Synchrotron EXAFS studies of Ti-doped Mg_2Ni alloy on the cycling behavior

摘要

In this study, Mg_(1.9)NiTi_(0.1) alloy was synthesized by mechanical alloying and its cyclic hydrogen storage behaviors were investigated. It was found that titanium substituting magnesium in Mg_(1.9)NiTi_(0.1) alloy notably improves the absorption/desorption kinetics. Upon cycling, the kinetic rates of absorption/desorption further increase, whereas the hydrogen storage capacity decreases. To identify the micro-structural evolution of Mg_(1.9)NiTi_(0.1) alloy during cycling, we used X-ray diffraction, scanning electron microscope, and extended X-ray absorption fine structure. After ball milling, the decrease of Mg-Ni atomic interaction lowers the stability of Ti-doped phases and has positive effect on the absorption/desorption behaviors. After 20 cycles, the decrease in the cycling capacity may be attributed to the increasing MgNi_2 content. Further studies revealed that some amounts of Mg_2Ni transform into MgNi_2, which result in great decrease in effective hydrogen storage capacity.