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

Abstract

A comparison of the hydrogen storage properties and thermal properties of amorphous Mg₆₀Ni₃₀La_10−xCo_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 Mg₆₀Ni₃₀La_10−xCo_x (A, B and C) samples at 573 K under 2 MPa hydrogen pressure, XRD pattern results indicate the formation of new phases of MgH₂ (A, B, C), Mg₂NiH₄ (A, B, C), La₄H_12·19 (A, B, C), Mg₂Ni_0·9Co_0·1H₄ (B), Mg₂NiH_0·26 (C) and Mg₂CoH₂ (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.