Scalable, fire-retardant, and spectrally robust melamine-formaldehyde photonic bulk for efficient daytime radiative cooling

Traditional building materials such as wood and concrete cannot effectively regulate the heat flux of buildings. Compressor-based cooling systems are used to provide comfortable interior environments for humans, contributing significantly to global energy consumption. It has recently been demonstrated that sub-ambient passive daytime radiative cooling has been obtained by efficiently radiating thermal energy to the cold outer space through the atmospheric transparent window while reflecting most of the solar irradiance. Here, we demonstrate a high-performance daytime radiative cooling material processed by hydraulic pressing melamine-formaldehyde (MF) particles and thermally annealing them into a cross-linked photonic cooling bulk as an efficient solar reflector and infrared thermal emitter. It reaches a sub-ambient stagnation temperature of 3.6 ∘C under direct sun irradiance (750 W m−2), which is 12 ∘C and 5 ∘C below the concrete and the wood as control group temperatures, respectively. The two-step fabrication process is straightforward and can be easily scaled up for industrial manufacturing. The as-prepared MF cooling material shows highly desirable fire-retardant properties and is self-extinguishing, make it excellent material for building safety. The material is durable, and spectrally robust in harsh environments, such as long exposure to the acidic and alkaline solutions.