A comparison of TiF(3) and NbF(5) catalytic effects on hydrogen absorption and desorption kinetics of a ball-milled Mg(85)Zn(5)Ni(10) alloy

In this investigation, the as-milled Mg(85)Zn(5)Ni(10)–4C (C = TiF(3), NbF(5)) composites were successfully produced via ball milling. The different influences between the catalysts TiF(3) and NbF(5) on the hydrogen storage behavior and microstructure of the composites were investigated by XRD, SEM, TEM and hydrogen absorption/desorption tests. The as-milled Mg(85)Zn(5)Ni(10)–4C (C = TiF(3), NbF(5)) alloys contain the major phase Mg, the secondary phase Mg(2)Ni, a small amount of MgZn(2), TiF(3) and NbF(5). After hydrogenation, MgH(2) and Mg(2)NiH(4) are formed, which convert back into Mg and Mg(2)Ni after dehydrogenation indicating that MgZn(2) and the catalysts TiF(3) and NbF(5) do not react with hydrogen. Compared with NbF(5) catalyzed alloy, the TiF(3) catalyzed alloy has a faster hydrogen absorption/desorption kinetics. On the basis of Arrhenius equation, the dehydrogenation activation energy values of the as-milled Mg(85)Zn(5)Ni(10)–4C (C = TiF(3), NbF(5)) alloys are 75.514 and 82.367 kJ mol(−1) H(2), respectively, while the value of ball-milled Mg(85)Zn(5)Ni(10) alloy is 109.830 kJ mol(−1) H(2). As a result, both TiF(3) and NbF(5) can significantly ameliorate the hydrogen storage thermodynamics. TiF(3) shows better catalytic influence on hydrogen storage property of Mg(85)Zn(5)Ni(10) than NbF(5).