Effect of Co substitution for La on hydrogen storage properties and thermal stabilities of amorphous Mg_(60)Ni_(30)La_(10-x)Co_x (x=0, 2 and 4) alloys prepared by melt spinning

摘要

A comparison of the hydrogen storage properties and thermal properties of amorphous Mg_(60)Ni_(30)La_(10-x)Co_x hydrogen storage alloys prepared by melt spinning has been investigated. A, B and C were used to represent each alloy composition when x=0, 2 and 4 respectively. Their microstructures, the hydrogen storage properties and the thermal stabilities were analysed by X-ray diffraction (XRD), PCTPro2000 and differential scanning calorimetry (DSC) respectively. After hydrogenation of Mg_(60)Ni_(30)La_(10-x)Co_x (A, B and C) samples at 573 K under 2 MPa hydrogen pressure, XRD pattern results indicate the formation of new phases of MgH_2 (A, B, C), Mg_2NiH_4 (A, B, C), La_4H_(12.19) (A, B, C), Mg_2Ni_(0.9)Co_(0.1)H_4 (B), Mg_2NiH_(0.26) (C) and Mg_2CoH_2 (C). It is observed that the experimental data of hydrogen desorption kinetics at 523, 573 and 623 K are well fitted through Avrami-Erofeev equation, and the hydrogen desorption kinetics is in the order of C>B>A. In addition, with increasing Co content, alloy C has the maximum hydrogen absorption capacity of 3.05 wt-% and the maximum hydrogen desorption capacity of 2.85 wt-%. Based on the results of DSC analysis, dehydrogenation activation energies of these alloys are determined to be 98.31 +2.82 kJ mol~(-1) (A), 96.33 + 5.61 kJ mol~(-1) (B) and 78-99 + 2.98 kj mol~(-1) (C), which are in accordance with the results of hydrogen desorption kinetics.