All-Season Dual-Mode Thermolator Based on Radiative Cooling and Solar Heating Technology

Passive radiative cooling and solar heating have received a great deal of scholarly attention as green and sustainable ways to maintain thermal homeostasis. However, most of the current passive radiative cooling and solar heating materials are optically static and cannot adapt to seasonal dynamic weather changes. Herein, we developed an HPC/CaCl2/C dual-mode device (HCC) that autonomously senses changes in ambient temperature to switch cooling/heating modes. When the ambient temperature reaches the low critical solution temperature (LCST approximate to 37 degrees C) of the hydrogel, the cooling side of HCC gradually turns white to reflect sunlight and radiative cooling happens by means of a high infrared emissivity (0.97) in the atmospheric window band (8-13 mu m). The heat-absorbing effect of the heated side accelerates the phase transition of the hydrogel and makes it change to the cooling mode more quickly. When the ambient temperature is higher than LCST, at an irradiance of 850 W/m2, the HCC-20 coating leads to a cavity cooling temperature of approximately 12.3 degrees C and the theoretical cooling power is 109.3 W/m2. When the ambient temperature is lower than the LCST, the upper hydrogel layer is transparent and HCC-20 transforms into a heating function. Under weather conditions with the irradiance of 500 W/m2 and a maximum ambient temperature of 6 degrees C, the average heating capacity is up to around 8 degrees C. The HCC dual-mode device can automatically switch between cooling and heating modes and has great application potential in fields such as buildings and automobiles, providing a favorable way to mitigate energy crises and reduce greenhouse gas emissions.