Heat storage: Hydration investigation of MgSO4/active carbon composites, from material development to domestic applications scenarios

The scarcity of durable and low-cost sorbent materials remains a significant technological barrier to long-term heat storage. In the present work, composite materials based on activated carbon supports and magnesium sulfate hydrates (labelled MgSO4/AC) were developed in order to increase the energy density and improve mass and heat transport phenomena. The results of composite characterization revealed uniform dispersion of magnesium sulfate in composites produced via incipient wetness impregnation. The hydration enthalpy increased as the MgSO4, content on AC increased, reaching a plateau for MgSO4 content of more than 30%wt (30-MgSO4/AC and 40-MgSO4/AC samples). The hydration experiment performed on the 30-MgSO4/AC sample at RH = 60% verified the relation between the salt hydration level and the hydration enthalpy. Higher water partial pressure enhanced water molecule transport and improved salt hydration. The hydration enthalpy of 30-MgSO4/AC showed an increase from 859 J/gdry material at RH = 30% to 1324 J/gdry material at RH = 60%. After 8 cycles of hydration/dehydration, the 30-MgSO4/AC sample was practically stable. Furthermore, the 30-MgSO4/AC) composite was modeled in two distinct scenarios for house heating and sanitary hot water generation. Finally, the experimentally obtained calorimetric data were used to implement a numerical model. Two different scenarios were considered, the first for heating a house and the second for producing hot sanitary water. Both scenarios show the possibility of using the MgSO4/AC composite in a multifunction thermochemical heat storage system.