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.

The conversion of atmospheric N₂ into NH₃ under ambient pressure is highly interesting but very challenging. In this study, the authors present a tandem air-NO_x and NO_x-NH₃ system that combines non-thermal plasma-enabled N₂ oxidation with Ni(OH)_x/Cu-catalyzed electrochemical NO_x⁻reduction, resulting in a high NH₃ yield from N₂ under ambient pressure conditions.