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

Abstract

The rationale design of better electrocatalysts for the oxidation of C1-C2 organic molecules requires the detailed knowledge of their oxidation mechanism. Pt single crystals are powerful tools to study, in a simple way, the surface structure effect on the different reaction pathways. Here, the oxidation mechanism of these molecules is compared so that the knowledge gained with the simpler mechanism is transferred in the analysis of the more complex ones. The goal is to design strategies so that the platinum electrodes improve their performance in their oxidation by the appropriate modification with other elements by attacking the bottlenecks in the reaction mechanism.

Investigating the presence of adsorbed species on Pt steps at low potentials

“…Furthermore, most of the electrocatalytic processes are surface-sensitive reactions. The use of well-defined surfaces, namely, single crystal electrodes, has allowed studying in detail such dependencies between reactivity and surface structure 1 , 2 . Moreover, the nature of the species adsorbed on the electrode surface has been revealed to exert a significant impact on the electrocatalytic response 3 – 6 .…”

“…This fact has not yet been demonstrated and the presence of OH adsorbed on the steps in the hydrogen adsorption/desorption region is a question that needs to be clarified. Most of the oxidation reactions of organic molecules and even oxygen reduction reaction, which are of paramount importance for fuel cells and batteries, require the presence of adsorbed OH ads 1 , 6 , 24 . Moreover, these peaks observed in the voltammogram of stepped surfaces have a clear counterpart in similar peaks observed for polycrystalline or nanoparticle samples, which are of practical interest, stressing the importance of understanding this issue in the behavior of platinum as an electrocatalyst.…”

Insights into the Electronic Effects in Methanol Electro-Oxidation by Ternary In1–xSnxPd2 Intermetallic Compounds

“…Not only in the MOR but also in the oxidation of most small organic molecules, there are strong indications that complete oxidation to CO 2 proceeds simultaneously through a different path from the partial oxidation to formic acid (formate in alkaline media) in the reaction networkthe so-called dual-pathway mechanism. − For methanol, Figure summarizes the complicated six-electron oxidation process that may occur through different paths, ultimately leading to the formation of CO 2 as a final product. Here, the direct pathway progresses via the formation of reactive intermediates such as formaldehyde and/or formic acid while, in parallel, the indirect pathway proceeds via the formation of adsorbed carbon monoxide (CO*).…”

Alkaline CO electro-oxidation: Mechanistic Differences between Copper and Gold Single Crystals and Peculiarities of various Copper Facets

“…The reactions shown in Eqns. ( 1)-( 4) and ( 5)- (7) in the main text were used in the microkinetic model for e-COOR on Cu(111) and Au(111), respectively. A pre-exponential factor of 10 13 s −1 as obtained from transition-state theory S14 was used for all the reaction steps.…”

“…For example, it has been used to understand pH dependence in electrochemical reactions, 4 it occurs in the electro-oxidation of biomass derived molecules 5 and can be applied to remove CO impurities from reactant streams to avoid poisoning of electrodes used in direct alcohol fuel cells. 6,7 CO thus has an ambivalent role in electrocatalysis being a central intermediate in many reactions on the one hand and a disruptive contaminant on the other.…”