engleski

Towards Understanding a Mechanism of Reversible Hydrogen Storage in Transition Metal Doped Sodium Alanate

A mechanism of the dehydrogenation of transition metal doped sodium alanate is proposed. Insertion of scandium and titanium in light metal hydrides is considered, both of which are very promising systems for achieving the reversible and efficient chemical hydrogen storage. The mechanism is deduced from studies on the decomposition of a model system consisting of one transition metal atom and two NaAlH4 units. Subsequently, the significance of such minimal cluster model systems to the real materials is tested by embedding the systems into the surface of the NaAlH4 crystal. It is found that the dehydrogenation proceeds via breaking of the bridge H–Al bond and consequent formation of intermediate coordination compounds in which the H2 molecule is side-on (hapto-)bonded to the transition metal centre analogous to the Kubas complexes. The total barrier to the H2 release is thus dependent upon both the strength of the Al–H bond to be broken and the depth of the coordinative potential. The analogous mechanism applies for the recognized three successive dehydrogenation steps, in line with what is observed experimentally.

Energy; Catalysis; Hydrogen Storage; Sodium Alanate; Titanium; Scandium

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