Physicochemical and electrochemical hydriding-dehydriding characteristics of amorphous MgNix (x=1.0, 1.5, 2.0) alloys prepared by mechanical alloying

Physicochemical and electrochemical hydriding-dehydriding characteristics of amorphous MgNix, (x = 1.0, 1.5, 2.0) alloys prepared by mechanical alloying have been investigated. It was found that the increase of Ni content in the alloys resulted in greatly enhanced kinetics for both absorption and desorption of hydrogen, while the saturation capacity showed the reverse tendency. Charge-discharge tests showed that the increase in Ni content lead to a significant enhancement in cycle performance of MgNix alloy electrodes. X-ray photoelectron spectroscopic and X-ray excited Auger electron spectroscopic investigations indicated the existence of a significantly thicker Ni-enriched layer for the MgNi1.5 and MgNi2.0, alloys than for the MgNi alloy. These results reveal that excess of Ni in MgNix alloys may improve the cycle performance of alloy electrodes by suppressing the segregation of Mg during electrochemical cycling, and the Ni in the topmost surface layer is mainly responsible for the improvement in the kinetics of hydrogen absorption.