Thin-layer electrochemistry

If the film is nonconductive, the ion must diffuse to the electrode surface before it can be oxidized or reduced, or electrons must diffuse (hop) through the film by self-exchange, as in regular ionomer-modified electrodes.9 Cyclic voltammograms have the characteristic shape for diffusion control, and peak currents are proportional to the square root of the scan speed, as seen for species in solution. This is illustrated in Fig. 21 (A) for [Fe(CN)6]3 /4 in polypyrrole with a pyridinium substituent at the 1-position.243 This N-substituted polypyrrole does not become conductive until potentials significantly above the formal potential of the [Fe(CN)6]3"/4 couple. In contrast, a similar polymer with a pyridinium substituent at the 3-position is conductive at this potential. The polymer can therefore mediate electron transport to and from the immobilized ions, and their voltammetry becomes characteristic of thin-layer electrochemistry [Fig. 21(B)], with sharp symmetrical peaks that increase linearly with increasing scan speed. 

Figures 12.1 and 12.2 show that the spectroelectrochemical cell is basically a thin-layer electrochemistry cell (TLE) with a solution gap of 25 pm [Hubbard, 1973]. The metal working electrode may be polycrystalline or a single crystal. Emptying the gap out of the adsorbate molecules due to molecules oxidation, and refilling via molecular...

Lu GQ, Lagutchev A, Dlott DD, Wieckowski A. 2005. Quantitative vibrational sum-frequency generation spectroscopy of thin layer electrochemistry CO on a Pt electrode. Surf Sci 585 3-16. 

Fenn, R. J., Siggia, S., and Curran, D. J., Liquid chromatography detector based on single and twin electrode thin-layer electrochemistry application to the determination of catecholamines in blood plasma, Anal. Client., 50, 1067,1978. 

Occasionally (e.g., thin-layer electrochemistry, porous-bed electrodes, metal atoms dissolved in a mercury film), diffusion may be further confined by a second barrier. Figure 2.7 illustrates the case of restricted diffusion when the solution is confined between two parallel barrier plates. Once again, the folding technique quickly enables a prediction of the actual result. In this case, complete relaxation of the profile results in a uniform finite concentration across the slab of solution, in distinct contrast to the semi-infinite case. When the slab thickness t is given, the time for the average molecule to diffuse across the slab is calculable from the Einstein equation such that... 

An operational definition of thin-layer electrochemistry is that area of electrochemical endeavor in which special advantage is taken of restricting the diffii-sional field of electroactive species and products. Typically, the solution under study is confined to a well-defined layer, less than 0.2 mm thick, trapped between an electrode and an inert barrier, between two electrodes, or between two inert barriers with an electrode between. Diffusion under this restricted condition has been described in Chapter 2 (Sec. II.C). Solution trapped in a porous-bed electrode will have qualitatively similar electrochemical properties however, geometric complexities make this configuration less useful for analytical purposes. The variety of electrical excitation signals applicable to thin-layer electrochemical work is large. Three reviews of the subject have appeared [28-30]. 

Figure 3.12 Double-potential-step thin-layer electrochemistry. (A) Chronoampero-metry. (B) Chronocoulometry. Dashed line, same experiment for semi-infinite situation.

Thin layer electrochemistry thus offers a very convenient way of controlling the oxidation state of a very thin (< 1 mm) layer of an electrochemically generated species. 

Soriaga, M. P. and Hubbard, A. T. (1982) Determination of the orientation of adsorbed molecules at solid-liquid interfaces by thin-layer electrochemistry Aromatic compounds at platinum electrodes. J. Am. Chem. Soc. 104, 2735-2742. 

Fig. 1. Sketch of a LEED-thin layer electrochemistry (TLE) system [6], References pp. 126-127...

In 1972, Professor Ralph Adams of the University of Kansas had just redirected his research group from dectroanalytical chemistry to neurochemistry. His postdoctoral associate at the time, Peter Kissinger, had just completed thesis wmk in thin-layer electrochemistry under C. N. Reilley. The two sdentists coupled their n for better neurochemical techniques of analysis with their electrochemical expertise and subsequently tried the obvious experiment one night with great success (Kissinger et al.. 1973). 

The technique of optically transparent thin-layer electrochemistry (ottle) was first applied to the characterization of the stoichiometry and thermodynamics of horse heart cytochrome c by Heineman et alP This report showed how the special features of ottle can be combined with optical monitoring of a mediated biological electrode response to provide a simple, accurate, and precise means of characterizing the stoichiometry and thermodynamics of a biological molecule. The mechanism of mediation is described by the following equations ... 

OTTLE optically transparent thin-layer electrochemistry... 

The metal-metal interactions in the polymer network were investigated by controlled potential electrolysis with the aid of an optically transparent thin-layer electrochemistry (OTTLE) cell. In the visible/near-IR spectrum of the fully reduced deep-red/orange gel the lowest-energy visible band is assigned to a d-d transition. Upon oxidation, two new absorption peaks emerge one at 640 nm is due to a li-gand-to-metal charge-transfer (LMCT) of the ferrocenium moiety, whereas the... 

MODELS FOR UBIQUINONES AND THEIR ANIONS. INVOLVED IN PHOTOSYNTHETIC ELECTRON TRANSFER, CHARACTERIZED BY THIN-LAYER ELECTROCHEMISTRY AND FTIR/UV/VIS SPECTROSCOPY... 

The combination of thin-layer electrochemistry and FTIR spectroscopy,... 

Characterized by Thin-Layer Electrochemistry and FTIRAJVA IS Spectroscopy 81... 

Developments in spectroelectrochem-istry based on TCO electrodes under semi-infinite diffusion conditions were reviewed by Kuwana and Winograd in 1974 [244]. Since 1974, significant developments in absorption spectroelectrochem-istry have occurred under semi-infinite diffusion conditions and in optically transparent thin-layer electrochemistry, several new TCO electrodes have heen characterized, and the indirect coulometric titration technique has been developed and apphed to biological systems [245]. 

Thin-layer electrochemistry with an optically transparent electrode (OTE) enables simultaneous monitoring of both the electrochemical and optical responses of the system [1-3]. The oxidation state of the electroactive species in a cell can be precisely controlled by regulating the potential of the OTE and the species in the cell can be completely electrolysed within a short time (typically 20-120s). The electrochemical technique combined with a gold minigrid OTE was first applied to biological molecules to characterize the thermodynamic parameters of the redox reaction of horse heart cytochrome c in the presence of redox mediators [4]. 

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