Photocatalytic Dinitrogen Fixation with Water on Bismuth Oxychloride in Chloride Solutions for Solar-to-Chemical Energy Conversion

Ammonia is an indispensable chemical. Photocatalytic NH₃ production via dinitrogen fixation using water by sunlight illumination under ambient conditions is a promising strategy, although previously reported catalysts show insufficient activity. Herein, we showed that ultraviolet light irradiation of a semiconductor, bismuth oxychloride with surface oxygen vacancies (BiOCl-OVs), in water containing chloride anions (Cl^-) under N₂ flow efficiently produces NH₃. The surface OVs behave as the N₂ reduction sites by the photoformed conduction band electrons. The valence band holes are consumed by self-oxidation of interlayer Cl^- on the catalyst. The hypochloric acid (HClO) formed absorbs ultraviolet light and undergoes photodecomposition into O₂ and Cl^-. These consecutive photoreactions produce NH₃ with water as the electron donor. The Cl^- in solution compensates for the removed interlayer Cl^- and inhibits catalyst deactivation. Simulated sunlight illumination of the catalyst in seawater stably generates NH₃ with 0.05% solar-to-chemical conversion efficiency, thus exhibiting significant potential of the seawater system for artificial photosynthesis.