Fluidisable mesoporous silica composites for thermochemical energy storage

Salt hydrate based thermochemical energy storage has been widely recognised as a promising long-duration storage technology to decarbonize heating/cooling in buildings.However, currently there are few salt hydratebased energy storage materials capable to fulfil the requirements for energy density, efficiency, scalability and stability due to inappropriate particle size of the material. In this study, a commercially available mesoporous silica with large pore volume and good fluidisability was used as the porous matrix to prepare salt composites containing different salts (CaBr2, MgBr2, MgSO4, CaCl2, and Al(NH4)(SO4)2) via a facile incipient wetness impregnation method. A variety of techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), nitrogen physisorption measurements and thermogravimetric analysis (TGA) were used to characterize the physicochemical properties and water hydration/ dehydration performance of mesoporous silica-based salt composites. The results showed that both salt loading level and salt type play critical roles in determining the water adsorption performance of salt composites. Tested under hydration conditions of 30 degrees C and vapour pressure of 25 mbar, the CaCl2 based salt composites exhibited the highest water adsorption capacity, which reached 109 wt% at the CaCl2 loading level of 50 wt%, while the MgBr2 based salt composites had faster water adsorption rates than other salt composites. Most of the salt composites were capable of desorbing 70-80% of the adsorbed water at temperatures below 90 degrees C, highlighting their great potential to store low-grade heat such as industrial waste heat or solar thermal energy. Advanced characterization demonstrated that the large pore volume and pore size improved the salt molecules' accessibility and water diffusivity inside the pores, leading to high water adsorption capacity and fast hydration/ dehydration rate. In the aspects of particle size for future upscaling, this work presents an all new scalable and fluidisable salt composite material that opens up the potential to develop low-temperature fluidised bed based thermal energy storage systems for the first time.

Automated summary

This study used commercially available mesoporous silica as a porous matrix to prepare salt composites containing different salts. The physicochemical properties and water hydration/dehydration performance of the composites were characterized. The results showed that the salt loading level and type of salt played critical roles in determining the water adsorption performance of the composites, and most of the composites were capable of storing low-grade heat effectively.