| Summary: | This thesis has mainly focused on the electrochemical synthesis of ammonia at atmospheric pressure using three different catalyst types (nitride, spinel and perovskite). Attention also has been given to developing new electrolyte materials based on oxide-carbonate composites, with the aim of exploring their application in ammonia synthesis at low operating temperature (< 500 °C). Ammonia was synthesised from H₂ and N₂ using an electrolyte supported cell based on LiAlO₂-(Li/Na/K)₂CO₃ as electrolyte, Ag-Pd as anode and either nitride (e.g. Co₃Mo₃N) or spinel (CoFe₂O₄) as cathode. The maximum rate of ammonia formation (3.27 x 10⁻¹⁰10 mol s⁻¹ cm⁻² at 450 °C and 0.8 V) was obtained when Co₃Mo₃N was used as a cathode. Ammonia was also synthesised from H₂ and N₂ in an electrolytic cell based on Sm-doped ceria-carbonate composite (SDC-(Li/Na/K)₂CO₃) as an electrolyte, NiO-SDC as anode and perovskite oxide La₀.₆Sr₀.₄Fe₀.₈Cu₀.₂O₃-δ (LSFCu) catalyst as a cathode. The maximum rate was found to be 5.39 x 10⁻⁹ mol s⁻¹ cm⁻² at 450 °C and 0.8 V. Ammonia was also synthesised successfully from water vapour (3% H₂O) and nitrogen, using a new electrolyte material based on Ca and Gd co-doped ceria-carbonate composite (CGDC-(Li/Na/K)₂CO₃). Perovskite oxide Sm₀.₅Sr₀.₅CoO₃-δ (SSCo) was used as an anode and either spinel or perovskite based catalysts were used as cathodes. The maximum rate of ammonia formation (4.0 x 10⁻¹⁰ mol s⁻¹ cm⁻² at 375 °C and 1.4 V) was attained with a La₀.₇₅Sr₀.₂₅Cr₀.₅Fe₀.₅O₃-δ (LSCrF) cathode. Ammonia was synthesised directly from air and water vapour (3% H₂O) in a symmetrical cell composed of LSCrF as electrodes (cathode and anode) and CGDC-(Li/Na/K)₂CO₃ composite as electrolyte. The maximum rate was found to be 1.94x10⁻¹¹ mol s⁻¹ cm⁻² at 375 °C with an applied voltage of 1.2 V.
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