The prediction of electrochemical reactivities from contemporary theory: some comparisons with experiment

Hupp, Joseph T.; Liu, H. Y.; Farmer, Jane Kim; Gennett, Thomas; Weaver, Michael J.

doi:10.1016/0368-1874(84)87107-5

Cited by 30 publications

(11 citation statements)

References 42 publications

(1 reference statement)

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“…Excellent fits between experimental and simulated voltammograms yielded k 0 at the generator electrode in addition to gap width and CF length (∼50 μm). Both generator and collector responses were quasi-reversible in 1 M KCl solution of extremely pure water with low total organic carbon (TOC) of 2–3 ppb to yield a k 0 value of 0.9 cm/s, which is close to a k 0 value of 2.2 cm/s predicted for the Ru(NH 3 ) 6 3+/2+ couple by Marcus theory for adiabatic outer-sphere electron transfer . In contrast, other electrode materials yielded k 0 values of ≥10 cm/s for the Ru(NH 3 ) 6 3+/2+ couple to exceed the theoretical value .…”

supporting

confidence: 49%

“…Both generator and collector responses were quasi-reversible in 1 M KCl solution of extremely pure water with low total organic carbon (TOC) of 2–3 ppb to yield a k 0 value of 0.9 cm/s, which is close to a k 0 value of 2.2 cm/s predicted for the Ru(NH 3 ) 6 3+/2+ couple by Marcus theory for adiabatic outer-sphere electron transfer. 20 By contrast, other electrode materials yielded k 0 values of ≥10 cm/s for the Ru(NH 3 ) 6 3+/2+ couple to exceed the theoretical value. 21 These anomalously high k 0 values are attributed to inner-sphere electron transfer as discussed qualitatively in our recent work 21 and quantitatively in Appendix of Supporting Information to estimate k 0 values of 30–46 cm/s, which are comparable to those measured in low-TOC ultrapure water (e.g., 36 ± 4 cm/s at single Pt nanoparticles 22 ).…”

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confidence: 86%

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Nanogap-Based Electrochemical Measurements at Double-Carbon-Fiber Ultramicroelectrodes

2018

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Electrochemical measurements with unprecedentedly high sensitivity, selectivity, and kinetic resolution have been enabled by a pair of electrodes separated by a nanometer-wide gap. The fabrication of nanogap electrodes, however, requires extensive nanolithography or nanoscale electrode positioning, thereby preventing the full exploration of this powerful method in electrode design and application. Herein, we report the simple fabrication of double-carbon-fiber ultramicroelectrodes (UMEs) with nanometer-wide gaps not only to facilitate nanogap-based electrochemical measurements, but also to gain high time resolution, signal-to-background ratio, and kinetic selectivity for dopamine against ascorbic acid. Specifically, ~7 μm-diameter carbon fibers are inserted into a double-bore glass capillary, heat-pulled, and milled by focused-ion-beam technology to yield ~50 μm-long double-cylinder UMEs. The redox cycling of the Ru(NH3)63+/2+ couple across a nanogap between voltammetric generator and amperometric collector electrodes reaches quasi-steady states at fast scan rates of 100 V/s as demonstrated experimentally and even 1000 V/s as predicted theoretically. The transient background of the amperometric collector response is suppressed ~100 times in comparison with that of the voltammetric generator response. Nanogap voltammograms based on the collector response against the cycled generator potential are quantitatively analyzed without background subtraction to reproducibly yield nanogap widths of ~0.18 μm and a standard electron-transfer rate constant of 0.9 cm/s. Moreover, nanogap-mediated redox cycling can be initiated by dopamine oxidation at the generator electrode to largely improve the dopamine selectivity of the collector response against ascorbic acid, which is also oxidized at the generator electrode to immediately and irreversibly produce a redox-inactive species.

