Cobalt Vanadium Oxide Research Articles

Oxidative C=C Cleavage of Styrenes with Supported Cobalt Vanadium Oxide

Key words cobalt catalysis - vanadium catalysis - graphene oxide - styrenes - oxidation - aldehydes

Cobalt Vanadium Oxide Supported on Reduced Graphene Oxide for the Oxidation of Styrene Derivatives to Aldehydes with Hydrogen Peroxide as Oxidant

Cobalt vanadium oxide supported on reduced graphene oxide showed excellent performance in the oxidation of styrene derivatives to the corresponding aldehydes with hydrogen peroxide as oxidant. An electron-donating group at the para-position of the aromatic ring facilitates the formation of the corresponding aldehyde. Compared with conventional methods, the newly designed heterogeneous catalytic system offers a promising prospect because of its economic applicability and environmental friendliness.

Amorphous Cobalt Vanadium Oxide as a Highly Active Electrocatalyst for Oxygen Evolution.

The water-splitting reaction provides a promising mechanism to store renewable energies in the form of hydrogen fuel. The oxidation half-reaction, the oxygen evolution reaction (OER), is a complex four-electron process that constitutes an efficiency bottleneck in water splitting. Here we report a highly active OER catalyst, cobalt vanadium oxide. The catalyst is designed on the basis of a volcano plot of metal–OH bond strength and activity. The catalyst can be synthesized by a facile hydrothermal route. The most active pure-phase material (a-CoVOx) is X-ray amorphous and provides a 10 mA cm–2 current density at an overpotential of 347 mV in 1 M KOH electrolyte when immobilized on a flat substrate. The synthetic method can also be applied to coat a high-surface-area substrate such as nickel foam. On this three-dimensional substrate, the a-CoVOx catalyst is highly active, reaching 10 mA cm–2 at 254 mV overpotential, with a Tafel slope of only 35 mV dec–1. This work demonstrates a-CoVOx as a promising electrocatalyst for oxygen evolution and validates M–OH bond strength as a practical descriptor in OER catalysis.

Production and characterization of cobalt/vanadium boride nanocomposite powder by mechanochemical method

In this research, cobalt-vanadium boride (Co-VB) nanocomposite was synthesized from powder mixture of cobalt oxide (Co3O4), vanadium oxide (V2O5), boron oxide (B2O3) and magnesium (Mg), via high energy ball milling. Regarding the value of adiabatic temperature, Co-VB nanocomposite has a potential to be the result of an induced self-sustaining reaction. The produced composite powder at various milling times was evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). After milling for 15 min, an ignition occurred in the milling vial and, according to XRD, Co, VB, MgO, VO2 and Mg3(BO3)2 phases were generated. Findings showed that with increasing the time of milling to 30 min, the Mg3(BO3)2 unwanted phase was decomposed, the remaining vanadium oxide was reduced and the final reaction fully occurred. Regarding to XRD results and the X-ray mapping analysis, MgO which was the byproduct of the system, was completely removed from the produced powder by dissolving in hydrochloric acid 9%. Finally, TEM image also confirmed that the composite powder had a grain size of 30 nm after the leaching process.

A Mesoporous High-Performance Supercapacitor Electrode Based on Polypyrrole Wrapped Iron Oxide Decorated Nanostructured Cobalt Vanadium Oxide Hydrate with Enhanced Electrochemical Capacitance

Here, we demonstrate synthesis of grass-like cobalt vanadium oxide hydrate (CVO) nanocanes arrays followed by decoration of CVO by iron oxide nanospheres (FeO@CVO) using iron nitrate and CVO through a cost-effective hydrothermal method. Finally, a high-performance robust mesoporous hybrid composite electrode (PPy/FeO@CVO) was fabricated through wrapping up of polypyrrole (PPy) over FeO@CVO using low-temperature in-situ oxidative polymerization of pyrrole. Electrochemical studies of PPy/FeO@CVO with 1 M KOH reveals highest specific capacitance of ∼1202 F/g with exceptionally high cyclic stability at 1 A/g in a three-electrode configuration. Furthermore, a two-electrode based asymmetric supercapacitor using PPy/FeO@CVO as positive and graphene nanoplates (GNP) as negative electrodes and KOH-soaked paper as a separator reveals an outstanding energy density of 38.2 Wh/kg (power density 700 W/kg at 1 A/g) with amazing cyclic stability (95% capacitance retention after 5000 cycles), suggesting great prospective ...

Homogeneous and Heterogeneous Anion Sensing by a Molecular Cobalt-Vanadium Oxide.

