L. M. Kolchina

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 (

Optimization of composite cathode based on praseodymium cuprate for intermediate-temperature solid oxide fuel cells

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

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

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.

Electrochemical Properties of Composite Cathode Materials Pr1.95La0.05CuO4–Ce0.9Gd0.1O1.95 for Intermediate Temperature Solid Oxide Fuel Cells

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).

Influence of structural arrangement of R2O2 slabs of layered cuprates on high-temperature properties important for application in IT-SOFC

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.

Electrochemical characterization of Pr2CuO4–Ce0.9Gd0.1O1.95 composite cathodes for solid oxide fuel cells

A complex study of thermal, conducting, and electrocatalytic properties of cuprates La1.8‒xPrxSr0.2CuO4–δ (х = 0.2; 0.4) with the K2NiF4 structure is carried out in order to assess their prospects as the cathode materials for solid-oxide fuel cells. The thermal analysis reveals stability of samples heated up to 950°С in air. The conductivity of cuprates measured in the temperature range of 100–900°С and the partial oxygen pressure from 10–3 to 1 atm is of the metallic nature and varies from 70 to 40 S/cm in the temperature interval of 500–900°С in air. The studies of chemical stability of cuprates with respect to solid electrolytes demonstrate the absence of their chemical interaction with Ce0.9Gd0.1O1.95 (GDC) at 900°С and with La0.8Sr0.2Ga0.85Mg0.15O3–δ (LSGM) at 1000°C after 25 h annealing. For La1.6Pr0.2Sr0.2CuO4–δ electrodes deposited on the surface of GDC or LSGM solid electrolytes, the studies of electrocatalytic activity in the oxygen reduction reaction demonstrate that the smallest polarization resistance is typical of electrodes deposited on the GDC surface.

Thermal expansion behavior and high-temperature electrical conductivity of A2−xAx′Cu1−yCoyO4±δ (A = La, Pr; A′ = Pr, Sr) oxides with the K2NiF4-type structure

Pr2−xCexCuO4 (x = 0.05; 0.1; 0.15) samples were synthesized and systematically characterized towards application as a cathode material for solid oxide fuel cells (SOFCs). High-temperature electrical conductivity, thermal expansion, and electrocatalytic activity in the oxygen reduction reaction (ORR) were examined. The electrical conductivity of Pr2−xCexCuO4 oxides demonstrates semiconducting behavior up to 900 °C. Small Ce-doping (2.5 at%) allows an increase in electrical conductivity from 100 to 130 S cm−1 in air at 500–800 °C. DFT calculations revealed that the density of states directly below the Fermi level, comprised mainly of Cu 3d and O 2p states, is significantly affected by atoms in rare earth positions, which might give an indication of a correlation between calculated electronic structures and measured conducting properties. Ce-doping in Pr2−xCexCuO4 slightly increases TEC from 11.9 × 10−6 K−1 for x = 0 to 14.2 × 10−6 K−1 for x = 0.15. Substitution of 2.5% of Pr atoms in Pr2CuO4 by Ce is effective to enhance the electrochemical performance of the material as a SOFC cathode in the ORR (ASR of Pr1.95Ce0.05CuO4 electrode applied on Ce0.9Gd0.1O1.95 electrolyte is 0.39 Ω cm2 at 750 °C in air). The peak power density achieved for the electrolyte-supported fuel cell with the Pr1.95Ce0.05CuO4 cathode is 150 mW cm−2 at 800 °C.