Passive cooling, particularly those combining evaporative and radiative mechanisms, has attracted growing interest due to its low energy requirements for powering electronic devices and integrated systems. However, complex fabrication, low thermal conductivity, and inherent trade-offs between competing cooling mechanisms hinder their potential for commercial application. To address these challenges, we combine hexagonal boron nitride (hBN) with 1-ethyl-3-methylimidazolium acetate (Emim Ac, EA) ionic liquid and fabricate an ionic composite film via a facile, scalable solvent evaporation method. This approach eliminates the need for specialized equipment and intricate steps in traditional cooling materials. The composite film achieves synergistic passive cooling by simultaneously leveraging the evaporative and radiative mechanisms. The incorporation of hBN significantly enhances thermal conductivity to 0.51 W·m-1·K-1, representing a 200% improvement over conventional materials such as silica gel and MOFs. The optimized film structure demonstrates a high-water sorption capacity (0.55 g/g) and an exceptional desorption enthalpy (1307 J/g), enabling efficient evaporative cooling. Furthermore, the film demonstrates a low desorption temperature of 40 °C and remarkable flexibility, making it suitable for diverse thermal management applications. Practical tests verify its effectiveness, lowering the temperature of computer CPUs by more than 5 °C within 8 min and reducing the temperature of photovoltaic (PV) cells by up to 10 °C. By integrating thermal conduction, water evaporation, and thermal radiation, this work presents a high-performance, zero-energy-consumption cooling strategy with broad applicability in electronics and energy systems.
Yang et al. (Tue,) studied this question.