Investigations on the morphological and thermophysical characteristics of graphene oxide incorporated sodium nitrate for high-temperature thermal energy storage applications

Sodium nitrate (SN) is a promising molten salt phase change material with high energy storage capacity and thermal stability for high-temperature latent heat thermal energy storage systems. To address the low thermal conductivity of SN, we have incorporated graphene oxide (GO) (0.5-2 wt%) as a nanoadditive and evaluated the variation of thermophysical properties of SN. The structural and functional characteristics of graphene oxide – sodium nitrate (GO-SN) composites were studied using TEM, XRD, FT-IR, and Raman spectroscopy. A thermal conductivity improvement of 31.4% at 200 °C was achieved for 1 wt% GO-SN composite than that of sodium nitrate. The thin sheet-like morphology and high surface area of GO promoted the heat transfer by creating longer conduction paths and lower interfacial thermal resistance between GO and SN. The specific heat of 2 wt% GO-SN composite was higher by 15.8% and 16.8% in solid-phase and liquid-phase, respectively, compared to that of SN due to high surface area and high interfacial energy. After 1000 thermal cycles, the 1 wt% GO-SN composite retained 85% of its initial latent heat, as against 88% retention in pure SN. These findings establish the GO-SN composites as an efficient thermal energy storage material for high-temperature solar thermal applications.