Switching Type-II to S-scheme Charge Transfer Through Fermi Level Modulation.

Abstract

Directly switching the type of electron transfer from Type-II to S-scheme at the heterojunction interfaces of a two-component photocatalyst is crucial for improving charge separation efficiency in semiconductor-based photocatalysis technology. A major challenge lies in the effective control of the interfacial band-edge position or electronic properties of a two-component photocatalyst. Here, we constructed a "directional valve" in a Zn_xCd_2-xS₂-crystalline carbon nitride (Zn_xCd_2-xS₂-CN) heterojunction through Fermi level modulation to selectively switch Type-II to S-scheme charge transfer. Experimental validation using advanced scanning probe microscopy and in situ photoemission directly observed the switched electron transfer dynamics. The metal probe-assisted in situ X-ray photoelectron spectroscopy (XPS) directly demonstrates the electron transition from Type-II to S-scheme pathways at the interface, corroborated by illumination-induced surface potential shifts. Furthermore, the S-scheme charge transfer in Zn_xCd_2-xS₂-CN heterojunction contributed to a four times higher CO₂ photoreduction activity than the Type-II one. This study provides a new paradigm for rationally controlling interfacial charge dynamics through band engineering.