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supporting

confidence: 49%

mentioning

confidence: 86%

Nanogap-Based Electrochemical Measurements at Double-Carbon-Fiber Ultramicroelectrodes

2018

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“… a From eq . b This work. c From ref . d From ref . e This work, with Au/eC electrode instead of Au/TiC/eC. …”

Section: Resultsmentioning

confidence: 99%

Ultraflat, Pristine, and Robust Carbon Electrode for Fast Electron-Transfer Kinetics

et al. 2017

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Electron-beam (e-beam) deposition of carbon on a gold substrate yields a very flat (0.43 nm of root-mean-square roughness), amorphous carbon film consisting of a mixture of sp- and sp-hybridized carbon with sufficient conductivity to avoid ohmic potential error. E-beam carbon (eC) has attractive properties for conventional electrochemistry, including low background current and sufficient transparency for optical spectroscopy. A layer of KCl deposited by e-beam to the eC surface without breaking vacuum protects the surface from the environment after fabrication until dissolved by an ultrapure electrolyte solution. Nanogap voltammetry using scanning electrochemical microscopy (SECM) permits measurement of heterogeneous standard electron-transfer rate constants (k°) in a clean environment without exposure of the electrode surface to ambient air. The ultraflat eC surface permitted nanogap voltammetry with very thin electrode-to-substrate gaps, thus increasing the diffusion limit for k° measurement to >14 cm/s for a gap of 44 nm. Ferrocene trimethylammonium as the redox mediator exhibited a diffusion-limited k° for the previously KCl-protected eC surface, while k° was 1.45 cm/s for unprotected eC. The k° for Ru(NH) increased from 1.7 cm/s for unprotected eC to above the measurable limit of 6.9 cm/s for a KCl-protected eC electrode.

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“…The pioneering works of Weaver have allowed one to gain insight into the complexity of even the simplest one electron transfer reactions, for which kinetics was demonstrated to be dictated by both static and dynamic solvent effects as well as by the electrode/reactant orbital overlap and reaction layer structure. , A vast number of attempts to reach molecular level understanding of solvent effect on electrode processes was performed for heterogeneous as well as homogeneous ET for different reactants (transition and noble metal complexes with various ligands, metallocene derivatives, etc. ). − Unfortunately, not only model estimates of the rate constants are uncertain, but also the experimental data often exhibits a significant scatter due to the difficulties in estimating very high rate constants. For instance, some examples in literature illustrate a very weak solvent dependence of the ET rate constant for the ferrocenium/ferrocene (Fc + /Fc) redox couple in nonaqueous solvents, most likely due to the influence of uncompensated ohmic resistance on the fast scan cyclic voltammetry results. , Moreover, the rate constant values for Fc + /Fc couple in acetonitrile (AN) reported by different groups differ by 4 orders of magnitude, , which demonstrates difficulties associated with the experimental determination of high rate constants.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Nature of Heterogeneous Electron Transfer in Molecular and Ionic Solvents: Experiment, Theory, and Computations

2019

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We report a combined experimental and computational study on the heterogeneous electron transfer kinetics for a simple one electron transfer reaction (ferrocene/ferrocenium Fc+/Fc couple) in a series of molecular solvents and ionic liquids. We focus on the diagnostics of the electron transfer regime (adiabatic vs nonadiabatic) and assess the parameters of the quantum mechanical electron transfer theory, which determine the observed tendencies in the solvent effect on the electron transfer rates. The applicability of the linear plots of the electron transfer rate constant vs longitudinal relaxation time (or solvent viscosity) for distinguishing between different ET kinetic regimes is analyzed. Classical molecular dynamics simulations were performed to calculate the potential of mean force for Fc and Fc+. The structure of the reaction layer derived from molecular dynamics is thoroughly investigated. The experimental dielectric spectra for the both type of solvents are used for quantum corrections of the outer-sphere reorganization energy as well as for estimations of the effective frequency factor in the limit of strong and weak electronic coupling. The electron transfer rate constants are calculated and discussed in the viewpoint of available experimental data.

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The prediction of electrochemical reactivities from contemporary theory: some comparisons with experiment

Cited by 30 publications

References 42 publications

Nanogap-Based Electrochemical Measurements at Double-Carbon-Fiber Ultramicroelectrodes

Nanogap-Based Electrochemical Measurements at Double-Carbon-Fiber Ultramicroelectrodes

Ultraflat, Pristine, and Robust Carbon Electrode for Fast Electron-Transfer Kinetics

Understanding the Nature of Heterogeneous Electron Transfer in Molecular and Ionic Solvents: Experiment, Theory, and Computations

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