A comparison of TiF and NbF catalytic effects on hydrogen absorption and desorption kinetics of a ball-milled MgZnNi alloy.

In this investigation, the as-milled MgZnNi-4C (C = TiF, NbF) composites were successfully produced ball milling. The different influences between the catalysts TiF and NbF on the hydrogen storage behavior and microstructure of the composites were investigated by XRD, SEM, TEM and hydrogen absorption/desorption tests. The as-milled MgZnNi-4C (C = TiF, NbF) alloys contain the major phase Mg, the secondary phase MgNi, a small amount of MgZn, TiF and NbF. After hydrogenation, MgH and MgNiH are formed, which convert back into Mg and MgNi after dehydrogenation indicating that MgZn and the catalysts TiF and NbF do not react with hydrogen. Compared with NbF catalyzed alloy, the TiF catalyzed alloy has a faster hydrogen absorption/desorption kinetics. On the basis of Arrhenius equation, the dehydrogenation activation energy values of the as-milled MgZnNi-4C (C = TiF, NbF) alloys are 75.514 and 82.367 kJ mol H, respectively, while the value of ball-milled MgZnNi alloy is 109.830 kJ mol H. As a result, both TiF and NbF can significantly ameliorate the hydrogen storage thermodynamics. TiF shows better catalytic influence on hydrogen storage property of MgZnNi than NbF.