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Within the framework of the linear theory of small potential oscillations the article studies the structure and characteristics of internal and surface waves in a two-layer stably stratified fluid. Dispersion relations have been obtained and analyzed. The Boussinesq approximation has been studied. We have determined the existence of two types of waves: a fast wave and a slow wave. The fast wave differs little from a surface wave in a homogeneous fluid. The main results of studying the case of n=1 are as follows: obtaining expressions for fluid particles velocity components and hydrodynamic pressure in the upper layer of the considered two-layer fluid, as well as obtaining relations, which connect the oscillation amplitudes of the free surface and the interface of the considered two-layer fluid. The main results of studying the case of n=2 are as follows: obtaining expressions for fluid particles velocity components and hydrodynamic pressure in the lower layer of the considered two-layer fluid, as well as obtaining dispersion relations in the considered two-layer fluid. In the case of implementing the Boussinesq approximation, the fast wave differs little from a surface wave in a homogeneous fluid, andthe velocity of slow waves is proportional to the square root of the squared ratio ρ/Δρ​, i.e. it is very small.

• The influence of different anion adsorption over glycerol electrooxidation affects the electroactivity of surface reaction. • In situ FTIR demonstrates different CO recovery according to anion adsorption. • Potential oscillations show that OH ads formation is inhibited in the presence of coordinated anion and slows down the CO cleaning process. • Electrolyte composition provides better designing and optimizing electrocatalysts for glycerol electrooxidation. This research explores the glycerol electrooxidation reaction (GEOR) on a platinum electrode, with a special emphasis on the role of the chemical properties of the anion present in the electrolyte composition. Essential knowledge of the mechanism and dynamics of glycerol electrooxidation is obtained through comprehensive studies that involve in situ FTIR measurements and the analysis of electrochemically oscillatory responses. This study addresses on the complex interplay between anion adsorption strength and the GEOR, focusing on the differences in CO adsorption coverage, which is the main strongly adsorbed intermediate. The anion adsorption strength, with the order HClO 4 < H 2 SO 4 < H 3 PO 4 , affects significantly not only the CO coverage on the platinum surface but also the overall glycerol electrooxidation rate. The observed differences in the electroactivity are attributed to competitive adsorption phenomena, in which specific coordinated ions have greater adsorption capabilities than perchlorate ions. These findings highlight the critical relevance of designing and optimizing electrocatalysts for glycerol electrooxidation and related processes with careful consideration of the electrolyte composition, notably the anion. [Display omitted] This study investigates how anion properties in electrolytes affect glycerol electrooxidation on platinum electrodes, revealing HClO 4 < H 2 SO 4 < H 3 PO 4 in adsorption strength order, crucial for designing efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

In this contribution a spatially distributed Electrochemical Preferential Oxidation (ECPrOx) reactor is evaluated and the influence of the temperature, CO inlet concentration, feed flow rate and relative humidity on the polarization curve, the local current distribution and the CO outlet concentration, selectivity and conversion are investigated. For that, six different cases are studied under galvanostatic and potentiostatic operation. For Galvanostatic operation, it was observed that depending on the operation conditions, the bifurcation point as well as the frequency and amplitude of the oscillations can be modified. Additionally, several spatiotemporal profiles of the local current density were found. For potentiostatic operation, the spatiotemporal profiles are constant with time, however they are affected by the anode overvoltage. Finally, after the bifurcation point, the temporal averaged anode overvoltage and the CO outlet concentration is always lower for galvanostatic control.

