Two-Dimensional CdX/C ₂N (X = S, Se) Heterostructures as Potential Photocatalysts for Water Splitting: A DFT Study

Abstract

Global environmental issues, in addition to limited fossil fuel resources, are being addressed by quests in search of efficient visible-light-driven water splitting catalysts for hydrogen production. The photocatalytic water splitting activities of CdX/C ₂N (X = S, Se) heterostructures have been investigated here using hybrid density functional theory calculations. The calculated band gaps of CdS/C ₂N and CdSe/C ₂N heterostructures are 1.48 and 2.12 eV, respectively. These are ideal band gap values that make possible harvesting of more visible light from the solar spectrum, which will result in high solar to energy conversion efficiencies. Charge density difference analysis shows that the charge redistributions mainly occur in the interface regions and that the charges transfer from the C ₂N to CdX layers. It is interesting to note that the CdX/C ₂N heterostructures possess a type-II band alignment, where the relative band alignment of the C ₂N and CdX monolayers promotes a spatial separation of the electrons (that resides in C ₂N) and holes (that resides in CdX). Importantly, the band edges of the heterostructures straddle the water redox potential under different pH conditions. This study demonstrates that the CdS/C ₂N and CdSe/C ₂N heterostructures are suitable materials to split water (from various sources) in different ranges of pH values.