Influence of the CO Adsorption Environment on Its Reactivity with (111) Terrace Sites in Stepped Pt Electrodes under Alkaline Media

Abstract

The effect of the electrode potential in the reactivity of platinum stepped single crystal electrodes with (111) terraces towards CO oxidation has been studied. It is found that the CO adlayer is significantly affected by the potential at which the adlayer is formed. The electrochemical and FTIR experiments show that adsorbed CO layer formed in acidic solution at ~0.03 V vs. SHE is different from that formed at -0.67 V vs. SHE in alkaline solutions. The major effect of the electrode potential is a change in the long-range structure of CO adlayer. The adlayer formed in alkaline media presents a higher number of defects. These differences affect the onset and peak potential for CO stripping experiments. The stripping voltammogram for the adlayer formed at -0.67 V vs. SHE always shows a pre-wave and the peak potential is more negative than that observed for the adlayer formed at 0.03 V vs. SHE. This means that the apparent higher activity for CO oxidation observed in alkaline media is a consequence of the different CO adlayer structure on the (111) terrace, and not a true catalytic effect. The different behavior is discussed in terms of the different mobility of CO observed depending on the electrode potential. Also, the FTIR frequencies are used to estimate the pzc (potential of zero charge) for the Pt(111) electrode covered with a CO adlayer.

Influence of the metal loading on the electrocatalytic activity of carbon-supported (100) Pt nanoparticles

“…Thus, whereas the 2-3-nm Pt nanoparticles displayed a voltammetric response in 0.5 M H 2 SO 4 similar to that characteristic of an electrochemically activated polyoriented Pt electrode [34,24], that is, a Pt surface without (100) and (111) ordered domains, the current Pt nanoparticles show a preferential (100) surface structure. In this respect, it is well established from Pt single crystals studies with basal plane, stepped and kinked surfaces that the CO stripping reaction is structure-sensitive [53][54][55][56][57][58][59][60][61][62]. In addition, this surface structure sensitivity is also present on the nanoscale as is demonstrated by the use of shape-controlled Pt nanoparticles [6,44,45].…”

Towards the understanding of the interfacial pH scale at Pt(1 1 1) electrodes

“…Another point deals with the evaluation of the charge remaining at the surface covered by CO. The determination of the capacitive currents in alkaline solutions are difficult because the permanent presence of the prewave oxidation at low potentials, probably due to a defective CO adlayer [53]. However, it was possible to perform this calculation by careful control of the potential range.…”

“…In this respect the strategy used was that described previously [53]: in separate experiments, the CO was dosed in acidic solution and then transferred to alkaline solutions of different pH. This leads to a slightly better ordered layers in which the prewave is not observed [53].…”

Ionic Liquid-Modified Electrocatalysts: The Interaction of [C 1 C 2 Im][OTf] with Pt(1 1 1) and its Influence on Methanol Oxidation Studied by Electrochemical IR Spectroscopy

“…The shift to higher potential can be explained if we take into account that CO oxidation involves oxygen-containing species (OH ads species) which are formed by activation of H 2 O [57]. High CO coverage is known to block the access of H 2 O, thereby shifting the CO oxidation signal to higher potential [57,66,67]. In the present case, we attribute the shift in the onset potential in the presence of [C 1 C 2 Im][OTf] to a blocking effect of the adsorbed [OTf] À .…”