The oscillatory electro-oxidation
of methanol was studied on polycrystalline
Ptpc and Ptpc/Rh2.0/Pt1.0 metallic multilayers. The surfaces investigated consisted of 1.0
Pt outlayer surface deposited onto 2.0 Rh intralayers beneath a Pt
outlayer and over the polycrystalline Ptpc substrate. In
addition to experimental studies, numerical simulations were performed
using a dimensionless kinetic model for the electro-oxidation of methanol
in order to provide a better understanding of the role played by the
nanostructured metallic multilayer electrode in the electrocatalytic
activity. A comparable electrochemical behavior found for cyclic voltammetry
in blank acidic media was observed in both electrodes. Remarkably,
an increase of 90% in the peak current density around 0.88 V vs. RHE
in the electro-oxidation of methanol appeared when Ptpc/Rh2.0/Pt1.0 was utilized. The numerical simulations
suggested that this increase in the electrocatalytic activity for
the metallic multilayer electrode is due to the prevention of carbon
monoxide adsorption on the surface and a consequent increase in the
production of carbon dioxide from the direct pathway. Indeed, a decrease
in the reaction rate constant of carbon monoxide formation resulted
in an increase of the current density associated with CO2 formation in the potentiodynamic sweep, in addition to the decrease
in amplitude and frequency of the oscillatory time series. As the
rate of carbon monoxide adsorption is suppressed by the presence of
the metallic multilayers, the intrinsic drift usually found in the
oscillatory electro-oxidation of methanol was enhanced and oscillations
ceased earlier. Overall, the combination of electrochemical experiments
and numerical simulations suggests that carbon monoxide acts as a
poisoning species instead of a reaction intermediate in the electro-oxidation
of methanol.
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