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Pulsed co-electrolysis of carbon dioxide and nitrate for sustainable urea synthesis

Nature Sustainability volume 7, pages 442–451 (2024)Cite this article

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Abstract

The urea industry is energy intensive and responsible for high levels of carbon emissions. Electrocatalytic co-reduction of carbon dioxide (CO2) and nitrate (NO3−) powered by renewable energy offers an alternative and sustainable synthetic pathway to this chemical that is vital in agriculture, chemical engineering and other fields, but the yield rate cannot compete with the state-of-the-art petrochemical processes. Here we show a urea electrosynthesis route using an iron tetraphenylporphyrin molecular electrocatalyst that delivers a maximum Faradaic efficiency of 27.70% for urea while suppressing the competing hydrogen evolution reaction. At the heart of our strategy is electrolysis under pulsed potentials between −0.2 and −0.8 V versus the reversible hydrogen electrode, which increases the local concentration of CO2/NO3− but reduces the local pH to enrich *CO and *NH2 intermediates favoured by C–N coupling. Importantly, our strategy can be applied to more catalyst systems such as ZnO and PdCu, and save more than 41% energy consumption compared with static co-electrolysis, with PdCu enabling a maximum urea Faradaic efficiency of 70.36% for pulsed electrolysis. Our work opens an avenue for efficient urea production and provides insights into the role of the local reaction environment, which can inform the rational design of electrocatalysts.

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Fig. 1: Structural characterization.
Fig. 2: Electrochemical performance characterization.
Fig. 3: Operando mass spectrum.
Fig. 4: Operando ATR-SEIRAS spectroscopy measurements for the CO2/NO3− co-reduction over Fe-TPP/CNTs at various potentials from OCP to −1.2 V versus RHE.
Fig. 5: Theoretical calculations of the local pH, and concentrations of CO2 and NO3− at the electrode surface.

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All data required to evaluate the conclusions of the paper are present in the paper and/or Supplementary Information. Source data are provided with this paper.

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (U21A20312, 22379100, 22309115), the Shenzhen Science and Technology Program (grant numbers 20231121200418001, RCYX20200714114535052) and the Guangdong Basic and Applied Basic Research Foundation (2022B1515120084). We also acknowledge the help of the Electron Microscopy Centre of Shenzhen University in testing the HAADF-STEM.

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Authors and Affiliations

  1. College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen, People’s Republic of China

    Qi Hu, Weiliang Zhou, Shuai Qi, Qihua Huo, Xuan Li, Miaoyuan Lv, Xinbao Chen, Chao Feng, Jiaying Yu, Xiaoyan Chai, Hengpan Yang & Chuanxin He

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  1. Qi Hu
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Contributions

C.H. conceived the idea and directed the project. Q. Hu designed the experiments and wrote the paper. W.Z., S.Q., Q. Huo, X.L., M.L. and X. Chen performed the experiments. Q. Hu, W.Z., C.F., J.Y., X. Chai and H.Y. analysed the data.

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Correspondence to Chuanxin He.

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Nature Sustainability thanks Dehui Deng, Min-Rui Gao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Notes 1 and 2, Figs. 1–48, Tables 1–4 and References.

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Source data

Source Data Fig. 1

Structural characterization.

Source Data Fig. 2

Electrochemical performance characterization.

Source Data Fig. 3

Operando mass spectrum.

Source Data Fig. 4

Operando ATR-SEIRAS spectroscopy measurements.

Source Data Fig. 5

Simulation calculations.

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Hu, Q., Zhou, W., Qi, S. et al. Pulsed co-electrolysis of carbon dioxide and nitrate for sustainable urea synthesis. Nat Sustain 7, 442–451 (2024). https://doi.org/10.1038/s41893-024-01302-0

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