Uncompensated Resistance Research Articles

Convolution Analysis in Electrodeposition

Convolution is a well established method for data analysis for electrochemical processes where both product and reactants are soluble. Advantages of convolution analysis include (a) facile evaluation of kinetic and system parameters, (b) ready corrections for nonfaradaic uncompensated resistance and double layer charging, (c) track of surface concentrations with time, independent of the voltage perturbation sequence, and (d) ease of convolution calculation from digitized current data. Here, equations are derived for convolution of electrodeposition data and a data analysis protocol is presented. Advantages are found for convolution analysis in electrodeposition. Parameters that can be determined from convolution analysis in electrodeposition are standard heterogeneous rate constant k 0 and exchange current density j 0, transfer coefficients α and β, formal potential E0′ , resistance to charge transfer, and diffusion coefficient of the solution soluble reactant D M . Convolution in electrodeposition is illustrated for silver deposited from an ionic liquid onto a glassy carbon electrode, where experimental data are tracked cyclic voltammetrically.

Mechanism, Kinetics and Simulation of Electrocatalytic Oxidation of Dimethylamine Borane (DMAB) on Electroless Gold

Dimethylamine borane ((CH3)2NHBH3) or DMAB, is broadly used as a reducing agent in electroless autocatalytic platings like gold and nickel-boron, hydrogen storage, and reductive amination. However, the mechanism of its DMAB oxidation procedure remains unclear. This project is based on the hypothesis that a multi-step electron transfer mechanism exists for oxidizing the reducing agent DMAB on gold in alkaline media. According to this mechanism, the active species produced when DMAB is used at high hydroxide content is the BH3OH-. This species is created through a series of irreversible electrochemical oxidation producing the following intermediates BH2(OH)2-, BH(OH)3- and B(OH)4-, which is the final product. Multiple electrochemical methods have been used to uncover the properties of DMAB oxidation progress and verify above-mentioned hypothesis. Electrochemical Impedance Spectroscopy (EIS) was used to test the uncompensated resistance between the working electrode and reference electrode and calibrated in the following experiments: Cyclic voltammetry (CV) showed that DMAB in hydroxide electrolytes have three half-wave potentials with E_(1/2) of -0.778, -0.174 and 0.248 V. Kinetic current values obtained from the Koutecky-Levich plot decreased with temperature with -4.065, -3.62 and -1.45 mA/cm2 at 25°C, 41°C and 52°C, respectively. Rotating Disk Electrode (RDE) and Chronoamperometry (CA) were used to determine the Diffusion Coefficient of BH3(OH)-; BH2(OH)2- and BH(OH)3- 1.38E-05, 3.31E-05 and 1.01E-04, respectively. Tafel analysis was used in obtaining the transfer coefficient, whereas Klingler and Kochi’s method evaluated the constant. These kinetic parameters were used in KISSA-1D software to simulate the CVs. Gas Chromatography with Mass Spectrometry (GC/MS) was used to verify the existence of B(OH)4- and a peak at m/z 78.8 was recorded. All of this provided evidence that the three intermediates are involved in the proposed mechanism. In the future, simulated and experimental approaches will be investigated for other amine boranes compounds such as Sodium cyanoborohydride (NaBH3CN), Sodium triacetoxyborohydride (NaBH(O2CCH3)3), and Sodium borohydride (NaBH4). This work will have far-reaching consequences in enhancing the practical applications of gold and nickel in microelectronics and fuel cells.

The HER performance of 2D materials is underestimated without morphology correction

2D transition metal dichalcogenides (2D-TMDs) are considered promising materials for electrochemical catalysis and energy storage. However, large differences in electrochemical performance have been reported for 2D-TMD electrodes with different morphology, such as thickness, edge density, and porosity. We here demonstrate that limitations in the homogeneous charge transfer of 2D-TMDs are responsible for the significant observed variations in hydrogen evolution reactions (HER). Statistical electrochemical characterization was conducted on microscopic MoS2 and WS2 devices with compositional uniformity and controllable morphology by localized HER measurements. Detailed analysis establishes the dominating effect of the uncompensated resistance on overpotential and Tafel slope, which are commonly utilized as HER figures of merit. A correction scheme is presented that reveals the intrinsic electrocatalytic properties of 2D materials electrodes, independent of morphology. This approach was applied to previously reported polarization data and revealed differences between extracted and intrinsic Tafel slopes of up to 400% leading to potentially erroneous assignments of the HER mechanism. Finally, the correlation of two-terminal carrier transport measurements and electrochemical characterization demonstrates the in-plane conduction as the origin of the low electrochemical activity in 2D-TMDs. Our results highlight the impact of morphology-dependent carrier transport on the electrochemical properties of 2D materials.

