A switchable dual-mode film with designed intercalated and hierarchical structures for highly efficient passive radiation cooling and solar heating

Abstract

A single-mode solar heating (SH) and passive radiative cooling (PRC) have been fast developed in outdoor thermal management. However, they hardly change with the temperature fluctuations of the hot and cold seasons. Herein, a flexible and stable dual-mode film with photo responsibility was engineered by integrating heating coating and cooling coating on the opposite surfaces of a porous polypropylene (PP) membrane. Flip the surfaces of the dual-mode film-facing solar light to switch between PRC and SH. The cross-linked heating side was fabricated from reduced graphene oxide (rGO) nanosheets intercalated with carbon black (CB) particles via spraying. A thick intercalated film can enhance solar absorptivity (96.4 %) and low infrared emissivity (8.0 %) due to the multiple solar reflections and adsorption between the interlayers, leading to high solar heating. The cooling side was derived from polyvinylidene fluoride (PVDF) coating embedded micro-nano Al2O3 particles via water vapor-induced phase separation (VIPS). The hierarchical coating with a pore size of 8.4 ± 0.1 µm and roughness of 4.0 ± 0.3 µm exhibits high solar reflectivity (92.2 %) and infrared emissivity (96.9 %), resulting in excellent passive radiative cooling. The net heating power (Pheating) and net cooling power (Pcooling) of the dual-mode film are 845.9 and 96.7 W m−2. Moreover, the dual-mode film exhibits outdoor thermoregulation capacity upon covering buildings, cars, and ice. In outdoor environments under solar radiation of 611 ∼ 716 W m−2, it has a temperature increase/decrease of 17.8/5.3 °C to the ambient temperature. Owing to the scalable fabrication processes and excellent thermoregulation characteristics, the dual-mode film is promising for applications in personal thermal management, energy-efficient buildings, in-car temperature control, and food freezing-thawing.