Interfacial ion aggregation at SiO2 nanoparticles enhances thermal energy storage of chloride molten salts: a molecular dynamics study

Abstract

Chloride molten salts have emerged as a promising heat transfer medium for concentrated solar power plants owing to their low cost. However, their widespread adoption has been hindered by limited specific heat capacity and thermal conductivity. In this work, the thermal properties of binary chloride molten salts (NaCl–KCl) were enhanced by adding varying amounts of amorphous SiO₂ nanoparticles. Molecular dynamics simulations were employed to investigate the effects of many-particle effects of SiO₂ nanoparticles on the thermal properties of molten salts instead of the normal one-particle doped model. The underlying mechanism for the improved thermal performance is elucidated by examining the evolution of microstructure, thermal diffusivity, and energy variations. Results demonstrate that with increasing nanoparticle content, the viscosity, specific heat capacity, and thermal conductivity are enhanced by approximately 51.21%, 8.25%, and 7.08%, respectively. It is revealed that the selective adsorption of Na⁺ and K⁺ ions onto the surface of SiO₂ nanoparticles leads to the formation of a compressed interfacial layer roughly 6 Å in thickness, which contributes to the enhancement in thermal conductivity. This study offers valuable insights for the design and optimization of chloride molten salt-based nanocomposites for next-generation CSP systems.