Exploring the Role of the Connection Length of Screen-Printed Electrodes towards the Hydrogen and Oxygen Evolution Reactions.

Zero-emission hydrogen and oxygen production are critical for the UK to reach net-zero greenhouse gasses by 2050. Electrochemical techniques such as water splitting (electrolysis) coupled with renewables energy can provide a unique approach to achieving zero emissions. Many studies exploring electrocatalysts need to "electrically wire" to their material to measure their performance, which usually involves immobilization upon a solid electrode. We demonstrate that significant differences in the calculated onset potential for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) can be observed when using screen-printed electrodes (SPEs) of differing connection lengths which are immobilized with a range of electrocatalysts. This can lead to false improvements in the reported performance of different electrocatalysts and poor comparisons between the literature. Through the use of electrochemical impedance spectroscopy, uncompensated ohmic resistance can be overcome providing more accurate Tafel analysis.

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.

Pitfalls and Protocols: Evaluating Catalysts for CO2 Reduction in Electrolyzers Based on Gas Diffusion Electrodes

The evaluation of catalysts on gas diffusion electrodes (GDEs) have propelled the progress of electrochemical CO2 reduction reaction (CO2RR) at industry-relevant activities. However, high experimental complexities exist in GDE-based flow electrolyzers, whereby various experimental factors can influence the evaluation of catalytic CO2RR performances. Not accounting for these experimental factors could result in inconsistent conclusions and thus hinder rational catalyst developments. This Perspective highlights a range of experimental factors that can affect the performance metrics for electrocatalysts. Specifically, the product faradaic efficiency can be influenced by the overestimation of the effluent gas flow rate, unaccounted losses of products, and unintended alteration of microenvironments. In addition, cathodic voltage can be inaccurately determined due to the unaccounted dynamic changes in uncompensated resistance. By raising awareness of these potential pitfalls and establishing appropriate protocols, we foresee a more meaningful benchmarking of catalytic performances across the literature.

Comparison of the In Vitro and In Vivo Electrochemical Performance of Bionic Electrodes

The electrochemical performance of platinum electrodes was assessed in vitro and in vivo to determine the impact of electrode implantation and the relevance of in vitro testing in predicting in vivo behaviour. A significant change in electrochemical response was seen after electrode polarisation. As a result, initial in vitro measurements were poor predictors of subsequent measurements performed in vitro or in vivo. Charge storage capacity and charge density measurements from initial voltammetric measurements were not correlated with subsequent measurements. Electrode implantation also affected the electrochemical impedance. The typically reported impedance at 1 kHz was a very poor predictor of electrode performance. Lower frequencies were significantly more dependent on electrode properties, while higher frequencies were dependent on solution properties. Stronger correlations in impedance at low frequencies were seen between in vitro and in vivo measurements after electrode activation had occurred. Implanting the electrode increased the resistance of the electrochemical circuit, with bone having a higher resistivity than soft tissue. In contrast, protein fouling and fibrous tissue formation had a minimal impact on electrochemical response. In vivo electrochemical measurements also typically use a quasi-reference electrode, may operate in a 2-electrode system, and suffer from uncompensated resistance. The impact of these experimental conditions on electrochemical performance and the relevance of in vitro electrode assessment is discussed. Recommended in vitro testing protocols for assessing bionic electrodes are presented.

