Multiscale electric fields direct charges to single-atom cobalt sites for photocatalytic H(2) production.

The photocatalytic efficiency of covalent organic frameworks is often limited by poor charge separation and inaccessible catalytic sites. Here, we overcome these challenges by constructing a biomimetic "alveoli-on-lamina" heterostructure through coordination-directed assembly. This strategy concurrently exfoliates a bulk covalent organic framework into ordered lamellae and creates atomic-scale Co-N/O bridges, anchoring high-density, atomically dispersed cobalt sites. Crucially, this architecture spontaneously generates a multi-scale electric field, integrating a strong interfacial field for charge separation with an intra-structure potential gradient for directional electron transport. This field-driven vectorial charge flow delivers electrons to the catalytic sites, enabling a competitive photocatalytic performance: a hydrogen evolution rate of 534.6 mmol g h under standard irradiation without noble metals, an apparent quantum yield of 90.2% at 500 nm, and retained stability. This work demonstrates that engineering built-in electric fields across multiple scales is a valuable paradigm for advanced solar-to-fuel conversion.