Potential difference, interfacial interface

An electric current flowing through an ITIFS splits into nonfaradaic (charging or capacity) and faradic current contributions. The latter contribution comprises the effects of both the transport of reactants to or from the interface, and the interfacial charge transfer, the rate of which is a function of the interfacial potential difference. By applying a transient electrochemical technique, these two effects can be resolved... 

Samec et al. [15] used the AC polarographic method to study the potential dependence of the differential capacity of the ideally polarized water-nitrobenzene interface at various concentrations of the aqueous (LiCl) and the organic solvent (tetrabutylammonium tetra-phenylborate) electrolytes. The capacity showed a single minimum at an interfacial potential difference, which is close to that for the electrocapillary maximum. The experimental capacity was found to agree well with the capacity calculated from Eq. (28) for 1 /C,- = 0 and for the capacities of the space charge regions calculated using the GC theory,... 

FIG. 9 Differential capacity C of the interface between 0.1 M LiCl in water and 0.02 M tetrabu-tylammonium tetraphenylborate ( ) or tetrapentylammonium tetrakis[3,5-bis(trifluoromethyl)phe-nyl]borate ( ) in o-nitrophenyl octyl ether as a function of the interfacial potential difference (From Ref 73.)... 

The dependence of the interfacial tension at the W/NB interface on the interfacial potential difference [29,30] was investigated by using an aqueous solution dropping electrode [26,31]. In this investigation, the aqueous solution was forced upward dropwise in NB and the drop time of W was measured as a function of potential difference applied at the W/ NB interface. When W contained 1 MMgS04 and NB contained 4 x 10 " M Cs" TPhB ... 

The description of the sorption of charged molecules at a charged interface includes an electrostatic term, which is dependent upon the interfacial potential difference, Ai//(V). This term is in turn related to the surface charge density, electric double layer model. The surface charge density is calculated from the concentrations of charged molecules at the interface under the assumption that the membrane itself has a net zero charge, as is the case, for example, for membranes constructed from the zwitterionic lecithin. Moreover,... 

Direct measurement of the change in interfacial potential difference at the oxide-electrolyte interface with change in pH of solution can be measured with semiconductor or semiconductor-oxide electrodes. These measurements have shown d V g/d log a + approaching 59 mV for TiC (36, 37). These values are inconsistent with the highly sub-Nernstian values predicted from the models with small values of K. (Similar studies 138.391 have been performed with other oxides of geochemical interest. Oxides of aluminum have yielded a value of d t)>q/A log aH+ greater than 50 mV, while some oxides of silicon have yielded lower values.)... 

We can contrast this interface with the C/Ag4Rbl5 interface where no charged species start to equilibrate once the bulk phases have been brought into contact. For a range of interfacial potential differences extending to 0.7 V there is an electrostatic equilibrium whereby the charge on the surface of the carbon is balanced by an equal and opposite charge... 

The interface structure for non-blocking interfaces is similar to that for related blocking interfaces. Thus the distribution of charge at the C/ Ag4Rbl5 interface will be similar to that at the Ag/Ag4Rbl5 interface. The major difference is that there is one particular interfacial potential difference at which the silver electrode is in equilibrium with Ag ions in the bulk electrolyte phase. At this value of A, there is a particular charge on the electrolyte balanced by an equal and opposite charge — on the metal. At any potential different from value of q different... 

It is now necessary to take a more unified view by considering situations in which the rate of the electrodic process at the interface is subject both to activation and to transport limitations. One refers to a combined activation-transport control of the electrodic reaction. Under such conditions, there will be, in addition to the overpotential T)c produced by the concentration change (from c° to c ) at the interface, an activation overpotential because the charge-transfer reaction is not at equilibrium. The total overpotential rj is the difference between the interfacial-potential difference... 

Use of a reference electrode to measure the electrode—electrolyte potential difference also introduces a new reference—solution interface, but this is designed so that the potential gradient at the new interface is constant regardless of whatever electrode process occurs isothermally at the working electrode. Changes in electrode potential are thus proportional to changes in the interfacial potential difference... 

With any electrochemical technique to study kinetics, the electrode-solution interface is perturbed from its initial situation. The initial conditions may be such that the system is in a chemical equilibrium and this usually means that the interfacial potential difference is determined by Nernst s law holding for the two components O and R of a redox couple being present... 

Although the equilibrium principle was available (equality of electrochemical potential of each ion that reversibly equilibrates across an immiscible liquid/liquid interface), the elementary theory and consequences were not explored until recently (6). To develop an interfacial potential difference (pd) at a liquid interface, two ions M, X that partition are required. However,... 

