The intermittent availability of renewable energy poses a significant challenge that must be overcome to fully harness its potential. One promising solution is the storage of excess renewable energy in the form of carbon-free chemical fuels like hydrogen (H₂) and ammonia (NH₃). These energy-dense alternatives provide the means to transport renewable energy independently, without relying on traditional power grids. However, the current production of NH₃ primarily relies on the costly Haber-Bosch process, limiting its use as a chemical fuel. To address this limitation, there is a need for a sustainable production method, such as the electrochemical reduction of nitrogen gas (N₂) into NH₃. Among various electrochemical processes, the lithium-mediated nitrogen reduction reaction (Li-NRR) currently stands out as the sole method capable of achieving this conversion.¹

At Monash University, we have made significant advancements in Li-NRR, achieving close to 100% faradaic efficiency for NH₃ selectivity.^2,3 However, our focus now lies on reducing the energy demands and enhancing the overall sustainability of the Li-NRR process. This calls for the intelligent design of catalysts and electrolytes, which can be facilitated by expanding our knowledge of the solid electrolyte interface (SEI) which forms atop the reactive lithium deposit. Similar SEI layers have been extensively demonstrated to play a critical role in enhancing cell efficiency and lifespan in lithium-ion batteries. However, in the context of the lithium-mediated nitrogen reduction reaction (Li-NRR) system, the SEI may also hold the key to achieving NH₃ selectivity and preventing the undesired hydrogen evolution reaction.

This presentation covers the preliminary efforts of our ongoing work using in situ neutron reflectometry to gain insight into the Li-NRR mechanism occurring at the electrode interface and characterize the SEI environment that contributes to achieving exceptional faradaic efficiency.

Using NR, we have been able to observe dynamic surface changes in the scattering length density (SLD) profile of the catalytic deposit during Li-NRR, operating at a modest 10% faradaic efficiency, limited by the experimental constraints of the NR cell. To further deepen our understanding, we are utilizing operando galvanostatic electrochemical impedance spectroscopy to establish correlations between these surface changes and the electrochemical response of the cell. This multidimensional approach allows us to unlock crucial insights into the intricate processes taking place at the electrode interface, paving the way for more efficient and sustainable ammonia production through Li-mediated electrochemical reduction of nitrogen gas.