Probing the interfaces of electrocatalytic lithium-mediated nitrogen reduction: revealing a route to sustainable, localised ammonia production

The production of ammonia (NH3) is a vast industry, contributing nearly 2% of global CO2 emissions and, crucially, is dependent on huge, highly centralised, energy- and investment-intensive industrial plants owing to requirements for high temperatures and pressures. However, ammonia is a critical chemical for modern life, relied on greatly by the agricultural sector as a key fertiliser component for food security, and has potential as an important green, zero-carbon fuel. Consequently, sustainable ammonia production technologies are of significant global interest, especially towards achieving synthesis under ambient conditions. Furthermore, an electrochemical synthesis route would exploit the rapid growth in renewable electrical energy, using electrons (e.g., from solar, wind) to drive the synthesis for sustainable, zero-carbon ammonia production in small-to-moderate, localised facilities. This development would help to reduce the vulnerability of ammonia-dependant sectors to political and economic instabilities, improving the accessibility of NH3 production, helping to alleviate fertiliser inequity and improve access to clean, sustainable, and affordable fuel/energy.
Among possible electrochemical technologies, the lithium-mediated nitrogen reduction reaction (Li-NRR) is one of only two electrocatalytic routes proven to synthesise ammonia directly from nitrogen gas. The Li-NRR exploits the reactive surface of electroplated Li-metal to break the strong nitrogen triple bond, subsequently reacting to ideally regenerate reactants and yield ammonia. The technique has advanced in recent years, with commercialisation prospects, but in-depth spectroscopic characterisation has not yet been reported. Intricate characterisation of the reaction interface is important for understanding fundamental mechanisms that impact the critical properties and bottlenecks of the process, providing insights needed to optimise conditions for performance.
I propose to utilise advanced, surface-sensitive, Raman and infrared vibrational spectroscopies and optical/electron microscopies to characterise the reaction interface of electrochemical Li-NRR under operando electrochemical conditions. By revealing chemical and morphological changes, at micron to sub-micron resolutions, I aim to understand the roles of surface films, reactants, and intermediates, to inform the development of rigorous empirical models describing the reaction mechanisms and pathways. This will provide the necessary insights into critical factors and properties for rationalising the design of new materials and configurations to better control the process and innovate towards maximising efficiencies and production rates.
In parallel, due to the ever-growing global demand for lithium, I aim to develop the reaction using alternate earth-abundant metals (e.g., M=K, Mg, Ca). I will apply electrochemical and spectroscopic methods to identify which metals provide suitable reactive interfaces, between electrolyte and candidate metal, to favour NRR for ammonia production. Furthermore, tuning the liquid electrolyte component will be essential to drive the desired reaction and overcome competing parasitic processes. Realisation of the non-Li M-NRR to produce ammonia would have significant impact to maximise the sustainability and scalability of the process. Latterly, I aim to translate these developments, through interactions with collaborative industry and academic networks, towards scale-up of optimised materials and cell/device configurations for Li-NRR and M-NRR for ammonia synthesis.
Achieving breakthroughs in the understanding of Li-NRR, and M-NRR, will help drive the realisation of sustainable electrocatalytic ammonia production. Applying this within the development of small-scale, scalable synthesis plants creates avenues to reap the benefits of decentralising this process, critically improving accessibility to the means of ammonia production. Furthermore, the advancement of spectroscopic techniques in this area will benefit research in other emerging fields of electrosynthesis for more sustainable routes to high-value chemicals.