Study of paraffinic and biobased microencapsulated PCMs with reduced graphene oxide as thermal energy storage elements in cement-based materials for building applications

Addition of different types of phase change materials (PCMs) to cement-based materials for thermal energy storage has been broadly investigated in the literature. Many studies have researched the addition of organic PCMs and the thermal performance of the PCM-cement system. However, drawbacks such as leakage and poor thermal conductivity of the PCMs have stimulated studies to improve thermal properties within the PCM-cement system. Among the different solutions, addition of carbonous materials (such as graphite and carbon nanotubes) to improve thermal conductivity of the PCMs have been investigated. In the current work, an innovative system that contains microencapsulated PCMs (MPCMs) and purposely synthesized reduced graphene oxide (rGO) has been designed and assessed. The addition of rGO has two aims. The first one is to speed up the heat storage/release velocity by improving the thermal conductivity of the whole system. The second one is to improve the electrical conductivity of the system in order to actively (by applying voltage) be able to turn on the thermal storage/release feature. Up to the authors' knowledge, this is a novel approach for the development of active PCM-cement based thermal energy storage systems. Furthermore, in the present study, the use of paraffinic PCMs was compared with that of biobased PCMs in order to provide a more sustainable solution to the design of cement-based elements for buildings applications. A comprehensive thermal characterization (heat storage capacity, thermal conductivity and diffusivity) has been carried out as well as microstructural characterization. Moreover, broadband dielectric spectroscopy was used to characterize the electrical conductivity of the novel MPCM-rGO-cement system.