Element Substitution Of Zr-based Ab <sub> 2 </ Sub>-type Hydrogen Storage Alloy Phase Structure And Electrochemical Properties

Zr-based AB₂ type Laves phase hydrogen storage alloys have been extensively investigated as Ni/MH battery anode material which have good application prospects, because of its much higher discharge capacity and longer life. In this paper, the principle of hydrogen storage alloy and the factors affecting properties of hydrogen storage alloys have been comprehensively reviewed. Based on the review above, multi-component alloying was chosen to research the effect to the properties of hydrogen storage alloys by substituting elements and its mechanism by means of XRD,SEM,EDX and electrochemical methods et al.The effects of substituting Ti for Zr on the phase structures and the electrochemical properties of ZrCro.4Mn_0.4Ni_1.2 have been investigated. The phase structures mainly include C15 Laves phase and C14 Laves phase, with a little second phase Zr₉Ni_<sub>11 in it. When x=0.1, the content of C15 Laves phase reaches maximum. With the content of Ti increasing, C15 Laves phase gradually converts to C14 Laves phase, while the second phase gradually decreasing. When x=0.4, the second phase disappears. The addition of Ti is propitious to convert C15 Laves phase into C14 Laves phase, and inhibit the formation of the second phase. The electrochemical test results show that it is conducive to the activating performance and discharge capacity increase by adding a small amount of Ti in the alloy. When x=0.1 or 0.2, the alloy has best activating properties. When x=0.1, the alloy exhibits the maximum discharge capacity 274 mAh/g. The addition of Ti can elevate the discharge cycle stability of the hydrogen storage alloys. The linear polarization, the anode polarization, the constant potential step and the EIS test show that the exchange current density and the limiting current density first increase then decrease with the content of Ti increasing. When x=0.1, the hydrogen storage alloy electrode exhibit the maximum exchange current density and limiting current density. The EIS test show that the reaction impedance is the minimum among the alloys when x=0.1, which notes that the addition of a small amount of Ti in the alloy electrode is conducive to the improvement of dynamic performance.Choosing Zr_0.9Ti_0.1Cr_0.4Mn_0.4Ni_1.2 alloy as the research object which possesses the best comprehensive electrochemical properties based on the study above. Cr in the alloy was partly substituted by V, and the effect to the electrochemical properties of Zr_0.9Ti_0.1V_xCr_0.4-xMn_0.4Ni_1.2(x=0～0.3)alloys by substitute V for Cr are investigated. It is found that the discharge capacity increases while the activate properties improved with the content of V. When x =0.3, the alloy exhibits the maximum discharge capacity 314.8 mAh/g. It improves the discharge cycle stability by substituting Cr for V, which decreases the high rate discharge ability at the same time. The pressure platform of P-C-T curves decreases during the hydrogen discharge, while the hydrogen discharge capacity increases as the content of V increased. It is found that the exchange current density and the limiting current density descends by V₀> V_<sub>0.2> V_0.3> V_0.1 as the linear polarization and the anode polarization result indicating. The diffusion coefficient tested by the constant potential step basically follows the trends above. The reaction impedance increases with the content of V increasing in the alloy that can be seen from the EIS test.