Electrochemical Oscillations Research Articles

Electrochemical Oscillation during Galvanostatic Charging of LiCrTiO4 in Li-Ion Batteries.

In the late 1960s, the establishment of Prigogine’s dissipative structure theory laid the foundation for the (electro)chemical oscillation phenomenon, which has been widely investigated in some electrochemical reactions, such as electro-catalysis and electro-deposition, while the electrochemical oscillation of Li-ion batteries has just been discovered in spinel Li4Ti5O12 a few years before. In this work, spinel LiCrTiO4 samples were synthesized by using a high-temperature solid-state method, characterized with SEM (Scanning electron microscope), XRD (X-ray diffraction), Raman and XPS (X-ray photoelectron spectroscopy) measurements, and electrochemically tested in Li-ion batteries to study the electrochemical oscillation. When sintering in a powder form at a temperature between 800 and 900 °C, we achieved the electrochemical oscillation of spinel LiCrTiO4 during charging, and it is suppressed in the non-stoichiometric LiCrTiO4 samples, especially for reducing the Li content or increasing the Cr content. Therefore, this work developed another two-phase material as the powder-sintered LiCrTiO4 exhibiting the electrochemical oscillation in Li-ion batteries, which would inspire us to explore more two-phase electrode materials in Li-ion batteries, Na-ion batteries, etc.

Emergence of Temporal Instabilities during Electro-Dissolution of Nickel-Iron Alloy

Dynamics instabilities are often observed in many systems, such as biological, chemical, physical, and others. Some very commons examples are the circadian rhythms that regulates biological process during the rotation of the Earth every 24 hours, and dunes formations where the topographical structures are built with large masses of sand accumulated. These instabilities can be classified as spatial, where the vicinity affect the emergence of instabilities, and temporal, when the instabilities are time dependent. In chemical systems there is a well-known Belousov-Zhabotinsky reaction where the instabilities rise between citric acid, bromate ions and ceric ions (or similar set of substances) and is possible to emerge spatial and temporal instabilities.Among many chemical systems the electrochemical has been of great interest due to the fine adjustment that is possible by the potential or current control. Another advantage is that electrochemical setup is relatively simple, formed in most cases by a working electrode, counter-electrode and reference electrode emerging from an electrolyte inside a container. Anodic dissolution of metals has been studied since 1828, with the reports by Fechner. Many studies were performed using different metals like Cu, Fe, Ni, among others, as electrochemical oscillators using single or multielectrode configuration coupled under different network topologies, where the latter configuration has been made often using similar electrodes. In this present work, we report experimental studies of the coupling between two different electrochemical oscillators during the electro-dissolution of Ni and Fe, not as two separated electrodes but like an alloy.To perform the experiments was utilized a glass electrochemical cell with 3 electrodes, a platinum sheet as counter-electrode, a saturated calomel electrode as reference electrode, and a Ni-Fe(80-20) alloy embedded in Teflon with a cylindrical shape and a diameter of 0.5 cm as working electrode. For comparison, all experiments were performed also using a pure Ni and a pure Fe with the same geometry of the alloy as working electrode. All experiments were carried out using H2SO4 1 mol L-1 as electrolyte and before each electrochemical experiment the working electrode was polished to ensure that the surface will be the same, i.e., the absent of oxides and other substances on the surface. The phenomenon observed during the experiments is described in terms of stationary and dynamic electrochemical techniques such as chronoamperometry and cyclic voltammetry, varying the external resistance Rext of the system. For each Rext applied there is a different potential range where the oscillations occur during cyclic voltammetry and by different Rext applied was built a bifurcation diagram (Rext vs. E). In each region of oscillations was performed chronoamperometry experiments, choosing different potential applied values, where is possible to note the electrode potential change, revealing that occurs a separation of the activation and passivation processes during an oscillatory cycle.Comparing with the Ni and Fe pure electrodes, these results suggest that there is a change in the mechanism during the emergence of the oscillations in the Ni-Fe alloy. For the alloy at low potentials, there is a mixed contribution from both Ni and Fe dissolution on the oscillations, that occurs before the Flade potential, while the pure Ni dissolution occurs in the transpassive domain with range of ~1.2 to 1.5 V vs. SCE (both with Rext 392 Ω cm2) and the pure Fe dissolution ~0.4 to 0.6 vs. SCE (without Rext). The mixed contribution produced by Ni and Fe in the alloy during the oscillatory electro-dissolution are caused because of their oxides and salts present in the passivation step, which impacts on the instabilities generated during the nonlinear dynamics of the system. With these results we can conclude that a small amount of Fe (only 20%) on the Ni electrode at electro-dissolution process is enough to induce a change in the mechanism during the emergence of oscillations, suggesting that a new process is taking place, from high potentials for Ni (~1.2 to 1.5 V) to lower overpotentials for Ni-Fe alloy (~-0.1 to 0.1 V). Also, there is a suppression of the transpassive state, i.e, is observed in pure Ni and absent in the Ni-Fe alloy. The Figure compares the shape and period of the oscillations for each electrode at some fixed potentials, Ni (a), Ni-Fe (b), and Fe (c).As perspectives of the work we are working to observe the instabilities using other conditions to be able to understand more deeply the mechanism found by the Ni-Fe alloy. We also intend to develop simulations to describe this phenomenon more accurately. Figure 1

