Taffit: An Excel Tool for Fitting Tafel Data

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

ABSTRACTKinetics of chloride ion oxidation was studied on graphite, glassy carbon (GC), and platinum electrodes. The performance of the electrodes was monitored using the cumulative productivity and current efficiency of the cell as indicators. It was seen that the performance of the working electrode improved with repeated uses, the current efficiency increased from 22% in the third use to about 46% in the tenth use. The study also revealed that the role of diffusion to the total anodic current was insignificant and chloride ions were transported at the electrode surface only by conduction. The hypochlorite production in case of platinum was about 3.66 times than that of graphite and GC with the current efficiency of 75% in contrast to 46% found in graphite and GC. But platinum undergoes passivation to a significant extent unlike the graphite and GC electrodes. Chronopotentiometry experiments confirmed the passivation process in platinum electrodes, showed a steep rise in potential from 1.2 to 2 V while the electrode potential was uniformly maintained at 1.7 V in carbon electrodes. The highest io, exchange current density value was observed at 0.45 mA/cm2 in 0.5 M electrolyte, which is an indication of improved electrocatalytic activity with increased molar concentration. After continuous uses the corrosion rate studies revealed that platinum and GC electrodes were corrosion resistant whereas graphite underwent corrosion at the rate of 0.006 mm/h. The study dictated that carbon electrodes has great potential to be used as an alternatives to platinum electrodes, however, further investigations are required to assess its practical applicability in the public water supply system.

Effect of electrode materials on the kinetics of the electro-reduction of peroxyacetic acid

Effect of electrode materials on the kinetics of the electro-reduction of peroxyacetic acid

Voltammetric investigations on the relative deactivation of boron-doped diamond, glassy carbon and platinum electrodes during the anodic oxidation of substituted phenols in room temperature ionic liquids

Tafel analysis is widely used to characterize electrochemical kinetics and assess the properties of electrocatalysts for use in fuel cells, electrolyzers, and other applications. Conventional Tafel analysis is an extension of the Butler-Volmer equation at high overpotentials under conditions where mass transport is not significant and the reverse reaction rate is negligible compared to the studied half-reaction. Determination of kinetic parameters from a Tafel plot involves linear regression in regions of large overpotential. This method is limited in part by the subjective determination of linearity, as the kinetic parameters obtained by the regression may vary significantly depending on the chosen linear region.In an effort to increase measurement quality and decrease subjectivity, an algorithm has been developed that generates a Tafel plot from a linear sweep voltammogram (LSV) and determines the exchange current density j 0, charge transfer coefficient α, and Tafel slope of closest fit. Comparisons of kinetic parameters between conventional and algorithmic Tafel analysis are made for the hydrogen evolution reaction (HER, 2H+ + 2e- → H2) on different metal electrodes and Nafion® composite electrodes. The algorithmic Tafel analysis parameters correlate well with conventional methods. Similar agreement is observed between literature and algorithmically fitted kinetic parameters for different electrochemical systems. The developed algorithm allows for straightforward, rapid, and user bias independent Tafel analysis and can be easily used to increase measurement quality.

Electrocatalysts for hydrogen evolution and oxidation (HER and HOR) reactions, oxygen reduction and evolution (ORR and OER) reactions, and carbon dioxide reduction reactions (CO2RR) are evaluated by Tafel analysis. The Tafel equation specifies the log-linear relationship between current and overpotential \U0001d6c8. Heterogenous electron transfer parameters of exchange current density j o and transfer coefficient \U0001d6c2 are found. Standard heterogenous electron transfer rate k 0 can be found from j o.Conventionally, Tafel analysis is an extension of the Butler-Volmer equation applied at high overpotentials but where mass transport is not significant and the reverse reaction rate is negligible. Applicable at high \U0001d6c8 when electron transfer rates are slow, kinetic parameters are extracted by linear regression. The conventional method is, however, subject to inaccuracies because the linear region is often determined subjectively, without attention to the constraints on overpotential range, no mass transport limitations, and low j o.An algorithm is developed to automate Tafel analysis with the objective to increase measurement accuracy and decrease subjective identification of the linear region. From linear sweep voltammograms (LSVs), j o and α are determined from Tafel slopes in the best fit, linear range.Comparisons of kinetic parameters between conventional and algorithmic Tafel analyses are made for the hydrogen evolution reaction (HER, 2H+ + 2e- ⇌ H2) on various unmodified electrodes and electrodes modified with Nafion® composites. The algorithmic Tafel analysis parameters correlate well with conventional Tafel analyses that respect constraints on mass transport, \U0001d6c8, and j o. Similar agreement is observed between literature and algorithmically fitted kinetic parameters for different electrochemical systems. The algorithm allows for straightforward, rapid Tafel analysis for improved measurement of rate parameters that is independent of user bias in selection of the linear region. Acknowledgments This work was supported by the Army Research Office.

An electrochemical study related to the redox characteristics of Ethyl-3-acetyl-6-methyl-1,4-diphenyl-4,3a-dihydro-1,3,4-triazolino[3,4-a] pyrimidine-5-carboxylate ester and its derivatives (1a-f) and (2a-e) in nonaqueous solvents such as 1,2-dichloroethane (DCE), dichloromethane (DCM), acetonitrile (AN), dimethylsulphoxide(DMSO) and tetrahydrofurane (THF) using 0.1 mol dm-3 tetrabutylammonium perchlorate (TBAP) as a supporting electrolyte at platinum, glassy carbon and gold electrodes , has been performed using cyclic voltammetry (CV). Controlled potential electrolysis (CPE) is also carried out to elucidate the course of different electrochemical reactions through the separation and identification of the intermediates and final electrolysis products .The redox mechanism is suggested and proved. It was found that all the investigated compounds in all solvents are oxidized in a single irreversible one electron donating process following the well known pattern of the EC-mechanism to give a dimer. On the other hand, these compounds are reduced in a single irreversible one electron step to form the anion radical, which is basic enough to abstract proton from the media forming the radical which undergoes tautomerization and then dimerization processes to give also another bis-compound through N-N linkage formation. Key words: Cyclic voltammetry, oxidation, reduction, triazolopyrimidine, non-aqueous media, platinum electrode, glassy carbon electrode, gold electrode.

