Bismuth-mesoporous silica-based phase change materials for thermal energy storage

Effective heat storage at temperatures above 200 degrees C enables large scale, concentrated solar thermal energy storage or heating applications. Metals can be used for latent heat storage, as they provide high volumetric energy densities at low cost. The volume change during transition limits their stability, but it can be overcome through encapsulation or impregnation into porous matrices. We report the first study on Bismuth-based phase change materials using mesoporous silica matrices or silica shells. High metal fractions (50-70% wt.) were obtained. The metal phase form sub-micron sized domains, with good dispersion inside the silica matrix. Samples obtained by encapsulation show low enthalpy and reliability. High enthalpy values (22-32 Jg(-1)), comparable to that of Bi particles were obtained for samples containing mesoporous silica. These composites exhibit good thermal reliability and shape-stability above the metal melting point, in contrast to Bi particles, which show molten metal leakage. Nanoconfinement of the metal phase decreases its melting point by 1-3 degrees C and its heat of fusion by less than 1%. The good heat storage capacity of composites containing 70% wt. Bi could be explained by a reduction in metal oxidation, caused by the presence of the mesoporous silica matrix.