Interfacial engineering of carbon quantum dot/metal-organic framework heterostructures for boosted urea electrosynthesis from carbon dioxide and nitrate

Abstract

Electrocatalytic urea synthesis from CO₂ and NO₃⁻ offers a sustainable alternative to conventional energy-intensive industrial processes. However, it remains hindered by sluggish CN coupling kinetics and mismatched CO₂/NO₃⁻ reduction rates. Herein, a carbon quantum dots (CQDs)/metal-organic framework (MOF) heterostructure (Cu-MOF-CQD) was constructed by integrating amino-rich CQDs into the porous Cu-BTC framework (BTC = 1,3,5-benzenetricarboxylic acid) via a one-step ultrasonic-static strategy. The integration of CQDs markedly enhances the electrical conductivity of Cu-MOF and modulates the interfacial electronic structure through interactions between CQDs surface groups and unsaturated Cu sites within Cu-MOF, thereby enriching high-valence Cu species and facilitating charge transfer. Operando spectroscopic characterizations combined with density functional theory calculations unveil that the interface effect of Cu-MOF-CQD provides a stronger driving force for *COOH to *CO conversion and accelerates the coupling of *CO and *NH₂ intermediates, thus promoting efficient CN bond formation. Benefiting from this synergistic interface, in a flow cell, Cu-MOF-CQD achieves a maximum urea Faradaic efficiency of 18.5 ± 0.7 % at −0.5 V vs. RHE and the corresponding urea yield rate of 260.2 ± 10.1 μg h⁻¹ mg_cat⁻¹, surpassing the performance of pristine Cu-MOF. This work establishes a generalizable strategy of zero-dimensional carbon/MOF heterostructures for boosting CN coupling performance, offering new design principles for next-generation electrocatalysts in sustainable CN coupling reactions.