Photodeposited IrO2 on TiO2 support as a catalyst for oxygen evolution reaction

A simple, alternative, catalyst preparation method was proposed in order to combine the properties of photoactive and stable TiO2 with state-of-the art of IrO2 for the oxygen evolution reaction (OER). IrO2 nanoparticles were obtained in the process of photodeposition on the surface of TiO2 powder by UV illumination from appropriate Ir salt aqueous solution. Physicochemical characterization of the resulting IrO2/TiO2 composite, containing 25% w/w Ir, was carried out by transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the prepared IrO2/TiO2 catalyst was compared with that of commercial unsupported IrO2. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) were performed to identify the surface electrochemistry and OER of the IrO2/TiO2 catalyst. Electrochemical impedance spectroscopy (EIS) was used to determine uncompensated and charge transfer resistance. CA experiments were carried out in order to evaluate the stability of the IrO2/TiO2 composite during OER in the dark and under UV light irradiation. The photodeposition method on a TiO2 support resulted in 1–2 nm Ir nanoparticles, very well dispersed on the surface and in their oxidized state (IrO2). Electrochemical results indicated that despite its lower conductivity, the IrO2/TiO2 composite exhibits comparable intrinsic electrocatalytic activity for OER with that of the commercial IrO2 catalyst. It was found that under UV light irradiation there has been improvement of the stability of the IrO2/TiO2 performance during oxygen evolution (presumably due to sustained activation of reactive species via photogenerated holes or OH radicals) as well as current enhancement (due to the interaction between the photogenerated holes in TiO2 support and IrO2 nanoparticles). These would be beneficial effects in prolonged water photo-electrolysis.

An Interpretation of the CPE from the Percolation Theory in Graphite+Poliethylene Composite Electrodes

Technological composites based on polymeric materials reinforced with fibers or inorganic fillers are increasingly used due to their mechanical and thermal properties. In general, the polymeric materials that are commonly used, whether they are thermostable or thermoplastic, provide a low specific weight and also a greater ease of machining compared to the technological metals and ceramic materials used in the Industry. This is why they are also increasingly used in the manufacture of electrodes and membranes for conventional electrochemical cells and reactors, as well as in electronic devices for everyday use, such as mobile phones or personal computers. Historically, the first conductive polymers were manufactured by dispersing micrometric carbonaceous or metallic particles in insulating polymeric matrices. Nowadays, the number of possible benefits and applications of the composites of the polymer + conductive charge type has increased enormously, but it is worth noting that the theoretical concepts on the Percolation Theory, developed mainly during the 20th century, are still useful for trying to understand the passage of electric current through the polymer + charge composite electrodes [1,2] and, therefore, the Percolation Theory can also contribute to the design of supercapacitors, electrochemical reactors or sensors in which these composite materials are used. It is well known that the ohmic drop through electrodes causes one of the greatest efficiency losses in technological devices for storing or generating energy, which is why the tests for the measurement of electrical resistance in conventional cells are very useful for the design of electrodes, membranes and of the electrochemical reactors and sensors themselves in which polymer composite + charge are used This work focuses on the impedance spectroscopy, EIS response of the polyethylene / graphite composite system. An attempt is made to correlate the concept of fractality of the Percolation Theory with its phenomenological electrochemical behavior. In the case of a conventional three-electrode cell in which the most significant contribution for practical purposes is that of the electrode / solution interfacial region, the experimentally measured impedance can be associated with that of an equivalent circuit consisting of a resistance in series with a constant phase element CPE, given the heterogeneity of the electrode surface and the predictable distribution of electrical potentials on its surface .Where j = √ (-1), is the sum of the electrical resistance of the composite electrode and the rest of the cell, while and are adjustment coefficients of the imaginary component of the impedance that, like the real component they must depend on the graphite content and therefore on the electrical percolation of the material. The CPE coefficients also depend on the concentration of electrolyte present in the interfacial region.1) Navarro-Laboulais J; Trijueque J; Garcia-Jareño JJ; Benito D; Vicente F. Determination of the electroactive area of graphite plus polyethylene composite electrodes. Uncompensated resistance effects and convolution analysis of chronoamperograms. Journal of Electroanalytical Chemistry . 443-1 (1997) 41 - 48.2) Navarro-Laboulais J; Trijueque J; Garcia-Jareño JJ; Benito D; Vicente F. Electrochemical impedance spectroscopy of conductor-insulator composite electrodes: properties in the blocking and diffusive regimes. 905795 - Journal of Electroanalytical Chemistry. 444 – 2 (1998) 173 – 186.

