On the Redox Cycling of Anode-Supported SOFCs: Mechanical Properties and Damage Mechanisms

Investigations on SOFCs using Ni-based anode supports are presented aiming at the understanding of how much oxidation such a cell can tolerate before incurring irreversible mechanical damage. The dimensional strains, elastic modulus and porosity of typical anode supports were measured as a function of the degree of oxidation. The mechanical stability of cells incorporating such substrates was studied as a result of oxidation by air and by electrochemical oxidation. The different oxidation procedures performed showed different damage modes. In free-standing cells the main damage mode was electrolyte cracking, but in cell test configurations the cells failed by substrate cracking. This was mainly due to the non-uniform nature of anode oxidation in the cell test configurations which can lead to cell failure when the degree of oxidation is only 5 %. The observations are interpreted using models of the stress generation and fracture processes.