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.

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.

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 CO 2 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 CO 2 . 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.

Using a combination of experimental and computational methods, mainly FTIR and DFT calculations, new insights are provided here in order to better understand the cleavage of the C−C bond taking place during the complete oxidation of ethanol on platinum stepped surfaces. First, new experimental results pointing out that platinum stepped surfaces having (111) terraces promote the C−C bond breaking are presented. Second, it is computationally shown that the special adsorption properties of the atoms in the step are able to promote the C−C scission, provided that no other adsorbed species are present on the step, which is in agreement with the experimental results. In comparison with the (111) terrace, the cleavage of the C−C bond on the step has a significantly lower activation energy, which would provide an explanation for the observed experimental results. Finally, reactivity differences under acidic and alkaline conditions are discussed using the new experimental and theoretical evidence.

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.