(653a) Techniques for the Examination of Aqueous and Nonaqueous Electrocatalytic N2 Reduction

The electrocatalytic N₂ reduction reaction (N₂RR) offers an alternative route to the traditional Haber-Bosch method for production of NH₃. Electrifying NH₃ synthesis promises a route to the decarbonization and decentralization of ammonia production, which currently accounts for >1% of our annual CO₂ emissions. While there have been many studies examining the electrochemically-driven production of NH₃ in aqueous electrolytes at low-temperature (≤ 50^o C) and low-pressure (≤20 bar), lithium-mediated N₂ electroreduction in nonaqueous electrolytes at low-T and low-P has emerged as a promising method for obtaining reliable selectivity and activity toward NH₃. The proposed mechanism of this Li-mediated N₂RR method entails the production of reduced-Li species as key intermediates — these Li species are well-known to be reactive, introducing challenges in controlling and studying the solid-electrolyte interphase (SEI) that plays a crucial role in dictating electrochemical behavior.

Herein, we review our efforts at SUNCAT to search for aqueous N₂RR electrocatalysts, and we emphasize our recent work to improve our understanding of Li-mediated N₂RR by developing complementary tools for operando interrogation of electrode-electrolyte interfaces. Among these tools, we are actively developing operando, time-resolved, neutron reflectometry as well as operando X-ray diffractometry (XRD). The neutron-based methods are inherently sensitive to Li and amorphous layers and serve as a complement to XRD methods that offer superior compositional insight for crystalline products. We have used them to observe the growth of apparent Li-rich SEI layers on one-minute timescales under applied current and under varying electrolyte conditions, opening an avenue to understand how changing electrolyte and potential/current conditions dictate the growth rate and composition of SEI layer formation from initial ‘t = 0 s’ conditions. Finally, we will discuss our recent exploration of directed chemical modification of the N₂RR SEI layer using inorganic additives to attempt to exert control over the SEI and improve N₂RR performance.