Electrode diffusion layer

The advantages of a solid electrode of fixed area that functions in the voltammetric experiment with a constant diffusion-layer thickness have led to the development of the rotated-disk and ring-disk electrodes.52-54 By rotation of a disk, the electrode diffusion layer becomes fixed such that the current is constant as a function of time and does not decay [in contrast to conventional voltammetry Eq. (3.6)]. Voltammetry with such an electrode system gives a current-potential wave that is analogous to a polarogram and follows the relationship... 

Raman spectroelectrochemistry (71, 72) is a field in which one studies electrogenerated species on electrode surfaces, in electrode diffusion layers and bulk solution by Raman spectroscopy. Thus, the surface-enhanced Raman scattering (SERS) discussed in the preceding section is part of Raman spectroelectrochemistry. Here, we discuss Raman spectroscopic studies on electrogenerated species in bulk solution and in electrode diffusion layers. Since no enhancement from SERS is expected and since the concentrations of these electrogenerated species are rather low, it is imperative to take advantages of resonance Raman (RR) scattering (Section 1.15). 

Calculation ofTransfer Processes in the Near-electrode Diffusion Layer 831... 

The transfer processes in the gap within the quasi-steady-state approximation are calculated similarly for both the direct and inverse problems. To simplify the calculation of transfer processes in the gap, the boundary-layer approximation is commonly used. According to this approximation, the current density is calculated separately in the bulk gap and in the near-electrode diffusion layers, and their congruence is provided via the boundary conditions. The transfer processes in the... 

For solving Eq. (15), appropriate boundary conditions must be prescribed. Normally, the boundary of the machining zone consists of several sections at which the boundary conditions of different types are prescribed. The type of the boundary conditions depends on the character of the boundary section TE, WP, insulator, or the line (the plane of symmetry), and also on the operating conditions of the power supply the conditions of stabilization of the applied voltage, the conditions of current stabilization, and the natural current-voltage characteristics. In the general case, the boundary conditions that account for the kinetics of the electrode reactions and the transfer processes in the near-electrode diffusion layers can be written as follows ... 

The calculation of the transfer processes in the near-electrode diffusion layer is based on the set of equations of anisothermic ionic mass transfer, which is caused by diffusion, migration, convection, and homogeneous chemical reactions ... 

Lim, K.G., Palmore, G., and Tayhas, R. (2007) Microfluidic biofuel cells the influence of electrode diffusion layer on performance. Biosensors and Bioelectronics, 22 (6), 941-947. 

The diffusion layer widtli is very much dependent on tire degree of agitation of tire electrolyte. Thus, via tire parameter 5, tire hydrodynamics of tire solution can be considered. Experimentally, defined hydrodynamic conditions are achieved by a rotating cylinder, disc or ring-disc electrodes, for which analytical solutions for tire diffusion equation are available [37, 4T, 42 and 43]. 

Volt mmetiy. Diffusional effects, as embodied in equation 1, can be avoided by simply stirring the solution or rotating the electrode, eg, using the rotating disk electrode (RDE) at high rpm (3,7). The resultant concentration profiles then appear as shown in Figure 5. A time-independent Nernst diffusion layer having a thickness dictated by the laws of hydrodynamics is estabUshed. For the RDE,... 

Examples of such irreversible species (12) include hydroxjiamine, hydroxide, and perchlorate. The electrochemistries of dichromate and thiosulfate are also irreversible. The presence of any of these agents may compromise an analysis by generating currents in excess of the analytically usehil values. This problem can be avoided if the chemical reaction is slow enough, or if the electrode can be rotated fast enough so that the reaction does not occur within the Nemst diffusion layer and therefore does not influence the current. 

The equilibrium potentials and E, can be calculated from the standard electrode potentials of the H /Hj and M/M " " equilibria taking into account the pH and although the pH may be determined an arbitrary value must be used for the activity of metal ions, and 0 1 = 1 is not unreasonable when the metal is corroding actively, since it is the activity in the diffusion layer rather than that in the bulk solution that is significant. From these data it is possible to construct an Evans diagram for the corrosion of a single metal in an acid solution, and a similar approach may be adopted when dissolved O2 or another oxidant is the cathode reactant. 

Fig. 20.1 Potential and concentration gradients in the electrolytic cell CU/CUSO4/CU. (a) The electrodes are unpolarised the potential dilference is the equilibrium potential and there is no concentration gradient in the diffusion layer. (f>) The electrodes are polarised Ep of the anode is now more positive than E. whilst E of the cathode is more negative and concentration gradients exist across the diffusion layer c, C), are the concentrations at the electrode...

Diffusion Layer the thin layer of solution adjacent to an electrode through which transport of species to or from the electrode surface occurs by diffusion rather than by convection. 

In the thin-layer cavity cell technique, a cell is constructed to give a thin cavity on one wall of which the metal-plate working electrode is mounted. This wall is separated by a Teflon sheet in which a central aperture has been cut out, from the opposite wall of the cavity this wall contains entry and exit tubes for the test solution which is caused to flow past the working electrode provision is made for connections to the other electrodes. If the Teflon sheet is thin enough (about 0.05 mm), the distance between the two walls of the cavity is less than the normal thickness of the diffusion layer of the electrolyte when undergoing electrolysis, and so electrolysis within the cavity is rapid.26... 

The total charge of the compact and diffuse layers equals (and is opposite in sign to) the net charge on the electrode side. The potential-distance profile across the double-... 

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