Ammonia (NH3) is one of the most widely produced chemicals worldwide. It has application in the production of many important chemicals, particularly fertilizers. It is also, potentially, an important energy storage intermediate and clean energy carrier. Ammonia production, however, mostly uses fossil fuels and currently accounts for more than 1.6% of global CO₂ emissions (0.57  Gt in 2015). Here we describe a solar-driven nanostructured photoelectrochemical cell based on plasmon-enhanced black silicon for the conversion of atmospheric N₂ to ammonia producing yields of 13.3 mg m^-2h^-1 under 2 suns illumination. The yield increases with pressure; the highest observed in this work was 60 mg m^-2 h^-1 at 7 atm. In the presence of sulfite as a reactant, the process also offers a direct solar energy route to ammonium sulfate, a fertilizer of economic importance. Although the yields are currently not sufficient for practical application, there is much scope for improvement in the active materials in this cell.

Nature Communications 7, Article number: 11335 doi:10.1038/ncomms11335
Received 17 November 2015 Accepted 16 March 2016 Published 20 April 2016

http://www.nature.com/ncomms/2016/160420/ncomms11335/full/ncomms11335.html