Changes in Physical and Mechanical Properties of SOFC Ni–YSZ Composites Caused by Redox Cycling

The investigations of sequential cyclic reduction and oxidation (redox) of solid oxide fuel cell (SOFC) Ni–yttria-stabilized zirconia (YSZ) anode substrates presented here are aimed at monitoring and understanding changes in critical physical and mechanical properties as a function of degree of oxidation at . The commonly observed expansion on oxidation, and its irreversibility on subsequent reduction, was confirmed but was found to be greatly dependent on oxidation conditions, giving strains in the range 0.55–0.8%. Nevertheless, redox cycling was accompanied by reversible changes in elastic modulus and no significant damage was detected in the YSZ network. Microstructure observations of oxidized Ni particles revealed the formation of closed porosity of a similar magnitude to that observed in oxidized composites (ca. 5%), suggesting that this is a major cause of the expansion on oxidation of the composite.