The catalytic effect of additive [formula omitted] on the reversible hydrogen storage performances of [formula omitted] composite

Abstract

LiBH 4 – MgH 2 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, Nb 2 O 5 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 NbH 2 , 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 ( MgB 2 ) in the milling process. The hydrogen storage capacity of the LiBH 4 – MgH 2 ( mass ratio , 1 : 2 ) + 16 wt % Nb 2 O 5 composite decreased gradually during the dehydrogenation/hydrogenation cycles and still maintained 5.16 wt% in the third dehydrogenation process. The activation energies E A of LiBH 4 – MgH 2 (mass ratio, 1:2) with 16 wt% Nb 2 O 5 and without Nb 2 O 5 were estimated to be 139.96 and 156.75 kJ mol - 1 by Kissinger method. It indicates that the additive Nb 2 O 5 can decrease the activation energy of LiBH 4 – MgH 2 composite.