N. V. Lyskov

Drastic change of electrical conductivity in Pr2CuO4 by isovalent La doping

How to affect the transport properties of complex oxides was considered using the uncommon example of Pr2−xLaxCuO4. It was established that appropriate La doping in Pr2CuO4 leads to a noticeable increase in high-temperature electrical conductivity. The reason for such changes are discussed from the viewpoint of possible charge redistribution in Pr2−xLaxCuO4.

Features of high-temperature behavior in NdCaCoO4—the catalyst of the partial oxidation of methane to syngas

The peculiarities of the high-temperature (373–1173 K) behavior and transport properties of NdCaCoO4, which is a highly active and selective catalyst of the partial oxidation of methane to syngas, were considered. A relationship between its thermal and electrophysical properties and the structure and defectiveness of the oxygen sublattice was found. The electric conductivity of this compound, which is a two-dimensional analog of perovskite, was found to be almost independent of the oxygen pressure (

High-temperature properties of new perovskite-like oxides

p_{O_2 } = 10^{ - 4} - 1

Polymorphism in the family of Ln6−xMoO12−δ (Ln = La, Gd–Lu; x = 0, 0.5) oxygen ion- and proton-conducting materials

atm) and to increase with temperature, reaching ∼100 S/cm at 1173 K. The temperature dependence of the conductivity of the n-type semiconductor NdCaCoO4 has two thermoactivation regions (373–573 and 573–873 K), in which the activation energy is almost doubled (0.46 and 0.81 eV, respectively). The discovered tendencies that determine the unique catalytic properties of this material are probably due to the change in the energy spectrum of this compound. The hypothetical reasons for this change are discussed.

Electrotransport properties of SOFC cathode materials based on lanthanum cuprate doped with praseodymium and strontium oxides

The electrochemical behavior of a porous electrode based on Pr2CuO4 (PCO) screen printed on the surface of Ce0.9Gd0.1O1.95 (CGO) solid electrolyte is studied by impedance spectroscopy. The rate-determining stages of the oxygen reduction reaction at the PCO/CGO interface are found for the oxygen partial pressure interval of 30–105 Pa and temperatures of 773–1173 K. Changeover of the rate-determining stage of electrode reaction is shown to occur depending on the temperature and the oxygen partial pressure. The PCO electrode polarization resistance is 1.7 Ω cm2 at 973 K in air and remains constant at thermocycling of the electrochemical cell in the temperature range of 773–1173 K. Based on the found data, PCO can be considered as the promising cathodic material for solid-oxide fuel cells operating at moderate temperatures (773–973 K).

Evaluation of Ce-doped Pr2CuO4 for potential application as a cathode material for solid oxide fuel cells

New complex oxides of composition Pr1–yCayFe0.5 + x(Mg0.25Mo0.25)0.5–xO3, 0.0 ≤ x ≤ 0.1, 0.42 ≤ y ≤ 0.8 having an orthorhombically distorted perovskite structure have been prepared. The thermal expansion and electric conductivity of the new phases have been studied in the temperature range between 100–900°C. The results of our study imply that thin films of the oxides studied can be treated as electrode materials for symmetric solid-oxide fuel cells.

Metal-free current collectors based on graphene materials for supecapacitors produced by 3D printing

A complex study of conducting and catalytic properties of composite materials of Pr2CuO4−xCe0.9Gd0.1O1.95 (x = 20, 33, 50 wt %) is carried out. Conductivity of composites is measured using a four probe technique in air. Analysis of the dependence of conductivity on the composition at a given temperature shows that the conducting properties of composites can be described based on the percolation model. Electrocatalytic properties of composite cathodes supported on the surface of the Ce0.9Gd0.1O1.95 (GDC) solid electrolyte using the screen printing technique were studied by the impedance spectroscopy technique in the range of oxygen partial pressures of 10−2 to 0.21 atm at the temperatures of 500–900°C. Analysis of polarization resistance (Rη) isotherms on the partial pressure of oxygen shows that the rate-determining steps of the oxygen reduction reaction on the cathode are dissociation of adsorbed molecular oxygen and charge transfer. It is found that the minimum of polarization resistance corresponding to 0.4 Ohm cm2 at 700°C in air is reached in the range of intermediate temperatures (500–750°C) for the composition containing 33 wt % GDC. On the basis of the obtained data, the PCO-33GDC composite can be considered as a promising cathode material for intermediate-temperature solid oxide fuel cells.

Computer simulation of ion transport in a new cathode material PrSrCuO4-δ

The formation of Ln6−xMoO12−δ (Ln = La, Gd, Dy, Ho, Er, Tm, Yb, Lu; x = 0, 0.5) rare-earth molybdates from mechanically activated oxide mixtures has been studied in the range 900–1600 °C. The morphotropy and polymorphism (thermodynamic phase and kinetic (growth-related) transitions) of the Ln6−xMoO12−δ (Ln = La, Gd–Lu; x = 0, 0.5) molybdates have been analyzed in detail. As a result we have observed two new types of oxygen ion- and proton-conducting materials with bixbyite (Ia, no. 206) and rhombohedral (R, no. 148) structures in the family of Ln6−xMoO12−δ (Ln = La, Gd–Lu; x = 0, 0.5) molybdates. The heavy rare-earth molybdates Ln6−xMoO12−δ (Ln = Er, Tm, Yb; x = 0, 0.5) have been shown for the first time to undergo an order–disorder (rhombohedral–bixbyite) phase transition at 1500–1600 °C, and we have obtained compounds and solid solutions with the bixbyite structure (Ia). The stability range of the rhombohedral phase (R) increases with decreasing Ln ionic radius across the Ln6−xMoO12−δ (Ln = Er, Tm, Yb, Lu) series. We have detected a proton contribution to the conductivity of the rhombohedral La5.5MoO11.25 (2 × 10−4 S cm−1 at 600 °C in wet air) and high-temperature polymorph Yb6MoO12−δ bixbyite structure, (Ia) below 600 °C. At these temperatures, rhombohedral (R) Yb6MoO12 seems to be an oxygen ion conductor (Ea = 0.53–0.58 eV). The total conductivity of rhombohedral (R) Yb6MoO12 exceeds that of bixbyite Yb6MoO12−δ by more than one order of magnitude and is 3 × 10−5 S cm−1 at 500 °C. According to their high-temperature (T > 600 °C) activation energies, the lanthanum and ytterbium molybdates studied here are mixed electron–ion conductors.