Optically Triggered Synchronous Heat Release of Phase-Change Enthalpy and Photo-Thermal Energy in Phase-Change Materials at Low Temperatures

Phase-change materials (PCMs) are used in several energy recycling utilization systems due to their latent-heat-storage and -release ability. However, the inability of PCMs to release heat at temperatures below their freezing point limits their application in distributed energy utilization systems. This paper reports optically-triggered low-temperature heat release in PCMs based on a solid-liquid phase change (PC) controlled by the trans-cis (E-Z) photo-isomerization of azobenzene. To achieve this, a photo-responsive alkyl-grafted Azo is incorporated into tetradecane (Ted) to create a photo-sensitive energy barrier for the PC. The Azo/Ted composite exhibits controllable supercooling (4.04-8.80 degrees C) for heat storage and achieves synchronous heat release of PC enthalpy and photo-thermal energy. In addition, the Azo reduces the crystallization of Ted by intercalating into its molecular alignment. Furthermore, under light illumination, the Azo/Ted composite releases considerable heat (207.5 J g(-1)) at relatively low temperatures (-1.96 to -6.71 degrees C). The temperature of the annular device fabricated for energy utilization increases by 4 degrees C in a low-temperature environment (-5 degrees C). This study will pave the way for the design of advanced distributed energy systems that operate by controlling the energy storage/release of PCMs over a wide range of temperatures.