A Janus film coupling radiative cooling and heating for all-day active/passive personal thermal management

Abstract

Textiles with passive radiative cooling (PRC)/passive radiative heating (PRH) capabilities have been developed to address human thermal comfort in different climate scenarios. Although materials with single PRC/PRH function have been reported, they tended to exhibit only one function of either cooling or heating, which was restrictive in achieving efficient and controllable personal thermal management. Herein, we propose a dual-mode Janus film composed of a PVDF-HFP/ZrO₂ cooling layer and a Mxene/CNT heating layer for efficient all-day PRC/PRH. Owing to the natural high refractive index of ZrO₂ nanoparticles and the strong scattering of sunlight by the PVDF-HFP nanofibers, the cooling side exhibits a high solar reflectance of 97.1 %. With an infrared emittance of 93 % in atmospheric window, the cooling side achieves subambient cooling temperatures of 8.8 °C during daytime and 7 °C during nighttime. Meanwhile, the Mxene/CNT synergy enables the heating side to exhibit high solar absorbance and electrical conductivity, resulting in a significant PRH capability of up to 19 °C and an outstanding active Joule heating capability as a temperature compensation. The dual-mode Janus film is able to switch cooling/heating modes by simply flipping the interface to alter the sky-facing side, enabling efficient and continuous personal thermal management in complex and changeable environments.