High-Entropy Hexagonal Manganites for Fast Oxygen Absorption and Release

Hexagonal manganites (RMnO3) display a large capacity for oxygen storage and release at temperatures below 400 degree celsius. A challenging trade-off is that larger R3+ cations improve both the absorption capacity and the exchange kinetics but also destabilize the layered hexagonal structure with respect to the competing orthorhombic perovskite phase. Here, high-entropy RMnO3 materials with 5 or 6 rare earth elements are prepared as both bulk and nanocrystalline materials, and the hexagonal phase is stabilized for compositions RMn1-xTixO3 where R = Y, Gd, and Er and x = 0, 0.15. These high-entropy hexagonal manganites show similar oxygen storage capacity as the best-known single or double R3+ compositions and greatly enhanced oxidation kinetics. Even bulk samples show significant oxygen absorption at rapid cooling rates of up to 20 K/min in O-2. Importantly, both the oxygen capacity and the oxidation kinetics are insensitive to the exact R3+ composition. This improves the commercial application potential of hexagonal manganites for oxygen storage and separation from air. Finally, sustainability implications are discussed.