Innovative clay based hybrid materials for thermochemical energy storage applications

The capacity to decrease and reuse energy is pivotal for preserving the environment. Thermal energy storage (TES) systems are commonly employed for these purposes. Although sensible and latent heat storage technologies represent convenient alternatives, thermochemical materials (TCM) are the most interesting candidates for their high energy storage density. TCM usually exploit a reversible solid-vapour reaction in which the direct endothermic process represents the charge step, while with the subsequent reverse stage the heat stored is released.1 Recently, hydrated organic salts such as Calcium Lactate pentahydrate (CL) have been suggested to overcome deliquescence issues in low temperature applications.2 CL presents a large storage capacity (1127 J/g) and it is an environmentally safe material, however it exhibits a slow hydration kinetic.3 The possibility of distributing CL onto the surface of a natural clay could promote not only hydration kinetics but also avoiding salt agglomeration during multiple dehydration/hydration cycles. In this work CL was impregnated with sepiolite at different load of salt respect clay (30-90 %wt.). The obtainment of a hybrid TCM/sepiolite material represents a novelty in the present literature. Complementary characterization techniques were used for studying the composite materials. The salt presence and its transition phase from dehydrated to hydrate in composite was investigated by X-Ray Diffraction. Infrared spectroscopy analyses show only the spectra of the constituent material. On a morphological point of view, micrographs obtained by scanning electron microscope show the formation of agglomerates where CL is uniformly distributed among sepiolite particles. Thermal analyses were carried out to investigate the water losses suffered by hybrid materials and the corresponding storage capacities. On the other hand, the water uptake was tested in both static and dynamic vapour conditions resulting in a clear enhancement of hydration kinetics and vapour sorption at higher mineral content. Considering the low cost of CL and the large natural reserve of sepiolite, in view of the preliminary studies carried out, the mineral results a valid support for hydrated salt loadings, promoting, therefore, the combination of both as a promising technology for TES applications. References: [1] R.-J. Clarke, A. Mehrabadi, M. Farid, Journal of Energy Storage 2020, 27, 101145 – 101162. [2] E. Mastronardo, E. La Mazza, D. Palamara, E. Piperopoulos, D. Iannazzo, E. Proverbio, C. Milone, Energies 2022, 15, 4339 – 4351. [3] Y. Sakata, S. Shiraishi, M. Otsuka, Colloids and Surfaces B: Biointerfaces 2005, 46, 135 – 141.