The Effect of Tin Addition to Platinum Catalysts with Different Morphologies towards Methanol Electrooxidation in Alkaline Media
Rebecca P. R. Anjos, Aila O. Santos, Rodolfo M. Antoniassi, Odivaldo C. Alves, Eduardo A. Ponzio, Júlio César M. Silva
Abstract
Direct methanol fuel cells (DMFCs) using anion exchange membranes have been attracting great interest. Thus, it is very important to develop electrocatalysts for methanol electrooxidation reaction (MEOR) in alkaline media. In this study, the effects of platinum nanoparticle morphology and presence of tin oxide in the electrocatalysts were investigated. Platinum and platinum-tin nanoparticles with cubic-like shape and (100) preferential orientation supported on carbon, Pt/C(100) and PtSnO2/C(100), were synthesized by the alcohol-reduction process using KBr as the shape-directing agent. Polycrystalline nanoparticles supported on carbon, Pt/C, and PtSnO2/C were also synthesized. The catalytic activity of the nanomaterials toward MEOR in alkaline media was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analysis showed cubic Pt nanoparticles and SnO2 dispersed on the carbon support. X-ray diffraction (XRD) showed peaks of SnO2 cassiterite and peaks of the face-centered cubic (FCC) structure of Pt. CV experiments showed that the maximum current density from MEOR on Pt/C(100) (current density of about 108 mA cm–2 mg–1 of Pt) is about 2.4, 2.1, and 1.1 times higher than on Pt/C, PtSnO2/C, and PtSnO2/C(100), respectively. The same trend was observed in CA experiments. The higher catalytic activity of Pt(100) might be related to the OHads species coverage on it. SnO2 increases the catalytic activity on polycrystalline platinum, probably due to the OHads species provided by it. On the other hand, for Pt(100), the presence of SnO2 results in a decrease of the catalytic activity towards MEOR.