The catalytic effect of additive Nb2O5Nb2O5 on the reversible hydrogen storage performances of LiBH4–MgH2LiBH4–MgH2 composite

LiBH4LiBH4–MgH2MgH2 composite exhibits excellent reversible hydrogen capacity, but it still presents high decomposition temperature over 350∘C and sluggish kinetics. For the purpose of optimizing its reaction performance, Nb2O5Nb2O5 was doped into this composite as a catalyst to form a more destabilized and reversible composite system. It possesses a maximum capacity of approximately 6–8 wt% hydrogen releasing below 400∘C and could be hydrogenated to 5–6 wt% hydrogen capacity at 400∘C under 1.9 MPa. XRD and SEM analysis revealed that NbH2NbH2, formed and highly dispersed in the composite, played a key role in changing the original path and resulted in the formation of an intermediate compound (MgB2)(MgB2) in the milling process. The hydrogen storage capacity of the LiBH4LiBH4–MgH2(massratio,1:2)+16wt%Nb2O5 composite decreased gradually during the dehydrogenation/hydrogenation cycles and still maintained 5.16 wt% in the third dehydrogenation process. The activation energies EAEA of LiBH4LiBH4–MgH2MgH2 (mass ratio, 1:2) with 16 wt% Nb2O5Nb2O5 and without Nb2O5Nb2O5 were estimated to be 139.96 and 156.75kJmol-1 by Kissinger method. It indicates that the additive Nb2O5Nb2O5 can decrease the activation energy of LiBH4LiBH4–MgH2MgH2 composite.