Uncompensated Solution Resistance Research Articles

Insights into enhanced electrochemiluminescence of a multiresonance thermally activated delayed fluorescence molecule

AbstractThe electrochemiluminescence (ECL) behavior of a multiresonance thermally activated delayed fluorescence molecule has been investigated for the first time by means of ECL‐voltage curves, newly designed ECL‐time observatory, and ECL spectroscopy. The compound, Mes3DiKTa, shows complex ECL behavior, including a delayed onset time of 5 ms for ECL generation in both the annihilation pathway and the coreactant route, which we attribute to organic long‐persistent ECL (OLECL). Triplet‐triplet annihilation, thermally activated delayed fluorescence and uncompensated solution resistance cannot be ruled out as contributing mechanisms to the ECL. A very long ECL emission decay was attributed to OLECL as well. The absolute ECL efficiencies of Mes3DiKTa were enhanced and reached 0.0013% in annihilation route and 1.1% for the coreactant system, which are superior to those of most other organic ECL materials. It is plausible that ECL materials with comparable behavior as Mes3DiKTa are desirable in applications such as ECL sensing, imaging, and light‐emitting devices.

Theory for influence of ohmic resistance and electrode roughness on admittance voltammetry of reversible E and EE reactions

• Admittance voltammetric response for E and EE processes is influenced by roughness. • Random roughness is modeled through power spectrum of roughness. • Diffusion and uncompensated solution resistance are non-linearly coupled phenomena. • Characteristic peaks in admittance voltammetric response depend on finite fractal roughness. • Work emphasize on the enhanced sensitivity of this technique for E and EE processes. The theory is developed for the admittance voltammetry of reversible EE process under the influence of uncompensated solution resistance at random and fractally rough electrode. The theory accounts for the influence of random roughness through the power spectrum of roughness. The finite fractal model, with its three response controlling statistical parameters, viz. fractal dimension ( D H ), topothesy length ( ℓ τ ) or width of the interface and lower cut-off length ( ℓ ), is used to analyze the admittance voltammogram. DC biased admittance response of a rough electrode is determined by an interplay of morphological and phenomenological length scales. The characteristic phenomenological length scales of processes involved are diffusion length ( D / ω ) and DC bias dependent diffusion-ohmic coupling length ( L Ω ). These characteristic lengths significantly influence the potential dependent magnitude of admittance at a given temporal frequency or scan rate. The characteristic electron transfer admittance voltammetric peaks are significantly influenced by roughness in intermediate and high-frequency scans, i.e., ω > D/( L Ω 2 + ℓ τ 2 ). Similarly, at sufficiently low frequency, ω < D/( L Ω 2 + ℓ τ 2 ), the influence of roughness diminishes around the admittance peaks. The uncompensated solution resistance suppresses the height of admittance peaks and also alters the value of peak width at half peak height of both the electron transfer steps in moderately and strongly supported systems.

Theory for influence of uncompensated solution resistance on EIS of diffusion limited adsorption at rough electrode

Theory is developed for the electrochemical impedance spectroscopy (EIS) of the diffusion-limited adsorption process coupled with reversible charge transfer at rough electrodes under the influence of ubiquitous uncompensated solution resistance. This study quantitatively relates the impedance response of rough electrode to its phenomenological components, viz., diffusion limited adsorption, reversible charge transfer and uncompensated solution resistance. The random roughness of electrode is expressed by the surface statistical property, i.e., power spectrum of roughness. The fractal nature of roughness is characterized in terms of fractal dimension, lower cut-off length and topothesy length. The high-frequency regime is controlled by the uncompensated solution resistance whereas the low-frequency regime is governed by the adsorption process. The magnitude of impedance as well as phase decreases with rise in adsorption isotherm (length) parameter. The intermediate frequency regime is controlled by the coupling of adsorption and uncompensated solution resistance with the diffusion process. The fractal roughness parameters has quantitative influence on the magnitude of impedance over whole frequency regime while the phase plot shows qualitative difference in the intermediate frequency regime. The governing length scales which controls the characteristic crossover frequencies are: diffusion length, adsorption-ohmic coupling length and topothesy length (or width of interface). The three emergent crossover frequencies are: (i) ohmic reduced inner crossover frequency (ii) adsorption roughness topothesy dependent pseudo-quasireversibility characteristic frequency (iii) outer crossover frequency. Synopsis: This study quantitatively relates the impedance response of rough electrode to its phenomenological components, viz., diffusion limited adsorption, reversible charge transfer and uncompensated solution resistance. The random roughness of electrode is expressed by the surface statistical property, i.e., power spectrum of roughness.

