SiO2 hydrophilic modification of expanded graphite to fabricate form-stable ternary nitrate composite room temperature phase change material for thermal energy storage

Abstract

A form-stable ternary nitrate (LiNO3·3H2O-KNO3-NaNO3) composite phase change material (CPCM) with modified expanded graphite (MEG) as carrier was investigated. In order to improve the hydrophilicity of expanded graphite (EG) and its compatibility with ternary nitrate, the SiO2 particles prepared by sol–gel method was used as modifier to form a hydrophilic coating on EG to obtain MEG. The pore structure morphology as well as the adsorption capacity for ternary nitrate of EG and MEG were analyzed in detail. The shape-stability and thermal properties of the obtained CPCM were also evaluated. The results showed that the MEG with 15 wt% SiO2 exhibited optimal affinity to water and ternary nitrate PCM. With the addition of 20 wt% MEG, the configured CPCM owned a suitable phase change temperature (21.66 °C), high phase change enthalpy (158.7 J/g), low supercooling degree (1.56 °C) and outstanding thermal conductivity (4.565 W/m·K). Moreover, the thermal performance differences of the CPCM were relatively small after 200 thermal cycles, indicating that the prepared CPCM can be applied in the room temperature thermal energy storage technology.