The catalytic effect of additive Nb2O5 on the reversible hydrogen storage performances of LiBH4-MgH2 composite

LiBH4-MgH2 composite exhibits excellent reversible hydrogen capacity, but it still presents high decomposition temperature over 350 degrees C and sluggish kinetics. For the purpose of optimizing its reaction performance, Nb2O5 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 degrees C and could be hydrogenated to 5-6 wt% hydrogen capacity at 400 degrees C under 1.9 MPa. XRD and SEM analysis revealed that NbH2, 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) in the milling process. The hydrogen storage capacity of the LiBH4-MgH2 (mass ratio, 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 EA of LiBH4-MgH2 (mass ratio, 1:2) with 16 wt% Nb2O5 and without Nb2O5 were estimated to be 139.96 and 156.75 kJ mol(-1) by Kissinger method. It indicates that the additive Nb2O5 can decrease the activation energy of LiBH4-MgH2 composite. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.