Abstract Galvanostatic potential oscillations during the oxidation of formic acid were studied by time-resolved Surface-Enhanced Infrared Absorption Spectroscopy in the attenuated total reflection configuration (ATR-SEIRAS) and reflectance measurements in the ultraviolet (UV) region. ATR-SEIRAS allowed monitoring oscillations in the coverage of adsorbed CO (CO ad) and adsorbed bridge-bonded formate (HCOO bi), while UV reflectance revealed oscillations in the coverage by specifically adsorbed anions (namely, adsorbed sulfate). The potential oscillations and the coverage of all these species are strongly interconnected, and an analysis of their correlation provides detailed insight into the autocatalytic loop responsible for the emergence of non-linear dynamics. Graphical abstract Unlabelled Image Highlights • All present species in solution and on the surface compete for active sites. • Adsorbed anions and bridge-bonded formate interfere in the removal of adsorbed CO. • Formic acid oxidation takes place in a complex, potential dependent network. • All active processes have to be considered to understand the catalytic performance. [ABSTRACT FROM AUTHOR]

Abstract We report the study of the oscillatory electro-oxidation of ethanol on platinum surfaces under galvanostatic conditions. In order to correlate the features of potential oscillations with the surface chemistry of different adsorbates, we use in situ surface-enhanced infrared absorption spectroscopy in the attenuated total reflectance mode (ATR-SEIRAS). Results show that the maintenance of the oscillatory state does not seem to be particularly correlated with the CO surface coverage, conversely to what is observed for methanol. Indeed, our data suggest that oscillations continue as long as the coverage of molecular fragments from ethanol (regardless its nature) remain within a range that allows the coexistence of surface oxides (responsible for the activation of the surface throughout oxidation steps). Our results throw some light in the oscillatory kinetics of ethanol by establishing an unequivocal correlation between the features of the galvanostatic oscillations and the dynamics of the adsorbed species. Highlights • The oscillatory electro-oxidation of ethanol on platinum was studied by ATR-SEIRAS. • The oscillation pattern is different from that observed for methanol. • ATR-SEIRAS show that the oscillation persists even in the absence of CO. • CO cannot explain the sustenance of oscillatory loops. • Species containing carbonyl seem to be co-responsible for the oscillations. [ABSTRACT FROM AUTHOR]

In the present paper, the influence of electrogenerated (110) defects in the methanol oxidation reaction (MOR) on a Pt(111) electrode has been studied. It is shown that methanol oxidation is favored at the defected surfaces as evidenced by the displacement of the onset potential to lower values and the increase of the peak current density. The currents obtained by transient curves at short times (0.015 – 0.50 s) at 0.50 V vs RHE demonstrate the faster formation of strongly adsorbed species on disordered surfaces when compared to Pt(111). On the other hand, for long-term transient currents (600 s), the surface with a higher surface density of (110) defects presented the best activity among all ones studied. Galvanostatic results showed that potential oscillations emerged only on disordered surfaces. The large induction time up to the beginning of the oscillations as well as the lower frequency registered on these surfaces demonstrates the enhancement of CO formation on defects. This point is confirmed by in situ FTIR experiments. From the results obtained by using electrochemical techniques, it was possible to infer that the dehydration rate constant (k dh) and the rate constant for CO oxidation (k CO) are affected by the number of (110) defects, which give rise to k CO and k dh values higher than those obtained for Pt(111). [ABSTRACT FROM AUTHOR]

Potential oscillations caused by electrochemical overoxidation of graphite in aqueous nitric acid were observed for the first time. Deep oxidation of graphite was carried out in 18 M HNO 3 by galvanostatic method. During the electrochemical treatment enormous anodic charge was consumed to change graphite into the graphite oxide (GO). Thus synthesized GO exhibits significantly increased concentration of epoxy, alkoxy as well as carbonyl groups. On the basis of the gained results mechanism of graphite transformation into GO in aqueous solutions of HNO 3 was proposed. Our investigations indicated that to achieve an effective transformation of graphite into GO, the compromise between electrolyte concentration and the stage of intercalation of intermediately formed graphite intercalation compound (HNO 3 -GIC) should be reached. X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the obtained GO. Additionally, the influence of electrochemical oxidation of graphite in aqueous nitric acid on its chemical surface composition was investigated using FTIR spectroscopy. [ABSTRACT FROM AUTHOR]

