Tailoring properties of platinum supported catalysts by irreversible adsorbed adatoms toward ethanol oxidation for direct ethanol fuel cells

Abstract

In this work ethanol oxidation on carbon supported Pt catalysts modified with irreversibly adsorbed adatoms is reported. This study concerns understanding of the effect of a second metal on real catalysts in conditions as close as possible to those applied in fuel cells systems. The results were acquired using cyclic voltammetry, chronoamperometry and in situ infra-red techniques always taking into account the future application of the electrocatalyst materials in fuel cells. Foreign adatoms, both Bi and Sb, irreversibly adsorbed on a Pt electrode were studied, and revealed to enhance catalytic activity toward a more efficient ethanol oxidation. The catalytic enhancement continuously increased with the coverage of the adatom on the surface up to coverages close to saturation. With these high coverages a decrease of the activity was observed suggesting that free platinum atoms are required to oxidize ethanol. The results suggest that the adatoms play a third body role avoiding the poisoning of the Pt sites that will then be free for oxidizing ethanol. However, electronic effects on Pt/C–Bi and bifunctional mechanism at Pt/C–Sb are also suggested. The oxidation products were identified by in situ FTIR and are mainly acetaldehyde and acetic acid for the three catalysts. CO2 was also observed for the unmodified Pt/C and interestingly for the Pt/C–Sb electrodes.