Interface Coordination Nucleation of Copper Nanoclusters on Covalent Organic Frameworks for Electrocatalytic Ammonia Synthesis.

Abstract

Copper nanoclusters stand out as one of the most promising catalysts in the electrochemical nitrate reduction reaction (NITRR) for ammonia (NH₃) synthesis, owing to their well-defined structures and high metal utilization. Herein, we report an interface coordination nucleation strategy for the uniform growth of copper nanoclusters (Cu NCs) on hydrazone-linked covalent organic frameworks (HL-COF). The periodically arranged hydrazone bonds in COF structure ensure uniform growth of copper nanoclusters, fully exposing active sites in electrocatalysis. Theoretical calculations reveal that the abundant low-coordinate Cu atoms within the Cu nanoclusters on HL-COF significantly enhance the adsorption of *NO₃ intermediates. Moreover, these Cu nanoclusters effectively reduce the energy barrier for the rate-determining step (*NO→*NHO). The resulting 0.5-Cu NCs/HL-COF catalyst shows an impressive Faradaic efficiency (FE_NH3) of 98.6% at -1.0 V vs RHE, even with a very low nitrate concentration (0.01 M NO₃^-). In a flow cell test, it maintains an industrially applicable nitrate reduction current of 203.8 mA·cm^-2 for a long duration. This study provides an interface coordination nucleation strategy that leverages the inherent periodic arranged active groups of COFs to controllably synthesize uniformly dispersed metal nanoclusters for various catalytic reactions.