Enhanced electrochemical kinetics of magnesium-based hydrogen storage alloy by mechanical milling with graphite

Magnesium nickel alloy (Mg2Ni) which used as the negative electrode material in the nickel-metal hydride (Ni/MH) secondary battery is modified by graphite via mechanical milling. The effects of graphite on the Mg2Ni are systematically investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and a series of electrochemical tests. The results show that the cycle stability of the Mg2Ni alloy is improved with the addition of 10 wt.% graphite and the discharge capacity at the 20th cycle increase from 116.9 mA g−1 to 178.5 mA g−1. The Tafel polarization test indicates better corrosion resistance of the Mg2Ni/graphite composite. Meanwhile, the results of electrochemical tests indicate that both the charge-transfer reaction rate on the surface of the alloy and the hydrogen diffusion rate inside the bulk of alloy are boosted with the introduction of graphite.