Advantages of the application of programmed currents to microelectrodes

Equations corresponding to the application of programmed currents of the form I(t)=I0 eωt and I(t)=I0tu, with u>0 and ω>0, to spherical microelectrodes under steady-state conditions have been deduced. The use of chronopotentiometry with programmed currents in microelectrodes allows us to obtain potential–time (E/t) responses from which the transition time can be easily measured, as well as current potential (I(t)/E) curves which are independent of the particular form of the programmed current. In contrast, when a constant current is applied to a microelectrode, a single potential is obtained. We have also analyzed the evolution from transient to stationary potential–time and current–potential responses by using two successive programmed currents alternating in sign, (−I(t) and I(t)), since the second response tends to disappear in the neighborhood of the steady state. We propose methods for determining thermodynamic and kinetic parameters of the charge transfer process. The validity of the theoretical predictions has been experimentally tested with ferrocene oxidation in acetonitrile.