Built-in electric field induced S-scheme g-C₃N₄ homojunction for efficient photocatalytic hydrogen evolution: Interfacial engineering and morphology control

S-scheme possesses superior redox capabilities compared with the II-scheme, providing an effective method to solve the innate defects of g-C₃N₄ (CN). In this study, S-doped g-C₃N₄/g-C₃N₄ (SCN-tm/CN) S-scheme homojunction was constructed by rationally integrating morphology control with interfacial engineering to enhance the photocatalytic hydrogen evolution performance. In-situ Kelvin probe force microscopy (KPFM) confirms the transport of photo-generated electrons from CN to SCN. Density functional theory (DFT) calculations reveal that the generation of a built-in electric field between SCN and CN enables the carrier separation to be more efficient and effective. Femtosecond transient absorption spectrum (fs-TAS) indicates prolonged lifetimes of SCN-tm/CN3 (τ₁: 9.7, τ₂: 110, and τ₃: 1343.5 ps) in comparison to those of CN (τ₁: 4.86, τ₂: 55.2, and τ₃: 927 ps), signifying that the construction of homojunction promotes the separation and transport of electron hole pairs, thus favoring the photocatalytic process. Under visible light irradiation, the optimized SCN-tm/CN3 exhibits excellent photocatalytic activity with the hydrogen evolution rate of 5407.3 μmol·g⁻¹·h⁻¹, which is 20.4 times higher than that of CN (265.7 μmol·g⁻¹·h⁻¹). Moreover, the homojunction also displays an apparent quantum efficiency of 26.8% at 435 nm as well as ultra-long and ultra-stable cycle ability. This work offers a new strategy to construct highly efficient photocatalysts based on the metal-free conjugated polymeric CN for realizing solar energy conversion.