Adsorption and nucleation mechanism of molten carbonate on nano-SiC surface

Abstract

Molten carbonate is an important thermal storage media for high temperature thermal energy storage system. However, the specific heat capacity (SHC) of carbonate is less than 2 J/g K, which limits its application prospects. Nano-SiC was used to improve the SHC of carbonate at high temperature in our previous work. The SHC of binary carbonate increased by 83 % with the addition of nano-SiC. However, the improvement mechanism is not clear. In this study, the adsorption and nucleation mechanism of molten carbonate on nano-SiC surface were clarified. The DFT calculation results show that the adsorption energy of Li+, Na+ and CO32− is −310, −259 and −654 kJ/mol, respectively, which means the addition of nano-SiC causes a non-uniform distribution of molten carbonate ions around its surface. This affects the subsequent nucleation and results in carbonate segregation. Na2CO3 is the most thermodynamically favorable to adsorb and nucleate, followed by LiNaCO3, and Li2CO3 is the most difficult. The crystalline phase changes of carbonate on nano-SiC surface from solid to liquid phase during melting process were obtained in-situ and the results are consistent with the DFT calculations. Therefore, the adsorption and nucleation mechanism of molten carbonate on nano-SiC surface is well elucidated by the calculations and experiments of this study.