Performance improvement of Na4SiO4 doped with Li2CO3-K2CO3 for high-temperature CO2 capture and thermochemical energy storage

Na4SiO4 is regarded as a new candidate of high-temperature CO2 sorbent. However, the sorption/desorption temperature of Na4SiO4 is high, and cyclic sorption capacity is low. In this study, Na4SiO4 sorbents doped with Li2CO3-K2CO3 (LiKCO3) were synthesized, and the dynamic, isothermal, and cyclic CO2 capture performances were investigated to improve the performance. The maximum CO2 sorption capacity of Na4SiO4-20LiKCO3 reached 20.64 wt% at 725 degrees C, and the cyclic sorption capacity was about 50 % higher than that of pure Na4SiO4. The results indicated that LiKCO3 doping could efficiently decrease the optimal sorption/desorption temperature of Na4SiO4. Furthermore, the maximum conversion efficiency and energy storage density of Na4SiO4-20LiKCO3 reached high levels of 95.7 % and 788 kJ/kg, respectively. Finally, the CO2 chemisorption mechanisms on the Na4SiO4 and Na4SiO4-LiKCO3 co-adsorption surfaces were studied via density functional theory calculations. LiKCO3 doping could enhance CO2 adsorption energy and C-OS covalent interaction on the sorbent surface and the energy levels of the CO2/Na4SiO4-LiKCO3 system were reduced. These changes were beneficial to CO2 chemisorption and agreed well with the experimental values. Thus, Na4SiO4 doped with LiKCO3 had high potential for high-temperature CO2 capture and thermochemical energy storage.