Stretchability-adjustable Janus composite fiber membrane for passive radiant cooling and heating

With the frequent occurrence of extreme climates, passive daytime radiant cooling (PDRC) and passive daytime radiant heating (PDRH) technologies are receiving more and more attention as green and sustainable ways to regulate temperature. Here we present a Janus composite porous fiber membrane (MXene@PVDF/TPU), prepared by controlling the ratio of two components, PVDF and TPU, in the electrospinning precursor solution, to regulate the optical, mechanical, and other properties of the fiber membrane. By spraying MXene on one side of the fiber membrane, we achieve radiative heating performance, while the side without MXene spraying exhibits radiative cooling performance. Switching between cooling and heating modes can be accomplished by simply flipping the composite fiber membrane. The cooling side of the fiber membrane has high solar reflectance (93.75 %) and mid-infrared emissivity (83.09 %), and can cool the ambient temperature up to 8.2 °C at noon. At the same time, the heating side of the fiber membrane has low reflectance (14.18 %) and mid-infrared emissivity (24.22 %), and can heat the environment up to 7.4 °C at noon. Besides, due to the electrical and thermal properties of MXene, the MXene@PVDF/TPU fiber membrane exhibits excellent Joule heating characteristics, which can effectively compensate for the PDRH. Switching between the modes of cooling and heating can be achieved by a simple flip of the composite fiber membrane, which is important to reduce carbon emissions to alleviate the energy crisis.