A density functional theory study of the mechanism and onset potentials for the major products of NO electroreduction on transition metal catalysts

Highlights: • Electrocatalytic reduction of NO was studied with density functional theory. • Theoretical onset potentials are calculated for planar transition metal surfaces. • Mechanisms via NOH and HNO are key for ammonia and hydroxylamine formation. • Formation of nitrous oxide proceeds via an Eley–Rideal mechanism on most metals. Electrocatalytic reduction of nitrate (NO₃⁻) and other NO_x species is a potential solution to reactive nitrogen pollution. Various products are possible in the electroreduction reaction, however, the mechanisms toward each product are not yet well understood. Herein we explore possible mechanisms from NO toward the formation of major products, NH₄⁺, H₃NOH⁺, and N₂O, on planar transition metal catalysts, using density functional theory; the majority of metals studied produce NH₄⁺ via an NOH intermediate, while for H₃NOH⁺ both NOH and HNO are key intermediates. Onset potentials, scaling relations, and limiting potential volcanoes have been calculated for NH₄⁺ and H₃NOH⁺; it is found that the onset potential of NO reduction is not strongly influenced by the energy of N binding. For N₂O formation, two mechanisms were found to be plausible: a Langmuir–Hinshelwood mechanism, possible on Ag, Au, and Cu, and an Eley–Rideal mechanism, possible on all of the metals studied.