(560gs) Design and Evaluation of Nanostructured Doped Perovskite Oxygen Carriers

Doped perovskites have demonstrated facile oxygen vacancy formation and stability over many reduction cycles, making them good candidate materials for oxygen carriers in chemical looping processes [1]. Prior work has illustrated that the introduction of dopant in the perovskite lattice can have a dramatic impact on the material's phase stability and reducibility [2,3]. We consider a BaFe_1-xIn_xO₃ doped perovskite that has been shown to release oxygen at lower temperatures upon addition of In in the lattice.

Using density functional theory (DFT)+U method, we have evaluated the oxygen vacancy formation energy for a set of 74 rotationally-distinct motifs spanning a range of dopant concentrations. From these data, we can make simplified structure-function relationships to predict the reducibility of different patterns of dopant in the lattice. Since the placement of dopant is highly combinatorial, it is intractable to enumerate the possible dopant patterns. Instead, we have formalized the search space in a mathematical optimization model that allows an efficient search over the entire space of dopant positions to identify patterns with optimal properties [4].

In this work, we investigate the sensitivity of oxygen excess energy against several parameters that are expected to impact the material performance. Specifically, we first consider the impact of multiple oxygen removals on the trends of oxygen excess energy. We investigated trends with both the number of oxygen removals and the distance between vacancies. We also study the energy of forming different combinations of dopant and vacancy structures in the lattice, improving our predictions for the likelihood of structures forming spontaneously. This allows us to relax some of our previous modelling assumptions and develop more refined models for the performance of our doped perovskite oxygen carrier.

The specific model improvements are demonstrated in the context of a BaFe_1-xIn_xO_3-δ doped perovskite, but are formulated in a generic way so as to be applicable to a wide range of material systems. Generally, we demonstrate how simplified structure-function relationships can be refined and embedded in an optimization model in a modular way, preserving the overall structure of the optimization problem. The resulting optimization models can be solved via standard optimization approaches and provide solutions that can inform future synthesis efforts and provide theoretical bounds of material performance.

References

[1] Motohashi, T., Ueda, T., Masubuchi, Y., Takiguchi, M., Setoyama, T., Oshima, K., & Kikkawa, S. (2010). Remarkable oxygen intake/release capability of BaYMn2O 5+δ: Applications to oxygen storage technologies. Chemistry of Materials, 22(10), 3192–3196.

[2] Baiyee, Z. M., Chen, C., & Ciucci, F. (2015). A DFT+U study of A-site and B-site substitution in BaFeO_3-δ. Phys. Chem. Chem. Phys., 17(36), 23511–23520.

[3] Ishihara, T., Matsuda, H., & Takita, Y. (1995). Effects of Rare-Earth Cations Doped for La Site on the Oxide Ionic-Conductivity of LaGaO₃-Based Perovskite-Type Oxide. Solid State Ionics, 79, 147–151.

[4] Hanselman, C.L., Alfonso, D.R., Lekse, J.W., Tafen, D.N., Matranga, C., Miller, D.C., & Gounaris, C.E., Tuning oxygen desorption in a doped BaFe_1-xIn_xO₃ perovskite oxygen carrier. Accepted for Publication.