Effect of Reaction Atmosphere on the Electrocatalytic Activities of Pt/C and PtRu/C Obtained in a Polyol Process

Pt and PtRu nanoparticles supported on Vulcan XC-72R carbon obtained under different atmospheres (air and N 2 ) were prepared via a polyol process in ethylene glycol solution and denoted as Pt/C−N 2, Pt/C−air, PtRu/C−N 2, and PtRu/C−air, respectively. The catalysts were characterized by XRD (X-ray diffraction), TEM (transmission electron microscopy), and XPS (X-ray photoelectron spectroscopy). TEM images show that metal nanoparticles are uniform in size and are well dispersed on the carbon support for all the catalysts. The mean particle sizes of Pt/C−N 2, Pt/C−air, PtRu/N 2, and PtRu/C−air are 2.6, 2.7, 2.3, and 1.8 nm, respectively. Among these samples, PtRu/C−air catalyst has the smallest nanoparticle size with a narrow size distribution. The three strongest diffraction peaks of both Pt/C−N 2 and Pt/C−air catalysts are located at 2θ = 39°, 46°, and 67°, corresponding to the Miller indices of (111), (200), and (220) of a Pt fcc (face-centered cubic) crystal structure. The XRD pattern of PtRu/C−N 2 displays an fcc structure similar to that of Pt but different from that of PtRu/C−air. XPS analyses indicate that the amount of metallic Pt(0) and Ru(0) species present in Pt/C−N 2 and PtRu/C−N 2 catalysts are higher than those obtained in air atmosphere. Electrochemical voltammetry methods and single cell tests were employed to evaluate the activities of these catalysts. The results show that Pt/C−N 2 and PtRu/C−N 2 catalysts exhibit much better activities for oxygen reduction and methanol oxidation reactions in direct methanol fuel cells than the corresponding Pt/C−air and PtRu/C−air catalysts.