Potential of zero total charge of palladium modified Pt(111) electrodes in perchloric acid solutions

Abstract

The electrochemical behaviour of palladium-modiÐed Pt(111) electrodes in perchloric acid solutions has been studied by means of cyclic voltammetry and CO charge displacement. From the results of the charge displacement experiments, values of the potentials of zero total charge (pztc) have been determined and their dependence on the palladium coverage has been studied in solutions without speciÐcally adsorbing anions. These pztc values are compared to those obtained in sulfuric acid solutions. Whilst in the presence of bisulfate anions the pztc decreases signiÐcantly as a consequence of the deposited palladium, in the case of perchloric acid solutions the pztc remains constant within experimental error. This constancy has been explained by means of a compensation between the displacement of the potential of zero free charge toward less positive potentials and the increase of hydrogen coverage on the palladium-covered electrode surfaces. The inÑuence of the concentration of speciÐcally adsorbed (bi)sulfate anions at constant pH has been pointed out. The oxidation of the CO adlayer resulting from the charge displacement has also been studied. Despite the apparently easier OH adsorption, the oxidation of adsorbed CO takes place at higher potentials on the modiÐed surfaces. CO coverage values, calculated from knowledge of the pztc value and the CO stripping charge, diminish as the amount of palladium increases.

Mechanism of hydrogen adsorption/absorption at thin Pd layers on Au(111)

“…Baldauf and Kolb [14] have attributed the more positive peak to hydrogen adsorption on the perimeter of Pd islands and the more negative peak to hydrogen adsorption on terraces. No H absorption was found at a monolayer of Pd in electrochemical conditions [13][14][15][16][22][23][24][25] but it seems to start even at coverages as low as 2 ML, as evidenced by the increase in current at the most positive potentials. This suggests that the growth of palladium on Au(1 1 1) is not exactly layer by layer after the first monolayer.…”

“…It was suggested in the literature that the peaks in the presence of sulfuric acid may contain contribution due to the bisulfate adsorption, and the charge in perchloric acid is expected to be lower than in sulfuric acid considering the adsorption of (bi)sulfate anion in sulfuric acid and the absence of anion adsorption in perchloric medium.Álavarez et al [25] integrated cyclic voltammograms of 0.8 ML Pd on Pt(1 1 1) and found a total (anion and hydrogen adsorption) charge of 250 C cm −2 in perchloric acid and 265 C cm −2 in sulfuric acid. They also found, using CO displacement technique, that (bi)sulfate adsorption charge is 90 C cm −2 and in perchloric acid the anion adsorption charge is 50 C cm −2 .…”

Tuning Reaction Rates by Lateral Strain in a Palladium Monolayer

“…The so-called CO displacement method has shown that (bi)sulfate is adsorbed on the palladium surface at potentials positive of the characteristic peaks in Figure 3, and hydrogen at potentials negative of them. [4,39] Though influenced by anion adsorption, the peak potentials serve as a measure for the hydrogenadsorption strength (the free enthalpy of adsorption can be derived directly from them) in such a solution. We assume that hydrogen adsorbs much stronger than sulfate, since the hydrogen peak potentials for sulfuric acid are more positive than the potentials of zero charge.…”

Gezielte Veränderung der katalytischen Aktivität einer Palladium‐Monoschicht durch Dehnung oder Kompression

“…Durch Verdrängen der elektrischen Doppelschicht mit Kohlenmonoxid konnte gezeigt werden, dass negativ vom jeweiligen Strompeak in Abbildung 3 Wasserstoff und positiv davon (Hydrogen)-Sulfat adsorbiert ist. [4,39] Aus den Peakpotentialen kann die freie Adsorptionsenthalpie von Wasserstoff direkt abgeleitet werden, wobei wir annehmen, dass Wasserstoff viel stärker als Sulfat adsorbiert, da die Strompeaks in Schwefelsäure positiv vom Null-Ladungspotential liegen. [40] In atomen mit den Abständen zu den nächsten Nachbarn ändert; dies hat einen direkten Einfluss auf die Bindungsenergien.…”