A sustainable and robust Janus film Inspired by the bird’s nest structure for efficient year-round outdoor thermal management

Abstract

Janus structures combining radiative cooling and heating have attracted considerable interest for providing thermal comfort in dynamic environments. However, most of the strategies ignore the weak interfacial bonding due to the differences in material properties of the cooling and heating sides, which ultimately results in a lack of durability. Herein, inspired by the bird’s nest structure, we demonstrated a dual-mode Janus film with bonded interfaces through a simple vacuum-assisted filtration and PDMS modification. The unique structure of film ensures efficient thermal management including a sub-ambient temperature drop of ∼6.7 °C and a rise of ∼19.8 °C under direct sunlight irradiance. The cooling performance is activated by the synergistic enhancement with BaSO4 and BC porous networks, which exhibits high solar reflectivity (∼95.6 %) and MIR emissivity (∼95.2 %). The heating performance is derived from solar heating (∼71.6 °C at one sun irradiation) and Joule heating (∼88.6 °C at a low voltage of 2.5 V) as a complement, benefiting from the photothermal and electrothermal conversion of MXene. The cooling and heating can be easily obtained by flipping. In addition, the film maintains efficient cooling and heating even after being immersed in water and exposed to sunlight, thereby ensuring outdoor thermal management. Overall, this dual-mode Janus film shows great potential for regulating outdoor thermal comfort and alleviating the energy crisis.