Ethanol oxidation on carbon supported (PtSn)alloy/SnO2 and (PtSnPd)alloy/SnO2 catalysts with a fixed Pt/SnO2 atomic ratio: Effect of the alloy phase characteristics

To evaluate the effect of the alloy phase characteristics on the ethanol oxidation activity, carbon supported (PtSnPd)_alloy/SnO₂ catalysts were prepared and their electrocatalytic activity compared with that of carbon supported (PtSn)_alloy/SnO₂. Pt-Sn-Pd/C samples in the atomic ratio (1:1:0.3) and (1:1:1) were characterized by energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD analysis shows the presence of fcc Pt reflexions, shifted to lower angles, and SnO₂ reflexions. By comparison with the XRD patterns of carbon supported Pt-Sn (1:1) and Pt-Pd (3:1) samples, prepared by the same method, the formation of ternary PtSnPd alloys is postulated. The crystallite size of the ternary catalysts is smaller than that of both binary Pt-Sn/C (1:1) and Pt-Pd/C (3:1) catalysts. Chronoamperometry experiments and tests in direct ethanol fuel cells of the as-prepared catalysts shows that the activity for ethanol oxidation of (PtSn)_alloy/SnO₂ is higher than that of (PtSnPd)_alloy/SnO₂. This result, obtained with the same Pt/SnO₂ atomic ratio in all the samples, indicates the critical role of the alloy phase characteristics of these catalysts on their activity for ethanol oxidation.