The Use of Multivariate Analysis for Accurate Control of the Oscillation Frequency of Homogeneous and Heterogeneous Systems

The control of the frequency of oscillation from experimental parameters is extremely important for a better understanding of how oscillatory systems work. Knowing this, much effort has been made to understand the effect of experimental parameters on it. Two-dimensional diagrams are constructed by varying each parameter individually, while the others are kept constant. However, as these oscillators have many control parameters, the use of multivariate statistical analysis is necessary for the accurate selection of the oscillation frequency. In addition, through this analysis it is possible to measure the possible synergistic combinations between the experimental parameters. Knowing this, in this work we performed a multivariate statistical analysis of homogeneous and heterogeneous oscillators. The homogeneous oscillator used is the Belousov-Zhabotinsky reaction while the heterogeneous system is an electrochemical deposition of Cu/Cu2OThe experiments of the homogeneous system (BZ reaction) were performed by a CSTR to keep the frequency of oscillation constant. For the experiments, two solutions were used, one of NaBrO3 and H2SO4 and the other of malonic acid (MA) and ferroin. These solutions were pumped by a peristaltic pump in a cuvette. The oscillations were monitored with a UV-visible spectrophotometer (λ=520nm). The experiments were conducted by a factorial design 23 with a central point in which the parameters analyzed were [NaBrO3], [MA] and temperature.The experiments of the heterogeneous system (Cu/Cu2O oscillatory deposition) were carried out in an electrochemical cell with three electrodes. These are a platinized-platinum foil as a counter electrode, a saturated calomel electrode as a reference electrode and a polycrystalline platinum sheet as a working electrode. The solution used was Cu(II) lactate (0.5mol L-1 + 2.50 mol L-1 of lactate) was prepared and was left under stirring for 4 days at 2000 RPM. The experiments were conducted according to Central Composite Design (CCD), with the axial distance set at α = 1. The factors were defined as pH, current density, and temperature.The factorial design 23 with the central point for the BZ reaction observed in Figure-1a shows that the dependence of the experimental parameters on the frequency is linear. We also see in Figure-1c that the parameter that most affected the oscillation frequency was [NaBrO3] followed by the temperature. Another important information that we observed in this graph is that there is a synergistic effect between [NaBrO3] and temperature, which is information that is not obtained through univariate analysis.The CDD used for the electrochemical system demonstrated a dependence on a wide combination of parameters, resulting in quadratic terms. This quadratic dependency can be seen in Figure-1b, d. We note that the parameter that most affects the frequency of oscillation is the current density followed by the pH. It is evident that the interaction effects demonstrated by this type of analysis contribute to the non-linearity of the system.The differences observed between the oscillators in which the most evident is the linearity of the oscillation frequency with the experimental parameters for the BZ reaction and the quadratic dependence on the oscillatory deposition of Cu/Cu2O can be attributed to the intrinsic nature of the oscillators. For the BZ reaction, the reaction rate constants are kept unchanged during oscillations. The oscillatory system, however, the rate constants are described by the Butler-Volmer kinetics and, therefore, exhibit a potential dependency. In addition, it is necessary to consider the mass transport processes present in the electrochemical system that is absent in the BZ reaction. It is also important to note that the electrochemical oscillators show a transient time series, even though we used the most stable region of the time series. All these characteristics justify the differences observed between the chemical and electrochemical oscillatory systems.The observed results can contribute, for example, in the synthesis of self-organized materials, in which an accurate selection of frequencies is necessary and, depending on their value, different physicochemical properties are obtained. In addition, the results demonstrate the importance of using multivariate statistical analysis due to the possibility of measuring the interactions between experimental parameters. Figure 1

