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We report a simple physics-based model leading to an analytical expression for impedance of the gas-diffusion layer (GDL) in a PEM fuel cell. We show that this expression differs from the classic Warburg finite-length impedance due to large double layer capacitance Cdl of a porous catalyst layer the GDL is attached to. It follows that the Warburg solution is obtained for the transport layer attached to a planar electrode with vanishingly small Cdl. Keywords: GDL impedance, Warburg impedance, Modeling

International audience; The morphological and electrocatalytic properties of ITO and nanostructured carbon screen printed electrodes (nanoSPCE) modified with thin films of MnO2 particles, alone or as hybrid with SiO2, as obtained using electrodeposition techniques, were studied. The time and potential of MnO2 electrodeposition influenced the electrocatalytic properties of the modified electrodes towards H2O2. The highest electrocatalytic current was observed at deposition potential E=-0.8 V and deposition time of 10 s. MnO2 particles with uniform distribution were obtained onto the electrode surface when prepared under optimal conditions. The nanoSPCE-MnO2 has demonstrated larger effective surface area and faster charge transfer rates compared to ITO-MnO2. The electrodeposited silica, in addition to MnO2, improved the operational stability of the electrodes without noticeable decreasing of their performance. Modified electrodes were used for hydrogen peroxide determination.

Recently, the strongly inhomogeneous current density occurring near a microelectrode was identified as driving a thermocapillary electrolyte flow near gas bubbles growing during electrolysis (Massing et al., 2019) [1]. The present paper is investigating this effect in more detail under various operating conditions. Furthermore, by simplified modeling, the question is answered of whether this effect is also of importance at large planar electrodes. The direction of the thermocapillary force on the bubble is found to change from retarding to advancing the bubble release when the size of the electrode is increased. Conclusions are drawn on how the thermocapillary effect at planar electrodes depends on the electrode coverage and the bubble departure size, also considering industrially relevant values of the current density.

The standards that establish water’s quality criteria for human consumption include organoleptic analysis. These analyses are performed by taste panels that are not available to all water supply companies with the required frequency. In this work, we propose the use of an electronic tongue to perform organoleptic tests in drinking water. The aim is to automate the whole process of these tests, making them more economical, simple, and accessible. The system is composed by an array of electrochemical microsensors and chemometric tools for multivariable processing to extract the useful chemical information. The array of sensors is composed of six Ion-Sensitive Field Effect Transistors (ISFET)-based sensors, one conductivity sensor, one redox potential sensor, and two amperometric electrodes, one gold microelectrode for chlorine detection, and one nanocomposite planar electrode for sensing electrochemical oxygen demand. A previous study addressed to classify water samples according to taste/smell descriptors (sweet, acidic, salty, bitter, medicinal, chlorinous, mouldy, and earthy) was performed. A second study comparing the results of two organoleptic tests (hedonic evaluation and ranking test) with the electronic tongue, using Partial Least Squares regression, was conducted. The results show that the proposed electronic tongue is capable of analyzing water samples according to their organoleptic characteristics, which can be used as an alternative method to the taste panel., This research was funded by a direct contract between Mina Pública d’Aïgues de Terrassa, S.A. and CSIC, and by the Ministry of Science, Innovation and Universities (MICIU), project number TEC2014-54449-C3-1-R (BIOSENSLOC). This work has made use of the Spanish ICTS Network MICRONANOFABS partially supported by MICIU.

In this work, we explore generation-collection electrochemistry in a rotating droplet hydrodynamic system, where a 70 μL droplet containing a redox active species (ferrocyanide) is sandwiched between an upper rotating rod and bottom nonmoving generator and collector planar electrodes. In such a system, we studied the effect of the counter electrode reaction on the recorded generator current, and the effect of the generator-collector distance (ranging from 3 to ca. 500 μm) on the collection efficiencies obtained at rotation rates ranging from 50 to 1100 rpm. We found that the counter electrode reaction competes with the collector reaction for the regeneration of the electroactive species; thus, collection efficiencies of 100% are probably impossible to obtain with this system geometry. We found that the collection efficiency increases with the droplet rotation rate and decreases with the generator-collector distance. The highest collection efficiency we obtained is 62% for the generator-collector distance of 3 μm, which is more than two times higher than that for typical bulk experiments with a commercial rotating ring disk electrode. We show that the increased collection efficiency can be successfully used in epinephrine detection for filtering out signals from ascorbic acid and uric acid interferents.