In this contribution a well-mixed electrochemical preferential oxidation (ECPrOx) reactor for hydrogen purification is considered and the influence of the CO concentration on the polarization curve, the conversion, the selectivity and the specific energy required is investigated. For that, a wide range of CO concentrations are studied and two different control modes are evaluated: voltage and current control. It was established that the oscillations, which arise during current control, enhance the reactor performance. They decrease the specific energy required and increase, as does the CO concentration, the selectivity and the conversion. Furthermore, it was found that the bifurcation current and potential vary nonlinearly with the CO concentration. [ABSTRACT FROM AUTHOR]

We investigated the potential oscillations near a hollow cathode for ring-type anode configuration and planar disc anode configuration using diagnostic tools. The waveform of potential oscillations, amplitude of plasma potential and ion density were measured. The plasma potential oscillations show rapid rising but slow decrease. The results show that ionization in a ring-type anode is more effective than that in a planar disc anode and the amplitude of plasma potential in a ring-type anode is much larger than that in a planar disc anode at the same operating conditions. The highest amplitude of plasma potential that occurred corresponds to the area where the highest ion density appeared for both anode configurations, which shows that xenon ions in space play an important role for this kind of plasma potential. [ABSTRACT FROM AUTHOR]

We report the microwave-assisted hydrothermal synthesis of bimetallic Pt-Au nanoparticles with different Pt/Au mole ratio, and investigate their performance towards the electro-oxidation of formic acid. The as-synthesized Pt-Au sol was dispersed on a graphite electrode, without any binding agents, which allowed us to control the mass of alloy deposited. Pt-Au alloys showed better activity than bulk Pt and/or Pt nanoparticles towards the oxidation of formic acid, as evidenced by the decrease in the onset potential and the higher currents in the corresponding cyclic voltammograms. The higher activity is due both to atomic-ensemble effects, which lead the reaction through the so-called direct pathway with insignificant CO poisoning, and to electronic effects, which optimised the interaction between the catalyst surface and the reactive intermediate in the direct path. Further insight into the individual contributions of atomic-ensemble and electronic effects and their effect on the catalytic activity was provided by the analysis of galvanostatic potential oscillations. [ABSTRACT FROM AUTHOR]

Chemical perturbation of the Fe|HSO electrochemical system caused by adding a critical chloride ion concentration induces sustained potential oscillations under a galvanostatic control. The potential oscillates between the active and passive states of Fe due to a local breakdown/rebuilding of the iron oxide. This work investigates how nitrates modify and eventually suppress the chloride-induced potential oscillations, which can be used as a probe to sense and evaluate the nitrate inhibiting effect. It is shown that adding an appropriate concentration of nitrates into the Fe|0.75 M HSO + x M Cl system causes distinct differences in system temporal patterning revealed in galvanodynamic and galvanostatic curves. Depending on the chloride concentration and the current imposed to the system, the number of potential oscillations decreases, while the oscillatory waveform alters by increasing gradually the nitrate concentration. Above a critical concentration, nitrates suppress completely potential oscillations resulting in a stable passive state of Fe. This situation resembles that of the chloride-free system, which under current-controlled conditions shows only bistability, without potential oscillations. A quantitative characterization of the inhibiting effect of nitrates is carried out using diagnostic criteria related to the oscillation features. The inhibiting effect of nitrates and the suppression of oscillations are discussed by considering a competitive adsorption of nitrates and chlorides along with nitrate redox reactions. [ABSTRACT FROM AUTHOR]

The effect of reformate H 2 mixture composition on Pt/C based high temperature PEMFC anode was thoroughly studied, in order to understand the anode's tolerance under varying CO and steam partial pressures. It is shown that under steam partial pressure over 12 kPa a high overpotential region appears at current densities over 0.3 A/cm 2 . This negative effect appears in relation to the structure of the electrochemical interface (EI), as this is specified by the amount of H 3 PO 4 (PA) within the anode catalytic layer. As also shown, the sustainable operation of the anode under reformate containing steam and CO as high as 30 kPa and 2 kPa respectively requires significantly lower loadings of PA. This malfunctioning is attributed to the hydrophobic/hydrophilic properties of the Pt/C-PA EI and its modification when water from the gas phase is dissolved in the PA, in combination with the polarization and the adsorption of CO and H 2 on Pt surface. These phenomena and the capillary forces within the catalytic layer are responsible for the alternating contraction (ganglia formation and loss of ionic link within the EI) and spreading (thin film formation and well developed EI) of PA, thus giving rise to oscillatory behavior and unstable performance of the anode. [ABSTRACT FROM AUTHOR]

