Abstract:The effects of ball milling time and Ni content on the dehydrogenation performance of MgH₂/Ni composite were systematically investigated. The structural evolution of ball milled MgH₂+x%Ni (x=0, 2, 4, 8, 20, 30, mass fraction) samples during mechanical milling process and dehydrogenation properties were investigated by a series of experimental techniques. The results show that the desorption kinetics is independent of particle size, grain size and defects as the temperature is above 380 ^oC. The desorption kinetics is improved by prolonged milling time due to refined and uniformly distributed Ni. The formation of Mg₂Ni after dehydrogenation is proposed to explain the degradation of hydrogen storage properties of MgH₂ during de-/hydrogenation cycling process. The desorption activation energy of MgH₂ decreases with the increase of Ni content due to the catalytic effect of Ni. It is found Ni favors the nucleation of magnesium phase and accelerates the recombination of hydrogen atoms.

Key words: magnesium hydride; nickel; nucleation; recombination; high-energy ball milling