Controlling the Reaction\nPathways of Mixed NO<sub><i>x</i></sub>H<sub><i>y</i></sub> Reactants\nin Plasma-Electrochemical Ammonia Synthesis

Electrochemical activation of dinitrogen (N<sub>2</sub>) is notoriously\nchallenging, typically yielding very low ammonia (NH<sub>3</sub>)\nproduction rates. In this study, we present a continuous flow plasma-electrochemical\nreactor system for the direct conversion of nitrogen from air into\nammonia. In our system, nitrogen molecules are first converted into\na mixture of NO<sub><i>x</i></sub> species in the plasma\nreactor, which are then fed into an electrochemical reactor. To selectively\nconvert the generated NO<sub><i>x</i></sub> species into\nNH<sub>3</sub>, we employed a graph theory approach combined with\nfirst-principles calculations to comprehensively enumerate all possible\npathways from N<sub>2</sub>-to-NH<sub>3</sub>, pinpointing key intermediates\n(NH<sub>2</sub>* and NO*). A series of bimetallic catalysts was then\ndesigned to target the optimal adsorption and conversion of the limiting\nintermediate in the NO<sub><i>x</i></sub>-to-NH<sub>3</sub> pathway. Using an optimized CuPd foam catalyst, we demonstrated\nan ammonia production rate of 81.2 mg h<sup>–1</sup> cm<sup>–2</sup> with stability over 1000 h at an applied current\nof 2 A.