Inverted Current−Time Transients. A New Method for the Determination of the Potential of Maximum Adsorption in Condensed Layers

Abstract

The role of the potential of zero charge (PZC) and of the potential of maximum adsorption Em 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 complications. But under certain circumstances this process can be utilized to obtain additional information about the adsorbate system and the electrochemical double layer. On these grounds a new method for the determination of the potential of maximum adsorption in condensed layers is proposed. This method is based purely on a qualitative analysis of the shape of current-time transients, which change their sign at the potential of maximum adsorption and become inverted. From this datum and the corresponding capacity-potential curves of the adsorbate system and of the pure electrolyte one can construct the true charge-potential characteristics of the system and obtain the value of the PZC. This method 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 function of the temperature, the pH-value, and the prepolarization potential. This latter result can only be explained in terms of a kinetic argumentation.

Interference of Adsorption, Condensation, and Double-Layer Charging in Kinetic Studies of Film Formation. 1. Constant Double-Layer Potential

“…There are principal differences between the two kinds of phase transitions on electrodes. In nonfaradaic processes, apart from the transient shape as shown in Figure , other shapes, the so-called inverted current transients, are found experimentally (see Figures , , and 7).…”

Coadsorption of the DNA bases thymine and adenine at the Au(111) electrode

“…Thymine represents a well investigated system at the mercury electrode [8][9][10][11] as well as at gold single crystal electrodes. 12,13 At mercury electrodes a first order phase transition of physisorbed thymine near the potential of zero charge (p.z.c.)…”

“…From electrochemical experiments we conclude that the plane of the thymine molecules in the condensed film is oriented parallel to the electrode surface. In the state of random adsorption molecules are slightly tilted with one of its nitrogen bonds towards the surface 11 (Fig. 1).…”

Interaction of thymine and copper adatoms on Au(111) electrodes

“…For low bulk concentrations only a diluted adsorption layer is formed at the Au(1 1 1) surface. The molecules are orientated slightly tilted with respect to the electrode surface, which can be concluded from detailed chronoamperometric studies performed at the mercury electrode [24].…”