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.

Convolutive modeling of cyclic voltammetry, AC-voltammetry, sine wave voltammetry and impedance spectroscopy with interfacial CPE behaviour and uncompensated ohmic resistances: A Unified Theory

The constant phase element (CPE) is a well-established circuit component for the frequency domain simulation of electrochemical reactions at disperse and heterogeneous electrodes. Computing the time-dependent current response of voltammetric experiments with interfacial CPE behaviour is, however, not a straightforward task, owing to the lack of analytical time domain solutions of the convoluted capacitive current. In this paper, a universal framework for the convolutive treatment of cyclic voltammetry (CV), alternating current cyclic voltammetry (ACCV), (large) sine wave voltammetry (LSWV) and electrochemical impedance spectroscopy (EIS) in presence of interfacial CPEs and uncompensated Ohmic resistances is presented. A combination of numerical and analytical inverse Laplace transformation techniques allows the accurate assessment of the non-ideal capacitive behaviour, which can be used in turn for classical convolution algorithms. The convolutive approach bears the advantage that different electrode geometries with any kind of spatial boundary conditions as well as first order homogeneous chemical reactions, coupled to the charge transfer step, can be implemented readily. This offers an exceptionally large degree of flexibility in the simulations for the electrochemical system at hand.

Modeling and Experimental Study of the Electron Transfer Kinetics for Non-ideal Electrodes Using Variable-Frequency Square Wave Voltammetry.

The knowledge of nonequilibrium electron transfer rates is paramount for the design of modern hybrid electrocatalysts. Herein, we propose a general simulation-based approach to interpret variable-frequency square wave voltammetry (VF-SWV) for heterogeneous materials featuring reversible redox behavior. The resistive and capacitive corrections, inclusion of the frequency domain, and statistical treatment of the surface redox kinetics are used to account for the non-ideal nature of electrodes. This approach has been validated in our study of CoII/CoI redox transformation for Co tetraphenylporphyrin (CoTPP) immobilized on carbon cloth and multiwalled carbon nanotubes (CNTs) - one of the most active heterogeneous molecular catalysts in carbon dioxide (CO2) electroreduction. It is demonstrated that the modeling of experimental data furnishes the capacitance of the surface double layer C, uncompensated resistance Ru, symmetry coefficients α, kinetic constants k0, and equilibrium redox potentials E0 in one experiment. Moreover, the proposed method yields a stochastic map of the redox kinetics rather than a single value, thus exposing the inhomogeneous nature of the electrochemically active layer. The computed parameters are in excellent agreement with the results of the classic methods such as cyclic voltammetry and fall in line with the reported CoTPP catalytic activity. Thus, VF-SWV is suitable for the study of high-level composites such as covalent organic frameworks and organometallic-CNT mixtures. The resulting insights into the electron transfer mechanisms are especially useful for the rational development of the catalyst-support interfaces and immobilization methods.

In Memoriam of Jean‐Michel Savéant (1933–2020)

In Memoriam of Jean‐Michel Savéant (1933–2020)

Seven steps to reliable cyclic voltammetry measurements for the determination of double layer capacitance

Discovery of electrocatalytic materials for high-performance energy conversion and storage applications relies on the adequate characterization of their intrinsic activity, which is currently hindered by the dearth of a protocol for consistent and precise determination of double layer capacitance (C DL). Herein, we propose a seven-step method that aims to determine C DL reliably by scan rate-dependent cyclic voltammetry considering aspects that strongly influence the outcome of the analysis, including (a) selection of a suitable measuring window, (b) the uncompensated resistance, (c) optimization of measuring settings, (d) data acquisition, (e) selection of data suitable for analysis, (f) extraction of the desired information, and (g) validation of the results. To illustrate the proposed method, two systems were studied: a resistor–capacitor electric circuit, and a glassy carbon disk in an electrochemical cell. With these studies, it is demonstrated that when any of the mentioned steps of the procedure are neglected, substantial deviations of the results are observed with misestimations as large as 61% in the case of the investigated electrochemical system. Moreover, we propose allometric regression as a more suitable model than linear regression for the determination of C DL for both the ideal and the non-ideal systems investigated. We stress the importance of assessing the accuracy of not only highly specialized electrochemical methods, but also of those that are well-known and commonly used as it is the case of the voltammetric methods. The procedure proposed herein is not limited to the determination of C DL, but can be effectively applied to any other analysis that aims to deliver quantitative results via voltammetric methods, which is crucial for the study of kinetic and diffusion phenomena in electrochemical 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.

