Oleksandr Vasylyev

La0.8Sr0.2Ni0.4Fe0.6O3–Ce0.8Gd0.2O2–δ Nanocomposite as Mixed Ionic–Electronic Conducting Material for SOFC Cathode and Oxygen Permeable Membranes: Synthesis and Properties

Mixed ionic–electronic conducting nanocomposite La0.8Sr0.2Ni0.4Fe0.6O3 (LSNF)–Ce0.8Gd0.2O2– δ (GDC) was prepared via ultrasonic dispersion of nanocrystalline powders of perovskite and fluorite oxides in water with addition of surfactant, followed by drying and sintering up to 1300°C. Analysis of the real structure of nanocomposite (studied by XRD and TEM with EDX) and its surface composition (studied by XPS) revealed moderate redistribution of elements between phases favoring their epitaxy. Results of impedance spectroscopy, oxygen isotope exchange, O2 TPD and H2 TPR experiments revealed a positive effect of composite interfaces on the oxygen mobility and reactivity agreeing with the ambipolar transport behavior of MIEC composite. Preliminary testing of button-size cell with functionally graded LSNF–GDC cathode layer supported on thin YSZ layer covering Ni/YSZ cermet demonstrated high and stable performance, which is promising for its practical application.

Doped Nanocrystalline Pt-Promoted Ceria-Zirconia as Anode Catalysts for IT SOFC: Synthesis and Properties

Ceria-zirconia samples doped with Gd, Pr, Sm, or La cations were prepared via Pechini route and promoted by Pt. Effect of their real structure and surface properties (characterized by neutronography, EXAFS, XPS, FTIRS of adsorbed CO) on the mobility and reactivity of the lattice oxygen (by oxygen isotope exchange and CH 4 TPR) was analyzed. For the reaction of CH 4 steam reforming (SR), catalytic performance is determined both by Pt dispersion and lattice oxygen mobility. Ni-YSZ anodes promoted by these catalysts possess a stable and efficient performance in CH 4 SR in the 600-800°C range in stoichiometric feeds without coking.

Fractal analysis of surface topography of solid oxide fuel cell materials

In this work, we investigate the hierarchical surface topography of solid oxide fuel cell electrolytes consisting of zirconia stabilized with 10% Sc2O3 and 1% CeO2 (1Ce10ScSZ) synthesized at 1300–1400 °C and anodes of 60 wt% 1Ce10ScSZ and 40 wt% NiO synthesized at 1250 to 1550 °C. The fractal dimension of AFM images of the films was determined by the cube counting method, the triangulation method and by means of the PSD slope at large wavenumbers. RMS roughness and correlation lengths were derived from the fit to the model PSD.

Characterization of Sc 2 O 3 &CeO 2 -Stabilized ZrO 2 Powders Via Co-Precipitation or Hydrothermal Synthesis

As the presence of Sc₂O₃ and CeO₂ is known to largely enhance the ionic conductivity in the temperature range of 600-800°C, compared with the conventional yttria-stabilized ZrO₂, Sc₂O₃&CeO₂-stabilized ZrO₂ provide its applicability as electrolytes in solid oxide fuel cells. The current study introduces the methodology to synthesize Sc₂O₃&CeO₂-stabilized ZrO₂ powders by using co-precipitation technique or high-temperature hydrothermal reaction, and further describes the structural characterization of the zirconia powders synthesized by the above-mentioned two methods. The co-precipitation technique was found to allow obtaining powders of cubic phase, whereas high-temperature hydrothermal synthesis results in the presence of a monoclinic phase as well. The scanning transmission electron microscope observations also confirm that the size of the synthesized ZrO₂ powders in this study is found to be much smaller than that of commercially available powders.

