Identity of the Most and Least Active Sites for Activation of the Pathways for CO₂ Formation from the Electro-oxidation of Methanol and Ethanol on Platinum

In the field of catalysis on solid surfaces, discrimination of the site-specific chemistry taking place on surfaces consisting of multiple types of sites is challenging, especially at electrified solid/liquid interfaces. In this study, site-specific chemical labeling on Pt stepped surfaces was achieved by attaching the ¹³CO species exclusively on the top side of the (110) steps, while making all of the (111) sites available. The catalysts were then employed in a spectro-electrochemical study of the electro-oxidation of methanol and ethanol. The onset potentials for the formation of ¹³CO₂ and ¹²CO₂ revealed the existence of two channels of carbon dioxide formation, separated by about 0.22 V, on the same Pt surface. The active sites with lower overpotential requirement (or lower energy input) for activation of the reaction pathway of CO₂ formation resided on the (111) terraces. On the other hand, the active sites with higher overpotential requirement (or higher energy input) for activation of the reaction pathway for electro-oxidation of ¹³CO_ads species to ¹³CO₂ were at the top of the (110) steps. The findings revealed the identities of the most active sites and least active sites involved in the formation of CO₂ during the electro-oxidation of alcohols. On Pt surfaces, the complex interplay involving the steps on the surface favors activation of the pathways for CO_ads oxidation on the (111) terraces, rather than promoting reaction steps directly on the steps themselves.