Abstract
Ammonia is crucial as a fertilizer and in the chemical industry and is considered to be a carbon-free fuel1. Ammonia electrosynthesis from nitrogen under ambient conditions offers an attractive alternative to the Haber–Bosch process2,3, and lithium-mediated nitrogen reduction represents a promising approach to continuous-flow ammonia electrosynthesis, coupling nitrogen reduction with hydrogen oxidation4. However, tetrahydrofuran, which is commonly used as a solvent, impedes long-term ammonia production owing to polymerization and volatility problems. Here we show that a chain-ether-based electrolyte enables long-term continuous ammonia synthesis. We find that a chain-ether-based solvent exhibits non-polymerization properties and a high boiling point (162 °C) and forms a compact solid-electrolyte interphase layer on the gas diffusion electrode, facilitating ammonia release in the gas phase and ensuring electrolyte stability. We demonstrate 300 h of continuous operation in a flow electrolyser with a 25 cm2 electrode at 1 bar pressure and room temperature, and achieve a current-to-ammonia efficiency of 64 ± 1% with a gas-phase ammonia content of approximately 98%. Our results highlight the crucial role of the solvent in long-term continuous ammonia synthesis.
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Acknowledgements
We thank M. Ribergaard Vinther and floor managers B. P. Knudsen and J. Ejler Sørensen for help with the connection of laboratory gas lines and the building of the mass spectrometer for isotope studies. We also thank the NMR Center of the Technical University of Denmark. We gratefully acknowledge funding from Villum Fonden, part of the Villum Center for the Science of Sustainable Fuels and Chemicals (V-SUSTAIN grant no. 9455); Innovationsfonden (E-ammonia grant no. 9067-00010B); the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 741860); the Danish National Research Foundation (VISION DNRF146) and MSCA European Postdoctoral Fellowships (Eelctro-Ammonia Project no. 101059643). We thank X. Sun for her assistance with the schematic diagram.
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S.L., Y.Z., J.K.N. and I.C. conceived the study. S.L. conducted the electrochemical experiments and collected and analysed SEM and XPS data. Y.Z. performed the theoretical calculations. X.F. contributed to the ion chromatography measurements and electrochemical experiments. J.B.P. and S.L. did the operando mass spectrometry experiments. M.S. carried out XRD measurements, and K.E.-R. did the NMR measurements. P.J.K., C.D.D. and S.L. conducted the cryo-TEM experiments and data analysis. S.Z.A., A.X., R.S., J.B.V.M., N.H.D., J.K. and P.C.K.V. contributed to the data analysis and discussions. S.L., Y.Z., J.K.N. and I.C. co-wrote the manuscript. All authors discussed the results and assisted during manuscript preparation.
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A patent application titled ‘Flow cell for electrochemical ammonia synthesis’ was submitted on 9 September 2022 (application number: EP22194879) regarding the DG solvent reported in this paper (inventors: M.S., J.B.P., X.F., S.Z.A., R.S., S.L., Y.Z., K. Li, J.K., P.C.K.V., J.K.N., I.C. J.B.V.M and N.H.D.; institution: Technical University of Denmark). M.S. and S.Z.A. have equity ownership in NitroVolt ApS, a Danish company working on commercializing electrochemical ammonia synthesis. The other authors declare no competing interests.
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Li, S., Zhou, Y., Fu, X. et al. Long-term continuous ammonia electrosynthesis. Nature (2024). https://doi.org/10.1038/s41586-024-07276-5
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DOI: https://doi.org/10.1038/s41586-024-07276-5
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