One of the main challenges is the optimization of the selectivity and reduction of the required overpotential. While the reduction of N2 to NH3 has been studied extensively, the development of molecular ammonia oxidation catalysts has only recently started gaining attention. Several molecular electrocatalysts have been developed to convert ammonia to dinitrogen and hydrogen, the reverse of the Haber-Bosch process. In particular, ruthenium-based molecular catalysts were investigated by several groups, including the ones of Llobet and Bullock. Very recently, the application of non-noble metal-based catalysts, such as iron, nickel and copper, has been explored, opening the possibilities for catalysis with more sustainable systems. Along with the discovery of non-noble metal based catalysts for AO, the replacement of organic solvents with water was investigated. In 2022, the group of Brudvig demonstrated the electrocatalytic transformation of NH3 to NO2 -and NO3 -in a homogeneous electro-catalytic approach with a Cu-complex, with high faradaic efficiencies. Ammonia oxidation in water is not only environmentally friendlier but also offers the opportunity to release 4 equivalents of H2 per ammonia molecule while forming a value-added product (NO3 -), which is used in fertilizers.