Engineering disorder in high-entropy metal oxides for advanced functional applications

High-entropy metal oxides (HEMOs) have emerged as a transformative class of multifunctional materials owing to their unique compositional complexity, tunable crystal structures, and remarkable physicochemical properties. Unlike conventional single-component or low-entropy oxides, HEMOs incorporate five or more metal cations in near-equimolar ratios, leading to high configurational entropy that stabilizes disordered solid-solution phases. This engineered disorder significantly influences electronic structure, defect chemistry, lattice distortion, ionic transport, and surface reactivity, thereby enabling superior performance in a wide range of advanced functional applications. Recent progress in synthesis strategies, including solid-state reactions, sol–gel processing, hydrothermal methods, spray pyrolysis, and mechanochemical approaches, has enabled precise control over morphology, phase stability, and elemental distribution in HEMOs.This review comprehensively discusses the principles of entropy stabilization and disorder engineering in high-entropy metal oxides, emphasizing the relationship between structural disorder and functional performance. Various characterization techniques used to investigate crystallographic, electronic, thermal, magnetic, and electrochemical properties are critically examined. Particular attention is given to the role of oxygen vacancies, cationic disorder, lattice strain, and multivalent states in enhancing catalytic activity, energy storage capability, ionic conductivity, magnetic behavior, and environmental remediation performance. The applications of HEMOs in electrocatalysis, photocatalysis, batteries, supercapacitors, solid oxide fuel cells, gas sensing, dielectric materials, and biomedical systems are systematically reviewed. Furthermore, current challenges associated with synthesis scalability, phase prediction, mechanistic understanding, and long-term stability are highlighted. Finally, future research directions focusing on computational design, machine learning-assisted material discovery, defect engineering, and sustainable synthesis routes are proposed to accelerate the practical implementation of HEMOs in next-generation technologies.