Emilie Courbon

Design of salt–metal organic framework composites for seasonal heat storage applications

Porous materials are recognized as very promising materials for water-sorption-based energy storage and transformation. This study presents the first attempt to use Metal Organic Frameworks (MOFs) as host matrices of salts for the preparation of composite sorbents for seasonal heat storage. We have considered six water stable MOFs (i.e. MIL-127(Fe), MIL-100(Fe), MIL-101(Cr), UiO-66(Zr)–NH2, MIL-125(Ti)–NH2 and MIL-160(Al)) differing in their crystalline structure, hydrophilic–hydrophobic balance, pore size/shape and pore volume. The successful encapsulation of CaCl2 in the pores of MOFs leads to two series of MOFs–CaCl2 composites whose salt content could be finely tuned depending on the pore volume of MOFs and the synthesis conditions. These materials were fully characterized by combining multiple techniques (i.e. powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, X-ray energy-dispersive spectrometry elemental mapping, N2 sorption and elemental analysis). The water sorption properties of these composites were studied under conditions of a solar heat storage system (i.e. adsorption at 30 °C, desorption at 80 °C, both steps at a water vapour pressure of 12.5 mbar) in comparison to the parent MOFs. We analyze how the physico-chemical and structural properties of these host matrices impact the energy density of composite sorbents. We show that two mesoporous MOFs–CaCl2 composites (i.e. MIL-100(Fe)/CaCl2 and MIL-101(Cr)/CaCl2) with the highest salt loading (46 and 62 wt% respectively) exhibit very high energy storage capacities (up to 310 kW h m−3 (485 W h kg−1)) outperforming the best composites or physical sorbents reported so far together with very little loss upon adsorption–desorption cycling and high chemical stability upon ageing (up to 18 months).

Synthesis Optimization, Shaping, and Heat Reallocation Evaluation of the Hydrophilic Metal–Organic Framework MIL‐160(Al)

The energy-storage capacities of a series of water-stable porous metal-organic frameworks, based on high-valence metal cations (Al3+ , Fe3+ , Cr3+ , Ti4+ , Zr4+ ) and polycarboxylate linkers, were evaluated under the typical conditions of seasonal energy-storage devices. The results showed that the microporous hydrophilic Al-dicarboxylate MIL-160(Al) exhibited one of the best performances. To assess the properties of this material for space-heating applications on a laboratory pilot scale with an open reactor, a new synthetic route involving safer, greener conditions was developed. This led to the production of MIL-160(Al) on a 400 g scale, before the material was shaped into pellets through a wet-granulation method. The material exhibited a very high energy-storage capacity for a physical-sorption material (343 Wh kg-1 ), which is in full agreement with the predicted value.