Electrochemical hydrogen storage properties of composites

For further improving the electrochemical properties of nonstoichiometric AB 3 -type La 0.7 Mg 0.3 Ni 3.5 alloy as negative electrode of Ni-MH battery, its related composites La 0.7 Mg 0.3 Ni 3.5 – x wt% Ti 0.17 Zr 0.08 V 0.35 Cr 0.1 Ni 0.3 ( x = 5 , 10, 25, 40) are prepared by ball milling method. It is found that all these composites are mainly composed of (LaMg) Ni 3 and LaNi 5 phases according to XRD patterns. When x ⩽ 25 , the V-based solid solution BCC phase and C14 Laves phase in Ti 0.17 Zr 0.08 V 0.35 Cr 0.1 Ni 0.3 alloy are not detectable. As x further increases to 40 wt%, however, these two phases appear in XRD pattern. Electrochemical studies show that the maximum discharge capacity of these electrodes decreases slightly from 348.5 mAh/g ( x = 5 ) to 335.2 mAh/g ( x = 40 ) , while the cyclic capacity retention rate of composite electrodes is significantly improved from 29.7% ( x = 5 ) to 63.0% ( x = 40 ) after 70 charge–discharge cycles. This improvement of cyclic life can be ascribed to the enhanced anti-corrosion performance of composite electrode in alkaline solution. Moreover, the electrochemical kinetics properties, including the charge-transfer resistance R ct , the polarization resistance R p , the exchange current density I 0 , the limiting current density I L and the hydrogen diffusion coefficient D , of the composite electrodes were retarded first with x increasing from 5 to 25 and then improved when x reaches to 40.