Mutual Diffusion and Microstructure Evolution at the Electrolyte−Anode Interface in Intermediate Temperature Solid Oxide Fuel Cell

The microstructure and elemental distribution of the gadolinium-doped ceria (GDC) thin film electrolyte, Ni-GDC cermet anode, and the interface between them were comprehensively characterized by high-resolution transmission electron microscopy (HR-TEM) and energy-dispersive X-ray spectroscopy (EDX) operated in scanning TEM (STEM) mode. HR-TEM observations show newly appeared microstructure (i.e., superstructures) formations at both GDC and metallic Ni grains at the electrolyte−anode interface. STEM-EDX mapping and line scan analyses illustrate that not only can Ni diffuse into GDC grains as previously reported but also Ce and Gd can diffuse into metallic Ni particles with equal diffusion lengths as that of Ni diffusion. Such mutual diffusion is independent of ionic radii and can result in the valence state change of diffusing ions, verified by electron energy loss spectroscopy investigations. Therefore, the mutual diffusion and related microstructural evolutions are elucidated to be dominating factors that lead to the interfacial layer formation between anode and electrolyte, which is identified to have a considerable influence on the ionic conductivity behavior in intermediate temperature solid oxide fuel cells.