Kinetic Enhancement of Direct Hydrogenation of MgB2 to Mg(BH4)2 upon Mechanical Milling with THF, MgH2, and/or Mg

Modification of magnesium diboride, MgB ₂ , by mechanical milling with THF, MgH ₂ , and/or Mg results in a lowering of the conditions required for its direct, bulk hydrogenation to magnesium borohydride, Mg(BH ₄ ) ₂ , by 300 bar and 100 °C. Following mechanical milling with MgH ₂ or THF and Mg, MgB ₂ can be hydrogenated to Mg(BH ₄ ) ₂ at 300 °C under 700 bar of H ₂ while achieving ∼54–71 % conversion to the borohydride. The discovery of a means of dramatically lowering the conditions required for the hydrogenation of MgB ₂ is an important step towards the development of a practical onboard hydrogen storage system based on hydrogen cycling between Mg(BH ₄ ) ₂ and MgB ₂ . We suggest that mechano-milling with THF, Mg, and/or MgH ₂ may possibly introduce defects in the MgB ₂ structure which enhance hydrogenation. The ability to activate the MgB ₂ through the introduction of structural defects transcends its relevance to hydrogen storage, as a method of overcoming its chemical inertness provides the key to harnessing other interesting properties of this material.