The interfacial potential difference (pd) for the partition equilibrium interface is given by the equality of electrochemical potential in terms of all ions in equilibrium, equation (4). 

The potential in the solution has to vary from the value at one electrode, V l. to that at the other electrode, y/g. The major portion of this potential drop y/j - y/g occurs across the two electrode-solution interfaces (see Chapter 6) i.e., if the potentials on the solution side of the two interfaces are y/ and y/g, then the interfacial potential differences are y/ - y/ and y/g - y/g (Fig. 4.42). The remaining potential drop, y/ -y/g, occurs in the electrolytic solution. The electrolytic solution is therefore a region of space in which the potential at a point is a function of the distance of that point from the electrodes. 

Ion transfer across phospholipid monolayers at liquid-liquid interfaces has been studied with the aim of elucidating the mechanism and kinetics of ion transport across a bilayer lipid membrane (BLM). The main advantage of using these systems is in the possibility of controlling the interfacial potential difference, which in the case of the BLM has to be inferred indirectly [141]. 

The potential difference between metal and solution, < - ( )s, is the total electrical driving force across the reaction interface, which for the condition of equilibrium can be defined as (t)M,rev - s,rev Th f ct is, however, that the transition-state complex will exist at some unknown position along the reaction coordinate across the double layer (see Fig. 1) between the substrate and the bulk of solution and hence it does not experience the entirety of this potential difference, but only a fraction that corresponds to an intermediate potential ( ). It is convenient to assume that the potential difference at this point, <]), rev interfacial potential difference, that is, P(0M rev-0s,rev). Where PzF(Sjev) would be the energy (in J mol ) associated with transfer of zFcoulombs across the metal/solution interface under standard conditions. 

Actually, interfacial potential differences can develop without an excess charge on either phase. Consider an aqueous electrolyte in contact with an electrode. Since the electrolyte interacts with the metal surface (e.g., wetting it), the water dipoles in contact with the metal generally have some preferential orientation. From a coulombic standpoint, this situation is equivalent to charge separation across the interface, because the dipoles are... 

The first and last terms are interfacial potential differences arising from an equilibrium balance of selective charge exchange across an interface. This condition is known as Donnan equilibrium (24, 51). The magnitude of the resulting potential difference can be evaluated from electrochemical potentials. Suppose we have Na" and as interfacially active ions. Then at the a/m interface,... 

The interface between two immiscible liquids is used as a characteristic boundary for study of charge equilibrium, adsorption, and transport. Interfacial potential differences across the liquid-liquid boundary are explained theoretically and documented in experimental studies with fluorescent, potential-sensitive dyes. The results show that the presence of an inert salt or a physiological electrolyte is essential for the function of the dyes. Impedance measurements are used for studies of bovine serum albumin (BSA) adsorption on the interface. Methods for determination of liquid-liquid capacitance influenced by the presence of BSA are shown. The potential of zero charge of the interface was obtained for 0-200 ppm of BSA. The impedance behavior is also discussed as a function of pH. A recent new approach, using a microinterface for interfacial ion transport, is outlined. 

In each case, the ion, species, or electron (boldface in Equation 19) that crosses or reacts at the interphase establishes the chemical equilibrium at the interface (equality of the electrochemical potential between solid or surface phase and solution) and thus determines (or influences) the interfacial potential difference. (The electron in Equations a and b may stand for a suitable reductant.) However, without further information the validity of the Nernst equation may not be inferred. 

The accumulation of electric charges (nontransferable across the interface in the absence of electrochemical process) on each part of the interface results from the existence of mobile charge carriers in the two phases in contact with each other and an interfacial potential difference [153]. The charge... 

In all cases such interfaces are non-polarizable, since the only way to change the interfacial potential difference is to modify the bulk properties of the phase(s), for example, the degree of doping or stoichiometry for semiconductors. 

Analogous ionic systems are represented by a contact of two electrolyte solutions in immiscible liquids, which contain a common ion. Owing to its interfacial exchange the electrochemical potential of this ion is to be constant throughout the system, and it leads again to a relation for the interfacial potential difference similar to Eq. (1) (called Dorman equation this time), that is, the interface is nonpolarizable without a change of the bulk media properties. 

If phases a and contain at least one common ion that can freely pass across the interface, the interface may be called reversible ornonpolarizable (Fig. 2). Although the latter term is commonly accepted, it does not correctly describe the state of the system. A reversible (nonpolarizable) interface can be partially polarizable or completely nonpolarizable. A completely nonpolarizable interface containing at least one common ion can pass a high current in either direction without causing a deviation of the interfacial potential difference from the equilibrium value. Although, in practice we encounter neither ideally polarizable nor completely nonpolarizable interfaces, under certain conditions the... 

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