Bioelectrochemical Haber–Bosch Process: An Ammonia‐Producing H 2 /N 2 Fuel Cell

Nitrogenases are the only enzymes known to reduce molecular nitrogen (N 2 ) to ammonia (NH 3 ). By using methyl viologen ( N , N ′‐dimethyl‐4,4′‐bipyridinium) to shuttle electrons to nitrogenase, N 2 reduction to NH 3 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 NH 3 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 NH 3  mg −1 MoFe protein, corresponding to a Faradaic efficiency of 26.4 %.