Effect of Redox State of PtRu Electrocatalysts on Methanol Oxidation Activity

Abstract

PtRu is a promising catalyst for methanol oxidation in direct methanol fuel cells. However, the most active Pt:Ru ratio and oxidation state of the Ru component are still under investigation. PtRu black was obtained from Johnson Matthey, and the as-received catalyst was treated with either hydrogen or oxygen at elevated temperatures to alter the oxidation state. The samples were characterized by cyclic voltammetry (CV), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and X-ray diffraction (XRD) to confirm their redox states and for correlation with their methanol oxidation activity. All of the characterization techniques support successful oxidation and reduction of the PtRu catalyst. The methanol oxidation activity was measured, and the sequence at 25 °C was found to be reduced > as-received > oxidized ≫ strongly oxidized. The effect of the drying regime and the dispersing agent for the catalysts was also investigated, and it was found that samples supported using acetic acid were more active than those supported by Nafion, but were less stable and more susceptible to change in catalyst state from heat gun drying.