Ketazine-Linked Covalent Organic Framework for Metal-Free Electrocatalytic Nitrate-to-Ammonia Conversion

The electrocatalytic nitrate reduction reaction (NO₃RR) enables sustainable nitrate remediation and simultaneous ammonia synthesis as an alternative to the energy-intensive Haber-Bosch process. Recently, covalent organic frameworks (COFs) have garnered attention as NO₃RR platform due to their intrinsic porosity and structural tunability, which enable active-site engineering. However, current COF-based systems largely rely on metal active sites, undermining their sustainability and obscuring the catalytic activity of the framework. Here, we introduce a metal-free COF, that is highly active for NO₃RR. The electrocatalyst is a fluorinated ketazine-linked COF (F-Ketazine COF), which incorporates electron-withdrawing fluorine atoms that enhance π-π stacking interactions and promote efficient linkage formation. Synthesized via a rapid solvothermal reaction, the F-Ketazine COF exhibits superior crystallinity and enhanced electrocatalytic activity compared to its non-fluorinated analog (n-Ketazine COF). Under neutral pH conditions, the F-Ketazine COF achieved a Faradaic efficiency of 59.9% for NH₃ and an NH₃ yield rate of 1639.9 µmol h^-1 mg_COF ^-1 at -0.9 V versus RHE. To the best of our knowledge, this is the first example of a ketazine-linked COF applied in electrocatalysis and the first a metal-free COF for NO₃RR. This work demonstrates the potential of fluorinated ketazine linkages in developing sustainable and efficient COF-based electrocatalysts.