Synthesis of Hybrid Graphene/TiO2 Nanoparticles Based High-Temperature Quinary Salt Mixture for Energy Storage Application

Abstract

Abstract High temperature and low melting point eutectic mixtures play a significant role in thermal energy storage (TES) and as a heat transfer fluid (HTF). These eutectic mixtures, when dispersed with nanoparticles, further enhance their thermophysical properties. The hybrid Graphene Oxide and titanium (GO/TiO2) nanoparticles (0.01-0.1 wt%) were synthesised using the hydrothermal technique at 180°C for 12 hours in an autoclave. Eutectic salts from a system of nitrate salt mixture composed of sodium (0.558 wt%), potassium (2.118 wt%), lithium (0.738 wt%), calcium (2.478 wt%), and cesium (4.098 wt%) were dispersed into nanosuspension to form a hybrid eutectic mixture for high-temperature applications via series of sonication and heating procedure. The eutectic point (65 oC) was predicted using the phase diagram and validated with experimental value observed at 61 oC using differential scanning calorimetry (DSC). The enhancement in specific heat in the presence of hybrid nanoparticles ranged from 9.8-19.6% compared to the base salt. Moreover, the addition of 0.05 wt% of hybrid nanoparticle showed the highest specific heat improvement (19.6%) compared to other single nanoparticle concentrations in the literature. The eutectic mixtures showed excellent thermal stability over a temperature range of 580 oC, with no significant decomposition in the presence of hybrid nanoparticles. The samples were characterised for structural and morphological changes using ESEM and EDX that showed well-dispersed nanoparticles into the eutectic mixture. FTIR studies confirmed the presence of O-N-O, NO3, and C=N stretching. The interaction between all the nitrate salts and the addition of hybrid nanoparticles did not alter the morphology of the base salts. Raman spectroscopy highlighted the increase in ID/IG ratio from 0.91 to 1.05 due to the presence/binding of TiO2 nanoparticles on the graphene sheet. Therefore, a new hybrid GO/TiO2 based high temperature quinary salt mixture showed better reliability and stability for energy storage applications.