Immobilized Ionic Liquid Sorption Composites: High-Energy-Density Thermal Storage at Ambient Temperatures for Solar and Waste Heat

Sorption-based thermal energy storage using water vapor sorbents represents a highly promising strategy for the efficient storage and utilization of low-grade energy sources, such as waste heat and solar energy. However, the high desorption temperature, liquid leakage issues, and relatively low energy storage density of conventional sorbents significantly hinder their practical applications. In this study, a series of novel ionic liquid-based composite sorbents composed of 1-ethyl-3-methylimidazolium acetate and graphene aerogel were developed to enhance the thermal storage density for effective low-grade energy storage. Among these composites, the most attractive one demonstrated an exceptional water sorption capacity of 1.01 g/g without any liquid leakage and achieved an outstanding thermal storage density of 2824 J/g, which is 272% higher than that of the traditional silica gel. Moreover, this composite sorbent exhibited superior performance in waste heat storage capacity across a broad low-temperature range of 35–80 °C and also achieved remarkable efficiency in harvesting solar energy. This work could pave the way for more efficient and sustainable strategies for low-grade thermal energy storage and utilization based on ionic liquid sorbents.