Electrochemical characteristics of the ball-milled alloys with Ni powders ( and 2)

The electrochemical hydrogen storage properties of the ball-milled LaMg 10 - x Ti x Ni 2 alloys with Ni powders ( x = 1 and 2) were investigated. It was found that the first discharge capacity of the ball-milled LaMg 9 TiNi 2 + 150 wt % Ni composite was 909.5 mAh/g, but the value of the ball-milled LaMg 8 Ti 2 Ni 2 + 150 wt % Ni composite was only 750.2 mAh/g. By EIS analysis, it is shown that the existence of a small quantity of TiNi phase in LaMg 9 TiNi 2 alloy increased the electro-catalytic activity and reduced the electrochemical reaction resistance. This probably played an important role in the increase of discharge capacity of the ball-milled LaMg 9 TiNi 2 – Ni composite. The presence of LaMg 2 phase and excessive TiNi phase resulted in the lower discharge capacity of the ball-milled LaMg 8 Ti 2 Ni 2 – Ni composite. Besides the higher discharge capacity, the ball-milled LaMg 9 TiNi 2 – Ni composite exhibited the better cycle performance. The main reason for the better cycle performance was analyzed by X-ray diffraction (XRD), electrochemical impedance spectra (EIS) and steady-state polarization (SSP) experiments. It is verified that the main reason is that the electrochemical reaction resistance of the ball-milled LaMg 9 TiNi 2 – Ni composite is always lower than that of the ball-milled LaMg 10 Ni 2 – Ni composite because the former one contains a small quantity of TiNi phase which has high electro-catalytic activity.