Physically driven enhancement of the stability of Bi2O3-based ionic conductors via grain boundary engineering

Abstract

Fast oxygen-ion conductors for use as electrolyte materials have been sought for energy conversion and storage. Bi2O3-based ionic conductors that exhibit the highest known oxygen-ion conductivities have received attention for use in next-generation solid electrolytes. However, at intermediate temperatures below ~600 °C, their conductivities degrade rapidly owing to a cubic-to-rhombohedral phase transformation. Here, we demonstrate that physical manipulation of the grain structure can be used to preserve the superior ionic conductivity of Bi2O3. To investigate the effects of microstructural control on stability, epitaxial and nanopolycrystalline model films of Er0.25Bi0.75O1.5 were fabricated by pulsed laser deposition. Interestingly, in situ impedance and ex situ XRD analyses showed that the grain boundary-free epitaxial film significantly improved the stability of the cubic phase, while severe degradation was observed in the conductivity of its polycrystalline counterpart. Consistently, the cation interdiffusion coefficient measured by the Boltzmann–Matano method was much lower for the epitaxial thin film compared to the polycrystalline thin film. Furthermore, first-principles calculations revealed that the presence of grain boundaries triggered the structural resemblance between cubic and rhombohedral phases, as evidenced by radial distribution functions. Additionally, phase transition energetics predicted that the thermodynamic stability of the cubic phase with respect to the rhombohedral counterpart is reduced near grain boundaries. Thus, these findings provide novel insights into the development of highly durable superionic conductors via microstructural engineering.

On the Role of Bimetal‐Doped BaCoO3−𝛿 Perovskites as Highly Active Oxygen Electrodes of Protonic Ceramic Electrochemical Cells

“…[17] The doping strategy with high-valence cations (e.g., Nb 5+ and Ta 5+ ) has been suggested to stabilize the SrCoO 3-𝛿 (SCO) structure. [18,19,20] Du et al demonstrated that Sc-involved bimetal doping effectively enhances the ORR activity of SCO-based oxygen electrode in solid oxide electrochemical cells (SOCs). [21] Similarly, the incorporating Ta into BCO transformed hexagonal perovskite into cubic perovskite, resulting in notable improvements in its electrochemical characteristics.…”

Electrophoretic Deposition and Characterization of Er-Doped Bi2O3 Cathode Barrier Coatings on Non-Conductive Ce0.8Sm0.2O1.9 Electrolyte Substrates

“…Alternative electrolytes having higher ionic conductivity than conventional stabilized zirconia have therefore become increasingly attractive for use in IT-SOFCs [2,3]. To date, most studies on electrolytes possessing satisfactory oxygen ion conductivity at decreased temperatures have been focused on oxide materials with cubic fluorite structures, such as doped CeO 2 [4,5] and Bi 2 O 3 [6,7]. Nevertheless, despite high ionic conductivity, which is very attractive for designing IT-SOFCs, these electrolytes, along with having advantages over traditional electrolytes based on zirconium dioxide, have a number of disadvantages.…”