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Electrocatalytic Oxidation of Ammonia on Transition-Metal Surfaces: A First-Principles Study
journal contribution
posted on 2015-07-02, 00:00 authored by Jeffrey
A. Herron, Peter Ferrin, Manos MavrikakisWe
investigate the catalytic electro-oxidation of ammonia on model
close-packed surfaces of Au, Ag, Cu, Pd, Pt, Ni, Ir, Co, Rh, Ru, Os,
and Re to derive insights for the reaction mechanism and evaluate
the catalysts based on their energy efficiency and activity in the
context of their application in fuel cells. Two mechanisms, which
are differentiated by their N–N bond formation step, are compared:
(1) a mechanism proposed by Gerischer and Mauerer, whereby the N–N
bond formation occurs between hydrogenated NHx adsorbed species, and (2) a mechanism in which N–N
bond formation occurs between N adatoms. The results of our study
show that the mechanism proposed by Gerischer and Mauerer is kinetically
preferred and that the formation of N adatoms poisons the surface
of the catalyst. On the basis of a simple Sabatier analysis, we predict
that Pt is the most active monometallic catalyst followed by Ir and
Cu, whereas all other metal surfaces studied here have significantly
lower activity. We conclude by outlining some design principles for
bimetallic alloy catalysts for NH3 electro-oxidation.