On-Demand Modulation of Radiative Cooling Performance with Hygroscopic Salt-Cellulose Fiber for Building Applications

Radiative cooling of buildings with low carbon footprints has drawn widespread attention. However, the possible overcooling effect at night may increase building heating energy consumption in transition seasons, especially in mild climates. Herein, we developed a simple, low-cost, and high-performance hygroscopic salt-cellulose fiber to modulate diurnal radiative cooling performance. With the transition of desorption and adsorption of the cooling fiber, the sub-ambient temperature reduction can reach 2.4 °C during the day, and be limited to below 2 °C at night. The daytime cooling performance is dominated by thermal radiation when ambient relative humidity is low, and dominated by evaporation when relative humidity is high. The nighttime adsorption enthalpy is contributed by multiscale mechanisms, including the adsorption of hydrophilic functional groups, capillary condensation, as well as the deliquesce of CaCl₂ salt. The profusion of cellulose and hygroscopic salt features desirable cost-effectiveness, and the simple preparation process allows large-scale applications.