Spatiotemporal phase change materials for thermal energy long-term storage and controllable release

Phase change materials (PCMs) have attracted much attention in the field of solar thermal utilization recently, due to their outstanding thermal energy storage performance. However, PCMs usually release their stored latent heat spontaneously as the temperature below the phase transition temperature, rendering thermal energy storage and release uncontrollable, thus hindering their practical application in time and space. Herein, we developed erythritol/sodium carboxymethylcellulose/tetrasodium ethylenediaminetetraacetate (ERY/CMC/EDTA-4Na) composite PCMs with novel spatiotemporal thermal energy storage properties, defined as spatiotemporal PCMs (STPCMs), which exhibit the capacity of thermal energy long-term storage and controllable release. Our results show that the composite PCMs are unable to lose latent heat due to spontaneous crystallization during cooling, but can controllably release thermal energy through cold crystallization during reheating. The cold-crystallization temperature and enthalpy of composite PCMs can be adjusted by proportional addition of EDTA-4Na to the composite. When the mass fractions of CMC and EDTA-4Na are both 10%, the composite PCMs can exhibit the optical cold-crystallization temperature of 51.7 °C and enthalpy of 178.1 J/g. The supercooled composite PCMs without latent heat release can be maintained at room temperature (10–25 °C) for up to more than two months, and subsequently the stored latent heat can be controllably released by means of thermal triggering or heterogeneous nucleation. Our findings provide novel insights into the design and construction of new PCMs with spatiotemporal performance of thermal energy long-term storage and controllable release, and consequently open a new door for the development of advanced solar thermal utilization techniques on the basis of STPCMs.