Catalyst design strategy enhances green urea synthesis efficiency

A research team from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has constructed a copper (Cu) single-atom catalyst (Cu-N₃ SAs) with a nitrogen-coordination structure. They used two-dimensional g-C₃N₄, derived from melamine pyrolysis, as a carrier to achieve efficient electrocatalytic urea synthesis under mild conditions.

The results are published in Angewandte Chemie International Edition.

Urea is mainly synthesized via the energy-intensive and highly polluting Bosch-Meiser process. Therefore, it is crucial to develop sustainable urea synthesis methods driven by clean energy. However, synthesizing urea via the electrocatalytic co-reduction of CO₂ and NO₃^, still faces many challenges, including multi-electron reaction processes, complex C,N coupling reaction mechanisms, and competitive side reactions. These factors greatly reduce the efficiency of urea synthesis.

In this study, the researchers used a two-dimensional g-C₃N₄ carrier derived from melamine pyrolysis to stabilize copper atoms in a Cu,N₃ coordination structure. Using a tandem impregnation,pyrolysis method, they constructed copper single-atom electrocatalysts (Cu,N₃ SAs). Advanced characterization techniques, including X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS), confirmed the precise atomic structure and electronic state of the catalysts.

The Cu,N₃ SAs demonstrated exceptional activity, achieving a urea yield of 19,598 ± 1,821 mg h⁻¹ mgCu⁻¹ and a Faradaic efficiency of 55.4% at -0.9 V (vs. RHE). Further insights from in situ infrared spectroscopy, mass spectrometry, and X-ray absorption spectroscopy revealed that under reaction conditions, the Cu,N₃ sites dynamically reconstruct into an N₂,Cu,Cu,N₂ configuration, which significantly boosts urea synthesis performance.

Complementary density functional theory (DFT) calculations revealed that this reconstruction occurs within the ring structure of single-layer g-C₃N₄. The resulting copper bisite structure enhances CO adsorption, accelerates multi-electron transfer, and lowers the energy barrier for the crucial *CONH intermediate formation—the first C,N coupling step in urea production.

According to the researchers, this study provides important theoretical guidance for understanding the dynamic evolution of actual catalytic active sites in efficient urea electrolysis.