Multilayered YSZ/GZO films with greatly enhanced ionic conduction for low temperature solid oxidefuel cells

Abstract

Strain confinement in heterostructured films significantly affects ionic conductivity of the electrolytes for solid oxide fuel cells based on a multi-layered design strategy. Nearly ideal tensile strain can be achieved by a dedicated manipulation of the lattice mismatch between adjacent layers and fine control of the layer thicknesses to minimize the formation of dislocations and thus to achieve optimized ionic conduction. This strategy was demonstrated by a model system of multilayered 8 mol%Y₂O₃ stabilized ZrO₂ (YSZ) with Gd₂Zr₂O₇ (GZO) films, which were epitaxially grown on Al₂O₃ (0001) substrates by pulsed laser deposition (PLD) with the {111} planes of YSZ/GZO along the Al₂O₃ [0 1 −1 0] direction. The tensile strain (3%) resulting from the lattice mismatch can be confined in individual YSZ layers with the formation of a coherent, dislocation-free interface upon the manipulation of the layer thickness below a critical value, e.g., down to 5 nm. The strained heterostructure displays a two order-of-magnitude increase in oxide-ion conductivity as compared with bulk YSZ, and a high ionic conductivity of 0.01 S cm⁻¹ at 475 °C can be achieved, five times greater than that of Gd-doped ceria/zirconia. The approach of strain confinement by fine control of lattice mismatch and layer thickness represents a promising strategy in developing advanced electrolytes enabling the miniaturization of solid-state ionic devices that can be operated at low temperatures below 500 °C.