Spatiotemporal Patterns of Oscillatory Electrochemical Reactions in the Presence of a Low-Pass Filter

In many electrochemical measurements, the measured signals are often filtered to remove experimental noise, for example, with a low-pass filter (LPF). At the same time, various electrical coupling (potential drop in the electrolyte) and feedback (galvanostatic constraints) effects can generate spatiotemporal patterns. In this contribution, we study the synchronization patterns of electrochemical oscillators induced by feedback in the presence of a low-pass filter. Close to a Hopf bifurcation, without the filter, as expected[1], the synchronization transition took place above a critical coupling strength following a second-order phase (Kuramoto) transition. With LPF, the transition occurred through explosive synchronization, which corresponds to a first-order phase transition and multistability between synchronized and desynchronized states. These experimental results confirm recent theoretical development on the impact of LPF on the synchronization of Stuart-Landau oscillators[2]. Further away from Hopf bifurcation, the LPF can generate patterns with one- and two-cluster states from a desynchronized state. The cluster formation and stability can be understood using a theory that estimates the LPF induced amplitude attenuation and phase shift of the coupling functions in the phase model of the oscillatory process. Our study points to the importance of using filtering in engineering synchronization states of oscillatory electrochemical reactions. Kiss, I.Z., Y. Zhai, and J.L. Hudson, Emerging Coherence in a Population of Chemical Oscillators. Science, 2002. 296(5573): p. 1676.Zou, W., M. Zhan, and J. Kurths, Phase transition to synchronization in generalized Kuramoto model with low-pass filter. Physical Review E, 2019. 100(1): p. 012209.

Oscillatory Electrodeposition of Cu/Cu2o: A Study on the Influence of Ligands in Cu(II) Complexes

