Enhancing\nthe Stability\nof CaO-Based Looping Materials\nin Thermochemical Energy Storage by Codoping Y and Mg

Aiming to improve the decay in thermochemical\nenergy\nstorage (TCES)\nperformance of CaO-based looping materials with the number of carbonation/calcination\ncycles, a series of Y/Mg-codoped CaO-based materials were prepared\nby using the classical sol–gel method and citric acid as a\ncarbon template to enhance the porosity and specific surface area.\nThe structural characterizations showed that Y and Mg were presented\nin two forms. Part of Y/Mg was presented in the form of Y<sub>2</sub>O<sub>3</sub> and MgO nanoparticles with an average size of 15 and\n40 nm, respectively. These Y<sub>2</sub>O<sub>3</sub> and MgO nanoparticles\nwith high Tammann temperature and thermal conductivity were highly\ndispersed to retard the sintering and growth of CaO grains. The rest\nof Y and Mg were doped into the framework of the CaO lattice in atomic\nform by substituting Ca atoms. These Y and Mg created a large amount\nof the oxygen vacancies surrounding Ca atoms to facilitate the electron\ntransfer from Ca<sup>2+</sup> ions to dopants, which enhanced the\nCO<sub>2</sub> capture capacity of CaO-based materials by improving\nthe kinetics of the carbonation reaction. As a result, the optimal\nCaO-based composite denoted as Ca/Y5/Mg10 exhibited a high initial\nenergy storage density of up to >2300 kJ/kg and held an excellent\nlooping reaction stability after 25 carbonation/calcination cycles\nowing to the cooperation of Y with Mg additives. This work provided\neffective and economical CaO-based looping materials for application\nin thermochemical energy storage.