Efficient ammonia synthesis from the air using tandem non-thermal plasma and electrocatalysis at ambient conditions.

Abstract

While electrochemical N₂ reduction presents a sustainable approach to NH₃ synthesis, addressing the emission- and energy-intensive limitations of the Haber-Bosch process, it grapples with challenges in N₂ activation and competing with pronounced hydrogen evolution reaction. Here we present a tandem air-NO_x-NO_x^--NH₃ system that combines non-thermal plasma-enabled N₂ oxidation with Ni(OH)_x/Cu-catalyzed electrochemical NO_x^- reduction. It delivers a high NH₃ yield rate of 3 mmol h^-1 cm^-2 and a corresponding Faradaic efficiency of 92% at -0.25 V versus reversible hydrogen electrode in batch experiments, outperforming previously reported ones. Furthermore, in a flow mode concurrently operating the non-thermal plasma and the NO_x^- electrolyzer, a stable NH₃ yield rate of approximately 1.25 mmol h^-1 cm^-2 is sustained over 100 h using pure air as the intake. Mechanistic studies indicate that amorphous Ni(OH)_x on Cu interacts with hydrated K⁺ in the double layer through noncovalent interactions and accelerates the activation of water, enriching adsorbed hydrogen species that can readily react with N-containing intermediates. In situ spectroscopies and density functional theory (DFT) results reveal that NO_x^- adsorption and their hydrogenation process are optimized over the Ni(OH)_x/Cu surface. This work provides new insights into electricity-driven distributed NH₃ production using natural air at ambient conditions.