Fe- and Mn-Doped Ca-Based Materials for Thermochemical Energy Storage Systems

Abstract In recent years, CaO/CaCO3 has attracted great attention in the field of thermochemical energy storage. However, due to its very low optical absorption, thermochemical energy storage materials made of pure CaO/CaCO3 struggle to reach reaction temperatures when only absorbing solar energy directly in a calciner, making the overall system inefficient. Therefore, in this paper, calcium-based materials with both high optical absorption and high energy release density were synthesized to directly convert solar energy to chemical energy for storage. Doping metal elements into a Ca-based material was demonstrated to play a positive role in improving cycling stability on the energy release process. Here, we developed a loose and porous Ca-based composite consisting of two phases including CaCO3 and Ca2FeMnO5, exhibiting excellent cycling stability and high energy release density. The highest energy release density after 20 cycles reached 2.51 MJ/kg, which is 2.62 times that of pure CaCO3. Meanwhile, the highest optical absorption reached 76.8%, which is 7.11 times that of pure CaCO3. The Ca-based materials developed in this paper can improve cycling stability and enhanced optical absorption simultaneously, providing guidance for the efficient development of calcium looping thermochemical energy storage systems in the future.