Alloying Methods To Modulate The Phase Structure And Hydrogen Storage Performance Of Y(Zr)-Fe Alloy

Hydrogen is an important clean energy carrier,and high-performance hydrogen storage materials are one of the key technologies for hydrogen energy development.A wide variety of intermetallic compounds with easily tunable structures are important sources of hydrogen storage materials.In this paper,we address the problem of low hydrogen storage capacity of rare earth-based YFe3-based,YFe2-based alloys,and transition metal ZrFe2-based alloys,and use alloying and over-stoichiometric methods to regulate their crystal structure and mechanical properties to improve their hydrogen storage performance.The hydrogen storage alloys of single-phase were prepared by arc melting and high-temperature annealing.The phase structure and microstructure of the alloy were characterized by XRD and SEM.The hydrogen storage properties of each alloy were studied by measuring hydrogen absorption kinetics and hydrogen absorption/desorption PCI.The effects of alloying elements such as Sc,Y,Zr,Al and Mo on the crystal structure and hydrogen storage thermodynamic properties of the above mentioned hydrogen storage alloys were studied.The main findings of the study are as follows.The cell structure and hydrogen storage properties of YFe3 alloys were improved using partial substitution of Y by Sc,Zr.Firstly,Y1+xFe3 alloys with different excess ratios were designed for the difficult preparation of YFe3 single-phase alloys,and it was found that the Y1.1Fe3 alloy with 10 % excess on the A side had a higher YFe3 phase content,and the complete single-phase alloy could be obtained by partial substitution with Sc in this alloy.Since the atomic radius of Sc is smaller than that of Y,the cell parameters of Y1.1-yScyFe3 alloy decrease with the increase of Sc substitution.It makes the dehydriding equilibrium pressure increases from 0.037 MPa for Y1.1Fe3 to 0.216 MPa for Y0.77Sc0.33Fe3 and 0.3 MPa for Y0.88Zr0.22Fe3.In addition,the alloy absorbs hydrogen faster at near-room temperature and can absorb hydrogen to saturation within 80 s.However,the Sc substitution reduces the hydrogen storage capacity of the alloy.Y1.1-yZryFe3 does not yield a single-phase alloy,but its improvement on the desorption temperature of the alloy is more obvious.The effects of partial substitution of Fe by Al and Mo on the cell structure and hydrogen storage properties of Y(Sc)Fe2 alloys were investigated.The (Y0.7Sc0.3)1.05Fe2-xAlx alloy without YFe3 second phase was prepared by a 5 % over stoichiometric composition design on the A-side.It was found that with the substitution of Al from 0.2 to 0.4,the cell parameters of the alloy gradually increased and the hydrogen hydriding equilibrium pressure gradually decreased from 0.066 MPa for (Y0.7Sc0.3)1.05Fe1.8Al0.2 to 0.048 MPa for (Y0.7Sc0.3)1.05Fe1.6Al0.4,which implies an increase in hydride stability.However,the hydrogen storage capacity does not get elevated with the increase of the cell parameters,but decreases with the reduction of the cell deformation ?VH caused by the entry of each hydrogen atom into the lattice interstice,from 2.05 wt% for (Y0.7Sc0.3)1.05Fe1.8Al0.2 to 1.78 wt% for (Y0.7Sc0.3)1.05Fe1.6Al0.4.This indicates a close relationship between ?VH and hydrogen storage capacity.To further investigate the effect of ?VH on the hydrogen storage capacity,the Fe of (Y0.7Sc0.3)1.05Fe2 alloy was partially replaced with Mo.It was found that the cell parameters of the alloy gradually increased with the amount of Mo substitution from 0.1 to 0.2,and the ?VH of the alloy also gradually increased,which make the hydrogen storage capacity increase to 2.11 wt%for (Y0.7Sc0.3)1.05Fe1.8Mo0.2.This indicates that the hydrogen storage capacity of the alloy is related to its mechanical properties.The relationship between the alloy hydrogen storage capacity and mechanical properties was further verified by partial substitution of Al and Mo for Fe in Zr(Y)Fe2-based alloys.The Zr0.8Y0.2Fe2 single-phase alloy was obtained by replacing Zr in ZrFe2 with 20% Y.With the substitution of Al,although the cell parameters of the Zr0.8Y0.2Fe2-xAlx alloy gradually increased,the bulk (B) and shear modulus (G) of the alloy occurred to decrease and increase,respectively,which made the improvement of the hydrogen storage capacity of the alloy insignificant and only increased from 1.09 wt% of Zr0.8Y0.2Fe1.7Al0.3 to 1.09 wt% of Zr0.8Y0.2Fe1.5Al0.5 of 1.18 wt%.This is because the decrease in bulk modulus makes the alloy less resistant to deformation caused by hydrogen atoms entering the interstice,and the increase in shear modulus increases the dislocation formation energy,making it difficult to coordinate the deformation of the alloy through dislocations after hydrogen absorption,which results in insufficient hydrogen absorption of the alloy.In order to improve the mechanical properties of the alloy,the Zr0.8Y0.2Fe2-x(Al2/3Mo1/3)x alloy was obtained by partially replacing Al with Mo,and its bulk and shear modulus increased and decreased,respectively,compared with those of the Zr0.8Y0.2Fe2-xAlx alloy,i.e.,the G/B value of the alloy decreased from Zr0.8Y0.2Fe1.7Al0.3 0.60 to 0.42 for Zr0.8Y0.2Fe1.7Al0.2Mo0.1.It means that the elastic shear strain energy caused by the entry of hydrogen atoms into the interstices of the latter is more easily released,resulting in an increase in the hydrogen storage capacity of the alloy from 1.09 wt%for Zr0.8Y0.2Fe1.7Al0.3 to 1.24 wt% for Zr0.8Y0.2Fe1.7Al0.2Mo0.1.This indicates that the improvement in mechanical properties (G/B) of the alloy contributes to the increase in hydrogen storage capacity.