Thermochemical energy storage in composite materials: MOFs impregnated by hygroscopic salts

SSCI-VIDE+ATARI+QTL:GPO:AAUNational audienceThe recovery and storage of waste heat sources and the use of sustainable renewable energy would contribute to decrease dependency on fossil fuels and decarbonization of energy system. Energy storage systems have therefore been developed in order to reduce the discrepancy between demand and supply. In particular, thermochemical heat storage systems, using reversible sorption/desorption reactions, offer high energy storage density over variable amounts of time with minimal heat losses. Water sorption storage systems using hygroscopic salts, such as CaCl2, inside a porous matrix (composite salts porous matrix (CSPM)) are widely used. These composite materials allow the storage of energy (solar or from any other source) during dehydration (charge) and its release during hydration (discharge). Among porous materials, Metal-Organic-Frameworks (MOFs) have recently been of particular interest because of their high sorption capacity due to a very high surface area and tunable properties.This work proposes a study of the heat storage/release and water sorption/desorption capacities of CSPM materials. Aluminium fumarate-based MOFs impregnated by different amount of CaCl2 were synthetized (MOF-Cax), with 25, 37, 58 wt.%. Materials are subjected to analysis by TG-DSC coupled to humidity generator during successive hydration/dehydration cycles. A concomitant increase of water sorption/desorption capacity determined by thermogravimetric analysis is observed (Figure 1).DSC analysis showed that after impregnation, the heat storage/release capacity of MOFs gradually increases with the amount of salt until reached 1840 kJ kg-1 for MOF-Ca3 sample (MOF + 58 wt.% of CaCl2). A concomitant increase in water sorption/desorption capacity, determined by thermogravimetric analysis is observed (figure 1). Besides, storage properties of MOF-Ca3 decreases of only 6% in the 3 dehydration/hydration cycles, and remains stable after, showing high stability.The impact aluminium fumarate impregnation by the salt on sturctural and morphological properties has been investigated