The Controllable Preparation And Electrochemical Properties Of The Single-phase Pr-Mg-Ni Alloys With Superlattice Structure

In this paper,the AB3,A2B7 and A5B19-type single phase Pr-Mg-Ni-based alloys were prepared via powder sintering method through adjuist the molar ratio of PrMgNi4/PrNi5(x)precursors,and the mechanism of the alloys with different structures was studied,which provided the theory foundation for the controllable preparation of the alloys with a specific phase structure.In addition,combined with the oxidation of active components and the pulverization of alloy particles,the mechanism of the capacity degradation was analyzed in detail.Besides,the relationship between the phase structure and the electrochemical properties,the solid solubility of Mg in the PuNi3-type phase,the effect of the Mg content to the phase structure of the Pr-Mg-Ni alloy,as well as the hydrogen storage properties of the single phase RE2MgNi9(RE = La,Pr,Nd)alloys were studied in this paper.Based on the Pr-Ni binary diagram and peritectic reaction,we have been successively prepared the AB3-type Pr2MgNi9,A2B7-type Pr3MgNi14 and A5B19-type Pr4MgNi19 single phase alloys.The studies on the formational mechanism of the single phase alloys show that the peritectic reaction formational temperatures for the three single-phases are 900 ?C,925 ?C and 950 ?C respectively.The studies on the electrochemical properties found that the maximum discharge capacity of the alloy is depended on the element electronegativity,the proportion of the [A2B4] subunit in the superlattice structure and the number of the hydrogen storage sites in [A2B4] and [AB5] subunits,which decreased with the increasing [AB5]/[A2B4] subunit ratio,while the HRD and cycling stability show a reverse trend.The studies on the cycling stability of the alloys found that the expansion rate of [A2B4] and [AB5] subunits is inconsistent,which cause the increase of the internal stress of the alloy and futher accelerate the pulverization of the alloy particles.In addition,we studied the kinetic properties of the alloys and found that the changing trend of HRD is well consistent with the trend of I0,which implies that the main factor affecting HRD is I0.The content of Mg in the alloys had an important effect on the phase structure,and the phase transformation occurred to increase the super-stacking phase endowed more [A2B4] slabs with increase of Mg content.By changing Mg content in Pr3-x MgxNi9(x = 0.45-1.2)alloy,the PuNi3-type single-phase Pr2MgNi9 alloy was prepared,and the solid-gas hydrogenation/dehydrogenation and electrochemical property of the PuNi3-type single-phase RE-Mg-Ni(RE = La,Pr,Nd)alloys have been studied comparatively.The studies found that Pr2MgNi9 and Nd2MgNi9 alloys possess superior HRD and cycling stability,both of the HRD1500 and the S100 prosperities were enhanced by 20% than the La2MgNi9 alloy.The studies on the solid-gas hydrogenation revealed that the hydrogenation rate of Pr2MgNi9 and Nd2MgNi9 allos was higher than the La2MgNi9 alloy,the uptake time for hydrogen content to reach 90% of its maximum storage capacity for Pr2MgNi9 alloy was 12 s.