V2O5-anchored carbon nanotubes for enhanced electrochemical energy storage

Functionalized multiwalled carbon nanotubes (CNTs) are coated with a 4-5 nm thin layer of V(2)O(5) by controlled hydrolysis of vanadium alkoxide. The resulting V(2)O(5)/CNT composite has been investigated for electrochemical activity with lithium ion, and the capacity value shows both faradaic and capacitive (nonfaradaic) contributions. At high rate (1 C), the capacitive behavior dominates the intercalation as 2/3 of the overall capacity value out of 2700 C/g is capacitive, while the remaining is due to Li-ion intercalation. These numbers are in agreement with the Trasatti plots and are corroborated by X-ray photoelectron spectroscopy (XPS) studies on the V(2)O(5)/CNTs electrode, which show 85% of vanadium in the +4 oxidation state after the discharge at 1 C rate. The cumulative high-capacity value is attributed to the unique property of the nano V(2)O(5)/CNTs composite, which provides a short diffusion path for Li(+)-ions and an easy access to vanadium redox centers besides the high conductivity of CNTs. The composite architecture exhibits both high power density and high energy density, stressing the benefits of using carbon substrates to design high performance supercapacitor electrodes.     

Spectral and electrochemical properties of polyaniline-V2O5 composites of the intercalation type

We propose a new approach to obtaining composites of the intercalation type based on polyaniline and V₂O₅. We have determined the characteristics of these composites using x-ray diffraction, IR spectroscopy, and EPR. We show that the compounds obtained exhibit stable redox properties in aqueous and aprotic electrolytes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 6, pp. 361–364, November–December, 1995.We would like to express our thanks to V. G. II'in for help in carrying out the x-ray phase investigations. This work was made possible with the partial support of the International Science Foundation (grant N U6B000).     

Effect of intercalation of metal ions on the colloidal and solid properties of vanadium pentaoxide hydrate,V2O5 nH2O

The colloidal stability of V₂O₅ nH₂O was studied on the basis of the measurements of critical flocculation concentration (CFC) by metal ions, amount of ions exchanged (or intercalated), and -potential. In total, the CFC values obeyed the Schulze Hardy law and strong Hofmeister's series was found in the systems including alkaline ions. The sequence of colloidal stability of V₂O₅ nH₂O in the electrolyte solutions was related to the intercalation of metal ions in the interlayer spaces of the solid. The largest CFC value for Li⁺ (87 mmol dm^–3) was explained by smaller affinity of Li⁺ to be intercalated in V₂O₅ nH₂O as well as smaller Hamaker constant of the intercalated solid compared to the other systems.Effect of intercalation of metal ions on the crystalline properties of the materials was measured by use of XRD and electron microscope. Under highly dehydrated condition the ions whose radii are smaller than 0.1 nm are captured in the structure of V₂O₅ nH₂O without changing interlayer distances, while those larger than 0.1 nm increase the interlayer distance. In a saturated H₂O vapor interlayer distances increased with increasing charge of intercalated ions. However, when intercalated with ions carrying the same valency the interlayer distances of the sample decreased with decrease in the hydration property of ions. Hydrolyzable Cr³⁺ gave exceptionally larger interlayer distances, both in a vacuum and in H₂O vapor.     

V2O5 nanobelt-carbonized bacterial cellulose composite with enhanced electrochemical performance for aqueous supercapacitors

Journal of Solid State Electrochemistry - V2O5 nanobelt-carbonized bacterial cellulose (V2O5-CBC) nanocomposite was synthesized via a hydrothermal process in a single step. The prepared samples...     

Effects of thermal annealing on the Li(+) intercalation properties of V(2)O(5) x nH(2)O xerogel films

V(2)O(5) x nH(2)O xerogel films with n = 1.6, 0.6, and 0.3 have been prepared from the sol-gel route by reacting V(2)O(5) with H(2)O(2) followed by drying under ambient conditions and thermal annealing at 110 and 250 degrees C, respectively. After dehydration, V(2)O(5) crystallizes at 300-330 degrees C, as revealed by thermal gravimetric analysis and X-ray diffraction. Electrochemical characterization demonstrated that V(2)O(5) x 0.3H(2)O film exhibits the best Li(+) intercalation performance, with an initial capacity of 275 mAh/g and a stabilized capacity of 185 mAh/g under a high current density of 100 microA/cm(2) after 50 cycles. Under a low current density of 10 microA/cm(2), the capacity of this film can reach 390 mAh/g. Such an enhanced electrochemical property by thermal treatment is ascribed to the reduced water content, the retained interlayer spacing, and the dominant amorphous phase in the film.     

