Decentralised electrochemical synthesis of ammonia provides a promising alternative to the
carbon-intensive Haber-Bosch process, of which the non-aqueous lithium-mediated system is
the most advanced thus far. Electrodeposited lithium reacts with N2 to form Li3N, which can
be selectively protonated to ammonia by controlling the transport of reagents through a solid electrolyte interphase (SEI) layer on the cathode. The performance of the lithium-mediated
system has developed rapidly since its verification in 2019, but it is still far from a commercial
reality.
While the SEI layer is generally accepted as critical to the success of this system, details of its
formation and the relationship between its structure, composition and performance are poorly
understood. This thesis focusses on the role of water in LiClO4-based electrolytes. We find that,
contrary to the deleterious effects of water in fluorine-containing electrolytes, trace water can
boost the selectivity of the reaction towards ammonia within a very narrow parameter space.
The addition of water leads to an SEI dominated by Li2O and LiOH, revealed by operando
infrared spectroscopy, X-ray photoelectron spectroscopy, and cryo-microscopy, which provide
an insoluble protective layer on the electrolyte. We also detect the real-time reduction of the
organic proton donor and show that it dominates the initial stages of SEI formation. This
provides crucial insight which could inform future SEI engineering.
A preliminary study of the poisoning of the anode using surface-enhanced infrared
spectroscopy indicates that the oxidation of ethanol to CO is a source of deactivation of the
platinum anode, as is the presence of CO impurities in the H2 gas. This lays the foundations for
a detailed spectroscopic study of the poisoning effects of organic proton sources on the anode,
and of the anode’s long-term performance and stability.