Thermal-Electro-Synthesis of Ammonia over Molybdenum Oxynitride at 250°C

NH₃ is a critical global resource for fertilizers and chemical intermediates and can also serve as an easily transported hydrogen vector in support of a hydrogen economy. An electrochemically driven process generates high chemical potential of reactant species allowing us to circumvent pressurization of the system. Thus, electrochemical NH₃ synthesis would reduce capital costs, decrease energy consumption, and enable NH₃ synthesis at smaller scales than the incumbent high-pressure process (Haber-Bosch). In this work, we electrochemically synthesized ammonia (NH₃) using protons, steam (H₂O), and N₂ as reactants over molybdenum oxynitride using cesium dihydrogen phosphate (CsH₂PO₄) solid acid electrolytes (Cathode conditions of 38% H₂O, 62% N₂, anode conditions of 38% H₂O, 62% H₂, both at 1 atm total pressure, 250°C and -0.7 V_OCV). We first discuss the challenge of eliminating false positives and protocols to confidently detect and quantify NH₃ using NMR. Molybdenum oxynitrides were synthesized from molybdenum trioxide (MoO₃) precursors and utilized in the cathode. We find that the NH₃ synthesis rate is only marginally lower when the system is starved of N₂ reactant, indicating that the majority, if not all, of the N in NH₃ originates from N in the oxynitride.