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 °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.