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 %.

We demonstrate a novel hydrogel material to facilitate direct bioelectrochemistry of a wide range of redox proteins and enable ATP-independent electroenzymatic reduction of N ₂ by nitrogenase.