Chronopotentiometry double layer

Chronopotentiometry. Paunovic and Oechslin (8) measured the adsorption of peptone on lead-tin alloy electrodes using chronopotentiometric and double-layer measurements. This case is different from the adsorption of HCOOH because peptone is not an electroactive species in the conditions smdied but only blocks the surface used for the electrodeposition of lead-tin alloys from solutions containing Sn and Pb ions. Chronopotentiometric analysis is based on the following principles (7). In the absence of adsorption, the relationship between the transition time r (for reduction of Sn and Pb in this case), the bulk concentration c° of the substance reacting at the electrode, and the current I is given by the equation... 

The applicability of chronopotentiometry in kinetic studies will, of course, be limited by the presence of the double layer. As the faradaic process causes E to change most rapidly both at short and long times, deviation from the theoretical behaviour described above will be most severe at the extreme parts of the chronopotentiogram. It may be worth noting that eqn. (25) provides the possibility of an internal check since, on variation of j, a certain pair of E, kt values will be found at different values of tin/r1/2. 

This would suggest that chronopotentiometry could be a sensitive electroanalytical technique. It is rarely used in this context, however, since it is often difficult to determine the transition time accurately, because of double-layer charging at short times and competing reactions at long times. The same limitations apply when one attempts to use Eq. 49K to measure the diffusion coefficient. On the other hand this equation can be used as a quick method of obtaining n,... 

Figure 6.19 Current- and potential-time dependence in chronopotentiometry. The double-layer charging retards the potential increase and can, similar to chronoamperometry, distort the extrapolation.

In chronopotentiometry, after switching on a current, the time dependence of the potential is monitored. Potential- and current-time dependence are shown schematically in Figure 6.19. Similar to chronoamperometry, the charging of the double layer can overshadow the region of charge-controlled behavior. 

Fig 13. Influence of double layer capacitance on chronopotentiometrie curve. 

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