Effects Of V,Ti And Zr Based Catalysts On The Hydrogen Storage Properties Of Mg₁₇Al₁₂

In this paper,Mg₁₇Al₁₂ alloy is prepared by powder metallurgy process,and then Mg₁₇Al₁₂ based composites processed by mechanical alloying with the addition of different catalysts are evaluated for their phase structures and hydrogen storage properties.Firstly,Mg₁₇Al₁₂+xwt%V?x=0,2.5,5.0,7.5?are prepared by ball milling,and the effect of V content on hydrogen storage properties of Mg₁₇Al₁₂ alloy are explored.It is found that the comprehensive performance of Mg₁₇Al₁₂ alloy is best when the mass fraction of V is 5.0.In addition,the effects of the addition of V based compounds?V2O5,VC,VF4?on Mg₁₇Al₁₂ are studied.Mg₁₇Al₁₂ shows a good hydrogen storage performance with V2O5 as catalyst.It transforms into MgH2 and Al after hydrogen absorption,and returns to the original phases after hydrogen desorption except for a little Mg1.84Al3.16,which shows a good reversibility.Compared with hydrogen absorption/desorption properties of pure Mg₁₇Al₁₂,the initial hydrogen absorption and desorption temperature of Mg₁₇Al₁₂+5.0wt%V2O5 are reduced by 50? and 75?;hydrogen absorption and desorption enthalpy are decreased from-74.1kJ/mol and 95.2kJ/mol to-55.4kJ/mol and 62.4kJ/mol,respectively;hydrogen activation energy is reduced from 248.8kJ/mol to 117.7kJ/mol.It indicates that the thermodynamic and kinetic properties of hydrogen absorption and desorption for Mg₁₇Al₁₂+5.0wt%V205 are greatly improved.Secondly,the samples are prepared by ball milling to explore the effects of xwt%Ti?x=0,2.5,5,7.5?on the hydrogen storage properties of Mg₁₇Al₁₂ alloy.In these samples,Mg₁₇Al₁₂+5.0wt%Ti shows a good reversible hydrogen absorption and desorption capability.Additionally,in the effect of 5.0wt%Ti based compounds?TiO2,TiC,TiF3?on hydrogen storage properties of Mg₁₇Al₁₂ alloy,Mg₁₇Al₁₂+5.0wt%TiO2 has the best hydrogen storage properties.It transforms MgH2 and Al into Mg₁₇Al₁₂ after hydrogen desorption,and has a good reversibility.For example,Mg₁₇Al₁₂+5.0wt%TiO2 has a lower initial absorption and desorption hydrogen temperature than Mg₁₇Al₁₂,which is lower than 50? and 70?,and shows good hydrogen adsorption and desorption kinetics.In addition,with Ti02 as the catalyst,the material can reversibly absorb and release hydrogen at 250?,and the reversible hydrogen storage capacity is up to 3.1wt%,while the other materials are difficult to reversibly absorb/desorb hydrogen at the same temperature.The dehydrogenation activation energy calculated by Kissinger method is found to be the lowest,with Ti02 as catalyst.Obviously,the addition of TiO2 can not only improve the dynamic hydrogen storage properties of the materials,but also improve the thermodynamic hydrogen storage properties.Finally,xwt%Zr?x=0,2.5,5,7.5?are added respectively in Mg₁₇Al₁₂ to explore the hydrogen storage properties of mechanical alloying samples.It is obviously found that the addition of 5.0wt%Zr improves the hydrogen storage performance of Mg₁₇Al₁₂.Moreover,the effects of different Zr-based compounds?ZrO2,ZrF4?on Mg₁₇Al₁₂ are studied.The hydrogenation of Mg1Al12 can be directly converted to MgH2 without Mg2Al3 intermediate phase by using Zr-based compounds?ZrO2,ZrF4?as the catalyst.Similarly,in the Zr-based catalysts,the Zr oxide?Zr02?shows good catalytic properties.As for the improvement of the kinetic properties of Mg₁₇Al₁₂,ZrO2 is the best,followed by ZrF4,and finally Zr.The dehydrogenation activation energy of Mg1Al12 is 248.8kJ/mol,with Zr?Zr,ZrF4,Zr02?as the catalyst,the dehydrogenation activation energy decreases by 36.4kJ/mol,55.3kJ/mol and 78.9kJ/mol,respectively.