Effects Of Modified Graphene On Hydrogen Storage Properties Of LiBH₄

LiBH₄ has been widely investigated because of its high theoretical hydrogen storage capacity?18.5 wt.%?.However,stable thermodynamic and slow hydrogen sorption kinetic properties limit its practical application in the hydrogen storage field.Based on the modified graphenes as additives,we prepared a series of Li BH4-based hydrogen storage materials by mechanical ball milling method.The relation between the hydrogen storage properties and the micro-structures of the composites were investigated,and the reaction mechanisms of hydrogenation/dehydrogenation processes were further studied.In this work,using hydrogen thermal reduction method that reduced graphene?rGO?was prepared,and then ball milled with LiBH₄ to prepare the LiBH₄–20 wt.% rGO hydrogen storage composite.The onset dehydrogenation temperature of LiBH₄ decreased by 103.5 °C,and hydrogen desorption activation energy decreased by 19.26 kJ/mol.At400 °C,the composite can release 3.98 wt.% hydrogen in 3600 s,and it can absorb 4.86 wt.% hydrogen under 5 MPa H2.After 5 cycles of hydrogen absorption/desorption processes,its hydrogen absorption capacity is still as high as 72.8 % of initial hydrogen uptake,showing excellent cyclic hydrogen absorption performance.The significant improvements of hydrogen storage performances of LiBH₄ are mainly attributed to micro-confinement and heterogeneous nucleation of the rGO,meanwhile in situ generated Li3BO3 also plays a catalytic effect.A novel fluorinated graphene?FG?with three-dimensional porous structure was synthesized by one-pot hydrothermal reaction,and the onset dehydrogenation temperature of the LiBH₄–20 wt.% FG composite is 204 °C,120 °C lower than that of pure LiBH₄,and the hydrogen desorption activation energy was also dramatically reduced.At 400 °C,the composite can release 3.91 wt.% hydrogen in 3600 s.And it still has the fast hydrogen absorption rate and high hydrogen absorption capacity at the 4th cycle.The remarkably improved hydrogen storage performances of LiBH₄ are largely ascribed to the combined effects of the nano-modifying and the function of F anion of the FG.Fe₃O₄ nanoparticles supported graphene sheets?Fe₃O₄@G?was synthesized by the hydrothermal reaction,and the Li BH4–20 wt.% Fe₃O₄@G composite starts to releasehydrogen at 74 °C,the hydrogen activation energy is reduced to 102.02 kJ/mol.The composite can release 3.84 wt.% hydrogen at 400 °C.The hydrogen absorption capacity up to 5.47 wt.% hydrogen at the 1st rehydrogenation is achieved,and the composite still can absorb 3.73 wt.% hydrogen after five de/rehydrogenation cycles.The nanodispersion of the Fe₃O₄@G nanosheets and in situ generated Li3BO3 and Li5FeO4 during the dehydrogenation process jointly promoted the hydrogen absorption/desorption properties of LiBH₄.