Influence of hydrogen and halogen adsorption on the photocatalytic water splitting activity of C2N monolayer: A first-principles study

Adsorption of impurity atoms or molecules on the surface of photocatalysts may improve or worsen the photocatalytic activity due to chemical bond relaxations. Herein, we demonstrate the influence of molecular adsorbates such as H-2, F-2, Cl-2, Br-2, and I-2 on the electronic properties and photocatalytic activity of the nitrogenated holey graphene (C2N) using hybrid density functional calculations including van der Waals interaction. Hydrogen and halogen molecules prefer to physisorb on the holey site except F-2 which has substantial chemisorption. The halogens tend to draw electrons from C2N monolayer due to their high electronegativity and thereby introduce new band states which significantly alters the optoelectronic and photocatalytic properties. Although F-2 and Br-2 adsorbed C2N have favorable band edge positions, I-2 adsorbed C2N is more promising for hydrogen production because of its appropriate band edge positions relative to the water redox potentials. Optical absorption spectra reveals that all these systems are visible light active and therefore they could harvest more incoming light. We have demonstrated here for the first time that intermediate bandgap states can be introduced in C2N system by adsorbing halogen molecules and our theoretical findings suggest that I-2 adsorbed C2N monolayer is a promising candidate for photocatalytic water splitting. (C) 2018 Elsevier Ltd. All rights reserved.