On the absence of a beneficial role of Rh towards C C bond cleavage during low temperature ethanol electrooxidation on PtRh nanoalloys

Numerous reports in scientific literature claim the increased activity of Rh-containing systems towards C-C bond scission in the electrocatalytic oxidation of ethanol at ambient temperatures. Due to the claimed C-C bond breaking ability, Rh-containing systems are intensively investigated and widely recognized as the most promising candidates for anode materials in ethanol-feed low temperature fuel cells. Contrary to those claims, we determined that the surfacenormalized amounts of CO2 produced during ethanol oxidation are comparable on Pt, Rh and PtRh nanoalloys, and smaller than CO2 amounts obtained on exactly the same electrode when a monolayer of adsorbed CO is being oxidized. The whole amount of CO2 detected during ethanol oxidation, regardless of Rh presence or lack of thereof, seems to come exclusively fromoxidation of submonolayer of COads produced fromethanol, undergoing dissociative adsorption of ethanol at low electrode potential, and its subsequent oxidation at sufficiently high electrode potential. Our work suggests that Rh-containing alloys are not more active towards C-C bond scission than pure Pt, and on both metals the mechanism of oxidation of ethanol to CO2 roceeds via the submonolayer of COads, which limits the quantity of CO2 produced from ethanol at room temperature to negligible amount. Additionally, based on critical literature analysis we determined that the higher activity of Rh-containing materials towards C-C bond scission claimed in literature, was an over-interpretation of data.