A Single‐Crystalline Melon Photocatalyst for Overall Water Splitting with Visible Light

ABSTRACT Melon, as an attractive polymeric semiconductor photocatalyst, holds great potential for efficient one‐step excitation of overall water splitting, yet its quantum yields remain limited by low exciton migration efficiency caused by short exciton diffusion lengths and long migration paths. To address this challenge, we employ a flux‐assisted strategy to synthesize sub‐50 nm single‐crystalline melon, which not only prolonged the exciton diffusion length but also shortened the exciton migration path from the bulk exciton coupling region to the catalyst surface. Experimental characterization and structural simulations confirm the successful synthesis of nanoscale single‐crystalline melon via molten salt post‐treatment of amorphous melon in a NaCl‐KCl‐CaCl 2 ternary system. More importantly, charge carrier dynamics reveal that single‐crystalline melon, owing to its lower defect density, higher interlayer stacking order, and optimized interlayer stacking mode, exhibits reduced non‐radiative recombination, longer exciton diffusion lengths, and a higher concentration of surface‐reaching charges compared to conventional melon. Consequently, the melon nanocrystals exhibit nearly two orders of magnitude higher H 2 evolution efficiency in overall water splitting compared to conventional melon. These findings pave the way for manufacturing polymeric semiconductor nanocrystals for efficient solar energy conversion.