Double layer models: Bockris

Bockris-Devanathan-Muller model - double-layer models... 

FIGURE 1.9 Model of electric double layer after Bockris et al. (1963). 

The importance of the dipolar nature of the solvent and of the interactions between solvent and electrode were recognized in the double layer model by Bockris, Devanathan and Muller [9], Water hydrates the electrode, which is regarded as a giant ion, and so contributes to the electric fields near the interface. Starting with the work of Damaskin and Frumkin [10] the differences between sp and transition metals were described by a series of chemical models. More details on double layer models can be found, e.g., in Refs. 2, 11, 12. 

Calculate the capacity of the Helmholtz layer per unit area for an interface of mercury in contact with a 0.0 XM NaF electrolyte. Model the value of the double layer thickness assuming a two-state water model, a positive charge on the electrode, and a local dielectric constant of six. (Bockris)... 

Fig. 3.9 The model of Bockris et al. of the double layer, (a) Arrangement of ions and solvent molecules represents a water molecule (b) Variation of the electrostatic potential, 0, with distance, x, from the electrode.

R. Reeves, The electrical double layer The current status of data and models, with particular emphasis on the solvent, in Modem Aspects of Electrochemistry. Vol. 9, B. E. Conway and J. O M. Bockris, editors. Plenum Press, New York, 1974, pp. 239-368. 

S. Trasatti. The Electrode Potential, in Comprehensive Treatise of Electrochemistry, Vol. 1, J. O M. Bockris, B.E. Conway and E. Veager. Eds. Plenum (1980), chapter 2 B.E. Conway, The State of Water and Hydrated Ions at Interfaces, Adv. Colloid Interface Sci. 8 (1977) 91 W.R. Fawcett, Molecular Models for Solvent Structure at Polarizable Interfaces. Isr. J. Chem. 18 (1979) 3 M.A. Habib, Solvent Dipoles at the Electrode-Solution Interface. in Modem Aspects of Electrochemistry, Vol. 12, J. O M. Bockris and B.E. Conway. Eds. Plenum (1977) 131 S. Trasatti, Solvent Adsorption and Double Layer Potential Drop at Electrodes, in Modem Aspects of Electrochemistry, B.E. Conway and J. O M. Bockris, Eds. Vol. 13 Plenum (1979) chapter 2 J. O M. Bockris. K-T. Jeng, Water Structure at Interfaces The Present Situation. Adv. Colloid Interface Set 33 (1990) 1. 

Several theories have been proposed in the past 20 years for changing solvent polarization in the double layer with electrode potential. One of the most useful has been that of Mott and Watts-Tobin and the development of it by Bockris et The model represents the inner region of the double layer in terms of two-states of orientation of solvent dipoles, parallel and antiparallel, ti, to the electrode field across the interphase, analogous to the... 

After the pioneering observation by Hansen [28] that electrodes could be removed from the solution by maintaining their electric double layer it became possible to investigate the water adsorption configuration on metal surfaces in the UHV environment [29]. Although his studies were accomplished under very different circumstances from those in electrochemistry, the information on the energies of metal-water interactions was extremely useful to check the accuracy of the classical double-layer Bockris-Devanathan-Miiller model. The interaction of water with the commonly used electrode metals was much less than previously assumed. 

Fig. 3. BDM (Bockris, fkvanathan, Muller) model of the electrical double layer at the interfece between a positively charged metal oxide sur % and an aqueous solution.

The validity of this equation is pretty much connected to that of the Gouy-Chapmann equation [26], i.e. it is hinited to moderate concentrations. For a solution containing a (1 1) electrolyte at a 0.1 M ionic strength in water (e = 78.5), the predicted electric field rate is thus 1.04.10 (V.cm ).V . Note that this value is pretty close to the one proposed by Bockris et al namely (2.9 0.3).10 (Vcm ).V [50]. hi the model of Bockris et al., no reference is made to any specific model of the EDL. Rather, the electric field rate is directly connected to the capacitance, C, of the double layer ... 

J. O M. BOCKRIS, M. A. V. DEVANATHAN and K. MULLER pubUsh their model of the electrical double layer (1963) Proc Royal Soc (London) A 274 55... 

Attard, P. (1993) Asymptotic analysis of primitive model electrolytes and the electrical double layer. Phys. Rev. E 48, 5, 3604-3621, ISSN 1063-651X Bahe, L. W., (1972a) Structure in concentrated electrolyte solutions. Field-dielectric-gradient forces and energies. /, Phys. Chem., 76, 7,1062-1071, ISSN 0022-3654 Bahe, L. W., (1972b) Relative partial molar enthalpies and heats of dilution of electrolytes in water. /, Phys. Chem., 76,11,1608-1611, ISSN 0022-3654 Bahe, L. W. Parker, D. (1975) Activity coefficients of 2 1 electrolytes in structured electrolyte solutions. /, Am. Chem. Soc., 92, 20, 5664-5670, ISSN 0002-7863 Bockris, J. O M. Reddy, A. K. N (2000) Modern Electrochemistry. Vol. 1 Ionics. 2 edition. 

Lastly, in 1963 John O Mara Bockris (1923-2013) together with M. Devantant and K. Muller developed a model which takes into consideration the effect of solvent (H O dipoles), of its ions and pH value of the solution on the charge of the diffusion layer. So, the modern concept was formed of the structure of double electric layer, according to which are distinguished three consecutively connected capacitors slip plane, Helmholtz plane and the interface plane (Figure 2.10). 

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