Nanocomposites with the layered structure of V2O5 · nH2O xerogel

New layered nanocomposites of V₂O₅ · nH₂O xerogels with poly(vinyl alcohol) (PVA), pyrocatechol (PC), and hydroquinone (HQ) were synthesized with the compositions (C₂H₃)_0.32V₂O_4.90 · nH₂O, (C₆H₄)_xV₂O_4.60 · nH₂O, and (C₆H₄)_0.17V₂O_4.94 · nH₂O and the interlayer distances d ₀₀₁ = 11.73, 12.85, and 15.28 ± 0.05 Å, respectively. IR and Raman spectroscopy was used to analyze which structural changes occur in the V-O layers of the xerogel upon composite formation. X-ray photoelectron spectroscopy showed V⁴⁺ and V⁵⁺ ions in the layers with binding energies lower than in V₂O₅ · nH₂O. The electrical conductivity of the nanofilms and the thermal properties of the nanopowders were studied.     

Efficient charge transfer and separation of TiO2@NiCo-LDH core-shell nanowire arrays for enhanced photoelectrochemical water-splitting

Journal of Solid State Electrochemistry - Efficient charge transfer and separation play a significant role in determining the photoelectrochemical (PEC) water-splitting performance of...     

Controllable growth of conical and cylindrical TiO2-carbon core-shell nanofiber arrays and morphologically dependent electrochemical properties

Quasi‐aligned cylindrical and conical core–shell nanofibers consisting of carbon shells and TiO₂ nanowire cores are produced in situ on Ti foils without using a foreign metallic catalyst and template. A cylindrical nanofiber has a TiO₂ nanowire core 30–50 nm in diameter and a 5–10 nm‐thick cylindrical carbon shell, while in the conical nanostructure the TiO₂ nanowire core has a diameter of 20–40 nm and the thickness of the carbon shell varies from about 200 nm at the bottom to about 5 nm at the tip. Electrochemical analysis reveals well‐defined redox peaks of the [Fe(CN)₆]^3?/4? redox couple and heterogeneous charge‐transfer rate constants of 0.010 and 0.062 cm s^?1 for the cylindrical and conical nanofibers, respectively. The coverage of exposed edge planes on the cylindrical and conical carbon shells is estimated to be 2.5 and 15.5 % respectively. The more abundant exposed edge planes on the conical nanofiber decrease the overpotential and increase the voltammetric resolution during electrochemical detection of uric acid and ascorbic acid. Our results suggest that the density of edge‐plane sites estimated from Raman scattering is not necessarily equal to the density of exposed edge‐plane sites, and only carbon electrodes with a large density of exposed edge planes or free graphene sheet ends exhibit better electrochemical performance.     

Nb2O5-carbon core-shell nanocomposite as anode material for lithium ion battery

Nb₂O₅-carbon nanocomposite is synthesized through a facile one-step hydrothermal reaction from sucrose as the carbon source, and studied as an anode material for high-performance lithium ion battery. The structural characterizations reveal that the nanocomposite possesses a core-shell structure with a thin layer of carbon shell homogeneously coated on the Nb₂O₅ nanocrystals. Such a unique structure enables the composite electrode with a long cycle life by preventing the Nb₂O₅ from volume change and pulverization during the charge-discharge process. In addition, the carbon shell efficiently improves the rate capability. Even at a current density of 500 mA·g^?1, the composite electrode still exhibits a specific capacity of ～100 mAh·g^?1. These results suggest the possibility to utilize the Nb₂O₅-carbon core-shell composite as a high performance anode material in the practical application of lithium ion battery.     

Vertically aligned mixed V2O5-TiO2 nanotube arrays for supercapacitor applications

Highly ordered mixed V(2)O(5)-TiO(2) nanotubes can be formed by self-organizing anodization of Ti-V alloys with vanadium content of up to 18 at%. In the resulting oxide nanotube arrays, the vanadium is electrochemically switchable leading to a specific capacitance that can reach up to 220 F g(-1) and an energy density of 19.56 Wh kg(-1) with perfect reversibility and long-term stability. Thus these mixed oxide nanotubes may be considered as a promising candidate for supercapacitors.     

Synthesis of In2O3@SiO2 core-shell nanoparticles with enhanced deeper energy level emissions of In2O3

In(2)O(3)@SiO(2) core-shell nanoparticles were prepared using an organic solution synthesis approach and reverse-microemulsion technique. In order to explore the availability of various silica encapsulations, a partial phase diagram for this ternary system consisting of hexane/cyclohexane (1:29 wt), surfactant (polyoxyethylene(5)nonylphenyl ether, i.e., Igepal CO-520), and aqueous solution containing ammonium hydroxide was also established. It is realized that the shell-thickness can be tuned by several parameters such as the concentration of In(2)O(3) nanocrystal suspension and the dose of the Si-precursor, tetraethyl orthosilicate. It was observed that the deeper energy level emissions of In(2)O(3) were apparently enhanced when In(2)O(3) was confined by the silica-shell in such core-shell nanoparticles. However, this enhancement could be degraded by increasing the shell-thickness.     

Sulfide@hydroxide core-shell nanostructure via a facile heating-electrodeposition method for enhanced electrochemical and photoelectrochemical water oxidation

Designing low-cost,easy-fabricated,highly stable and active electrocatalysts for oxygen evolution reaction (OER) is crucial for electrochemical (EC) and solar-d...     

