Mechanism insight into triple S-Scheme intermolecular carbon nitride homojunction with robust built-in electric field for highly enhanced photocatalytic hydrogen evolution

We have meticulously designed a triple S-Scheme intermolecular g-C3N4 homojunction that boasts a robust built-in electric field and facilitates charge transfer. Importantly, the nature of the built-in electric field and the mechanism for enhanced photocatalytic hydrogen evolution are profoundly revealed. [Display omitted] •A triple S-Scheme intermolecular carbon nitride homojunction is prepared.•Enhancement of BIEF through molecular-level domains promoted carrier separation.•PHE rate of UTMCN is about 38.9 times higher than that of pristine g-C3N4.•Enhanced mechanism of PHE activity is insightfully elucidated. Photocatalytic hydrogen evolution (PHE) from water using graphitic carbon nitride (gCN) is considered a promising way to approach the energy crisis. Homojunction photocatalysts, especially intermolecular homojunction, provide an ideal candidate for photocatalytic hydrogen production. Here, we employ an eutectic salt-assisted thermal polymerization strategy to create a novel ternary gCN homojunction photocatalyst (denoted as UTMCN). The molecular-level contacts across components promote rapid charge carrier transfer and separation. Meanwhile, the fluctuation of the composition within the conjugate plane results in a unique triple S-Scheme energy band arrangement, thus possessing a more than tenfold enhanced built-in electric field (BIEF), and also leads to the separation of the active center. At the same time, the adsorption-free energy of the intermediate hydrogen species (H*) is reduced, thus promoting proton reduction kinetics. As expected, the UTMCN exhibits outstanding photocatalytic performance, which is 38.9 times that of intrinsic carbon nitride. Importantly, the mechanism for the enhanced BIEF to promote PHE performance is elucidated in detail. This work guides the rational construction of intermolecular homojunction with a robust BIEF to improve the performance of PHE.