Hierarchical Cellulose Aerogel Reinforced with In Situ-Assembled Cellulose Nanofibers for Building Cooling.

The development of new structural materials for passive daytime radiative cooling (PDRC) of buildings will significantly reduce global building energy consumption. Cellulose aerogels are potential PDRC materials for building cooling, but the cooling performance and mechanical strength of cellulose aerogels are considered as challenges for their practical applications. Herein, a bio-inspired hierarchically structured cellulose aerogel (HSCA) was fabricated through an assembly strategy assisted by a high-voltage electrostatic field. The HSCA possesses outstanding PDRC performance and moderate mechanical strength owing to aligned hierarchical porous network microstructures reinforced with in situ-assembled crystalline cellulose nanofibers. Promisingly, the HSCA achieves a max cooling temperature of 7.2 °C and exhibits 1.9 MPa axial compressive strength. There was no significant cooling performance degradation after the hydrophobically modified HSCA was placed outdoors for 3 months. A simulation of potential cooling energy savings shows that by using HSCA as the building envelopes (side wall and roof), it can save 52.7% of cooling energy compared to the building baseline consumption. This new strategy opens up the possibility of developing advanced functionally regenerated cellulose aerogel, which is expected to provide a revolutionary improvement in aerogel materials for building cooling.