High performance colored passive daytime radiative cooling device based on a CNC film/cellulose aerogel bilayer structure

Passive daytime radiative cooling (PDRC) technologies have emerged as a promising solution to reduce energy consumption in air conditioning and facilitate sustainable development. In this work, a colored bilayer cooler (CBC) was fabricated through an energy-efficient and sustainable strategy that integrates unidirectional freeze-drying and hydrogen bond-driven wet adhesion (HBWA). This multifunctional structure provides an innovative and practical approach toward energy-efficient thermal management through the synergy effect of efficient thermal insulation and radiative cooling, along with aesthetically viable property. Such cooler bilayer consists of a colored cellulose nanocrystal (CNC) film as the top layer and a cellulose aerogel as the substrate. The CNC film selectively reflects sunlight through ordered molecular arrangements, endowing the device with structural coloration. The cellulose aerogel contributes an ultralow thermal conductivity of 0.024 W m−1 K−1, a high solar reflectivity of 90%, and a high mid-infrared emissivity of 94%. Outdoor tests reveal that the CBC can achieve a sub-ambient cooling of 1.9 °C under a solar irradiance of 700 W m−2, demonstrating exceptional PDRC performance. Leveraging the combined effects of low thermal conductivity and excellent radiative cooling capability, the CBC can reduce cooling energy consumption by over 55% in typical Chinese cities.