Influence of electrode roughness on DC biased admittance of quasi-reversible charge transfer with uncompensated solution resistance

Abstract The theory is developed for the DC potential biased electrochemical impedance spectroscopy (EIS) of quasi-reversible charge transfer with uncompensated solution resistance developed for rough and fractal electrodes. Theory shows that the influence of the real and apparent kinetics is contained in DC bias dependent characteristic length called the diffusion-kinetics-ohmic coupling length (LQΩ). Theory characterizes fractal irregularities of an electrode through its power spectrum which is experimentally obtained from SEM or AFM recordings. EIS response of DC biased quasi-reversible systems is an interplay of phenomenological lengths, i.e., LQΩ, diffusion length (LD) and morphological characteristics (fractal dimension and lengths in roughness), manifesting themselves at different frequencies. High frequency regime, LD > LQΩ, electrode kinetics follows the Warburg response with the macroscopic area of the electrode. There is an emergence of anomalous intermediate region, LD ~ LQΩ, which is influenced by various fractal morphological characteristics. This regime has maximum in phase angle (ϕ > 450) as well as signature of the fractal roughness.

The effects of printing orientation on the electrochemical behaviour of 3D printed acrylonitrile butadiene styrene (ABS)/carbon black electrodes

Additive manufacturing also known as 3D printing is being utilised in electrochemistry to reproducibly develop complex geometries with conductive properties. In this study, we explored if the electrochemical behavior of 3D printed acrylonitrile butadiene styrene (ABS)/carbon black electrodes was influenced by printing direction. The electrodes were printed in both horizontal and vertical directions. The horizsontal direction resulted in a smooth surface (HPSS electrode) and a comparatively rougher surface (HPRS electrode) surface. Electrodes were characterized using cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. For various redox couples, the vertical printed (VP) electrode showed enhanced current response when compared the two electrode surfaces generated by horizontal print direction. No differences in the capacitive response was observed, indicating that the conductive surface area of all types of electrodes were identical. The VP electrode had reduced charge transfer resistance and uncompensated solution resistance when compared to the HPSS and HPRS electrodes. Overall, electrodes printed in a vertical direction provide enhanced electrochemical performance and our study indicates that print orientation is a key factor that can be used to enhance sensor performance.

Investigating the Enhancement of Microfluidics-Based Electrochemical Biosensor Response with Different Microchannel Dimensions

The microfluidics-based electrochemical biosensor (MBEB) is a new approach to laboratory diagnostics that offers many advantages over the conventional bulky and expensive laboratory instruments. Despite its small size and portability, the biosensor requires a specific sample volume to completely cover the detection zone and be analyzed. However, the sample volume for a particular microchannel size is of crucial importance, and the use of an inadequate sample volume results in less accurate measurements, lower sensitivity and increased detection limits. Therefore, this paper investigated the effects of microchannel size on sensor performance. First, microchannels ranging in size from 100- 1000 μm were fabricated, integrated and bonded to an electrode chip. Cyclic voltammetry scans for four different microchannel sizes fabricated for an electrode size of 100 μm were then conducted. The response and sensitivity of the fabricated biosensor increased with increasing microchannel size. The highest sensor sensitivity was observed using a microchannel size of 400 μm, and the response was maximized when a sufficient amount of the target was loaded in the microchannel. However, further increasing the microchannel size decreased the response current of the sensor due to the uncompensated solution resistance, which was considered a minor factor affecting the sensitivity of the sensor. Thus, optimizing the size of the channel is critical for maximizing the sensor performance. Keywords: Microfluidics, electrochemical biosensor, SEM, microchannel, electrodes, cyclic voltammetry.

