Role of milling time and Ni content on dehydrogenation behavior of MgH2/Ni composite
(State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China)
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