Ethylene glycol electrooxidation on carbon supported Pt, PtRu and Pt3Sn catalysts—A comparative DEMS study

We present results of a comparative study on the interaction of ethylene glycol (EG) with carbon supported Pt, PtRu and Pt3Sn nanoparticle catalysts, employing electrochemical and quantitative differential electrochemical mass spectroscopy (DEMS) measurements under continuous reaction and continuous electrolyte flow conditions. For all three catalysts EG adsorption is inhibited at very cathodic adsorption potentials, dissociative adsorption starts above 0.06 V and increases with increasing potential. Based on the electron yield per formed CO2 molecule and on the similarity with the COad stripping characteristics COad is identified as the main stable adsorbate; the relative coverage in terms of adsorbed C1 species, relative to that of a saturated CO adlayer on the respective catalyst, reaches a maximum of ca. 0.6 at around 0.4 V on Pt/Vulcan, ca. 0.2 at around 0.2 V on PtRu/Vulcan and ca. 0.4 at around 0.35 V on Pt3Sn/Vulcan. Bulk EG electrooxidation under steady-state conditions shows a very small current efficiency for CO2 formation of below 6% for 0.1 M EG on all three catalysts, the oxidation of EG mainly generates partly oxidized C2 by-products. Catalyst modification by Ru or Sn improves the activity for EG oxidation at low potentials (≤0.56 V), but does not lead to better selectivities for complete EG oxidation to CO2 at potentials with significant oxidation rates. Hence, C–C bond breaking is rate limiting for complete oxidation under present reaction conditions for all three catalysts. The data are consistent with a parallel pathway reaction mechanism, with formation and subsequent oxidation of COad in the one pathway and partial oxidation, via a sequence of reaction steps, to increasingly oxidized C2 species in the other pathway.