On the Lack of Beneficial Role of Rh Towards C-C Bond Cleavage During Low Temperature Ethanol Electrooxidation on Pt-Rh Nanoalloys

Numerous reports in scientific literature claim the increased activity of Rh-containing systems towards C-C bond scission in 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 as anode materials for ethanol-feed low temperature fuel cells. This study aims at verifying the claim of beneficial role of Rh towards C-C bond scission during low temperature ethanol electrooxidation on Pt-Rh nanoparticles. We determined that the surface-normalized amounts of CO₂ produced during ethanol oxidation are comparable on Pt, Rh and Pt-Rh nanoalloys, and smaller than CO₂ amounts obtained on exactly the same electrode from oxidation of monolayer of adsorbed CO. The whole amount of CO₂ detected during ethanol oxidation, regardless of Rh presence, or lack of thereof, seems to come exclusively from oxidation of submonolayer of CO_ads produced during dissociative adsorption of ethanol at low electrode potential, and its subsequent oxidation at sufficiently high electrode potential. Our work suggest 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 proceeds via the submonolayer of CO_ads, which limits the quantity of CO₂ produced from ethanol at room temperature to negligible amount. The higher activity of Rh-containing materials towards C-C bond scission claimed in literature was determined to be due to overinterpretation of selectivity data.
To characterized the samples we used techniques like XPS, TEM, and cyclic voltammetry. For drove a conclusions we compere amount of CO₂ detected in DEMS during ethanol oxidation reaction and so called CO stripping experiment.