Metal–Tannin Coordination Assembly Route to Nanostructured High-Entropy Oxide Perovskites with Abundant Defects

High-entropy oxide perovskites (HEOPs), the incorporation of five or more elements into ABO3, possess great flexibility in the composition and electron structure and thus merit untold scientific and technological potential. However, the conventional synthetic methods at high temperatures tend to obtain the bulk with a low surface area, limited exposed active sites, and result in poor catalytic activity. Herein, we report a metal–tannin coordination assembly strategy to synthesize HEOP nanoparticles (NPs) with a size of 10–30 nm and abundant oxygen vacancies. Interestingly, up to 10 immiscible metal elements could be confined into the single HEOP NPs. Meanwhile, the as-synthesized La(FeCoNiCrMn)3 NPs exhibit better CO oxidation activity than single-metal–oxide perovskites and the conventionally solid-state prepared HEOP catalysts. Moreover, the entropy-stabilized NPs function well in moisture- or SO2-containing reaction conditions. This work opens up new opportunities to design nanostructured high-entropy materials for heterogeneous catalysis.