The application of bio-electrochemical system (BESs) is strongly depended on the development of the engineering applicable electrode. Here we described an economical and readily processable electrode module with three-dimensional structure, the corrugated stainless-steel mesh electrode module (c-SMEM). This novel developed electrode module was demonstrated to provide a good hydrodynamic characteristic and significantly enhanced the decolorization performance of the BES when serving for treating azo dye (acid orange 7, AO7) containing wastewater. Compared to the conventional planar electrodes module (p-SMEM), c-SMEM was found to prolong the mean residence time (MRTθ) of AO7 and change the flow pattern closer to the plug flow. As a result, the maximum enhancement of the volumetric decolorization rate (vDR) can reach to 255%, even when the c-SMEM and p-SMEM have the same electrode surface area. In addition, a techno-economic analysis model was established to elucidated the effects of the decolorization performance and the material cost on the initial capital cost, which revealed the BES with c-SMEM could be economically comparable to or even better than the traditional bio-decolorization technologies. These results suggest c-SMEM holds great potential for engineering application, which may help paving the way of applying BES at large-scale.

Author(s): Maslyn, JA; Mcentush, KD; Harry, KJ; Frenck, L; Loo, WS; Parkinson, DY; Balsara, NP | Abstract: Lithium metal is a high-energy-density battery electrode material, but the largely irreversible growth of lithium protrusions on an initially planar electrode during cycling makes it unsuitable for incorporation into a commercial battery. In this study, a lithium electrode with globular protrusions was stripped electrochemically, and the local morphology of the electrode as a function of time was determined by hard X-ray tomography. We demonstrate that globules are preferentially stripped compared to a planar electrode in our system, which incorporates a nanostructured block copolymer electrolyte. We report current density at the electrode as a function of micron-scale position and time. The local current density during the electrode healing process calculated from a reference frame at the electrode/electrolyte interface provides insight into the driving forces responsible for selective stripping of the globule. These results imply the possibility of discharging protocols that may return a lithium electrode to its initial planar state.

An analytical model is proposed to describe the two-dimensional distribution of potential and current in planar electrodes of pouch-type lithium-ion batteries. A concentration-independent polarization expression, obtained experimentally, is used to mimic the electrochemical performance of the battery. By numerically solving the charge balance equation on each electrode in conjugation with the polarization expression, the battery behavior during constant-current discharge processes is simulated. Our numerical simulations show that reaction current between the electrodes remains approximately uniform during most of the discharge process, in particular, when depth-of-discharge varies from 5% to 85%. This observation suggests to simplify the electrochemical behavior of the battery such that the charge balance equation on each electrode can be solved analytically to obtain closed-form solutions for potential and current density distributions. The analytical model shows fair agreement with numerical data at modest computational cost. The model is applicable for both charge and discharge processes, and its application is demonstrated for a prismatic 20 Ah nickel-manganese-cobalt lithium-ion battery during discharge processes.

Intracellular action potential signals reveal enriched physiological information. Patch clamp techniques have been widely used to measure intracellular potential. Despite their high signal fidelity, they suffer from low throughput. Recently, 3D nanoelectrodes have been developed for intracellular potential recording. However, they are limited by scalability, yield, and cost, directly constraining their use in monitoring large number of cells and high throughput applications. In this paper, we demonstrate intracellular potential monitoring of cardiomyocytes using simple 2D planar electrode array in a standard CMOS process without patch clamps or post fabricated 3D nanoelectrodes. This is enabled by our unique cardiomyocytes/fibroblasts co-culturing technique and electroporation. The co-cultured fibroblasts promote tight sealing of cardiomyocytes on electrodes and enable high-fidelity intracellular potential monitoring based on 2D planar electrode. Compared to existing technologies, our platform has a unique potential to achieve an unprecedented combination of throughput, spatiotemporal resolution, and a tissue-level field-of-view for cellular electrophysiology monitoring.

