Brodnikovskyi I. The regularities of structure formation, mechanical behavior and electrochemical properties of Ni-ZrO2 anode for solid oxide fuel cell

The aim of the work is to establish the regularities of structure formation and properties of Ni-ZrO2(c) anode for solid oxide fuel cell, made of powders ZrO2(с) with different properties, their evolution during the reduction and oxidation processes of Ni and improving the structure and properties of the anode. The object of the work is the regularities of the relationship between structure and properties of Ni- ZrO2(с) anode for solid oxide fuel cell, made by different regimes from ZrO2(с) powders with different agglomeration and morphology. For the first time in scientific practice, based on the systematic study, relationship between structure and properties of Ni-ZrO2(с) anode made of stabilized in the cubic phase of zirconia powders (ZrO2(с)) with different agglomeration and morphology, and their evolution during the reduction and oxidation processes of Ni is established. The influence of a complex properties of ZrO2(c) powder (size, morphology of agglomerates, size of primary particles) on structure of anode are identified and explained. It was found that the powder ZrO2(c), agglomerated in a relatively "soft" agglomerates of nano-sized particles, is the best to provide the necessary highly porous structure of anode with high physical-mechanical properties. The influence of the redox cycling on Ni-ZrO2(с) anode structure, namely, modification of the nickel phase, which transforms it into a sponge and increases its volume. This improves the connectivity between the particles of reduced nickel in anode structure, which provides a simultaneous increase of its electrical conductivity and strength. Structure of anode is optimized via the use of the framing anode concept, in which the porous ZrO2(с) frame impregnated with nickel nitrate salt solution followed by Ni reduction. This method provides the Ni-ZrO2(с) anode cermet strength around 130 MPa after the Ni reduction and optimal distribution of three phases: ZrO2(с), Ni and porosity, which improves stability of the anode significantly. The thesis has received the support and high value by foreign scientists from research centers in Germany (Dr. Robert Steinberger-Wilckens, Forschungszentrum Julich) and U.S.A. (Alevtina Smirnova, PhD Assistant Professor, Department of Chemistry, South Dakota School of Mines and Technology). These scientists were as directors of international scientific research projects aimed on development and improvement of solid oxide fuel cells, in which some part of the researches of this thesis was done.