The effect of tert-butanol adsorption on the two-step electroreduction of Zn2+ and its dependence on the NaClO4 concentration

The influence of water molecules on the adsorption of organic substances and kinetics of electroreduction of inorganic depolarizers is very often overlooked. The electroreduction of Zn2+ is a typical example of a reaction controlled by both diffusion and charge transfer. This process in 1.0, 0.5 and 0.1 M NaClO4 solutions at a mercury electrode in the presence of tert-butanol is expected to involve two consecutive one-electron transfer steps in the overall reaction. Solutions of tert-butanol were prepared to cover the concentration range from 0.01 to 0.3 M. Measurements were performed using an impedance method for a wide range of both the potential and frequency. The difference between the potential of the anodic and cathodic peaks, which was obtained from the cyclic voltammetry method, increases with an increase in the concentration of both tert-butanol and NaClO4. From the dependences of ln⁡kft=f(E), the true standard rate constants kst and the constants ks1t and ks21 characterizing the stage of the first electron transfer and the stage of the second electron exchange, respectively, were determined. The obtained results indicate that the inhibiting properties of tert-butanol are the weakest in 0.1 M NaClO4. In addition the stage of the second electron transfer is less sensitive to the inhibiting effect of tert-butanol than the stage of the first electron exchange.