Tamás Pajkossy

Impedance aspects of anion adsorption on gold single crystal electrodes

Abstract In order to explore the origins of the capacitance dispersion observed for single crystal electrodes, voltammetric and impedance measurements on Au(l 11) and Au(100), in the absence and the presence of specifically adsorbed anions, mostly Br − , have been carried out. Interfacial capacitances and rate coefficients characterizing the kinetics of adsorption have been evaluated from the impedance spectra. We present evidence that the double layer behaves as an ideal capacitance in the absence of specific adsorption. The approximation with a constant phase element yields an exponent larger than 0.99. The “capacitance dispersion” observed in the presence of specific adsorption is either assigned to a slow diffusion or adsorption process, or to transformations within the adlayer or the substrate surface.

Double layer capacitance of Pt(111) single crystal electrodes

Abstract In order to determine the double layer capacitance of the Pt(111) electrode, impedance and capacitance measurements were carried out in neutral and acidic aqueous perchlorate solutions. Separation of the double layer and adsorption contributions of the interfacial capacitance were based on the adsorption impedance theory. The double layer capacitance versus potential plot exhibits a peak at about 0.12 V versus SCE in the 1.5–7 pH range; from here towards cathodic potentials the capacitance attains a value of about 20 μF/cm 2 . The peak may be related to the potential of zero free charge of the Pt(111) electrode.

Capacitance dispersion on solid electrodes: anion adsorption studies on gold single crystal electrodes

In order to explore the origin of the capacitance dispersion observed on solid electrodes, voltammetric and impedance measurements on single crystal gold electrodes have been carried out in the absence and presence of specifically adsorbed anions, mostly Br−. Evidence is presented showing that (i) in the absence of specific adsorption, the double layer on these electrodes behaves as an ideal capacitance (were the impedance approximated by a constant phase element, the exponent would be larger than 0.99); (ii) in the presence of specific adsorption, capacitance dispersion can be observed due to the sluggishness and/or diffusion control of the adsorption step, to the surface reconstruction/deconstruction and to adlayer structural transformations.

The interface between Au(100) and 1-butyl-3-methyl-imidazolium-hexafluorophosphate

The electrochemical interface of Au(100) and 1-butyl-3-methyl-imidazolium hexafluorophosphate has been characterized by cyclic voltammetry, electrochemical impedance spectroscopy and in situ STM, especially in two distinct potential ranges. In the vicinity of the potential of zero total charge--the value of which has been determined by immersion experiments--charging of the double layer is rather slow, it appears as if the ions comprising the ionic liquid would slowly exchange each other at the surface. In the other, very negative region the ordering of the cations has been observed by STM.

On the origin of the double layer capacitance maximum of Pt(111) single crystal electrodes

Abstract The double layer capacitance vs potential, C dl ( E ), curve of Pt(1xa01xa01) electrodes in aqueous KClO 4 and NaF solutions exhibits a maximum at about 0.1 V vs SCE. Since with lowered solute concentrations no Gouy–Chapman minimum can be found in C dl ( E ), the peak is not related to the potential of zero free charge.

The double layer capacity of Pt(100) in aqueous perchlorate solutions

Abstract The double layer capacity of the unreconstructed Pt(1xa00xa00) electrode in slightly acidic (4⩽pH⩽7) KClO 4 solutions was determined by impedance measurements as function of potential. It was found to be between 20–30 μF / cm 2 except around −0.1 V vs SCE, where the capacity–potential curve exhibits a peak of about 50 μF / cm 2 .