Thermodynamic and kinetic studies of Mg–Fe–H after mechanical milling followed by sintering

Abstract

The transition metal complex hydride Mg 2 FeH 6 has been successfully synthesized utilizing mechanical milling of a 2Mg-Fe mixture followed by heating at 673 K under 6 MPa of hydrogen pressure, without pressing step. The obtained yield of Mg 2 FeH 6 was about 50%. Hydrogen storage properties of the Mg-Fe-H system, i.e. capacities, absorption/desorption kinetics and thermodynamic parameters, were examined. The pressurecomposition isotherm (PCI) measurements of the samples at 548-673 K showed that the alloys possessed good cyclic stability and reversibility. Enthalpies and entropies of decomposition of the Mg-Fe-H system were evaluated by van't Hoff plots. The absorption/desorption rates at 573 K were very fast in comparison with the reported data. The non-isothermal desorption of hydrogen was found greatly dependent on the thermal history of the sample.

Thermodynamic Properties and Reversible Hydrogenation of LiBH4–Mg2FeH6 Composite Materials

“…[20,21]; line (b) represents the equilibrium pressure of the dehydrogenation of Mg2FeH6, according to Refs. [22][23][24].…”

Formation reaction of Mg2FeH6: effect of hydrogen absorption/desorption kinetics

“…It is important to emphasize that the complex hydride Mg 2 FeH 6 has a lower equilibrium pressure than β-MgH 2 [2,4,8] . This means that Mg 2 FeH 6 is a more stable hydride than β-MgH 2 .…”

“…Some authors suggested that Mg 2 FeH 6 is formed directly from the reaction of 2Mg+Fe+3H 2 [1,2,6,8] , while others reported that the reaction involves two steps: the first one is the formation of MgH 2 , and secondly, the reaction of magnesium hydride with Fe [5,[9][10][11] . Polanski et al 11 using in-situ synchrotron X-ray diffraction showed that MgH 2 is the Mg 2 FeH 6 precursor.…”

Thermodynamics study of hydrogen storage materials

“…Puszkiel et al [48] synthesized Mg-Fe-H composites by mechanical milling followed by sintering at 400°C at 6 MPa of hydrogen pressure. The yield of obtained Mg 2 FeH 6 was about 50%.…”