Insights into the Reactivity of Brookite TiO₂ Nanorods in Liquid Water from Ab Initio Molecular Dynamics Simulations

Brookite TiO₂, a rare natural polymorph of TiO₂, has been reported to be an excellent photocatalyst for the production of hydrogen from water and aqueous alcohol solutions, especially when it is reduced and synthesized in the form of nanorods. Here, we investigate the reactivity of stoichiometric and reduced brookite nanorods in liquid water using ab initio molecular dynamics and hybrid density functional theory calculations. Our simulations show a much higher water dissociation fraction on reduced nanorods than on stoichiometric ones, with an accumulation of the resulting bridging hydroxyls (O_brH) and terminal hydroxyls (Ti-OH) on different facets of the nanorod. O_brH groups accumulate preferentially on low-energy (210) facets, where they are stabilized by adjacent reduced Ti (Ti³⁺) sites, while Ti-OH groups prefer to form at the 4-fold coordinated Ti atoms on high-energy (010) facets. This hydroxylation pattern also favors the spatial localization of excited holes on the (010) facets. This coupling between water-induced surface chemistry and charge separation underpins the enhanced photocatalytic activity of brookite nanorods, providing useful information for the design of more efficient TiO₂-based nanostructures for solar-driven hydrogen evolution.