Plasma-Enhanced Electrochemical Ammonia Synthesis from Nitrogen and Water Using an Oxygen-Ion-Conducting Solid Oxide Electrolysis Cell

The development of alternative ammonia synthesis methods that are compatible with fluctuating renewable electricity and suitable for distributed production is critical for sustainable chemical manufacturing. In this study, we developed a hybrid reactor that integrates an oxygen-ion-conducting solid oxide electrolysis cell (SOEC) with plasma for the direct synthesis of ammonia from water and nitrogen. Unlike previous hybrid systems employing proton-conducting SOECs, our design exposes the cathode to a mixture of nitrogen, water vapor, and SOEC-generated hydrogen under a plasma environment, thereby enabling the exploration of potential synergistic effects between plasma chemical reactions and electrochemical reactions in a reaction field containing a potentially more diverse set of chemical species. Experimental results demonstrate a pronounced synergistic effect: the SOEC and plasma hybrid system achieves a maximum ammonia formation rate of 2.56 × 10–9 mol·s–1·cm–2 with a Faradaic efficiency of 0.60%, exceeding the simple sum of the SOEC-only and plasma-only contributions by more than an order of magnitude, with an energy efficiency of ∼0.0478 g-NH3·kWh–1 (energy consumption of 1.28 × 103 MJ/mol-NH3). The Faradaic efficiency and ammonia selectivity also increased substantially relative to SOEC-only operation. Control experiments suggest that ammonia formation is promoted not solely by gaseous hydrogen from SOEC but through interactions between plasma and hydrogen species on the SOEC cathode surface and that optimizing the plasma intensity relative to the oxygen-ion-conducting SOEC could substantially enhance the selectivity and Faradaic efficiency to ammonia, highlighting the considerable potential of such hybrid systems as flexible and scalable platforms for sustainable ammonia production.