Anodic charge transfer coefficient

Anodic charge-transfer coefficient It Mobility of ionic species i... 

Electrokinetic parameters [10] Ideal potential Anodic preexponential coefficient Cathodic preexponential coefficient Anodic activation energy Cathodic activation energy Anode charge transfer coefficient Cathode charge transfer coefficient 0.8961 V 1.6e9 3.9e9 120 J mol-1 120 J mol-1 0a = 2, 0C = 1 ea = 1.4, 0C = 0.6... 

In these equations occ and oca are the cathodic and anodic charge transfer coefficients and are a measure of the symmetry of the activation barrier, being close to 0.5 for a metallic electrode and a simple electron transfer process. As mentioned above, the standard rate constant is the rate constant at E = E... 

Anodic preexponential coefficient Cathodic preexponential coefficient Anodic activation energy Cathodic activation energy Anode charge transfer coefficient Cathode charge transfer coefficient... 

From a kinetic point of view a describes the influence of a change of the electrode potential on the energy of activation for the charge transfer reaction which in turn influences the partial current density. The transfer coefficients % for the anodic charge transfer reaction and for the cathodic reaction add up according to... 

A similar relationship is valid for the charge transfer coefficient of the anodic electrode reaction, aa. 

Here ia is the exchange current density of the electrode reaction based on the bulk concentration aa and ac are the anodic and cathodic charge transfer coefficients, respectively and y is a dimensionless kinetic parameter. 

So, what is the variation of the rate constant with potential The charge transfer coefficient, or, anodic or cathodic, is given by... 

The first-order derivatives correspond to the charge-transfer coefficients for the anodic and cathodic processes, respectively. 

Experimentally, it is often found that the anodic and cathodic charge transfer coefficients are about 1/2. This is typically the case for outer-sphere electron transfer. Values between zero and one are found for several more complex reactions. We now consider whether this behavior is reasonable in the framework of the phenomenological model presented here. In an outer-sphere process, the oxidized and reduced species are outside the electrochemical double layer. The chemical potential of these species is then not influenced by the electrode potential, and the following is valid ... 

Calculated as average values of anodic ( pa) and cathodic peak potentials for all depolarizator concentrations and scan rates used. Charge transfer coefficients ( and np) for the anodic and cathodic processes, respectively. 

For desorption (an anodic process with the charge transfer coefficient aj... 

One problem with the electrochemical hterature is that the definition of the charge transfer coefficient is not universal. Some groups prefer to use ct for the cathodic reaction and 1 — c anodic reaction. Other symbols (preferentially / ) can be found. 

Charge transfer coefficient, anodic partial current density... 

This equation represents the net current density i in the anodic direction. The first term is the rate of charge transfer in the anodic direction and the second term is the rate of charge transfer in the cathodic direction, and ac are the asymmetry factors or charge transfer coefficients in the anodic and cathodic directions, respectively. The transfer coefficient is a fraction of... 

For a special case of a = p, a case of symmetric charge transfer coefficient for anodic and cathodic reactions. Equation 5.77 becomes... 

Here, /oa and /oc are the exchange current densities for anode and cathode, respectively. Since reactions are different in anode and cathode, /oa joc- The forward (reduction) reaction charge transfer coefficients for anode and cathode are and aRed,c/ respectively. Similarly, backward (oxidation) reaction charge transfer coefficients for anode and cathode are aox,a and Uox c/ respectively. The oxidation and reduction transfer coefficients are related by the following expressions ... 

For the equal charge transfer coefficient on the anode and cathode electrode, that is, Ua = Uc = a, the general Butler-Volmer equation (Equation 11.3) can be written as... 

The parameters in Equations 12.10 through 12.14 are defined as follows. AG(, and AG are the standard-state free energy of activation for chemisorptions (J/mol) at the cathode and anode, respectively, and A is the active cell area (cm ). k° and are the intrinsic rate constants (cm/s) for the cathode and anode reaction, respectively, and Ch o respectively the concentration of hydrogen ion and water at the membrane gas interface on the cathode side of the cell, is called the cathodic charge transfer coefficient or chemical activity parameter. R is the gas constant. The ohmic overvoltage can be represented using Ohm s law as discussed in Chapter 7 as... 

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