Theory for electrochemical impedance spectroscopy of heterogeneous electrode with distributed capacitance and charge transfer resistance

Abstract Randles-Ershler admittance model is extensively used in the modeling of batteries, fuel cells, sensors etc. It is also used in understanding response of the fundamental systems with coupled processes like charge transfer, diffusion, electric double layer charging and uncompensated solution resistance. We generalize phenomenological theory for the Randles-Ershler admittance at the electrode with double layer capacitance and charge transfer heterogeneity, viz., non-uniform double layer capacitance and charge transfer resistance (\(c_d\) and \(R_{CT}\)). Electrode heterogeneity is modeled through distribution functions of \(R_{CT}\) and \(c_d\), viz., log-normal distribution function. High frequency region captures influence of electric double layer while intermediate frequency region captures influence from the charge transfer resistance of heterogeneous electrode. A heterogeneous electrode with mean charge transfer resistance \(\overline{R_{CT}}\) shows faster charge transfer kinetics over a electrode with uniform charge transfer resistance (\(\overline{R_{CT}}\)). It is also observed that a heterogeneous electrode having high mean with large variance in the \(R_{CT}\) and \(c_d\) can behave same as an electrode having low mean with small variance in the \(R_{CT}\) and \(c_d\). The origin of coupling of uncompensated solution resistance (between working and reference electrode) with the charge transfer kinetics is explained. Finally, our model provides a simple route to understand the effect of spatial heterogeneity.Graphical Abstract SYNOPSIS An electrochemical system consisting of heterogeneous working electrode (non-uniform charge transfer (CT) resistance (\(R_{CT}^{(i)}\)) and electric double layer capacitance (\(c_{d}^{(i)}\))) and ohmic losses (\(R_\Omega \)) between working and reference electrode. The analysis suggests that electrode with heterogeneity results in faster CT kinetics as compared to CT kinetics over homogeneous electrode.

Experimental corroboration of the theory of chronoamperometry at high roughness electrode for reversible charge transfer

An asymptotic theory for the single potential step chronoamperometry is validated for ferrocene in 1-Butyl-3-methylimidazolium tetrafluoroborate ([bmim] [BF4]) room temperature ionic liquid (RTIL) at nano-particles deposited mesoporous gold wires. The elegance of asymptotic equation arises due to minimal need of (only two) morphological surface characteristics, viz. roughness factor (R*) and width of roughness of mesoporous layer (h). It also accounts for the contribution from unequal diffusion coefficient of electro-active species and uncompensated solution resistance. Theory is also corrected for electric double layer contribution. Mesoporous electrodes are created (with R* >10) over mechanically roughened gold wires by depositing electrochemically synthesized gold nano-particles. Morphological parameters, R* and h, are determined using cyclic voltammetry (CV) and scanning electron microscopy (SEM), viz. CV and SEM method (see S.Dhillon and R.Kant, 2013). Asymptotic equation shows quantitative agreement with the experimental data over a broad time scale (between 0.2ms and 100s). Finally, this asymptotic equation can be used for the extraction of statistical roughness along with usual electrochemical quantities.

Influence of viscosity on chronoamperometry of reversible redox system on rough and nanoparticles deposited Pt electrode: Aqueous/glycerol and RTIL medium

Recently developed theories allow us to predict expected electrochemical response from quantitative surface texture information obtained from various microscopies. We generalized power spectrum based chronoamperometry theory involving species with unequal diffusion coefficient of electroactive species in presence of uncompensated solution resistance. Chronoamperometric response in two viscous media, like ionic liquid and glycerol, is studied and it shows strong influence of electrode roughness up to longer time scales. Measurements were carried out for two reversible charge transfer systems: (i) solution of Fe(CN)63− and Fe(CN)64− in 3M NaNO3 at various compositions of glycerol and (ii) ferrocene in [bmim][BF4] RTIL. Viscous medium induces suppression in growth of diffusion length which allows us to see enhanced and prolonged roughness effect in chronoamperometry. It is found that the enhanced viscosity: (i) induces delay, through enhanced ohmic contribution, in the onset of anomalous regime and (ii) causes dilation in roughness influenced time regime (the enlargement of roughness influenced region). These two effects allow determination of microscopic area from short time chronoamperometric data which is not possible in non-viscous aqueous medium. The corrections in the chronoamperometric current for the electric double layer and the random convective flow are also accomplished.

A Microfluidic Electrochemical Cell with Integrated Palladium Hydride Reference Electrode

