Electrochemical Oscillations Research Articles

Oscillating electrochemical reaction in copper-containing imidazolium ionic liquids

An example of an electrochemical oscillator in ionic liquids is presented. Solutions of the ionic liquid 1-ethyl-3-methylimidazolium chloride, [C(2)mim]Cl, which contain both Cu(+) and Cu(2+) ions, show current oscillations during potentiostatic polarization. The oscillations were analyzed by the Quartz Crystal Microbalance (QCM) technique and by Electrochemical Impedance Spectroscopy (EIS). The electrochemical oscillations are of the N-NDR-type, because the low frequency end of the impedance spectrum has negative real impedances. The oscillating current leads to an oscillating growth speed of a metallic copper layer. Besides the presence of both Cu(+) and Cu(2+), the presence of chloride is a necessary, yet not a sufficient, condition for the occurrence of current oscillations. Oscillating currents were also observed for the ionic liquids 1-butyl-3-methylimidazolium chloride and 1-butyl-2,3-dimethylimidazolium chloride, but not for tributyltetradecylphosphonium chloride and N-butylpyridinium chloride.

MULTIPHYSICS MODELING OF IONIC GEL ACTUATORS

ABSTRACTWhen an electrocatalyst, platinum, was coated on ionic-polymer gel surfaces and was immersed into an acidic formaldehyde solution, an input dc current will produce oscillatory ac on the surfaces of the ionic-polymer-metal-composites(IPMC), which eventually causes self-oscillatory bending of the actuators. Typical IPMC actuators have a large length-to-height ratio, exhibiting large deformation during bending and relaxation processes. A multiphysics modeling of self-oscillations of IPMC actuator was carried out, incorporating the electrochemical oscillations, electrokinetics, electrostatics and nonlinear large deformation of the actuators.

Dynamics of electrochemical oscillators with electrode size disparity: asymmetrical coupling and anomalous phase synchronization

Experiments are carried out in dual electrode oscillatory Ni electrodissolution in which the two electrodes have different surface areas. The transition to phase synchronization is analyzed as asymmetrical coupling strength, induced by placing a cross resistance between the electrodes, is varied. It is shown that because of nonisochronicity (phase shear, i.e., strong dependence of period on amplitude) of the oscillators, anomalous phase synchronization effects can be observed: advanced/delayed synchronization and, to a lesser extent, frequency difference enhancement. The type of synchronization is strongly affected by the underlying heterogeneities of the oscillators; in the experiments with a slow driver (large surface area) electrode the synchronization is advanced, with a fast driver electrode the synchronization is delayed with respect to symmetrical coupling. The findings thus reveal that the interplay of asymmetrical coupling with the types of inherent heterogeneities plays an important role for the interpretation of size effects in the dynamical behavior of a nonlinear chemical reaction.

Subharmonic phase clusters in the complex Ginzburg-Landau equation with nonlinear global coupling

A wide variety of subharmonic n -phase cluster patterns was observed in experiments with spatially extended chemical and electrochemical oscillators. These patterns cannot be captured with a phase model. We demonstrate that the introduction of a nonlinear global coupling (NGC) in the complex Ginzburg-Landau equation has subharmonic cluster pattern solutions in wide parameter ranges. The NGC introduces a conservation law for the oscillatory state of the homogeneous mode, which describes the strong oscillations of the mean field in the experiments. We show that the NGC causes a pronounced 2:1 self-resonance on any spatial inhomogeneity, leading to two-phase subharmonic clustering, as well as additional higher resonances. Nonequilibrium Ising-Bloch transitions occur as the coupling strength is varied.

Noise-induced cooperative dynamics and its control in coupled electrochemical models

We have investigated the feedback control of the cooperative dynamics of two coupled electrochemical oscillators that is induced merely by external noise. The interacting electrochemical cells are modeled with parameter values at which no autonomous oscillations occur, and each unit is forced by its own source of random fluctuations. Application of delayed feedback to only one of two subsystems is shown to be able to change the coherence and time scales of noise-induced oscillations either in the given subsystem or globally. It can also induce or suppress stochastic resonance under the certain conditions.

