Ceria-Zirconia Composite Electrolyte for Solid Oxide Fuel Cells

Ceria-zirconia-ceria sandwich structured composite film electrolytes were designed in order to offer high ionic and low electronic conductivity electrolyte films. Calculation of oxygen potential profile in the composite film electrolyte indicates that a very thin zirconia film kills the electronic current of ceria without affecting the ionic conductivity. The composite films were successfully prepared by a co-fire process. The main problem was the fact that the ceria and zirconia green films had different shrinkage behaviors. Successful co-firing was achieved by controlling the temperature program and amount of binder. De-lamination between yttria stabilized zirconia(YSZ) and gadolinia doped ceria(GDC) layers was overcome by the formation of a solid solution phase at the interface of the two films. The resultant composite films, however, showed poor electrical conductivity compared with theoretical values. The formation of a solid solution phase can have a negative effect on composite electrolytes. Also, the composite film is unsatisfactory in terms of mechanical strength. This could be due to the lattice expansion in reducing atmospheres, thermal expansion coefficient mismatch, or the intrinsic weakness of the ceria texture.