Development of novel composite PCM for thermal energy storage using CaCl2·6H2O with graphene oxide and SrCl2·6H2O

The inorganic salt hydrate PCM, CaCl2·6H2O, has a promising potential for thermal energy storage. However, this salt hydrate has tremendous issues of supercooling (the supercooling degree was 25.5 °C as found in this research) which restricts its utilization in practical applications. The present study aimed to reduce the supercooling degree of CaCl2·6H2O through the innovative use of hydrophilic graphene oxide (GO) nano-sheets and SrCl2·6H2O as nucleating agents. The percentages of these nucleating agents in PCM were 0.005, 0.01, 0.02, 0.05 and 0.08 wt% for GO and 0.2, 0.5 and 0.8 wt% for SrCl2·6H2O, respectively. Based on the synergistic/additive effects, a novel composite PCM based on CaCl2·6H2O, GO and SrCl2·6H2O was proposed and developed. The test results showed that the composite PCM containing 0.02 wt% GO nano-sheets and 0.8 wt% SrCl2·6H2O effectively lowered the supercooling degree of CaCl2·6H2O from 25.5 °C to as low as 0.2 °C (approximately 99.2% supercooling degree of CaCl2·6H2O was reduced). To the best of authors' knowledge, it was the first time that the combination of GO and SrCl2·6H2O was found effective in reducing supercooling degree of CaCl2·6H2O. Moreover, 99.2% supercooling reduction of CaCl2·6H2O is considered the best achievement so far when compared to other studies related to supercooling reduction of CaCl2·6H2O. Finally, the solidification enthalpy of the composite PCMs was found to be as high as 207.90 J/g. Therefore, the developed composite PCM is an excellent candidate for thermal energy storage applications in buildings.