Current density dependence of changes in the microstructure of SOFC anodes during electrochemical oxidation

The effect of current density during electrochemical oxidation on the microstructure of solid oxide fuel cell anodes was investigated. Anode-supported cells were subjected to electrochemical oxidation by oxide ions and chemical reduction by H₂ gas. Two anodes were electrochemically oxidized by the same quantity of electricity of 15 C using different current densities of 25 mA/cm² and 250 mA/cm². When Ni particles were oxidized at 25 mA/cm², little morphological change occurred in the Ni particles, resulting in only a small change in the microstructure of the anode. On the other hand, when Ni particles were oxidized at 250 mA/cm², the morphology of the particles changed to a more textured outer surface and the Ni particle seemed to divide into smaller ones. Neither cell showed a decrease in open circuit voltage nor cracks in the electrolyte, resulting in that the microstructure changes observed in the tested cells were caused by electrochemical oxidation and subsequent reduction (redox cycle). Furthermore, this suggests that the differences in the resulting microstructures of the Ni particles were caused by the differences in current density during electrochemical oxidation.