High entropy hexagonal manganites for fast oxygen absorption and release

Abstract

Hexagonal manganites (RMnO3) display large capacity for oxygen storage and release at temperatures below 400 °C. 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 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 resulting configurational entropy stabilizes the hexagonal phase for compositions RMn1-xTixO3 where R = Y, Gd-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. Importantly, both the oxygen capacity and 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.