(Invited) Gold Nanoparticles Modified with Platinum and Palladium As Electrocatalysts for Ethanol Oxidation Reactions

Abstract

Electrooxidation of ethanol on noble metals, such as Pt in acidic and Pd in alkaline solutions is of particular interest due to its potential application in low-temperature direct ethanol fuel cells (DEFCs). The slow, incomplete oxidation of ethanol as well as the high price of Pt and Pd has impeded the wide application of DEFCs. In response to these challenges, several resembling core-shell electrocatalysts using Au nanoparticles were synthesized and evaluated for ethanol oxidation reaction (EOR). It was found that the Pd shell is not uniform consisting of tiny Pd clusters with a coverage of 0.5-0.6. The EOR activity of this kind of structure is much higher than Pd/C in an alkaline solution. The forward peak current density of was 5 times higher than that of Pd/C. Furthermore, the onset potential for EOR of the former was ~100 mV more negative. An interesting particle size dependent EOR activity was also observed. With increasing the Au particle size (2.9 to 5.8 and 6.5 nm), the EOR activity increases. The strain and ligand effects from the Au core, together with the bifunctional mechanism from the core and shell can explain the observed activity trend. Similar core-shell catalysts with a Pt shell were also synthesized and evaluated for EOR in acidic electrolytes. In a further study, the core-shell particles were modified with Ru and SnO 2 , which showed enhanced activities. In situ spectroscopic studies were conducted to reveal the reaction intermediates and products of various catalysts to give more insights into the reaction pathway and activity enhancement mechanisms.