Enhancement of hole capture and water dissociation on rutile TiO2(110) by intermolecular hydrogen bonding: time-domain ab initio study

Abstract

Photocatalytic water splitting has been a focal point of research to solve energy and environmental issues. However, the understanding of photocatalytic water splitting and coupled dynamics of photogenerated charge carriers at molecule/semiconductor interfaces is still limited. We have combined ab initio molecular dynamics, real-time time-dependent density functional theory, and nonadiabatic molecular dynamics to study the dissociation of water and capture of photogenerated holes on the pristine rutile TiO₂(110) surface. Our simulations indicate that intermolecular hydrogen bonding (IHB) between water molecules facilitates water dissociation. The dissociation energy of water molecules in a pristine, non-dissociated structure is reduced by 15%, from 0.26 eV to 0.21 eV, due to IHB. In the semi-dissociated structure, the dissociation energy of a water molecule is only 0.13 eV, owing to proton transfer induced by IHB. In the semi-dissociated structure, IHB between H₂O and terminal hydroxyl (O_tH) stabilizes the dissociated structure. Furthermore, IHB promotes spatial isolation of O_tH and bridging hydroxyl (O_brH) and inhibits their recombination. The stabilized dissociated structure activates high-frequency vibrational modes that increase the nonadiabatic coupling and promote hole capture on a femtosecond timescale, accelerating the capture rate by 36%. The findings provide important insights into photo-dissociation of water on rutile TiO₂(110), particularly shedding light on the impact of key intermediates on the photocatalytic process.