Artificial photosynthetic reduction of nitrogen to ammonia at room temperature using natural seawater

Natural photosynthesis uses light and water to fuel cellular activity. While great strides have been made in reproducing elements of photosynthesis, efficiently coupling dinitrogen reduction to ammonia with water oxidation remains challenging. Here we report the light-driven production of ammonia from dinitrogen reduction with a quantum yield of 5.0% in water at normal temperature and pressure by leveraging inexpensive iron(II) salts, which produce solvated electrons upon ultraviolet C light irradiation, to reduce a Mo catalyst. The resulting Fe(III) ions also absorb ultraviolet light and undergo reduction back to Fe(II) while oxidizing water, thus coupling water oxidation with nitrogen reduction. Although the low solubility of nitrogen in water limits catalysis, we circumvented this limitation by using elevated dinitrogen pressures to reach photochemical quantum yields of 10.8%. We further demonstrate this reactivity to operate even in unpurified seawater or in ambient air. The process is calculated to be endoergonic by 329.2 kJ mol^-1 in agreement with a photosynthetic process possessing a light-to-chemical energy conversion efficiency of 7.6%.