Preparation and hydrogen storage properties of Mg_2Ni intermetallic nanoparticles

摘要

In this work we investigated the hydrogen storage properties of stoichiometric Mg_2Ni intermetallic nanoparticles produced from Mg and Ni nanoparticles. The mean size of the Mg_2Ni particles is about 30-50 nm and the lattice constants of the Mg_2Ni compound are a = 5.22 A, c = 13.29 A. The Mg_2Ni compound showed excellent hydrogen storage properties without activation. It can absorb 2.77, 2.93 and 3.03 wt percent hydrogen at 523, 573 and 623 K respectively. After one simple activation process, the obtained Mg_2Ni absorbed 1.74, 2.07, 2.31 and 2.82 wt percent hydrogen at 293, 348, 426 and 493 K respectively. The absorption and desorption plateau hydrogen pressures are about 2.5 and 0.8 bar at 523 K, 5.9 and 3.4 bar at 573 K and 12.7 and 9.7 bar at 623 K. The resulting van't Hoff equation is log(P/bar) = -3464/T + 6.541 and the formation enthalpy (DELTA H) and entropy (DELTA S) for the Mg_2NiH_4 are -66.32 kJ/mol H_2 and -125.3 J K~(-1)/mol H_2.