Thermodynamic–kinetic characterization of the synthesized Mg2FeH6–MgH2 hydrides mixture

The increasing relevance of hydrogen economy has generated interest in finding a safe way to transport hydrogen. In order to contribute to a better comprehension of Mg–Fe–H system's behavior, we have examined thermodynamic and kinetic characteristics of a material originally composed of complex hydride Mg2FeH6 (49 wt%), magnesium hydride MgH2 (18 wt%) and unreacted magnesium and iron. Such material was synthesized via mechanical milling of a 2Mg–Fe elemental powder mixture with a subsequent hydriding process at 673 K and 6 MPa for 15 h.

Thermodynamics of the Mg2FeH6–MgH2 hydrides mixture was evaluated by pressure–composition isotherm (PCI) measurements in the range of 573–673 K. The van’t Hoff graph was plotted and the thermodynamic parameters, i.e. decomposition enthalpy and entropy, were calculated. The kinetics of the system was also studied to analyze the dependence of hydrogen absorption rate on the temperature and the rate of hydrogen release at a given temperature.