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 and mixed diffusional and migrational transport. The hydrogen couple, H(+)/H(2), fulfills the above criteria. For strong acids there is no preceding reaction, whereas for weak acids the preceding reaction is HA = H(+) + A(-). The computed voltammograms are compared with experimental voltammograms for the reduction of strong and weak acids at Pt microelectrodes with excess of and without supporting electrolyte. The key assumption in the calculations is that the flux of hydrogen ion is independent of the anion. This assumption is supported by the experimental fact that the wave heights in the absence of supporting electrolyte of several strong acids of equal concentration and with anions of various size are identical.