Study of degradation of Na2Тi3O7-based electrode during cycling

Journal of Solid State Electrochemistry - The degradation of electrodes based on sodium titanate (Na2Ti3O7) was studied using the methods of galvanostatic cycling, cyclic voltammetry, Raman...     

Heat-treatment induced evolution of the morphology and microstructure of zirconia prepared from chloride solutions during

The properties of hydrous zirconia prepared from ZrOCl₂ solutions were studied as functions of precipitation pH and subsequent heat treatment. Precipitation at pH ≤ 6 yields hydrous zirconia containing excess sorbate anions (Cl^?), and at pH ≥ 7, ammonium ions. This difference considerably affects the thermolysis and morphology of the resulting samples. The samples prepared at pH ≥ 7 have far better developed surfaces. The morphological and structural evolution of hydrous zirconia samples during heat treatment is described. The involved processes are interpreted. At initial stages, the major process is the formation of metastable tetragonal ZrO₂, which transforms to the monoclinic phase during subsequent heating.     

Hydrogen Evolution on a Mercury Electrode: The Effect of a Condensed Adsorption Layer

The electroreduction of hydrogen on a dropping mercury electrode with and without condensed adsorption layers (CAL) of organic compounds is studied by methods of classical polarography and laser photoemission. An analysis of effects CAL has on some reactions reveals that the CAL influence on the first-electron transfer and on reactions involving intermediates can retard or even completely block the process. The most profound changes occur in the processes that involve a proton donor. Possible reasons for different effects of CAL on the electron transfer processes are discussed.     

Determining Sodium Kryptate Adsorption Parameters on a Mercury Electrode in 1 M Na2SO4

The adsorption of a complex of sodium cations with a macrocyclic ligand (Kryptofix^R 222, composition C₁₈H₃₆N₂O₆) as a function of its concentration in 1 M Na₂SO₄ is studied by measuring the differential capacitance on a stationary Hg drop. Adsorption parameters of sodium kryptate are found using a regression analysis method and various versions of a model of two parallel capacitors complemented with the Frumkin adsorption isotherm. The differential capacitance curves, calculated on the basis of these, are compared with experimental data. The difference in model versions that most adequately describe the adsorption data, established for systems in 0.1 and 1 M Na₂SO₄, is explained by the influence of the supporting electrolyte on the adsorption layer structure. Conclusions are made on the absence in the system under study of the salting-out from the bulk solution and on a change in the properties of an adsorption layer of sodium kryptate in the region of potentials of the anodic adsorption–desorption peak following expansion of the adsorption region.     

Effects of carbon coating from sucrose and PVDF on electrochemical performance of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C composites in different potential ranges

The carbon coated nanoflower-like Li₄Ti₅O₁₂/C composites were prepared via hydrothermal method followed by surface modification using sucrose or polyvinylidene fluoride (PVDF) as carbon sources. X-ray diffraction, SEM, TEM, Raman spectroscopy, TGA, and the electrochemical measurements were used for the materials characterization. Such modification leads to the formation of a high-conductive carbon coating. In the case of polyvinylidene fluoride use, fluorination of Li₄Ti₅O₁₂ surface takes place also. As a result, electrochemical performance of the obtained composites is improved. In the potential range of 1–3 V, Li₄Ti₅O₁₂, Li₄Ti₅O₁₂/C_PVDF, and Li₄Ti₅O₁₂/C_sucrose exhibit, respectively, the discharge capacities of 142.5, 154.3, and 170.4 mAh/g at a current of 20 mA/g and 57.2, 82.1, and 89.3mAh/g at a current of 3200 mA/g. When cycled in a potential range of 0.01–3 V, the discharge capacity of Li₄Ti₅O₁₂/C_PVDF increases up to 252 mAh/g at 20 mA/g.     

Effect of Precipitation pH and Heat Treatment on the Properties of Hydrous Zirconium Dioxide

The effect of the precipitation pH and subsequent heat treatment is studied on the properties of hydrous zirconium dioxide precipitated by ammonia from nitrate solutions. Precipitation at pH ≤ 6 generates hydrous zirconium dioxide, which contains excess sorbate nitrate ions; the product precipitated at pH ≥ 7 contains excess ammonium ions. This distinction considerably affects the course of thermolysis and the morphology of products. The exotherm associated with the formation of the crystal structure of zirconia becomes more pronounced with rising precipitation pH. In addition, the samples prepared at pH ≥ 7 have a more developed surface. The morphologic and microstructural evolution of hydrous zirconium dioxide samples during thermolysis is described.     

Synthesis and characterization of MF-4SK + SiO<Subscript>2</Subscript> hybrid membranes modified with tungstophosphoric heteropolyacid

Composites based on MF-4K perfluorinated cation-exchange membranes doped with hydrous silica nanoparticles, which were precipitated under various conditions, and with tungstophosphoric heteropolyacid nanoparticles were synthesized. The proton conductivity of the composites was studied as a function of temperature and relative ambient humidity. As a result of modification, the water content and ion conductivity of the membranes in low humidities increase by 2.5 orders of magnitude compared to unmodified MF-4SK membranes and the material is rendered less water-dependent.     

Method for determining rate constants of processes in atoms and molecules

A variant method is proposed for determination of rate constants of elementary processes occurring within a plasma, including irradiation of the plasma by resonant radiation. In the proposed variant the radiant power is varied during experiment, but remains less than the value which causes saturation of fluorescence. It is shown that this method permits simultaneous determination of several constants. The technique is demonstrated for a C₂ molecule. The effective section for thermal excitation of the level d³_g from states (X¹ _g ⁺ + a³_u) is determined, equal to 3·10^–18 cm²±80%.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 19–23, October, 1988.     

Cation mobility in modified Li1 ? xTi2 ? xNbx(PO4)3 lithium titanium NASICON phosphates

Li_{1 − x} Ti_{2 − x} Nb _x (PO₄)₃ NASICON materials are prepared and studied by X-ray diffraction, ⁷Li and ³¹P NMR spectroscopy, and impedance spectroscopy. Vacancy mobility in Li_{1 − x} Ti_{2 − x} Nb _x (PO₄)₃ is lower than interstitial lithium mobility. Nb⁵⁺ cations with low doping levels increase cation mobility in LiTi₂(PO₄)₃. Original Russian Text ? I.Yu. Pinus, I.A. Stenina, A.I. Rebrov, N.A. Zhuravlev, A.B. Yaroslavtsev, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 8, pp. 1240–1244.     

Monolayers of Supramolecular Cryptate Complexes at the Electrode/Solution Interface

Russian Journal of General Chemistry - The results of investigation of the electrochemical properties of cryptand 222 from the macropolycyclic ligands group and its complexes with cations were...