Electrochemical kinetics, double layer effect

Z. Nagy and R. F. Hawkins, J. Electrochem. Soc. 138 1047 (1991). Analysis of the correction of the corrosion measurement kinetics for double-layer effects. 

Refs. [i] Frumkin A (1933) Z phys Chem A 164 121 [ii] Frumkin AN (1961) Hydrogen overvoltage and adsorption phenomena, part 1, mercury. In Delahay P (ed) Advances in electrochemistry and electrochemical engineering, vol 1. Interscience, New York [iii] Frumkin AN, Petrii OA, Nikolaeva-Ferdorovich NV (1963) Electrochim Acta 8 177 [iv] Frumkin AN, Nikolaeva-Fedorovich NV, Berezina NP, Keis KhE (1975) J Electroanal Chem 58 189 [v] Fawcett WR (1998) Double layer effects in the electrode kinetics of electron and ion transfer reactions. In Lipkowski J, RossPN (eds) Electrocatalysis. Wiley-VCH, New York, p 323... 

Gennett and Weaver [192] have found, when studying double-layer effects on electrochemical kinetics in nonaqueous media, that the rate constants of metallocenes M(Cp)2 °, where M = Fe, Mn and Co, were virtually independent of the double-layer structure. However, the structurally similar anionic couple Co(Cp)2 and some other metallocenes have exhibited the expected sensitivity upon changes of the double layer. These differences in behavior of cationic and anionic metallocenes were explained in terms of charge distribution between the cyclopentadienyl (Cp) ring and the metal. 

One can derive the Butler-Volmer kinetic expressions by an alternative method based on electrochemical potentials (8, 10, 12, 19-21). Such an approach can be more convenient for more complicated cases, such as requiring the inclusion of double-layer effects or sequences of reactions in a mechanism. The first edition develops it in detail. ... 

ABSTRACT. The effect of the electrolyte concentration and solvent on the electrochemical oxidation of Cr(CO)6 at microelectrodes has been investigated. It is shown that reproducible data are obtained in media without the deliberate addition of electrolyte or in very resistive solvents such as toluene. The voltammetric realises are interpreted in the light of ohmic drop, migration, kinetics and double layer effects. 

The parameter a in Equation (11.6) is positive for electrophobic reactions (5r/5O>0, A>1) and negative for electrophilic ones (3r/0Oelectrochemical promotion behaviour is frequently encountered, leading to volcano-type or inverted volcano-type behaviour. However, even then equation (11.6) is satisfied over relatively wide (0.2-0.3 eV) AO regions, so we limit the present analysis to this type of promotional kinetics. It should be remembered thatEq. (11.6), originally found as an experimental observation, can be rationalized by rigorous mathematical models which account explicitly for the electrostatic dipole interactions between the adsorbates and the backspillover-formed effective double layer, as discussed in Chapter 6. 

Studies in nonaqueous dipolar aprotic solvents allowed the elucidation of the complicated role of the solvent nature in determining the - double layer structure and kinetics of electrochemical reactions. Special attention was paid to the phenomenon of ion - solvation and its effect on -> standard electrode potentials. Experimental studies of the various electrochemical systems in nonaqueous media greatly contributed to the advancement of the theory of elemental electron-transfer reactions across charged interfaces via the so-called energy of solvent reorganization. 

We then discuss the recently established rules of promotion and electrochemical promotion and an extension of Langmuir-Hinshelwood kinetics, based on an effective medium double-layer isotherm model, which is in good qualitative agreement with experiment and allows one to make predictions about the effect of promoters, but also of catalyst supports, on the kinetics of different catalytic reactions. 

Most of the electrochemical phenomena occur in size regimes that are very small. The effects of size on diffusion kinetics, electrical double layer at the interface, elementary act of charge transfer and phase formation have recently been reviewed by Petrri and Tsirlina [12]. Mulvaney has given an excellent account of the double layers, optical and electrochemical properties associated with metal colloids [11]. Special emphasis has been given to the stability and charge transfer phenomenon in metal colloid systems. Willner has reviewed the area of nanoparticle-based functionalization of surfaces and their applications [6-8]. This chapter is devoted to electrochemistry with nanoparticles. One of the essential requirements for electrochemical studies is that the material should exhibit good conductivity. 

Equation (a), with set equal to ( >, is surprisingly successful in describing the effect of varying the double-layer structure upon the kinetics of electrochemical reactions at Hg electrodes, at least in the absence of specific adsorption of the supporting electrolyte (i.e., when the inner-layer region adjacent to the electrode contains only solvent molecules). However, this does not necessarily imply that average electrostatic interactions provide the sole contribution to the work terms, because contributions may arise from other sources that remain constant under these conditions. In particular, inner-sphere pathways commonly involve reaction sites within the outer Helmholtz plane. Consequently, the overall work terms consist of separate contributions from transporting the reactant from the bulk solution to this outer plane and from this plane to the reaction site within the inner layer. The latter will then be independent of and, therefore, influence only k j.. in Eq. (a). 

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