High-emissivity infrared coatings for radiative cooling: research progress in high-temperature protection of metals

Radiative cooling is the inherent mechanism for direct heat transfer to surroundings via infrared electromagnetic wave emission. Developed to enhance the radiative cooling capacity of metallic substrates, high-emissivity infrared coatings boost surface radiation, thereby enabling efficient thermal-to-electromagnetic energy conversion. This provides a contactless solution to the limited efficiency of conventional high-temperature protection methods. This review comprehensively addresses the infrared radiation generation mechanisms, radiation performance enhancement strategies, and fabrication techniques of high-emissivity infrared coatings. Fundamental mechanisms generating infrared radiation are elucidated from macroscopic and microscopic perspectives, followed by a critical interrogation of performance enhancement strategies based on crystal structure-radiative property correlations, including compositional design and multiscale structural optimization, in which appropriate doping in specific parent materials to improve the radiative cooling performance of infrared coating is the mainstream method. Subsequent evaluation of mainstream coating fabrication techniques focuses on processing parameters and industrial applicability. Finally, future research directions are proposed to address existing technical and scientific challenges, with the goal of advancing the development and application of high-emissivity infrared coatings.