Microfluidic devices have potential to be a great addition to the aqueous electrochemistry toolbox, for instance as an analog to the rotating ring-disk electrode, with an enhanced control of mass transport due to laminar flow. The photolithography process makes fabrication of various cell designs relatively fast, and it is possible to make electrodes of many different materials, including electrocatalyst particles. While the restricted volume of a microchannel provides excellent mass transport control, it introduces a very high solution resistance. This will create a significant shift in solution potential in the channel even at moderate currents, and makes the measurement of electrode potentials in the microchannel a challenge. In order to accurately measure potentials of electrodes in a microfluidic cell it is essential to characterize and minimize the effects of this potential distribution. Using a traditional reference electrode, and placing it in an outlet chamber essentially maximizes the uncompensated solution resistance, due to the necessity of having the counter electrode downstream of the working electrode. To solve the problems with the potential distribution, we fabricated a microfluidic electrochemical cell with an integrated palladium hydride reference electrode in a side channel upstream of the working electrode. A schematic of a cell is shown in Figure 1a. The cell design is relatively simple, and does not require salt bridges or ion conducting membranes in the cell to provide electrical contact to the reference electrode. This configuration results in low uncompensated resistance for single electrode experiments, and minimizes it for multiple electrode experiments. The placement of the reference electrode in a stagnant side channel eliminates influence of the species in the main channel on the reference electrode potential. Using PdH as the reference electrode makes the use of a wide range of acid and buffered electrolytes possible, and the presence of unfavorable ions such as chlorine can be eliminated. The reference electrode was charged in situ from a thin-film palladium electrode, and was able to hold a stable potential for up to eight hours of experiments. The relationship between the potential shift at one electrode, the cell geometry, and current through electrodes located upstream was probed using the half-wave potential of Ru(bpy)3 3+ oxidation and oxygen evolution as model reactions. Figure 1b shows how the potential for oxidation of Ru(bpy)3 3+ shifts at the SE at different anodic currents through the WE. This is the best case scenario for a cell with 100 µm wide electrodes and a 100 µm gap between the electrodes. If we allow for potential shifts up to 5 mV at the SE, the maximum current at the WE becomes 4 µA, using a 0.1 M Na2SO4 supporting electrolyte. Figure 1

Influence of Uncompensated Solution Resistance on Diffusion Limited Chronocoulometric Response at Rough Electrode

Theory is developed for the charge transient under ohmic effect in reversible charge transfer process at disordered electrodes. Preliminary experimental results are also analyzed using this theory. Our results show that the deviation from Anson response is stemming from surface disorder and solution resistance. Detailed theoretical results are obtained and analyzed for fractal roughness with self-affine statistical properties. Expressions for concentration, charge density, and total charge have operator structure in Fourier transformed (deterministic) surface profile function. An elegant mathematical formula between the average charge transient and surface structure factor of roughness is obtained. Initial response is attributed to resistive effects of the electrolyte. The intermediate response is attributed to the interplay between various characteristics of the power spectrum and “ohmic equilibration layer thickness”. The theory marks that ohmic effects penetrate farther in time so much so to merge with time regimes which are outside the diffusion regimes giving nonideal behavior at electrode/electrolyte interface. Our results help with the quantitative understanding of generalized Anson response for Nernstian system affected by the uncompensated resistance at rough electrode/electrolyte interface.

Role of Introduction of a Resistor in Series with the Working Electrode in Impedance Related Electrochemical Measurements

AbstractIntentional introduction of a resistor in series with the working electrode during electrochemical measurements can apparently change the constituents of the electrochemical system. The introduced resistor behaves like the uncompensated solution resistance, which was often regarded as an unwanted factor. However, the introduction of the resistor brings substantial benefits in some circumstances such as (a) compressing the impedance dynamic range of an electrochemical system and making the time domain EIS measurement more reliable; (b) tuning the RC time constant of an electrochemical system to a larger or even desired value and making the potential step based capacitive biosensing more flexible.

Measurements of the double layer capacitance for electrodes in supercritical CO2/acetonitrile electrolytes

Electrochemical impedance measurements were made in the single supercritical phase of CO2 with 11wt% acetonitrile as the co-solvent at temperatures and pressures between 306 and 316K and 15.5 and 20.2MPa over the potential range from −0.45 to +0.75V vs. Pt. Gold, platinum and glassy carbon electrodes were studied together with the effects of electrolyte concentration for [NBu4n][BF4]. Two other electrolytes, [NBu4n][B{3,5-C6H3(CF3)2}4] and [NMe4][BF4], were also studied. We find that the impedance data can be described by a simple RC equivalent circuit where the uncompensated solution resistance is independent of the electrode potential and is consistent with earlier measurements for the electrolyte conductivity. The results for the double layer capacitance can be described by a simple Helmholtz layer model and are very similar to those found for similar electrolytes in non-aqueous solvents such as propylene carbonate. For glassy carbon the double layer capacitances show a parabolic like potential dependence which we attribute to the lower density of states near the Fermi level.

