Thermodynamic destabilisation of SrH2 using Al for the next generation of high temperature thermal batteries

Abstract Thermal batteries are ideal for storing renewable energies or excess electricity from the grid. The most efficient thermal batteries utilise reversible thermochemical reactions where the heat produced during discharge drives a heat engine. Metal hydrides can be used as the thermal energy storage (TES) material in these batteries, since when heated, hydrogen is released in an endothermc process, charging the battery. When this hydrogen is reintroduced to the metal the metal hydride is reformed during the exothermic reaction (discharge). The optimal thermal battery would have a high operating temperature, low operating pressure and low material cost. SrH2 could meet these demands except its operating temperature is above 1000 °C. Adding aluminium to strontium hydride causes thermal destabilisation allowing an operating temperature of 1 bar hydrogen at 846 ± 36 °C, providing ideal properties as a TES material. The SrH2-2Al system reacts in two stages with the second step exhibiting only a 32% reduction in capacity over 50 cycles. Pressure-composition isotherm analysis determine the thermodynamics of H2 desorption to be ΔHdes = 132 ± 2 kJ/mol H2 and ΔSdes = 118 ± 2 J/K/mol H2. Further studies by scanning electron microscopy have determined changes in morphology over cyclic activity, while simultaneous thermal analysis and powder X-ray diffraction have identified the reaction pathways of the process. A cost analysis of the system has shown that a reduction in materials cost would enhance tenchnological application of this material.