Tuning Of Components,Structure And Hydrogen Storage Properties Of Zirconium-Based AB₂-Type Alloys

A_xB_ytype intermetallic alloy consisting of strong hydride forming elements on the A side and weak hydride forming elements on the B side is an important source of hydrogen storage materials with important applications in solid state hydrogen storage,hydrogen compression,hydrogen purification,chemical power sources,etc.AB₂ type（A for Ti;Zr,B for Cr,Mn,V,Fe,and other transition elements）hydrogen storage alloys are generally C14 or C15 type Laves phase structures,which have a higher hydrogen storage capacity than AB₅ type rare earth based hydrogen storage alloys.ZrFe₂ is a type of C15 structured hydrogen storage alloy with a room temperature plateau pressure of up to 325 atm and a theoretical hydrogen storage capacity of up to 1.97 wt%,but there are problems such as large hysteresis coefficients for hydrogen absorption and desorption.Compared to the Ti-based AB₂-type hydrogen storage alloys with C14 structure that have been extensively studied,the alloying and application studies of Zr-based AB₂-type hydrogen storage alloys are not systematic.To address these problems and applications in high/low pressure hydrogen storage and hydrogen compression,this paper investigates the component-microstructure-properties of Zr-based AB₂ hydrogen storage alloys by modulating the phase structure,electron concentration,and average atomic radius of the alloys through elemental substitution of Y and Ti on the A-side and Al and Ga on the B-side and quenching process optimization to improve the platform properties of ZrFe₂-based alloys such as hydrogen absorption and desorption pressure,hysteresis,slope,and capacity.The constitutive relationships of the properties were studied,and a series of new Zr-Y-Fe,Zr-Y-Fe-Mo,Zr-Fe-Al,Zr-Fe-Ga,Zr-Ti-Fe-Ni-V alloys were obtained,and the preparation,structure,and hydrogen storage properties of AB₂-type high-entropy alloys were explored,with the following main conclusions.In order to reduce the platform pressure and increase the hydrogen storage capacity of the ZrFe₂ alloy,element Y,which has a large atomic radius and a high affinity for H,was chosen for the A-side substitution.Meanwhile,in order to solve the problem that Y is difficult to dissolve in ZrFe₂ alloy,the sample was prepared by applying arc melting.and the optimized annealing process yielded a single-phase alloy with a C15 structure.It is shown that the addition of Y in the Zr_1-xY_xFe₂ alloy increases the cell volume of the C15 phase,which significantly reduces the hydrogen absorption and desorption plateau pressure and slightly increases the hydrogen storage capacity.In order to solve the problem of low reversible capacity due to the tilted Zr_1-xY_xFe₂ platform,the Mo element with high bulk modulus was chosen to be alloyed on the B side.Zr_0.8Y_0.2Fe_2-xMo_x（x=0.05,0.10,0.15）alloys were prepared,increasing the reversible capacity from 1.26 wt%to 1.59 wt%for the Zr_1-xY_xFe₂ alloy.To address the problem that previous Al alloying substantially reduced the hydrogen storage capacity of ZrFe₂,High-capacity Zr-Fe-Al hydrogen storage alloys were obtained by modulating the organisation of the alloys through a quenching process.It was found that the as-cast ZrFe_2-xAl_x alloy contains a large amount of Zr₂Fe second phase,which leads to a significant decrease in the hydrogen storage capacity.The Zr-Fe-Ga alloy was prepared for the first time using the same process,and its structure and hydrogen storage properties were investigated.The quenched ZrFe_1.8Al_0.2 alloy has a maximum hydrogen storage capacity of 1.62 wt%,which is much higher than the 1.43 wt%of the as-cast alloy and the results reported in the literature.Zr-Fe-Ga alloys were also prepared for the first time using the same process and compared with Zr-Fe-Al alloys.the ZrFe_2-xGa_x alloy has a slightly higher equilibrium pressure for hydrogen absorption and desorption than the ZrFe_2-xAl_x alloy.The hydrogen dissociation pressures at 298K for ZrFe_1.9Ga_0.1 and ZrFe_1.9Al_0.1 are 164.0 atm and 130.7 atm,respectively,due to the higher bulk modulus of the ZrFe_2-xGa_x alloy.ZrFe₂-based alloys with small amounts of Ga or Al substitution are suitable for high-pressure hydrogen storage applications.Hydrogen compressors require a higher level of hydrogen storage performance,requiring both a flatter slope and a smaller hysteresis.Based on the ZrFe₂alloy,the plateau pressure is regulated by alloying the A/B side with Ti,Ni and V simultaneously and overcomes the problem of a large platform hysteresis coefficient and also maintains a low platform slope.The Zr_1-xTi_xFe_1.9-yNi_yV_0.1（x=0.1,0.2,0.3;y=0.7,0.8,0.9）alloy with uniformly distributed elements and a single C15 structure obtained by quenching at 1423 K has a good combination of properties with high hydrogen storage capacity,flat plateau and low hysteresis.The Zr_1-xTi_xFe_1.2Ni_0.7V_0.1（x=0.1,0.2）alloy is able to increase the hydrogen supply pressure from 60.4atm to 334.5 atm over the temperature range 283 K-353 K with an effective hydrogen compression above 0.81 wt%and an effective hydrogen compression ratio above 2.61.The hydrogen compression performance is better than that of Ti-based hydrogen compression alloys.Zr_1-xTi_xFe_1.9-yNi_yV_0.1 can be applied to hydrogen storage materials and hydrogen compression alloys.The concept of high-entropy alloys was introduced to improve the activation and capacity of AB₂ alloys.A series of Zr-based AB₂-type high-entropy alloys were designed and prepared,and their structures and hydrogen storage properties were investigated.The phase formation rules,the characteristics of phase composition changes,and the relationships between the high entropy alloys,between the high entropy alloys and the matrix phases,and between the as-cast and quenched states are studied.The study shows that AB₂-type high entropy alloys have the characteristics of AB₂ alloys and have the unique properties of high entropy alloys.The phase structure and plateau pressure of the high entropy alloy are related to the average valence electron concentration VEC.The high entropy alloy Zr_xTi_2-xV_yMn_zFe_2-yNi_2-z is capable of reversible hydrogen storage at room temperature,with a significant hydrogen absorption and desorption plateau characteristic and a small hysteresis coefficient.Zr_0.8Ti_1.2V_0.8Mn_0.8Fe_1.4Ni has a hydrogen storage capacity of 1.71 wt%at 303 K,a hydrogen desorption plateau pressure of 3.38 atm,a hysteresis coefficient and slope of 0.09 and 1.10 respectively,and the time required to complete 90%of the hydrogen storage capacity T_0.9 is only 1.02 min.XPS and TEM tests show that the high content of Ti and V on the surface of the high entropy alloy as well as the presence of a large number of defects in the high entropy alloy,give the high entropy alloy excellent activation properties.