Hydrogen sorption kinetics of MgH2 catalyzed with titanium compounds

Identification of effective catalyst is a subject of great interest in developing MgH2 system as a potential hydrogen storage medium. In this work, the effects of typical titanium compounds (TiF3, TiCl3, TiO2, TiN and TiH2) on MgH2 were systematically investigated with regard to hydrogen sorption kinetics. Among them, adding TiF3 leads to the most pronounced improvement on both absorption and desorption rates. Comparative studies indicate that the TiH2 and MgF2 phases in situ introduced by TiF3 fail to explain the superior catalytic activity. However, a positive interaction between TiH2 and MgF2 is observed. Detailed comparison between the effect of TiF3 and TiCl3 additive suggests the catalytic role of F anion. XPS examination reveals that new bonding state(s) of F anion is formed in the MgH2 + TiF3 system. On the basis of these results, we propose that the substantial participation of F anion in the catalytic function contributes to the superior activity of TiF3.