Structural features and gas tightness of EB-PVD 1Ce10ScSZ electrolyte films

The structure of Ceria doped Scandia Stabilized Zirconia (1Ce10ScSZ) electrolyte film deposited by EB-PVD (Electron Beam-Physical Vapour Deposition) technique on NiO-ZrO2 substrate was characterized by electron microscopy. The highly porous substrate was densely covered by deposited film without any spallation. The produced electrolyte layer was of a columnar structure with bushes, bundles of a diameter up to 30 μm and diverse height. Between the columns, delamination cracks of few microns length were visible. The annealing of zirconia film at 1000 °C resulted in its densification. The columnar grains and delaminating cracks changed their shape into a bit rounded. High magnification studies revealed nanopores 5–60 nm formed along the boundaries of the columnar grains during annealing. High-quality contacts between the electrolyte film and anode substrate ensured good conductivity of the electrolyte film and high efficiency of SOFC.

Design of Anodes for IT SOFC: Effect of Complex Oxide Promoters and Pd on Activity and Stability in Methane Steam Reforming of Ni/YSZ (ScSZ) Cermets

Effect of fluorite-like or perovskite-like complex oxide promoters and Pd on the performance of Ni/YSZ and Ni/ScSZ cermets in methane steam reforming or selective oxidation by O 2 into syngas at short contact times was studied. Spatial uniformity of dopants distribution in composites was controlled by TEM combined with EDX, while the lattice oxygen mobility and reactivity was elucidated by CH 4 and H 2 TPR. Oxide promoters allow to operate even at stoichiometric H 2 O/CH 4 ratio by suppressing coke deposition through modification of Ni surface, while doping by Pd ensures reasonable performance at moderate (∼550 °C) temperatures required for Intermediate–Temperature Solid Oxide Fuel Cells (IT SOFC).

Effect of Porosity on Strength and Electrical Conductivity of NiO–3.5YSZ Composite and Its Ni–3.5YSZ Cermet

The change in porosity of the Ni–3.5YSZ (ZrO2 stabilized with 3.5 mol.% Y2O3) composite, when produced, and the effect of porosity on the strength and electrical conductivity is studied. The porosity was provided by adding granular starch to the mixture of NiO and 3.5YSZ powders. The content of 18 vol.% pore-forming agent in the Ni–3.5YSZ cermet provides open porosity 47.1%, while its strength and electrical conductivity are 74.3 MPa and 0.93 · 106 S/m, respectively.

Defect Structure of Nanosized Zirconium Oxide Powders Doped with Y2O3, Sc2O3, Cr2O3

The formation mechanisms of paramagnetic centers originating from Zr3+ and Cr3+ ions and the influence of the nanoparticle composition on thermal generation processes of these paramagnetic centers in ZrO2 structure were studied by electron paramagnetic resonance. A set of nanosized zirconium oxide powders (nominally pure ZrO2, ZrO2 doped with correspondingly Y2O3 and Sc2O3, Cr2O3 and Y2O3, as well as Cr2O3) was investigated: The influence of annealing on the EPR lines of Zr3+ and Cr5+ ions was found to be different. Annealing curves of EPR signals caused by Cr5+ ions have a maximum in temperature range 500–600 °C. Mechanisms of Zr3+ and Cr5+ ions formation were discussed.

On nucleation and growth mechanisms of EBPVD zirconia films on porous NiO-ZrO 2 substrate

Thin structure of the anode-electrolyte interface (AEI) was studied, and plausible nucleation and growth mechanisms at electron-beam physical vapor deposition (EB-PVD) were established. ZrO2 condensates with two mechanisms - planar and cellular ones like it happens at solidification from liquid phase. ZrO2 condensation on ZrO2 and NiO phases occurs with two different routes. On ZrO2 phase, layer of planar growth is formed with “defective layer by defective layer” mechanism. On NiO, the layer is cellular from the very beginning of the deposition process. The layer of planar growth is formed as “dense layer by dense layer”. Deposition affected zone (DAZ) is clearly distinguished.

On the dependence of ionic conductivity of ScSZ electrolytes on temperature of their sintering

The dependencies of ionic oxygen conductivity of 10Sc1CeSZ electrolytes made of different zirconia powders those differ by their impurities and production technologies, and sintered in air at different temperatures after uniaxial pressing are analyzed in terms of their Arrhenius equations in 400–900°C temperature range. Deviation from a typical linear dependence of conductivity on temperature that is the most clearly visible in the electrolyte made of the purest powder is observed as a kink on the temperature dependency. A position of the kink point is determined by powder properties and is practically independent on temperature of powder sintering.