Decomposition pathway of Mg(BH4)2 under pressure: Metastable phases and thermodynamic parameters

The conditions of formation of polyborane intermediate species of Mg(BH4)2 during the partial dehydriding reaction and their properties have been experimentally investigated. A six step thermal decomposition pathway is first proposed. Hydrogen capacity, reaction enthalpy and activation energy values of each step are calculated to discuss the thermodynamically determined decomposition temperature and the kinetic barriers. In addition, a metastable MgB2H6 phase, which was previously predicted from density functional theory calculations, is confirmed by pressure-content isotherm measurements carried out at 277 °C.