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

The energy band alignment and photocatalytic performance of alpha-In2Se3/g-C3N4 heterojunctions of two configurations (A and B) are studied through first-principles calculations. The spontaneous out-of-plane electric polarization of alpha-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 alpha-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 alpha-In2Se3 causes the photogenerated electrons in alpha-In2Se3 to migrate across the interface region of alpha-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 alpha-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.