Preliminary investigation on the catalytic mechanism of TiF3 additive in MgH2-TiF3 H-storage system

A combined structure/property investigation is performed to understand the catalytic effect of TiF3 additive on the absorption /desorption reactions of MgH2. It was found that both TiH2 and MgF2 phases identified by x-ray diffraction cannot explain the observed kinetic enhancement in the MgH2-TiF3 system, whether they are incorporated in a direct or an in situ manner. In combination with the comparative investigation on the catalytic activity of TiF3 and its analog TiCl3, as well as the samples milled under inert and reactive atmospheres, we propose that the catalytically active species is a multicomponent metastable phase composed of host Mg, transition metal Ti, and F anion, the catalytic activity of which is dependent on its interaction with the surrounding chemical environment. © 2007 Materials Research Society.