Towards an agglomeration free Ca(OH)2/CaO thermochemical energy storage loop via nanofabricated hollow CaO microspheres with highly porous shells

The Ca(OH)₂/CaO loop offers a promising solution for seasonal thermochemical heat storage, vital for decarbonizing the heating sector thanks to its high energy density and abundant raw materials. However, cyclic hydration/dehydration of limestone-derived CaO (r-CaO) faces challenges like agglomeration and high-volume expansion, limiting its expected performances. This study focuses on fabricating hollow CaO microspheres (h-CaO) with porous shells via a facile one-pot hydrothermal synthesis method, without doping materials. These microspheres exhibit superior cyclic performance compared to r-CaO, with SEM-EDS confirming successful fabrication. Over 30 cycles in the temperature range of 400–550 °C, h-CaO achieves an average storage density of 1755 kJ/kg, peaking at 1835 kJ/kg, with kinetics twice as high as r-CaO. Most importantly, the hollow microstructure reduces dramatically the apparent volumetric expansion from 250 % to as little as 32 %, offering a potential solution to agglomeration at the reactor level and advan44cing the commercial viability of the Ca(OH)2/CaO thermochemical storage technology.