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

Abstract

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.