Potential oscillations appear under current-controlled conditions of the chlorate- and perchlorate-perturbed electrochemical Fe|HSO system. The potential oscillates between the active and passive states of Fe. It is shown that this oscillatory phenomenon is associated with localized corrosion of Fe due to the generation of chlorides via the reduction of chlorates and perchlorates by ferrous ions. Ferrous ions are generated either during the active dissolution of bare Fe (low-potential state) or during the passivation of Fe (high-potential state) due to a H-catalyzed chemical dissolution of the oxide. Potential oscillations can be utilized to detect and characterize pitting corrosion of Fe in acidic solutions because, under current-controlled conditions, the halide-free Fe|HSO system does not exhibit any kind of oscillatory phenomena. Characterization of pitting corrosion becomes possible through the analysis of galvanodynamic and galvanostatic curves obtained at various concentrations of chlorates and perchlorates. The variation of the anion concentration and applied current influence the onset and features of the potential oscillations. [ABSTRACT FROM AUTHOR]

The electrochemical corrosion of the porous layer system nickel/chromium was investigated combining classical open circuit measurements, cyclic voltammetry, and zero-resistance Ammeter experiments. Under moderate conditions as there are low chloride concentration, pH 6, and high oxygen content the nickel layer acts as sacrificial anode, whereas at the chromium top layer oxygen reduction takes place. Under conditions of limited access of oxygen into pores potential oscillations occur which indicates a change of corrosion mechanism. Thereby the anode reaction changes between nickel and chromium dissolution. The respective cathode reaction is oxygen reduction or hydrogen evolution. The modeling of the potential oscillation reveals the character of the potential-dependent Flade potential as function of the proton concentration. [ABSTRACT FROM AUTHOR]

Abstract: This work addresses the anodic response of passive Fe surfaces to a chemical perturbation caused by adding small amounts of halides into sulfuric acid media. Halides induce a localized breakdown of the passivity on Fe and hence pitting corrosion associated with potential oscillations observed under current-controlled conditions. The recorded macroscopic potential oscillations represent a kind of temporal pattern formation, which do not appear neither when uniform corrosion occurs nor when the pit population is low and interaction between pits does not occur to a sufficient extent. Validation of this behaviour comes by adding fluoride and iodide species. Fluorides are known to affect uniformly the passive Fe due to their strong tendency to form complexes with Fe(III). In the presence of iodides, though pitting corrosion is induced, pit growth and propagation are inhibited due to the formation of a stable iodine layer inside pits as a result of iodide electrochemical and chemical reactions. Galvanodynamic potential–current curves as well as galvanostatic potential–time curves allow a comparative study of the system oscillatory response as a function of halide concentration and imposed current values. Quantities related to oscillation attributes enable an estimation of the pitting kinetics and halide aggressiveness order. The oxide growth and its localized and/or uniform breakdown induced by halides are discussed in terms of a point defect model. This study may contribute to further applications of nonlinear dynamics in materials science; namely, the characterization and control of metal stability or electrochemical metal micro/nanostructuring. [Copyright &y& Elsevier]

