Catalytic Activity of WO<Subscript>3</Subscript> and MoO<Subscript>3</Subscript> with Pt and Pd Additives in Oxidation of Hydrogen

We have shown that WO₃ and MoO₃ with Pt or Pd additives exhibit high catalytic activity in the reaction of H₂ oxidation. In the temperature range 313 K to 353 K, we have studied the kinetic behavior of the reaction on 0.1 mass % Pt(Pd)/WO₃ and Pt(Pd)/MoO₃ samples. We have established that the kinetics of H₂ oxidation on these catalysts correspond to an Eley - Rideal mechanism. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 313–316, September–October, 2005.     

The effect of nanolayer AlF<Subscript>3</Subscript> coating on LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cycle life in high temperature for lithium secondary batteries

The surface of the spinel LiMn₂O₄ was coated with AlF₃ by a chemical process to improve its electrochemical performance at high temperatures. The morphology and structure of the original and AlF₃-coated LiMn₂O₄ samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM). All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. It was found that the surfaces of the original LiMn₂O₄ samples were covered with a nanolayer AlF₃ after the treatment. The charge/discharge of the materials were carried at 220 mA/g in the range of 3.0 and 4.4 V at 55°C. While the original LiMn₂O₄ showed 17.8% capacity loss in 50 cycles at 55°C, the AlF₃-coated LiMn₂O₄ (118.1 mA h/g) showed only 3.4% loss of the initial capacity (122.3 mA h/g) at 55°C. It is obvious that the improvement in cycling performance of the coated-LiMn₂O₄ electrode at 55°C is attributed to the presence of AlF₃ on the surface of LiMn₂O₄. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 817–819. The article is published in the original     

X-ray photoelectron study of the interaction of H<Subscript>2</Subscript> and H<Subscript>2</Subscript>+O<Subscript>2</Subscript> mixtures on the Pt/MoO<Subscript>3</Subscript> model catalyst

The effects of H₂ and H₂ + O₂ gas mixtures of varying composition on the state of the surface of the Pt/MoO₃ model catalyst prepared by vacuum deposition of platinum on oxidized molybdenum foil were investigated by X-ray photoelectron spectroscopy (XPS) at room temperature and a pressure of 5–150 Torr. For samples with a large Pt/Mo ratio, the XP spectrum of large platinum particles showed that the effect of hydrogen-containing mixtures on the catalyst was accompanied by the reduction of molybdenum oxide. This effect results from the activation of molecular hydrogen due to the dissociation on platinum particles and subsequent spill-over of hydrogen atoms on the support. The effect was not observed at low platinum contents in the model catalyst (i.e., for small Pt particles). It is assumed for the catalyst that the loss of its hydrogen-activating ability is a consequence of the formation of platinum hydride. Possible participation of platinum hydride as intermediate in hydrogen oxidation to H₂O₂ is discussed.     

Enhanced electrochemical performance of submicron LiCoO<Subscript>2</Subscript> synthesized by polymer pyrolysis method

Submicron LiCoO₂ was synthesized by a polymer pyrolysis method using LiOH and Co(NO₃)₂ as the precursor compounds. Experimental results demonstrated that the powders calcined at 800 °C for 12 h appear as well-crystallized, uniform submicron particles with diameter of about 200 nm. As a result, the as-prepared LiCoO₂ electrode displayed excellent electrochemical properties, with an initial discharge capacity of 145.5 mAh/g and capacity retention of 86.1% after 50 cycles when cycled at 50 mA/g between 3.5 and 4.25 V. When cycled between 3.5 and 4.5 V, the discharge capacity increased to 177.9 mAh/g with capacity retention of 85.6% after 50 cycles.     

Facile preparation and electrochemical properties of large-scale Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript> nanobelts

Large-scale Li_1+x V₃O₈ nanobelts were successfully fabricated using filter paper as deposition substrate through a simple surface sol–gel method. The nanobelts were as long as tens of micrometers with widths of 0.4–1.0 μm and thickness of 50–100 nm. The nanobelts were characterized by X-ray diffration (XRD), Fourier infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM). The formation mechanism of the nanobelts was investigated, showing that the morphology of the nanobelts is mainly determined by the calcination temperature. Electrochemical properties of the Li_1+x V₃O₈ nanobelts were characterized by charge–discharge experiments, and the results demonstrate that the Li_1+x V₃O₈ nanobelts exhibit a high discharge capacity (278 mAh g⁻¹) and excellent cycling stability.     