Simulating Cu electrodeposition in high aspect ratio features: Effect of control mode and uncompensated resistance in S-NDR systems

Void-free Cu electrodeposition in high aspect ratio features requires, at a minimum, an additive package containing micromolar halide and polyether that combine to form a co-adsorbed adlayer that inhibits metal deposition on the electrode interface. Successful feature filling relies on preferential growth proceeding from the most recessed surfaces where sustained breakdown of the polyether-halide suppressor layer occurs. Localization is the result of positive feedback between inhibitor breakdown and metal deposition subject to transport limitations of the suppressor precursor(s). This gives rise to a S-shaped negative differential resistance (S-NDR) that, convolved with uncompensated ohmic resistance, results in electrode bifurcation into active and passive zones. The interplay between the additive derived S-NDR behavior, uncompensated cell resistance, and potentiostatic regulation is explored in comparison to galvanostatic feature filling. Uncompensated resistance arises from the working electrode contact and electrolyte between the working and reference electrodes. For a CuSO4 – H2SO4 electrolyte containing 80 µmol/L Cl− and 40 µmol/L polyether, simulations of potentiostatic deposition with minimal uncompensated resistance reveal a narrow window between fully passive and voided feature filling; bottom-up filling terminates prematurely even under the most favorable conditions. In contrast, optimized galvanostatic operation enables void-free feature filling with termination dictated by coulometry. Increasing the uncompensated resistance along with application of accordingly more negative applied potentials produces filling dynamics that blend the positive attributes of galvanostatic and potentiostatic deposition to enable complete, void-free feature filling with spontaneous passivation near the feature opening. Importantly, these beneficial filling effects are also evident for trench arrays having variable widths or heights.

Combined Electrokinetic-Electrochemical Probe to Understand Electric Double Layer at Metal-Electrolyte Interface: Application to Polycrystalline Gold and Platinum

We developed a novel technique combining electrochemistry and electrokinetics to understand the structure of electric double layers (EDLs) at metal-electrolyte interface, and we applied it to study polycrystalline Au (poly-Au)-electrolyte and polycrystalline Pt (poly-Pt)-electrolyte interfaces. Traditional electrochemical methods are used to study Faradaic charge transfer reactions and EDLs at a polarized metal-electrolyte interface. On the other hand, electrokinetic methods, such as streaming current/potential are used to study ion distribution and surface conductance of ions in the diffuse layer at the interface of unpolarized solid material and electrolyte. In traditional electrokinetic experiments, the solid material to be studied is mounted inside a microchannel. An electrolyte of known chemical composition (pH, concentration, specifically adsorbing ions etc.) is flown through the microchannel at various pressures. The diffuse layer formed at the interface contains mobile ions with a net positive or negative charge. These ions, flowing with the electrolyte constitute streaming current. Zeta potential is calculated from the streaming current vs pressure data.We combined a 3-electrode electrochemical setup and a pressure regulated microfluidic setup to apply potential on a planar electrode mounted inside a microchannel and flow the electrolyte at various pressures at the same time. The equivalent circuit of our method is shown in Figure 1(a). As charge on the electrode surface strongly depends on the applied potential, different values of streaming currents are obtained for different values of applied potentials. Zeta potential at different applied potentials is calculated from the streaming current vs pressure data. These experimentally calculated zeta potential values are substituted into the exact analytical solution of Poisson-Boltzmann distribution in the diffuse layer to explicitly calculate ion density and ionic conductivity in this layer. The charging mechanism at the interface is studied using this data. We used the simplified Gouy-Chapman interfacial model in the capacitive region of the applied potential to compare the observations and gain insights about the charging behavior.The method was applied to electrochemically clean poly- Au and Pt surfaces. Electrolyte of high concentration (thin diffuse layer) was used to minimize the iR drop. For poly Au-electrolyte interface, we observed an approximately homogeneous charging at the interface, in the applied potential window where Au is known to behave as an ideal capacitor, and zeta potential was found to linearly increase with the iR corrected applied potential (Figure 1(b). Applied potential at which the diffuse layer is completely neutral (0 zeta potential) is found to lie within the experimental range of potential of zero charge (PZC) of Au, implying low adsorption of charges at inner Helmhotz plane (IHP). At high applied potentials ( 750 mV vs Ag/AgCl), an onset of chloride anion adsorption in a chloride rich solution was observed on Au surface. As a consequence of that, we observed a drop in zeta potential from its linearly increasing trend.For Pt, our initial experiments indicate a similar trend: zeta potential is found to increase in the capacitive region (Figure 1(c)). We observed an anomalous charging behavior in the H+ adsorption region (Vapp < PZC), where zeta potential decreased slightly. This drop is presumably a result of the chemisorbed H+ ions. For Pt EDLs, we observed the applied potential at which the diffuse layer is neutral is generally greater than the known PZC of 260 mV vs RHE. This is probably due to the pseudocapacitance which is caused by mild adsorption of ions at Pt IHP.The method developed by us is general and applicable to a broad electrochemistry and electrokinetics community. Ion distribution in the diffuse layer at a polarized metal-electrolyte interface, and its dependence on applied potential and electrolyte chemical composition can be studied efficiently using this method. At present the technical limitation of this method is a high uncompensated resistance, preventing the application of high potentials to observe the effects of surface oxides on the double layer. In future, the knowledge of ion distribution and ionic conductivity calculated from this method will be applied to understand the ion-conduction mechanism inside the micropores of PEM fuel cells, where ionomers cannot penetrate and enhanced double layer conductivity can help the transport of H+ ions to Pt particles. Figure 1

