Synergetic effect of Ni and Hb_2O_5 on dehydrogenation properties of nanostructured MgH_2 synthesized by high-energy mechanical alloying

摘要

Nanostructured MgH_2-Ni/Nb_2O_5 nanocomposite was synthesized by high-energy mechanical alloying. The effect of MgH_2 structure, i.e. crystallite size and lattice strain, and the presence of 0.5 mol% Ni and Hb_2O_5 on the hydrogen-desorption kinetics was investigated. It is shown that the dehydrogenation temperature of MgH_2 decreases from 426 ℃ to 327 ℃ after 4 h mechanical alloying. Here, the average crystallite size and accumulated lattice strain are 20 nm and 0.9%, respectively. Further improvement in the hydrogen desorption is attained in the presence of Ni and Hb_2O_5, i.e. the dehydrogenation temperature of MgH_2/Ni and MgH_2/Nb_2O_5 is measured to be 230℃ and 220 ℃, respectively. Meanwhile, the dehydrogenation starts at 200 ℃ in MgH_2-Ni/Hb_2O_5 system, revealing synergetic effect of Ni and Hb_2O_5. The mechanism of the catalytic effect is presented.