Electrochemical ammonia synthesis via the nitrogen reduction reaction (NRR) has been poised as one of the promising technologies for the sustainable production of green ammonia. In this work, we developed extensive process models of fully integrated electrochemical NH ₃ production plants at small scale (91 tonnes per day), including their techno-economic assessments, for (Li-)mediated, direct and indirect NRR pathways at ambient and elevated temperatures, which were compared with electrified and steam-methane reforming (SMR) Haber-Bosch processes. The levelized cost of ammonia (LCOA) of aqueous NRR at ambient conditions only becomes comparable with SMR Haber-Bosch at very optimistic electrolyzer performance parameters (FE > 80% at j ≥ 0.3 A cm ⁻²) and electricity prices (<$0.024 per kW h). Both high temperature NRR and Li-mediated NRR are not economically comparable within the tested variable ranges. High temperature NRR is very capital intensive due the requirement of a heat exchanger network, more auxiliary equipment and an additional water electrolyzer (considering the indirect route). For Li-mediated NRR, the high lithium plating potentials, ohmic losses and the requirement for H ₂, limits its commercial competitiveness with SMR Haber-Bosch. This incentivises the search for materials beyond lithium.

@en

Ammonia (NH3) is a bulk commodity chemical known for its large production volumes and application in the global fertiliser industry, and is more recently being explored for its role as a sustainable energy vector. The industry standard ammonia production method is the century-old Haber-Bosch (HB) process, which is power by fossil fuels, and is accompanied with high energy intensity and large carbon-dioxide emissions. In this research, conceptual processes for the electrochemical synthesis of ammonia via the direct electrochemical nitrogen reduction reaction (e-NRR) from air and water were developed to assess their technical and economic viability compared to the HB benchmark. Different scales (91, 544 and 2055 t d-1) and electrolyzer cell configurations (alkaline electrolyzer (AEL), gas-diffusion electrode flow cell (GDE) and solid oxide electrolyzer (SOEL)) were considered. The results showed that small-scale production is more feasible for e-NRR NH3 synthesis due to the economies of scale of the HB benchmark. Among different electrolyzer types, the gas-diffusion electrode flow cell was found to be the most practical and economical for e-NRR NH3 synthesis. A sensitivity analysis showed that the electricity price is the most important parameter for the feasibility of e-NRR, and should ideally be as low as possible. Performance parameters of the electrolyzer, such as stack cost, operational current density, and faradaic efficiency, were optimized for minimal NH3 production cost, but were challenging to estimate due to the early stage of e-NRR technology. An optimized case was presented that demonstrated e-NRR NH3 can reach HB-parity, but the validity of the optimised parameters was difficult. It is advised that reliable laboratory-scale demonstrations are needed for an accurate assessment of the commercial feasibility of electrochemical NH3 synthesis.