The
unified reaction valley approach combined with the local vibrational
mode and ring puckering analysis is applied to investigate the hydrogen
evolution from water in the presence of small hydrides such as BH3, metal hydrides as AlH3, and their derivatives.
We studied a series of reactions involving BH3, AlH3, B2H6, Al2H6,
and AlH3BH3 with one- and two-water molecules,
considering multiple reaction paths. In addition, the influence of
the aqueous medium was examined. A general reaction mechanism was
identified for most of the reactions. Those that deviate could be
associated with unusually high reaction barriers with no hydrogen
release. The charge transfer along the reaction path suggests that
a viable hydrogen release is achieved when the catalyst adopts the
role of a charge donor during the chemical processes. The puckering
analysis showed that twistboat and boat forms are the predominant
configurations in the case of an intermediate six-membered ring formation,
which influences the activation barrier. The local mode analysis was
used as a tool to detect the H–H bond formation as well as
to probe catalyst regenerability. Based on the correlation between
the activation energy and the change in the charge separation for
cleaving O–H and B(Al)–H bonds, two promising subsets
of reactions could be identified along with prescriptions for lowering
the reaction barrier individually with electron-donating/withdrawing
substituents.