A theoretical study of the effect of a non-aqueous proton donor on electrochemical ammonia synthesis

Abstract

Ammonia synthesis is one of the most studied reactions in heterogeneous catalysis. To date, however, electrochemical N₂ reduction in aqueous systems has proven to be extremely difficult, mainly due to the competing hydrogen evolution reaction (HER). Recently, it has been shown that transition metal complexes based on molybdenum can reduce N₂ to ammonia at room temperature and ambient pressure in a non-aqueous system, with a relatively small amount of hydrogen output. We demonstrate that the non-aqueous proton donor they have chosen, 2,6-lutidinium (LutH⁺), is a viable substitute for hydronium in the electrochemical process at a solid surface, since this donor can suppress the HER rate. We also show that the presence of LutH⁺ can selectively stabilize the *NNH intermediate relative to *NH or *NH₂via the formation of hydrogen bonds, indicating that the use of non-aqueous solvents can break the scaling relationship between limiting potential and binding energies.