Hydrogen storage properties and thermal stability of amorphous Mg70(RE25Ni75)30 alloys

Abstract

In this study, amorphous Mg70(RE25Ni75)30 (RE=La, Pr, Nd) alloys were produced by melt spinning, their hydrogen storage properties and the thermal stabilities have been studied by means of PCTPro2000 and Differential Scanning Calorimetry (DSC), respectively. After hydrogenation of Mg70(RE25Ni75)30 samples at 573K under 2MPa hydrogen pressure, XRD results indicate the formation of new phases of MgH2, Mg2NiH4, LaH3.01 (RE=La), PrH2.92 (RE=Pr) and Nd2H5 (RE=Nd). The experimental data of hydrogen desorption kinetics at 523K, 553K, 573K are well fitted through Avrami–Erofeev equation, and the hydrogen desorption kinetics were in the order of Pr>La>Nd. Based on the results of DSC analysis, dehydrogenation activation energies of these samples were determined to be 68.81±2.50kJ/mol (RE=La), 64.79±1.09kJ/mol (RE=Pr) and 73.37±3.23kJ/mol (RE=Nd), which are in accordance with the results of hydrogen desorption kinetics. As shown in the P–C isotherm curves, two hydrogen absorption plateaus at about 0.07MPa and 0.2MPa have been observed for Mg70(RE25Ni75)30 (RE=La, Pr) tested at 573K, while there is only one sloping hydrogen absorption plateau in the range of 0.06–0.3MPa for Mg70(Nd25Ni75)30 alloy. The maximum hydrogen absorption capacity is 4.21wt.% for Mg70(Nd25Ni75)30 and the maximum hydrogen desorption capacity is 2.74wt.% for Mg70(Pr25Ni75)30.