Configurational Entropy-Driven Synergy of Stability and Reactivity in Calcium-Looping Thermochemical Energy Storage Materials

Abstract Calcium looping (CaL) thermochemical energy storage offers high energy density and low cost for large-scale solar storage. However, CaO sinters severely at high temperatures, causing rapid capacity decay. To suppress sintering, inert supports have been used, but single oxides like CeO2 cannot meet both stability and reactivity demands. Here, this work tunes configurational entropy from 0 to 1.61R by incorporating Ce, Zr, La, Nd, and Yb into CaO and investigates its effect on storage performance. Increased entropy improves performance via two mechanisms. Thermodynamically, entropy compensates mixing enthalpy, enhancing interfacial adhesion from −0.015 to −0.048 eV/Å2, and suppressing sintering, so the quinary system retains a porous structure after 25 cycles. Chemically, multielements create distributed adsorption sites, broadening CO2 adsorption energy from a single value of −0.60 eV to a range of −1.40 to −2.18 eV, facilitating CO2 capture and migration. Consequently, the quinary system achieves 1.883 MJ/kg after 25 cycles, outperforming the unary by 5.45% and other systems by 2.09–15.56%. Thus, configurational entropy engineering simultaneously enhances thermal stability and CO2 kinetics, providing a strategy to overcome the stability–activity trade-off.