Efficient and Stable Ammonia Synthesis from Ambient Air and Water via Integrated Plasma-Electrocatalytic Process.

Abstract

Electricity driven nitrogen (N₂) reduction (eNRR) presents one green and ambient alternative to Haber-Bosch ammonia (NH₃) synthesis. However, NH₃ yield rate and selectivity are extremely low due to failures in sufficient N₂ activation and suppressing robust competitive reaction. Herein, efficient plasma N₂ activation is matched with thermodynamically favorable electrocatalytic hydrogenation in the specially integrated system and achieves sustainable and ambient NH₃ synthesis directly using air and water. Through this well-designed reactor with an optimal Cu mesh electrode, high NH₃ Faradaic efficiency of 91.42% and yield rate of 14.01 mg h^-1 cm^-2 are achieved, largely surpassing eNRR and sole nitrite (NO₂ ^-) electroreduction in a similar electrolyte. Using in situ experiments and theoretical calculations, it is found that NH₃ synthesis mainly goes through plasma N₂ oxidation into gaseous nitric oxide (NO) and aqueous NO₂ ^-, followed by the electroreduction of these intermediates to NH₃. The slightly oxidized Cu species with low coordination state and high NO affinity, which are stabilized by plasma treatment, account for the accelerated reaction kinetics of ^*NO hydrogenation and the suppressed combination of ^*H into hydrogen. This work highlights the possibility of sustainable NH₃ synthesis directly from ambient air and water beyond the fossil fuel-driven synthesis process.