Large‐Sized Poly (Triazine Imide) Crystals with Minimized Defects for High‐Efficiency Overall Water Splitting

Poly (triazine imide) (PTI), a highly crystalline carbon nitride, has attracted considerable attention due to its capacity to achieve one-step-excitation overall water splitting. The crystallinity of PTI crystals can be substantially enhanced by manipulating the polymerization temperature and the type of molten salt. However, the particle size of synthetic crystals is usually less than 200 nm, and the synthesis of larger and well-defined PTI crystals has yet to be accomplished. In this study, a novel precursor engineering strategy is implemented utilizing melon-type carbon nitride as the architectural template, coupled with LiCl/KCl eutectic molten salt system, to orchestrate the crystallization of PTI under high-temperature/high-pressure conditions. Comparative analysis reveals that the PTI synthesized through this methodology exhibits marked crystallographic superiority over conventional dicyandiamide-derived counterparts, manifesting as notably reduced lattice imperfections and an extended π-conjugated network. These structural enhancements culminate in the formation of faceted single-crystalline domains with characteristic dimensions exceeding 500 nm. The optimized single-crystal PTI showcases a high apparent quantum efficiency of 13.1% (λ = 365 nm) in overall water splitting for hydrogen production. This work establishes the critical role of precursor architectural compatibility in governing crystalline perfection and functional performance in carbon nitride-based photocatalytic systems.