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-NOx-NOx−-NH3 system that combines non-thermal plasma-enabled N2 oxidation with Ni(OH)x/Cu-catalyzed electrochemical NOx− 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 NOx− 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 NOx− 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.