Toward Understanding the Relationship between the Surface Structure and Properties of SrNbO2N Photocatalyst

As one of the representative perovskite-type oxynitride photocatalysts, SrNbO2N has the ability to split water in the visible-light region. It was found that the surface modification and interfacial design of SrNbO2N-based materials are closely related to the photocatalytic activity, but the microscopic mechanisms of these experimental phenomena are not well understood. In this work, we utilize density functional theory calculations to investigate the effect of anion order and exposed terminations on the electronic structures, optical absorption, water adsorption, and mechanisms of water oxidation and reduction reactions of SrNbO2N. Our results indicate that the relaxed crystal structures and optical absorption characters of trans configurations have better agreement with the experimental data than those of cis configurations, while the band gaps of cis configurations are closer to the experimental values than those of trans configurations. The terminations exposed with Nb atoms are more stable and have bigger work functions than those exposed with Sr atoms due to the bonding ionicity and surface dipoles. The dissociative adsorption of water is energetically more favorable than the molecular adsorption on most of surfaces. The highly active sites of hydrogen evolution reaction are the surface oxygen atoms. Compared with Sr terminations, Nb terminations have lower overpotentials of oxygen evolution reaction. This study sheds light on the relationship between the termination structure with different anion orders and the photocatalysis-related properties of SrNbO2N at the molecular level, which provides guidance for the construction of highly active photocatalytic materials.