Enhanced Performance of Oxygen-Functionalized Multiwalled Carbon Nanotubes as Support for Pt and Pt-Ru Bimetallic Catalysts for Methanol Electrooxidation

The performance of Pt-Ru catalysts for methanol electrooxidation has been greatly enhanced by replacing the standard carbon XC72 support with oxygen-functionalized multiwalled carbon nanotubes (MWCNTs). Highly dispersed, intimately contacted Pt-Ru nanoparticles were synthesized on MVVNT supports by a combination of strong electrostatic adsorption (SEA) and electroless deposition (ED) methods. The catalysts have been characterized by X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), chemisorption, and X-ray photoelectron spectroscopy (XPS) and evaluated by cyclic voltammetry (CV) for the methanol electrooxidation reaction. The results showed that oxygen-functionalized MWCNTs not only influenced the chemical nature and morphology of the surfaces relative to XC72 but also enhanced the electrocatalytic properties of the resulting Pt and Pt-Ru electrocatalysts. STEM images revealed homogeneous dispersion of uniformly sized nanoparticles (NPs) for the two types of functionalized MWCNTs with relatively high particle density and no notable aggregation. The results also showed that the activities of Pt-Ru on functionalized MWCNT catalysts prepared by SEA and ED for methanol oxidation were much higher than those for commercial catalysts. The activities of -OH- and -COOH-terminated Pt-Ru/MWCNT-OH and Pt-Ru/MWCNT-COOH catalysts for methanol oxidation were up to 7 times higher than that for commercial Pt/XC72 and up to 4 times higher than that for a commercial Pt-Ru/XC72 catalyst with a 1:1 = Pt/Ru bulk atomic ratio.