Effects Of Metal Sulfides And Rare Earth Compounds On Hydrogen Storage Properties Of LiBH₄

LiBH4has become one of the research hotspots owing to significant advantages intheoretical volume and mass of hydrogen storage density. But its high initialdehydrogenation temperature and poor reversibility limit it to be used in the practicalapplication. The composites of LiBH4+20wt.%REO(RE=La, Pr)、 LiBH4+20wt.%MS2(M=Mo, W) were prepared by ball milling and the hydrogen storage propertiesof composites were investigated in this paper.It was found that REO(RE=La, Pr) could notably improve the hydrogen absorptionand desorption kinetics, speeded up the rate and increased the capacity of LiBH4. In thecondition of350oC and5MPa hydrogen pressure, the absorption capacity of the pristineLiBH4just could reach0.72wt.%, meanwhile, LiBH4+20wt.%La2O3could absorbe2.66wt.%hydrogen with a quick speed. By analyzing the structure, the main reason for theimprovements of REO(RE=La, Pr) was the REB6(RE=La, Pr) which formed during thehydrogen release process. It could be transformed into REB4(RE=La, Pr) after absorbinghydrogen and accelerated the hydrogen absorption/desorption speed of LiBH4.MoS2could modify the reversibility of LiBH4by making the composite of metalsulfide and LiBH4. Under the condition of550oC and5MPa hydrogen pressure, theabsorption capacity of LiBH4+20wt.%MoS2could be8.0wt.%both for the first cycle andthe second cycle. But the absorption capacity of LiBH4declined from6.4wt.%to5.0wt.%for the pure LiBH4under the same experiment condition. The preferable reversibilityperformance of LiBH4doped with MoS2was attributed to the formation of MoB2and Li2Sby summarizing the XRD patterns. They acted together to improve the reversibility ofLiBH4.The effects of MoS2-REH3(RE=Ce, Pr) composite additives were studied. It wasconcluded that by adding the MoS2-CeH3, the initial decomposition temperature of LiBH4reduced from300oC to182oC, lower than adding additives separately. The reason wasthat it was a valid way to decrease the energy barrier recession and make it easy todehydrogenate for LiBH4by adding the composite additives. The composite of LiBH4+MoS2-CeH3showed the most obvious effect in term of the desorption activationenergy. It was82.94kJ·mol-1, which declined20.39kJ·mol-1compared with the pristineLiBH4.