Water‐Cluster–Mediated Amorphous‐to‐Crystalline Transition Enables Scalable Fabrication of Stable Surfactant‐Free MOF Nanocatalyst

Metal–organic framework (MOF) nanocatalysts are promising for solar‐to‐chemical conversion but often suffer hydrolytic degradation, especially in surfactant‐free, highly surface‐active forms. Here, we report a dual‐functional design that integrates amorphous nanostructuring with water‐triggered self‐coordinated crystallization to produce scalable, stable surfactant‐free MOF nanocatalysts. An amorphous pyridyl‐porphyrinic precursor is first prepared as hexagonal nanosheets via an ultrasonic‐assisted process. Upon exposure to water, cyclic hexameric water clusters bind pyridyl sites and drive reorganization into a corner‐sharing porphyrinic‐hexagon 3D honeycomb lattice, yielding robust hexagonal nanorods. Confined water clusters stabilize the lattice for >2 months and generate a pronounced potential gradient that promotes charge separation. The resulting nanocatalysts achieve a hydrogen evolution rate of 223.81 mmol g −1 h −1 , representing one of the better values reported for molecular photocatalysts. This work introduces water‐cluster–induced amorphous‐to‐crystalline self‐assembly as a versatile strategy for stabilizing surfactant‐free MOF nanophotocatalysts.