Study On The Laws Of Elemental Substitution On The Microstructure And Hydrogen Storage Thermomechanical Properties Of Rare Earth-based Hydrogen Storage Alloys

Rare-earth AB₅hydrogen storage alloys have relatively good thermodynamic and kinetic properties for hydrogen absorption/release,which can meet the environmental adaptability of solid-state hydrogen storage materials and achieve rapid hydrogen storage and release under mild conditions.However,in the process of hydrogen uptake/release,the hydrogenation/release reaction is accompanied by heat release/absorption,so its large-scale application is still limited by heat management and significantly affects the performance of hydrogen storage.In this thesis,we use the rare earth elements Ce to replace the A-side metal La in the base alloy La Ni_4.5Al_0.5,and Fe to replace the B-side metal Ni in the base alloy La Ni_4.5Al_0.5,and then modulate the microstructure of the hydrogen storage alloy to investigate the thermodynamic properties of the alloy during hydrogen absorption/exhaustion.In this thesis,we prepared the hydrogen storage alloy by vacuum melting.In this thesis,two system alloys,La_1-xCe_xNi_4.5Al_0.5（x=0～0.4）and La_0.8Ce_0.2Ni_4.5-xFe_xAl_0.5（x=0.1～0.4）,were prepared by vacuum melting method,and the alloys were annealed uniformly,and then the phase structure,thermodynamics and kinetics of each system alloy were investigated separately.The XRD material characterization revealed that the main phase of the La_1-xCe_xNi_4.5Al_0.5（x=0～0.4）series alloys is the hexagonal crystalline La Ni₅phase,and with the increase of Ce substitution（x=0～0.4）,the a-axis of the alloy crystal structure shows a decreasing trend,and the c-axis and anisotropy（c/a）show a fluctuating decrease;with the increase of Fe substitution,the alloy La_0.8Ce_0.2Ni_4.5-xFe_xAl_0.5（x=0.1～0.4）showed a trend of increasing and then decreasing characteristic peak intensity,the a b and c axes of the alloy and the cell volume of the alloy showed a trend of increasing,the half-peak width showed a trend of decreasing and then increasing,and the anisotropy（c/a）showed a trend of decreasing and then increasing with the increase of Fe substitution The anisotropy（c/a）tends to decrease and then increase with the increase of Fe substitution,and has a maximum value at x=0.4（c/a=0.8025）.The thermodynamic and kinetic studies of hydrogen absorption and discharge show that the maximum hydrogen storage capacity of the La_1-xCe_xNi_4.5Al_0.5（x=0～0.4）series alloys decreases as the Ce substitution increases and the plateau pressure of hydrogen absorption/discharge increases.The degree of thermal optimization of the alloy hydrogen uptake/release reaction shows the same trend as the anisotropy（c/a）,and the enthalpy change of the alloy hydrogen uptake/release reaction decreases to 26.33 KJ/mol and 24.30KJ/mol when x=0.2.La_0.8Ce_0.2Ni_4.5-xFe_xAl_0.5（x=0.1～0.4）series alloys with the increase of Fe substitution,the the hydrogen absorption and discharge plateau pressure decreases and the thermomechanical properties of the alloy are optimized to a lesser extent relative to alloy La_0.8Ce_0.2Ni_4.5Al_0.5.Alloy La_0.8Ce_0.2Ni_4.5Al_0.5was prepared neutrally and tested in a solid-state hydrogen storage test system,and it was found that the heat loss of alloy La_0.8Ce_0.2Ni_4.5Al_0.5was23.92 KJ/mol and the thermodynamic enthalpy change of alloy La_0.8Ce_0.2Ni_4.5Al_0.5was almost the same as that of alloy La_0.8Ce_0.2Ni_4.5Al_0.5at 24.3 KJ/mol,which indicates that the alloy can meet the requirements of the results.And the comparison experiment of heat management system and hydrogen release rate control shows that the alloy with a heat management system of 3k W and at a release rate of 1 liter per minute per kilogram of hydrogen storage alloy,the hydrogen release process is almost at a plateau with no heat loss,which is more in line with industrial use.