Sergei Bredikhin

Peculiarity of NO Decomposition by Electrochemical Cell with a Mixed Oxide Working Electrode

The decomposition activity was measured on nonsymmetric electrochemical cell oxide (cathode) yttria-stabilized zirconia (YSZ) (anode) by applying dc voltage lower then 3.5 V in the temperature range from 550 to 700°C It was found that covering the Pt cathode by a mixture of oxygen ionic conductor (YSZ) and electronic conductor (NiO) increased the NO decomposition even in the presence of excess oxygen. The microstructure of YSZ-NiO mixed oxide electrodes was investigated depending on the mixed oxide electrode sintering temperature. A strong correlation between the microstructure of the mixed oxide electrode and the conversion rate of NO decomposition was observed and investigated. A mechanism for the NO decomposition is proposed and discussed.

Effect of the thickness of the gas-sensitive layer on the response of solid state electrochemical CO2 sensors

Abstract This paper reports the effect of the sensitive layer thickness on the response of Nasicon based electrochemical CO 2 sensors. It was found that: (a) the cell voltage dependence on the thickness of the thin film Na 2 CO 3 auxiliary electrode is well described within the theory of Schottky barriers formation in ionic crystals; and (b) sensors with relatively thick gas-sensitive layer are more reliable in dry CO 2 atmosphere.

Pt-YSZ Cathode for Electrochemical Cells with Multilayer Functional Electrode

YSZ (X) -Pt (1-X) (YSZ, yttria-stabilized zirconia) ceramics have been studied as a cathode for electrochemical cells (electrocatalytic electrode)|(cathode)|YSZ|(anode) for selective NO decomposition. A YSZ-Pt cathode with high electronic conductivity along the cathode plane and with high oxygen ionic conductivity in the direction perpendicular to the electrocatalytic electrode through the cathode to the YSZ solid electrolyte was successfully designed. The conductivity of the YSZ-Pt cathode was investigated and correlated with the composition of the cathode using the two-dimensional percolation model. The optimum cathode composition (YSZ ≤ 50% by volume) resulted in a decrease of the cell operating voltage and a decrease in the electrical power required for NO decomposition. The electrochemical properties of a cell with a multilayer electrode for NO decomposition were investigated and correlated with the composition of the cathode. Structure evolution of the NiO-YSZ electrocatalytic electrode was studied by X-ray diffraction and correlated with the YSZ (X) -Pt (1-X) cathode composition. It was found that the highest rate of reduction of NiO into Ni in the NiO/YSZ interface regions occurred at the optimum cathode composition.

Peculiarity of O2− and Li+ electrodiffusion into lithium niobate single crystals

Abstract Congruently grown LiNbO3 single crystals show both a high oxygen and lithium ionic conductivity at temperatures above 500°C. The high oxygen ionic conductivity can be understood in terms of a certain amount of oxygen vacancies already present in congruently as-grown LiNbO3 single crystals. The electrocoloration phenomenon in LiNbO3 single crystals is due to a process where lithium ions and electrons are injected by a double charge mechanism into LiNbO3. Optical and electrical properties of electrocolored LiNbO3 crystals were investigated. The motion of stoichiometric domains (regions with different stoichiometry) through a LiNbO3 crystal from one electrode to the other is studied and described in terms of electrodiffusion of the ions and electrons.

Ionic photoconductivity of RbAg4I5 superionic crystals

A new effect of illumination on ionic conductivity and activation energy of migration of mobile Ag+ cations in RbAg4I5 superionic crystals has been detected and studied. Reversible changes in the ionic conductivity due to illumination of superionic crystals are caused by reversible changes in the structure of electronic centers caused by elastic strain around these centers. The effect of elastic deformation on the process of ionic transport and activation energy for diffusion of mobile silver cations has been studied. Photostimulated recovery of the ionic conductivity after its change due to preliminary illumination of a RbAg4I5 superionic crystal with light of wavelength λ≃430 nm has been detected. This recovery of the ionic conductivity is due to excitation of centers in complexes generated by previous illumination of tested samples.

Change of the stoichiometry and electrocoloration due to the injection of Li and O ions into lithium niobate crystals

Congruently grown LiNbO3 single crystals show both high oxygen and lithium ion conductivity at temperatures above 500 °C. The high oxygen ion conductivity can be understood in terms of a certain amount of oxygen vacancies already present in congruently grown LiNbO3 single crystals. Thermal treatment of LiNbO3 produces additional oxygen vacancies. The absorption bands introduced by this procedure are investigated. It is found that the electrons which are generated during the reduction process are homogeneously distributed among all oxygen vacancies in the LiNbO3 single crystals. The electrocoloration phenomenon in LiNbO3 single crystals is due to the process of injection of lithium ions and electrons into LiNbO3 by a double charge mechanism. Investigations of the optical and electrical properties of electrocolored LiNbO3 crystals are reported. It is shown that the absorption spectra of thermally and electrochemically reduced samples are identical and that the origin of the absorption processes has to be therefore the same in both cases. That means, additional electrons produced by the double charge injection of lithium ions and electrons are also homogeneously distributed among the oxygen vacancies. This supports our hypothesis that a certain amount of oxygen vacancies has to be present already in as-grown LiNbO3 single crystals.

Pecularity of lithium electrodiffusion into fulleride single crystals

Diffusion of lithium cations in C60 single crystals driven by an electric field has been studied. It was found that the stoichiometry of C60 single crystals can be changed with respect to lithium by injection of Li+ ions through the heterojunction Li7SiPO8|C60 and electrons through the heterojunction C60| Graphite. The double charge injection changes the stoichiometry of lithium in a C60 single crystal and increases both the lithium ionic and electronic conductivity. The electronic conductivity in LixC60 crystals is non-metallic in nature. The temperature dependence of the electronic conductivity lithium doped C60 single crystals was investigated. It was found that electrons occupied the lowest singlet exited states (LUMO) and that this leads to the appearance of an intensive EPR signal. The temperature dependence of the concentration of paramagnetic centers was investigated.

Ionic photoconductivity: new physical phenomenon in superionic crystals

Abstract A new effect of illumination on ionic conductivity and activation energy of migration of mobile Ag + cations in RbAg 4 I 5 superionic crystals has been detected and studied. Reversible changes in the structure of electronic centers caused by elastic strain around these centers. The effect of elastic deformation on the process of ionic transport and activation energy for diffusion of mobile silver cations has been studied. Photostimulated recovery of the ionic conductivity after its change due to preliminary illumination of a RbAg 4 I 5 superionic crystal with light of wavelength λ =430 nm has been detected. This recovery of the ionic conductivity is due to excitation of centers in complexes generated by previous illumination of tested samples.