Spectroscopic anion sensing is a vital non-invasive tool in chemistry and biology. Here, a molecular cobalt-vanadium-oxide cluster was shown to be capable of selectively binding and detecting various mono-anions in solution and immobilized on a solid support. The cluster anion [Co(X)V4 O12 ]3- (X=mono-anion, for example, halide, pseudohalide, carboxylate, etc.) was formed spontaneously upon anion addition by self-assembly in solution. The cluster showed distinct spectral changes upon anion binding that could be followed spectroscopically and visually owing to a significant change of the solution color. DFT computations showed that the anion binding observed experimentally was correlated to the relative cluster stabilities. Competitive-binding studies showed that selective anion binding was possible from a mixture of anions. Immobilization of the anion sensor on silica strips provided access to single-use dip-stick sensors for the facile detection of anions in solution. The system presented enables the development of homogeneous or heterogeneous molecular anion sensors with possible applications in chemistry, bio-medical scenarios, and under harsh environmental conditions.

Polymer-Assisted Solution Method to Metal Oxide Network Structures for Lithium-Ion Battery Electrodes

Rechargeable lithium-ion batteries have been extensively investigated for their promising application in hybrid electric vehicles because of their high energy and power densities and long cycle lifetime. A great effort has been made to synthesize a variety of electrode materials to improve the energy density, rate capability, and cycling stability. Nanostructured materials have received much attention as electrodes due to the short transport lengths for both electrons and lithium ions, higher electrode-electrode contact area, and better accommodation of the strain of lithium insertion/extraction. Here we report a facile polymer-assisted chemical solution method to grow cobalt oxide, nickel oxide, bismuth oxide, and vanadium oxide network structures for lithium-ion battery anodes and cathodes. The carbon left from the decomposition of polymers is an effective binder between metal oxides and the nickel foam. As compared to the metal oxide powders prepared in a conventional way by using polymer binder and carbon black, these one-step direct growth electrodes showed much better lithium storage properties with high capacities, stable cyclability, and rate capability. For example cobalt oxides on nickel foam gave a capacity of 900 mAh/g at a current density of 1 A/g and 600 mAh/g at 4 A/g. The good performances of these electrodes could be attributed to intimate contact between the active material and the nickel foam, the porosity of the current collector, and the network structure of the active materials.

Composite electrode material based on cobalt-vanadium oxide CoV3O8 and oxide compounds of molybdenum

Specific features of synthesis and capacity for reversible electrochemical intercalation of lithium were studied for the electrode composite material on a carbon support, based on cobalt-vanadium oxide and oxide molybdenum compounds deposited from aqueous solutions of their salts under polarization with an alternating asymmetric current.

Quasi-one-dimensional nanostructured cobalt (Co) intercalated vanadium oxide (V2O5): Peroxovanadate sol gel synthesis and structural study

Nanostructured cobalt vanadium oxide (V2O5) xerogels spread onto crystalline Si substrates were synthesized via peroxovanadate sol gel route. The resulting products were characterized by distinct experimental techniques. The surface morphology and the nanostructure of xerogels correlate with Co concentration. The decrease of the structural coherence length is followed by the formation of a loose network of nanopores when the concentration of intercalated species was greater than 4at% of Co. The efficiency of the synthesis route also drops with the increase of Co concentration. The interaction between the Co(OH2)62+ cations and the (H2V10O28)4− anions during the synthesis was suggested as a possible explanation for the incomplete condensation of the V2O5 gel. Finally the experimental results points for the intercalation of Co between the bilayers of the V2O5. In this scenario two possible preferential occupation sites for the metallic atoms in the framework of the xerogel were proposed.

Cobalt vanadium oxide thin nanoplates: primary electrochemical capacitor application.

Co3V2O8 thin nanoplates are firstly described as a kind of electrode material for supercapacitors. More importantly, from electrochemical measurements, the obtained Co3V2O8 nanoplate electrode shows a good specific capacitance (0.5 A g−1, 739 F g−1) and cycling stability (704 F g−1 retained after 2000 cycles). This study essentially offers a new kind of metal vanadium oxides as electrochemical active material for the development of supercapacitors.

The anion-binding polyanion: a molecular cobalt vanadium oxide with anion-sensitive visual response

An anionic molecular cobalt vanadium oxide cluster, (n-Bu4N)3[Co(AcO)V4O12] and its use as anion binding site is reported. Cluster formation is controlled by an anion-dependent dynamic solution equilibrium. Reversible anion binding in solution leads to significant spectral changes, allowing the ratiometric optical detection of the anion concentration in situ, even under harsh thermal conditions (T = 90 °C). Comparative studies showed that the spectral response is dependent on the type of anion so that carboxylates, weakly coordinating anions and halides can be distinguished.

Synthesis and Crystal Structure of the Mixed Metal Coordination Framework [Co2(H2O)2(pyrazine)V4O12](H2O)2

The coordination framework [Co2(H2O)2(pyrazine)V4O12](H2O)2 (1) was synthesized via hydrothermal synthesis using cobalt nitrate, vanadium oxide, and pyrazine. Compound 1 crystallizes in the monoclinic space group P21/n (a = 7.172(3) A, b = 9.907(4) A, c = 12.211(4) A, and β = 105.301(7)°) and contains a rare V4O12 trigonal bipyramidal double chain. [Co2(H2O)2(pyrazine)V4O12](H2O)2 (1) was synthesized hydrothermally from a vanadium oxide precursor, forming chains of edge-sharing distorted vanadium trigonal bipyriamids.