Numerical Resolving of Net Faradaic Current in Fast-Scan Cyclic Voltammetry Considering Induced Charging Currents.

In this paper, we study theoretically and experimentally the effect of induced charging currents on the fast-scan cyclic voltammetry. As explained in this paper, the phenomenon originates from the coupling between faradaic and capacitive currents in the presence of uncompensated resistance. Due to the existence of induced charging currents, the capacitive contribution to the total current is different from the capacitive current measured in the absence of electroactive species. In this paper, we show that this effect is particularly important when the ratio of the capacitive current and the total current is close to unity, even for a relatively low cell time constant. Consequently, the conventional background subtraction method may be inaccurate in these situations. In this work, we develop a method that separates the faradaic and capacitive currents, combining simulation and experimental data. The method is applicable even in the presence of potential-dependent capacitance. The theoretical results are compared with some previously reported results and with experiments carried out on the potassium ferrocyanide/ferricyanide redox couple. Platinum disk electrodes of different diameters and NaClO4 support electrolyte of different concentrations were used to obtain different cell time constants. The proposed method allowed us to separate the real capacitive current even in the situations where the conventional background subtraction used in many published papers is clearly inappropriate.

In-situ detection of single particle impact, erosion/corrosion and surface roughening

Particle impact is technologically important and can cause significant damage to a surface. Detecting the approach and impact of a particle would give key information on the process. High-speed imaging of this process gives information on a particle's velocity and movement but does not answer key questions relating to changes in electrochemical properties of a surface caused by the resultant damage on impact. Furthermore, it is difficult to apply in non-transparent media. To gain this key information, we have deployed a high-speed electrochemical impedance technique with the ability to determine the uncompensated resistance, Faradaic current and effective capacitance of an electrode. This technique has a time resolution of 1.25 μs. Individual impacts of sand particles in a fluid jet (jet velocity ~4–5 m s−1) are used to cause erosion/corrosion of an aluminium interface. Surface properties are shown to change after individual particle impacts, which is preceded by the electrochemical detection of the particle as it approached the solid/liquid interface. For the first time, the in-situ roughening of the electrode surface is reported for a single particle impact. A link between the effective mass loss of the electrode and the overall surface erosion is shown, with an equivalent roughening rate of 8.5 F g−1 as determined from the data. This study shows how individual sand particles, and the damage they cause to an interface, can be detected with high precision and new insight. This will improve our understanding of erosive environments.

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.