Generalization of Randles-Ershler admittance for an arbitrary topography electrode: application to random finite fractal roughness

Randles-Ershler admittance equation is generalized for an arbitrary topography electrode. This generalization incorporates various phenomenological components involved in complete dynamical response of an electrode, viz. the diffusion, the charge transfer reaction, the uncompensated solution resistance effect and the capacitance of the electric double layer. Generality of results allow their application to all frequency impedance response to both, stochastic and deterministic electrode roughness. The stochastic electrode roughness is characterized through its statistical property of structure factor or power spectral density. A detailed analysis of roughness effect is carried out for a finite self-affine fractal electrode. The dynamics of the system is found to depend on phenomenological lengths, viz. diffusion length, charge transfer kinetics-diffusion length and ohmic-diffusion length; and topographic lengths, viz. tiniest length scale of fractality, topothesy length and the self-similarity index (the fractal dimension). Various anomalous responses emerge through the coupling of phenomenological length scales with topographical scales of roughness. These responses of the rough electrode are described by three characteristic frequencies: charge transfer frequency, anomalous Warburg frequency and the electric double layer charging frequency. Delay and curtailment in anomalous superdiffusion regime is seen due to the influence of quasireversibility in charge transfer process and pseudo-quasireversibility (arising out of uncompensated solution resistance). Finally, one of the most widely employed model in electrochemical impedance analysis is generalized with inclusion of ubiquitous electrode disorder.

Theory of Double Potential Step Chronoamperometry at Rough Electrodes: Reversible Redox Reaction and Ohmic Effects

Theory is developed for the DPSC (double potential step chronoamperometry) response for finite fractal and nonfractal electrode roughness with and without uncompensated solution resistance. Mathematical equation for the statistically averaged current transient and its relation to surface structure factor of random roughness is highlighted for reversible charge transfer. Result shows the enhancement of current transient upto outer crossover time for the rough electrode. Current response after application of each potential steps can show upto three regimes, i.e. short, intermediate and long time regimes. In short time, when diffusion layer thickness is small, current response is controlled by the roughness factor. Crossover between short and intermediate time regimes is controlled by diffusion layer thickness scaled with mean square surface curvature. Current behavior in long time (after outer crossover time), when diffusion layer thickness is large compared to width of roughness, becomes identical to smooth electrode. Crossover between intermediate and long time regimes is controlled by mean square width scaled with diffusion layer thickness. For fractal roughness, current has anomalous power law behavior (in intermediate time regime) while for nonfractal roughness current shows crossover between two regimes. Increase in the ratio of reverse and forward current is usually understood as kinetic complications but here we show that this can also emerge out of electrode roughness. Uncompensated solution resistance correction is also included in our theory to account for realistic experimental conditions. Finally, results are compared with the experimental data of a reversible system in viscous medium.

Effect of uncompensated solution resistance on quasireversible charge transfer at rough and finite fractal electrode

Theory for the influence of uncompensated solution resistance on quasi-reversible charge transfer at an arbitrary rough electrode is developed. Detailed model analysis is performed for a finite fractal power spectrum; characterized with fractal dimension, lowest, highest cutoff-length scales of roughness and topothesy length (width) of the interface. The composite effect of the real and apparent kinetics is contained in LHΩ which is summation of diffusion-kinetics (LH) and diffusion-ohmic (LΩ) coupling lengths. The current time response is therefore an interplay of LHΩ, diffusion length, three finite fractal lengths and fractal dimension (manifesting themselves at different times). At short time, diffusion length is smaller than LHΩ, current is proportionate to the ratio of real microscopic area and LHΩ. These phenomenological coupling delays and curtails the onset of the anomalous response. As diffusion length becomes greater than LHΩ, there is an emergence of intermediate anomalous region. However, limiting case of large LHΩ approximately constant current is seen, without dynamic roughness effects.

