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 %.
Keywords: Haber-Bosch process; ammonia; fuel cells; nitrogen reduction; nitrogenase.
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