Controlling the Reaction Pathways of Mixed NOxHy Reactants in Plasma-Electrochemical Ammonia Synthesis

Electrochemical activation of dinitrogen (N₂) is notoriously challenging, typically yielding very low ammonia (NH₃) production rates. In this study, we present a continuous flow plasma-electrochemical reactor system for the direct conversion of nitrogen from air into ammonia. In our system, nitrogen molecules are first converted into a mixture of NO_x species in the plasma reactor, which are then fed into an electrochemical reactor. To selectively convert the generated NO_x species into NH₃, we employed a graph theory approach combined with first-principles calculations to comprehensively enumerate all possible pathways from N₂-to-NH₃, pinpointing key intermediates (NH₂* and NO*). A series of bimetallic catalysts was then designed to target the optimal adsorption and conversion of the limiting intermediate in the NO_x-to-NH₃ pathway. Using an optimized CuPd foam catalyst, we demonstrated an ammonia production rate of 81.2 mg h^–1 cm^–2 with stability over 1000 h at an applied current of 2 A.