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Calcium-mediated nitrogen reduction for electrochemical ammonia synthesis

Nature Materials volume 23, pages 101–107 (2024)Cite this article

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Abstract

Ammonia (NH3) is a key commodity chemical for the agricultural, textile and pharmaceutical industries, but its production via the Haber–Bosch process is carbon-intensive and centralized. Alternatively, an electrochemical method could enable decentralized, ambient NH3 production that can be paired with renewable energy. The first verified electrochemical method for NH3 synthesis was a process mediated by lithium (Li) in organic electrolytes. So far, however, elements other than Li remain unexplored in this process for potential benefits in efficiency, reaction rates, device design, abundance and stability. In our demonstration of a Li-free system, we found that calcium can mediate the reduction of nitrogen for NH3 synthesis. We verified the calcium-mediated process using a rigorous protocol and achieved an NH3 Faradaic efficiency of 40 ± 2% using calcium tetrakis(hexafluoroisopropyloxy)borate (Ca[B(hfip)4]2) as the electrolyte. Our results offer the possibility of using abundant materials for the electrochemical production of NH3, a critical chemical precursor and promising energy vector.

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Fig. 1: Investigation of the Ca-NRR.
Fig. 2: Electrochemical testing of the Ca-NRR in the flow cell.
Fig. 3: Isotope labelling experiments using 15N2 in 0.2 M Ca[B(hfip)4]2 in the flow cell.
Fig. 4: XPS investigation of the post-reaction cathode deposits without exposure to air at different argon-ion sputtering times.

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All data are available in the main text or Supplementary Information. Source data are provided with this paper.

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Acknowledgements

We gratefully acknowledge the funding by Villum Fonden, part of the Villum Center for the Science of Sustainable Fuels and Chemicals (V-SUSTAIN grant 9455), Innovationsfonden (E-ammonia grant 9067–00010B) and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 741860). X.F. was supported under the MSCA European Postdoctoral Fellowships (Electro-Ammonia Project 101059643). V.A.N. was supported under the National Science Foundation Graduate Research Fellowship Program under grant no. DGE-1656518 and the Camille and Henry Dreyfus Foundation. A.C.N. was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Catalysis Science Program through the SUNCAT Center for Interface Science and Catalysis.

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  1. These authors contributed equally: Xianbiao Fu, Valerie A. Niemann, Yuanyuan Zhou.

Authors and Affiliations

  1. Department of Physics, Technical University of Denmark, Kongens Lyngby, Denmark

    Xianbiao Fu, Yuanyuan Zhou, Shaofeng Li, Ke Zhang, Jakob B. Pedersen, Mattia Saccoccio, Suzanne Z. Andersen, Aoni Xu, Niklas H. Deissler, Jon Bjarke Valbæk Mygind, Jakob Kibsgaard, Peter C. K. Vesborg, Jens K. Nørskov & Ib Chorkendorff

  2. Department of Chemical Engineering, Stanford University, Stanford, CA, USA

    Valerie A. Niemann, Peter Benedek & Thomas F. Jaramillo

  3. SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, Menlo Park, CA, USA

    Valerie A. Niemann, Peter Benedek, Adam C. Nielander & Thomas F. Jaramillo

  4. Department of Chemistry, Technical University of Denmark, Kongens Lyngby, Denmark

    Kasper Enemark-Rasmussen

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Contributions

Conceptualization of the work was by X.F., V.A.N., Y.Z., J.K.N., T.F.J. and I.C. Data curation was by X.F., V.A.N., Y.Z., J.B.P., S.L., K.Z., M.S. and K.E.-R. Formal analysis was carried out by X.F., V.A.N., Y.Z., P.B., K.Z., A.X., J.B.V.M., N.H.D. and A.C.N. Investigation was by X.F., V.A.N., Y.Z., S.L. and M.S. Equipment design was by X.F., V.A.N., M.S., J.B.P. and S.Z.A. Visualization was by X.F., V.A.N. and Y.Z. The project was supervised by I.C., T.F.J., J.K., P.C.K.V., J.K.N. and A.C.N. The original draft was written by X.F., V.A.N. and Y.Z., and the manuscript was reviewed and edited by X.F., V.A.N., Y.Z., S.Z.A., A.C.N., J.K., T.F.J. and I.C.

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Correspondence to Jens K. Nørskov, Thomas F. Jaramillo or Ib Chorkendorff.

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Fu, X., Niemann, V.A., Zhou, Y. et al. Calcium-mediated nitrogen reduction for electrochemical ammonia synthesis. Nat. Mater. 23, 101–107 (2024). https://doi.org/10.1038/s41563-023-01702-1

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