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 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 implantation of Pd-porphyrin to promote the generation of H* and meanwhile the graft of ethoxyphenyl groups to create hydrophobic microenvironment and inhibit 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 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.