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Imaging of nitrogen fixation at lithium solid electrolyte interphases via cryo-electron microscopy

Abstract

Ammonia is an important industrial chemical and is also being discussed as a potential energy carrier. Electrifying ammonia synthesis could help to decarbonize the chemical industry, as the Haber–Bosch process contributes markedly to global carbon emissions. A lithium-mediated pathway is among the most promising ambient-condition electrochemical ammonia synthesis methods. However, the role of metallic lithium and its passivation layer, the solid electrolyte interphase (SEI), remains unresolved. Here we use cryogenic transmission electron microscopy as part of a multiscale approach to explore lithium reactivity and the SEI, discovering that the proton donor (for example, ethanol) governs lithium reactivity towards nitrogen fixation. Without ethanol, the SEI passivates lithium metal, rendering it inactive for nitrogen reduction. Ethanol disrupts this passivation layer, enabling continuous reactivity at the lithium surface. As a result, metallic lithium is consumed via reactions with nitrogen, proton donor and other electrolyte components. This reactivity across the SEI is vital to device-level performance of lithium-mediated ammonia synthesis.

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Fig. 1: Previously proposed reaction mechanisms of lithium-mediated ammonia synthesis.
Fig. 2: Quantification of key products.
Fig. 3: Imaging results from the ‘no HA, N2’ and ‘EtOH, N2’ model systems.
Fig. 4: XPS results from the four model systems.
Fig. 5: SEI materials and their role in LiMEAS.

Data availability

The data collected and analysed for this work are included in the paper and its Supplementary Information. Source data are provided with this paper.

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Acknowledgements

K.M., K.S. N.L., and C.K.K. gratefully acknowledge support by the National Science Foundation under grant number 2204756. K.S. and N.L. acknowledge support from the National Science Foundation Graduate Research Fellowship under grant number 1745302. Cryo-EM data were acquired at the Electron Imaging Center for Nanomachines (EICN) at the University of California, Los Angeles’s California NanoSystems Institute (CNSI). Y.L. and X.Y. were supported in part by the National Science Foundation under grant number CBET-2143677. This work also made use of the MRSEC Shared Experimental Facilities at Massachusetts Institute of Technology (MIT), supported by the National Science Foundation under award number DMR-1419807. We thank the staff scientists at both UCLA EICN and MIT MRSEC for their training and expertise. We also thank M. Wolski of Daramic for providing us with polyporous separator samples, F. Frankel for feedback on figure design and K. Williams, N. Corbin, H. J. Song, G. Junor, G. Hobold and all the members of the Li and Manthiram research groups for productive and helpful discussions.

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Contributions

K.S., K.M. and Y.L. conceptualized the paper. K.S. developed the experimental methodology for product quantification, sample preparation for imaging and characterization and collection of XPS spectra. X.Y. and Y.L. developed the experimental methodology for SEM and cryo-EM. K.S. performed product quantification, SEM imaging and XPS experiments, and K.S. and C.K. prepared samples for cryo-EM. X.Y. carried out cryo-EM and SEM imaging. Y.L. performed EELS characterization. M.M. advised on microscopy and imaging analysis. C.K. and K.S. performed the validation. K.S. prepared the figures and wrote the original draft of the manuscript and Supplementary Information, and N.L, Y.L., K.M., C.K., X.Y. and K.S. reviewed and edited its contents. K.M. and Y.L. supervised the work.

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Correspondence to Karthish Manthiram or Yuzhang Li.

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Nature Energy thanks Matteo Cargnello, Chongmin Wang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Steinberg, K., Yuan, X., Klein, C.K. et al. Imaging of nitrogen fixation at lithium solid electrolyte interphases via cryo-electron microscopy. Nat Energy (2022). https://doi.org/10.1038/s41560-022-01177-5

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