High-entropy oxides for catalysis: A diamond in the rough

The notion of “entropy engineering” has breathed new life into the research and development of sophisticated functional materials in recent years. High-entropy materials (HEMs) have garnered considerable attention in environmental science and renewable energy technology because of their distinctive structural characteristics, customizable element composition, and tunable functional capabilities. Among them, previous research has shown that high-entropy alloys (HEAs) have many advantages over traditional single-component alloys in terms of model, composition design, microstructure control, and performance. However, systematic research on high-entropy ceramics (HECs) is still relatively lacking, especially for their functional applications and mechanism disclosure. Notably, recent research indicates that high-entropy oxides (HEOs), which belong to HECs, exhibit the potential to be next-generation catalysts since they inherit the “four core effects” of HEAs (high-entropy effect, delayed diffusion effect, lattice distortion effect, and cocktail effect). This review briefly discusses the basic notion of HEOs and their synthesis methods, emphasizing the advantages of their structural characteristics as catalysts (high oxygen mobility, plentiful oxygen vacancies, and efficient dispersion of metal elements). Further, we provide a comprehensive overview of recent achievements in thermal/photo/electrocatalysis involving HEOs. By comparing the catalytic performance of HEOs to that of conventional low/medium-entropy metal oxides, we highlight their advantages as novel functional catalytic materials with excellent catalytic activity, abundant catalytic active sites, and high-temperature stability. Finally, the prospects and remaining obstacles for the selection and production of HEOs in functional catalytic materials, as well as general guidelines for the engineering development of HEOs are discussed.