| The high-pressure hybrid hydrogen storage tank（HPHT）that combines the advantages of gaseous and solid state hydrogen storage owns high volumetric and gravematric hydrogen storage density.Meanwhile,it lowers the hydrogen filling pressure and provides a method to realize the safe and high-density hydrogen storage for mobile applications.The performance promotion of HPHT depends upon the development of materials with excellent hydrogen sorption performances under high pressure.ZrFe2 based alloys are promising candidates for HPHT owing to its fast kinetics,thorough dehydrogenation and good cycle stability.However,ultrahigh equilibrium pressure,low hydrogen storage capacity,large hysteresis and high slope of plateau hinder its application.Based of non-stoichiometric Zr1.05Fe2 alloy,a series of ternary and quaternary Zr-Fe based alloys added with transition elements were prepared by arc melting.The structure of the alloys was characterized by XRD and SEM.The hydrogen storage properties of Zr-Fe based alloys were measured by PCI plot.The main results are as follows.Firstly,the effect of adding transition elements is preliminarily explored by investigating the properties of Zr1.05Fe1.8M0.2（M=V,Cr,Mn,Mo）ternary alloys.The results show that V can effectively reduce the equilibrium pressure and hysteresis,but the dehydrogenation of the alloy at low temperature is incomplete and the slope of the plateau increases.The influence of Cr on reducing equilibrium pressure and increasing hydrogen storage capacity is inferior to that of V.The hysteresis of the alloy is more obvious,but it is completely reversible at low temperature.In comparison,the effect of Mn and Mo is relatively poor.The equilibrium pressure of Mn-substitution alloy is still high and the hysteresis increases.The alloy completely transforms into C14 phase after Mo substitution,which not only has a low hydrogen storage capacity,but also further aggravates the hysteresis phenomenon.Based on the above results,the hydrogen storage properties of Zr-Fe-Cr and Zr-Fe-Mn alloys are systematically studied by varying their content.It is found that Zr1.05Fe2-x-x Crx（x=0.1,0.15,0.2,0.25）still maintains the C15 structure and the equilibrium pressure decreases gradually with the increase of Cr content.Besides,the hysteresis is alleviated,but the hydrogen capacity decreases due to the increased electron concentration.Zr1.05Fe1.7Cr0.3converts to C14 structure and the hydrogen storage capacity and equilibrium pressure decrease further.However,the structure transformation aggravates hysteresis.Among Zr-Fe-Cr alloys,Zr1.05Fe1.85Cr0.15 exhibits the best properties.Its hydrogen capacity reaches1.53wt%.Also,calculated by van’t Hoff equation,its desorption equilibrium pressure at 298K is 60.03 atm and the Hf is 0.78.Mn has little effect on the structure of the alloy.C14 phase does not appear in the alloy even until the content of Mn reaches 0.6.The experiment shows that with the increase of Mn content,the equilibrium pressure of the alloy decreases and the hydrogen storage capacity increases,while the hysteresis phenomenon gets worsen.The desorption pressure of Zr1.05Fe1.4Mn0.6 is about 5.18 atm at 298 K and hydrogen capacity is1.58wt%respectively,but its Hf is up to 1.59.To further reduce hysteresis and increase hydrogen storage capacity,V and Ti were used as fourth component on the basis of Zr-Fe-Cr and Zr-Fe-Mn alloys.The adding of V increases the slope of the alloy plateau,but has a significant effect on reducing hysteresis.The hysteresis of Zr1.05Fe1.85Cr0.05V0.1 at room temperature basically disappeared,but the hydrogen capacity is not increased greatly.Similarly,the hysteresis of Zr-Ti-Fe-Cr and Zr-Ti-Fe-Mn alloys decreases with the increase of Ti content.Also,the equilibrium pressure is increased at the same time.Particularly,they show a rather flat plateau reagion when the atomic ratio of Zr to Ti is 6:4 for Zr-Ti-Fe-Mn alloys.(Zr0.4Ti0.6)1.05Fe1.2Cr0.8 and(Zr0.5Ti0.5)1.05FeMn have the best hydrogen storage performances among the quaternary alloys.The hydrogen storage capacity of(Zr0.4Ti0.6)1.05Fe1.2Cr0.8 is 1.55wt%and the calculated ab-/desorption pressure at298 K is 28.09 atm and 20.84 atm.For(Zr0.5Ti0.5)1.05FeMn,its hydrogen storage capacity is1.58wt%.Besides,the calculated ab-/desorption pressure of(Zr0.5Ti0.5)1.05FeMn at 298 K is38.44 atm and 10.22 atm respectively and the Hf reaches up to 1.33. |
