Promoting photocatalytic nitrogen fixation with alkali metal cations and plasmonic nanocrystals

Photocatalytic nitrogen fixation can produce ammonia from nitrogen and water under ambient conditions in the presence of sunlight. Here, we report that alkali metal cations (Li⁺, Na⁺, and K⁺) can significantly promote nitrogen activation and plasmonic nanocrystals (Au and Ag) can sensitize photocatalysts under visible light. The ammonia yield and selectivity on Au/P25 under UV-vis irradiation could be increased from 0.085 mmol g^-1 h^-1 and 75% to 0.43 mmol g^-1 h^-1 and 94.5% when promoted by K⁺, showing a visible-light-driven activity of 0.14 mmol g^-1 h^-1 and an AQE of 0.62% at 550 nm. The activity could be further increased to 1.02 (UV-vis) and 0.32 (visible) mmol g^-1 h^-1 with AQE of 0.93% at 550 nm with methanol added as the sacrificial agent. This strategy could be applied to a series of photocatalysts (e.g. TiO₂, ZnO, and BiOBr) and may represent a general approach for designing efficient nitrogen fixation processes.