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 (NOx⁻, x = 2 and 3) reduction with favorable thermodynamics represents a promising alternative for NH₃ production, provided that NOx⁻ can be supplied from the atmosphere. Here, through leveraging water microdroplet chemistry and dynamic photoelectrode-electrolyte interface engineering, we report a tandem air-NOx⁻-NH₃ conversion system that integrates catalyst-free N₂ oxidation with pulsed photoelectrochemical NOx⁻ reduction (mNOR-pPNOxR). The system achieves efficient and selective NH₃ production with a yield rate of 24.5 μmol cm⁻² h⁻¹ at -0.2 VRHE, 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.