Room‐Temperature Synthesis of High‐Entropy Oxides via NH ₄ F Modulation for Dark •OH Radical‐Enhanced Photothermal Catalysis

Abstract High‐entropy oxides (HEOs) are attracting extensive attention due to their flexible composition, tunable structures, and promising properties. However, their synthesis remains challenging, requiring high temperature, tedious steps, and expensive equipment. Herein, a room‐temperature strategy is reported for synthesizing HEO as the dominant phase through a competitive complexation‐precipitation equilibrium using NH 4 F as a modulator. The resulting F‐modulated HEO (HEO‐F) tailored by NH 4 + and F − synergy, exhibits optimized lattice oxygen (O latt ), and oxygen vacancies (OVs) that significantly enhance the activation of reactants. Notably, HEO‐F demonstrates superior capability for generating hydroxyl radicals (•OH) in the dark, which plays a critical role in promoting adsorption oxidation and sustaining catalytic stability. Under mild photothermal conditions (“light+120 °C”), it achieves complete toluene conversion with 100% CO 2 selectivity over 300 min and maintains long‐term cyclic stability for more than 30 h. Detailed characterization and density functional theory (DFT) calculations are performed to link their properties to composition and structure. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveals that the key factors for facilitating deep oxidation and catalyst self‐regeneration. This work demonstrates a simple, economicscopyal, and green room‐temperature route for HEOs design and reveals the vital role of dark •OH for stable photothermal catalysis.