CdS/DBTSO-BDTO S-scheme photocatalyst for H2 production and its charge transfer dynamics

Photocatalytic hydrogen (H₂) production is a clean energy technology, with great potential for addressing the global energy crisis and related environmental problems. However, single-component photocatalysts often suffer from low efficiency primarily due to fast charge carrier recombination and the tradeoff between light-absorbing capacity and redox capabilities. Constructing heterojunctions provides a promising strategy to overcome these drawbacks, and S-scheme heterojunctions have recently stood out, demonstrating the capability to efficiently facilitate electron/hole separation, while maximizing the redox capability. Among them, polymer-based S-scheme photocatalysts are emerging, though the charge carrier dynamics in inorganic-organic S-scheme heterojunctions remain to be elucidated. Herein, we fabricated an S-scheme heterojunction comprised of the conjugated polymer dibenzothiophene-S,S-dioxide-alt-benzodithiophene (DBTSO-BDTO) and cadmium sulfide (CdS) for photocatalytic H₂ production. The S-scheme mechanism was verified using in situ irradiated X-ray photoelectron spectroscopy, and the charge carrier transfer dynamics were analyzed in depth using femtosecond transient absorption spectroscopy, which revealed that a considerable fraction of electrons undergo interfacial charge transfer in the CdS/DBTSO-BDTO composite. Owing to the improved charge separation efficiency and redox capability, the performance of the composite surpassed that of DBTSO-BDTO and CdS, and the H₂ evolution rate of the optimized CdS/DBTSO-BDTO material reached 3313 ​μmol ​h⁻¹ g⁻¹, three times that of pure CdS. The findings provide new insights into the electron transfer mechanisms of S-scheme heterojunctions, and can guide the design of polymer-based photocatalysts for solar fuel production.