Enhanced Hydriding−Dehydriding Performance of CeAl₂-Doped NaAlH₄ and the Evolvement of Ce-Containing Species in the Cycling

One of the major questions in a catalytically enhanced NaAlH 4 system used for hydrogen storage that remains is where catalysts like Ti/Ce reside and present as what form improving the kinetics and reversible hydrogen storage performance. In the present study, by directly introducing Ce−Al species with a structure of CeAl 2 into NaAlH 4, a dramatic enhancement in the hydrogen release and uptake kinetics of NaAlH 4 was achieved. CeAl 2 -doped NaAlH 4 can be reloaded 4.9 wt % hydrogen at moderate conditions in 20 min, which is among the highest values ever reported for NaAlH 4 . Besides, the material exhibits an exceptional performance under low pressures. For example, a capacity of more than 4.0 wt % hydrogen can be achieved at a hydrogen pressure as low as 4.0 MPa. The apparent activation energy of NaAlH 4 doped with 2 mol % CeAl 2 is estimated to be 72.3−90.4 kJ/mol and 93.6−98.9 kJ/mol for the first and the second dehydrogenation step respectively by using Kissinger’s approach, much lower than those of pristine NaAlH 4 . After prolonged cycling, the Ce−Al species transforms to a more stable species of CeAl 4 . On the basis of these findings and the previous investigations, the active species and mechanism of catalysis in doped NaAlH 4 were discussed.