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Electroreduction of nitrogen with almost 100% current-to-ammonia efficiency

Abstract

In addition to its use in the fertilizer and chemical industries1, ammonia is currently seen as a potential replacement for carbon-based fuels and as a carrier for worldwide transportation of renewable energy2. Implementation of this vision requires transformation of the existing fossil-fuel-based technology for NH3 production3 to a simpler, scale-flexible technology, such as the electrochemical lithium-mediated nitrogen-reduction reaction3,4. This provides a genuine pathway from N2 to ammonia, but it is currently hampered by limited yield rates and low efficiencies4,5,6,7,8,9,10,11,12. Here we investigate the role of the electrolyte in this reaction and present a high-efficiency, robust process that is enabled by compact ionic layering in the electrode–electrolyte interface region. The interface is generated by a high-concentration imide-based lithium-salt electrolyte, providing stabilized ammonia yield rates of 150 ± 20 nmol s−1 cm−2 and a current-to-ammonia efficiency that is close to 100%. The ionic assembly formed at the electrode surface suppresses the electrolyte decomposition and supports stable N2 reduction. Our study highlights the interrelation between the performance of the lithium-mediated nitrogen-reduction reaction and the physicochemical properties of the electrode–electrolyte interface. We anticipate that these findings will guide the development of a robust, high-performance process for sustainable ammonia production.

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Fig. 1: Electrolyte effects in the Li-NRR.
Fig. 2: Influence of the potential on the composition of the electrode surface during N2 electroreduction mediated by 2 M LiNTf2.
Fig. 3: Li-NRR performance with a bare Ni wire electrode (geometric surface area 0.15 cm2) as a function of time.
Fig. 4: Longer-term Li-NRR performance with isolated Ni electrodes.

Data availability

All data are available in the paper and its Supplementary Information. Source data that support the findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

We acknowledge funding of this work by the Australian Research Council (Discovery Project DP200101878, Centre of Excellence for Electromaterials Science CE140100012, Future Fellowship to A.N.S. (FT200100317)) and the Australian Renewable Energy Agency (‘Renewable Hydrogen for Export’ project 2018RND/009 DM015); and the Monash Centre for Electron Microscopy, Monash X-ray platform and Monash Analytical platform for providing access to the physical characterization and spectroscopic facilities. We thank Nippon Shokubai for a gift of LiFSI and F. Shanks for his assistance with the Fourier-transform infrared attenuated total reflectance spectroscopic measurements.

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Contributions

H.-L.D. conceived and did the electrochemical experiments, viscosity and conductivity measurements and co-wrote the manuscript. M.C. did the XRD and  Fourier-transform infrared attenuated total reflectance spectroscopic analyses, and assisted with monitoring long-term experiments. R.Y.H. contributed to the reproducibility studies and performed the 1H NMR analysis of ammonia. P.V.C. collected and analysed XPS data. C.K.N. did nitrite/nitrate measurements, and the SEM and EDS analyses. K.M. contributed to conductivity measurements and collected the NMR data for the electrolyte stability. D.R.M. and A.N.S. conceived the experiments, directed the project and co-wrote the manuscript.

Corresponding authors

Correspondence to Douglas R. MacFarlane or Alexandr N. Simonov.

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Competing interests

H.-L.D., D.R.M. and A.N.S. are inventors on an Australian provisional patent application that covers aspects of the work reported here, and which has been licensed to Jupiter Ionics. D.R.M. and A.N.S. have minority equity ownership, as well as management and consulting roles, in Jupiter Ionics.

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Du, HL., Chatti, M., Hodgetts, R.Y. et al. Electroreduction of nitrogen with almost 100% current-to-ammonia efficiency. Nature 609, 722–727 (2022). https://doi.org/10.1038/s41586-022-05108-y

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