Three-dimensional (3D) electrodes of Cu@Fe3O4 nanowire arrays for Li-ion batteries are prepared by an electrochemical route. XRD, SEM, TEM and HRTEM are used to characterize the micromorphology. The structures are improved, which is beneficial for the electrochemical performances. The obtained electrodes show a higher initial capacity than the traditional Cu@Fe3O4 planar electrodes. Moreover, the 3D electrodes exhibit better long-term cycling stability and an appealing rate capability.

It is present mathematical modeling of plane-parallel electrochemical electrolyzes with a perforated cathode. It is performed mathematical modeling of plane-parallel electric and concentration fields of electrolyte in electrolyzes with planar electrodes, coinciding with boundary surfaces of opposite faces.

A general mathematical model for cyclic voltammetry at a planar electrode modified with an insulating surface coating containing non-interconnected cylindrical pores is developed and solved using numerical simulation. Electroactive species are assumed to diffusionally access the electrode only via the pores. The model allows us to explore the effects of different physical and electrochemical parameters on the mass transport properties of such systems and to highlight how they deviate from linear diffusion to a macroelectrode. © 2005 Elsevier B.V. All rights reserved.

The differential pulse voltammetry (DPV) experiment has been simulated using the backwards implicit finite difference approach. Results are reported for the general case of a one-electron redox transfer process at a planar electrode in stationary solution with a semiinfinite diffusion layer and are in excellent agreement with those predicted by an analytical approach, confirming the validity of the finite difference simulation. In addition, concentration profiles are presented and the effect of diffusion layer thickness on the voltammetric response quantified with experimental considerations indicated, suggesting an extension of this simulation to cover DPV at hydrodynamic electrodes.

Trends in disposable and handheld biosensors have called for miniaturized and planar electrodes in the place of conventional bulky ones. In this work, thin tin-doped indium oxide (ITO) film coated on glass were used as a based electrode in a three-electrode electrochemical system to follow some biochemical activities, such as NADH and phenol activity. The reference electrode is made on ITO layer by electro-deposition of thin nickel layer and silver layer, consecutively, followed by chlorination of silver surface by electrochemical potentiostatic method. The plain planar ITO-coated glasses were used as both counter electrode and working electrodes. Cyclic-voltammetry measurements; which follow an oxidation of 200 μM nicotinamide adenine dinucleotide (NADH) in 0.1 M KCl, show current peak of 8.5 μA. Another case was also to follow the NADH oxidation but in competition with its coupling activity with flavin mononucleotide (FMN). In this case, cyclic-voltammetry measurements were carried out of 200 μM NADH in 50 mM sodium phosphate; current peak of 1.3 μA was observed.

Photosystem I (PSI), a photoactive protein complex that participates in the light reactions of natural photosynthesis, can exhibit photocatalytic capabilities when incorporated to electrochemical systems. Here we present a simulation for the photoelectrochemical behavior of an electrode modified with a monolayer of Photosystem I complexes during photochronoamperometric experiments in which the electrode is exposed to periods of darkness and irradiation. A kinetic model is derived from conservation statements for the various oxidation states of the reaction centers of PSI complexes and electrochemical mediators within the system. The kinetic parameters that dictate the performance of the simulation are extracted from experimental data and the resulting simulation is capable of predicting the photochronoamperometric behavior of the system over a range of overpotentials. The model is used to investigate the various contributions to the photocurrent production of the system as well as the effects of the orientation of PSI complexes adsorbed to the electrode surface.

The non-steady-state concentration for an EC reaction at planar electrode is derived. The analytical expression for the concentration for EC reaction is reported for small and large value of reaction rate. The asymptotic expression for the non-steady-state current for EC reaction is also derived. The analytical solutions for normalized current response were formulated using the method of Laplace transformation. The concentration and current are compared with available limiting case results, and are found to be in good agreement.

