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Published online by Cambridge University Press: 15 February 2011
The development of light weight hydrogen storage systems with high volumetric and gravimetric hydrogen densities is indeed essential for the on-board fuel cell vehicular applications [1]. Among the different hydrogen storage systems designed and developed so far, Ti- doped sodium aluminum hydrides exhibit potential promise of reversible hydrogen storage capacity (4-5 wt.%) at moderate temperatures [2,3]. However, the poor cyclic stability of these hydrides due to the partial reversibility of the two step reactions necessitates the development of exotic materials or tailoring the known hydride systems. On the other hand, transition metal complex hydrides, TMHx (T = Mg; M = Fe, Co, Ni) have also been identified as potential candidates for hydrogen storage [4-6] and/or analogous to alanates [7]. These hydrides especially Mg2FeH6, have shown excellent cyclic capacities (more than 500 cycles) even without a catalyst [8]. Besides, Mg2FeH6 possesses the highest volumetric and gravimetric hydrogen densities of 150 kg/m3 and 5.6 wt.% respectively [9]. However, at low temperatures, the rate of release of hydrogen and the effective reversible hydrogen capacity seems poor. Recent reports declared that the enhancement in the cycling kinetics and reduction in the operating temperature is very much possible by using a distorted nano-scale Mg structure [10, 11], doping the host lattice with Ti- species and/or lattice substitution [12]. Keeping these facts in view, the present investigation aims to improve the sorption kinetics and thermodynamics of Mg2FeH6, by 1) preparing nano-scale Mg-Fe-H system using mechano-chemical synthesis process, 2) surface localized catalyst (Ti- species) doping and 3) cationic substitution of Na+/Li+ for Mg2+ by incorporating NaH/LiH. The synergistic behavior of the tailored nano-scale transition metal complex for hydrogen storage is outlined.