Electrochemical and structural characterization of electroless nickel coating on Mg₂Ni hydrogen storage alloy

Mg₂Ni alloys were prepared by high-energy ball milling, followed by an electroless nickel coating, and their electrochemical properties were investigated. The results indicated that the thickness of Ni-P coatings determined the discharge capacity of Ni-coated Mg₂Ni alloys. The measuring amount of deposited Ni particles was used to represent the thickness of Ni-P coatings. With an increase in the amount of deposited Ni particles, the discharge capacity reached to a maximum value of 148 mA h g^-1 at the deposited Ni particles of 2320 ppm, followed by declining to 106 mA h g ^-1. From the electrochemical impedance spectroscopy experiments, the charge transfer resistance increased and meanwhile the diffusion coefficient decreased, if the amount of deposited Ni particles was greater than 2320 ppm. According to the X-ray diffraction studies, with an increase in the deposited amount of Ni particles the structure of Ni-P spherical particles, with a diameter of 50-250 nm, changed from nanocrystalline to amorphousness.