Diffusion active electrode

Figure C2.8.4. The solid line shows a typical semilogaritlimic polarization curve (logy against U) for an active electrode. Different stages of reaction control are shown in tlie anodic and catliodic regimes tlie linear slope according to an exponential law indicates activation control at high anodic and catliodic potentials tlie current becomes independent of applied voltage, indicating diffusion control.

Various pc electrode models have been tested.827 Using the independent diffuse layer electrode model74,262 the value of E n = -0.88 V (SCE) can be simulated for Cd + Pb alloys with 63% Pb if bulk and surface compositions coincide. However, large deviations of calculated and experimental C,E curves are observed at a 0. Better correspondence between experimental and calculated C,E curves was obtained with the common diffuse-layer electrode model,262 if the Pb percentage in the solid phase is taken as 20%. However, the calculated C, at a Ois noticeably lower than the experimental one. It has been concluded that Pb is the surface-active component in Cd + Pb alloys, but there are noticeable deviations from electrical double-layer models for composite electrodes.827... 

Iliev I., Mrha J., Gamburzev S., Kaisheva A., On the effect of various active carbon catalysts on the behaviour of carbon gas-diffusion air electrodes, Journal Power Sources 1976/77 1 35-46. 

Eor the purpose of modeling, consider a planar SOEC divided into anode gas channel, anode gas diffusion electrode, anode interlayer (active electrode), electrolyte, cathode interlayer (active electrode), cathode gas diffusion electrode, and cathode gas channel. The electrochemical reactions occur in the active regions of the porous electrodes (i.e., interlayers). In an SOFC, oxidant reduction occurs in the active cathode. The oxygen ions are then transported through the electrolyte, after which oxidation of the fuel occurs in the active anode by the following reactions. 

Diffusion coefficient of the reactant gas = Active electrode area = Diffusion layer thickness... 

According to Raistrick (162), prefabricated gas diffusion electrodes (PTFE-bonded, Pt-activated soot, Prototech) are soaked with an alcohol solution of the monomer, and the solvent is subsequently evaporated. As the solution is wetting the electrode fairly well the active electrode layer is evenly impregnated by the ionomer. The impregnated electrode is subsequently glued to the membrane by hot pressing. 

In photoelectrochemical work, it is usual to plot only the highest values of the photocurrent as a function of potential. This is necessarily an S-shaped curve, with the highest values of the photocurrent eventually being controlled by diffusion of carriers inside the semiconductor. (A thermally activated electrode reaction on a metal has a similar shape near the limiting current caused by transport of ions to the electrode.)... 

The initiation of dendritic growth is followed by an increase of the deposition current density, and the overall current density will be larger than the limiting diffusion current on a flat active electrode. Based on the above discussion, the polarization curve equation in the Ohmic-controlled electrodeposition of metals can be determined now by 9... 

The surface active sites in the ERZ (denoted as LSC ) play a very important role in the dissociation of O2 molecules to form Oad (step 3 ) and/or in the sequential charge transfer (step 5). The number of LSC sites and their activity strongly depend on the 7 celb gas-diffusion rate, electrode composition, etc. 

MIXED MIGRATION AND DIFFUSION NEAR AN ACTIVE ELECTRODE... 

Mixed Migration and Diffusion Near an Active Electrode V 141... 

Raman data can also be obtained on species in the diffusion layer at a faradaically active electrode (73, 75). Whole spectra are gathered as the electrode is cycled through a repeated double-step waveform involving, for example, a short period of forward electrolysis and a long reversal step. 

If more than a single type of ion contributes to the measured potential in Equation 5.4, the potential can no longer be used to quantify the ions of interest. This is the interference in a potentiometric sensor. Thus, in many cases, the surface of the active electrode often incorporates a specific functional membrane which maybe ion-selective, ion-permeable, or have ion-exchange properties. These membranes tend to selectivity permit the ions of interest to diffuse or migrate through. This minimizes the ionic interference. 

The former case is intriguing since the discrete active electrode site is a micro-electrode . The radial diffusion gives rise to steady-state sigmoidal voltammetric waves, but since mass transport is very efficient, the current that is obtained from an array of sites need not be greatly lower than that obtained for a uniformly active surface. For a reversible electrode reaction the potential E1/2 at which half-maximal current is obtained is equivalent to the formal reduction potential E°. 

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