Abstract
Electrooxidation of ethanol on noble metals is of particular interest due to its potential application in low temperature direct ethanol fuel cells (DEFCs). However there is no known ethanol electrooxidation reaction (EOR) catalyst, allowing for complete electrooxidation of ethanol to CO2. Even for the most active systems, incomplete and slow EOR renders the DEFCs not economically viable. As a result significant effort has been devoted to understand the reasons of low activity of known catalysts and to finding better, more active and selective systems. It is widely accepted that systems consisting of platinum, and platinum alloyed with other metals are most active towards ethanol electrooxidation. Pt-Ru and Pt-Sn systems are often reported as those with the highest current density in acidic media. However, despite the higher current, addition of Ru or Sn to Pt further decrease the already small amount of CO2, produced in EOR on pure Pt. Selectivity of a given catalyst towards CO2 in EOR is especially important, due to the facts, that CO2 is the product of complete, 12-electron oxidation of ethanol molecule, where acetaldehyde and acetic acid (other possible products) yields respectively 2- or 4-electrons. Additionally acetic acid cannot be further oxidized in a working fuel cell, thus it is effectively a dead-end of EOR in a working low temperature DEFC. As a result other catalysts, more active and selective toward ethanol electrooxidation to CO2 are needed for a commercially viable DEFC. In this report we used unsupported ultra-pure platinum-containing nanoalloys as a catalyst for EOR, to determine the possible changes in mechanism of EOR (based on product distribution determined by DEMS) as a function of nanoalloy composition. We focused on possible changes in surface morphology and changes in electronic properties due to alloying and how those factor impact electrode reaction mechanisms. Using DEMS experiments we determined how the amounts of products like carbon dioxide, acetaldehyde and acetic acid per active surface area changed as a function of nanoparticle composition and how it impacted the onset potential for particular products. As a result we were able to comment on the selectivity and activity of unsupported Pt-containing nanoalloys in EOR as well as on the activity of this material in C-C bond scission.
Published Version
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