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

Abstract

Electrocatalytic reduction of nitrate (NO3−) and other NOx 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.