The bioelectrochemistry of the blue copper protein, pseudoazurin, at glassy carbon and platinum electrodes that were modified with single-wall carbon nanotubes (SWNTs) was investigated by multiple scan rate cyclic voltammetry. The protein showed reversible electrochemical behavior at both bare glassy carbon electrodes (GCEs) and SWNT-modified GCEs (SWNT|GCEs); however, direct electrochemistry was not observed at any of the platinum electrodes. The effect of the carbon nanotubes at the GCE was to amplify the current response 1000-fold (nA at bare GCE to µA at SWNT|GCE), increase the apparent diffusion coefficient D app of the solution-borne protein by three orders of magnitude, from 1.35 × 10−11 at bare GCE to 7.06 × 10−8 cm2 s-1 at SWNT|GCE, and increase the heterogeneous electron transfer rate constant k s threefold, from 1.7 × 10−2 cm s−1 at bare GCE to 5.3 × 10−2 cm s−1 at SWNT|GCE. Pseudoazurin was also found to spontaneously adsorb onto the nanotube-modified GCE surface. Well-resolved voltammograms indicating quasi-reversible faradaic responses were obtained for the adsorbed protein in phosphate buffer, with I pc and I pa values now greater than corresponding values for solution-borne pseudoazurin at SWNT|GCEs and with significantly reduced ΔE p values. The largest electron transfer rate constant of 1.7 × 10−1 cm s−1 was achieved with adsorbed pseudoazurin at the SWNT|GCE surface in deaerated buffer solution consistent with its presumed role in anaerobic respiration of some bacteria.

The electrochemistry of the Nb(V)/Nb(IV) redox couple in the KCl-K2NbF7 melt has been studied at 1073-1173 K on glassy carbon and platinum electrodes by transient electrochemical techniques. The diffusion coefficients of Nb(V) and Nb(IV) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry. The values obtained by these methods at the different substrates are also in a good agreement. Diffusion coefficients decreased when niobium oxidation state increased, while the activation energies for diffusion increased. The standard rate constants of charge transfer (ks) on platinum and glassy carbon electrodes for Nb(V)/Nb(IV) redox couple were calculated on the basis of cyclic voltammetry data at a sweep rate 0.75 < v ≤ 2.0 V s-1, where a mixed diffusion and electron-transfer control was observed. It was found that ks increased with increasing temperature and values of ks obtained at platinum electrode were higher than at a glassy carbon electrode. The values of the standard rate constants testify that the redox process Nb(V) + e- ↔ Nb(IV) proceeds quasi-reversibly, mostly under diffusion control.

Tafel analysis and electrochemical impedance spectroscopy (EIS) have been widely used to characterize many kinds of electrocatalysts. The former provides the kinetic information of an electrochemical reaction with the exchange current while the latter does with the charge transfer resistance closely related to the exchange current. Both techniques, however, suffer from practical troubles which often decrease their reliabilities. In order to circumvent those troubles, an alternative was suggested that Tafel analysis was combined with EIS, even though its theoretical background was not clearly established. Tafel analysis is based on dc measurement, and EIS is on an ac one, respectively. Here, inspired by the second generation of EIS from chronoamperometry, we try to find how those techniques are correlated by investigating an amperometric response from EIS. The first step is Fourier transform of an arbitrary dc potential signal in the time domain to obtain the amplitudes and phases of the Fourier series which are equivalent to ac signals of each frequency. Second, with the Fourier series being applied onto the impedance data, the responding currents of each frequency are calculated by Ohm’s law. Third, the current in the frequency domain is transferred back to the time domain by inverse Fourier transform to yield chronoamperometric or Tafel plots depending on the type of the applied dc potential. Finally, we can study Tafel plots based on EIS at different conditions and their correlations which are expected to be a better indicator for characterizing electrocatalysts instead of the slope of the classical Tafel analysis.

Insights on the kinetics of concanavalin A adsorption on platinum and glassy carbon electrodes from electrochemical impedance spectroscopy data

Tafel analysis is widely used to characterize electrochemical kinetics and assess the properties of electrocatalysts for use in fuel cells, electrolyzers, and other applications. This method is limited in part by the subjective determination of linearity, as the kinetic parameters obtained by the regression may vary significantly depending on the chosen linear region. In an effort to increase measurement quality and decrease subjectivity, an algorithm has been developed in Microsoft® Excel® that generates a Tafel plot from an LSV and determines the exchange current density j 0, charge transfer coefficient α, and Tafel slope of closest fit. Comparisons of kinetic parameters between conventional and algorithmic Tafel analysis are made for the hydrogen evolution reaction (HER, 2H+ + 2e- ⇌ H2) for different electrodes. The algorithmic parameters correlate well with conventional methods and show increased measurement precision. Similar agreement is observed between literature and algorithmic fits of representative Tafel plots. The developed algorithm allows for straightforward, rapid, and user bias limited Tafel analysis and can be used to increase measurement quality.

Ab initio computational modeling of the electrochemical reactivity of quinones on gold and glassy carbon electrodes

Comparison of electrochemiluminescence and amperometric detection of lipid hydroperoxides