S‐Scheme Photocatalytic Mechanism of Type‐I Band Alignment in α‐In2Se3/g‐C3N4 Heterostructure

Abstract

The energy band alignment and photocatalytic performance of α‐In2Se3/g‐C3N4 heterojunctions of two configurations (A and B) are studied through first‐principles calculations. The spontaneous out‐of‐plane electric polarization of α‐In2Se3 points away from g‐C3N4 for configuration A, in which the layer spacing and formation energy are lower than those of configuration B. Configuration A of α‐In2Se3/g‐C3N4 is characteristic of the I‐type energy band alignment and S‐scheme heterojunction for photocatalytic performance, which is different from the II‐type band alignment characteristic of the previous traditional Z‐scheme heterojunctions with a larger built‐in electric field. The existence of a stronger intrinsic electric field of α‐In2Se3 causes the photogenerated electrons in α‐In2Se3 to migrate across the interface region of α‐In2Se3/g‐C3N4 to reach the valence band maximum (VBM) of g‐C3N4 for configuration A. The recombination of the photogenerated electrons from the conduction band minimum (CBM) of α‐In2Se3 with holes from the VBM of g‐C3N4 reduces the number of photogenerated holes in the VBM of g‐C3N4. The photogenerated electrons in the CBM of g‐C3N4 due to the absence of holes move toward the surface of g‐C3N4 and play a significant role in the hydrogen generation activity.