Synthesis of Co 3(OH) 2V 2O 7·1.7H 2O nanosheets and its application in lithium ion batteries

Cobalt vanadium oxide hydroxide hydrate (Co 3(OH) 2V 2O 7·nH 2O) nanosheets are successfully synthesized by a simple hydrothermal method. The composition of Co 3(OH) 2V 2O 7·nH 2O is studied by thermal gravity (TG) analysis in N 2 atmosphere and subsequent X-ray powder diffraction (XRD) characterization of the sample obtained via annealing Co 3(OH) 2V 2O 7·nH 2O nanosheets in N 2 atmosphere at 800 °C for 6 h. The results indicate that there are 1.7 water molecules in a Co 3(OH) 2V 2O 7·nH 2O molecular formula. Electrochemical properties of Co 3(OH) 2V 2O 7·1.7H 2O nanosheets as negative electrode of lithium ion batteries are studied by conventional charge/discharge test, which show an initial capacity of 730 mAh g −1 with steady plateau near 0.9 V at a current density of 0.05 mA cm −2.

Carbothermal reduction of metal-oxide powders by synthetic pitch to carbide and nitride ceramics

The carbothermal reduction potential of mesophase synthetic pitch was investigated. Powders of cobalt oxide, iron oxide, zirconium oxide, manganese oxide, silicon oxide, vanadium oxide, tantalum oxide, tungsten oxide, chromium oxide, and titanium oxide were mixed with pitch and pyrolyzed at a variety of temperatures up to 1500 °C in nitrogen, 5% hydrogen balance argon, and anhydrous ammonia. Pitch was found superior to graphite (and both were superior to charcoal) in carbothermal reactivity by forming carbides and nitrides more completely and at lower temperatures and, in some instances, where no conversion was observed for graphite. It is hypothesized that wetting of the liquid pitch at high temperatures before graphitization leads to better surface contact, and thus, increased kinetics of the carbothermal reduction.

Lithium Intercalation Behavior of Cobalt Vanadium Oxide CoV3O8 Studied on the Basis of Rietveld Analysis

The lithium intercalation property of cobalt vanadium oxide having tunnel space along the -axis of the crystal structure was investigated. Lithiated samples, , were structurally analyzed by the Rietveld analysis. From the linear variation in the lattice parameters during lithiation, it was found that lithium was intercalated in the host compound for in . For , no change in the lattice parameters was observed and an amorphous substance was formed. The variation in the interatomic distances between oxide ions indicated that O(5) was at the apex of polyhedra. On the basis of the cavity size and molar ratio , the site in the tunnel space was found to be suitable for lithium intercalation.

Structural Change Induced by Electrochemical Lithium Insertion in Cobalt Vanadium Oxide

We investigated the open-circuit potentials (OCPs) and structure of in the first discharge and charge processes. The OCPs in the discharge and charge processes traced different routes. In the discharge process, the OCPs declined slowly at and reduced more slowly at . From the change in the cell parameters, lithium was found to be intercalated in the tunnel space of at low lithium contents. Further lithium insertion induced an amorphous material and a crystalline one. The generation reaction of these substances containing lithium ions resulted in an irreversible capacity in the first cycle. Considering that the observed OCPs were distributed over a wide range of potentials in the charge process, it was probable that lithium was extracted dominantly from the newly generated amorphous substance. We concluded that the amorphous substance exhibited a reversible discharge-charge cycle performance after the second cycle.

Lithium Insertion and Extraction of Cobalt Vanadium Oxide

Lithium Insertion and Extraction of Cobalt Vanadium Oxide

Syntheses and characterization of Co2(4,4′-bipy)2(V4O12), Co(pz)(VO3)2 and Co2(2-pzc)(H2O)(VO3)3 (4,4′-bipy = 4,4′-bipyridine, pz = pyrazine, 2-pzc = 2-pyrazinecarboxylate)

By using different organic ligands, three new inorganic–organic hybrid compounds of cobalt vanadium oxide have been synthesized hydrothermally: Co2(4,4′-bipy)2(V4O12) 1, Co(pz)(VO3)22 and Co2(2-pzc)(H2O)(VO3)33, where 4,4′-bipy = 4,4′-bipyridine, pz = pyrazine, 2-pzc = 2-pyrazinecarboxylate. Crystal data: 1, triclinic, space group P-, a = 8.164(2), b = 8.587(2), c = 10.162(2) Å, α = 87.04(3), β = 75.72(3), γ = 75.02(3)°; 2, orthorhombic, space group Pnna, a = 10.2793(8), b = 11.5639(9), c = 7.4822(6) Å; 3, orthorhombic, space group Pna21, a = 15.253(1), b = 8.2554(7), c = 10.6784(9) Å. Compound 1 contains {CoV2O6} layers cross-linked by 4,4′-bipyridine ligands. Compounds 2 and 3 are three-dimensional frameworks containing both infinite metavanadate chains and either {Co(pz)} or {Co2(2-pzc)} chains. The magnetic properties of 1–3 are reported.