Supramolecularly Directed Confined Crystallization of Lamellar Carbon Nitride for Efficient Photocatalytic Hydrogen Generation

ABSTRACT Sustainable hydrogen generation through water splitting is key to realizing a future hydrogen economy. In this study, we achieved molecular‐level control over self‐assembled supramolecular complexes of cyanuric acid and 3‐amino 1,2,4 triazole (AT) monomers. This was coupled with molten‐salt‐assisted thermal polymerization in a eutectic mixture of lithium chloride and potassium chloride to synthesize a crystalline carbon nitride with a high surface area and specific crystal structure. Conventional eutectic molten salt synthesis typically yields a mixture of poly (heptazine imide) (PHI) and poly (triazine imide) (PTI) phases. In contrast, the supramolecular complex‐derived approach confines crystal growth through molecular alignment, resulting in the formation of pure PHI phase. To date, the advantages of supramolecular complex precursors have been largely limited to their enhanced surface area and unique morphologies. Here, we demonstrate that this strategy can be extended to direct crystal growth toward a specific phase. This insight enables the synthesis of phase‐pure crystalline carbon nitride at low temperatures, even in eutectic molten salt systems, which was not possible previously. The supramolecular complex in LiCl/KCl eutectic mixture suppresses PTI formation and promotes Li‐ and K‐stabilized PHI, delivering a maximum hydrogen generation of 2820 µmol g −1 h −1 , approximately ten times higher than that of bulk carbon nitride.