Catalytic influence of Ni-based additives on the dehydrogenation properties of ball milled MgH₂

The catalytic influence of Ni, Zr2Ni5, and LaNi5on the dehydrogenation properties of milled MgH2was investigated. MgH2milled in the presence of Ni (5 wt%) and Zr2Ni5(5 wt%) catalysts for 2 h showed apparent activation energies,EA, of 81 and 79 kJ/mol, respectively, corresponding to ~50% decrease inEAand a moderate decrease (~100 °C) in the decomposition temperature(Tdec).A further 27 °C decrease inTdecwas observed after milling with 10 wt%Ni. Based on theEAvalues, the catalytic activity decreased in the following order: Ni ≈ Zr2Ni5> LaNi5. X-ray photoelectron spectroscopy analysis of the milled and dehydrogenated states of the hydrides modified with Ni catalyst revealed that the observed reduction inEAmay be due to the ability of Ni catalyst to decrease the amount of oxygen atoms in defective positions that are capable of blocking catalytically active sites thereby enhancing the dehydrogenation kinetics. In particular, our results reveal a strong correlation between the type of oxygen species adsorbed on Ni-modified MgH2and theEAof the dehydrogenation reaction.