Influence of minerals with different porous structures on thermochemical heat storage performance of CaCl2-based composite sorbents

Abstract

Thermochemical heat storage has been successfully employed as a reliable solution for enhancing the utilisation of renewable energy. In this paper, we report novel composite sorbents fabricated by impregnating CaCl2 into porous minerals with different structural properties. Sepiolite (SP), diatomite (DT), and expanded perlite (EP) were chosen as the mesoporous, macroporous, and foamed macroporous matrices, respectively. The pore structure of the matrix exerts a vital influence on the loading of salt hydrates and the performance of the composite material. EP/Ca had the highest energy storage density of 2166 J/g with a water exchange amount of 1.20 g/g, while the energy storage densities of SP/Ca and DT/Ca were 1026 J/g and 1520 J/g, respectively. The foamed macropores of EP provided more space for salt hydrate loading, whereas DT and SP only possessed mesoporous pores with limited pore volumes, thus contributing to lower salt hydrate content. Moreover, EP/Ca exhibited good structural stability during heat storage cycles because of the foamed macroporous structure. In contrast, the restrictive effect of the holes of DT on the salt solution was low, thus causing DT/Ca leakage and caking. Therefore, EP was chosen as the most suitable matrix for supporting salt hydrates. Moreover, this work presents an excellent perspective for exploring new sorption heat-storage materials with low cost, mass production, and high performance.