Exploring the spatially resolved charge transfer mechanism in the Al-doped SrTiO3/C3N5 S-scheme heterojunction for boosted solar-driven photocatalytic hydrogen evolution

Light-assisted Kelvin-probe force microscopy (KPFM) was employed to uncover the spatially resolved features of the kinetics of charge transfer in the ASTO/C3N5 S-scheme heterojunction. It reveals that photogenerated electrons gather on the surface of C3N5 as a reduction photocatalyst (RP) in the heterojunction, resulting in a reduced surface photovoltage (SPV) compared to pure C3N5, whereas holes accumulate on the surface of ASTO as an oxidation photocatalyst (OP) in the heterojunction, providing higher SPV than pure ASTO.

Moreover, the large work function difference (0.41 eV) between ASTO and C3N5 induces a robust interfacial electric field (IEF). This strong IEF facilitates the photogenerated electrons in ASTO’s conduction band (CB) recombine with holes in C3N5’s valence band (VB), preserving high redox potentials. Furthermore, active free radical measurement confirms the enhanced •O2− and •OH signals for the 5%-ASTO/C3N5 heterojunction, confirming the S-scheme mechanism and excluding the type-II mechanism, which is also demonstrated by in-situ X-ray photoelectron spectra (XPS).

Overall, this work offers some evidence regarding the spatially resolved characteristics of the kinetics of charge transfer in the S-scheme heterojunction.