Li4(OH)3Br/MgO shape stabilized composite as novel high temperature thermal energy storage material

Li-4(OH)(3)Br/Porous-MgO shape stabilized composites were developed in this study as novel high temperature thermal energy storage materials. Li-4(OH)(3)Br, as storage material, owns a large reaction enthalpy (247 J/g) at 288 C and excellent thermal cycling stability over 600 cycles. Solid MgO nanopowder was selected in a previous study among several metal oxides as the most promising shape stabilizer for Li4(OH)3Br salt satisfying the criteria of wettability, thermochemical compatibility, structural stability and cycling stability. However, this material ensures the structural stability of the composite at a minimum oxide loading of 50 wt%. This relatively high oxide loading will drastically decrease the overall storage capacity of the composite, which is not practical for TES applications. In order to reduce the MgO loading, new mesoporous MgO particles were tested as supporting materials. The idea is to benefit from the mesoporosity in improving the antileakage efficiency of the composite. To do so, three different porous MgO samples were synthesized and tested. Namely, i) Porous MgO (PMgO) synthesized by combustion using Magnesium nitrate, giving a BET surface area of 40 m2/g and a pore volume of 0.217 cm3/g. ii) MgO synthesized by calcination of basic magnesium carbonate (MgO-BMC), giving a high BET surface area of 129 m(2)/g and a pore volume of 0.294 cm3/g. iii) nanocrystalline MgO (MgO-BM64h) obtained by ball-milling process of commercial MgO micropowder, giving a BET surface area of about 55 m2/g and pore volume of 0.088 cm3/g. The three porous MgO materials exhibit various pore structures. The composites were synthesized following a simple fabrication method by cold compression, mixing and sintering. The results were promising for PMgO based composites where appreciable thermal and structural stability were achieved as 30 wt % oxide loading, whereas MgO-BMC and MgO-BM64h showed poor cycling stability at the same loading. SEMEDS analyses of PMgO based composite showed an improvement of the homogeneity of the composite structure over 50 melting/solidification cycles. Moreover, the overall thermal conductivity of the composite was enhanced by 33% over pure salt.