Microstructures and electrode performances of Mg_(50)Ni_((50-X))Pdx alloys

摘要

Magnesium and several of its alloys can absorb large amounts of hydrogen. This feature is desirable for several technological applications such as solid state hydrogen storage tanks and anodes of nickel-metal hydride (Ni-MH) batteries. For the latter, Mg-Ni alloys are considered very promising due to their high discharge capacities. Conversely, the low stability of Mg-Ni alloys in alkaline electrolytes have hindered their practical use. In the present manuscript, the effects of palladium black addition on the structure and electrochemical properties of the Mg_(50)Ni50 (in at.%) alloy were investigated. The studied ternary alloys have general composition of Mg_(50)Ni_((50-X))Pd_x, with 0 ≤ x ≤ 5 (in at.%). These alloys were synthesized by mechanical alloying from pure elements. The alloy powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS) while their electrode performances were evaluated by galvanostatic cycles of charge and discharge. The investigated alloys have multi-phase structures composed of amorphous and nanocrystalline phases, with nano-grain sizes of nearly 5 nm. Concerning the electrode performance, the best results were attained by the Mg_(50)Ni_(47.5)Pd_(2.5) alloy, which kept a high discharge capacity and improved the cycling stability.