Mechanics Behavior Induced by Chemical Expansion for Oxide Anode of Solid Oxide Fuel Cells^†

Oxide anodes of solid oxide fuel cells are usually stable in the redox cycling process. However, they may be subjected to mechanical stresses associated with chemical expansion due to the stoichiometrical variation. A novel method is presented to detect the mechanical stresses by combining the Fick's second law, oxygen surface exchange, and oxygen-ion diffusion properties. The surface tensile stress is weak for the small structural dimensions due to the short diffusion length. When the surface exchange kinetics is increased by means such as surface modification, the improved surface exchange rate may result in large mechanical stress and the stress-loading rate, and consequently, reduce the redox stability. A new modulus (ω) is introduced to predict the mechanical behavior, and larger ω means higher mechanical stress. Finally, the prediction is experimentally confirmed with (La_0.75Sr_0.25)_0.95Cr_0.5Mn_0.5O_3–δ (LSCM) samples, where the fracture is related to its conductivity. It is found that porous LSCM has excellent stability in the atmosphere change process. However, fractures are observed with Ni impregnated porous LSCM due to the increased surface exchanged coefficient, which means larger ω.