Volmer electrode processes

As ksh in this instance is very small, then according to the Butler-Volmer formulation (eqn. 3.5) the reaction rate of the forward reaction, K — 8,he "F(E 0)/flr, even at E = E°, is also very low. Hence Etppl. must be appreciably more negative to reach the half-wave situation than for a reversible electrode process. Therefore, in the case of irreversibility, the polarographic curve is not only shifted to a more negative potential, but also the value of its slope is considerably less than in the case of reversibility (see Fig. 3.21). In... 

For the forward reaction, the sign of b is negative, so 77 reduces the EMF. Equations 15.65, 15.68, and 15.69 can be combined and rearranged to give the Butler-Volmer equation (Eq. 15.70) for the net current density, i, of an electrode process involving a single electrochemical step ... 

In this chapter we derive the Butler-Volmer equation for the current-potential relationship, describe techniques for the study of electrode processes, discuss the influence of mass transport on electrode kinetics, and present atomistic aspects of electrodeposition of metals. 

Up to now, the treatment of non-reversible electrode process has focused on the usual Butler-Volmer kinetics for which the rate constants take the form (see Sect. 1.7.1) ... 

The seminal paper by Erdey-Gruz and -> Volmer appeared in 1930 [i] in that the hydrogen overpotential was elucidated by using a kinetic model for the - electrode processes when the - charge transfer step, i.e., the... 

Interestingly, little work has been done on non-metallic p-block elements in ILs. Besides the oxidation of Bmim-I and alkali metal iodides discussed above [163], also the electrochemical reduction of iodine in Bmim-NTf2 was studied. Similar to the oxidation study, the authors report two reduction peaks. A detailed mechanistic and kinetic analysis was performed and the electrode process was found to be consistent with Buder-Volmer kinetics [171]. 

Unfortunately, mechanisms of elementary steps, e.g., electron transfer, in electrode processes were not at all well understood during the period of early development of electro-organic chemistry, and the significance of the fundamental relation between overpotential ( polarization ) and current density was not appreciated until the work of Volmer, Gurney, Bowden,... 

Equation (3.21) is known as the Butler-Volmer equation, and it forms the basis for the theoretical description of electrode processes. The terms in the square brackets represent the anodic (positive) and cathodic (negative) contributions to the net current, and /q is a scaling factor that depends on the values of, Co and Cr (Equation (3.18)). The symmetry of the current-potential... 

Figure 4-1 Model for the electrode process includes diffusion (Pick s laws), electrode kinetics (the Butler-Volmer equation), and chemical reaction kinetics.

Metal dissolution usually follows the Butler-Volmer equation (Eqs. (1-26) and (1-28)) independent from which surface position the transfer of the metal cation may occur. The relation for the exchange current density may contain the concentration of a catalyzing or complexing anion. The catalysis of iron dissolution by OH" ions is a typical example which has been studied in detail (Bonhoeffer and Heusler, 1956). Its mechanism includes a sequence of partial reactions of an electrode process and its in-... 

Assuming the Butler-Volmer equation for most electrode processes yields a similar discussion as in Sec. 1.3.1 Eqs. (1-20) to (1-31). Simplifying the Butler-Volmer equation with the constants A and B, and assuming hydrogen evolution as a possible counter reaction, gives Eq. (1-63). For the rest potential, E= r follows an expression for the corrosion current density Iq. For... 

It was evident for Polanyi that they found a fundamental relationship since he wrote in their paper It is obvious that this relationship can be generalized even further. Its application to reactions which formally can be treated just like the ionogenic reactions is most obvious. Albeit the theory of electrode processes is the most important in the work of Horiuti and Polanyi, they also supplied a theoretical foundation for proton transfer including electrolytic dissociation, prototropy, as well as catalytic hydrolysis of esters. Although they mentioned Nemst s theory, they used the recent ideas of Erdey-Gruz and Volmer as well as of Fmmkin. (Fmmkin was cited as A. Fnimkin as it appeared in the title page of Acta Physicochim. URSS.)... 

We know that thermodynamics is a very powerful tool for the study of systems at equilibrium, but electrode processes are systems not at equilibrium when at equilibrium there is no net flow of current and no net reaction. Therefore electrode reactions should be studied using the concepts and formalities of kinetics. Indeed, the same period that saw the flourishing of solution electrochemistry, also saw the formulation of the fundamental theoretical concepts of electrode kinetics the work of Tafel on the relationship of current and potential was published in 1905 those of Butler and Volmer and Erdey Gruz, which formulated the basic equation for electrode kinetics, were published in 1924 and 1930 respectively. Frumkin in 1933 showed the correlation between the structure of the double layer and the kinetics of the electrode process. The first quantum mechanical approach to electrode kinetics was published by Gurney in 1931. 

Equation 3.63 is known as the Butler-Volmer equation. It was derived early in the history of the study of electrode processes following the experimental observations by Tafel (in 1905) that the current density is proportional to the exponent of potential, when E is not too near the equilibrium potential,... 

By considering the kinetic substantiation of the Nernst equation, Audubert[2] and Butler[3] were the first to formulate the semiquantitative concepts concerning the effect of electrode potential on the rate of an electrochemical process. In its present form, the concept of slow discharge was put forward by Erdey-Gruz and Volmer[4]. Their approach was based on a consideration of the effect of potential on the activation energy of an electrode process and led to the introduction of a measure of this effect, viz. the transfer coefficient a. 

This process is often called the Volmer reaction (I). In the second step, adsorbed hydrogen is removed from the electrode, either in a chemical reaction... 

It was demonstrated by R. Parsons and H. Gerischer that the adsorption energy of the hydrogen atom determines not only the rate of the Volmer reaction (5.7.1) but also the relative rates of all three reactions (5.7.1) to (5.7.3). The relative rates of these three reactions decide over the mechanism of the overall process of evolution or ionization of hydrogen and decide between possible rate-determining steps at electrodes from different materials. 

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