Self-hydrogenated shell promoting photocatalytic H2 evolution on anatase TiO2

Abstract

As one of the most important photocatalysts, TiO2 has triggered broad interest and intensive studies for decades. Observation of the interfacial reactions between water and TiO2 at microscopic scale can provide key insight into the mechanisms of photocatalytic processes. Currently, experimental methodologies for characterizing photocatalytic reactions of anatase TiO2 are mostly confined to water vapor or single molecule chemistry. Here, we investigate the photocatalytic reaction of anatase TiO2 nanoparticles in water using liquid environmental transmission electron microscopy. A self-hydrogenated shell is observed on the TiO2 surface before the generation of hydrogen bubbles. First-principles calculations suggest that this shell is formed through subsurface diffusion of photo-reduced water protons generated at the aqueous TiO2 interface, which promotes photocatalytic hydrogen evolution by reducing the activation barrier for H2 (H–H bond) formation. Experiments confirm that the self-hydrogenated shell contains reduced titanium ions, and its thickness can increase to several nanometers with increasing UV illuminance.

In‐situ Transmission Electron Microscope Techniques for Heterogeneous Catalysis

“…Basically, there are two strategies for guiding light through the optical fiber into the sample region. The optical fiber could be either introduced from a port on the column wall of TEM or threaded along the sample holder …”

“…To reveal the mechanism in a real reaction environment, Lu and Sui et al. developed a novel method to study photocatalytic water splitting by anatase TiO 2 . As the catalytic reaction proceeded, a shell layer appeared on the surface of TiO 2 nanoparticles in the aqueous phase and then, bubbles formed around the TiO 2 nanoparticles (Figure d, e).…”

In Situ Transmission Electron Microscopy on Energy‐Related Catalysis

“…Photocatalytic hydrogen evolution reaction (HER) at the water/anatase TiO 2 interface was observed in real time . Experimental setups for studying the photocatalytic reaction were realized using homemade liquid cell holder and UV light fiber introduced between the pole pieces of microscope ( Figure 6 ).…”

“…Purple vertical lines highlight the pre‐edge feature at ≈527 eV, before the O‐K edge in the spectrum of surface shell. Reproduced with permission . Copyright 2018, Springer Nature.…”

High‐Efficiency Photocatalysis of Self‐Hydroxylated TiO2 Nanocrystals for Water Splitting

“…Furthermore, Lu et al . observed that before the formation of H 2 bubbles during water splitting, a self‐hydrogenated shell formed on the TiO 2 surface, which could decrease the energy barrier of H 2 evolution . The self‐hydrogenated shell contained hydroxyl species and reduced Ti ions, resulting in the formation of isolated states between the bandgap and the enhancement of light absorption .…”