Nanostructured PtRu/C as Anode Catalysts Prepared in a Pseudomicroemulsion with Ionic Surfactant for Direct Methanol Fuel Cell

Abstract

Nanostructured PtRu/C catalysts have been prepared from a water-in-oil pseudomicroemulsion with the aqueous phase of a mixed concentrated solution of H₂PtCl₆, RuCl₃, and carbon powder, oil phase of cyclohexane, ionic surfactant of sodium dodecylbenzene sulfonate (C₁₈H₂₉NaO₃S), and cosurfactant n-butanol (C₄H₁₀O). Two different composing PtRu/C nanocatalysts (catalyst 1, Pt 20 wt %, Ru 15 wt %; catalyst 2, Pt 20 wt %, Ru 10 wt %) were synthesized. The catalysts were characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and thermogravimetric analysis, and the particles were found to be nanosized (2−4 nm) and inherit the Pt face-centered cubic structure with Pt and Ru mainly in the zero valance oxidation state. The ruthenium oxide and hydrous ruthenium oxide (RuO_xH_y) were also found in these catalysts. The cyclic voltammograms (CVs) and chronoamperometries for methanol oxidation on these catalysts showed that catalyst 1 with a higher Ru content (15 wt %) has a higher and more durable electrocatalytic activity to methanol oxidation than catalyst 2 with low Ru content (10 wt %). The CV results for catalysts 1 and 2 strongly support the bifunctional mechanism of PtRu/C catalysts for methanol oxidation. The data from direct methanol single cells using these two PtRu/C as anode catalysts show the cell with catalyst 1 has higher open circuit voltage (OCV = 0.75 V) and maximal power density (78 mW/cm²) than that with catalyst 2 (OCV = 0.70 V, P_max = 56 mW/cm²) at 80 °C.