Ambient ammonia synthesis from air via tandem water microdroplets–driven oxidation and pulsed photoelectrochemical reduction

Artificial N₂ reduction offers a sustainable approach to green NH₃ synthesis, but the practical implementation is challenged by N₂ activation and competing hydrogen evolution. Photoelectrochemical nitrate and nitrite (NO<i>_x</i>^-, <i>x</i> = 2 and 3) reduction with favorable thermodynamics represents a promising alternative for NH₃ production, provided that NO<i>_x</i>^- can be supplied from the atmosphere. Here, through leveraging water microdroplet chemistry and dynamic photoelectrode-electrolyte interface engineering, we report a tandem air-NO<i>_x</i>^--NH₃ conversion system that integrates catalyst-free N₂ oxidation with pulsed photoelectrochemical NO<i>_x</i>^- reduction (mNOR-pPNO<i>_x</i>R). The system achieves efficient and selective NH₃ production with a yield rate of 24.5 μmol cm^-2 h^-1 at -0.2 V_RHE, which are two to three orders of magnitude higher than conventional photo/electrocatalytic N₂ fixation. This study introduces insights for decentralized, on-demand ammonia production from air and water and broadens horizons of microdroplet chemistry and pulse strategy for sustainable chemical manufacturing.