Li<Subscript>0.99</Subscript>Ti<Subscript>0.01</Subscript>FePO<Subscript>4</Subscript>/C composite as cathode material for lithium ion battery

Three kinds of LiFePO₄ materials, mixed with carbon (as LiFePO₄/C), doped with Ti (as Li_0.99Ti_0.01FePO₄), and treated both ways (as Li_0.99Ti_0.01FePO₄/C composite), were synthesized via ball milling by solid-state reaction method. The crystal structure and electrochemical behavior of the materials were investigated using X-ray diffraction, SEM, TEM, cyclic voltammetry, and charge/discharge cycle measurements. It was found that the electrochemical behavior of LiFePO₄ could be increased by carbon coating and Ti-doping methods. Among the materials, Li_0.99Ti_0.01FePO₄/C composite presents the best electrochemical behavior, with an initial discharge capacity of 154.5 mAh/g at a discharge rate of 0.2 C, and long charge/discharge cycle life. After 120 cycles, its capacity remains at 92% of the initial capacity. The Li_0.99Ti_0.01FePO₄/C composite developed here can be used as the cathode material for lithium ion batteries.     

Synthesis and electrochemical properties of Ca-doped LiNi<Subscript>0.8</Subscript>Co<Subscript>0.2</Subscript>O<Subscript>2</Subscript> cathode material for lithium ion battery

LiNi_0.8Co_0.2O₂ and Ca-doped LiNi_0.8Co_0.2O₂ cathode materials have been synthesized via a rheological phase reaction method. X-ray diffraction studies show that the Ca-doped material, and also the discharged electrode, maintains a hexagonal structure even when cycled in the range of 3.0–4.35 V (vs Li⁺/Li) after 100 cycles. Electrochemical tests show that Ca doping significantly improves the reversible capacity and cyclability. The improvement is attributed to the formation of defects caused by the partial occupancy of Ca²⁺ ions in lithium lattice sites, which reduce the resistance and thus improve the electrochemical properties.     

Synthesis and electrochemical properties of yttrium-doped LiMn<Subscript>0.98</Subscript>Y<Subscript>0.02</Subscript>O<Subscript>2</Subscript> for lithium secondary batteries

Yttrium-doped lithium manganese oxide (LiMn_0.98Y_0.02O₂) was prepared by ion exchange of lithium for sodium in NaMn_0.98Y_0.02O₂ precursors obtained by using rheological phase reaction method. This material had small particle size, which was composed of grain size of about 100 nm. Especially, LiMn_0.98Y_0.02O₂ delivered the initial discharge capacity of about 191 mA h g⁻¹ at room temperature when cycled between 2.0 and 4.4 V vs Li/Li⁺. Moreover, it showed an excellent cycling behavior, its specific capacity remained above 173 mA h g⁻¹ after 20 cycles, and the material did not transform into spinel structure during the electrochemical cycling according to the cyclic voltammograms and X-ray powder diffraction. The electrochemical results revealed that the doping of Y³⁺ improved the performance of LiMnO₂ considerably.     

Fabrication of a novel Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MoO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> film modified electrode and its application as an electrochemical sensor of iodate

A novel organic gel film modified electrode was simply and conveniently fabricated by casting Li_xMoO_y and polypropylene carbonate (PPC) onto the surface of a gold electrode. The cyclic voltammetry and amperometry studies demonstrated that the Li_xMoO_y film modified electrode has a high stability and a good electrocatalytic activity for the reduction of iodate. In amperometry, a good linear relationship between the steady current and the concentration of iodate was obtained in the range from 3×10^–7 to 1×10^–4 mol L^–1 with a correlation coefficient of 0.9997 and a detection limit of 1×10^–7 mol L^–1.     

Effects of particle size on the electrochemical performances of a layered double hydroxide, [Ni<Subscript>4</Subscript>Al(OH)<Subscript>10</Subscript>]NO<Subscript>3</Subscript>

In this paper, the electrochemical performances of a layered double hydroxide, [Ni₄Al(OH)₁₀]NO₃, of different particle sizes are studied. The results show that the particle size of the sample has evident effects on its discharge capacity at high current density, although a larger capacity may be observed for the bigger particles when they are discharged at lower current densities, e.g. 0.2 A g⁻¹. However, the capacity decreases more quickly than that of the sample in smaller particle size when the current density increases. For example, the discharge capacity of the smallest particle remains as high as 180 mAh·g⁻¹ even at very high current density, e.g. 4.0 A g⁻¹. The results also show that long time soaked electrodes in 7 mol l⁻¹ KOH have improved performance, especially for the hydrothermal samples. It also seems that there is an optimal size for materials, which can maintain their performance for longer time.     

