Effects Of Doped Nano Porous Carbon Materials On Hydrogen Storage Properties Of LiBH₄

Among the numerous lightweight hydrogen storage materials,LiBH₄ has attracted much attention due to its superior hydrogen storage characteristics.The higher quality hydrogen storage density and volume hydrogen storage density of LiBH₄ are the most important basic conditions in the study of hydrogen storage materials.However,the development of LiBH₄ was seriously hindered by the stable thermodynamic properties,harsh adsorption and hydrogenation conditions,and slow dynamics properties.In this paper,the composite material with porous carbon doped by catalyst was selected as the additive and LiBH₄ was used as the hydrogen storage matrix.A series of composite hydrogen storage materials were prepared by impregnation and ball milling,respectively,such as LiBH₄@CNCs,LiBH₄-MnF₂@CNCs,LiBH₄-MgO@C and LiBH₄-MgF₂@C.Also,the hydrogen storage properties and structure of composite hydrogen storage materials were studied.The carbon nanocages with mesoporous structure and its derivative with catalyst were prepared by template carbonization method.The LiBH₄@CNCs composite hydrogen storage material,which was obtained by impregnation method has superior hydrogen absorption and desorption performance and cycle life.The peak temperature of hydrogen emission is 310 ?C,180 ?C lower than the pure LiBH₄.And the circulating hydrogen absorption capacity is 3.07 wt.%.Activation energy of the LiBH₄@CNCs is reduced to 113.5 kJ/mol.LiBH₄-MnF₂@CNCs composite hydrogen storage material was prepared by the high-energy ball milling method,which has a very excellent hydrogen evolution performance.Its maximal desorption peak occurs at about 290 ?C and about 5.0 wt.% hydrogen can be desorbed per minute.The activation energy is about 109 kJ/mol,which is 80.4 kJ/mol lower than that of pure LiBH₄,even lower than that of LiBH₄@CNCs.At 300 ?C,the rate of hydrogen evolution is 13.2 times higher than that of pure LiBH₄ under the same conditions.The MgO@C and MgF₂@C composites with many surface defects and a thin layer structure were obtained from the high temperature carbonization products of magnesium citrate,which can disperse the catalyst well and make it fully contacting with the hydrogen storage matrix.Therefore,LiBH₄-MgO@C and LiBH₄-MgF₂@C composite hydrogen storage materials show more excellent hydrogen desorption properties.The initial hydrogen evolution temperature of LiBH₄-MgO@C is 50 ?C lower than that of pure LiBH₄.And 5.0 wt.% of hydrogen can be released at a temperature of 500 ?C,40% more than pure LiBH₄.LiBH₄-MgF₂@C can release a small amount of hydrogen at about 75 ?C,and starts a large amount of hydrogen releasing at 250 ?C,100 ?C lower than the commercial LiBH₄.Moreover,the composites can release 89% of its hydrogen storage capacity at that temperature.At 350 ?C,the hydrogen evolution rates of LiBH₄-MgO@C and LiBH₄-MgF₂@C composite hydrogen storage materials are 4.1 times and 4.5 times as high as that of pure LiBH₄ under the same conditions,respectively.