Interfacial In–SV–N bond mediated d/p-band center up-shift in an S-scheme heterojunction for boosting photocatalytic H2 evolution

Abstract

Conventional heterojunction photocatalysts often suffer from inefficient charge separation and sluggish surface reactions due to poorly defined interfacial charge transport channels and insufficient active sites, both stemming from weak interfacial coupling between semiconductors. To address these limitations, we construct a novel ZnIn₂S₄/C₃N₅ heterojunction system with S vacancies (S_V-ZIS/CN), which synergistically optimizes carrier dynamics and surface reactions for enhanced photocatalytic performance. The optimized S_V-ZIS/5CN achieves an exceptional H₂ evolution rate of 4.85 mmol g⁻¹ h⁻¹ under visible light, surpassing pristine S_V-ZIS, CN and ZIS/5CN, respectively. Crucially, the formation of In–S_V–N bonds at the interface not only accelerates charge transfer but also facilitates water molecule adsorption and dissociation. This reinforced interfacial coupling is definitively confirmed by Density Functional Theory (DFT) calculations and in situ Kelvin Probe Force Microscopy (in situ KPFM), which reveal a reduced energy difference (9.42 eV) between the In d-band and N p-band centers in S_V-ZIS/CN compared to that in ZIS/CN (9.55 eV), alongside a strengthened interfacial electric field. DFT and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) also verified that S vacancies serve as key active sites to promote the dissociation of adsorbed H₂O into reactive hydroxyl intermediates in S_V-ZIS/CN, thereby accelerating the surface proton reduction process. This study breaks new ground by integrating defect engineering with heterojunction design, offering a strategic paradigm for developing high-efficiency photocatalytic systems for solar-to-fuel conversion.