Issue 13, 2016

On the mechanism of electrochemical ammonia synthesis on the Ru catalyst

Abstract

We theoretically investigate the electrochemical N2 reduction reaction (NRR) mechanism to produce NH3 on the Ru catalyst. All possible N–N dissociation steps during the reduction processes were evaluated along with the conventional associative and dissociative pathways. Based on the calculated free energy diagrams, it is revealed that the kinetically facile intermediate dissociative pathways during the NRR require a thermodynamic limiting potential (−0.71 V) similar to the associative pathway (−0.68 V), although the initial dissociative pathway as in the Haber–Bosch process has a substantial kinetic barrier for the N–N bond dissociation. The competitive hydrogen evolution is found to be a major hurdle for achieving a high efficiency for the electrochemical nitrogen reduction. In the low overpotential region, the hydrogen adsorption is thermodynamically more favorable than the protonation of N2, thereby reducing the number of active sites for the N2 activation. A comparison of free energies in the presence of different H-coverages on the Ru further demonstrates that the H-coverage can significantly increase the energy barrier for the first protonation of N2, resulting in a change of the potential determining step and an increase in the overpotentials.

Graphical abstract: On the mechanism of electrochemical ammonia synthesis on the Ru catalyst

Supplementary files

Article information

Article type
Paper
Submitted
30 nov 2015
Accepted
29 feb 2016
First published
01 mrt 2016

Phys. Chem. Chem. Phys., 2016,18, 9161-9166

On the mechanism of electrochemical ammonia synthesis on the Ru catalyst

S. Back and Y. Jung, Phys. Chem. Chem. Phys., 2016, 18, 9161 DOI: 10.1039/C5CP07363D

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