In Part I of this series 1, the Galvanostatic Reversed Coulostatic (GRC) pulse method was introduced for the determination of the kinetic parameters of an electrode reaction. In this method both ohmic drop and concentration polarization are eliminated and hence charge transfer overvoltages, caused by galvanostatic current pulses, are measured directly. The kinetic parameters evaluated pertain to the surface concentrations of the electroactive species at the time of measurement. These concentrations are defined by the concentration polarization which is measured in the same experiment. Furthermore, the value of the differential double layer capacity is determined simultaneously, in the presence of the electroactive species.
In this paper these statements are verified on the basis of experiments at the Cd 2 +/Cd(Hg) electrode in 1 M NaC104 and in 1 M KC1. The former system, with a rate constant of about 0.5 cm s-1, was chosen because its kinetic and double layer properties are well-known 2-7 from experiments with other relaxation techniques. Consequently it is a suitable redox system to test the experimental set-up and the theory described previously 1.
In KC1 the electrode reaction is faster but the values for the kinetic parameters reportedZ-4,6,v,14 -16 do not agree very well. It therefore seemed useful to bring this electrode into the present investigations, to provide a further test of the potentialities of the GRC pulse method.
EXPERIMENTAL
Apparatus and measurin9 procedure
The electrical circuit, in which no special arrangement to compensate ohmic drop need be made, is shown schematically in Fig. 1. To make direct reading of charge transfer overvoltages possible, only each second galvanostatic prepulse is followed by a coulostatic impulse with reversed sign. This is realized by leading the trigger pulses, generated by the galvanostatic pulse generator PG1, via a flipflop to the trigger input of the externally synchronized coulostatic impulse generator PG2. Thus the