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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 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.

Authors:
 [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:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1248379
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry Letters
Additional Journal Information:
Journal Volume: 7; Journal Issue: 3; Journal ID: ISSN 1948-7185
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
ammonia oxidation; bond-forming reactions; nitrogen cycle; pH effects; sequential proton-electron transfer

Citation Formats

Katsounaros, Ioannis, Chen, Ting, Gewirth, Andrew A., Markovic, Nenad M., and Koper, Marc T. M.. Evidence for decoupled electron and proton transfer in the electrochemical oxidation of ammonia on Pt(100). United States: N. p., 2016. Web. doi:10.1021/acs.jpclett.5b02556.
Katsounaros, Ioannis, Chen, Ting, Gewirth, Andrew A., Markovic, Nenad M., & Koper, Marc T. M.. Evidence for decoupled electron and proton transfer in the electrochemical oxidation of ammonia on Pt(100). United States. doi:10.1021/acs.jpclett.5b02556.
Katsounaros, Ioannis, Chen, Ting, Gewirth, Andrew A., Markovic, Nenad M., and Koper, Marc T. M.. Tue . "Evidence for decoupled electron and proton transfer in the electrochemical oxidation of ammonia on Pt(100)". United States. doi:10.1021/acs.jpclett.5b02556. https://www.osti.gov/servlets/purl/1248379.
@article{osti_1248379,
title = {Evidence for decoupled electron and proton transfer in the electrochemical oxidation of ammonia on Pt(100)},
author = {Katsounaros, Ioannis and Chen, Ting and Gewirth, Andrew A. and Markovic, Nenad M. and Koper, Marc T. M.},
abstractNote = {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 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 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. As a result, ammonia oxidation is a new example of a bond-forming reaction on (100) terraces which involves decoupled proton-electron transfer.},
doi = {10.1021/acs.jpclett.5b02556},
journal = {Journal of Physical Chemistry Letters},
number = 3,
volume = 7,
place = {United States},
year = {2016},
month = {1}
}

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