Lithium-Mediated Photoelectrochemical Ammonia Synthesis with 95% Selectivity on Silicon Photocathode

Ammonia synthesis via the energy-intensive Haber–Bosch process contributes to ∼1.8% global carbon emission. To this end, photoelectrochemical (PEC) ammonia synthesis using solar energy is an attractive alternative technique to significantly reduce carbon emission. Nevertheless, the PEC process is still limited by the low Faradaic efficiency and insufficient ammonia formation rate. Herein, we report a lithium-mediated PEC device composed of a Si photocathode and Li ions as the reduction mediator to show efficient nitrogen reduction into ammonia with a Faradaic efficiency of 95% and an ammonia yield rate of 52.4 μg cm–2 h–1 under ambient conditions. Our mechanistic studies reveal that the Si photocathode under light illumination provides photogenerated electrons to reduce Li+ ions into metallic Li and then initiates the Li-mediated nitrogen reduction process, where the solid electrolyte interphase (SEI) facilitates homogeneous lithium plating. This work offers a promising solar-driven catalytic system for ammonia synthesis under ambient conditions.