Carlos Busó-Rogero

Ethanol Oxidation on Pt Single‐Crystal Electrodes: Surface‐Structure Effects in Alkaline Medium

Ethanol oxidation in 0.1 M NaOH on single-crystal electrodes has been studied using electrochemical and FTIR techniques. The results show that the activity order is the opposite of that found in acidic solutions. The Pt(111) electrode displays the highest currents and also the highest onset potential of all the electrodes. The onset potential for the oxidation of ethanol is linked to the adsorption of OH on the electrode surface. However, small (or even negligible) amounts of CO(ads) and carbonate are detected by FTIR, which implies that cleavage of the C-C bond is not favored in this medium. The activity of the electrodes diminishes quickly upon cycling. The diminution of the activity is proportional to the measured currents and is linked to the formation and polymerization of acetaldehyde, which adsorbs onto the electrode surface and prevents further oxidation.

Surface structure and anion effects in the oxidation of ethanol on platinum nanoparticles

Ethanol oxidation on platinum nanoparticles with well-characterized surfaces is studied using cyclic voltammetry and FTIR techniques. Their behavior is compared with that obtained for platinum single crystal electrodes, in order to rationalize their performance and to understand the effects of the surface structure and anion adsorption on the reactivity. The results clearly demonstrate that there are strong effects of anion adsorption and surface structure on the measured current and oxidation mechanism. Thus, the main product of ethanol oxidation on (111) preferentially oriented Pt nanoparticles is acetic acid, and the amount of CO2 produced can be considered negligible. On the other hand, (100) preferentially oriented Pt nanoparticles are effective for the cleavage of the C–C bond yielding adsorbed CO, which eventually is oxidized to CO2. This nanoparticles electrode has the highest catalytic activity at high potentials, whereas (111) preferentially oriented Pt nanoparticles are more active at low potentials. In addition, no significant differences in the activity are reported by using different supporting electrolytes, which indicates that adsorbed acetate, which results from the adsorption of acetic acid, hinders ethanol oxidation.

Mobility and Oxidation of Adsorbed CO on Shape-Controlled Pt Nanoparticles in Acidic Medium

The knowledge about how CO occupies and detaches from specific surface sites on well-structured Pt surfaces provides outstanding information on both dynamics/mobility of COads and oxidation of this molecule under electrochemical conditions. This work reports how the potentiostatic growth of different coverage CO adlayers evolves with time on both cubic and octahedral Pt nanoparticles in acidic medium. Data suggest that during the growth of the CO adlayer, COads molecules slightly shift toward low coordination sites only on octahedral Pt nanoparticles, so that these undercoordinated sites are the first filled on octahedral Pt nanoparticles. Conversely, on cubic Pt nanoparticles, adsorbed CO behaves as an immobile species, and low coordinated sites as well as (100) terraces are apparently filled uniformly and simultaneously. However, once the adlayer is complete, irrespectively of whether the CO is oxidized in a single step or in a sequence of different potential steps, results suggest that COads behaves as an immobile species during its oxidation on both octahedral and cubic Pt nanoparticles.

Formic acid oxidation on platinum electrodes: a detailed mechanism supported by experiments and calculations on well-defined surfaces

In spite of the fact that the formic acid oxidation reaction on electrode surfaces has been extensively investigated, a detailed mechanism explaining all the available experimental evidence on platinum has not been yet described. Herein, using a combined experimental and computational approach, the key elements in the mechanism of the formic acid oxidation reaction on platinum have been completely elucidated, not only for the direct path, through an active intermediate, but also for the CO formation route. The experimental results suggest that the direct oxidation path on platinum takes place in the presence of bidentate adsorbed formate. However, the results reported here provide evidence that this species is not the active intermediate. Monodentate adsorbed formate, whose evolution to the much more favorable bidentate form would be hindered by the presence of neighboring adsorbates, has been found to be the true active intermediate. Moreover, it is found that adsorbed formic acid would have a higher acid constant than in solution, which suggests that adsorbed formate can be originated not only from solution formate but also from formic acid. The CO formation path on platinum can proceed, also from monodentate adsorbed formate, through a dehydrogenation process toward the surface, during which the adsorbate transitions from a Pt–O adsorption mode to a Pt–C one, to form carboxylate. From this last configuration, the C–OH bond is cleaved, on the surface, yielding adsorbed CO and OH. The results and mechanisms reported here provide the best explanation for the whole of the experimental evidence available to date about this reaction, including pH, surface structure and electrode potential effects.