Significant breakthrough in developing passive radiative cooling materials
By : Michelle Liu, Jessica Leung
Passive radiative cooling technology has recently emerged as a promising solution for reducing space cooling energy consumption to mitigate the impact of climate change. However, existing passive radiative cooling materials are limited by high cost and poor compatibility, or lack weather resistance and effective solar reflection.
The cooling ceramic mimics the bio-whiteness of Cyphochilus.Inspired by the whitest beetle, Cyphochilus, researchers from City University of Hong Kong (CityUHK) recently developed a cooling ceramic, which has high-performance optical properties for energy- and refrigerant-free cooling generation. Its cost-effectiveness, durability and versatility make it highly suitable for commercialisation in numerous applications, particularly in building construction. By reducing the thermal load of buildings and providing stable cooling performance, the cooling ceramic enhances energy efficiency and helps combat global warming.
The cooling ceramic efficiently scatters almost all the wavelengths of sunlight, resulting in near-ideal solar reflectivity of 99.6%. It also achieves high mid-infrared thermal emission of 96.5%, outperforming current state-of-the-art materials.
In addition to its exceptional optical performance, the cooling ceramic exhibits excellent weather resistance, chemical stability and mechanical strength, making it ideal for long-term outdoor applications.
The research outcomes were published in the prestigious scientific journal Science, titled “Hierarchically structured passive radiative cooling ceramic with high solar reflectivity”.
Professor Tso (centre) and his research teamProfessor Edwin Tso Chi-yan, in the School of Energy and Environment (SEE) of CityUHK, and Professor Wang Zuankai, Adjunct Professor in the Department of Mechanical Engineering of CityUHK, are the corresponding authors. The first author is Lin Kaixin, and the second author is Chen Siru, both PhD students supervised by Professor Tso in SEE of CityUHK.
“Our experiment found that applying the cooling ceramic on a house roof can result in more than 20% electricity saving for space cooling, which confirms the great potential of cooling ceramic in reducing people’s reliance on traditional active cooling strategies,” said Professor Tso.
Building upon the findings of cooling ceramics, the team is exploring the possibility of mass production of cooling ceramic materials to facilitate practical applications.
Professor Tso’s team has made substantial progress in identifying potential photofluorescent materials that can be employed in coloured cooling ceramic applications. These materials can generate colours similar to traditional pigments by absorbing visible light. In addition, they can convert the absorbed visible light into radiation in other wavelengths, thereby recovering the cooling power of coloured cooling ceramic.
In addition to cooling ceramic, Professor Tso’s team has developed a passive radiative cooling paint for buildings. It has received an overwhelmingly positive response and collaboration opportunities from diverse stakeholders in the building and construction industry. They are working towards commercialisation to provide a high-quality, cost-effective cooling ceramic solution for sustainable building applications.
“We are currently developing an optical-adaptive cooling coating that can achieve thermal control in response to the surrounding environment. The remarkable aspect of this coating lies in its compatibility with various existing passive radiative cooling materials that possess high solar reflection, thus enabling intelligent thermal control in both hot and cold seasons,” Professor Tso explained.
To substantiate the thermal regulation capabilities of the coating, the team is conducting extensive experiments in different seasons and cities.
