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Electrosynthesis of urea by using Fe2O3 nanoparticles encapsulated in a conductive metal–organic framework

Nature Synthesis volume 3, pages 1404–1413 (2024)Cite this article

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Abstract

The synthesis of urea by the electrochemical co-reduction of CO2 and nitrate is a crucial and challenging task. Catalysts typically suffer from either low Faradaic efficiency (FE) or inadequate current density, leading to a restricted yield rate of urea. Here we report ultrasmall γ-Fe2O3 nanoparticles (<2 nm) encapsulated in the pores of a conductive (40 S cm−1) metal–organic framework Ni-HITP (HITP = 2,3,6,7,10,11-hexaaminotriphenylene), resulting in a composite material, γ-Fe2O3@Ni-HITP. Under neutral conditions, γ-Fe2O3@Ni-HITP exhibited a state-of-art electrocatalytic performance for urea synthesis through the co-reduction of CO2 and nitrate in CO2-saturated 1 M KHCO3 and 0.1 M KNO3 aqueous solutions, achieving a FEurea of 67.2(6)%, a current density of −90 mA cm−2 and an high yield rate of \(20.4(2)\,{\mathrm{g}}\,{\mathrm{h}}^{-1}\,{\mathrm{g}}_{\mathrm{cat}}^{-1}\) (7.7(1) mg h−1 cm−2), which is about five times higher than the rates of previously reported catalysts. No degradation was observed over 150 h of continuous operation at such a high yield rate. Enlarging the electrode area by 125 times yielded about 1.05(4) g of high-purity urea over 8 h. A mechanistic study revealed that Fe(III) ions in the γ-Fe2O3 nanoparticles exhibit high activity, generating the key intermediates *NH2 and *COOH. Furthermore, pairs of adjacent Fe(III) ions in the γ-Fe2O3 nanoparticles can act as highly active catalytic sites for catalysing the C–N coupling between *NH2 and *COOH, resulting in the formation of the subsequent key intermediate *CONH2, thereby contributing to the exceptionally high performance of γ-Fe2O3@Ni-HITP for urea production.

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Fig. 1: Schematic illustration of Ni-HITP and γ-Fe2O3@Ni-HITP synthesis.
Fig. 2: Morphology and structural characterization of γ-Fe2O3@Ni-HITP.
Fig. 3: Co-reduction performance of CO2 and nitrate by γ-Fe2O3@Ni-HITP.
Fig. 4: Performance of electrocatalytic CO2 and nitrate co-reduction by a flow cell with a larger window area (5 × 5 cm2).
Fig. 5: Study on the reaction mechanism of the electrochemical co-reduction of CO2 and nitrate.

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The data supporting the finding of the study are available in the paper and its Supplementary Information. Source data are provided with this paper.

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Acknowledgements

This work was supported by the National Key Research and Development Program of China (grant number 2021YFA1500401 to P.-Q.L.), the National Natural Science Foundation of China (grant number 21890380 to X.-M.C., grant numbers 22371304 and 21821003 to P.-Q.L. and grant number 223B2123 to Z.-H.Z.), the Special Fund Project for Science and Technology Innovation Strategy of Guangdong Province (grant number STKJ2023078 to X.-M.C. and P.-Q.L.) and the Guangzhou Science and Technology Program (grant number SL2023A04J01767 to P.-Q.L.).

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Authors and Affiliations

  1. MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, GBRCE for Functional Molecular Engineering, School of Chemistry, IGCME, Sun Yat-Sen University, Guangzhou, China

    Da-Shuai Huang, Xiao-Feng Qiu, Jia-Run Huang, Zhen-Hua Zhao, Pei-Qin Liao & Xiao-Ming Chen

  2. Multi-Scale Porous Materials Center, Institute of Advanced Interdisciplinary Studies & School of Chemistry and Chemical Engineering, Chongqing University, Chongqing, China

    Min Mao & Lingmei Liu

  3. Electron Microscopy Center, South China University of Technology, Guangzhou, China

    Yu Han

  4. School of Emergent Soft Matter, South China University of Technology, Guangzhou, China

    Yu Han

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  1. Da-Shuai Huang
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Contributions

P.-Q.L. designed the research. D.-S.H. performed the syntheses and measurements. X.-F.Q. performed the PDFT calculations. Y.H., M.M. and L.L. performed the STEM measurements. D.-S.H., J.-R.H., Z.-H.Z., P.-Q.L. and X.-M.C. wrote the paper.

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Correspondence to Pei-Qin Liao.

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Nature Synthesis thanks Marta Hatzell, Licheng Sun, Haihui Wang, Haimin Zhang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Alison Stoddart, in collaboration with the Nature Synthesis team.

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Huang, DS., Qiu, XF., Huang, JR. et al. Electrosynthesis of urea by using Fe2O3 nanoparticles encapsulated in a conductive metal–organic framework. Nat. Synth 3, 1404–1413 (2024). https://doi.org/10.1038/s44160-024-00603-8

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