INVERTED CURRENT-TIME TRANSIENTS - A NEW METHOD FOR THE DETERMINATIONOF THE POTENTIAL OF MAXIMUM ADSORPTION IN CONDENSED LAYERS

The role of the potential of zero charge (PZC) and of the potential of maximum adsorption E-m during the adsorption of neutral molecules at the electrode surface is not yet well understood. The phase transition of the adsorbed molecules to a condensed state adds further complicat ions. But under certain circumstances this process can be utilized to obtain additional information about the adsorbate system and the elect rochemical double layer. On these grounds a new method for the determi nation of the potential of maximum adsorption in condensed layers is p roposed. This method is based purely on a qualitative analysis of the shape of current-time transients, which change their sign at the poten tial of maximum adsorption and become inverted. From this datum and th e corresponding capacity-potential curves of the adsorbate system and of the pure electrolyte one can construct the true charge-potential ch aracteristics of the system and obtain the value of the PZC. This meth od was applied to the system thymine/mercury/0.1 M NaClO4. One result is that in this system the potential of maximum adsorption is a functi on of the temperature, the pH-value, and the prepolarization potential . This latter result can only be explained in terms of a kinetic argum entation.