Enhancement of electrochemical properties of MoO<Subscript>3</Subscript> nanobelts electrode using PEG as surfactant for lithium battery

Molybdenum trioxide (MoO₃) has attracted considerable attention due to their typical two-dimensional layered structure consisting of double layers of edge- and vertex-sharing MoO₆ octahedral being weakly held together by van der Waals bonds. These MoO₃ nanostructures and their polymer composites are currently drawing interest for the potential applications of Li batteries, supercapacitors, and other electrochemical as well as electrochromic display devices. In this paper, we report the synthesis of MoO₃ nanobelts and polyethylene glycol (PEG) surfactant MoO₃ nanobelts by hydrothermal method. Structure and morphology of the samples were investigated by X-ray diffraction, Fourier transform spectroscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The pure MoO₃ nanobelts show an initial specific capacity of 275 mAh g⁻¹, whereas the 0.5 mol% PEG surfactant MoO₃ nanobelts show 307 mAh g⁻¹ at constant current density of 30.7 mA g⁻¹ with the 1.0–3.0 V vs. Li/Li⁺ potential range. It was found that PEG surfactant MoO₃ nanobelts show not only a high initial specific capacity but also show better cyclic performance compared with that of pure MoO₃ nanobelts. The PEG surfactant MoO₃ nanobelts show stability and improvement of the specific capacity due to decreasing the length, width, and thickness of the nanobelts by surface reaction. Electrochemical impedance spectroscopy reveals that the PEG surfactant MoO₃ nanobelts exhibit low electrode resistance compared with pure MoO₃ nanobelts.     

Quantum-chemical modelling of nanotubes of titanium silicocarbides Ti<Subscript>2</Subscript>SiC,Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>, and Ti<Subscript>4</Subscript>SiC<Subscript>3</Subscript>

Atomic models are proposed for nanotubes of the titanium silicocarbides Ti₂SiC, Ti₃SiC₂, and Ti₄SiC₃, and their electronic structure and interatomic interactions are investigated by the density functional tight-binding method (DFTB) in comparison with the corresponding crystalline phases. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 88-92, March-April, 2009.     

Theoretical study on the reaction mechanism of (CH<Subscript>3</Subscript>)<Subscript>3</Subscript>CO<Superscript>.</Superscript> radical with NO

The reaction mechanism of (CH₃)₃CO^. radical with NO is theoretically investigated at the B3LYP/6-31G* level. The results show that the reaction is multi-channel in the single state and triplet state. The potential energy surfaces of reaction paths in the single state are lower than that in the triple state. The balance reaction: (CH₃)₃CONO⇔(CH₃)₃CO^.+NO, whose potential energy surface is the lowest in all the reaction paths, makes the probability of measuring (CH₃)₃CO^. radical increase. So NO may be considered as a stabilizing reagent for the (CH₃)₃CO^. radical.     

Phase relations in the CoO–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system in subsolidus area

Thermal properties of Co₂FeV₃O₁₁ have been reinvestigated. It has been proved that this compound does not exhibit polymorphism. It melts incongruently at the temperature of 770±5°C and the phase with lyonsite type structure is the solid product of this melting. Phase relations in the whole subsolidus area of the CoO–V₂O₅–Fe₂O₃ system have been determined. The solidus area projection onto the component concentration triangle plane of this system has been constructed using the DTA and XRD methods. 15 subsidiary subsystems can be distinguished in this system.     

Formation of Composites Based on CsHSO<Subscript>4</Subscript> and Cs<Subscript>5</Subscript>H<Subscript>3</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript> and Mechanism of Their Protonic Conduction

Vibrational spectra of finely divided amorphous CsHSO₄,Cs₅H₃(SO₄)₄ · H₂O, and composites based on these are measured and analyzed. An analysis of the spectra indicates the occurrence of substantial changes in the system of hydrogen bonds and in the spectral range of the sulfate group of acid sulfates in the composites. Structural dynamics of the SO₄ tetrahedrons is in full conformance with protonic conduction and the data of x-ray diffraction analyses accompanied by differential scanning calorimetry. It is shown that mobility of protons in the composites increases. A mechanism of the formation of the composites and their conduction is proposed.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 640–645.Original Russian Text Copyright © 2005 by Ponomareva, Lavrova, Burgina.     

