Multiscale electric fields direct charges to single-atom cobalt sites for photocatalytic H₂ 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^-1 h^-1 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.