Dehydrogenation kinetics and long term cycling behavior of Titanium doped NaAlH4

Abstract

ABSTRACTThe 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. Titanium doped NaAlH4 is right now considered as the potential hydrogen storage system, which satisfies the said criteria. The dehydrogenation of NaAlH4 consists of two consecutive steps of decomposition at 220 and 250° C with the total hydrogen release of 5.6 wt.%. However, doping a few mole concentrations of selected transition metal complexes to the host hydride reduces significantly the decomposition temperatures to 100 and 185° C (equilibrium H2 pressure ∼1 MPa) respectively. This breakthrough has been followed by a great deal of effort to develop NaAlH4 as a practical hydrogen storage material. For an ideal hydrogen storage material, the dehydrogenation kinetics and the cycling stability are important properties to be evaluated. Keeping these points to ponder, we have studied the dehydriding kinetics of the Ti-doped NaAlH4 over a number of dehydrogenation and rehydrogenation cycles. Besides, the Ti-doped NaAlH4 has been prepared from the hydrogenation of NaH and Al using the solvent mediated milling method. Comparing the initial and final cycling stages of Ti doped (NaH + Al), the synchrotron powder x-ray diffraction profiles exhibit, a growing resistance to the hydrogenation of Na3AlH6 to NaAlH4.