Nanoparticles-enhanced heat capacity of sulfate molten salt: Experimental and molecular dynamics analysis for advanced CSP applications

The development of third-generation concentrating solar power (CSP) systems demands molten salts with excellent thermal stability and high heat-storage capacity. In this study, molten salt nanocomposites suitable for thermal storage in third-generation CSP systems were prepared by incorporating 0.3-1.2 wt% nano-Al2O3 and SiO2 into the ternary sulfate 52 mol% Na2SO4-7 mol% K2SO4-41 mol% MgSO4 (NKM). The resulting nanocomposites were characterized through thermophysical measurements and molecular dynamics (MD) simulations. The specific heat capacity exhibited a non-linear dependence on nanoparticle concentration, with an optimum at 0.6 wt%. At this loading, the cp increased to 1.52 J g−1 °C−1 with Al2O3 (+15%) and 1.69 J g−1 °C−1 with SiO2 (+28%). Nanoparticles caused a modest rise in viscosity while having minimal effect on density. XRD, SEM, and EDS analyses revealed phase evolution during heating, including the formation of K2Mg2(SO4)3 and the transformation of Na6Mg(SO4)4. At higher nanoparticle loadings (≥0.9 wt%), particle agglomeration accounted for the decline in cp. MD simulations were further used to explore the mechanism underlying the enhancement in specific heat capacity: nanoparticles shorten cation-anion distances and promote the formation of a semi-solid interfacial layer whose thickness increases with temperature. These structural features are consistent with the experimentally observed increase in cp, suggesting that they may contribute to the improved heat storage performance. This work demonstrates a viable strategy for developing high specific heat molten salt nanocomposites for third-generation CSP systems.