Impact of Fluctuations on Electrochemical Oscillations at Nonoscale Electrodes

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Synchrony and Precision of Chaotic Electrochemical Oscillators: Effects of Temperature and Coupling

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Optimal Waveform for the Entrainment of a Weakly Forced Electrochemical Oscillator

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Effect of temperature on precision of chaotic oscillations in nickel electrodissolution

We investigate the effects of temperature on complexity features of chaotic electrochemical oscillations using the anodic electrodissolution of nickel in sulfuric acid. The precision of the "period" of chaotic oscillation is characterized by phase diffusion coefficient (D). It is shown that reduced phase diffusion coefficient (D/frequency) exhibits Arrhenius-type dependency on temperature with apparent activation energy of 108 kJ/mol. The reduced Lyapunov exponent of the attractor exhibits no considerable dependency on temperature. These results suggest that the precision of electrochemical oscillations deteriorates with increase in temperature and the variation of phase diffusion coefficient does not necessarily correlate with that of Lyapunov exponent. Modeling studies qualitatively simulate the behavior observed in the experiments: the precision of oscillations in the chaotic Ni dissolution model can be tuned by changes of a time scale parameter of an essential variable, which is responsible for the development of chaotic behavior.

Synchronization engineering: tuning the phase relationship between dissimilar oscillators using nonlinear feedback

A mild, nonlinear, time-delayed feedback signal was applied to two heterogeneous oscillators in order to synchronize their frequencies with an arbitrary and controllable phase difference. The feedback was designed using phase models constructed from experimental measurements of the intrinsic dynamical properties of the oscillators. The feedback signal produced an interaction function that corresponds to the desired collective behaviour. The synchronized phase difference between the elements can be tuned to any value on the interval 0 and 2pi by shifting the phase of the interaction function using the feedback delay. Numerical simulations were conducted and experiments carried out with electrochemical oscillators.

Electrochemical Oscillation in Electrohydrodynamic Fluid

We found that electrohydrodynamic (EHD) pressure is affected by a combination of surface conditions and shape of electrodes. A smooth surface of electrodes can generate a higher pressure in the low-current region. Under ac electric fields, rhythmic electrochemical oscillation of current is induced in the dielectric liquid C4F9OCH3. From the ac frequency dependence of rhythmic current, two types of relaxation time appeared. The relaxation times correspond to the Helmholtz layer and diffuse layer, which are regarded as an electric double layer. In the case of pressure as a function of ac frequency, a stable, high pressure was obtained using a smooth surface above the relaxation frequency of the diffuse layer.

Pattern Formation in Electrodeposited Silver-Cadmium Alloys

Electrochemical instabilities and potential oscillations with very high amplitude of up to about 800 mV are observed, which are connected with the simultaneous deposition of different phases of the alloy and intensive hydrogen evolution. The dependence of the potential oscillations on the electrolysis conditions is shown and discussed. Wide variety of spatio-temporal structures can be observed during electrodeposition of silver-cadmium alloys. The conclusion is made that the structures are possibly formed by periodical deposition of pure cadmium phase and very well oriented Cd3Ag phase.

Current oscillations during the anodic dissolution of copper in trifluoroacetic acid

A phenomenon of current oscillators was characterized crosswise active–passive potential region during the electrodissolution of copper electrode in trifluoroacetic acid (TFA). The current density-potential curves show two transition points. A potential region of current oscillations was found as a part of limiting current region. The Cu|TFA electrochemical oscillator was found to displaying rich dynamical response on varying the temperature and the applied potential. The Cu|TFA system display current oscillation behaviour from the mono-periodic to the mixed-mode (relaxation type). Changes of the electrode surface structure and morphology were investigated by X-ray diffraction spectroscopy, atomic forced microscopy and optical microscopy.

Observed Electrochemical Oscillations during the Catalytic Oxidation of Aqueous Sulfur Dioxide on a Platinum Electrode Surface

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An automated algorithm for the generation of dynamically reconstructed trajectories

The lack of long enough data sets is a major problem in the study of many real world systems. As it has been recently shown [C. Komalapriya, M. Thiel, M. C. Romano, N. Marwan, U. Schwarz, and J. Kurths, Phys. Rev. E 78, 066217 (2008)], this problem can be overcome in the case of ergodic systems if an ensemble of short trajectories is available, from which dynamically reconstructed trajectories can be generated. However, this method has some disadvantages which hinder its applicability, such as the need for estimation of optimal parameters. Here, we propose a substantially improved algorithm that overcomes the problems encountered by the former one, allowing its automatic application. Furthermore, we show that the new algorithm not only reproduces the short term but also the long term dynamics of the system under study, in contrast to the former algorithm. To exemplify the potential of the new algorithm, we apply it to experimental data from electrochemical oscillators and also to analyze the well-known problem of transient chaotic trajectories.

