Optimization of TiH2 content for fast and efficient hydrogen cycling of MgH2-TiH2 nanocomposites

Magnesium hydride is extensively examined as a hydrogen store due to its high hydrogen content and low cost. However, high thermodynamic stability and sluggish kinetics hinder its practical application. To overcome this last drawback, different Ti amounts (y = 0, 0.025, 0.05, 0.1, 0.2 and 0.3) were added to magnesium to form (1-y)MgH₂+yTiH₂ nanocomposites (NC) by reactive ball milling under hydrogen gas. Thermodynamic stability of the MgH₂ phase in NCs was determined using a manometric Sieverts rig. Reversible hydrogen capacity and reaction kinetics were determined at 573 K over 20 sorption cycles under a limited reaction time of 15 min. On increasing Ti amount, reaction kinetics are enhanced both in absorption and desorption leading to a higher reversibility for hydrogen storage with the MgH₂ phase. However, titanium increases the molar weight of NCs and forms irreversible titanium hydride. The highest reversible capacity (4.9 wt% H) was obtained for the lowest here studied TiH₂ content (y = 0.025).