Correlated Electron-Nuclear Dynamics of Photoinduced Water Dissociation on Rutile TiO2

Computational Chemistry Physical Chemistry Inorganic Non-Metallic Materials Materials Science Chemistry Physics Condensed Matter Physics
electron-nuclear dynamics photocatalysis water dissociation rutile TiO2 first-principles dynamics photoexcited carriers

Reaction Dynamics on TiO₂ and Water Surface

Electron-Nucleus Dynamics Study of Photocatalytic Water Splitting on Rutile Titanium Dioxide Surface

Background and Motivation

Photocatalytic water splitting is one of the important applications of photocatalytic technology, while titanium dioxide (TiO₂) is a photocatalytic material with significant application potential. Although TiO₂ performs remarkably in photocatalytic water splitting and practical applications, the microscopic mechanisms of its photogenerated water splitting are yet to be fully elucidated. Through first-principles dynamic simulations, this research team has analyzed the transport pathways of photogenerated carriers and the photogenerated water splitting process at the typical water-rutile TiO₂(110) interface. This study not only provides important insights into understanding photocatalytic surface reactions but also suggests new possibilities for enhancing photocatalytic performance.

Research Source and Author Introduction

This research was conducted by You Peiwei, Chen Daqiang, Liu Xinbao, and Zhang Cui from the Beijing National Laboratory for Condensed Matter Physics and the Institute of Physics, Chinese Academy of Sciences, Zhang Cui from the Songshan Lake Materials Laboratory, and Annabella Selloni and Meng Sheng from the Department of Chemistry, Princeton University. The paper was published in the journal “Nature Materials,” with the DOI 10.1038/s41563-024-01900-5.

Research Process

This paper uses real-time time-dependent density functional theory (rt-TDDFT) molecular dynamics simulations to study the atomic-level steps of photogenerated water splitting at the rutile TiO₂(110) and liquid water interface. The specific process is as follows:

  1. Model Construction and Excited State Dynamic Simulation:

    • A model of a four-layer defect-free rutile TiO₂ thin layer with a liquid water layer interface was used to simulate the photogenerated water splitting process under a specific light field intensity.
    • A laser pulse with photon energy of 3.1 eV was employed on the TiO₂/water interface to simulate photogenerated carrier dynamics.

  2. Electron-Nucleus Dynamic Correlation Study:

    • Two different water splitting mechanisms were discovered through simulation: electric field-guided proton transfer and hole-guided water molecule dissociation.
    • On the defect-free rutile surface, electric field-guided proton transfer dissociates adsorbed water molecules into protons on bridging oxygen (Obr).
    • In another mechanism, the adsorbed water molecules dissociate by transferring protons to the second layer of water molecules, a process accompanied by in-plane surface lattice distortion.

  3. Specific Experiment Steps and Methods:

    • Observing the dynamics of adsorbed water molecules dissociation under finely tuned light field intensity.
    • Using real-time TDDFT simulations and the climbing-image nudged elastic band (CINEB) method to evaluate hydrogen diffusion and hydrogen production energy barriers.

Research Results

  1. Refinement of Water Dissociation Mechanism:

    • In the first mechanism, water molecules dissociate by transferring a proton to the Obr atom, resulting in the formation of two hydroxyl groups (terminal hydroxyl and bridging hydroxyl).
    • The second mechanism relies on a hydrogen bond between the adsorbed water molecules and the second layer water molecules, facilitating hole transfer by forming a local exciton between a five-coordinated Ti ion and its four nearest-neighboring oxygen atoms.
    • Both mechanisms are validated by spatiotemporal evolution of proton transfer and electron distribution, initially revealing the dynamic characteristics of photogenerated water splitting.

  2. Migration of Photogenerated Electrons and Holes

    • Photogenerated electrons transfer from Obr to the oxygen (Ow) under light field action, resulting in the weakening of the OW-H bond and eventually facilitating water molecule dissociation.
    • Under excited states, the spatiotemporal evolution of Ti 3d orbital electrons and their promotion of lattice distortion demonstrate dissociation driven by hole transfer.

  3. Polaron-Based Two-Stage Mechanism of Photogenerated Water Splitting

    • The first stage involves excitation and expansion, where electrons transfer from oxygen atoms to titanium atoms, inducing dynamic expansion of the lattice;
    • The second stage involves recovery and dissociation, driven by the redistribution of Ti 3d orbital electrons and lattice distortion recovery, fostering proton transfer and water molecule dissociation.

  4. Experimental Evidence and Theoretical Support

    • Experimentally, such hole-driven water dissociation and electron-nucleus associated dynamic mechanisms can be verified using methods such as time-resolved absorption spectroscopy and two-photon photoelectron spectroscopy.

Conclusion and Significance

This study reveals the dynamic characteristics of strong correlation between photogenerated carriers and nuclear motion, which has significant implications for understanding and controlling photocatalytic reactions. By deeply analyzing the photogenerated polaron mechanism, the authors propose a new paradigm that can potentially be applied to explain and control other photocatalytic reactions. This research not only advances the understanding of the photogenerated water splitting mechanism on TiO₂ but also provides new insights for studying photocatalytic reactions on other metal oxide surfaces.

In future research, combining experiments and more theoretical simulations will further refine the understanding of photogenerated carrier dynamics in photocatalytic materials, ultimately enhancing the application efficiency of photocatalytic technology.