Enhanced hydrogen sorption properties of Ni and Co-catalyzed MgH2

MgH2 is one of the most promising hydrogen storage materials due to its high capacity and low cost. In an effort to develop MgH2 with a low dehydriding temperature and fast sorption kinetics, doping MgH2 with NiCl2 and CoCl2 has been investigated in this paper. Both the dehydrogenation temperature and the absorption/desorption kinetics have been improved by adding either NiCl2 or CoCl2, and a significant enhancement was obtained in the case of the NiCl2 doped sample. For example, a hydrogen absorption capacity of 5.17 wt% was reached at 300 degrees C in 60 s for the MgH2/NiCl2 sample. In contrast, the ball-milled MgH2 just absorbed 3.51 wt% hydrogen at 300 degrees C in 400 s. An activation energy of 102.6 kJ/mol for the MgH2/NiCl2 sample has been obtained from the desorption data, 18.7 kJ/mol and 55.9 kJ/mol smaller than those of the MgH2/CoCl2, which also exhibits an enhanced kinetics, and of the pure MgH2 sample, respectively. In addition, the enhanced kinetics was observed to persist even after 9 cycles in the case of the NiCl2 doped mgH(2) sample. Further kinetic investigation indicated that the hydrogen desorption from the milled MgH2 is controlled by a slow, random nucleation and growth process, which is transformed into two-dimensional growth after NiCl2 or CoCl2 doping, suggesting that the additives reduced the barrier and lowered the driving forces for nucleation. Crown Copyright (C) 2010 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. All rights reserved.