Ethanol electro-oxidation on partially alloyed Pt-Sn-Rh/C catalysts

Ternary Pt-Sn-Rh/C catalysts of Pt:Sn:Rh = 1:0.8:0.2 and 1:1:0.33 atomic ratios were synthesized using the formic acid method and their electrochemical activities were compared for ethanol oxidation with that of binary Pt-Sn/C (1:1) and Pt-Rh/C (1:0.11) catalysts. XRD analysis indicated the presence of Sn in both alloyed and oxide form and suggested the formation of a ternary Pt-Sn-Rh alloy in both catalysts. The particle size by TEM was around 3.5 nm for all catalysts. The efficiency for Pt utilization increased with Rh content. Pt-Sn-Rh/C catalysts exhibited higher catalytic activity for ethanol oxidation than Pt-Rh/C, but lower than Pt-Sn/C. Among ternary catalysts, Pt-Sn-Rh/C (1:0.8:0.2) was the most active. In situ IRRAS showed Rh plays a dual counteracting role during ethanol electro-oxidation on Pt-Sn-Rh/C catalysts, once it promotes C-C bond breaking, thus favouring CO2 formation, but hinders adsorption of ethanol, decreasing the production of acetic acid.