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High-level electronic structure calculations are carried out to obtain optimized geometries and excitation energies of neutral lithium, sodium, and potassium complexes with two ethylenediamine and one or two crown ether molecules. Three different sizes of crowns are employed (12-crown-4, 15-crown-5, 18-crown-6). The ground state of all complexes contains an electron in an s-type orbital. For the mono-crown ether complexes, this orbital is the polarized valence s-orbital of the metal, but for the other systems this orbital is a peripheral diffuse orbital. The nature of the low-lying electronic states is found to be different for each of these species. Specifically, the metal ethylenediamine complexes follow the previously discovered shell model of metal ammonia complexes (1s, 1p, 1d, 2s, 1f), but both mono- and sandwich di-crown ether complexes bear a different shell model partially due to their lower (cylindrical) symmetry and the stabilization of the 2s-type orbital. Li(15-crown-5) is the only complex with the metal in the middle of the crown ether and adopts closely the shell model of metal ammonia complexes. Our findings suggest that the electronic band structure of electrides (metal crown ether sandwich aggregates) and expanded metals (metal ammonia aggregates) should be different despite the similar nature of these systems (bearing diffuse electrons around a metal complex).
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This content will become publicly available on May 1, 2026
Sodium-mediated redox cascade for electrochemical ammonia synthesis
Artificial ammonia synthesis is vital to modern life; however, the Haber-Bosch process, by which most ammonia is synthesized, is capital and carbon intensive. Zero-valent-metal-mediated ammonia synthesis is a promising alternative but requires a metal that is both a strong reductant and forms a stable nitride. Only a small number of metals, like lithium, can satisfy these constraints. Therefore, we developed an electrochemical paradigm enabling the use of different reductants by orthogonalizing the roles of the zero-valent metal between sodium metal and a Ti active site. These components are cheaper than lithium by two orders of magnitude. Using a sodium-naphthalene-titanium cascade, we achieved a rate of 475 nmol cm-2 s-1 and a Faradaic efficiency of 24% and found that the reaction rate depends primarily on current density.
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- Award ID(s):
- 2204756
- PAR ID:
- 10618872
- Publisher / Repository:
- Cell Press
- Date Published:
- Journal Name:
- Joule
- Volume:
- 9
- Issue:
- 5
- ISSN:
- 2542-4351
- Page Range / eLocation ID:
- 101923
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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