Abstract: The oscillatory electro-oxidation of methanol was studied by means of in situ infrared (IR) spectroscopy in the attenuated total reflection (ATR) configuration using a platinum film on a Si prism as working electrode. The surface-enhanced infrared absorption (SEIRA) effect considerably improves the spectroscopic resolution, allowing at following the coverage of some adsorbing species during the galvanostatic oscillations. Carbon monoxide was the main adsorbed specie observed in the induction period and within the oscillatory regime. The system was investigated at two distinct time-scales and its dynamics characterized accordingly. During the induction period the main transformation observed as the system move through the phase space towards the oscillatory region was the decrease of the coverage of adsorbed carbon, coupled to the increase of the electrode potential. Similar transition characterizes the evolution within the oscillatory region, but at a considerably slower rate. Experiments with higher time resolution revealed that the electrode potential oscillates in-phase with the frequency of the linearly adsorbed CO vibration and that the amount of adsorbed CO oscillates with small amplitude. Adsorbed formate was found to play, if any, a very small role. Results are discussed and compared with other systems. [Copyright &y& Elsevier]

Abstract: We report experimental observations of potential oscillations in electrocatalytic oxidation of formic acid with bismuth ion on the Pt ring electrode. Potential oscillations were investigated under galvanostatic conditions. The presence of bismuth ion enables to get the low and stable potential values at larger current range. Periodic and Shil’nikov chaotic potential oscillations were observed at fixed current. To extract information from the oscillation pattern, we used time series, reconstructed attractor, next-maximum map, pattern formation of interfacial potential above ring electrode. [Copyright &y& Elsevier]

Abstract: The polarization performance of two PEM fuel cells (with anode PtRu/C catalyst) connected either in parallel or serial, was compared to the performance of a single PEM fuel cell in galvanostatic operation using CO-free H2 or 200ppm CO-containing H2 stream as anode feed at ambient temperature. Spontaneous potential oscillations were observed experimentally for the coupled configuration with two cells connected in serial or parallel using CO-containing H2 feed at various current densities applied. The potential oscillations are ascribed by the dynamic CO adsorption and subsequent electrochemical CO oxidation on the anode. The measured anode outlet CO concentration was found to decrease with the order: single cell>parallel cells>serial cells at various current densities and anodic flow rates. The low anode outlet CO concentration (<10ppm) at high current densities applied showed that CO in the anode feed was removed efficiently by the electrochemical CO oxidation occurring on the PtRu anode. The anode outlet CO concentration decreased as follows: a single cell>the parallel cells>the serial cells at broad range of current densities and anodic flow rates. The highest CO conversion and the highest average power output at equal hydrogen recovery degree were obtained with serially coupled fuel cells. [Copyright &y& Elsevier]

The dynamic behaviour of a single PEM fuel cell (PEMFC) with a PtRu/C anode catalyst using CO containing H2 as anode feed was investigated at ambient temperature. The autonomous oscillations of the cell potential were observed during the galvanostatic operation with hydrogen anode feed containing CO up to 1000 ppm. The oscillations were ascribed to the coupling of the adsorption of CO (the poisoning step) and the subsequent electrochemical oxidation of CO (the regeneration step) on the anode catalyst. The oscillations were dependent on the CO concentration of the feed gas and the applied current density. Furthermore, it was found that with CO containing feed gas, the time average power output was remarkably higher under potential oscillatory conditions in the galvanostatic mode than during potentiostatic operation. Accompanying these self-sustained potential oscillations, oscillation patterns of the anode outlet CO concentration were also detected at low current density (<100 mA/cm2). The online measurements of the anode outlet CO concentrations revealed that CO in the anode CO/H2 feed was partially electrochemically removed during galvanostatic operation. More than 90% CO conversion was obtained at the current densities above 125 mA/cm2 with low feed flow rates (100–200 mL/min). [ABSTRACT FROM AUTHOR]

