Hierarchically amorphous cellulose acetate porous membranes with spectral selectivity for all-weather radiative...

Passive radiative cooling has emerged as a promising approach for cooling without energy consumption. However, developing all-weather passive radiative cooling materials in response to diverse weather conditions remains a significant challenge, since such materials must simultaneously exhibit semi-emissive and transparent properties in the mid-infrared spectrum and high reflectivity to sunlight. Herein, we present a hierarchically amorphous cellulose acetate porous membranes (HAPM), fabricated using a solvent-template-assisted evaporation-induced phase separation (ST-EIPS) strategy, for all-weather passive radiative cooling. The HAPM exhibits exceptional spectral selectivity that satisfies the stringent spectral requirements for such applications, i.e., 64.1 % emissivity within the atmospheric window (ATW) and 74.5 % transmissivity in the non-ATW range due to its specific molecular backbone, while having 97.5 % solar reflectivity (especially 99.8 % reflectivity in the visible spectrum) enabled by the hierarchical porous structure with multistage scattering. These unique optical properties allow the HAPM to achieve sub-ambient maximal cooling of 15.8 °C under intense solar irradiance and 6.5 °C under cloudy conditions. Furthermore, a radiative cooling house model incorporating the HAPM is demonstrated and exhibits cooling temperatures of 25.0 °C on sunny days and 4.4 °C on cloudy days. This work underscores the potential of cross-scale structurally engineered porous membranes for all-weather radiative cooling applications.