A Green and Convenient Synthesis Strategy for High‐Entropy Oxide Colloidal Nanoparticles

Traditional colloidal synthesis methods for highly dispersed nanoparticles of high‐entropy oxides (HEOs) often involve complex reaction pathways and harmful organic solvents, thus impractical for large‐scale production. Herein, we report a green and convenient method integrating high‐gravity‐assisted instantaneous coprecipitation with low‐temperature hydrothermal treatment to synthesize nearly monodisperse HEO nanoparticles in an aqueous green solvent. This synthesis strategy is also very general and allows for customizable metallic compositions ranging from quinary to nonary. As a proof‐of‐concept, with excellent dispersity and high external active area, the optimal sample demonstrates remarkable activity for the oxygen evolution reaction with a low overpotential of 273 mV at 10 mA cm −2 , much surpassing the traditional calcined product and commercial RuO 2 benchmark. Therefore, this work establishes a novel and scalable synthetic route for nearly monodisperse HEO nanoparticles with tunable composition, enabling the further extension of fundamental studies on HEO nanomaterials.