Improved durability in thermochemical energy storage using Ti/Al/Mg Co-doped Calcium-based composites with hierarchical Meso/Micro pore structures

• The co-doped CaO composites that are rich in mesopores and micropores are synthesized by a modified sol-gel method. • MgCl 2 is the primary dopant and tetrabutyl titanate or aluminum nitrate is used as an auxiliary dopant. • More than 75% of CaO in the co-doped composites still maintains reactivity after 100 cycles. • The proposed relationship of multiple particle sizes can provide guidance for particle design and preparation. Calcium-based thermochemical energy storage is promising for high-temperature thermal utilization of the solar energy. However, the energy storage performances of calcium-based materials show sintering-induced decays after multiple cycles. Here, the co-doped CaO composites that are rich in mesopores and micropores are synthesized by a modified sol-gel method, where MgCl 2 is the primary dopant, and tetrabutyl titanate or aluminum nitrate is used as an auxiliary dopant. The decomposition of MgCl 2 into MgO leads to the formation of thin shell structures around the composites, which is further stabilized by the generated calcium titanate or calcium aluminate, as they work synergistically to improve the long-term cyclic stabilities. The conversions in CaO and cyclic stabilities of the co-doped composites are remarkable, higher than most of the existing composites. Their average energy storage densities exceed 1132 kJ kg -1 over 100 calcination/carbonation cycles and more than 75% of CaO still maintains reactivity after 100 cycles. Their porous thin-shell and interconnected network structures provide ample space for reaction, and the particle sizes are also uniform with relatively lower particle growth, which reflect the high anti-sintering feature. The CaO-based composite chemistry and synthesis methods developed here show great promises for their long-term industrial applications in concentrated solar energy storage.