In a single potential step voltammetric technique, several constant potentials (of increasing amplitude) are applied with a time length t 1. When stationary electrodes are used, the time interval between two consecutive potentials must be much greater than t 1, for the initial conditions to be restored (Scheme 2.1). If a Static Mercury Drop Electrode (SMDE) is used, the initial conditions are simply restored by making the drop fall. The measured current at a fixed time value \( t={t}_1 \) is plotted versus the corresponding potential steps discretely [1–3]. The resulting current–potential curve has a sigmoidal shape whose position and slope depend on the reversibility of the electrode process and the wave height is independent of the electron transfer rate. At each fixed potential value, the current–time variation (which has a typical cottrellian behavior for reversible processes at planar electrodes when considering diffusive transport only) can be registered. If the length time is in the range 2–200 ms, the electrochemical technique is called Normal Pulse Voltammetry (NPV), originally known as Normal Pulse Polarography (NPP). This technique was introduced by Barker [5–7] and it was originally designed for the Dropping Mercury Electrode (DME), in which the potential pulse is applied at the end of the life of the drop, with the current being dependent on the relation between the pulse time and the drop lifetime. The main reason for measuring the current at the end of short time intervals is to eliminate the capacitative component (see Sect. 1.9) in order to optimize the sensitivity. Today the DME electrode is scarcely used and most electrochemical techniques are used at stationary electrodes

Electrodes in neural prostheses may trigger stimulation-induced tissue damage if the magnitude of the stimulation exceeds safe levels. Consequently, the concentration of current densities at the periphery of planar electrodes has been studied extensively, and the use of electrode recesses has been suggested as a method of reducing such effects. Cochlear implant electrodes have significant geometrical differences from the planar electrodes used in earlier studies. We have previously used the finite element method to solve for current distributions on half-band cochlear implant electrodes. In this paper, we utilize similar models to investigate the effect of recessing half-band cochlear implant electrodes on their electrochemical safety. It was found that when recess depths were increased, the distribution of the electrodes became more uniform by up to 75.5%. The maximum reduction in irreversible faradaic reactions was found to be only 6.5% at the maximum recess depth, however other factors may contribute to the occurrence of irreversible faradaic reactions.

A new electrochemical double pulse potential technique called additive differential pulse voltammetry (ADPV) is proposed. This technique is inspired by the original idea of Birke et al. [Anal. Chem. 53 (1981) 852] of recording two differential pulse (DP) voltammograms and it consists of plotting the sum of these two signals versus the first pulse potential, although in this paper the proposal is to obtain the ADPV signal through just one experiment. ADPV behaves in an identical way to the triple-pulse technique double differential pulse voltammetry (DDPV) for reversible processes when diffusion coefficients are equal for spherical electrodes and for any value of diffusion coefficients in planar electrodes. In the case of reversible electrode processes with amalgamation of reaction product or other more complex processes, ADPV is more advantageous than DDPV. This is due, among other reasons, to the fact that, under these conditions, a double potential step is much simpler to analyse than a triple potential step. Keywords: Additive differential pulse voltammetry, Double differential pulse voltammetry, Reversible process

Analytical solutions for reversible multistep electrode processes in voltammetry with constant potential at planar electrodes whose areas increase with an arbitrary power of time and at spherical electrodes are presented. These solutions are valid when several or all species are initially present and, in the case of planar electrodes, when their diffusion coefficients are not necessarily equal. Interesting consequences and simplifications that clarify the experimental study of any multistep process can be deduced from these solutions.

The spatial propagation of synchronized activity in cortical slice cultures was characterized by multi-site extracellular recording. Spontaneous activity was studied in normal culture medium, and in bicuculline- or kainic acid-containing media. A common feature in all these conditions was that activity was generated first in superficial layers (i.e., layer I/II) before spreading over the whole area of the slice. In culture medium or bicuculline-containing medium, the initiation site of the activity was not constant and showed a large variety of patterns of horizontal propagation. Kainic acid induced epileptiform activity, consisting of intense initial bursts followed by repetitive after-discharges. Though the patterns of spatial propagation of the bursts were variable as in the other conditions, the after-discharges followed a constant path. Cross-correlation analysis indicated that the network moved in a graded fashion to a steady state during the sequence of after-discharges.