Abstract: Potential oscillations are demonstrated under reducing galvanostatic conditions in alkaline solutions of 0.4M Cu(II) and 1.2M citrate at elevated temperatures. The oscillations, which give rise to the deposition of layers of Cu and Cu2O, as verified by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) as well as Raman measurements, originate from local modulations of the pH in the vicinity of the working electrode. A reaction scheme for the oscillations is presented based on the model previously proposed by Leopold et al. [J. Electroanal. Chem., 547 (2003) 45–52] for the Cu(II)–lactate system. It is shown that the oscillations are due to the fact that the rate of the electrodeposition of Cu2O is modulated by the local pH variations. This causes this reaction to be switched on and off as the local pH increases and decreases, respectively. In analogy with the Cu(II)–lactate case, a local pH increase is obtained during the deposition of copper from the [Cu2H−2Cit2]4− complex ([Cu2H−2Cit2]4− +4e− +2H2O=2Cu+2[Cit]3− +2OH−) predominating in the solution. This increase stems from the protonation of the liberated citrate. As a result of this, electrodeposition of Cu2O ([Cu2H−2Cit2]4− +2e− +H2O=Cu2O+2[Cit]3−) becomes possible at the rate required by the constant current. However, electrochemical quartz crystal microbalance (EQCM) data clearly show that the onset of this reaction is accompanied by an electroless deposition of Cu2O. This reaction, which under oscillating conditions mainly involves a comproportionation reaction ([Cu2H−2Cit2]4− +2Cu+2OH− =2Cu2O+2[Cit]3−), can give rise to Cu2O deposition at current efficiencies much larger than 100%. As a result of the combined electroless deposition and electrodeposition of Cu2O, the local pH decreases rapidly, mainly due to the comproportionation reaction. When the local pH drops, the electrodeposition of Cu2O becomes unable to sustain the current and the potential shifts negatively. This causes the onset of the reduction of the previously deposited Cu2O (i.e. Cu2O+2e− +H2O=2Cu+2OH−). The EQCM and XRD results, however, clearly show that this reduction is incomplete during the oscillating conditions. This finding, which explains the presence of both copper and Cu2O in the deposits, is ascribed to the formation of a growing layer of copper on top of the remaining Cu2O. It is shown that the extent of the Cu2O reduction (and thus the amount of Cu2O in the obtained deposits) depends on the Cu(II) concentration in the solution. Finally, the oscillation cycle is completed by a gradual replacement of the reduction of Cu2O by the reduction of the [Cu2H−2Cit2]4−complex, which causes the local pH to increase again. The proposed model is discussed in detail with particular emphasis on the reactions taking place in the region of the oscillation potential peak. The requirements for the attainment of oscillations under quiescent and forced convection conditions are discussed as well as the applicability of the model with respect to other Cu(II)–complex systems. [Copyright &y& Elsevier]

Abstract: In this communication, we report some new oscillatory phenomena on the electrodissolution of gold in sulfuric solution containing Br− or in concentrated HCl. It was found that gas evolution and/or liquid film can play important roles in the oscillatory electrodissolution of gold, in addition to the solid film of gold oxides as previously recognized. Oscillatory electrodissolution of gold in bromide media is given here for the first time with two cases: (i) current oscillations only with lower concentrations of bromide (0.5M, M=mol dm−3) and sulfuric acid (0.2M) in the narrow potential range of active–passive transition and (ii) oscillations both in potential and in current with moderate concentrations of bromide (1M) and sulfuric acid (1M). The depletion and replenishment of Br− surface concentration by reactions under diffusion control and by convection through periodic oxygen evolution, respectively, account for the potential oscillations. Whereas the variation of available electrode surface area results in the irregular current oscillations due to the formation–removal of liquid bromine film rather than the periodic oxygen evolution. In addition, we first show both potential and current oscillations in concentrated HCl (8M). The depletion and replenishment of the surface Cl− concentration involving also periodic gas evolution are the main reasons for the potential oscillations like case (ii) in the Br−-containing solution. Two kinds of current oscillations were found relating the active–passive transitions (like case (i)) and the Cl− depletion–replenishment with periodic gas evolution, respectively. The current oscillations can transform from the former to the latter ones with a positive potential scan. Some preliminary explanations have been given on the mechanism of the oscillatory electrodissolution with the help of the crossed cyclic voltammagrams (CVs) and in situ Raman spectra. [Copyright &y& Elsevier]

