Insights into the role that Pt- and carbon-electrodes play in controlling the selectivity of electrochemical reactions.

While significant efforts have been devoted to understanding the mechanisms that govern electrolysis reactions, relatively little emphasis has been placed on elucidating the electrode/substrate interactions that are often key to reaction success. Toward this goal, the present work specifically examines the selectivity of competition studies using the TEMPO-mediated oxidation of 4-methoxybenzyl alcohol (MBA) and 4-nitrobenzyl alcohol (NBA). The selectivity for the reaction was found to be 1 : 1 when the reactions were confined to the surface of a Pt anode, but 19 : 1 when the reactions were confined to the surface of a reticulated vitreous carbon (RVC) anode. Potential-dependent ab initio molecular dynamics (AIMD) and density functional theory (DFT) simulations were carried out with explicit substrate and solvent molecules to elucidate the mechanistic features that control the observed selectivity differences. Our results indicate that the different selectivity originates from the changes in the substrate adsorption energies on the different electrodes along with the changes in their intrinsic activation barriers for selective oxidation. The Pt electrode strongly binds both benzyl alcohols and induces significant structural changes to the adsorbed aromatic. On the contrary, the positively charged carbon-electrode binds weakly to the two benzyl alcohols via van der Waals and π-π interactions, a situation that preserves the structure of the aromatic rings and allows for the electronic differences between the rings to dictate the selectivity of the reactions. This computational model was experimentally confirmed with studies that illustrated how fundamental insights into substrate/electrode interactions can be translated into new chemical selectivity.