Self-organization is a powerful tool for the synthesis of new materials, among a wide variety of processes that exhibit this phenomenon, electrochemical ones are promising candidates in which the main contributions can be divided between electrodeposition and electrodissolution systems.1 Potential and/or current oscillations have already been observed in several electrodeposition reactions and culminated in the formation of different structures under micro and nanoscale such as multilayers, spiral waves and dendrites.Periodic potential oscillations related to alternate electrodeposition of Cu and Cu/Cu2O, recorded in the form multilayered architecture were first reported by Switzer and collaborators,2 and further explored in the presence of other ligands such as tartrate and citrate.The oscillations that occur under galvanostatic regime are detected in a broad range of pH and current densities values, that directly affect the period and amplitude of the oscillations. Therefore, as the material morphology and properties are directed related to the dynamical behavior of the system, it is of major importance to understand deeply the role of the experimental variables on the system. Although direct relationships between experimental parameters, especially at short range studies, are consistently reported at the literature, multivariate statistical analysis revealed a more complex dependence on the frequency including quadratic terms.3 Concerning the chemical influence of the ligand over the oscillatory electrodeposition of Cu/Cu2O, we have investigated the effect of lactate (Figs. A and C) and tartrate (Figs. B and D) ligands in the oscillation period (Figs. A and B) and amplitude (Figs. C and D).4 The potential oscillations at the Cu(II)-lactate and Cu(II)-tartrate systems are detected in different ranges of pH and current densities values for each system, that affect the period and amplitude of the oscillations as portrayed at the diagrams in Figs. A to D. Although a strict parallel of the systems can not be performed, the main characteristics are the period and amplitude variation when the lactate is replaced by tartrate in the reaction media. On balance, the potential oscillations in the Cu(II)−tartrate system exhibit larger periods and lower amplitude values in relation to the Cu(II)−lactate one. Beyond that, there is a significant suppression of the oscillation domain in the tartrate system, that can be connected to an apparent inhibition effect, as a result of the stronger adsorption of tartrate anions and/or its metallic complexes. In fact, the presence of a poisoning species on the surface, that acts as spectator of the reaction, can induce the increase of the oscillation period and suppress the Hopf domain, as previously reported.The oscillation mechanism introduced by Switzer et al., further detailed by Leopold et al. and updated by our group, taking into account recent available structural information (Figs. E and F), describes the alternated deposition of copper and copper oxide, and considers pH interfacial variation as being an essential step for the oscillation mechanism. Supposing that only a buffering effect can alter the oscillation period, as stated before by previous investigations, the buffering capacity found in the lactate complex (Fig. E) should be less effective when compared to the tartrate one (Fig. F). This can be explained from the ligand structures: the second carbonyl and hydroxy groups available for protonation/deprotonation (tartrate vs. lactate complex) lead to an increase in the buffering capacity, besides the concentration of these species in solution. Since the oscillating period is reduced when the solution pH is increased, a longer period observed for the tartrate complex means that this system possesses a higher buffering capacity compared to that for the lactate complex.Even though of significant importance, this mechanism does not account for the anion adsorption and/or the respective complexes dissolved in the electrolyte and as observed experimentally, which is an important consideration to be made in the description of the oscillatory electrodeposition. The surface blocking and buffering effect are enhanced when tartrate molecules are utilized as the ligand (in comparison with lactate system), and both mechanisms seem to control the dynamic properties of the electrochemical oscillator simultaneously. Therefore, we show that chemical structures or functions of the reactants could be altered to induce an autonomous growth of a target material, giving rise to a bottom-up synthesis approach. This is of great value especially since Cu and Cu2O interfaces are employed in many fields, such as electrocatalysis in the CO2 electroreduction.[1] M. R. Pinto, et al. ChemElectroChem 2020. [2] J. A. Switzer, et al. Adv. Mater. 1997.[3] B. T. Kitagaki, et al. Phys. Chem. Chem. Phys. 2019.[4] M. R. Pinto, ei al. J. Phys. Chem. C 2020. Figure 1

Decoding Network Structure in Lab-on-Chip Cells with Synchronization of Electrochemical Oscillators

The analysis of network interactions among dynamical units and the impact of the coupling on self-organized structures is a challenging task with implications in many biological and engineered systems. We explore the coupling topology that arises through the potential drops in a flow channel in a lab-on-chip device that accommodates chemical reactions on electrode arrays. The networks are revealed by analysis of the synchronization patterns with the use of an oscillatory chemical reaction (nickel electrodissolution) and are further confirmed by direct decoding using phase model analysis. In dual electrode configuration, a variety coupling schemes, (uni- or bidirectional positive or negative) were identified depending on the relative placement of the reference and counter electrodes (e.g., placed at the same or the opposite ends of the ow channel). With three electrodes, the network consists of a superposition of a localized (upstream) and global (all-to-all) coupling. The synchronization patterns and the network configuration are compared for the linear and the branched channel configurations. The networked, electrode potential (current) spike generating electrochemical reactions hold potential for construction of an in-situ information processing unit to be used in electrochemical devices in sensors and batteries.

Modified brain storming optimization technique for transient stability improvement of SVC controller for a two machine system

Purpose Static VAR compensators (SVC) have been recognized to be one of the most important flexible AC transmission systems devices used for mitigating the low-frequency electrochemical oscillations occurring in the system and for reactive power compensation, thereby improving the overall dynamic stability and efficiency of the system. The purpose of this paper is to optimize and dynamically tune the control parameters of the classical proportional integral and derivative (PID) controller of the SVC for a two-machine system by designing a new robust optimization technique. Design/methodology/approach The angular speed deviation between the two machines is used as an auxiliary signal to SVC for generation of the required damping output. To justify the efficacy of the system undertaken, a light load fault at time t = 1 s is projected to the system. The simulation is carried out in MATLAB/Simulink architecture. Findings The proposed technique helps in the enhancement of system efficiency, reliability and controllability and by effectively responding to the non-linearities taking place in a power grid network. The results obtained are indicative of the fact that the proposed modified brain storming optimization (MBSO) technique reduces system disturbances very quickly, increases the system response in terms of better rise time, settling time and peak overshoot and improves the efficiency of the system. Originality/value A detailed comparison of the MBSO technique is compared with the conventional brain storming optimization (BSO) and PID technique. Total harmonic distortion through fast Fourier transform is also compiled to prove that the values of the proposed MBSO method found out to be confined well within the prescribed IEEE-514 boundaries.

