Influence of Anion Adsorption on the Parallel Reaction Pathways in the Oscillatory Electro-oxidation of Methanol

Nagao, Raphael; Cantane, Daniel A.; Lima, Fabio H. B.; Varela, Hamilton

doi:10.1021/jp4028047

Cited by 46 publications

(67 citation statements)

References 46 publications

(96 reference statements)

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“…In spite of the mechanistic similarities, the period 1 oscillations found in the electro‐oxidation of methanol on platinum are only slightly affected by drift 1. 19, 49 All the features caused by the spontaneous drift resemble those associated with an increase of the applied current. Indeed, as observed in a seminal paper, Tributsch and co‐workers2 noted a “striking phenomenological similarity between time‐transient and current‐transient”, and suggested that the spontaneous drift in time is equivalent to that in a galvanodynamic regime.…”

Section: Resultsmentioning

confidence: 99%

“…On the other hand, in typical electrocatalytic reactions, surface processes are pivotal. We have investigated this problem1, 15–19 with the aid of auxiliary experimental techniques15, 19 and developed an empirical method to stabilize transient oscillations 1. 17 The occurrence of uncontrollable changes in the oscillations’ features severely restricts the application of electrochemical oscillators in devices such as fuel cells20–25 and actuators,26 mainly because the systems are in general not reliable in the sense that they oscillate only for a limited number of cycles.…”

Section: Introductionmentioning

confidence: 99%

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Long‐Lasting Oscillations in the Electro‐Oxidation of Formic Acid on PtSn Intermetallic Surfaces

et al. 2014

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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.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Long‐Lasting Oscillations in the Electro‐Oxidation of Formic Acid on PtSn Intermetallic Surfaces

et al. 2014

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“…Comparable slowly evolving process has been also observed for the CO bulk electro-oxidation on platinum. 6,7 This problem has been recently tackled by our group, [8][9][10][11][12][13] and the knowledge acquired allowed to develop an empirical method to compensate the drift in the transient oscillations, experimentally applied to the electro-oxidation of methanol 8 and formaldehyde 12 on platinum in acidic media. a) Author to whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

Coupled slow and fast surface dynamics in an electrocatalytic oscillator: Model and simulations

Nascimento

Nagao

Eiswirth

et al. 2014

The Journal of Chemical Physics

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The co-existence of disparate time scales is pervasive in many systems. In particular for surface reactions, it has been shown that the long-term evolution of the core oscillator is decisively influenced by slow surface changes, such as progressing deactivation. Here we present an in-depth numerical investigation of the coupled slow and fast surface dynamics in an electrocatalytic oscillator. The model consists of four nonlinear coupled ordinary differential equations, investigated over a wide parameter range. Besides the conventional bifurcation analysis, the system was studied by means of high-resolution period and Lyapunov diagrams. It was observed that the bifurcation diagram changes considerably as the irreversible surface poisoning evolves, and the oscillatory region shrinks. The qualitative dynamics changes accordingly and the chaotic oscillations are dramatically suppressed. Nevertheless, periodic cascades are preserved in a confined region of the resistance vs. voltage diagram. Numerical results are compared to experiments published earlier and the latter reinterpreted. Finally, the comprehensive description of the time-evolution in the period and Lyapunov diagrams suggests further experimental studies correlating the evolution of the system's dynamics with changes of the catalyst structure.

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“…The competition for free surface sites coupled with the nonlinear dependence between the surface population of these poisoning species and the electrode potential induces the occurrence of chemical instabilities in these systems [3,4,5]. Examples of this phenomenon have been reported during the electro-oxidation of formic acid [6,7,8,9,10,11,12], formaldehyde [11,13,14,15], methanol [14,16,17,18], ethanol [19], ethylene glycol [20,21] and glycerol [22] in both acid and alkaline media (reference [21] provides a deeper description). Interestingly, the electro-oxidation under oscillatory regime can reveal unique features and even contribute to elucidate some mechanistic aspects, as for instance: the temperature (over)compensation phenomenon during the electro-oxidation of formic acid [8] [6]; the possibility of decoupling the parallel pathways [18,23] and, the direct estimation of kinetic parameter [24,25,26].…”

Section: Introductionmentioning

confidence: 99%

The Electro-Oxidation of Ethylene Glycol on Platinum over a Wide pH Range: Oscillations and Temperature Effects

2013

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We report a comprehensive study of the electro-oxidation of ethylene glycol (EG) on platinum with emphasis on the effects exerted by the electrolyte pH, the EG concentration, and temperature, under both regular and oscillatory conditions. We extracted and discussed parameters such as voltammetric activity, reaction orders (with respect to [EG]), oscillation’s amplitude, frequency and waveform, and the evolution of the mean electrode potential at six pH values from 0 to 14. In addition, we obtained the apparent activation energies under several different conditions. Overall, we observed that increasing the electrolyte pH results in a discontinuous transition in most properties studied under both voltammetric and oscillatory regimes. As a relevant result in this direction, we found that the increase in the reaction order with pH is mediated by a minimum (~ 0) at pH = 12. Furthermore, the solution pH strongly affects all features investigated, c.f. the considerable increase in the oscillatory frequency and the decrease in the, oscillatory, activation energy as the pH increase. We suggest that adsorbed CO is probably the main surface-blocking species at low pH, and its absence at high pH is likely to be the main reason behind the differences observed. The size of the parameter region investigated and the amount of comparable parameters and properties presented in this study, as well as the discussion that followed illustrate the strategy of combining investigations under conventional and oscillatory regimes of electrocatalytic systems.

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Influence of Anion Adsorption on the Parallel Reaction Pathways in the Oscillatory Electro-oxidation of Methanol

Cited by 46 publications

References 46 publications

Long‐Lasting Oscillations in the Electro‐Oxidation of Formic Acid on PtSn Intermetallic Surfaces

Long‐Lasting Oscillations in the Electro‐Oxidation of Formic Acid on PtSn Intermetallic Surfaces

Coupled slow and fast surface dynamics in an electrocatalytic oscillator: Model and simulations

The Electro-Oxidation of Ethylene Glycol on Platinum over a Wide pH Range: Oscillations and Temperature Effects

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