Catalytic effect on hydrogen desorption in Nb-doped microcrystalline MgH2

Mg and Nb-doped Mg films were deposited by radio frequency magnetron sputtering. Morphological and structural analysis were performed by scanning electron microscopy and x-ray diffraction. The desorption kinetics has been investigated by using a Sievert-type apparatus. The overall activation energy and the reaction order controlling desorption are (141+/-5) kJ mol(-1) H and n approximate to 4 for Mg and (51+/-5) kJ mol(-1) H and n approximate to1 for Nb-doped (5 at. %) Mg. It is suggested that Nb atoms dispersed in the MgH2 grains catalyzes the dissociation of the hydride phase and that the rate limiting step in the H2 desorption is given by the hydrogen atomic migration through interconnected transformed domains of h-Mg.