Potential oscillations in galvanostatic electrooxidation of formic acid on platinum: a mathematical modeling and simulation.
ABSTRACT We have modeled temporal potential oscillations during the electrooxidation of formic acid on platinum on the basis of the experimental results obtained by time-resolved surface-enhanced infrared absorption spectroscopy (J. Phys. Chem. B 2005, 109, 23509). The model was constructed within the framework of the so-called dual-path mechanism; a direct path via a reactive intermediate and an indirect path via strongly bonded CO formed by dehydration of formic acid. The model differs from earlier ones in the intermediate in the direct path. The reactive intermediate in this model is formate, and the oxidation of formate to CO2 is rate-determining. The reaction rate of the latter process is represented by a second-order rate equation. Simulations using this model well reproduce the experimentally observed oscillation patterns and the temporal changes in the coverages of the adsorbed formate and CO. Most properties of the voltammetric behavior of formic acid, including the potential dependence of adsorbate coverages and a negative differential resistance, are also reproduced.
- SourceAvailable from: Raphael NagaoThe Journal of Physical Chemistry C. 01/2014; 118(31):17699-17709.
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ABSTRACT: In order determine whether formate is a reaction intermediate of the direct pathway for formic acid oxidation at a Pt electrode, formic acid (HCOOH) oxidation at a Pt(111) electrode has been studied by normal and fast scan voltammetry in 0.1 M HClO solutions with different HCOOH concentrations. The relationship between the HCOOH oxidation current density (j) and formate coverage (θ) is quantitatively analyzed. The kinetic simulation reveals that the previously proposed formate pathway, with decomposition of the bridge-bonded formate (HCOO) as a rate determining step (rds), cannot be the main pathway responsible for the majority of the current for HCOOH oxidation. Instead, a kinetic model based on a mechanism with formic acid adsorption , along with simultaneous C-H bond activation as the rds for the direct pathway, explains the measured data well. It was found for the relatively slow rate of formic acid oxidation, that adsorption-desorption of the formate is faster, which competes for the surface sites for formic acid oxidation.Physical Chemistry Chemical Physics 02/2013; 15(12):4367-76. · 3.83 Impact Factor
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ABSTRACT: Even when in contact with virtually infinite reservoirs, natural and manmade oscillators typically drift in phase space on a time-scale considerably slower than that of the intrinsic oscillator. A ubiquitous example is the inexorable aging process experienced by all living systems. Typical electrocatalytic reactions under oscillatory conditions oscillate for only a few dozen stable cycles due to slow surface poisoning that ultimately results in destruction of the limit cycle. We report the observation of unprecedented long-lasting temporal oscillations in the electro-oxidation of formic acid on an ordered intermetallic PtSn phase. The introduction of Sn substantially increases the catalytic activity and retards the irreversible surface oxidation, which results in the stabilization of more than 2200 oscillatory cycles in about 40 h; a 30–40-fold stabilization with respect to the behavior of pure Pt surfaces. The dynamics were modeled and numerical simulations point to the surface processes underlying the high stability.ChemPhysChem 04/2014; · 3.35 Impact Factor