Solar thermal energy storage based on sodium acetate trihydrate phase change hydrogels with excellent light-to-thermal conversion performance

Phase change materials (PCMs) play significant roles in solar thermal energy storage. In this work, a novel PCM, light-to-thermal conversion phase change hydrogel (LTPCH) consisting of NaAc·3H2O, acrylamide-acrylic acid sodium co-polymer and CuS was prepared using a melt impregnation process. The morphologies, thermal physical properties, light-to-thermal conversion performance and cycling lifetimes of prepared LTPCHs were investigated. A fluid leakage test showed that LTPCH containing 87 wt% NaAc·3H2O can keep a solid-gel structure without liquid leakage in the phase change process. Scanning electron microscope micrographs confirmed that LTPCH was structured by near-spherical particles which were mainly composed of NaAc·3H2O confined in the three-dimensional polymer networks. Differential scanning calorimeter tests revealed that the melting temperature of LTPCH was 57.1 °C, close to that of NaAc·3H2O, and its latent heat was as high as 202.4 J/g. The light-to-thermal conversion experiments indicated that CuS was an effective photon capturer and it can provide LTPCH with an excellent light-to-thermal conversion efficiency of 87.1%. After 300 melting/freezing cycles, LTPCHs maintained good thermal physical properties and high light-to-thermal conversion efficiency, and therefore showed great potential for use in solar thermal energy storage.