Preparation and characterization of Na2HPO4·12H2O@polymethyl methacrylate nanocapsule for efficient thermal energy storage

Hydrated salts have been considered as a promising phase change material for usage in low-temperature thermal energy storage applications; however, they suffer from poor thermal reliability, corrosiveness, and inefficient thermal storage. Nanoencapsulation is an effective approach used to improve the thermal energy storage performance and reliability of phase change materials. At present, limited studies have been conducted on the core–shell encapsulation-based hydrated salt core. In this work, an efficient method was developed for the encapsulation of Na2HPO4·12H2O into the polymethylmethacrylate (PMMA) nanocapsules. The morphology and core–shell structure of the nanocapsules were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). The chemical composition of the nanocapsules was confirmed by Fourier transformation infrared spectroscopy (FTIR). The phase change performance of the nanocapsules was studied using a differential scanning calorimeter (DSC). Thermal cycling was adopted to reveal the thermal reliability of the nanocapsules. The corrosiveness of the nanocapsules was also investigated. In addition, the nanocapsules were combined with copper foam to prepare a novel composite phase change material (C-PCM) for efficient thermal energy storage. Results demonstrated that the melting and solidifying latent heat of the nanocapsules were 157.3 and 140.6 kJ/kg, respectively. The encapsulation ratio of the nanocapsules was 64.1 %, and 97.7 % was maintained after 500 thermal cycles. Hydrated salt nanocapsules were virtually non-corrosive to the metal. The latent heat of the composite PCM was calculated to be approximately 72.7 kJ/kg. The thermal conductivity of the composite PCM was about 1.25 W/(m·K), 5.5 times higher than that of the nanocapsules. The heat storage test showed that the time required for the heat storage of the C-PCM was reduced by about 82.8 % compared with that of the pure nanocapsules. This novel nanocapsule has high phase change properties and thermal reliability and exhibits good low-temperature thermal energy storage prospects.