Despite the fact that the majority of the catalytic electro-oxidation of small organic molecules presents oscillatory kinetics under certain conditions, there are few systematic studies concerning the influence of experimental parameters on the oscillatory dynamics. Of the studies available, most are devoted to C1 molecules and just some scattered data are available for C2 molecules. We present in this work a comprehensive study of the electro-oxidation of ethylene glycol on polycrystalline platinum surfaces and in alkaline media. The system was studied by means of electrochemical impedance spectroscopy, cyclic voltammetry, and chronoamperometry, and the impact of parameters such as applied current, ethylene glycol concentration, and temperature were investigated. As in the case of other parent systems, the instabilities in this system were associated with a hidden negative differential resistance, as identified by impedance data. Very rich and robust dynamics were observed, including the presence of harmonic and mixed mode oscillations and chaotic states, in some parameter region. Oscillation frequencies of about 16 Hz characterized the fastest oscillations ever reported for the electro-oxidation of small organic molecules. Those high frequencies were strongly influenced by the electrolyte pH and far less affected by the EG concentration. The system was regularly dependent on temperature under voltammetric conditions but rather independent within the oscillatory regime.

We report a detailed numerical investigation of a prototype electrochemical oscillator, in terms of high-resolution phase diagrams for an experimentally relevant section of the control (parameter) space. The prototype model consists of a set of three autonomous ordinary differential equations which captures the general features of electrochemical oscillators characterized by a partially hidden negative differential resistance in an N-shaped current-voltage stationary curve. By computing Lyapunov exponents, we provide a detailed discrimination between chaotic and periodic phases of the electrochemical oscillator. Such phases reveal the existence of an intricate structure of domains of periodicity self-organized into a chaotic background. Shrimp-like periodic regions previously observed in other discrete and continuous systems were also observed here, which corroborate the universal nature of the occurrence of such structures. In addition, we have also found a structured period distribution within the order region. Finally we discuss the possible experimental realization of comparable phase diagrams.

The study of complex reaction under oscillatory conditions has been proven to be useful in uncovering features that are hidden under close to equilibrium regime. In particular, for the electro-oxidation of small organic molecules on platinum and platinum-based surfaces, such investigations have provided valuable mechanistic information, otherwise unavailable under nonoscillatory conditions. We present here the dynamics of production of volatile species along the oscillatory electro-oxidation of formic acid, methanol, and ethanol on platinum, as measured by online differential electrochemical mass spectrometry (DEMS). Besides the presentation of previously unreported DEMS results on the oscillatory dynamics of such systems, we introduce the use of multivariate linear regression to compare the estimated total faradaic current with the one comprising the production of volatile species, namely: carbon dioxide for formic acid, carbon dioxide and methylformate for methanol, and carbon dioxide and acetaldehyde for ethanol. The introduced analysis provided the best combination of the DEMS ion currents to represent the total faradaic current, or, equivalently, the maximum possible faradaic contribution of the volatile products for the global current. The mismatch between estimated total current and the one obtained by the best combination of partial currents of volatile products was found to be small for formic acid, 4 and 5 times bigger for ethanol and methanol, respectively, evidencing the increasing role played by partially oxidized, soluble species in each case. These results were discussed in connection with the mechanistic aspects of each system. Moreover, we have defined some descriptors to account for the production of volatile species, and discussed dynamics in terms of sample and populational covariances

Particle-particle particle-mesh method for dipolar interactions: On error estimates and efficiency of schemes with analytical differentiation and mesh interlacing J. Chem. Phys. 135, 184110 (2011) Revisiting falloff curves of thermal unimolecular reactions J. Chem. Phys. 135, 054304 (2011) Collision limited reaction rates for arbitrarily shaped particles across the entire diffusive Knudsen number range J. Chem. Phys. 135, 054302 (2011) Simulating structural transitions by direct transition current sampling: The example of LJ38 J. Chem. Phys. 135, 034108 (2011) Optimizing transition interface sampling simulations J. Chem. Phys. 134, 244118 (2011) Additional information on J. Chem. Phys. A mechanism for the kinetic instabilities observed in the galvanostatic electro-oxidation of methanol is suggested and a model developed. The model is investigated using stoichiometric network analysis as well as concepts from algebraic geometry ͑polynomial rings and ideal theory͒ revealing the occurrence of a Hopf and a saddle-node bifurcation. These analytical solutions are confirmed by numerical integration of the system of differential equations.

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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