Two color up-conversion emissions of Er<Superscript>3+</Superscript>-doped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanopowders prepared by non-aqueous sol-gel method

Er³⁺-doped Al₂O₃ nanopowders have been prepared by the non-aqueous sol-gel method using the aluminum isopropoxide as precursor, acetylacetone as a chelating agent, nitric acid as a catalyzer, and hydrated erbium nitrate as a dopant under isopropanol environment. The different phase structure, including three crystalline types of (Al, Er)₂O₃ phases, α, γ, θ, and an Er–Al–O stoichiometric compound phase, Al₁₀Er₆O₂₄, was observed for the 0.01–0.5 mol% Er³⁺-doped Al₂O₃ nanopowders at the sintering temperature of 1,000 °C. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the ²H_11/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, were detected by a 978 nm semiconductor laser diodes excitation. With increasing Er³⁺ doping concentration from 0.01 to 0.1 mol%, the intensity of the green and red emissions increased with a decrease of the intensity ratio of the green to red emission. When the Er³⁺ doping concentration rose to 5 mol%, the intensity of the green and red emissions decreased with an increase of their intensity ratio. The maximum intensity of both the green and red emissions with the minimum of intensity ratio was obtained, respectively, for the 0.1 mol% Er³⁺-doped Al₂O₃ nanopowders composed of a single α-(Al,Er)₂O₃ phase. The intensity ratio of the green emission at 523 and 545 nm increased monotonously for all Er³⁺ doping concentrations. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er³⁺-doped Al₂O₃ nanopowders.     

Phase-pure nanocrystalline Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> for a lithium-ion battery

Phase-pure nanocrystalline Li₄Ti₅O₁₂ with BET surface areas between 183 and 196 m²/g was prepared via an improved synthetic protocol from lithium ethoxide and titanium(IV) butoxide. The phase purity was proved by X-ray powder diffraction, Raman spectroscopy and cyclic voltammetry. Thin-film electrodes were prepared from two nanocrystalline samples of Li₄Ti₅O₁₂ and one microcrystalline commercial sample. Li-insertion behavior of these electrodes was related to the particle size.Presented at the 3rd International Meeting on Advanced Batteries and Accumulators, 16–20 June 2002, Brno, Czech Republic     

Dielectric and tunable properties of highly (110)-oriented (Ba<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>)TiO<Subscript>3</Subscript> thin films deposited on Pt/LaNiO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrates

Highly (110)-oriented Ba_0.65Sr_0.35TiO₃ films were deposited on Pt/LaNiO₃/SiO₂/Si substrates by a sol–gel method. It was found that the (110)-preferred Pt film was very effective for growing (110)-oriented ferroelectric films with perovskite structure. The as-grown Ba_0.65Sr_0.35TiO₃ films showed good dielectric properties with dielectric constant and loss tangent tan δ = 0.026. Excellent dielectric tunability was also achieved in the (110)-oriented films. With applying an electric field of 230 kV/cm at 100 kHz, the dielectric tunability and the figure of merit can reach up to 63.4% and 16, respectively. These results indicate that the highly (110)-oriented Ba_0.65Sr_0.35TiO₃ film is a promising candidate for the applications in microwave tunable devices.     

Enthalpy of formation of BaCe<Subscript>0.9</Subscript>In<Subscript>0.1</Subscript>O<Subscript>3−δ</Subscript>(s)

Enthalpy of formation of the perovskite-related oxide BaCe_0.9In_0.1O_2.95 has been determined at 298.15 K by solution calorimetry. Solution enthalpies of barium cerate doped with indium and mixture of BaCl₂, CeCl₃, InCl₃ in ratio 1:0.9:0.1 have been measured in 1 M HCl with 0.1 M KI. The standard formation enthalpy of BaCe_0.9In_0.1O_2.95 has been calculated as −1611.7±2.6 kJ mol⁻¹. Room-temperature stability of this compound has been assessed in terms of parent binary oxides. The formation enthalpy of barium cerate doped by indium from the mixture of binary oxides is Δ_ox H ⁰ (298.15 K)=−36.2±3.4 kJ mol⁻¹.     

Determination of the enthalpy of fusion of K<Subscript>3</Subscript>TaO<Subscript>2</Subscript>F<Subscript>4</Subscript> and KTaF<Subscript>6</Subscript>

Areas of fusion and crystallization peaks of K₃TaO₂F₄ and KTaF₆ were measured using the DSC mode of a high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities, considering the temperature dependence of the calorimeter sensitivity, values of the fusion enthalpy of K₃TaO₂F₄ at the fusion temperature of 1181 K of (43 ± 4) kJ mol⁻¹ and of KTaF₆ at the fusion temperature of 760 K of (8 ± 1) kJ mol⁻¹ were determined.