Structural properties of CeO₂ and CeO₂-based composite oxide materials for passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) is an emerging strategy to improve energy efficiency in buildings and industrial processes by reducing the need for mechanical cooling. However, existing materials for PDRC often face challenges such as limited solar reflectivity or infrared emissivity, especially in the key atmospheric transparency window (ATW; 8–14 μm), which reduces their effectiveness in real-world applications. In this study, we address these challenges by synthesizing cerium oxide (CeO₂) and a composite oxide material, LaMnO₃/CeO₂/Fe₃O₄ (LCMF), using the solid-state reaction method. These materials are designed to achieve enhanced near-infrared reflectivity (R_NIR) and infrared emissivity (IR_e) within the ATW region. The synthesized CeO₂ and LCMF composites exhibit cubic phases after calcination at 1200 °C for 6 h. Microstructural analysis reveals a large-faceted morphology with particle agglomeration, characterized by an average grain size of 2 μm. We found that the band gap (E_g) and the presence of fewer oxygen vacancies (Vo••) significantly impact R_NIR and IR_e. Specifically, the CeO₂ and LCMF composites demonstrated high R_NIR (100 % and 50 %, respectively) and substantial increases in IR_e (0.97 for CeO₂ and 0.99 for LCMF). The surface temperatures of these materials were significantly lower when exposed to thermal radiation, indicating reduced absorption in the solar spectrum and promising cooling potential. These findings suggest that CeO₂ and LCMF composites are promising candidates for improving energy efficiency through enhanced radiative cooling, offering a potential solution to the limitations of current materials in PDRC applications.