Speaker
Description
The production of ammonia-based fertilizers is essential to supporting the food supply for an increasing global population. However, the industrial production of ammonia proceeds via the highly resource- and energy-intensive Haber-Bosch process, consuming more than 1% of the global energy supply and releasing more than 450 million metric tons of CO2 per year. One proposed alternative to this process is the electrochemical reduction of nitrogen (eN2R) to NH3, which would enable point-of-use NH3 production at ambient temperatures and pressures. Non-aqueous, Li-mediated electrochemical nitrogen reduction reaction (Li-NRR) systems are particularly promising, as limiting proton availability has been demonstrated to significantly increase selectivity toward NH3 relative to aqueous systems. In particular, cycling the current driving the reaction between open-circuit conditions and periods of applied current density has been shown to significantly improve Li-NRR performance. However, our understanding of the dynamic Li-plating and solid electrolyte interphase (SEI) processes under such conditions and their relation to Faradaic efficiency toward NH3 (FENH3) remains limited and difficult to achieve due to the reactivity of Li-containing materials, which renders ex situ characterization unrepresentative of the electrode surface during electrochemistry, and the amorphous nature of certain SEI species.
In this talk, I will discuss our investigation of the dynamics of the electrode-electrolyte interface under Li-NRR conditions during current cycling using in situ time-resolved neutron reflectometry and grazing-incidence synchrotron X-ray diffraction. During cycling, measured neutron reflectivity curves indicated bilayer formation in which Li-containing species such as LiOH, Li2O, and small quantities of Li3N and metallic Li primarily appeared in a thin layer at the cathode surface, above which formed a much larger, porous, ‘solid-electrolyte interface’ (SEI) layer. Upon return to open-circuit conditions, Li-containing species quickly moved out of the thin layer, leaving a compact, stable layer of decomposition products underneath the SEI layer. This SEI layer concomitantly filled with electrolyte or dissolved, becoming indistinguishable from the electrolyte. These time-resolved observations of SEI and plated layers during current cycling suggest that benefits associated with return to open-circuit conditions between periods of applied current density may be related to the concomitant loss of Li-containing species from a thin layer at the cathode surface into a porous SEI layer that becomes filled with electrolyte or dissolves. Ultimately, this interface was found to be highly dynamic, and a combination of in situ techniques will be required to continue to unravel the complexities associated with SEI formation during Li-NRR.
| Topic | Energy Transfer |
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