Molecular insight into further enhancement of thermal conductivity and heat capacity of K2CO3-SiO2 molten salt nanofluids by oxygen vacancy defects in SiO2 nanoparticles

Abstract

Nanoparticle-reinforced molten salt materials are gaining attention due to their capacity of improving thermal energy storage. However, the effect of charged nanoparticles by defects on the thermal performance improvement of molten salt remains unexplored. This study investigates how SiO₂ nanoparticles charged due to oxygen vacancy defects affect the thermal properties of K₂CO₃ molten salt for the first time by molecular dynamics (MD) simulation. It is found that as oxygen vacancies increase, the charge on nanoparticles increases, significantly enhancing both the specific heat capacity (SHC) and thermal conductivity (TC) of the SiO₂-K₂CO₃ system. In the K₂CO₃-SiO₂ system, the enhancement of SHC and TC with 25 % oxygen vacancy ratio in nanoparticles is 241 % and 197 % higher, respectively, than those with ideal nanoparticles. Microstructure analysis shows that oxygen vacancies in nanoparticles promotes the formation of alternating cation-anion compression layers around the nanoparticles, intensifying ion aggregation and mismatch. The results of the heat flow decomposition show that the nonbonded interaction dominates the heat transfer process and its influence is further strengthened with the increasing number of oxygen vacancies in nanoparticles. The idea of introducing charges through defecting process provides a new approach for further increasing molten salt thermal performance.