Functional Metasurfaces and Structures for Thermal Radiative Applications

This invited talk will focus on passive radiative cooling and solar-driven water desalination technologies and the issues that have hindered their development for real-life applications. Our goals are to improve buildings’ energy efficiency by reducing the need for traditional vapor-compression cooling systems and to enhance freshwater production by taking advantage of renewable energy. Part 1: The compressor-based cooling systems, providing comfortable interior environments for infrastructures, account for about 20% of the total electricity consumption around the world. Moreover, the resultant heating effect and greenhouse gas emissions towards the environment accelerate global warming and climate change. An energy-efficient and eco-friendly cooling approach is highly demanded. The emerging passive daytime radiative cooling (PDRC) technique can achieve sub-ambient cooling effects under direct sunlight without any energy consumption by simultaneously reflecting sunlight and radiating excessive heat as infrared thermal radiation to the cold outer space through the Earth’s atmospheric window. Such an approach is becoming an attractive candidate for improving energy efficiencies for buildings, because it eliminates the need for coolant, electricity, and compressor required by traditional mechanical cooling systems. Part 2: Interfacial solar steam generation is emerging as a promising technique for efficient desalination. Although increasing efforts have been made, challenges exist for achieving a balance among a plethora of performance indicators—for example, rapid evaporation, durability, low-cost deployment, and salt rejection. We have demonstrated that carbonized agricultural waste can convert 98% of sunlight into heat, and the strong capillarity of porous carbon fibers networks pumps sufficient water to evaporation interfaces. Salt diffusion within microchannels enables quick salt drainage to the bulk seawater to prevent salt accumulation. These advantages, together with facial deployment, offer an approach for converting farm waste to energy with high efficiency and easy implementation, which is particularly well suited for developing regions.