Hydrophilic modification of expanded graphite to develop form-stable composite phase change material based on modified CaCl2·6H2O

Abstract Cold energy storage using phase change materials (PCMs) in air-conditioning system is a favorable solution to the improvement of energy efficiency. In this work, the hydrophilic modification of EG through TiO2 coating was conducted to improve the compatibility of EG with modified CaCl2·6H2O PCM. Subsequently, the compressed modified EG (MEG) block was immersed into the melted modified CaCl2·6H2O to develop form-stable composite PCM. The results of contact angle and adsorption capacity tests confirmed that MEG possessed an enhanced hydrophilicity and improved adsorption property for modified CaCl2·6H2O PCM in comparison to EG. The results of SEM and pore analysis revealed that MEG still retained its inherent mesopore structure, contributing to the adsorption of MEG on the melted modified CaCl2·6H2O. The obtained composite PCM melted at 10.67 °C with the melting enthalpy of 88.39 J/g and a negligible supercooling degree (0.18 °C) as well as the enhanced thermal conductivity (8.831 W m−1K−1). Besides, the composite PCM exhibited a good thermal stability. The modified CaCl2·6H2O/MEG composite PCM shows good application prospects in cold energy storage, providing a new routine for improving the compatibility of EG with salt hydrates.