Unlocking carrier confluence in covalent organic frameworks for efficient photoreduction of dilute nitrate to ammonia

Photocatalytic reduction of nitrate to ammonia is a promising route for sustainable nitrogen recycling, but its efficiency is often limited by disordered charge migration, interlayer charge depletion, and insufficient reactant activation, especially under dilute conditions. To address these challenges, an asymmetric spatial polarity strategy is applied to regulate polar distribution in donor-acceptor covalent organic frameworks at both molecular and layered levels. Strong intramolecular polarity confines charge transfer pathways, while convergent interlayer polarity enhances the internal electric field and promotes directional charge migration. Differentiated polar active sites facilitate nitrogen-oxygen bond cleavage, hydrogen intermediate formation, and nitrate activation in water. Here, we show that the optimized photocatalyst achieves an ammonium production rate of 0.758 mmol g^-1 h^-1 and an areal activity of 20.363 mmol cm^-2 under natural sunlight, demonstrating competitive performance for nitrate reduction under dilute conditions.