Investigation on nano structure Mg-Ni alloy as hydrogen storage material and the effect of nano oxide particle on its properties The effects of TiO 2 additive on the electrochemical hydrogen storage properties of Mg 2 Ni alloy as anode in nickel-metal hydride batteries were investigated. Mg 2 Ni alloy was prepared through mechanical alloying. The metal powders of Mg and Ni elements mixed in a planetary ball-mill for 50 h under an argon protective atmosphere. Mg to Ni atomic ratio was 2:1. The rotational speed during the ball milling was 500 rpm and the ball-to-powder weight ratio was 20:1. Mg 2 Ni– x TiO 2 ( x = 1.5, 3, 5 and 10 wt %) composites were also produced by ball-milling of produced Mg 2 Ni and different amounts of TiO 2 powders for 2 h, by similar process described above. The crystalline structure and surface configuration of the produced alloys were characterized by means of X-ray diffractometer (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM), respectively. The produced alloy and composites were demonstrated as the particles with nanocrystalline/amorphous structure. The XRD pattern and crystalline size (6 nm) have not been changed by introducing TiO 2 particles. The result of the TEM images had a good agreement with XRD result. Irregular coarse particles that are usually formed during the continuous deformation and cold-welding through ball-milling process were seen in SEM images. The electrochemical technique used to determine the discharge capacity and cycle stability was galvanostat test in 6 M KOH electrolyte at 298?K. The first-cycle discharge capacities of the samples with 0, 1.5, 3, 5 and 10 wt% TiO 2 were 62, 26, 27, 80 and 66 mAh/g, respectively. The result showed that the TiO 2 addition exerts no systematic effect on discharge capacity. Adding of 5, 10 wt%TiO 2 increase the discharge capacity. On the other hand, 1.5, 3 wt%TiO 2 reduce it. The cycle stability of Mg 2 Ni has not been affected by TiO 2 addition. The peaks of Mg(OH) 2 confirm the formation of hydroxide layer on the alloy surface due to charge/discharge cycles and the subsequent loss of cycle performance. The smooth surface of alloy particles has changed to a rough one after the charge/discharge cycling indicate the pulverization of this alloy due to the expansion and contraction of cell volume during charge/discharge. The charge/discharge kinetics of electrodes was studied by using anodic polarization and electrochemical impedance spectroscopy techniques. The results showed that the exchange current density of hydrogen reaction was increased by the presence of 5, 10 wt%TiO 2 , while adding 1.5, 3 wt%TiO 2 reduced