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

Abstract

• ATR-SEIRAS is extended to study the AOR on Ir electrode in basic media. • NH x ,ad species is attributed to the pivot intermediate. • N 2 H x+y ,ad species is identified as the key active intermediate to generate N 2. • NO 2 − and NO 3 − byproducts arise from NO ad oxidation. 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 NH x, ad species to N 2 H x+y, ad species. And the broad and intense Peak II at a higher potential mainly involves the N 2 production from N 2 H x+y, ad species, NO ad species generation from NH x ,ad species and further successive oxidation into the NO 2 − and NO 3 − by-products at higher potentials. It is thus inferred that NH x species are the pivotal intermediates for AOR on Ir electrode, and the N 2 H x+y ,ad and NO ad species the key intermediates for the production of N 2 , NO 2 − and NO 3 − , respectively.