Electron Transfer Dynamics of Iridium Oxide Nanoparticles Attached to Electrodes by Self-Assembled Monolayers

Self-assembled monolayers (SAMs) of carboxylated alkanethiolates (-S(CH(2))(n-1)CO(2)(-)) on flat gold electrode surfaces are used to tether small (ca. 2 nm d.) iridium(IV) oxide nanoparticles (Ir(IV)O(X) NPs) to the electrode. Peak potential separations in cyclic voltammetry (CV) of the nanoparticle Ir(IV/III) wave, in pH 13 aqueous base, increase with n, showing that the Ir(IV/III) apparent electron transfer kinetics of metal oxide sites in the nanoparticles respond to the imposed SAM electron transfer tunneling barrier. Estimated apparent electron transfer rate constants (k(app)(0)) for n = 12 and 16 are 9.8 and 0.12 s(-1). Owing to uncompensated solution resistance, k(app)(0) for n = 8 was too large to measure in the potential sweep experiment. For the cathodic scans, coulometric charges under the Ir(IV/III) voltammetric waves were independent of potential scan rate, suggesting participation of all of the iridium oxide redox sites (ca. 130 per NP) in the NPs. These experiments show that it is possible to control and study electron transfer dynamics of electroactive nanoparticles including, as shown by preliminary experiments, that of the electrocatalysis of water oxidation by iridium oxide nanoparticles.

Anomalous Warburg Impedance: Influence of Uncompensated Solution Resistance

We present the theoretical results elucidating the influence of uncompensated solution resistance on anomalous Warburg’s impedance. Here, we obtain the mathematical expression which incorporates the diffusion at the rough electrode/electrolyte interface and bulk solution resistance via phenomenological length scales—diffusion length ((D/ω)1/2) and pseudoreaction penetration length (LΩ). The roughness at the interface is contained in the expression through the surface structure factor, which can be used to describe statistically any random surface morphology. Detailed analysis for realistic fractal electrodes, characterized as a finite self-affine scaling property with two lateral cutoff lengths, is presented. Limiting behavior in higher frequency is attributed to resistive effects of the electrolyte, and surface roughness is seen through the roughness factor. In the intermediate frequency regime, the anomalous power law behavior is attributed to the diffusion length weighted spatial frequency features of roughness (marking impedance loss) along with the interplay of LΩ and at lower frequencies the response crossover to classical Warburg’s behavior. This crossover frequency is dependent on the smallest of root-mean-square width (h) or lateral correlation length (L), while high-frequency crossover is dependent largely on LΩ. Phase response also shows the maximum phase gain for intermediate frequencies owing to the roughness features and is a signature to the fractal or nonfractal roughness at the interface. Our results show that owing to solution resistance the impedance response can mimic pseudo-quasireversibilty inducing a delay in the onset of diffusion-controlled regime and can hack the anomalous response due to roughness partially or completely.

Theory of Generalized Cottrellian Current at Rough Electrode with Solution Resistance Effects

A theory for effect of uncompensated solution resistance on Nernstian (reversible) charge transfer at an arbitrary rough electrode is developed. The significant deviation from the Cottrellian behavior is explained, as arising from the resistivity of the solution and geometric irregularity of the interface. Results are obtained for various electrode roughness models, viz., (i) deterministic surface profile, (ii) roughness as random surface profile with known statistical properties, and (iii) random functions with limited self-affine fractal properties. Expressions for concentration, current density, and total current transients have a systematic operator structure in Fourier transformed (deterministic) surface profile function. For a randomly rough electrode, the statistically averaged response is obtained by ensemble averaging over all possible surface configurations. An elegant mathematical formula between the average electrochemical current transient and surface structure factor of roughness is obtained. Realistic fractal roughness is characterized as self-affine scaling property over limited length scales. Limiting behavior in short time, is attributed to resistive effects of the electrolyte, roughness factor and surface curvatures. In the intermediate time, the anomalous power law behavior is attributed to the diffusion length weighted spatial frequency features of roughness. Our results help with the quantitative understanding of generalized Cottrellian response of moderately supported electrolytic solution at rough electrode/electrolyte interface.

Theoretical Analysis of Microscopic Ohmic Drop Effects on Steady-State and Transient Voltammetry at the Disk Microelectrode: A Quasi-Conformal Mapping Modeling and Simulation

The effect of uncompensated solution resistance on steady-state and transient voltammograms at the disk microelectrode was for the first time treated theoretically and numerically at the microscopic level using specific quasi-conformal mapping for the case of absence of electric migration. It has been shown that microscopic distributions of electric potential and current density at a disk microelectrode affect the voltammetric waves at different degrees across the electrode surface due to the variation of elementary resistances and elementary current fluxes over the electrode surface which leads to nonlinear effects that have not been discussed in existing theoretical treatments of ohmic drop at microelectrodes. The analysis of steady state voltammetry in strongly resistive media under Nernstian conditions has allowed justification by appropriate analytical derivations of the widely used potential-shift correction of steady state voltammograms by plotting i vs ( E - iR e).