Metal single atom-oxygen modification induced transformation of carbon nitride-based heterojunctions from type-II to S-scheme for efficient photocatalytic overall water splitting

Constructing semiconductor S-scheme hetero-(homo-)junctions (SSHs) is one of the most effective ways to enhance the photocatalytic overall water splitting (POWS) performance, but encumbered by deficiency of efficient water-oxidizing semiconductors. Herein, tungsten single atom-oxygen group (W-O) modified polymeric carbon nitride (WPCN, an example of metal single atom-oxygen group modified PCN) was used as a water-oxidizing semiconductor to construct a CdS/WPCN SSH, for which the W-O modification plays a key role that causes transformation from a PCN/CdS type-II heterojunction to the CdS/WPCN SSH which exhibits remarkably enhanced photoexcited charge separation than single CdS and WPCN. Pt-CdS/WPCN exhibits 2.6 and 7.2 times higher POWS activity than Pt-WPCN and Pt-CdS, respectively, further demonstrating the key role of the SSH, and lower activity than Pt@Cr2O3-CdS/WPCN that exhibits 5.4-fold higher activity than Pt@Cr2O3-PCN/CdS, and especially, higher photochemical stability by suppressing rapid photocorrosion of CdS. The solar-to-hydrogen conversion efficiency of Pt@Cr2O3-CdS/ WPCN reaches 0.014 %, with an external quantum yield of 0.093 % at 420 nm. This work reveals the role of metal single atom-oxygen modification of PCN in SSHs and provides a way to suppress rapid photocorrosion of CdS.