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.