title: Evidence for Decoupled Electron and Proton Transfer in the Electrochemical Oxidation of Ammonia on Pt(100).
abstract: The two traditional mechanisms of the electrochemical ammonia oxidation consider only concerted proton-electron transfer elementary steps and thus they predict that the rate-potential relationship is independent of the pH on the pH-corrected RHE potential scale. In this letter we show that this is not the case: the increase of the solution pH shifts the onset of the NH3-to-N2 oxidation on Pt(100) to lower potentials and also leads to higher surface concentration of formed NOad before the latter is oxidized to nitrite. Therefore, we present a new mechanism for the ammonia oxidation that incorporates a deprotonation step occurring prior to the electron transfer. The deprotonation step yields a negatively charged surface-adsorbed species that is discharged in a subsequent electron transfer step before the N-N bond formation. The negatively charged species is thus a precursor for the formation of N2 and NO. The new mechanism should be a future guide for computational studies aiming at the identification of intermediates and corresponding activation barriers for the elementary steps. Ammonia oxidation is a new example of a bond-forming reaction on (100) terraces that involves decoupled proton-electron transfer.
authors.affiliation: University of Illinois at Urbana-Champaign , Department of Chemistry, 600 South Mathews Avenue, Urbana, Illinois 61801, United States.|Argonne National Laboratory , Materials Science Division, 9700 South Cass Avenue, Lemont, Illinois 60439, United States.|Leiden University , Leiden Institute of Chemistry, Einsteinweg 55, P.O. Box 9502, 2300RA Leiden, The Netherlands.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Katsounaros
authors.affiliation: Leiden University , Leiden Institute of Chemistry, Einsteinweg 55, P.O. Box 9502, 2300RA Leiden, The Netherlands.|Shandong Jianzhu University , School of Science, 250101 Jinan, P. R. China.
authors.forename: Ting
authors.initials: T
authors.lastname: Chen
authors.affiliation: University of Illinois at Urbana-Champaign , Department of Chemistry, 600 South Mathews Avenue, Urbana, Illinois 61801, United States.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Gewirth
authors.affiliation: Argonne National Laboratory , Materials Science Division, 9700 South Cass Avenue, Lemont, Illinois 60439, United States.
authors.forename: Nenad M
authors.initials: NM
authors.lastname: Markovic
authors.affiliation: Leiden University , Leiden Institute of Chemistry, Einsteinweg 55, P.O. Box 9502, 2300RA Leiden, The Netherlands.
authors.forename: Marc T M
authors.initials: MT
authors.lastname: Koper