Synchronization in populations of electrochemical bursting oscillators with chaotic slow dynamics.

We investigate the synchronization of coupled electrochemical bursting oscillators using the electrodissolution of iron in sulfuric acid. The dynamics of a single oscillator consisted of slow chaotic oscillations interrupted by a burst of fast spiking, generating a multiple time-scale dynamical system. A wavelet analysis first decomposed the time series data from each oscillator into a fast and a slow component, and the corresponding phases were also obtained. The phase synchronization of the fast and slow dynamics was analyzed as a function of electrical coupling imposed by an external coupling resistance. For two oscillators, a progressive transition was observed: With increasing coupling strength, first, the fast bursting intervals overlapped, which was followed by synchronization of the fast spiking, and finally, the slow chaotic oscillations synchronized. With a population of globally coupled 25 oscillators, the coupling eliminated the fast dynamics, and only the synchronization of the slow dynamics can be observed. The results demonstrated the complexities of synchronization with bursting oscillations that could be useful in other systems with multiple time-scale dynamics, in particular, in neuronal networks.

Non-monotonic transients to synchrony in Kuramoto networks and electrochemical oscillators

We performed numerical simulations with the Kuramoto model and experiments with oscillatory nickel electrodissolution to explore the dynamical features of the transients from random initial conditions to a fully synchronized (one-cluster) state. The numerical simulations revealed that certain networks (e.g., globally coupled or dense Erdős–Rényi random networks) showed relatively simple behavior with monotonic increase of the Kuramoto order parameter from the random initial condition to the fully synchronized state and that the transient times exhibited a unimodal distribution. However, some modular networks with bridge elements were identified which exhibited non-monotonic variation of the order parameter with local maximum and/or minimum. In these networks, the histogram of the transients times became bimodal and the mean transient time scaled well with inverse of the magnitude of the second largest eigenvalue of the network Laplacian matrix. The non-monotonic transients increase the relative standard deviations from about 0.3 to 0.5, i.e., the transient times became more diverse. The non-monotonic transients are related to generation of phase patterns where the modules are synchronized but approximately anti-phase to each other. The predictions of the numerical simulations were demonstrated in a population of coupled oscillatory electrochemical reactions in global, modular, and irregular tree networks. The findings clarify the role of network structure in generation of complex transients that can, for example, play a role in intermittent desynchronization of the circadian clock due to external cues or in deep brain stimulations where long transients are required after a desynchronization stimulus.

Single-Nanoparticle Coulometry Method with High Sensitivity and High Throughput to Study the Electrochemical Activity and Oscillation of Single Nanocatalysts.

To explore nanocatalysts with high electro-catalytic performance and less loading of precious metals, efforts have been made to develop electrochemical methods with high spatial resolution at the single nanoparticle level. Herein, a highly sensitive single-nanoparticle coulometry method is successfully developed to study the electrochemical activity and oscillation of single PtTe nanocatalysts. Based on microbattery reactions involving the formic acid electro-oxidation and the deposition of Ag on the single PtTe nanocatalyst surface, this method enables the transition from the undetectable sub-fA electric signal of the formic acid electro-oxidation into strong localized surface plasmon resonance scattering signal of Ag detected by dark-field microscopy. The lowest limiting current for a single nanocatalyst is found to be as low as 25.8 aA. Different trends of activity versus the formic acid concentration and types of activity of the single nanocatalyst have been discovered. Unveiled frequency-amplitude graph shows that the two electrochemical oscillation modes of low frequency with high amplitude and vice versa coexist in a single PtTe nanocatalyst, indicating the abundantly smooth surfaces and defects of nanocatalysts. This conducted study will open up the new avenue for further behavioral and mechanistic investigation of more types of nanocatalysts in the electrochemistry community.

