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

摘要

Alloy-type Sn-Pt/C electrocatalysts with Pt/Sn= 1.8-3.0 ratios and exclusive Sn-Pt interaction haveudbeen prepared by means of Controlled Surface Reactions (CSRs). As demonstrated by XRD the incorporation ofudSn onto Pt/C was achieved satisfactorily yielding a near-stoichiometric fcc Pt3Sn alloy phase along with a certainudamount of the Pt(1-x)Snx solid solution. The content and dispersion of the fcc Pt3Sn phase within theudelectrocatalysts can be controlled by tuning the reaction conditions of CSRs. No evidence of the presence ofudSnO2 phases in the Sn-modified Pt/C samples were found by means of the XRD and EDS analysis. According toudin situ XPS studies the pre-treatment in hydrogen at 350°C resulted in complete reduction of tin to Sn0. Theseudresults demonstrate that the method of CSRs is a powerful tool to create of Pt-Sn bimetallic nanoparticlesudexclusively, without tin introduction onto the carbon support. The performance of the intermetallic SnPt/Cudcatalysts in the CO and methanol electrooxidation reactions depends on the actual composition of the exposedudsurface and the size of bimetallic particles. In the consecutive tin introduction the decrease of the amount ofudSnEt4 precursor added per period, accompanied with an increase of the number of anchoring periods, resulted inudan increase of the activity in both electrooxidation reactions as a consequence of an optimal balance of Pt/Snudratio, the content of fcc Pt3Sn phase and metal particle size. It was demonstrated that the increasing tin contentudabove a certain (optimal) amount gives rise to a negative effect on the catalyst performance in the CO andudmethanol electrooxidation.