Formation of a set of planar electrodes spaced about 10 nm apart by electrochemical “healing” of gaps 50 to 100 nm wide in half-finished electrodes is described. The method consists in complete healing of the gap followed by the creation of a discontinuity at the joint of the electrodes via relaxation of stresses arising in the course of film deposition.

The current density close to the edge of an electrode may be either enhanced or diminished compared with current densities remote from the edge. This effect is quantified here for the case of diffusion-controlled currents at a planar electrode which abuts either a second electrode face or an insulating plane. Concentrations in the vicinity of the electrodes are also investigated. The cases of right-angled junctions receive special attention.

Whenever a monochromatic collimated light beam illuminates a planar electrode surface parallel to that surface, a diffraction pattern characteristic of the beam's coherence is obtained. The electrode edge position is generally determined utilizing a procedure which assumes either a totally coherent or an incoherent source. In this work, the image of the diffraction pattern was magnified and focused on a diode array, and the resulting intensity profile was compared with that obtained from a slightly defocused image. Perturbation theory was applied to predict the position of the electrode's edge. Once the edge position was known, the source's coherence was determined from the normalized intensity at the electrode's edge. This technique can be utilized in situ with “parallel” spectroelectrochemical experiments. It does not depend on a priori knowledge of the light source's coherence nor does it require an opaque-translucent interface. A simple model and experimental data employing this method are presented. Measurements of the experimental electrode positions were reproducible within the theoretical magnifier/array limit, 1 μm.

The first two terms of the short-time reversible response to a potential step at a general planar electrode are given, showing both the area and edge contributions to the current. This result permits the determination of all electrochemical parameters for reversible simple electron transfer, including unequal diffusion coefficients, from short-time data obtained at microelectrodes.

The theoretical analysis of the application of a pure alternating current to stationary and non-stationary planar electrodes has been carried out. The response obtained is essentially different from any other previously appearing in the literature. The conditions under which the response is never accompanied by the reaction of the supporting electrolyte have been found. The degree of reversibility of the process can be characterized from the shape of the E/t curves. The applicability of the equations deduced is shown for several experimental systems.

Equations for a potentiostatic reaction with an adsorption process following Langmuir’s isotherm have been derived for the expanding sphere with any power law electrode model. This model is very general and includes, among others, the following ones: (a) stationary plane; (b) stationary sphere; (c) expanding plane; and (d) expanding sphere. Characteristics of these solutions and the behavior of the corresponding asymptotic solutions are discussed. A comparison of the results obtained for plane and spherical electrodes has also been performed.

Ascorbate and urea are present in body fluid at relatively high concentration and could cause interference during glucose sensing. The potential interference of these two substances was investigated using a small planar electrode in the low potential region of the cyclic voltammogram. that is, -0.750 V to +0.450 V versus Ag/AgCI. The ascorbate signal near -0.750 V was found to increase linearly as its concentration was increased from 1 to 10 mg/dl. The effect of changes in concentration of urea in the 20 to 60 mg/dl range did not cause an obvious variation in glucose current at -0.750 V. Regularities in signal variations at -0.750 V and in other regions of the voltammogram (for example at -0.530 V) were observed. Using these regularities, a scheme for signal processing was developed to compensate for the effect of the interferences.

The voltammetric response of metal complex systems with various labilities is analyzed by rigorous numerical simulation with the Finite Element Method of the time-dependent concentration profiles of the different species. The ensuing exact fluxes and the corresponding currents are compared to those derived from the Koutecký–Koryta (KK) approximation which assumes a discontinuous transition in the concentration profiles from non-labile to labile behavior. The results indicate a relatively far-reaching correctness of the KK approximation in the complete kinetic range from non-labile to labile complexes, as long as the kinetic flux is computed from the effective concentration of the complex in the reaction layer. Some approximate analytical expressions for this concentration are provided. The KK approximation is shown to be applicable for any metal-to-ligand ratio, provided that the thickness of the reaction layer is expressed in terms of the ligand concentration at the electrode surface.

