Molten Salt/Metal Foam/Graphene Nanoparticle Phase Change Composites for Thermal Energy Storage

The binary and ternary mixtures of nitrates are desirable phase change materials (PCMs) as latent heat thermal energy storage media for solar energy applications. In this study, graphene oxide was synthesized with graphite powder first and then it was doped into HITEC salt or solar salt solvent with sonication using two-step methods. Finally, metal foams including nickel and copper ones were impregnated with the salt seeded with graphene (nanocomposite). The morphologies of the synthesized composite PCMs were analyzed extensively, while the thermophysical properties of the composite PCMs were both theoretically predicted and experimentally investigated. The results indicated that metal foam was compatible with nanocomposite and the thermal stabilities of the composite PCMs were good regarding the thermal cycle characteristics. The effective thermal conductivities of the salt/graphene/metal foam composites were distinctly enhanced, while the latent heats of the present composite PCMs were smaller than that of pure salt to some extent. Furthermore, the phase change temperatures shifted slightly in the presence of porous metal foam and graphene, while the addition of graphene could compensate for the reduction of specific heats of the composite PCMs caused by metal foam. Finally, it was found that the thermal effusivities of the salt/graphene/metal foam composites were larger than those of pure salt, indicating the increments of 110%∼270% in solid state and 150%∼360% in liquid state, respectively. Fundamental information on the nanocomposites with porous media could broaden their application in thermal energy storage systems.