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

Abstract

ABSTRACT The electrocatalytic nitrate reduction reaction (NO 3 RR) 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 NO 3 RR 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 NO 3 RR. 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 NH 3 and an NH 3 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 NO 3 RR. This work demonstrates the potential of fluorinated ketazine linkages in developing sustainable and efficient COF‐based electrocatalysts.