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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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.
The authors declare no competing interests.
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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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