A methanol – Tolerant carbon supported Pt–Sn cathode catalysts

Abstract

Carbon supported Pt–Sn bimetallic electrocatalysts with a Pt:Sn 90:10 atomic ratio were prepared by impregnation method and then heat treated at 300 and 500 °C under Helium atmosphere. The purpose of this work is to investigate the effect of tin addition to platinum for methanol tolerant oxygen reduction reaction. In this sense, structure and morphological properties of supported bimetallic catalysts were correlated to the catalytic performance. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations confirm the formation of Pt–Sn bimetallic electrocatalysts with a Pt single-phase material alloy and revealed an increase in the average particle size after heat treatment. The electrocatalytic activities of these samples for the oxygen reduction reaction (ORR) were examined in acidic medium using both a rotating disk (RDE) and a rotating ring disk (RRDE) electrodes. Compared with the Pt/C, Pt–Sn/C bimetallic catalysts show superior electrocatalytic activity towards ORR with an approaching four electron pathway leading to water formation. The specific and mass activity for ORR follow the order of Pt–Sn/C-500 ≈ Pt–Sn/C-300 > Pt–Sn/C > Pt/C. Furthermore, it is found that among the three Pt–Sn samples, Pt–Sn/C-500 exhibits the highest methanol tolerance. These experimental observations indicate that the addition of Sn into Pt is favorable to maximize the ORR performances of platinum and further the heat treatment is beneficial to improve the methanol tolerance behavior. On this basis, the novel Pt–Sn catalysts can be considered as potential candidates to be used as cathodes in Direct Methanol Fuel Cells.