Enhancing the Stability of CaO-Based Looping Materials in Thermochemical Energy Storage by Codoping Y and Mg

Aiming to improve the decay in thermochemical energy storage (TCES) performance of CaO-based looping materials with the number of carbonation/calcination cycles, a series of Y/Mg-codoped CaO-based materials were prepared by using the classical sol–gel method and citric acid as a carbon template to enhance the porosity and specific surface area. The structural characterizations showed that Y and Mg were presented in two forms. Part of Y/Mg was presented in the form of Y2O3 and MgO nanoparticles with an average size of 15 and 40 nm, respectively. These Y2O3 and MgO nanoparticles with high Tammann temperature and thermal conductivity were highly dispersed to retard the sintering and growth of CaO grains. The rest of Y and Mg were doped into the framework of the CaO lattice in atomic form by substituting Ca atoms. These Y and Mg created a large amount of the oxygen vacancies surrounding Ca atoms to facilitate the electron transfer from Ca2+ ions to dopants, which enhanced the CO2 capture capacity of CaO-based materials by improving the kinetics of the carbonation reaction. As a result, the optimal CaO-based composite denoted as Ca/Y5/Mg10 exhibited a high initial energy storage density of up to >2300 kJ/kg and held an excellent looping reaction stability after 25 carbonation/calcination cycles owing to the cooperation of Y with Mg additives. This work provided effective and economical CaO-based looping materials for application in thermochemical energy storage.