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Selective electrochemical synthesis of urea from nitrate and CO2 via relay catalysis on hybrid catalysts

Nature Catalysis volume 6, pages 939–948 (2023)Cite this article

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Abstract

The nitrogen cycle needed for scaled agriculture relies on energy- and carbon-intensive processes and generates nitrate-containing wastewater. Here we focus on an alternative approach—the electrified co-electrolysis of nitrate and CO2 to synthesize urea. When this is applied to industrial wastewater or agricultural runoff, the approach has the potential to enable low-carbon-intensity urea production while simultaneously providing wastewater denitrification. We report a strategy that increases selectivity to urea using a hybrid catalyst: two classes of site independently stabilize the key intermediates needed in urea formation, *CO2NO2 and *COOHNH2, via a relay catalysis mechanism. A Faradaic efficiency of 75% at wastewater-level nitrate concentrations (1,000 ppm NO3− [N]) is achieved on Zn/Cu catalysts. The resultant catalysts show a urea production rate of 16 µmol h−1 cm−2. Life-cycle assessment indicates greenhouse gas emissions of 0.28 kg CO2e per kg urea for the electrochemical route, compared to 1.8 kg CO2e kg−1 for the present-day route.

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Fig. 1: Nitrogen cycles and their energetics.
Fig. 2: Screening of single-component and hybrid catalysts.
Fig. 3: Steering selectivity to C–N coupling on Zn/Cu hybrid catalysts.
Fig. 4: Mechanistic study elucidating a chemical picture of relay catalysis.
Fig. 5: 3D hybrid catalyst for urea synthesis at 16 µmol h−1 cm−2.
Fig. 6: Life cycle assessment.

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All data supporting the findings of this study are available within the Article and Supplementary Information. Source data are provided with this paper.

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Acknowledgements

We acknowledge the support of the Banting Postdoctoral Fellowships Program (no. 01353-000, Y.L.) and the National Science Fund of China for Distinguished Young Scholars (no. 52125309, B.L.). We thank the staff at the BL11B beamline of Shanghai Synchrotron Radiation Facility (SSRF) for their technical assistance.

Author information

Author notes

  1. Tao Peng

    Present address: Beijing Huairou Laboratory, Beijing, China

  2. These authors contributed equally to this work: Yuting Luo, Ke Xie, Pengfei Ou, Chayse Lavallais.

Authors and Affiliations

  1. Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada

    Yuting Luo, Ke Xie, Pengfei Ou, Tao Peng, Zhu Chen, Ning Wang, Xiao-Yan Li, Ivan Grigioni & Edward H. Sargent

  2. Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL, USA

    Chayse Lavallais & Jennifer B. Dunn

  3. Shenzhen Geim Graphene Center, Tsinghua-Berkeley Shenzhen Institute & Institute of Materials Research, Shenzhen International Graduate School, Tsinghua University, Shenzhen, P. R. China

    Zhiyuan Zhang & Bilu Liu

  4. Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada

    David Sinton

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Contributions

Y.L. and K.X. proposed the idea. Y.L. contributed to all experimental work, data analysis and the paper. K.X. contributed to the catalytic performance tests of the 2D hybrid catalysts and analysis. P.O. contributed to DFT calculations, with feedback from X.-Y.L. C.L. and J.B.D. contributed to LCA analysis with Y.L., with K.X.’s feedback. T.P. contributed to in situ IRRAS experiments. Z.Z. and B.L. contributed to in situ XAS characterization. Z.C. and Y.L. performed the in situ SERS characterization and analysis. N.W. and I.G. contributed to material synthesis. D.S. contributed to the discussion of the work. E.H.S. supervised the study.

Corresponding authors

Correspondence to Jennifer B. Dunn or Edward H. Sargent.

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Nature Catalysis thanks Feng Jiao, Yafei Li and Heiko Keller for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–35, Tables 1–12 and Notes 1 and 2.

Supplementary Data

The atomic coordinates of the optimized models.

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Source Data Fig. 2–6

Numerical data.

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Luo, Y., Xie, K., Ou, P. et al. Selective electrochemical synthesis of urea from nitrate and CO2 via relay catalysis on hybrid catalysts. Nat Catal 6, 939–948 (2023). https://doi.org/10.1038/s41929-023-01020-4

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