Optimized on melamine sponges for highly stable and efficient hydrated salt-based solar thermal energy storage

Hydrated salts as typical phase change materials (PCMs) have attracted intensive attention in solar thermal applications due to wide distribution and high energy storage density. A shape stable magnesium chloride hexahydrate/melamine sponge@graphene oxide (MMG) composites are composed of magnesium chloride hexahydrate (MCH) as energy storage materials, melamine sponge (MS) as the support materials and graphene oxide (GO) as light absorption modifiers. However, the stability of the materials remains unsatisfactory due to the loss of crystalline water during the repeated energy storage. In the current work, transparent and superhydrophobic SG is innovatively and facilely coated on composites to obtain MMG/SG, which improves the mechanical properties to maintain the shape stability of composite PCMs, and has good stability in the 100-cycles test. In addition, the SG coating can prevent the loss of generated water molecules during the dehydration reaction of MCH, and its supercooling degree is only 0.8 –1.6 °C. The photothermal conversion efficiency of MMG/SG is 91.21%, and energy storage density could reach 143.2 J/g. Herein, this work provides a new idea to solve the problems of supercooling, phase separation and leakage of hydrated salts in practical solar thermal conversion application.