A recent study reported stable and high oxide-ion conductors based on a new hexagonal perovskite-related oxide. These high-performance oxide-ion conductors have the potential to pave the way for the development of solid electrolytes for next-generation batteries and clean energy devices like solid oxide fuel cells.
Perovskite oxides are particularly intriguing because they have two cation sites on which to substitute lower valence cations, resulting in a much broader range of oxygen ion-conducting materials. Since Faraday’s discovery of ionic conductors at the Royal Institution in London over 200 years ago, they have provided a fascinating interdisciplinary field of study. The demand for new clean energy sources, sensors and high energy density batteries has accelerated the pace of research in recent years, particularly in the last decade.
Many metal oxides of fluorite and perovskite-related structures are oxide ion conductors with practical applications in oxygen sensors, solid oxide fuel cells (SOFC), and electrolyzer. Several structural and thermodynamic parameters have been proposed as predictors of high oxide ion conductivity, including (1) the critical radius of the pathway for oxide ion movement, (2) free lattice volume, and (3) average metal–oxide bond energy.
We aimed to create materials that could incorporate a large number of interstitial oxygens into their structure while also exhibiting high conductivity at intermediate and low temperatures. Furthermore, in a reducing atmosphere, ion conduction remained dominant.
Prof. Yashima
In a recent study, scientists from Tokyo Tech, Kojundo Chemical Laboratory Co. Ltd., and the Australian Nuclear Science and Technology Organisation (ANSTO) reported stable and high oxide-ion conductors based on a new hexagonal perovskite-related oxide. These high-performance oxide-ion conductors have the potential to pave the way for the development of solid electrolytes for next-generation batteries and clean energy devices like solid oxide fuel cells.
The modern technological era’s ever-increasing demand for clean energy and high-performance devices has necessitated the development of alternative energy materials. Oxide-ion conductors, in particular, have received a lot of attention on this front. The presence of highly mobile oxide ions in their crystal structure gives these materials unique electronic properties that could be used in the design of solid oxide fuel cells (SOFCs), a promising technology for generating clean energy.
Solid oxide-ion conductors with high conductivity and chemical and electrical stability are required for the development of efficient SOFCs. Unfortunately, conventional oxide-ion conductors do not exhibit adequate conductivity below 700°C. As a result, an alternative material with high ion conductivity at lower temperatures (300 — 600 °C) is in high demand.
Fig: Fueling the future with new perovskite-related oxide-ion conductors
Fortunately, perovskite-type oxides may be able to help. High ionic conductivity has been reported for hexagonal perovskite derivatives composed of barium (Ba), molybdenum (Mo), and niobium (Nb) oxides. However, certain drawbacks remain: the amount of oxygen in the crystal structure’s interstitial spaces, which is required for high conduction, is still low, electronic conduction competes with and hinders ionic conduction in a reducing atmosphere, and diffraction techniques are unable to shed light on the underlying oxygen migration mechanism.
A team of researchers led by Prof. Masatomo Yashima from Tokyo Institute of Technology (Tokyo Tech), Japan, addressed these issues in a recent study published in Small. Ba7Ta3.7Mo1.3O20.15, a new hexagonal perovskite-related oxide developed by the team, demonstrated excellent ionic conduction at intermediate and low temperatures.
“We aimed to create materials that could incorporate a large number of interstitial oxygens into their structure while also exhibiting high conductivity at intermediate and low temperatures. Furthermore, in a reducing atmosphere, ion conduction remained dominant” Prof. Yashima elaborates. Tokyo Tech, Japan, Kojundo Chemical Laboratory Co. Ltd., Japan, and the Australian Nuclear Science and Technology Organisation (ANSTO), Australia collaborated on this study.
The materials were then structurally analyzed using a combination of synchrotron X-ray and neutron diffraction data and numerical calculations by the team. They discovered that adding tantalum (Ta) to the structure improved stability and increased the number of interstitial oxygens compared to the other hexagonal perovskite-related oxides. Furthermore, the analyses and calculations revealed that the Mo ions occupied the oxygen-deficient layers responsible for the oxide-ion conduction preferentially.
The team is ecstatic about these findings, and Prof. Yashima is optimistic about their practical implications. “The findings of our study may provide an effective strategy for the development and commercialization of SOFCs,” he anticipates.
