Comparative investigation on the hydrogenation/ dehydrogenation characteristics and hydrogen storage properties of Mg_3Ag and Mg_3Y

摘要

The hydrogenation/dehydrogenation characteristics and hydrogen storage properties of nominal Mg_3Ag and Mg_3Y alloys prepared by induction melting were investigated. The as-melted Mg_3Ag alloy was composed of Mg_(54)Ag_(17) phase, while Mg_3Y consisted of Mg_(24)Y_5 and Mg_2Y phases. Mg_(54)Ag_(17) transformed into MgAg and MgH_2 during the first hydrogenation, and the phase transition of the following hy/dehydrogenation cycles was Mg_3Ag + 2H_2 ↔MgAg + 2MgH_2. Both Mg_(24)Y_5 and Mg_2Y undertook disproportion reactions and decomposed into MgH_2 and YH_3. Experimental and calculated results demonstrated that there was no necessary relation between the thermodynamic stabilities and the size interstices in these alloys. The dehydrogenation enthalpy change (ΔH) and entropy change (ΔS) of Mg_3Ag were calculated and compared with that of pure Mg, which indicated that the increase of ΔS could counteract the stabilization effect of ΔH, which offered a method for tuning the thermodynamic properties of Mg-based alloys.