Destabilization of lithium hydride and the thermodynamic assessment of the Li-Al-H system for solar thermal energy storage

Lithium hydride destabilised with aluminium, LiH-Al (1 : 1 mole ratio) was systematically studied and its suitability as a thermal energy storage system in Concentrating Solar Power (CSP) applications was assessed. Pressure composition isotherms (PCI) measured between 506 degrees C and 652 degrees C were conducted to investigate the thermodynamics of H-2 release. Above the peritectic temperature (596 degrees C) of LiAl, PCI measurements were not consistently reproducible, possibly due to the presence of a molten phase. However, below 596 degrees C, the hydrogen desorption enthalpy and entropy of LiH-Al was Delta H-des = 96.8 kJ (mol H-2)(-1) and Delta S-des = 114.3 J (K mol H-2)(-1), respectively LiH(s) at 956 degrees C, Delta H-des = 133.0 kJ (mol H-2)(-1) and Delta S-des = 110.0 J (K mol H-2)(-1). Compared to pure LiH, the Li-Al-H system has a reduced operating temperature (1 bar H-2 pressure at T similar to 574 degrees C) that, combined with favourable attributes such as high reversibility, good kinetics and negligible hysteresis, makes the Li-Al-H system a potential candidate for solar thermal energy storage applications. Compared to pure LiH, the addition of Al can reduce the cost of the raw materials by up to 44%. This cost reduction is insufficient for next generation CSP but highlights the potential to improve the properties and cost of high temperature hydrides via destabilisation.