Synergistic radiative-evaporative cooling coatings for advanced thermal management

Passive daytime radiative cooling represents a promising strategy for energy conservation, emission reduction, and carbon neutrality due to its zero-energy-consumption operation. However, conventional passive daytime radiative cooling coatings face challenges, including unstable performance and limited thermal regulation capabilities. To overcome these limitations, we developed a radiative-evaporative cooler (REC) coating by combining integrating titanium dioxide (TiO₂)-based radiative materials with hygroscopic lithium bromide (LiBr). The REC coating exhibits an infrared emissivity of approximately 94% within the 8-13μm atmospheric transparency window and a solar reflectance of 87%. Notably, under nocturnal environmental conditions, the coating containing 20 wt% LiBr demonstrates exceptional moisture absorption capacity, retaining moisture equivalent to 54% of its original weight. We systematically evaluated the thermal performance of the REC coating under diverse environmental conditions. Under solar irradiance of approximately 840.5 W/m², the REC coating with 15 wt% LiBr achieved optimal cooling, reducing temperatures by up to 5°C compared to conventional radiative cooling coatings. This study establishes a robust theoretical and experimental foundation for hybrid cooling strategies, validating their synergistic thermal management performance. The REC coating effectively addresses the insufficient cooling power of traditional radiative cooling, demonstrating significant potential for applications in building thermal regulation, electronic cooling, and renewable energy systems. This advancement represents a critical step toward sustainable and energy-efficient cooling technologies.