The double channel electrode

First-order collection efficiencies at the double channel electrode... 

The double channel electrode in the investigation of electrode reaction mechanisms... 

Mechanisms involving following chemical reactions treated by Matsuda and co-workers [126] for the double channel electrode... 

Tsuru et al. [129-131] applied the double channel electrode transient technique to the investigation of the anodic dissolution of iron in sulphate and chloride aqueous media, in the pH range 1-3. The upstream electrode served as the generator electrode at which the anodic dissolution reaction occurred. Overall this involves... 

The Double Channel Electrode (DCE) and Double Tube Electrode (DTE)... 

The homogeneous reaction may be of first or second order in the latter case, X is a non-electroactive species. Both these cases have been studied at the rotating ring—disc electrode and the first-order case at a double channel electrode. 

In this section, the discussion centres on the application of double channel electrodes in the study of electrode reaction mechanisms under conditions of laminar flow. (The modifications necessary to what follows when turbulent flow operates can be found in Sect. 6.2.) When employed in this way, the upstream (generator) electrode produces the species of interest, which is then detected on the downstream electrode. This procedure is illustrated schematically in Fig. 37. In general, the detector electrode is held at a potential at which the destruction of the species produced upstream is diffusion-controlled. Kinetic and mechanistic information about the electrogenerated species is then available from "collection efficiency , N, measurements, given by... 

Steady-state collection efficiencies as a function of double channel electrode geometry when the product of the generator electrode reaction is kinetically stable on the channel electrode timescale... 

That double channel electrodes are ideally suited to the study of electrode reaction mechanisms involving following chemical reactions is illustrated by reference to studies on the electrochemical oxidation of 4-amino-iV, N,-di-methylaniline (ADMA) in basic solution at a platinum electrode [125], This reaction is thought to proceed via the scheme... 

P.R. Unwin. The ECE-DISPl problem—General resolution via double channel electrode collection efficiency measurements. J Electroanal Chem. 297 103 (1991). 

The electroosmotic pumping is executed when an electric field is applied across the channel. The moving force comes from the ion moves in the double layer at the wall towards the electrode of opposite polarity, which creates motion of the fluid near the walls and transfer of the bulk fluid in convection motion via viscous forces. The potential at the shear plane between the fixed Stem layer and Gouy-Champmon layer is called zeta potential, which is strongly dependent on the chemistry of the two phase system, i.e. the chemical composition of both solution and wall surface. The electroosmotic mobility, xeo, can be defined as follow,... 

The apparatus needed for the experiments are a multichannel pH/ mV meter (for example, the six-channel Consort C864 multiparameter analyser), a double junction Ag AgCl reference electrode, (for example, Orion 90-02) and a magnetic stirrer. 

Basically, the impedance behavior of a porous electrode cannot be described by using only one RC circuit, corresponding to a single time constant RC. In fact, a porous electrode can be described as a succession of series/parallel RC components, when starting from the outer interface in contact with the bulk electrolyte solution, toward the inner distribution of pore channels and pore surfaces [4], This series of RC components leads to different time constant RC that can be seen as the electrical response of the double layer charging in the depth of the electrode. Armed with this evidence, De Levie [27] proposed in 1963 a (simplified) schematic model of a porous electrode (Figure 1.24a) and its related equivalent circuit deduced from the model (Figure 1.24b). 

Figures 8.3, 8.4, 8.5, and 8.6 show typical designs of double hydrodynamic electrodes (two working electrodes)—rotating, wall-jet, tube, and channel. Using only one of the two working electrodes one obtains /L as in Table 8.1. Use of the two electrodes simultaneously is described in Sections 8.5-8.8.

A streaming cell made of Perspex, holding a small amount of material (2 to 4 cc.), was used. The details of its construction have been published (34). The cell was fitted with two platinized platinum electrodes and two Ag/Ag halide electrodes and is shown in Figure 1. This cell was coupled with two Keithley electrometers Model 610A (one electrometer for each pair of electrodes), whose outputs were fed into a Varian double-channel recorder. Streaming potentials could, thus, be measured simultaneously using two different kinds of electrodes for comparison purposes. 

When performing potentiometric measurements with a traveling probe, one needs to take into account the effect of ohmic drop. Whereas this effect is the basis of SRET measurements, it becomes a nuisance in potentiometric SECM applications. If the substrate is an electrode involved in a Faradaic process, the current flowing between the substrate and the counterelectrode leads to potential gradients in solution. The tip will be sensitive to the potential distribution, and this may overcome the signal due to the concentration change for the ion of interest. This is particularly pronounced if the reference electrode associated to the tip is located far away in the bulk and of course if the solution conductivity is low. To remedy this situation some researchers have used double barrel electrodes where one channel acts as the ion-sensitive element and the other acts as a reference electrode (81,82). In the life sciences intracellular measurements are usually carried out in this way. Alternatively, it is possible to subtract the ohmic drop from the tip... 

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