Structural, Compositional, and Morphological Interrelationships in Rocksalt (FeCoMnMgZn)O High Entropy Oxide Nanocrystals for Oxygen Evolution Electrocatalysis

The colloidal synthesis of high entropy oxide (HEO) nanocrystals requires navigating and balancing competing reaction pathways, which are often unknown. There is also a limited understanding of HEO nanocrystal formation and growth pathways, which hinders morphological control. Here, we report on the colloidal synthesis of rocksalt-type (FeCoMnMgZn)O nanocrystals with different morphologies. Reaction pathway studies show a Fe-rich spinel-type intermediate and indicate that competing chemical reactivities dictate the final compositions and morphologies. Atomic resolution imaging analysis of concave cubic and dendritic (FeCoMnMgZn)O nanocrystals indicate a 1.73% lattice expansion relative to bulk FeO. The (FeCoMnMgZn)O nanocrystals are active electrocatalysts for the oxygen evolution reaction in alkaline media.