Effects of Unequal Diffusion Coefficients and Coupled Chemical Equilibria on Square Wave Voltammetry at Disc and Hemispherical Microelectrodes

Olmos, J.M.; Molina, Á.; Laborda, Eduardo; Martı́nez-Ortiz, Francisco

doi:10.1016/j.electacta.2015.07.048

Cited by 10 publications

(8 citation statements)

References 43 publications

(68 reference statements)

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“…[1][2][3][4][5][6][7] Although a strong theoretical basis exists, 8 the use of SWV for identifying electrode reaction mechanisms has been limited to a small number of electrochemists. Our goal is to broaden the use of SWV for determining electrode reaction mechanisms especially by nonexperts in electrochemistry who make occasional use of voltammetry in characterizing new compounds.…”

mentioning

confidence: 99%

Diagnostic Criteria for Identifying an ECE Mechanism with Cyclic Square Wave Voltammetry

Mann

Helfrick

Bottomley

2015

J. Electrochem. Soc.

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Theory for cyclic square wave voltammetry of an irreversible first-order chemical reaction coupling two electron transfers, i.e. an ECE mechanism, is presented. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. Note that the results presented herein are applicable only to ECE processes where E 0 for the second electron transfer step is negative of that for the first. Under this condition, disproportionation reactions do not occur. From the trends obtained, diagnostic criteria for this mechanism were deduced. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure reaction kinetics over the range −2 ≤ log k f ≤ 6. Square wave voltammetry (SWV) has been shown to be particularly useful in identifying electrode reaction mechanisms especially those involving chemical reactions coupled to the electron transfer step.1-7 Although a strong theoretical basis exists, 8 the use of SWV for identifying electrode reaction mechanisms has been limited to a small number of electrochemists. Our goal is to broaden the use of SWV for determining electrode reaction mechanisms especially by nonexperts in electrochemistry who make occasional use of voltammetry in characterizing new compounds. Cyclic square wave voltammetry (CSWV) is a modified form of SWV that steps through the region of the formal potential of the electroactive species under study and back to the initial potential as shown in Fig. 1a. The empirical parameters that comprise the CSWV waveform are period (τ), amplitude (E sw ), increment (δE), and the potential at which the direction of the sweep is reversed (E λ ).Our current effort is focused on identifying the specific mechanisms CSWV provides a straightforward means for determining the mechanism and associated kinetic parameters. [9][10][11][12][13][14] In this work, we critically evaluate CSWV for the analysis of consecutive electron transfers coupled by a homogeneous irreversible chemical reaction, i.e. an ECE mechanism. The process used to evaluate CSWV is as follows. Theoretical voltammograms were computed by systematic variation of each empirical parameter. Figures of merit that describe the shape of the voltammogram as shown in Fig. 1b (peak potentials, peak currents, and peak widths) were compiled and correlated with the empirical parameter being varied. Trends characteristic of this mechanism were identified from these correlations and provide diagnostic criteria for assigning an electrode reaction as an ECE process. Application of these criteria will enable non-specialists to accurately assign the mechanism and, in many instances, quantify the rate constant of the chemical reaction.The ECE mechanism has been the subject of considerable interest by electrochemists over the past five decades. [2][3][4][15][16][17][18][19][20][21][22][23][24] The continuing interest reflects: (1) the challenge in mathematically modeling the...

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confidence: 99%

Diagnostic Criteria for Identifying an ECE Mechanism with Cyclic Square Wave Voltammetry

Mann

Helfrick

Bottomley

2015

J. Electrochem. Soc.

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“…This behavior is a consequence of discwells having different internal and external diffusion regimes, while sphere-caps exhibit spherical diffusion both inside and outside the Hg phase. 44,45 The deviation of experimental disc-well stripping peak intensity from simulated behavior at fast scan rates (Figure 3D) coincides with pronounced broadening of the stripping peak and the appearance of a preceding anodic shoulder (Figure 3B). A full set of experimental and simulated CVs is available as Figure S5.…”

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confidence: 67%

Fabrication and Demonstration of Mercury Disc-Well Probes for Stripping-Based Cyclic Voltammetry Scanning Electrochemical Microscopy

Barton

Rodríguez‐López

2017

Anal. Chem.

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Scanning electrochemical microscopy (SECM) is a rising technique for the study of energy storage materials. Hg-based probes allow the extension of SECM investigations to ionic processes, but the risk of irreversible Hg amalgam saturation limits their operation to rapid timescales and dilute analyte solutions. Here, we report a novel fabrication protocol for Hg disc-well ultramicroelectrodes (UMEs), which retain access to stripping information but are less susceptible to amalgam saturation than traditional Hg sphere-caps or thin-films. The amalgamation and stripping behaviors of Hg disc-well UMEs are compared to those of traditional Hg sphere-cap UMEs and corroborated with data from finite element simulations. The improved protection against amalgam saturation allows Hg disc-wells to operate safely in highly concentrated environments at long timescales. The utility of the probes for bulk measurements extends also to SECM studies, where the disc geometry facilitates small tip-substrate gaps and improves both spatial and temporal resolution. Because they can carry out slow, high-resolution anodic stripping voltammetry approaches and imaging in concentrated solutions, Hg disc-well electrodes fill a new analytical niche for studies of ionic reactivity and are a valuable addition to the electrochemical toolbox.

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“…The concentration of arsine is specified as , which is generated as product of the chemical reaction. It is assumed that all involved species have a common diffusion coefficient, D = 4 × 10 -6 cm 2 s -1 , since the ratio between the effective diffusion coefficients does not affect the shape neither the height of peak current associated with macroelectrodes in SWV [23]. Thus, the reaction scheme of Eqs (1 -3) can be described according to the following set of boundary conditions:…”

Section: Proposed Modelmentioning

confidence: 99%

Mechanistic analysis of the cathodic stripping square-wave voltammetric response of the copper‑arsenic system at a mercury electrode

Avila

Gómez

Heredia

et al. 2021

Journal of Electroanalytical Chemistry

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This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Effects of Unequal Diffusion Coefficients and Coupled Chemical Equilibria on Square Wave Voltammetry at Disc and Hemispherical Microelectrodes

Cited by 10 publications

References 43 publications

Diagnostic Criteria for Identifying an ECE Mechanism with Cyclic Square Wave Voltammetry

Diagnostic Criteria for Identifying an ECE Mechanism with Cyclic Square Wave Voltammetry

Fabrication and Demonstration of Mercury Disc-Well Probes for Stripping-Based Cyclic Voltammetry Scanning Electrochemical Microscopy

Mechanistic analysis of the cathodic stripping square-wave voltammetric response of the copper‑arsenic system at a mercury electrode

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