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

Abstract

Electrifying ammonia synthesis will be vital to the decarbonization of the chemical industry, as the Haber-Bosch process contributes significantly 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 apply a multiscale approach that leverages the powerful cryogenic transmission electron microscopy (cryo-TEM) technique to reveal new insights that were previously inaccessible with conventional methods. We discover that the proton donor (e.g. ethanol) governs lithium reactivity toward nitrogen fixation. Without ethanol, the SEI passivates lithium metal, rendering it inactive for ammonia production. 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 lithiummediated ammonia synthesis.

Nonaqueous Li-Mediated Nitrogen Reduction: Taking Control of Potentials

“…The lithium-mediated ammonia synthesis, initially proposed by Tsuneto et al, allows the splitting of the N 2 bond by direct dissociation on metallic Li; much evidence suggests that the selectivity is due to the formation of a solid electrolyte interphase over the active surface (Figure ). − Despite several breakthroughs in performance, − the current understanding of this system is still largely limited, notably by the nature of experimental setups. To date, researchers in the field have mostly been using Pt or Ag wires as pseudoreferences in conventional three-electrode systems. − However, these metals do not have a well-defined redox couple in this medium, and the equilibrium defining their redox potential is unknown .…”

Li–N2 Battery for Ammonia Synthesis and Computational Insight

“…As the depth of discharge in Figure C, the shiny Ru nanoparticles almost disappeared, concealed by some filamentous, stripy, and flaky substances. According to the previous literature, the later-growing layer included lithium filaments and large agglomerations or solid electrolyte interfacial membranes usually observed in the Li-metal battery and Li-mediated ammonia synthesis. − In this case, it might be the undetectable Li 3 N, decomposition product, or other organic N-containing compounds. It was found that 2% of N existed by surface scan on the electrode interface after 24 h of discharge (Figure S10).…”

Approaching Molecular Definition on Oxide-Supported Single-Atom Catalysts

“…Despite some advances in the field of molecularly defined SACs in the past decade, we believe the following opportunities should be explored. While the SACs presented here exhibit improved structural definition compared to that of other catalyst systems, uncertainties still remain about exact active-site structures, an issue that could be solved with single-crystal X-ray diffraction or high-resolution (cryo) EM. Precedent exists for the structural resolution of single crystals of POM-based metal complexes, while high-resolution (cryo) EM has shown potential for the identification of the atomic structure of catalytic interfaces Active-site changes on half-life time scales relevant to transition states and short-lived intermediates should be explored to identify key differences in the substrate adsorption and reactivity between extended surfaces and supported SACs.…”

“…While the SACs presented here exhibit improved structural definition compared to that of other catalyst systems, uncertainties still remain about exact active-site structures, an issue that could be solved with single-crystal X-ray diffraction or high-resolution (cryo) EM. Precedent exists for the structural resolution of single crystals of POM-based metal complexes, while high-resolution (cryo) EM has shown potential for the identification of the atomic structure of catalytic interfaces …”

“…Precedent exists for the structural resolution of single crystals of POM-based metal complexes, 53 while high-resolution (cryo) EM has shown potential for the identification of the atomic structure of catalytic interfaces. 54 (2) Active-site changes on half-life time scales relevant to transition states and short-lived intermediates should be explored to identify key differences in the substrate adsorption and reactivity between extended surfaces and supported SACs. Femtosecond X-ray spectroscopy in conjunction with well-defined SACs would allow for identifying fundamental differences between active-site structures.…”