nanomaterials by plasma treatment – A SEM investigation of Nb2O5 nanowires

Plasma techniques for rapid synthesis of large quantities of metal oxide nanoparticles are presented. Suitable metal foils are exposed to cold oxygen plasma with a large density of neutral oxygen atoms of the order of 1021 m−3 and the ion density of the order of 1016 m−3. Depending on the flux of neutral atoms onto the sample surface as well as other plasma parameters, such as the positive ion kinetic energy and the sample temperature, different types of nanoparticles are synthesized, such as nanowires, nanocones and nanobelts. Nanowires are synthesized at extremely large flux of neutral oxygen atoms on the sample surface, often exceeding 1 × 1024 m−2 s−1. Other features are synthesized at moderate flux of atoms of the order of 1023 m−2 s−1. The phenomenon is explained by rapid nucleation of metal oxide on the sample surface followed by a one -dimensional growth of the nanowires due to balanced supply of neutral atoms and ions to the surface. Controlling the plasma parameters, a fair control on the nanostructure size as well as shape is achieved. The technique allows for synthesis of nanowires at the rate of almost 1 g/h, and therefore assures huge quantities of this material. The synthesis of niobium oxide nanowires is studied to some details by scanning electron microscopy.

Probing the photoresponse of individualNb2O5 nanowires with global and localized laser beam irradiation

Photoresponse of isolated Nb2O5 nanowires (NW) padded with platinum (Pt) at both ends were studied with globalirradiation by a laser beam and localized irradiation using a focused laserbeam. Global laser irradiation on individual NW in ambient and vacuumconditions revealed photocurrent contributions with different time characteristics(rapid and slowly varying components) arising from defect level excitations,thermal heating effect, surface states and NW–Pt contacts. With a spot size of < 1 µm, localized irradiation highlighted the fact that the measured photocurrent in thissingle NW device (with and without applied bias) depended sensitively on thephotoresponse at the NW–Pt contacts. At applied bias, unidirectional photocurrent wasobserved and higher photocurrent was achieved with localized laser irradiation atreverse-biased NW–Pt contacts. At zero bias, the opposite polarity of photocurrents wasdetected when the two NW–Pt contacts were subjected to focused laser beamirradiation. A reduced Schottky barrier/width resulting from an increase in chargecarriers and thermoelectric effects arising from the localized thermal heating due tofocused laser beam irradiation were proposed as the mechanisms dictating thephotocurrent at the NW–Pt interface. Comparison of photocurrents generatedupon global and localized laser irradiation showed that the main contribution tothe photocurrent was largely due to the photoresponse of the NW–Pt contacts.

Carbon coated Nb2O5 nanowires as enhanced field emitters

Nb2O5 nanowires with controllable carbon coating thickness were prepared by plasma enhanced chemical vapour deposition. These hybrid nanowires were found to be efficient field emitters where the turn-on and threshold fields decreased with increasing carbon coating thickness. Notably, high current density was obtained from these hybrid nanowires (a maximum of ∼59mA/cm2 at 11V/μm) which was an order of magnitude higher than pristine Nb2O5 nanowires. The emission sites were distributed uniformly and current stability tests showed a stable emission current density with<10% current fluctuation for a period of 400min.

Fabrication of Nb2O5 nanotrees with controlled branching degrees

Tree-like Nb2O5 nanostructures (nanotrees) can be fabricated in a highly controlled way, which involves the secondary nucleation of Nb2O5 nanowires under hydrothermal conditions. This bottom-up method can effectively control the branching degrees of these nanotrees by manipulating reaction parameters. XRD, SEM and TEM have been used to analyze current products, and the samples have continuous crystalline phases throughout the complex tree-like structures. UV–Vis adsorption spectra have also been obtained, indicating that the optical property of these nanotrees can be influenced by their branching degrees. The controlled growth method herein has good potential as a generic means of forming complex branching structures, and may also offer opportunities for important applications such as sensors and photocatalysts.