Preparation, Microstructure And Hydrogen Storage Properties Of TiFe-based Hydrogen Storage Materials

The greenhouse gases emitted by using fossil fuels in large quantities pollute the environment,so alternative fuels need to be developed.As an alternative energy source,hydrogen has been recognized as an ideal substitute for fossil fuels in mobile and stationary applications.But the production,storage and transportation of hydrogen is still the key technology in the field of hydrogen energy.Among the many hydrogen storage materials,TiFe alloy is a typical representative of AB type hydrogen storage alloy,which not only has good hydrogen absorption and desorption performance at normal temperature,but also has higher hydrogen storage density and lower cost.Despite years of research,there is still a certain distance to convert it into commercialization.In addition,problems such as the activation lag of TiFe alloy hindered the further commercial application of TiFe alloy in practice.In this paper,the Ti_1.1Fe_0.6Ni_0.3Zr_0.1Mn_0.2 ternary alloy with excellent activation performance is selected as the master alloy,and the method of element substitution is used to explore the substitution amount of different Pr elements on the as-cast Ti_1.1-xFe_0.6Ni_0.3Zr_0.1Mn_0.2Pr_x?x=0⁰.08?alloy microstructure and hydrogen storage performance.The test conditions were hydrogen pressure3 MPa and temperatures 313,333,353 and 373 K,respectively.The results show that element substitution has no effect on the phase composition of the alloy,only the TiFe phase,NiTi₂ phase and FeZr₂ phase.But the activation time is shortened,from 2640 s of the original alloy to within 30 s.The as-cast Ti_1.02Fe_0.6Ni_0.3Zr_0.1Mn_0.2Pr_0.08 alloy has the best activation performance,which can reach1.587 wt.%within 10 min.The as-cast Ti_1.04Fe_0.6Ni_0.3Zr_0.1Mn_0.2Pr_0.06 alloy has a maximum hydrogen absorption of 1.521 wt.%at 353 K,but the hydrogen evolution is incomplete and the hydrogen evolution continues to increase with increasing temperature.The role of the Pr element in the alloy is that the addition of Pr will promote the segregation of Ti,and the reaction with hydrogen to form a hydride is not easy to decompose.This will cause the amount of hydrogen released to become smaller and the amount of hydrogen absorbed to become larger.Therefore,the appropriate addition of Pr element can improve the hydrogen storage performance of the as-cast Ti_1.1-xFe_0.6Ni_0.3Zr_0.1Mn_0.2Pr_x?x=0⁰.08?alloy.The as-cast Ti_1.04Fe_0.6Ni_0.3Zr_0.1Mn_0.2Pr_0.06 alloy was mechanically ball milled to investigate the effect of ball milling time on the microstructure and hydrogen storage properties of the alloy.The ball milling time is 0,0.5,1,3 and 6 h.The results show that the ball milling alloy only has TiFe phase.With the increase of the ball milling time,the average particle size decreases from the original 42.49?m to 3.62?m for 6 h,and the specific surface area increases from 0.0638 cm³/g to0.3058 cm³/g.Short time ball milling is beneficial to the activation performance of the alloy.The minimum activation time of ball milling at 0.5 h is 24 s.The maximum hydrogen absorption capacity decreases with the increase of the ball milling time.For example,at 313 K,the maximum hydrogen absorption capacity is 1.471 wt.%,1.265 wt.%,1.112 wt.%,1.104 wt.%,0.98 wt.%,respectively.The 3 h ball milled alloy has the lowest hydrogen absorption platform,and the 1 h ball milled alloy has the highest hydrogen evolution platform.The effect of ball milling on the alloy is:ball milling will continuously reduce the particles of the alloy and the specific surface area will continue to increase,gradually forming nanocrystalline amorphous,polycrystalline boundaries and high specific surface area provide channels for hydrogen diffusion,thereby improving hydrogen storage performance.