Quantitative characterization of nickel migration in solid oxide fuel cells under redox cycling

Abstract

The migration of nickel during redox cycling in solid oxide fuel cells induces the evolution of the electrode microstructure, degrading the electrochemical performance of the electrode and causing severe mechanical damage. Thus, it is necessary to understand the Ni migration phenomenon during redox cycling, with particular attention to the interior of the electrode. In this study, an in-situ approach is proposed to investigate the migration of active metal materials in the anode during redox reactions. For this purpose, the same area at the surface and the same cubic volume in the anode during every redox cycle are investigated using scanning electron microscopy and a 3D X-ray microscope. It is found that nickel migrates from the interior of the anode to its surface, becomes agglomerative, and piles up to above 3 µm at the surface along with the pores. The mass-centered coordinates of the Ni bulk are measured and compared, and the results show that nickel migrates away from the electrolyte by approximately 1–3 µm. Nickel migration under long-term redox cycling accelerates fragmentation of the active element nickel within the anode, thus reducing its oxidation tolerance. The migration of nickel upon redox is also likely to promote cracking in YSZ and the fracture of electrolyte. In addition, a hypothesis is proposed to explain the nickel migration phenomenon upon redox reactions.