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Identification of effective catalyst is a subject of great interest in developing MgH(2) system as a potential hydrogen storage medium. In this work, the effects of typical titanium compounds (TiF(3), TiCl(3), TiO(2), TiN and TiH(2)) on MgH(2) were systematically investigated with regard to hydrogen sorption kinetics. Among them, adding TiF(3) leads to the most pronounced improvement on both absorption and desorption rates. Comparative studies indicate that the TiH(2) and MgF(2) phases in situ introduced by TiF(3) fail to explain the superior catalytic activity. However, a positive interaction between TiH(2) and MgF(2) is observed. Detailed comparison between the effect of TiF(3) and TiCl(3) additive suggests the catalytic role of F anion. XPS examination reveals that new bonding state(s) of F anion is formed in the MgH(2) + TiF(3) 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 TiF(3). (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.