Highly selective NH₃ synthesis from N₂ on electron-rich Bi⁰ in a pressurized electrolyzer.

Abstract

Electrochemical conversion of N₂ into ammonia presents a sustainable pathway to produce hydrogen storage carrier but yet requires further advancement in electrocatalyst design and electrolyzer integration. This technology suffers from low selectivity and yield owing to the extremely strong N≡N bond and the exceptionally low solubility of N₂ in aqueous systems. A high NH₃ synthesis performance is restricted by the high activation energy of N≡N bond and the supply insufficiency of N₂ to active sites. This paper describes the introduction of electron-rich Bi⁰ sites into Ag catalysts with a high-pressure electrolyzer that enables a dramatically enhanced Faradaic efficiency of 44.0% and yield of 28.43 μg cm^-2 h^-1 at 4.0 MPa. Combined with density functional theory results, in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy demonstrates that N₂ reduction reaction follows an associative mechanism, in which a high coverage of N-N bond and -NH₂ intermediates suggest electron-rich Bi⁰ boosts sound activation of N₂ molecules and low hydrogenation barrier. The proposed strategy of engineering electrochemical catalysts and devices provides powerful guidelines for achieving industrial-level green ammonia production.