Electrochemical quartz crystal microbalance (EQCM) has been employed to study the potential oscillatory mechanism for the IO3− reduction accompanying periodic hydrogen evolution. The new experimental results that were obtained by in situ EQCM monitoring clearly demonstrate the all key steps involved in the oscillation: the diffusion-limited depletion of IO3− by reduction, the formation, growth and departure of hydrogen bubbles on the surface, and the convection-induced replenishment of IO3− by the hydrogen evolution. In addition to the frequency response to the surface mass change as reported in the literature, our study first shows that simultaneous frequency responses to the changes of density and viscosity in the diffusion layer during the oscillation can also provide meaningful and even decisive information on the oscillatory mechanism for the oscillators involving the coupling of electrochemical reactions with diffusion and convection mass transfer. [Copyright &y& Elsevier]

The influence of Pb2+ ions in sulfuric acid medium on the behavior of a platinum catalyzed hydrogen diffusion electrode (HDE) in a filter press reactor has been studied. A voltammetric study of the H2 oxidation reaction on a polyoriented platinum electrode and a platinum rotating disk electrode (RDE) in presence of lead ions in solution has also been carried out. Potential oscillations were found in galvanostatic experiments of H2 oxidation using a HDE catalyzed with platinum when Pb2+ ions are present in solution. This oscillatory phenomenon was also observed when hydrogen oxidation was carried out in presence of Pb2+ ions using a platinum RDE. The oscillatory behavior observed has been attributed to an adsorption–oxidation–desorption process of lead on the platinum surface. Due to the low solubility of Pb2+ in sulfuric acid, at high values of coverage, lead is oxidised to insoluble lead sulfate that blocks the Pt surface. The coupling of the dissolution of lead sulfate and the Pb electrochemical adsorption–oxidation processes cause the oscillatory phenomenon. [Copyright &y& Elsevier]

Oscillatory changes in electrical parameters of cells of Nitellopsis obtusa (Desv. in Lois)J. Gr. and Nitella flexilis f. Atkahensis R. D. W, particularly in the membrane potential, were investigated with external Ag/AgCl electrodes. Three main types of oscillations were observed The measurements were carried out on 30 cells with the application of an inhibitor of cytoplasmic streaming (procaine) and revealed that there was no direct correlation between cytoplasmic streaming and oscillations in the membrane potential. [ABSTRACT FROM AUTHOR]

The kinetic behaviour of lead and lead–silver anodes, polarized under galvanostatic conditions in a H2SO4ZnSO4MnSO4 electrolyte, has been studied. Whereas the potential of the lead anode stabilizes during electrolysis, the potential of the lead–silver alloy anode oscillates between two limits after an induction time. Both silver on the anode surface and manganese in the electrolyte are required for the potential oscillations to appear. With increasing time the potential oscillations change in shape and period. From impedance data obtained earlier, at the beginning of, and during the potential oscillations, it is shown that the potential instabilities originate from electrode coverage by a silver salt adsorbate. [ABSTRACT FROM AUTHOR]

Oscillatory instabilities are ubiquitous in many electrocatalytic reactions. In the case of the electrocatalytic oxidation of small organic molecules, oscillating electrode potential and reaction current are very often found under different experimental conditions. Most of the experimental studies are devoted to C1 molecules such as formic acid and methanol, and very few reports concerning C2 compounds are available, in spite of their technological relevance as potential fuels. We report in this letter the observation of fast potential oscillations during the electro-oxidation of ethylene glycol on platinum and in alkaline media. Oscillations were studied under galvanostatic control, and oscillation frequencies as high as 16.8 Hz were observed. To the best of our knowledge, those potential oscillations are the fastest ones ever reported for the electro-oxidation of small organic molecules, and we named them beta oscillations in reference to the taxonomy employed to classify brain rhythms. Oscillations were observed at different temperatures, and the system’s dynamics was found to be rather insensitive to temperature, in contrast to that observed under non-oscillatory regime. [ABSTRACT FROM AUTHOR]

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. Unlabelled Image • Electrode surface area was found to induce consecutive bifurcations. • Current and potential oscillations were observed during the oxidation of bisulfite. • EIS suggests that the system belongs to a HN-NDR type electrochemical oscillator. [ABSTRACT FROM AUTHOR]