Nitrogenases are the only enzymes known to reduce molecular nitrogen (N-2) to ammonia (NH3). By using methyl viologen (N, N'-dimethyl-4,4'-bipyridinium) to shuttle electrons to nitrogenase, N-2 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 (H-2) results in an enzymatic fuel cell (EFC) that is able to produce NH3 from H-2 and N-2 while simultaneously producing an electrical current. To demonstrate this, a charge of 60 mC was passed across H-2/ N-2 EFCs, which resulted in the formation of 286 nmol NH3 mg (-1) MoFe protein, corresponding to a Faradaic efficiency of 26.4%.