Bioelectrochemical Haber-Bosch Process: An Ammonia-Producing H₂ /N₂ Fuel Cell

Nitrogenases are the only enzymes known to reduce molecular nitrogen (N₂ ) to ammonia (NH₃ ). By using methyl viologen (N,N'-dimethyl-4,4'-bipyridinium) to shuttle electrons to nitrogenase, N₂ reduction to NH₃ can be mediated at an electrode surface. The coupling of this nitrogenase cathode with a bioanode that utilizes the enzyme hydrogenase to oxidize molecular hydrogen (H₂ ) results in an enzymatic fuel cell (EFC) that is able to produce NH₃ from H₂ and N₂ while simultaneously producing an electrical current. To demonstrate this, a charge of 60 mC was passed across H₂  /N₂ EFCs, which resulted in the formation of 286 nmol NH₃  mg^-1 MoFe protein, corresponding to a Faradaic efficiency of 26.4 %.