Current migration

Foreign salts may frequently be present without interference and are, indeed, usually added as the supporting electrolyte in order to eliminate the migration current. 

Microphotometer 768 Microwave oven 97 Migration current 592, 596 Mixed indicators 267, (T) 268 Mobile phase 13, 217, 218, 222 Mobilities, ionic (T) 520 Modified voltammetric procedures 611 Modulation 791... 

Generally, an electrolyte may contain several ionic reactant species but no obvious excess of a foreign electrolyte. Then, as already mentioned, a calculation of the migration currents [or coefficients a in equations of the type (4.22)] is very complex and requires computer use. 

The electric field also gives rise to a migration current density Ea [see Eq. (1.4)]. Hence, in Eq. (31.4) we can replace the parameter of field strength E by current density, which is more readily measured ... 

Fig. 16.3 Quantum yield (QY) for electron and hole transfer to solution redox acceptors/donors as a function of the reduced variables y (related to the surface properties of the catalyst, i.e., ratio between interfacial electron transfer rate and surface recombination rate) and w (related to the ratio between surface migration currents of hole and electrons to the rate of bulk recombination), according to the proposed kinetic model [23],...

An awkward situation arises when dealing with a dilute solution where it has been observed that the depletion of the electrode layer ultimately leads to an enhancement of the resistance of the solution and thereby affecting subsequently an alteration in the Ohm s Law potential drop (I x R) in the cell. This ultimately gives rise to a doubtful observed potential operative at the electrode. In order to overcome this serious anomaly, it is a normal practice to add an excess of an indifferent electrolyte to the system, such as 0.1 M KC1, which renders the solution to remain stable at a low and constant resistance, whereas the migration current (Im) of the species under examination almost vanishes i.e., I = Id. 

Assuming that the migration current (Im) is virtually eliminated by the addition of a reasonably enough supporting electrolyte then the only cardinal factor which would affect the limiting current would be the rate of diffusion of the electro-active substance from the main body of the solution to the surface of the electrode. 

The total current density across the junction is therefore equal to the sum of the electron and hole current densities, just as the total ionic-migration current density in an... 

Supporting Electrolyte The electrolyte that is added to the electrolytic solution to make it electrically conductive as well as to control the reaction conditions. The supporting electrolyte also works to eliminate the migration current that flows in its absence. It may be a salt, an acid, a base or a pH buffer, which is difficult to oxidize or to reduce. It is used in concentrations between 0.05 and 1 M, which is much higher than that of electroactive species (usually 10-5 to 10 2 M). The supporting electrolyte sometimes has a great influence on the electrode reaction, changing the potential window of the solution, the double layer structure, or react-... 

The charge mobility of an ion represents the speed that acquires the ion per unit of electric field. The electric migration current corresponding to the ionic movement of a single kind of charge is equal to the flux of charge, i.e., to the rate at which the charge cross any plane normal to the flow (see Eq. 1.141) [56]... 

Equation (1.143) is valid for a single carrier. The total migration current is obtained as... 

This means that in a homogeneous case the migration current density in Eq. (11) is given by ... 

The repercussion of the insulator embedding the WE on the dynamics becomes most apparent when reformulating the migration current density in the following... 

Fig. 33. Schematic representation of the potential distribution in the electrolyte as a result of an inhomogeneous distribution of the electrode potential, DL, and the effect of migration currents induced by the inhomogeneous potential distribution on the local temporal evolution of the potential (a) for the case that the length of the WE is much smaller than the distance between the WE and the CE and (b) for the case that the length of the WE is much larger than the distance between the WE and the CE. The length of the arrows in the representations below the potential distributions indicate how the contribution of the migration couplings to the temporal evolution of DL changes as a function of distance from the disturbance. (x, z spatial coordinates parallel and perpendicular to the WE, respectively. The electrode is assumed to be one-dimensional and the electrolyte two-dimensional.)...

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