Sympathetic current oscillations at an enzyme electrode induced by potential oscillations at a Pt surface

A dual-electrode set-up is introduced in order to demonstrate that electrochemical oscillations at one electrode can induce sympathetic oscillations at the other electrode. A pure Pt surface is used as a primary electrode at which the potential oscillations of the [ Fe ( CN ) 6 ] 3 - system with convective feedback occur and stimulate current oscillations at a Pt or glucose oxidase enzyme (GOD) + tetraethyl silicate (TEOS) coated electrode placed in the vicinity. The current density of the primary electrode and glucose concentration can be used to influence the frequency and amplitude of oscillations at the GOD + TEOS electrode.

Chaotic Synchronization under Unidirectional Coupling: Numerics and Experiments

Synchronization for a pair of chaotic oscillators is studied both numerically and experimentally. The two oscillators are coupled unidirectionally, namely, in the master slave configuration. When the coupling strength is systematically varied, different regimes of chaotic synchronization such as no, phase, lag and complete are identified. The existence of natural lag synchronization for unidirectional coupling is by virtue of a small parameter mismatch between the master and the slave oscillators. Numerical calculations are carried out in the Rössler model whereas the experiments are performed using a pair of electrochemical oscillators.

Desynchronization and clustering with pulse stimulations of coupled electrochemical relaxation oscillators

Effects of pulse stimulations on the dynamics of relaxation oscillator populations were experimentally studied in a globally coupled electrochemical system. Similar to smooth oscillations, weakly and moderately relaxational oscillations possess a vulnerable phase, ϕ S ; pulses applied at ϕ S resulted in desynchronization followed by a return to the synchronized state. In contrast to smooth oscillators, weakly and moderately relaxational oscillators exhibited transient and itinerant cluster dynamics, respectively. With strongly relaxational oscillators the pulse applied at a vulnerable phase effected transitions to other cluster configurations without effective desynchronization. Repeated pulse administration resulted in a cluster state that is stable against the perturbation; the cluster configuration is specific to the pulse administered at the vulnerable phase. The pulse-induced transient clusters are interpreted with a phase model that includes first and second harmonics in the interaction function and exhibits saddle type cluster states with strongly stable intra-cluster and weakly unstable inter-cluster modes.

Arnold Tongue of Electrochemical Nonlinear Oscillators

We study the Arnold tongue of a nonlinear electrochemical oscillator entrained to an electrical periodic forcing. In our system, the width of the 1:3 entrainment region was broader than that of the 1:2 region. The 1:1 and 1:3 regions became monotonically broad when the conductance of the electrode cell was increased by the electrochemical redox reaction of Fe(CN)(6)(4-) <==> Fe(CN)(6)(3-) + e. In contrast, the 1:2 region changed nonmonotonically. In particular, the rate of change in the 1:2 region was greater than those of the 1:1 and 1:3 regions. These experimental results were qualitatively reproduced by the use of phase response curves of a corresponding mathematical model. We also discuss higher harmonics included in a limit cycle describing the isolated oscillator, dependence on the redox reaction, and hysteresis due to a bistability.

New electrochemical oscillator based on the cation-catalyzed reduction of nitroaromatic radical anions

Nitroaromatic compound bifenox (methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate) is used as a model system for a new NDR oscillator in the aprotic solvent acetonitrile. The reduction of bifenox yields the anion radical, which is further reduced by an overall addition of three electrons and four protons to the corresponding phenylhydroxylamine. The second reduction step is strongly influenced by the nature and concentration of the tetraalkylammonium salts used as the supporting electrolytes. At the low concentration of tetrahexylammonium hexafluorophosphate the anion radical reduction occurs at extremely negative potentials due to the double-layer effect on the negatively charged reactant. An addition of small amounts of the alkali metal cations (Li +, Na + and K +) to such a system has a remarkable acceleration effect on the electron transfer rate since these ions undergo pairing with in situ generated anion radicals and the double-layer effect on the resulting particles of a diminished charge is much weaker. At potentials where alkali metal cations are reduced to the corresponding amalgams the acceleration ceases. As a result the current–potential curves show a negative slope. Electrochemical impedance spectroscopy sensitively indicates the presence of the negative differential charge transfer resistance (NDR). The addition of a high external resistor in series with the electrochemical cell leads to the current oscillations at the stationary mercury electrode and to the current instabilities on the dropping mercury electrode. Described system is a new example of the NDR oscillator, in which the double-layer effect in connection with cationic catalysis rather than anionic catalysis plays a crucial role in the observation of NDR.