Band electrodes

In situ electron transport measurements on conducting polymers are commonly made by using a pair of parallel-band electrodes bridged by the polymer [Fig. 9(A)].141142 Other dual-electrode techniques in which the polymer film is sandwiched between two electrodes [Fig. 9(B)],139,140 rotating-disk voltammetry [Fig. 9(C)],60,143 impedance spectroscopy,144,145 chronoamperometry,146 and chronopotentiometry147 have also been used. 

Figure 9. Schematic diagrams of (A) parallel-band electrode,141 142 (B) sandwiched electrode,139 140 and (C) rotating-disk voltammetry60 143 methods for making in situ electron transport measurements on polymer films.

Figure 10. Cyclic voltammetry (top) and in situ electronic resistance (bottom) of poly(3-methylthiophene) from parallel-band electrode [Fig. 9(A)] experiments in S02(1) containing 0.1 M Bu4NPF6.37 (Reprinted with permission from J. Am. Chem. Soc. 112, 7869-7879, 1990. Copyright 1990, American Chemical Society.)...

Cyclic voltammetric studies involving polymers, 558 and the nature of charge carriers, 561 and the nucleation loop, 557 of poly (3-methylthiophene), 564 and parallel-band electrodes, 570 Cyclic voltammograms as a function of scan rate, 559 involving polymerization, 559 with polyanaline, 566 of polypyrrole film, 581... 

Screen-prinling of platinum interdigitated band electrodes on a ceramic sheet 1 ... 

Interdigitated band electrode characteristics length = 29 mm, width = I m m and inter-elecirode gap width =500 pm... 

P 42] Typically, a flow rate of 150 pi min was used [71]. A 0.1 M furan solution containing 0.1 M NaCl04 and 5 mM NaBr was used as reaction medium. Reaction was carried out at room temperature. Interdigitated band electrodes with 100 pm wide gaps and 500 pm band widths were tested in a 800 pm deep Perspex micro reactor. 

Fig. S-41. Band edge levels and Fermi level of semiconductor electrode (A) band edge level pinning, (a) flat band electrode, (b) under cathodic polarization, (c) under anodic polarization (B) Fermi level pinning, (d) initial electrode, (e) under cathodic polarization, (f) imder anodic polarization, ep = Fermi level = conduction band edge level at an interface Ev = valence band edge level at an interface e = surface state level = potential across a compact layer.

Applications have been reported for photoelectrochemical experiments, for example, splitting of water [11], local generation of photoelectrodes by spatially selective laser excitation [12], and steady-state electrochemiluminescence at a band electrode array [13,14]. Band electrodes prepared from very thin films approaching molecular dimensions have been used to assess the limits of theory describing electrode kinetics at ultramicroelectrodes [9]. Spectroelectrochemical applications have been extensively reviewed [1], In an intriguing approach, thin, discontinuous metal films have been prepared on a transparent semiconductor substrate they are essentially transparent under conditions in which a continuous metal film containing the same quantity of metal would be expected to substantially absorb [15]. 

Double- and triple-band electrodes have been constructed in a similar fashion by placing thin insulating films (e.g., Mylar) between the metal foils. These have been used in generator-collector experiments, in which one electrode (the collector) is used to monitor a product formed at the other electrode (the generator). This can be considered the microelectrode equivalent of the rotated ring-... 

Figure 12.2 (A) Cross section of a hemispherical or hemicylindrical electrode and the linear lines of flux to the electrode surface. (B) Cross section of a disk or band electrode and the nonlinear lines of flux.

The equivalency found between the behavior of hemisphere and that of disk electrodes also exists between cylinder and band electrodes [29]. Diffusion to a cylinder electrode is linear and described by Equation 12.7, while diffusion to a band is nonlinear. A plane of symmetry passes through the center of the band and normal to its surface, so the nonlinear diffusion process can be broken down into two planar components, one in the direction parallel to the electrode surface, x, and the other in the direction perpendicular to the electrode surface, y. So Fick s second law for a band electrode is... 

Figure 12.5 Cyclic voltammograms for the reduction of 1 mM cobaltocenium (Cp2Co+) hexafluorophosphate and oxidation of 1 mM ferrocene (Cp2Fe) in acetonitrile recorded at a band electrode (width = 4.6 / m) at a scan rate of 10 mV s 1. The supporting electrolyte is tetrabutylammonium hexafluorophosphate at (A) 0.02 M, (B) 0.2 mM, (C) 2.0 mM, and (D) 20 mM. [From Ref. 68, reprinted with permission of the copyright holder.]...

Band electrodes were the first to be fabricated with true nanometer dimensions [17,93]. Although small in only one dimension, the width, this controls the magnitude of the flux, while the finite length leads to easily measured currents. These electrodes can be fabricated with a smallest dimension as small as 2 nm by sealing deposited metal films between insulators. While voltammograms obtained with electrodes with widths greater than 50 nm follow the theory expected for diffusion-controlled mass transport, narrower electrodes show less... 

For a cartesian set of coordinates, like those used for band electrodes, q denotes coordinates x, y, and z, whereas for a cylindrical set of coordinates, like those corresponding to disc electrodes, q denotes coordinates r and z. In both cases, qs refers to z = 0. 

Scheme 2.5 Disc and band electrodes and relevant coordinates for each geometry (disc area, Ad = 7trd band area, Cl 12 ...

Note that if the electrode is not uniformly accessible such as disc and band electrodes, the diffusion layer thickness given by Eq. (2.162) has an average character [59], and in this case it will be denoted <5G. 

It is also possible to find expressions analogous to those given in Eqs. (5.71) for the limiting values of the diffusion layer thickness for other electrode geometries like disc or band electrodes [29, 30]. 

Closely spaced band electrodes (pairs or triples), with each electrode within the diffusion layer of the other, can be used for studying reactions, in a manner analogous to ring-disk generation-collection and redox recycling experiments (131,132). Unlike with rotating ring-disk electrodes, the product of the reaction at the collector electrode can diffuse back across the narrow gap to the... 

Girault et at. developed a ceramic electrochemical microreactor (CEM) in which an array of platinum interdigitated band electrodes (gap between electrodes 500 pm) was screen printed on the ceramic surface (Scheme 4.39) [5 3], A methanolic solution... 

Coen and coworkers [167, 177, 180] have presented solutions to the diffusion-limited current at a band electrode in the form of integral equations these must then be evaluated numerically, so this might be regarded as simulation. 

This will be called MWA here. This transformation is also used for band electrodes, with R replaced by X, measured as a distance from the centre of the band, across the band [46], It results, in the case of the disk electrode, in a new diffusion equation, whose form is deferred to a later place, below. 

A Simple Example The Band Electrode in a Channel Flow 241... 

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