Preface: Long-range interactions and synchronization

Spontaneous synchronization is a general phenomenon in which a large population of coupled oscillators of diverse natural frequencies self-organize to operate in unison. The phenomenon occurs in physical and biological systems over a wide range of spatial and temporal scales, e.g., in electrochemical and electronic oscillators, Josephson junctions, laser arrays, animal flocking, pedestrians on footbridges, audience clapping, etc. Besides the obvious necessity of the synchronous firings of cardiac cells to keep the heart beating, synchrony is desired in many man-made systems such as parallel computing, electrical power-grids. On the contrary, synchrony could also be hazardous, e.g., in neurons, leading to impaired brain function in Parkinson's disease and epilepsy. Due to this wide range of applications, collective synchrony in networks of oscillators has attracted the attention of physicists, applied mathematicians and researchers from many other fields. An essential aspect of synchronizing systems is that long-range order naturally appear in these systems, which questions the fact whether long-range interactions may be particular suitable to synchronization. In this context, it is interesting to remind that long-range interacting system required several adaptations from statistical mechanics \`a la Gibbs Boltzmann, in order to deal with the peculiarities of these systems: negative specific heat, breaking of ergodicity or lack of extensivity. As for synchrony, it is still lacking a theoretical framework to use the tools from statistical mechanics. The present issue presents a collection of exciting recent theoretical developments in the field of synchronization and long-range interactions, in order to highlight the mutual progresses of these twin areas.

Mechanism of Potential Oscillation (Named Oscillation K) Induced By pH Increase at Electrode Surface in “H2O2-H2so4-Pt Electrode” System

Electrochemical oscillations are attractive phenomena from the viewpoint of dynamic self-organization of molecular systems. In general, an N-shaped negative differential resistance (N-NDR) plays a crucial role for the appearance of oscillations because it gives rise to an oscillatory instability. Most of the oscillations can be classified into an N-NDR type or “hidden” N-NDR (HN-NDR) type oscillator. The former shows current oscillations under potential controlled conditions and hysteresis loops under current controlled conditions, whereas the latter shows not only current oscillations but also potential oscillations. Thus, an electrochemical system that shows potential oscillations mostly falls into an HN-NDR type oscillator.Interestingly, the reduction of H2O2 at Pt electrodes in H2SO4 solution shows eleven types of electrochemical oscillations, named sequentially from A to K [1-3]. Oscillations H, I, J, and K appear when a salt such as Na2SO4 and K2SO4 is added to the solution. In the presence of the alkali metal ions originated from the salt, the transport rate of H+ to the electrode surface decreases because the electromigration of H+ is inhibited by the metal ions. Thus, the local pH at the electrode surface becomes strongly basic during the H2O2 reduction even though the electrolyte solution is strongly acidic (e.g., 0.1 M H2SO4). In the vicinity of the electrode surface, H2O2, which is a weak acid with a pK a of 11.7, dissociates to form HO2 - ion. The ion is electrochemically reduced to OH- or oxidized to O2, leading to the appearance of the oscillations.In this work, the extent of the local pH increase is estimated by using a numerical simulation and the mechanisms of oscillation K is studied based on the simulation. REFERENCES [1] Y. Mukouyama, H. Kawasaki, D. Hara, Y. Yamada, S. Nakanishi, J. Electrochem. Soc., 164 (2017) H1.[2] Y. Mukouyama, H. Kawasaki, D. Hara, Y. Yamada, S. Nakanishi, J. Electrochem. Soc., 164 (2017) H675.[3] R. Mizuochi, M. Kikuchi, Y. Yamada, Y. Mukouyama, S. Nakanishi, ECS Meeting s, MA2018-02, 2122 (2018). FIGURE CAPTION Figure 1 Current (j) - potential (U) curves for 0.1 M H2SO4 + 0.3 M H2O2 + x M Na2SO4 where x = (top) 0 and (bottom) 0.1, measured (left) under potential controlled conditions and (right) under current controlled ones. Figure 1

