Crystallite growth characteristics of Mg during hydrogen desorption of MgH_2

MgH₂ is one of promising hydrogen storage materials, but Mg crystallites grow up very fast during hydrogen desorption, leading to the degradation of hydrogen storage properties. Therefore the growth behavior and mechanism of Mg crystallites during hydrogen desorption of nanocrystalline MgH₂ were investigated in this work. It was found that the transformation from MgH₂ to Mg occurred by the surface-controlled ‘nucleation and growth’ mechanism. After the instantaneous nucleation of Mg at free surfaces of MgH₂ particles, Mg crystallites grew through three stages, namely one-dimensional, then two-dimensional and finally one-dimensional growths. In the second stage, Mg crystallites grew quickly as compared with other stages. After complete hydrogen desorption, the average Mg crystallite size in MgH₂−10 wt% Pr₃Al₁₁ sample was smaller than that in pure MgH₂ sample due to the presence of Pr₃Al₁₁.