The Haber-Bosch process, responsible for producing NH₃ from H₂ and N₂, ranks as one of the most important discoveries in the history of chemistry. Its industrial application in synthetic fertilizers contributed to the continuously increasing population and their quality of life. The Haber-Bosch process, however, is a very energy-intensive process with high temperature (500 °C) and pressure (20 MPa) required for efficient NH₃ production. Over 1 % of the world’s energy sources were consumed in order to produce ~140 megatons of NH₃ in 2015. Additionally, 3 % of global CO₂ emissions are due to the Haber-Bosch related technology. A renewable strategy for ammonia production would therefore be valuable.

In nature, the ability to reduce N₂ to NH₃ is limited to a group of bacteria and archaea classified as diazotrophs, all of which share an enzyme called nitrogenase. Using methylviologen (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 which 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, 60 mC of charge 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 %. Importantly, this EFC produces NH₃ and electrical energy in a carbon-neutral manner.

A protective FeSII protein, which can reversibly lock nitrogenase into a multicomponent protective complex upon exposure to low concentrations of O₂, was incorporated into a nitrogenase bioelectrosynthetic cell whereby NH₃ was produced using air as a substrate. This marks a significant step forward in overcoming the crippling limitation of nitrogenase’s sensitivity toward O₂.