Determination of the number of electrons by chronoamperometry at small electrodes

The number of electrons transferred, n, was determined by taking the ratio of the square of the slope to the intercept of Cottrell plots by chronoamperometry at a small disk electrode without knowing values of diffusion coefficients. The intercept is ascribed to the contribution of spherical diffusion. This technique is useful for estimating reaction mechanisms of unstable species of which lifetime is shorter than the period of bulk electrolysis. It takes advantage not only of getting the simultaneous acquisition of two independent variables (the slope and the intercept) in one chronoamperometric curve but also of evaluating the dependence of n for multi-step charge transfer reactions on electrode potentials. Ferrocene and N,N′-bis(4-methoxyphenyl)-N,N′-diphenyl-1,4-phenylenediamine were used for redox species at n = 1 and 2, respectively. Chronoamperometric currents were obtained at the platinum disk electrode 50 μm in radius for the time less than 3 s, responding to the various stepped potential values. Values of n were obtained at each potential even for sluggish charge transfer reactions.