Study on physicochemical and thermal properties of tetrabutylammonium-based cation ionic salts induced by Al2O3 additive for thermal energy storage application

Abstract

The physicochemical and thermal properties of tetrabutylammonium bromide (TBA-Br) and tetrabutylammonium hexafluorophosphate (TBA-PF6), and their change with the addition of Al2O3, were investigated using infrared (IR) spectroscopy and by simultaneously conducting thermal thermogravimetric (TG) analysis and differential thermal analysis (DTA) to obtain the differential scanning calorimetry (DSC) thermogram. The change in the IR data is characterized by the growth of a large peak in the range of 3500 cm1 and the reduction of peaks below 1000 cm-1 with the additive concentration. The decomposition temperature determined from the peak in the DTG curve is nearly constant for TBA-Br, and it decreases with the addition of Al2O3 for TBA-PF6, although it does not depend on the concentration of the additives. The DTA curve of ionic salts with the addition of Al2O3 shows additional peaks, which indicates a change in the sample's temperature at disorder or phase transitions. The variation in the melting temperature with additive concentration is similar to that of decomposition temperature. The maximum heat of fusion value was approximately 67 kJ kg-1 for the doped TBA-Br and TBA-PF6 but was achieved at a different additive concentration. This is due to the additional disorder in the system induced by the dissolution of Al2O3.