Facile electrochemical synthesis of hexagonal Cu2O nanotube arrays and their application

Large-scale and highly oriented single-crystalline hexagonal Cu(2)O nanotube arrays have been successfully synthesized using a two-step solution approach, which involves the electrodeposition of oriented Cu(2)O nanorods and a subsequent dissolution technique along the c axis to form a tubular structure. Herein, NH(4)Cl was found to be an effectual additive, and it can successfully realize the dissolution process of Cu(2)O from nanorods to nanotubes. The dissolution mechanism of Cu(2)O from nanorods to nanotubes was illustrated in detail. These prepared Cu(2)O nanotube arrays were characterized by SEM, EDS, XRD, XPS, and TEM. The photoluminescence (PL) spectrum of Cu(2)O nanotube arrays was also measured, and it shows there is a greater fraction of copper or oxygen vacancies in these prepared Cu(2)O nanotubes. Finally, the applications of Cu(2)O nanotube arrays for gas sensors were investigated in this paper.     

Enhancement of intercalation properties of V2O5 film by TiO2 addition

Although it is well-known that TiO2 incorporation can greatly improve the cyclic stability of V2O5, the influences of TiO2 addition on the Li+ intercalation properties of V2O5 remain an issue of debate in literature. In this paper, we report on a systematic investigation of the preparation and intercalation properties of V2O5-TiO2 mixture films. The present work demonstrates that high Li+ intercalation rates and capacity in V2O5 films are achievable with TiO2 addition. For example, the addition of 20 mol % Ti into V2O5 polycrystalline demonstrated an approximated 100% improvement in Li+ intercalation performance as compared to single V2O5 electrodes. Such enhancement in intercalation properties of V2O5 films with TiO2 addition was attributed to changes in microstructure, crystallinity, and also a possible lattice structure and interaction force between adjacent layers in V2O5.     

Biomimetic core-shell fibril for enhanced adhesion

Fibrillar adhesive structures in nature are usually terminated by compliant plate-like elements that are critically important. We have fabricated a simple, model, core-shell fibrillar structure by coating an aluminum wire with (poly)dimethylsiloxane (PDMS). By partially etching the core metal, we obtain a compliant annular terminus. Measurements of the force required for this structure to detach from and slide against a glass substrate show that sliding is accommodated by a stick-slip mechanism and that substantial enhancement of adhesion can be achieved. A simple theoretical model, which is in good agreement with experimental data, shows that during the sticking phase the contact reduces in size and the mechanics of this process is controlled by the balance of energy release from the stretched PDMS and adhesion between it and the substrate.     

Microwave-mediated synthesis of spinel CuAl2O4 nanocomposites for enhanced electrochemical and catalytic performance

Research on Chemical Intermediates - The present study explores synthesis of spinel copper aluminate nanocomposites (CuAl2O4 NCs) for electrochemical applications and solvent-free synthesis of...     

Controllable template synthesis of Ni/Cu nanocable and Ni nanotube arrays: a one-step coelectrodeposition and electrochemical etching method

We describe a new synthetic approach to fabricate Ni/Cu nanocable arrays by co-depositing nickel and copper atoms into the pores of anodic alumina membranes and to fabricate Ni nanotube arrays by selectively etching the Cu cores from the Ni/Cu nanocable arrays. The formation of the Ni-shelled Ni/Cu nanocables is attributed to the Ni ions adsorbed on the pore walls by a chemical complexation through hydroxyl groups. By varying electrodepositon parameters in this technique, we can control the lengths of nanocables and nanotubes, the shell thickness of the nanocables, and the wall thickness and surface morphology of the nanotubes.     

Aligned Pt-diamond core-shell nanowires for electrochemical catalysis

Heavily boron-doped diamond electrode has been applied as a robust substrate for Pt based catalyst. However, by simply applying a planar electrode the effective surface area of the catalyst is limited. In this article we for the first time prepared vertically aligned Pt-diamond core-shell nanowires electrode in a convenient and scalable method (up to 6-inch wafer size). The diamond nanowires are first fabricated with reactive ion etching with metal nanoparticles as etching masks. The following Pt deposition was achieved by DC sputtering. Different amounts of Pt were coated on to the nanowires and the morphology of the core-shell wires is characterized by SEM and TEM. The catalytic oxygen/hydrogen adsorption/desorption response are characterized by cyclic voltammetry. The results show that the active Pt surface area is 23 times higher than a planar Pt electrode, and 4.3 times higher than previously reported on Pt nanoparticles on diamond by electro-deposition. Moreover, this highly active surface is stable even after 1000 full surface oxidation and reduction cycles.     

UO22+·nH2O和PuO22+·nH2O(n=2,4,5,6)密度泛函理论研究

首先用密度泛函理论(DFT)方法研究了铀酰和钚酰离子的几何与电子结构,计算结果与实验基本符合,表明DFT方法也能用于含铀和钚重原子的化合物计算.然后对铀酰和钚酰水合离子的几何构型、Mulliken集居数分布以及铀酰(钚酰)与配体水分子的结合能进行计算,计算结果表明UO22+·5H2O和PuO22+·5H2O分别为铀酰和钚酰系列水合离子中最稳定的配合物.