Tunable High Entropy Lanthanide Oxide Microspheres via Confined Electroprecipitation in Emulsion Droplet Scaffolds.

Emergent high entropy nanomaterials and their associated complex surface structure hold promise to unlock unique catalytic intermediate pathways and photonic/plasmonic interactions; however, synthetic strategies to tune the size, morphological, and stoichiometric properties remain limited. This work demonstrates a confined electro-precipitation mechanism for the formation of tunable, high-entropy oxide microspheres within emulsion droplet scaffolds. This mechanism complements a traditional confined electrodeposition mechanism and explains the previously observed anomalous formation of thermodynamically unfavorable particles, including lanthanide species. Mass transfer studies reveal that microsphere coverage over a surface may be tuned and modeled by using a time-dependent modified Levich equation. Additionally, morphological tuning was demonstrated as a function of experimental conditions, such as rotation rate and precursor concentration. Finally, extension to multimetallic species permitted the generation of high-entropy lanthanide oxide microspheres, which were confirmed to have equimolar stoichiometries via energy dispersive spectroscopy and inductively coupled plasma mass spectrometry. This novel method promises to generate tunable, complex oxides with applications to thermal catalysis, optics, and applications yet unknown.