AbstractThe removal of nitric oxide is an important environmental issue, as well as a necessary prerequisite for achieving high efficiency of CO₂ electroreduction. To this end, the electrocatalytic denitrification is a sustainable route. Herein, we employ reaction phase diagram to analyze the evolution of reaction mechanisms over varying catalysts and study the potential/pH effects over Pd and Cu. We find the low N₂ selectivity compared to N₂O production, consistent with a set of experiments, is limited fundamentally by two factors. The N₂OH* binding is relatively weak over transition metals, resulting in the low rate of as-produced N₂O* protonation. The strong correlation of OH* and O* binding energies limits the route of N₂O* dissociation. Although the experimental conditions of varying potential, pH and NO pressures can tune the selectivity slightly, which are insufficient to promote N₂ selectivity beyond N₂O and NH₃. A possible solution is to design catalysts with exceptions to break the scaling characters of energies. Alternatively, we propose a reverse route with the target of decentralized ammonia synthesis.