Electronic double layer interaction

Not only do double layers interact with double layers, the metal of one sphere also interacts with the metal of the second sphere. There is what is called the van der Waals attraction, which is essentially a dispersion interaction that depends on r-6, and the electron overlap repulsion, which varies as r-12. These interactions between the bulk... 

Colloidal particles are subjected to a number of attractive and repulsive forces and the stability of dispersions depends on the interplay of these various forces. The van der Waals attractive forces between particles have their origin in the electron wave fluctuations and are usually effective at close ranges. Electrical double layer interactions stem from the presence of ionized species at the interface and are effective at distances proportional to the double layer thickness for the given... 

Bravo-Diaz C —> Gonzalez-Romero E Briscoe WH, Horn RG Electrical double layer interactions in a non-polar liquid measured with a modified surface force apparatus 147 Brunner M, Bechinger C Colloidal systems in intense, two-dimensional laser fields 156 Buckin V Lehmann L Burrows HD, Kharlamov AA About energy and electron transfer processes in Cgo/phthalocyanine films 52 Burrows HD Kharlamov AA Burrows HD Hungerford G... 

The electron acceptor or electron donor character of adsorbates plays a very important role in their catalytic properties. It also plays a crucial role in their electrochemical promotion behaviour. This is to be expected since electrochemical promotion is catalysis in presence of a controllable double layer which interacts strongly with the adsorbate dipoles. 

That the synergistic action of an electron donor (Na8+) and electron acceptor (O5") promoter can cause dramatic enhancement in rate and selectivity. This is very likely due to the increase in the field strength, E, of the effective double layer discussed in Chapters 5 and 6 and to the concomitant enhanced interaction with the adsorbate dipoles, leading to more pronounced promotional behaviour (Chapter 6). 

In a simple electron transfer reaction, the reactant is situated in front of the electrode, and the electron is transferred when there is a favorable solvent fluctuation. In contrast, during ion transfer, the reactant itself moves from the bulk of the solution to the double layer, and then becomes adsorbed on, or incorporated into, the electrode. Despite these differences, ion transfer can be described by essentially the same formalism [Schmickler, 1995], but the interactions both with the solvent and with the metal depend on the position of the ion. In addition, the electronic level on the reactant depends on the local electric potential in the double layer, which also varies with the distance. These complications make it difficult to perform quantitative calculations. 

The theoretical modeling of electron transfer reactions at the solution/metal interface is challenging because, in addition to the difficulties associated with the quantitative treatment of the water/metal surface and of the electric double layer discussed earlier, one now needs to consider the interactions of the electron with the metal surface and the solvated ions. Most theoretical treatments have focused on electron-metal coupling, while representing the solvent using the continuum dielectric media. In keeping with the scope of this review, we limit our discussion to subjects that have been adi essed in recent years using molecular dynamics computer simulations. 

Several important energy-related applications, including hydrogen production, fuel cells, and CO2 reduction, have thrust electrocatalysis into the forefront of catalysis research recently. Electrocatalysis involves several physiochemical environmental dfects, which poses substantial challenges for the theoreticians. First, there is the electric potential which can aifect the thermodynamics of the system and the kinetics of the electron transfer reactions. The electrolyte, which is usually aqueous, contains water and ions that can interact directly with a surface and charged/polar adsorbates, and indirectly with the charge in the electrode to form the electrochemical double layer, which sets up an electric field at the interface that further affects interfacial reactivity. 

Fig. 1.6 DLVO interactions showing the energetics of colloidal particles as a competition between electrostatic double-layer repulsion and van der Waals attractions. The primary minimum is due to strong short-range electron overlap repulsion (shown in Figure 1.4... 

The positive S.P. observed when gases are adsorbed on a metal surface has been atrributed to (a) polarization of the adsorbate by the electron field of the metal double layer 73) and (6) charge-transfer effects 103). The importance of charge-transfer forces has been stressed by Mulliken 87) in his general theory of donor-acceptor interaction. If, as suggested, these charge-transfer forces contribute to the van der Waals attraction, then they probably take part in the physical adsorption process. The complex M X resulting from the adsorption of an inert gas on a metal surface M has been described as essentially no-bond with a small contribution from the structure As seen in Table VI, the S.P., and hence... 

Specific adsorption may involve short-range, strong interactions due to the overlapping of the electronic orbitals of the adsorbate and the electrode and ionic species or dipoles in the electrolyte. These will be considered in Sect. 6.1 together with the effect of changes of the structure of the interfacial region on electrode kinetics (double layer effects [3,5]). 

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