Migration and diffusion coupled with a fast preceding reaction. Voltammetry at a microelectrode

A mathematical model implemented by simulation is presented for voltammetry of a reversible couple that involves a fast preceding chemical reaction an d mixed diffusional and migrational transport. The hydrogen couple, H+/H-2, fulfills the above criteria. For strong acids there is no preceding reacti on, whereas for weak acids the preceding reaction is HA = H+ + A(-). The co mputed voltammograms are compared with experimental voltammograms for the r eduction of strong and weak acids at Pt microelectrodes with excess of and without supporting electrolyte. The key assumption in the calculations is t hat the flux of hydrogen ion is independent of the anion. This assumption i s supported by the experimental fact that the wave heights in the absence o f supporting electrolyte of several strong acids of equal concentration and with anions of various size are identical.