Mechanism and Active Species in NH₃ Dehydrogenation under an Electrochemical Environment: An Ab Initio Molecular Dynamics Study

The electrochemical ammonia oxidation reaction (AOR) has attracted considerable attention in the past decades. However, the AOR mechanism on the electrode surface is still ambiguous, and the identification of reactive OH species during dehydrogenation reactions is under debate. Herein we combined density functional theory-based ab initio molecular dynamics simulations with free-energy sampling method slow-growth to study the stepwise dehydrogenation from NH₃ to N during the electrochemical AOR on Pt(100). We found that the dehydrogenation assisted by adsorbed OH is almost insensitive to potentials applied, while the dehydrogenation by OH in bulk water is potential-dependent and the barrier of such reactions would increase with lowering the potentials. Our results revealed that the adsorbed OH is the reactive species during NH₃ dehydrogenation under reaction conditions rather than OH^– in bulk water. These findings bring new insights into the fundamental understandings of the AOR process under realistic electrochemical conditions.