Graphdiyne (CnH2n−2) based CuBr/GDY/MnMoO4 dual S-scheme heterojunctions proved with in situ XPS for efficient photocatalytic hydrogen evolution

•Successfully established a ternary dual S-scheme heterojunction system composed of CuBr/Graphdiyne/MnMoO4.•The transfer pathway of photoexcited electrons was verified by in situ XPS.•Density Functional Theory and UV–visible spectroscopy further confirmed the band structure of the catalyst.•Practical Method to Improve Hydrogen Production Efficiency. Developing composite catalysts that possess efficient charge separation and transfer mechanisms, along with outstanding light harvesting abilities, is essential for attaining elevated levels of photoelectrochemical conversion efficiency. In this study, copper iodide was utilized instead of copper foil as the catalytic substrate to synthesize CuBr/graphdiyne composite material. Subsequently, the CuBr/GDY composite was introduced onto rod-shaped MnMoO4, thus effectively establishing a ternary dual S-scheme heterojunction system consisting of CuBr/Graphdiyne/MnMoO4. In situ XPS was employed to validate the transfer pathway of photoexcited electrons and to propose potential reaction mechanisms, confirming that the formation of the CuBr/Graphdiyne/MnMoO4 dual S-scheme greaty enhanced the separation of electrons and holes, theory significantly boosting the photocatalytic efficacy. Density Functional Theory and UV–visible spectroscopy further confirmed the band structure of the catalyst. Result from the hydrogen evolution activity tests showed that the activity of the ternary CuBr/Graphdiyne/MnMoO4 photocatalyst was 144-fold, 26-fold, and 7-fold higher than that of MnMoO4, Graphdiyne, and CuBr alone, respectively. This research outlines a practical approach to improving hydrogen production efficiency in composite catalysts and systematically building dual S-scheme heterojunctions.