Electrodes charge distribution

On the electrode side of the double layer the excess charges are concentrated in the plane of the surface of the electronic conductor. On the electrolyte side of the double layer the charge distribution is quite complex. The potential drop occurs over several atomic dimensions and depends on the specific reactivity and atomic stmcture of the electrode surface and the electrolyte composition. The electrical double layer strongly influences the rate and pathway of electrode reactions. The reader is referred to several excellent discussions of the electrical double layer at the electrode—solution interface (26-28). 

The electrode reaction occurs in the region where by the influence of the electrode charge an electric field is formed, characterized by the distribution of the electric potential as a function of the distance from the electrode surface (see Section 4.3). This electric field affects the concentrations of the reacting substances and also the activation energy of the electrode reaction, expressed by the quantities wT and wp in Eq. (5.3.13). This effect can be... 

Figure 1. Schematic representation of potential profile and charge distribution across an anodic oxide film of thickness S on aluminum (a) hypothetical situation in the absence of any current (b) in the presence of an anodic current caused by corrosion or by an external source. RE, reference electrode to which the potential of aluminum is referred.

In this paper, some of the possibilities associated with the FREECE technique wil1 be described. Results referring to the charge distribution at the electrode-electrolyte interface and to charger-transfer reactions will be presented and briefly discussed. 

For the investigation of charge tranfer processes, one has the whole arsenal of techniques commonly used at one s disposal. As long as transport limitations do not play a role, cyclic voltammetry or potentiodynamic sweeps can be used. Otherwise, impedance techniques or pulse measurements can be employed. For a mass transport limitation of the reacting species from the electrolyte, the diffusion is usually not uniform and does not follow the common assumptions made in the analysis of current or potential transients. Experimental results referring to charge distribution and charge transfer reactions at the electrode-electrolyte interface will be discussed later. 

The charge distribution at metal electrode-electrolyte interfaces for liquid and frozen electrolytes has been investigated through capacity measurements using the lock-in technique and impedance spectroscopy. Before we discuss some of the important results, let us briefly consider some properties of the electrolyte in its liquid and frozen state. 

Fig. 9.1 The charge distribution around the electrode holes, the majority charge car-...

Fig. 9.3 The charge distribution around pores in a low doped, illuminated n-type silicon electrode. Three types of charge carriers are present electrons, which are the majority carriers (dashes), holes, which are the minor-...

The so-called diffusion layer is still a region dominated by an unequal charge distribution (i.e. in such a zone the principle of electro-neutrality is not valid) due to the electron transfer processes occurring at the electrode surface. In fact, the electrode acts as an electrostatic pump for species of... 

The electronic charge distribution in a semiconductor varies with applied electrode potential (Uf), which in turn determines the differential capacitance at the interface [11,78]. Relating charge density and electric field, the capacitance of a space charge (or depletion) region can be quantitatively derived. For an n-type semiconductor Poissons equation can be written ... 

The frontier between the depletion and the accumulation situations of the space charge layer is defined by the flat band potential. In fact, when the potential is constant all along the thickness of the electrode, the mobile charge (and naturally the fixed charge) distribution is uniform. In the case of the interface of Si electrode with an electrolyte, the corresponding bias potential has to be determined with respect to the reference electrode. The value of the flat band potential Vfb is expected... 

How Is the Charge Distributed inside a Solid Electrode Phenomena that depend on electric double layers comprise a general and very widespread part of the science of surfaces. They occur whoever phases (containing charged... 

Let us note one vital point, which is of methodological importance. It has been traditionally accepted in electrochemistry to choose the positive direction of the electrode potential

positive electrode charge. Here the zero potential is assumed to be that of the reference electrode, which coincides, within a constant, with the potential in the solution bulk (— oo). On the other hand, in physics of semiconductor surface the potential is usually reckoned from the value in the semiconductor bulk ( ) the enrichment of the surface with electrons, i.e., the formation of a negative space charge, corresponding to the positive potential of the surface. In particular, this statement directly follows from the Boltzmann distribution for electrons and holes in the space-charge region in a semiconductor ... 

At the present time, the theory of electrochemical impedance of electrodes with distributed potentials is not yet completed, and algorithms of parametrical and structural identification procedures are not available. In addition, the interpretation of the results is very complicated. For this reason, in this work we analyzed only the frequency characteristics of impedance s components in the modified electrode system. As a result, we obtained a set of response peculiarities in the frequency range under investigation. Rather low frequency dispersion was observed in a solution containing a ferri-ferrocyanide system for both active (Fig.3, curve 2) and reactive (Fig.4, curve 3) components. In our opinion, this fact confirms that the independent on frequency resistance of charge transfer determines the main contribution to the impedance. 

In order to develop selective electrodes, it is necessary to introduce specific interactions between the ionophore and the anion of interest. This can be achieved by designing an ion carrier whose structure is complementary to the anion. This type of design can be based on molecular recognition principles, such as the ones that involve complementarity of shape and charge distribution between the ion and the ionophore. 

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