Phase Structure And Hydrogen Storage Properties Of Sm-Mg-Ni Based Hydrogen Storage Alloys

New type Sm-Mg-Ni based hydrogen storage alloys have attracted much attention due to their large hydrogen storage capacity,hydrogen absorption/desorption cycle stability and high hydrogen absorption platform.However,there are few reports on the research progress of high pressure Sm-Mg-Ni based alloys.Improving the stability of hydrogen absorption/desorption cycle of hydrogen storage alloys is not only beneficial to the improvement of hydrogen storage performance,but also significantly improve the application scope of hydrogen storage materials,so as to promote the actual production and application of hydrogen storage materials.In this paper,AB₃ and A₂B₇ type Sm-Mg-Ni based hydrogen storage alloys were prepared by powder sintering and the phase structure and hydrogen storage properties were systematically studied.The Sm-Mg-Ni-Co-Al based alloy with A₅B₁₉ type phase structure were further obtained by induction melting and the phase structure,hydrogen storage properties and hydrogen absorption/desorption cycle of the alloys were systematically carried out.The PuNi₃ type Sm_0.68Mg_0.32Ni_2.53 and Gd₂Co₇ type Sm_0.80Mg_0.20Ni_2.95 superlattice stacking hydrogen storage alloys were prepared by powder sintering method.It is found that the two single-phase alloys were fully activated in the first cycle at 298 K under 3MPa H₂ atmosphere.The Pu Ni₃type Sm_0.68Mg_0.32Ni_2.53alloy can absorb 1.41 wt.%H₂ in25 min,and Gd₂Co₇ type Sm_0.80Mg_0.20Ni_2.95alloys could absorb 1.53 wt.%H₂ in 35 min.Both the two alloys can reach the maximum hydrogen absorption in 4 min for the fifth cycle.The hydrogen absorption capacity retention rates of the two single-phase alloys are96.2%and 99.2%after 20 cycles of hydrogen absorption and desorption,respectively.The enthalpy changes of Gd₂Co₇ type Sm_0.80Mg_0.20Ni_2.95 alloy during hydrogen absorption and desorption are-18.86 k J/mol and 23.66 k J/mol respectively,which are much smaller than those of single-phase Pu Ni₃ type Sm_0.68Mg_0.32Ni_2.53 alloy,and the latter are-10.92k J/mol and 6.02 k J/mol,respectively.Sm_0.8Mg_0.2Ni_3.7Co_0.11Al_0.06alloy was obtained by induction melting and annealing treatment.The alloy has not only excellent activation property and hydrogen storage property,but also excellent hydrogen absorption and desorption cycle.It is found that the alloy mainly contains Ce₅Co₁₉,Ce₂Ni₇ and Gd₂Co₇ phases.The maximum activated hydrogen absorption capacity of the alloy is 1.60 wt%under 8 MPa H₂ at 298 K.The hydrogen absorption rate of the alloy increases significantly after 25 weeks of hydrogen absorption and desorption cycle,and the hydrogen absorption rate can reach 1.29 wt.%in only 1.5 min under the same conditions;After 50 weeks of hydrogen absorption/desorption process,the retention rate of hydrogen absorption capacity of the alloy can still be reach to 87.8%.