Coulostatic methods

CS = coulostatic method, CV = cyclic voltamogram, FD = Faradaic distortion method, FR = Faradaic rectification, GD = galvanostatic double pulse method, IP = impedance method, PS = potential step method. See also list of... 

According to the parameter controlled. When this is the potential, we speak of potentiostatic and potentiodynamic methods when it is the current, we speak of galvanostatic and galvanodynamic methods (galvanodynamic methods are rarely used) in the coulostatic method a certain amount of charge is delivered to the elecnode (e.g., from a capacitor) and the potential-time variation is followed. 

Santos E, Iwasita T, Vielstich W. 1986. On the use of the coulostatic method for the investigation of fast redox systems. Electrochim Acta 31 431-437. 

In the closely related coulostatic method based on injection of a charge from a small condenser into an electrode in equilibrium with a redox system. The resulting time dependence of the electrode potential originates from the discharging of the electrical double layer by electrode reactions... 

With respect to chemical steps prior to the electron-transfer step, chrono-potentiometiy offers a convenient technique. The methods of measurement and the quantitative relationships are outlined in Chapter 4. Post-electron-transfer reactions to the electron-transfer step are most conveniently characterized by cyclic voltammetry (see Chapter 3). Although the techniques of cyclic voltammetry and chronopotentiometiy both provide a means for the qualitative detection of adsorption processes at an electrode, the coulostatic method and chrono-coulometry are the methods of choice for quantitative measurements of adsorption. 

There are two advantages of the coulostatic method in the study of kinetics of electrode reactions. First, the ohmic drop is not of importance, therefore the measurements can be carried out in highly resistive media. Second, since Ic = IF, Q does not interfere in the measurement. By the help of this technique jo values up to about 0.1 A cm-2 and - standard rate constants up to 0.4cms 1 can be determined. A detailed discussion of coulostatic techniques can be found in Ref. [vi]. 

The unique feature of the coulostatic method is that measurement is made at open circuit. This leads to two important consequences. 

Inserting the preceding numerical values, we can show the effect of the solution resistance on the limits of applicability of the coulostatic method, as given, for example, in Table 2K. 

Fig. 7K Charge injection followed by open-circuit decay (the coulostatic method). Diffusion limitation (low values of /x ) slows down the decay transient, as expected from the equivalent circuit shown in Fig. 2K.

Note that the choice of T/x = 2 as the optimum time scale is specific to the coulostatic method. For galvanostatic measurements the... 

The coulostatic method was applied to in situ measurement of the polarization resistance i p (Eq. (25)). Thus, the rate of electroless plating was determined by Suzuki et al. [21-23]. Two advantages of this technique have been cited by the inventors (1) measured values are not influenced by the solution resistance, and (2) measurements can be finished very rapidly, within a few tens of milliseconds. The principle is briefly explained below. 

Figure 8.7.1 Circuit for charge-step or coulostatic method. In practice, the cell may be held initially at a potential eq by means of a potentiostat that is disconnected immediately before the charge injection.

Charge Step (Coulostatic) Methods 323 For the circuit in Figure 8.7.1, when the relay is in position A, the capacitor,... 

The open-circuit ILIT response is analogous to the open-circuit response for the coulostatic method [43-45] where the initial perturbation is effected by charge injection. We will confine our analysis to systems where the redox species are attached to the electrode surface. 

Controlled Charge Charge Step Coulostatic Methods ... 

Another transient method which may be used to study fast electrode processes is the coulostatic method. Here a known amount of electricity is injected into the electrode in a very short time. The electrode, Initially at... 

Fig. 77. A schematic circuit for the coulostatic method B battery L relay switch Ci, Ci capacitors C cell O oscilloscope P potentiometer.

Since the charge is injected in a very short time (preferably 1 is or less), measurement can often be completed before diffusion limitation has become significant In this respect the charge-injection (coulostatic) method is similar to the double-pulse galvano static method, except that one has more freedom in the choice of the parameters of the pulse, since there is no need to match it to the second pulse. 

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