Hidden N-Shaped Negative Differential Resistance Induced By Hydrogen Bubble Evolution during Reduction of Nitrate Ions on Cu Electrode

Electrochemical oscillations are attractive phenomena from the viewpoint of dynamic self-organization of molecular systems. In general, an N-shaped negative differential resistance (N-NDR) plays a crucial role in the appearance of oscillations because it gives rise to an oscillatory instability [1]. Most of the oscillations can be classified into an N-NDR type or “hidden” N-NDR (HN-NDR) type oscillator. The former shows current oscillations under potential controlled conditions and hysteresis loops under current controlled conditions, whereas the latter shows not only current oscillations but also potential oscillations. Thus, the electrochemical system that shows potential oscillations falls into an HN-NDR type oscillator. However, it is not always true because there are different types of oscillators that show potential oscillations, namely, strictly potentiostatic type, S-shaped NDR (S-NDR) type, coupled N-NDR (CN-NDR) type, and electrochemical reactions and diffusion–convection (ERDC) type oscillators [2].Electrochemical reduction reactions are accompanied with hydrogen bubble evolution when the electrode potential is much more negative than the onset potential of hydrogen evolution reaction (HER). The bubble evolution often causes a disturbance in the electrochemical measurements and analysis. Thus, electrochemical studies are mostly conducted in the potential region where the HER does not occur or where bubbles do not affect the electrochemical reactions. Probably for this reason, little has been studied on the electrochemical reduction of nitrate ions in the potential region of the HER, though the reduction has been extensively studied for years.We recently found that three types of oscillations (named oscillations I, II, and III) occurred during the reduction on Cu electrode [3, 4]. Interestingly, as shown in Figure 1, they appeared as current and potential oscillations in the potential region of the HER. The appearance of oscillations I and III depended on the acidity of solutions: oscillation I appeared when the nitrate reduction occurred in acidic solutions (the left panels) whereas oscillation III did in basic ones (the right panels). On the other hand, oscillation II appeared irrespective of the acidity.This work focuses on studying the mechanism of oscillation II. A high-speed video recording showed that hydrogen bubbles evolved synchronously with oscillation II. More importantly, electrochemical impedance measurements indicated that oscillation II was an HN-NDR type oscillator (the panels d1 and d2). These led to a clear conclusion that the bubble evolution induced positive and negative feedback effects during the nitrate reduction. Interestingly, a detailed study showed that the potential oscillation that was observed when the solution was acidic (e.g., oscillation II shown in b1 and c1) behaved like an ERCD type oscillator. In the presentation, we will discuss the difference between the HN-NDR and ERDC oscillators and explain the mechanism of oscillation II. Figure 1

Electrochemical Behaviors of MnO2 on Lead Alloy Anode during Pulse Electrodeposition for Efficient Manganese Electrowinning

The electrochemical performances of deposited MnO2 on lead alloy anode by pulse current (PC) and direct current (DC) electrodeposition in manganese sulfate solution were investigated by performing measurements of galvanostatic polarization, cyclic voltammetry (CV), and Tafel tests. The composition and morphology of MnO2 were observed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The anode deposited with MnO2 layers by PC electrodeposition presented a lower anodic potential of 60 mV and more uniform potential oscillating attractor with fractal dimension of 1.0337 compared with those of DC electrodeposition. In addition, MnO2 layers exhibited excellent corrosion resistance because less intermediate oxide Mn(III) appeared in anode deposits. Furthermore, the cathodic current efficiency improved by 3.11∼3.77% and energy consumption decreased by 5.30∼8.17% after galvanostatic electrolysis for 2∼8 h by using PC instead of DC for manganese metal electrodeposition. As an external control method, PC electrodeposition not only regulated the structure and surface morphology of MnO2 but also affected the anode electrochemical behaviors and cathode manganese metal deposition. Electrochemical oscillations and other characteristics of anode reaction described in this study could inspire future work on promoting the whole electrowinning process.

Development of Electrochemical Oscillation Method for Identification of Prunus persica, Prunus davidiana, and Prunus armeniaca Nuts.

