Catalysis of H2 sorption in NaAlH4: General description and new insights

Abstract Sodium alanate NaAlH 4 is a very suitable material for solid-state hydrogen storage owing to its relatively high hydrogen capacity (7.5 wt.% H 2 ) and moderate temperatures for reversible H 2 release/uptake (100–150 °C) compatible with PEM fuel cells. These temperatures are obtained by adding a dopant. TiCl 3 , ScCl 3 or CeCl 3 are known to be efficient dopants but the details of the catalytic mechanism are not fully understood yet. In this work, the H 2 sorption of NaAlH 4 doped with TiCl 3 , ScCl 3 or CeCl 3 is systematically studied. The doped samples were prepared in one step by reactive ball milling of NaH and Al with 4 mol.% dopant in an H 2 atmosphere. The efficiencies of the dopants are different for desorption and absorption, indicating that different catalytic mechanisms and rate limiting steps are taking place during both steps and these are described here. TiCl 3 is more efficient for desorption and CeCl 3 for absorption. ScCl 3 is less efficient than the first two for all reactions. A mixture of TiCl 3 and CeCl 3 is thus added to NaAlH 4 to act at the same time on the desorption and the absorption processes. The results show enhanced overall performances for H 2 sorption when using this mixture compared to NaAlH 4 milled with TiCl 3 or CeCl 3 only.