Photocatalytic Conversion of Nitrogen to Ammonia with Water on Surface Oxygen Vacancies of Titanium Dioxide.

Ammonia (NH) is an essential chemical in modern society. It is currently manufactured by the Haber-Bosch process using H and N under extremely high-pressure (>200 bar) and high-temperature (>673 K) conditions. Photocatalytic NH production from water and N at atmospheric pressure and room temperature is ideal. Several semiconductor photocatalysts have been proposed, but all suffer from low efficiency. Here we report that a commercially available TiO with a large number of surface oxygen vacancies, when photoirradiated by UV light in pure water with N, successfully produces NH. The active sites for N reduction are the Ti species on the oxygen vacancies. These species act as adsorption sites for N and trapping sites for the photoformed conduction band electrons. These properties therefore promote efficient reduction of N to NH. The solar-to-chemical energy conversion efficiency is 0.02%, which is the highest efficiency among the early reported photocatalytic systems. This noble-metal-free TiO system therefore shows a potential as a new artificial photosynthesis for green NH production.