On the mechanism of the electrochemical conversion of ammonia to dinitrogen on Pt(1 0 0) in alkaline environment

[Display omitted] •Potential-dependent characterization of adsorbed/desorbed NH3 oxidation products.•NN bond formation takes place via ∗NH dimerization.•The coverage with ∗NH is decisive for the formation of N2.•Strongly adsorbed ∗N and ∗NO inhibit NN formation via ∗NH coupling.•A new reaction scheme, which includes ∗NO formation is proposed. The electrochemical oxidation of ammonia to dinitrogen is a model reaction for the electrocatalysis of the nitrogen cycle, as it can contribute to the understanding of the making/breaking of NN, NO, or NH bonds. Moreover, it can be used as the anode reaction in ammonia electrolyzers for H2 production or in ammonia fuel cells. We study here the reaction on the N2-forming Pt(1 0 0) electrode using a combination of electrochemical methods, product characterization and computational methods, and suggest a mechanism that is compatible with the experimental and theoretical findings. We propose that N2 is formed via an ∗NH + ∗NH coupling step, in accordance with the Gerischer-Mauerer mechanism. Other NN bond-forming steps are considered less likely based on either their unfavourable energetics or the low coverage of the necessary monomers. The NN coupling is inhibited by strongly adsorbed ∗N and ∗NO species, which are formed by further oxidation of ∗NH.