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

Abstract

The investigations of sequential cyclic reduction and oxidation redoxof solid oxide fuel cell SOFC Ni--yttria-stabilized zirconia YSZanode substrates presented here are aimed at monitoring and understandingchanges in critical physical and mechanical properties as a functionof degree of oxidation at 800 \,^{\circ}C. The commonly observedexpansion on oxidation, and its irreversibility on subsequent reduction,was confirmed but was found to be greatly dependent on oxidationconditions, giving strains in the range 0.55--0.8%. Nevertheless,redox cycling was accompanied by reversible changes in elastic modulusand no significant damage was detected in the YSZ network. Microstructureobservations of oxidized Ni particles revealed the formation of closedporosity of a similar magnitude to that observed in oxidized compositesca. 5%, suggesting that this is a major cause of the expansionon oxidation of the composite.