Synergistic radiative and evaporative cooling in LiCl-cellulose nanofiber xerogels for temperature reduction and energy saving

Passive daytime radiative cooling (PDRC) is an emerging technology for regulating indoor temperatures without electrical energy consumption by reflecting incoming solar light and emitting thermal infrared radiation into outer space. However, the cooling efficiency of existing PDRC materials remains limited. In this work, we developed a porous composite xerogel integrated with hygroscopic lithium chloride (LiCl) and cellulose nanofibers (CNFs). Benefiting from its highly porous structure and the abundant C-O-C and C O functional groups of CNFs, the xerogel exhibits exceptionally high solar reflectance (97.76%) and mid-infrared emissivity (95.36%) within the atmospheric transparency window (8–13 μm), endowing it with superior radiative cooling properties. Furthermore, the evaporation of water molecules captured by the hygroscopic LiCl under solar irradiation induces additional heat absorption, which effectively suppresses temperature rise and further enhances cooling performance. Consequently, through the combination of radiative and evaporative cooling, the composite xerogel achieves maximum outdoor temperature reductions of 12.65 °C in spring and 27.76 °C in summer, compared to traditional porous polystyrene foam. Energy consumption simulation calculations indicate that the application of the CNF composite xerogel could reduce cooling energy consumption by over 30% in most regions of China. This study demonstrates a highly efficient PDRC material achieved through the synergistic integration of radiative and evaporative cooling strategies, showing strong utilization potentiality on the energy-saving capabilities of dual-functional materials.