Engineering hydrophobic covalent organic frameworks for electroreduction of nitrate to ammonia

Abstract

The development of efficient electrocatalysts for the nitrate reduction reaction (NO₃RR) to ammonia is crucial for sustainable nitrogen management, but remains challenging due to its intricate multi-step mechanism and competing side reactions. A key bottleneck is the severe imbalance between the generation and consumption of H*, which critically constrains ammonia selectivity and yield. Herein, a molecular engineering strategy was developed through the incorporation of Pd-porphyrin to promote the generation of H*, while grafting ethoxyphenyl groups to create a hydrophobic microenvironment and inhibit the hydrogen evolution reaction. The covalent organic framework of Pd-PCOF-2(Cu₃), which was prepared from the reaction of Pd(II) diaminoporphyrin and trinuclear copper cluster aldehyde, achieved a high NH₃ faradaic efficiency of 94.7% and a production rate of 15.09 mg h⁻¹ cm⁻². A rechargeable Zn–NO₃⁻ battery with Pd-PCOF-2(Cu₃) as the cathode was further constructed, which served as a dual-function system for both power output and ammonia production.