The Role of Surface Sites on the Oscillatory Oxidation of Methanol on Stepped Pt[n(111) × (110)] Electrodes

Abstract

Reaction rates and mechanisms of most electrocatalytic reactions are known to critically depend on the structure of the electrode surface. Examples of structure sensitive electrocatalytic systems include the reduction of oxygen and the oxidation of small organic molecules on platinum, for instance. Even more intricate is the effect of the interfacial structure on the oscillatory dynamics commonly observed in some systems. This is somewhat expected because several adsorption and reaction steps are simultaneously active during self-organized potential or current oscillations. Herein we present results of the effect of surface structure on the oscillatory electro-oxidation of methanol in acidic media on Pt(111), Pt(110), and on stepped surfaces Pt(776), Pt(554), Pt(775), and Pt(332). The system was investigated at two methanol concentrations and under voltammetric and galvanostatic regimes. The voltammetric activity towards the electro-oxidation of methanol on stepped surfaces followed this sequence: Pt(776) < Pt(554) < Pt(775) < Pt(332), at high methanol concentration. The reaction rates increase with the density of (110) sites, but small (111) terraces was also found to contribute to the overall process. In terms of potential oscillations, we found specificities that were unambiguously assigned to the surface structure. In particular, the following features were found according to the specific surface studied: periodadding sequences of mixed-mode oscillations; a new type of mixed-mode oscillation; and a particular separation between two types of sequential oscillations. The understanding of the relationship between the surface structure and the underlying dynamics of the surface chemistry during oscillations is a key challenge and our findings in this direction are discussed.

On the oxidation mechanism of C1-C2 organic molecules on platinum. A comparative analysis

“…Indeed, when strongly adsorbed anions are present in the electrolyte, such as sulfate or phosphate [29], currents diminish significantly, even for relatively high methanol concentrations and the typical profile observed in the absence of methanol is superimposed to the small methanol oxidation currents. Thus, the typical phase transition in the adsorbed sulfate layer on the Pt(111) electrode can be still observed in the presence of methanol ( figure 2B), implying that the presence of methanol has not disturbed the adsorption of sulfate [30][31][32]. The large decrease in the currents in the presence of specifically adsorbed anions and the observation of the typical features of the supporting electrolyte clearly implies that the interaction with the surface is very weak, which makes the electrocatalysis more difficult.…”

The effect of Pt surface orientation on the oscillatory electro-oxidation of glycerol

“…All Pt electrodes used in the present study were checked in acid media (see Fig. SI1 in the supporting information), the electrochemical characterization recorded indicated a high degree of surface crystalline order and cleanliness of the system, as seen detailed in elsewhere [20].…”

“…After each typical surface characterization step in electrolyte media [20], the first scan of glycerol electro-oxidation was recorded (Fig. 1A-B) for the two electrolyte concentrations selected (0.1/0.5 M H2SO4).…”

“…The influence of the surface structure, namely basal planes, and stepped surfaces, on the electro-oxidation of small organic molecules, has revealed an interesting aspect of these surfaces' electroactivities. For instance, the electro-oxidation of methanol and ethanol is favored over (110) steps on the (111) terraces [20,31,32], because the steps catalyze the reaction at low potentials as well as promote the oxidation of the CO species formed. However, the same effect is not observed for GEOR, wherein the reaction is considerably affected at a low potential, and the currents decay linearly with the addition of (110) step sites [9].…”

Single‐Nanoparticle Coulometry Method with High Sensitivity and High Throughput to Study the Electrochemical Activity and Oscillation of Single Nanocatalysts

“…[ 26,37 ] The increase in defect density also promotes the catalytic activity of Pt(111) facets on other electro‐oxidation systems. [ 38 ]…”