Investigation On The Phase Structure And Electrochemical Performances Of La-mg-ni System A₂b₇ -type Hydrogen Storage Alloys

With the development of application of hydrogen storage material, requirements for hydrogen storage material have become increasingly high. It's necessary to discover a new kind of hydrogen storage material with higher capacity, longer cycle life and low cost.In order to improve its cyclic stability, the La-Mg-Ni system A₂B₇-type hydrogen storage alloy was determined as the object of this work based on the review of the research and development of the La-Mg-Ni system hydrogen storage alloys both from home and abroad. By means of X-ray diffractometer (XRD), sanning electronic microscope (SEM), electrochemical testing and kinetics testing, the influence of element substitution on the phase structure, electrochemical properties and dynamic characteristics of alloys were systemically studied to discover the relationship between phase structure, composition and edectrochemical performances of alloys. The main conclusions were received.Investigation both the La_0.8-xR_xMg_0.2Ni_3.35Al_0.15(R = Sm, Nd, Pr, x= 0 0.4) alloys and the La_0.8-xR_xMg_0.2Ni_3.15Co_0.2Al_0.15(R = Sm, Nd, Pr, x= 0 0.4) alloys show that all of the alloys are composed of multi-phase containing LaNi5(CaCu5-type) and La₂Ni₇(Ce₂Ni₇-type) main phases. All the alloys have excellent activation characteristic.The partial Sm, Nd and Pr substitution for La, respectively, increases the cycle stability both of the La_0.8-xR_xMg_0.2Ni_3.35Al_0.15(R = Sm, Nd, Pr, x= 0 0.4) alloys and the La_0.8-xR_xMg_0.2Ni_3.15Co_0.2Al_0.15(R = Sm, Nd, Pr, x= 0 0.4) alloys inordinately. Investigation of the dynamic characteristic of the La_0.8-xR_xMg_0.2Ni_3.35Al_0.15(R = Sm, Nd, Pr, x= 0 0.4) alloys show that the partial substitution of La with Sm, Nd and Pr, respectively, impairs the high-rate dischargeabilities of the alloys. With the increasing Sm, Nd and Pr content, the charge transfer resistance of alloy electrodes increase first then decrease, and limit current density and hydrogen diffusion coefficient decrease first then increase.The dynamic characteristic of the La_0.8-xSm_xMg_0.2Ni_3.15Co_0.2Al_0.15(x= 0 0.4) were investigated. The high-rate dischargeabilities of the alloys increase with the increasing Sm content, which of the charge transfer resistance decrease, and limit current density and hydrogen diffusion coefficient increase.The dynamic characteristic of the La_0.8-xR_xMg_0.2Ni_3.15Co_0.2Al_0.15(R = Nd, Pr, x= 0 0.4) were investigated. The high-rate dischargeabilities of the alloys increase first then decrease with the increasing Nd, Pr content, which of the charge transfer resistance decrease first then increase, and limit current density and hydrogen diffusion coefficient increase first then decrease.