Size dependent catalytic effect of TiO2 clusters in water dissociation

We performed systematic first principles calculations based on density functional theory to probe the energetics of dissociation of water molecules on small (TiO2)n (n = 3, 4, 6, 8, and 10) clusters. We found that the (TiO2)n clusters have a strong ability to adsorb water molecules and the dissociative adsorption of water molecules on the surface of (TiO2)n clusters with a three step process is irreversible, size-dependent and energetically more favorable than the same on the surfaces of titanium oxide. Charged (TiO2)n cluster also have strong ability in H2O molecule splitting similar as neutral ones. The efficiency of water molecules dissociating on (TiO2)n cluster surface varies inversely with the cluster size due to the steric effect. Our results indicate a higher efficiency of small clusters of titanium oxide in dissociating water molecules than its low index surfaces of bulk terminated.

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► Water molecule dissociation occurs in three steps on (TiO2)n clusters via a metastable state.
► The dissociation is irreversible.
► The barriers for water dissociation on (TiO2)n get smaller at larger sizes and saturate at n ≥ 10.
► The efficiency of water molecules dissociating varies inversely with the cluster size.