In this work, an electrochemical oscillation system has been developed using the Belousov–Zhabotinsky reaction. The effect of the combination of each reagent, reaction temperature, and stirring speed on the induction period, oscillating period, and oscillating life were optimized. The nuts of Prunus persica, Prunus davidiana, and Prunus armeniaca have been widely used for medical purposes. The proposed electrochemical oscillation system was then used for the identification of P. persica, P. davidiana, and P. armeniaca. Three nuts exhibited very different electrochemical oscillation profiles. The dendrogram was divided into three main principal infrageneric clades. Each cluster only contains one species, suggesting that no outlier was observed in this study. Based on the discussed results, we proposed a simple method for herbal medicine identification.

Characteristic and Control of Electrochemical Oscillation at the Anode during Electrolytic Refining Copper

Characteristic and Control of Electrochemical Oscillation at the Anode during Electrolytic Refining Copper

Coherent Dynamics Enhanced by Uncorrelated Noise.

Synchronization is a widespread phenomenon observed in physical, biological, and social networks, which persists even under the influence of strong noise. Previous research on oscillators subject to common noise has shown that noise can actually facilitate synchronization, as correlations in the dynamics can be inherited from the noise itself. However, in many spatially distributed networks, such as the mammalian circadian system, the noise that different oscillators experience can be effectively uncorrelated. Here, we show that uncorrelated noise can in fact enhance synchronization when the oscillators are coupled. Strikingly, our analysis also shows that uncorrelated noise can be more effective than common noise in enhancing synchronization. We first establish these results theoretically for phase and phase-amplitude oscillators subject to either or both additive and multiplicative noise. We then confirm the predictions through experiments on coupled electrochemical oscillators. Our findings suggest that uncorrelated noise can promote rather than inhibit coherence in natural systems and that the same effect can be harnessed in engineered systems.

Bifurcations induced by the electrode surface area during the electrochemical oxidation of bisulfite

Abstract Electro-oxidation behavior of bisulfite was found to depend qualitatively on the surface area of a glassy carbon electrode, where a transition from stable to oscillatory behavior took place as the surface area of the working electrode was increased to above a critical value. The size-dependent nonlinear behavior was observed at both potentiostatic and galvanostatic conditions. Preliminary characterization with electrochemical impedance spectroscopy illustrates the emergence of a hidden-negative differential resistance at the above threshold surface area. The conclusion that the studied system belongs to the class of HN-NDR type electrochemical oscillator is consistent with the result that oscillations also take place under a galvanostatic control.

Discerning the oscillatory electrochemical response during electrodeposition of cobalt in the presence of but-2-yne-1,4-diol

We present a new observation of electrochemical oscillation during the reduction of Co2+ from sulfate solution in the presence of but-2-yne-1,4-diol (butynediol) as an additive. Cyclic voltammetry, hydrodynamic voltammetry at galvanostatic condition, and electrochemical impedance spectroscopic studies suggest that the electrochemical oscillation observed was a relaxation type and was the manifestation of adsorbed hydrogen formation by electrochemical reduction of protons on cobalt and their chemical removal by semi-hydrogenation of butynediol to butenediol during the initial stages of electrodeposition.

Chloride ion inhibition of electrochemical oscillations on the anode of an electrolytic manganese metal cell

ABSTRACT In industrial electrolytic manganese metal process, the energy consumption closely related to the electrolysis of cathode and anode. The effect of Cl- concentration on electrochemical oscillation at the anode of the electrolytic manganese metal cell was investigated. The results showed that the electrochemical oscillation at the anode was inhibited by Cl-, and the amplitude and frequency of the electrochemical oscillation decreased as the increase of Cl- concentration. When the concentration of Cl- was 2.68 g/L, the cathode and anode electrodes could be effectively activated, and the manganese current efficiency reached its minimum, correspondingly, the power consumption reached its maximum. In addition, the presence of the chloride reduced the production of MnO2 at the anode surface. ClO4 − and free ions formed insoluble amorphous structures on the surface of the anode with the increase in reaction time and chloride ion concentration, and the insoluble amorphous structures prevented further generation of MnO2. Thus, electrolytic manganese metal energy consumption decreased.