Effect Of Cu On Microstructure And Hydrogen Storage Properties Of Hypereutectic Mg-Ni Alloy And Its Kinetic Analysis

Magnesium?Mg?-based hydrogen storage alloy,which is regarded as the ideal hydrogen storage material in the future,stands out from many hydrogen storage alloys due to its advantages in hydrogen absorption/desorption and cost.In this paper,firstly,the classification of hydrogen storage alloys is briefly summarized,and the preparation methods and properties of Mg-based hydrogen storage alloys are described.Among the Mg-based hydrogen storage alloys that have been studied,Mg-based hydrogen storage alloys have a higher hydrogen storage capacity,and the theoretical gravimetric hydrogen storage capacity can reach 7.66 wt%.Compared with Mg-based hydrogen storage alloy,Mg₂Ni-based hydrogen storage alloy has better kinetic properties,but the hydrogen storage capacity is 3.62 wt%.Based on the respective characteristics of the two matrix hydrogen storage alloys,this article studied the Mg₂Ni-based hypereutectic Mg₄₀Ni₁₀ alloy with relatively few studies.The Cu element on the B side was used to replace Ni in the experimental part.First,the as-cast Mg₄₀Ni_10-x Cu_x?x = 0,2,4,6?alloy was prepared by electric resistance furnace,and the microstructure of the alloy was analyzed by scanning electron microscope?SEM?,electron energy dispersion spectrum?EDS?,X-ray diffraction?XRD?and other analytical methods.The structure and phase composition were analyzed,and it was found that the as-cast structure of Mg₄₀Ni₁₀ was composed of a coarse Mg₂Ni primary phase and lamellar Mg-Mg₂ Ni eutectic.The addition of Cu changes the morphology of the structure,making the primary phase grow lager,and the eutectic structure changes from lamellar to lath and rod.The as-cast alloy was ball milled and crushed using a planetary ball mill,and the activation performance of the alloy was compared using the Sieverts volumetric method.The hydrogen storage capacity and kinetic performance were tested at 200,225,250,and 275°C,respectively.The results show that the Mg₄₀Ni₁₀ alloy has good activation performance,and Cu substitution of Ni makes the activation performance worse.A small amount of Cu substitution can improve the hydrogen storage performance of the alloy.With the increase of the substitution amount,the hydrogen storage efficiency increases,and the maximum hydrogen storage capacity of Mg₄₀Ni₈Cu₂ can be It is up to 5.57 wt%,which is higher than that of hypereutectic Mg-Ni alloy.The addition of Cu also significantly promotes the hydrogen release performance of the alloy.Test and analysis of the evolution of the structure during hydrogen absorption and desorption revealed that the Mg₂NiH_0.3 intermediate product of Mg₂ NiH₄ appeared in the hydrogen release process,and the absorbed hydrogen could not be completely released under the experimental temperature and pressure.DSC analysis of the decomposition temperature of the hydride revealed a small endothermic peak and a lower decomposition temperature than for pure MgH₂.In order to further study the dynamic properties of Mg₄₀Ni_10-xCu_x alloy,Jander Diffusion Model?JDM?,Chou Model,Shrinking Core Model?SCM?and JohnsonMehl-Avrami-Kolomogorov?JMAK?model were used to fit the kinetic data measured by Sieverts method.The applicability of the model was judged by the goodness of the fitting results,and the mechanism of controlling the macro hydrogen absorption and desorption reaction rate was analyzed.It is found that the hydrogenation reaction of Mg₄₀Ni_10-xCu_x alloy is influenced by multiple steps.For the dehydrogenation reaction,the diffusion of H is the main factor that restricts the reaction rate.And the activation energy of the hydrogen absorption and dehydrogenation reaction of each alloy was calculated by Van't Hoff relation.Due to the simplification of different models in data processing,the results of some data fitting calculation are not satisfactory.Therefore,in the analysis of the characteristics of different models,some of the models have been modified in this paper.The results show that the modified model has a higher goodness of fit than the traditional model,so the modified model has a wider applicability.