Scalable Production of EP/CaCl2@C Multistage Core–Shell Sorbent for Solar-Driven Sorption Heat Storage Application

Abstract

The sorption heat storage based on composites with salt hydrates enables the efficient utilization and trans-seasonal storage of solar energy. Nevertheless, the limitation of heat and mass transfer of salt hydrates has restricted the implementation of this technology. Here, a novel strategy is proposed to synthesize a multistage core–shell sorbent, where salt hydrates are dispersed in the macropores of the expanded perlite (EP) before being coated with a carbon layer outside the EP/Ca particles. The abundant macropores in the matrix are beneficial to the high salt loading and efficient mass transfer. Moreover, the carbon shell significantly enhances the light-to-heat conversion performance of the sorbent, and the heat can be directly transferred from the shell to the internal salt hydrates for desorption, thus realizing the absorption, conversion, and storage of solar energy in the multistage core–shell sorbent. The sorption capacity of EP/Ca@C-0.25 is determined to be 1.22 g-H₂O/g-sorbent under the conditions of 20 °C and RH 80%, and 84% of the water can be desorbed after irradiation under the 1 kW/m² simulated sunlight for 2 h, with a heat storage density of 1698 J/g-sorbent in the heat storage process. Additionally, we also studied the performance of EP/Ca@C-0.25 in a solar-driven thermal energy storage system. In summer, the sorbent is placed outdoors and desorbed under sunlight within 2 h to achieve heat storage. In winter, the sorbent is placed in a fixed bed for adsorption, and the heat released during adsorption increases the air temperature by 5 °C for 10 h. Typically, the multistage core–shell sorbent demonstrates a potential sorbent for large-scale use in solar-driven thermal energy storage for practical purposes.