Water sorption and heat storage in CaCl2 impregnated aluminium fumarate MOFs

Abstract

Composite materials based on aluminium fumarate (AF) and CaCl 2 have been developed for the storage of energy from renewable and waste sources. Composite Salt-Porous Matrix (CSPM) was synthesised by impregnating aluminium fumarate MOF host matrix with various relative CaCl 2 salt contents (25-60 wt.%). The resulting CSPMs were fully characterized by X-ray diffraction, N 2 and H 2 O sorption isotherms at −196 and 25 °C, respectively, scanning electron microscopy and thermal analysis. The high surface area of the AF matrix (959 m 2 g -1 ) drastically decreases upon the addition of salt, to about 50 m 2 g -1 . The heat storage performance of the composites was found to depend on the added amount of salt to the MOF matrix, with higher amounts of salt leading to better performance. The maximum water sorption capacity of 0.68 kgH O kg -1 , coupled with a high heat of water sorption (1840 kJ kg -1 ), makes these composites interesting when used at a rehydration level not exceeding CaCl 2 .4H 2 O to avoid any deliquescence and washing out of the salt. A kinetic study of the hydration demonstrated that salt deposition increases the water sorption rate in comparison with the host matrix. Moreover, the impact of salt deposition on the activation energy of dehydration of the host matrix was also determined by applying integral isoconversional methods.

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