Controlled synthesis of Pt3Sn/C electrocatalysts with exclusive Sn-Pt interaction designed for use in direct methanol fuel cells

Borbáth, Irina and Gubán, Dorottya and Pászti, Zoltán and Sajó, István and Drotár, Eszter and Tompos, András and Gómez de la Fuente, José Luis and Herranz, Tirma and Rojas, Sergio (2013) Controlled synthesis of Pt3Sn/C electrocatalysts with exclusive Sn-Pt interaction designed for use in direct methanol fuel cells. TOPICS IN CATALYSIS, 56. pp. 1033-1046. ISSN 1022-5528

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Abstract

Alloy-type Sn-Pt/C electrocatalysts with Pt/Sn= 1.8-3.0 ratios and exclusive Sn-Pt interaction have been prepared by means of Controlled Surface Reactions (CSRs). As demonstrated by XRD the incorporation of Sn onto Pt/C was achieved satisfactorily yielding a near-stoichiometric fcc Pt3Sn alloy phase along with a certain amount of the Pt(1-x)Snx solid solution. The content and dispersion of the fcc Pt3Sn phase within the electrocatalysts can be controlled by tuning the reaction conditions of CSRs. No evidence of the presence of SnO2 phases in the Sn-modified Pt/C samples were found by means of the XRD and EDS analysis. According to in situ XPS studies the pre-treatment in hydrogen at 350°C resulted in complete reduction of tin to Sn0. These results demonstrate that the method of CSRs is a powerful tool to create of Pt-Sn bimetallic nanoparticles exclusively, without tin introduction onto the carbon support. The performance of the intermetallic SnPt/C catalysts in the CO and methanol electrooxidation reactions depends on the actual composition of the exposed surface and the size of bimetallic particles. In the consecutive tin introduction the decrease of the amount of SnEt4 precursor added per period, accompanied with an increase of the number of anchoring periods, resulted in an increase of the activity in both electrooxidation reactions as a consequence of an optimal balance of Pt/Sn ratio, the content of fcc Pt3Sn phase and metal particle size. It was demonstrated that the increasing tin content above a certain (optimal) amount gives rise to a negative effect on the catalyst performance in the CO and methanol electrooxidation.

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