Insights into the Rate-Determining Step of the Ethanol Electro-oxidation Reaction on the Pd(111) Surface through Ab Initio Molecular Dynamics Simulations

The ethanol electro-oxidation mechanism on a Pd(111) surface in alkaline media has been studied through ab initio molecular dynamics simulations. It is known that, under these conditions, ethanol undergoes partial oxidation to acetate and that hydroxylation of the acetyl radical plays a fundamental role in the overall reaction kinetics. Therefore, we focused on this reaction step, specifically addressing the interplay of the acetyl and hydroxyl radicals and especially the effect of their arrangement over the Pd surface on the hydroxylation process. We observed that the strength of the interactions of the reacting species with the Pd surface significantly modulates the propensity of the reaction. In fact, for minimum-energy arrangements of the acetyl-surface and OH-surface systems, hydroxylation appears hindered by the strong interactions between the surface and substrates, while it readily takes place when the substrates are moved away from the surface. These results open to the idea of rational design of cocatalysts based on the tuning of surface chemical properties addressed to weaken the adsorbate/adsorbent interactions, eventually enhancing the exchange current density.