Oxygen Vacancy Structure Associated Photocatalytic Water Oxidation of BiOCl

TLDR

Photocatalytic water splitting on oxide surfaces depends critically on how water adsorbs and reacts. The study demonstrates that surface oxygen vacancies can activate water for enhanced photocatalytic oxidation, with the activation level governed by the vacancy structure. Geometric analysis shows that the (010) surface vacancy enables barrierless O–H bond cleavage and localized electron transfer to dissociatively adsorbed water, whereas the (001) vacancy hinders these steps. Dissociatively adsorbed water on the (010) vacancy oxidizes more readily than molecularly adsorbed water on the (001) vacancy, highlighting the essential role of crystalline surface structure and pointing to surface engineering for efficient photocatalysts.

Abstract

A central issue in understanding photocatalytic water splitting on a stoichiometric or defective nanostructured oxide surface is its adsorption mode and related reactivity. More than just improving the adsorption of water on oxide surfaces, we demonstrate in this work that surface oxygen vacancies (OVs) also offer a possibility of activating water toward thermodynamically enhanced photocatalytic water oxidation, while the water activation state, as reflected by its capability to trap holes, strongly depends on the structures of OVs. Utilizing well-ordered BiOCl single-crystalline surfaces, we reveal that dissociatively adsorbed water on the OV of the (010) surface exhibits higher tendency to be oxidized than the molecularly adsorbed water on the OV of the (001) surface. Analysis of the geometric atom arrangement shows that the OV of the BiOCl (010) surface can facilitate barrierless O–H bond breaking in the first proton removal reaction, which is sterically hindered on the OV of the BiOCl (001) surface, and also allow more localized electrons transfer from the OV to the dissociatively adsorbed water, leading to its higher water activation level for hole trapping. These findings highlight the indispensable role of crystalline surface structure on water oxidation and may open up avenues for the rational design of highly efficient photocatalysts via surface engineering.