Close-packed coupled multielectrode arrays simulating a planar electrode were used to monitor the anodic current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel (UNS S31600) and Ni-Cr-Mo alloy 625 (UNS N06625). Scaling laws x 2 crit vs G and x* 2 crit vs G derived from polarization data in simulated crevice solutions guided the implementation of rescaled crevices with greater spatial resolution. x crit and x* crit are the distances from the mouth to the location where the potential reaches two different critical values, and G is the crevice gap. Scaling laws were also used along with anodic polarization data in simulated crevice solution to predict crevice corrosion behavior of alloy 22 (UNS N06022). Crevice corrosion of AISI 316 stainless steel in 0.6 mol/L NaCl at 50°C readily initiated close to the crevice mouth (i.e., x crit ≈ 0) at modest applied potentials (e.g., E app = 0 V SCE ) and spread both inward and outside the crevice with time. Crevice corrosion initiated farther inside the crevice (i.e., x crit is large) and required higher applied potentials (e.g., E app = 50 mV SCE ) in the case of alloy 625. The local crevice current density increased dramatically over a short period of time to reach a limiting value in the case of AISI 316; while metastable dissolution behavior over a large area was observed for alloy 625. The ramification of the larger critical depth for Ni-Cr-Mo alloys toward crevice corrosion susceptibility in the case of crevice formers of finite length is discussed. Crevice corrosion shifts to the mouth of the crevice for the less corrosion-resistant materials in crevice solutions saturated in metal salts but remains confined at a distance x crit for alloy 625 under the conditions tested.

Close packed coupled multielectrode arrays simulating a planar electrode were used to measure the current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel. Scaling laws derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCI at 50°C was found to initiate close to the crevice mouth and to spread inward and outward with time. The local crevice current density increased dramatically over a short period to reach a limiting value.

The equations for the influence of non-equilibrated, linear adsorption of a reactant, an intermediate and a product of the reversible redox reaction at stationary, planar electrode, under potentiostatic regime, have been derived.

An analytical solution is presented for the case of double potential step chronoamperometry at a stationary planar electrode for the case of heterogeneous charge transfer control. Extension of the result to multiple potential steps gives the current—potential response for differential normal pulse voltammetry. The dependence of the response on the experimental parameters is examined. The dependence on duration of the first pulse is especially significant, for the case of long duration of the first pulse corresponds to the widely-used technique of differential pulse voltammetry. The advantage of using shorter durations for the first pulse ( ie using differential normal pulse voltammetry) when examining irreversible reactions is shown.

The deflection of a laser beam parallel to a planar electrode surface, or mirage effect, has been described by means of a mathematical model. The experimental results of ac and transient photoelectro-chemical experiments are shown to agree well with the predictions of this model. From the best fit of the data the following parameters are deduced: the thermal and ionic diffusivity of the electrolyte and the thermal power dissipated at the electrochemical interface.

La voltammetrie cyclique, a balayages multiples, appliquee a l'electrodepot sur une electrode plane stationnaire dans des conditions de diffusion lineaire semi-infinie est analysee en termes de fonctions de densite de charge et de courant

Electrolysis of metal ions in dilute solutions using vertical planar electrodes results in low recovery. Therefore, an electrolytic cell arranged concentrically with extended cathode surface areas was designed to improve the rate of mass transfer. Three types of gold solutions obtained from industrial sites were used. Despite an initial gold level of 110 mg l −1 , the electrolytic cell was effective in reducing the gold concentration to as low as 0.1 mg l −1 .

The equation for the pulse polarogram influenced by the reversible, linear adsorption of a reactant of a reversible redox reaction on a stationary, planar electrode is developed. The numerical method is applied for calculating the dependence of pulse polarograms on the parameters of the excitation signal and adsorption equilibria. Henry's and Langmuir's isotherms are considered. The possible influence of adsorption-induced capacitive current on the pulse polarograms is investigated. The probable origin of the maxima in pulse polarography is discussed.

Coupled diffusion of two substances taking part in a potentiostatic electrode reaction can lead to a maximum concentration change at finite time for one of the substances. It is shown that this phenomenon can occur at spherical and cylindrical electrodes, with first‐order and with higher‐order reactions, but not at planar electrodes.