Characterization on the kinetics and thermodynamics of Mg-based hydrogen storage alloy by the multiple alloying of Ce, Ni and Y elements

In this work, the multi-element Mg-based alloys, Mg90Ce10, Mg90Ce5Ni5, Mg90Ce3Ni4Y3, were prepared by combination technology of induction smelting and mechanical milling. Meanwhile, the phase evolution in reversible reaction as well as hydrogen storage behaviors of these alloys were investigated in detail by X-ray diffraction, Transmission Electron Microscope, and Pressure-Capacity-Temperature characterization methods. The results showed that the reaction mechanism of the Mg90Ce10 alloy can be concluded as the reversible circulation of Mg/MgH2 catalyzed by CeH2.73 phase. After the addition of Ni and Y elements, the new reaction path is introduced in the system, including Mg2Ni + H2 <-> Mg2NiH4 and YH2 + H2 <-> YH3. Thereinto, the Ni elements have a very obvious effect on improving the hydrogen absorption and desorption kinetics of the Mg-Ce alloy, which optimizes the optimal hydrogenated temperature to 250 degrees C and reduces the activation energy of hydrogen desorption from127.3 to 79.7 kJ/mol H2. Meanwhile, the Ni elements also altered the rate limiting step of hydrogen desorption process of the Mg-Ce alloy from surface control to nucleation and growth control. However, after further addition of Y elements on this basis, the desorption kinetics of the Mg-Ce-Ni-Y-alloy could not be further improved, but its hydrogen absorption kinetics had an obvious enhancement.