A team of researchers from City University of Hong Kong has developed a new passive radiative cooling (PCR) material that boosts energy efficiency in the construction sector.

Called “cooling ceramic,” the material demonstrates what the researchers call high-performance optical properties for energy-free and refrigerant-free cooling generation.

Source: City University of Hong Kong

"The color, weather resistance, mechanical robustness and ability to depress the Leidenfrost effect — a phenomenon that prevents heat transfer and makes liquid cooling on the hot surface ineffective — are key features ensuring the durable and versatile nature of the cooling ceramic," the researchers explained.

The material’s properties are due to its “hierarchically porous structure," which is reportedly easy to construct using inorganic elements like alumina via a two-step process that includes phase inversion and sintering. The researchers suggest that alumina’s high bandgap enables the cooling ceramic to minimize solar absorption.

Additionally, by mimicking the bio-whiteness of the Cyphochilus beetle and optimizing the porous structure based on Mie scattering, the cooling ceramic reportedly managed to scatter virtually all the wavelengths of sunlight, thereby achieving 99.6% solar reflectivity.

"The cooling ceramic is made of alumina, which provides the desired UV resistance degradation, which is a concern typical of most polymer-based PRC designs. It also exhibits outstanding fire resistance by withstanding temperatures exceeding 1,000° C, which surpasses the capabilities of most polymer-based or metal-based PRC materials," the researchers added.

The City University of Hong Kong team found that when it applied the cooling ceramic to a roof, it reportedly achieved more than 20% electricity for space cooling, thereby confirming the potential of cooling ceramic in reducing people's reliance on traditional active cooling strategies.

An article detailing the material, "Hierarchically structured passive radiative cooling ceramic with high solar reflectivity," appears in the journal Science.