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Title: Evidence for decoupled electron and proton transfer in the electrochemical oxidation of ammonia on Pt(100)

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 NH 3-to-N 2 oxidation on Pt(100) to lower potentials and also leads to higher surface concentration of formed N Oad before the latter is oxidized to nitrite. Therefore, we present a new mechanism for the ammonia oxidation which incorporates a deprotonation step occurring prior to the electron transfer. The deprotonation step yields a negatively charged surface-adsorbed species which 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 N 2 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. As a result, ammonia oxidation is a new example of a bond-forming reaction on (100) terraces which involves decoupled proton-electron transfer.
 [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Univ. of Illinois-Champaign, Urbana, IL (United States); Argonne National Lab. (ANL), Lemont, IL (United States); Leiden Univ., Leiden (The Netherlands)
  2. Leiden Univ., Leiden (The Netherlands); Shandong Jianzhu Univ., Jinan (People's Republic of China)
  3. Univ. of Illinois-Champaign, Urbana, IL (United States)
  4. Argonne National Lab. (ANL), Lemont, IL (United States)
  5. Leiden Univ., Leiden (The Netherlands)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry Letters
Additional Journal Information:
Journal Volume: 7; Journal Issue: 3; Journal ID: ISSN 1948-7185
American Chemical Society
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
ammonia oxidation; bond-forming reactions; nitrogen cycle; pH effects; sequential proton-electron transfer
OSTI Identifier: