By means of linear polarization, Tafel polarization and galvanostatic discharge methods, the kinetic properties of MlNi4.3-XCoXAl0.7 (X=0.0, 0.3, 0.5, 0.7, 0.9, 1.1 and 1.3) hydride electrodes, including high rate dischargeability HRD, exchange current density I0, limiting current density IL, the symmetry factor β, and the apparent diffusion coecient of hydrogen in the a phase Da have been studied systematically. The results show that the HRD of the electrode with high Co content is lower than that with low Co content. For the MlNi4.3-XCoXA10.7 hydride electrodes, with Co content increasing from 0.0 to 1.3, the values of 10, IL, β and Da decreased from 395 to 33mA/g, 2263 to 308 mA/g, 0.85 to 0.43, 1.42×10-10 to 2.1×10-11cm2/s, respectively. In order to calculate the electrochemical polarization ηe and concentration polarization ηc based on anodic polarization curve, the experimental anodic polarization curve should be divided into three regions to discuss according to discharge current density Id, namely, Id<IP, IP<Id<If, and Id>If. The calculation of ηe and ηc should use di€erent formula in different regions. When discharge current density Id is smaller than Ip, the traditional equation used to calculate the electrochemical overpotential can not be used, when Ip is between Ip and If, both equations used to calculate the electrochemical overpotential and concentration overpotential can be used, and when Id is larger than If, because there exists absorption and adsorption of hydrogen, the traditional equation used to calculate concentration overpotential can not be used in the system of hydride electrodes.

In this paper, the structural and electrochemical properties of the superstoichiometric (Ti0.8Zr0.2) (V0.533Mn0.107Cr0.16Ni0.2)x (x=2, 3, 4, 5, 6) hydrogen storage alloys have been studied systematically. It is found by X-ray diffraction and energy dispersive spectra analysis that all these alloys mainly consist of two phases, a C14 Laves phase with hexagonal structure and a V-based solid solution phase with body-centered cubic structure. The lattice parameters and thus the cell volumes of the two phases all decrease when x is increased. The electrochemical measurements indicate that the maximum discharge capacity, the discharge equilibrium potential, the high rate dischargeability, the cyclic stability, the exchange current density 10, and the limiting current density IL of the alloys all increase with increasing x from 2 to 5. When x reaches 6, the discharge equilibrium potential, the high rate dischargeability, and the cyclic stability are still increasing proportionately, while the maximum discharge capacity, the exchange current density 10, and the limiting current density IL all decrease. Furthermore, the alloy electrodes are activated with more difficulty for the alloys with higher stoichiometry x. Consequently, we believe that the superstoichiometry is an effective way to improve the overall electrochemical properties of the Ti-based Laves-phase hydrogen storage alloys used for the negative electrodes of the Ni-MH secondary batteries.

In this paper, the structural and electrochemical properties of La0.7Mg0.3 (Ni0.85Co0.15)x (x=2.5, 3.0, 3.5, 4.0, 4.5, 5.0) hydrogen storage alloy electrodes were studied systematically. X-ray diffraction Rietveld analyses show that all these alloys consist of a (La, Mg) Ni3 phase with the PuNi3-type rhombohedral structure and a LaNi5 phase with the CaCu5-type hexagonal structure. The (La, Mg) Ni3 phase abundance first increases to a high percentage (～75%) and then decreases with increasing x. In contrast, the LaNi5-phase abundance first remains low and almost unchanged and then increases to a high percentage (～70%) with increasing x. The pressure-composition isotherms shows that for each isotherm the plateau region widens and the plateau pressure is maintained almost unchanged when x increases from 2.5 to 3.5. However, as x increases further, the plateau region is shortened and becomes flatter, and the plateau pressure increases with x. Electrochemical studies indicate that all important electrochemical properties, including the maximum discharge capacity, the high rate dischargeability, the exchange current density, and the limiting current density of the alloy electrodes increase as x increases from 2.5 to 3.5 and then decrease when x increases further from 3.5 to 4.5.

In this paper, the influence of heat treatment on the electrochemical properties of La0.67Mg0.33Ni2.5Co0.5 alloy electrodes has been studied. The results show that, after heat treatment, the electrochemical properties including the discharge capacity, width of discharge plateau and cyclic stability have been improved markedly. The discharge capacity of the alloy annealed at 1123K is the highest and the cycle life of the alloy annealed at 1223K is the longest, respectively. In addition, the exchange current density I0 and the limiting current density IL of the alloy electrode both increase when annealed at 1123K and then decrease when the annealing temperature increases to 122 K.

The effect of partial substitution of Mn for Ni on the structural and electrochemical properties of the La0.7Mg0.3Ni2.975-xCo0.525Mnx (x=50.0, 0.1, 0.2, 0.3, 0.4, 0.5) hydrogen storage alloys has been investigated systematically. The results of X-ray powder diffraction and Rietveld analyses showed that all alloys consisted of the (La, Mg) Ni3 phase and the LaNi5 phase, and the content of the (La, Mg) Ni3 phase first remained unchanged (～77wt%) and then decreased, but the content of the LaNi5 phase increased progressively with increasing x. Meanwhile, the lattice parameters and cell volumes of the (La, Mg) Ni3 phase and the LaNi5 phase all increased with increasing Mn content. The pressure composition isotherms showed that the hydrogen storage capacity first remained almost unchanged and then decreased with increasing x from 0.0 to 0.5, and the equilibrium pressure decreased from 0.51atm to 0.06atm. The electrochemical measurements indicated that the maximum discharge capacity first remains unchanged (～400mAh/g) with increasing x from 0.0 to 0.2 and then decreased when x increased further. Moreover, the high rate dischargeability, the exchange current density I0, the limiting current density IL, and the hydrogen diffusion coefficient D of the alloy electrodes all increased first and then decreased with increasing x, which indicates that the kinetics of hydriding/dehydriding of the La0.7Mg0.3Ni2.975-xCo0.525Mnx (x=50.0, 0.1, 0.2, 0.3, 0.4, 0.5) hydrogen storage alloys increased first up to x=0.1 and then decreased with further increasing x.