Mg2FeH6-based nanocomposites with high capacity of hydrogen storage processed by reactive milling

Abstract

The compound Mg 2 FeH 6 was synthesized from a 2Mg-Fe mixture in a single process through high-energy ball milling under hydrogen atmosphere at room temperature. The complex hydride was prepared from Mg powder and granulated or powdered Fe using a planetary mill. The phase evolution during different milling times was performed by X-rays diffraction technique. The dehydrogenation behavior of the hydride was investigated through simultaneous thermal analyses of differential scanning calorimetry and thermogravimetry coupled with mass spectrometer. The use of powdered iron as starting material promoted conversion to complex hydride at shorter milling times than when granulated iron was used, nevertheless, after 24 hours of milling the 2Mg-Fe (powdered or granulated) mixtures presented similar dehydrogenation behavior. The hydrogen absorption during milling was on average 3.2 wt. (%), however, changing the proportions of the reagents to 3Mg-Fe a Mg 2 FeH 6 -MgH 2 based nanocomposite with higher density of hydrogen (5.2 wt. (%)) was obtained.

Investigation of Effect of Milling Atmosphere and Starting Composition on Mg2FeH6 Formation

“…The difference in hydrogen capacity between these two samples could be explained by the reaction pathway of Mg 2 FeH 6 formation. During ball milling of the metallic elements (2Mg + Fe) under H 2 pressure, the β-MgH 2 phase is firstly formed and then, it reacts with Fe to form the complex hydride Mg 2 FeH 6 [22]. Using instead MgH 2 as starting material is a shortcut to Mg 2 FeH 6 formation and result in higher hydrogen capacity.…”

“…The synthesis of Mg 2 FeH 6 by ball milling has been studied by several authors using different milling parameters, such as: type of mill; ball to powder ratio; number and size of balls; milling time; rotational speed; milling atmosphere and hydrogen pressure [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Irrespective of the milling conditions, some iron was always detected in the milled powder representing an incomplete Mg 2 FeH 6 formation.…”