Ammonia oxidation on iridium electrode in alkaline media: An in situ ATR-SEIRAS study

Mechanistic understanding of electrochemical ammonia oxidation reaction (AOR) is important for designing efficient AOR catalysts. In this work, in situ attenuated total reflection surface-enhanced infrared spectroscopy (ATR-SEIRAS) is employed to study the AOR at varied potentials on an Ir electrode in alkaline media. The AOR on Ir contains two sequential oxidation peaks in the anodic voltammograms. The in situ ATR-SEIRAS results indicate that the small Peak I at a lower potential is mainly due to dehydrogenation of interfacial ammonia and dimerization of as-generated NHx,ad species to N2Hx+y,ad species. And the broad and intense Peak II at a higher potential mainly involves the N2 production from N2Hx+y,ad species, NOad species generation from NHx,ad species and further successive oxidation into the NO2− and NO3− by-products at higher potentials. It is thus inferred that NHx species are the pivotal intermediates for AOR on Ir electrode, and the N2Hx+y,ad and NOad species the key intermediates for the production of N2, NO2− and NO3−, respectively.