Tailoring p-Orbital Electron Delocalization Induced by Sulfur Defect Engineering for Enhancing Photoelectrochemical Water Splitting Performance

Indium sulfide (In₂S₃) as water splitting photocatalyst has been broadly investigated due to its narrow bandgap (2.0–2.3 eV) and optimized opto-electronic properties. However, In₂S₃ still suffers from a rapid photogenerated charge carrier recombination rate. In addition, the main group metals (such as In) lack active d-orbital electrons for catalysis, thus limits activation of intermediates during catalytic water splitting reaction. Herein, to overcome the above limitations of In₂S₃, In₂S₃/TiO₂ heterojunction with sulfur defects are constructed by temperature control strategy. The sulfur vacancy (Sv) can induce the electron density transformation of In 5p-orbital from localized states to delocalized states, which efficiently enhances the chemical affinity to ^*OOH. Thus, the p-orbital interaction between In and O atoms greatly facilitates the rate-determining step (^*OOH → ^*+O₂), realizing a high O₂ yield rate of 10.00 µmol cm⁻² h⁻¹ at 1.23 V versus RHE. Furthermore, the heterogeneous structure also can enhance interfacial electric field (IEF) and stability for promoting oxygen generation. This work provides an efficient pathway to improve photoelectrochemical (PEC) activity by manipulating p-orbital electron delocalization of main group metals through defect engineering.