Study On Dehydrogenation Performance Of LiAlH₄ Modified By Ni And Ti Transition Metal-based Materials

LiAlH₄ has a high theoretical hydrogen content（10.6 wt%）,but its disadvantages such as high dehydrogenation temperature,slow hydrogen release rate,and poor rehydrogenation performance restrict LiAlH₄ apply to hydrogen storage fields.Three dopants named Ni/C,TiO₂@C,NiTiO₃were prepared in this paper,and their effects on LiAlH₄ hydrogen release performance were studied.The main conclusions of the thesis are drawn as follows:Rod-like Ni/C material was prepared by pyrolysis of self-assembled Ni complexes which obtained by self-assembly reaction at room temperature.The Ni/C was doped into LiAlH₄ by ball milling.The dehydrogenation test reveals that the LiAlH₄ of doping 6 wt%Ni/C start to release of hydrogen at 68℃,which 125℃lower than the initial hydrogen release temperature of pristine LiAlH₄;at isothermal dehydrogenation test,LiAlH₄-6 wt%Ni/C system can release of 4.88 wt%H₂ at 180℃in 60 min and the dehydrogenation content is 11.3 times of the pristine LiAlH₄ under the same dehydrogenation conditions.Activation energy of the first two steps dehydrogenation reaction of LiAlH₄-6 wt%Ni/C system decreases to 74.49 k J/mol and 69.92 k J/mol,respectively.Through XRD analysis,amorphous Ni/C can be used as active sites for LiAlH₄ hydrogen release reaction,and thus improve hydrogen release performance of LiAlH₄.Flower-like TiO₂@C material was prepared through solvothermal method and doped into LiAlH₄ by ball milling.The dehydrogenation test found that LiAlH₄-6 wt%TiO₂@C system begin to dehydrogenate at 57℃,which 136℃lower than the initial hydrogen release temperature of pristine LiAlH₄;at isothermal hydrogen release test,LiAlH₄-6 wt%TiO₂@C system can release of 5.98 wt%H₂ at 180℃in 60 min and the hydrogen release content is 13.9 times of the pristine LiAlH₄ under the same dehydrogenation conditions.Activation energy of the first two steps dehydrogenation reaction of LiAlH₄-6 wt%TiO₂@C system decreases to 45.84 k J/mol and 62.31 k J/mol,respectively.Through XRD analysis,it is concluded that the amorphization of TiO₂@C occurs during ball milling process,while amorphous TiO₂@C can provide active sites and increase hydrogen diffusion channels for LiAlH₄ hydrogen release reactions,and thus improve hydrogen release properties of LiAlH₄.NiTiO₃ as a dopant for improving dehydrogenation properties of LiAlH₄ in the first time.The dehydrogenation test reveals that LiAlH₄-6 wt%NiTiO₃ system begin to dehydrogenate at 72℃,which 121℃lower than the initial hydrogen release temperature of pristine LiAlH₄;at isothermal hydrogen release test,LiAlH₄-6 wt%NiTiO₃ system can release of 4.86 wt%H₂ at 180℃in 60 min and the hydrogen release content is 11.3 times of the pristine LiAlH₄ under the same dehydrogenation conditions.Activation energy of the first two steps dehydrogenation reaction of LiAlH₄-6 wt%NiTiO₃ system decreases to71.56 k J/mol and 122.49 k J/mol.Through XRD analysis,the stability of the NiTiO₃ is destroyed during ball milling process,and make NiTiO₃amorphization,while amorphous NiTiO₃ can provide active sites and increase hydrogen diffusion channels for nucleation,growth of hydrogen release reactions and improve hydrogen release performances of LiAlH4.