Low-temperature oxide-ion conduction in Aurivillius-type ((Na0.5Bi0.5)n–1TinO3n)(Bi2O2) phases

Abstract

Solid oxide-ion conductors are key functional materials in high-temperature (>500 °C) electrochemical energy technologies, such as solid oxide fuel cells. Operating these devices at lower temperatures could simplify system design, reduce degradation and broaden material options, but few conductors exhibit sufficient ion mobility in this regime. Here we report a family of oxide-ion conductors based on ((Na0.5Bi0.5)n–1TinO3n)(Bi2O2) (where n = 4, 5, 7 and 8) Aurivillius-type thin films with promising low-temperature performance. These Aurivillius phases, characterized by periodic bismuth oxide layers and a tetragonally distorted Na0.5Bi0.5TiO3 lattice, establish well-defined periodic fast ion-conducting channels allowing ionic conductivity of 0.025 S cm−1 at 350 °C. Combining atomic-scale electron ptychography imaging with first-principles calculations, we attribute these intriguing properties to localized lattice stretching and the unique dual-ion conduction pathways induced by the specific bismuth oxide intercalation. Based on this design, we constructed fuel cells that achieve a maximum power density of 0.726 W cm−2 at 400 °C, showing promising potential for technological applications. Solid oxide-ion conductors are essential for high-temperature electrochemical technologies, yet few materials maintain sufficient ion mobility at lower temperatures, where degradation is reduced and a broader range of materials can be used for auxiliary components. Here the authors introduce Aurivillius-type thin-film conductors that form periodic fast ion channels and achieve promising conductivity at 350 °C.