Synchrotron EXAFS studies of Ti-doped Mg2Ni alloy on the cycling behavior

• Ti substituting Mg in Mg1.9NiTi0.1 alloy notably improves the kinetics.
• The submission of Mg(6i) by Ti increased the Ni–Ni and Ni–Mg distances.
• The metastable Ti-doped Mg2Ni phases enhanced the absorption/desorption kinetics.
• The kinetics increased after 20 cycles, but the hydrogen capacity decreased.
• The decrease in hydrogen storage capacity is attributed to the formation of MgNi2.

In this study, Mg1.9NiTi0.1 alloy was synthesized by mechanical alloying and its cyclic hydrogen storage behaviors were investigated. It was found that titanium substituting magnesium in Mg1.9NiTi0.1 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 Mg1.9NiTi0.1 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 MgNi2 content. Further studies revealed that some amounts of Mg2Ni transform into MgNi2, which result in great decrease in effective hydrogen storage capacity.

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