Significantly improved electrochemical hydrogen storage properties of magnesium nickel hydride modified with nano-nickel.

Magnesium nickel hydride (Mg 2 NiH 4 ) used as negative electrode material in nickel-metal hydride (Ni-MH) secondary battery is modified by nano-nickel via mechanical milling. In this paper, we systematically investigate the microstructure and electrochemical properties of the modified system with different milling durations. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) analyses confirm the amorphous transformation of Mg 2 Ni-based hydride and a novel NiH 0.75 nanocrystalline with a diameter of about 5 nm embedding or covering on the surface of the base particle has been observed. Its formation mechanism and positive effects on electrochemical properties of the Mg 2 NiH 4 have also been elaborated. Electrochemical measurements show that the 5 h milled composite possesses markedly increased discharge capacity up to 896 mAh g −1 . With prolonging the milling duration from 5 h to 40 h, the discharge capacity at the 10th cycle increases from 99 mAh g −1 to 359 mAh g −1 . Besides, the discharging procedure changes from stepwise processes to one single-step process with increasing the milling duration. Tafel polarization test shows that the nano-nickel modified system exhibits a much better anti-corrosion ability during charging/discharging cycles. Meanwhile, both the charge-transfer reaction on the alloy surface and hydrogen diffusion inside the alloy bulk are enhanced with nano-nickel modification. [ABSTRACT FROM AUTHOR]