Peroxodisulfate reduction as a probe to interfacial charge

Abstract

Peroxodisulfate reduction has been investigated on Pt(111) on a broad range of pH values as a way to test interfacial charge. The reaction always proceeds in a potential window that is almost pH independent, regardless changes in the presence of adsorbed species. Comparison with other available information for these interphases allows to conclude that this reaction is very sensitive to the free charge on the metal, being inhibited when the latter is negative. This explains the complete current inhibition when the potential is lower than the potencial of zero free charge. Most remarkably, the inhibition at high potentials can be related with the existence of a second potential of zero charge, above which the surface becomes again negatively charged. This conclusion agrees with classical results for polycrystalline platinum (which has been reexamined), results from laser induced T-jump experiments and recent theoretical models of the interphase. In this way, this reaction is postulated as a new probe to locate the values of the potential of zero free charge.

Double Layer at the Pt(111)–Aqueous Electrolyte Interface: Potential of Zero Charge and Anomalous Gouy–Chapman Screening

“…In conclusion, we have determined the double layer properties and the potential of zero charge (pzc) of Pt(111) in perchlorate solution by identifying the Gouy–Chapman capacitance minimum. The value of 0.30 V NHE agrees very well with the value obtained by other methods . In contrast to double‐layer measurements on gold or mercury electrodes, the Gouy–Chapman capacitance minimum is only observed at electrolyte concentrations lower than 10 −3 m , and only if the pH is between 2 and 5.…”

“…The value of 0.30 V NHE agrees very well with the value obtained by other methods. [3][4][5][6][7] In contrast to double-layer measurements on gold or mercury electrodes, the Gouy-Chapman capacitance minimum is only observed at electrolyte concentrations lower than 10 À3 m, and only if the pH is between 2 and 5. In practice this means that the GC capacitance minimum can be measured only near pH 4.…”

“…Therefore many studies have aimed at measuring the pzc of Pt(111) in a nonspecifically adsorbing electrolyte such as perchloric acid. Recently, the Alicante group has concluded a value of 0.30 V (vs. SHE) based on three different methods, that is, CO displacement studies, [3,4] peroxodisulfate reduction, [5] and laser-induced temperature jump measurements of the potential of maximum entropy. [6,7] This value of the pzc of Pt(111) is also in good agreement with recent first-principles predictions.…”

“…If the potential of zero charge is at 0.3 V vs. NHE, [5,18] then the pzc is expected at 0.36 V RHE for pH 1 and at 0.48 V RHE for pH 3. Therefore, only for pH 3 the pzc is in the DL window.…”

Double Layer at the Pt(111)–Aqueous Electrolyte Interface: Potential of Zero Charge and Anomalous Gouy–Chapman Screening

“…If the potential of zero charge is at 0.3 V vs. NHE, then the pzc is expected at 0.36 V RHE for pH 1 and at 0.48 V RHE for pH 3. Therefore, only for pH 3 the pzc is in the DL window.…”