Carbon-Supported Palladium-Polypyrrole Nanocomposite for Oxygen Reduction and Its Tolerance to Methanol

Carbon-supported palladium-polypyrrole (Pd-PPy/C) nanocomposite was synthesized by oxidative polymerization of pyrrole and reduction of palladium (II) precursor salt in the presence of Vulcan XC-72R. The Pd-PPy/C composites were characterized by X-ray diffraction (XRD), Fourier transform IR, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) techniques. The XRD analysis of Pd-PPy/C shows the formation of the face-centered cubic structure of Pd particles and the mean particle size calculated from TEM was 5.3 + 2.0 nm. The electrochemical stability of Pd-PPy/C was examined by cyclic voltammetry in an acid solution. The thermal stability and Pd loading in the composite was assessed using TGA. The introduction of Pd in the conducting PPy/C matrix gives better catalytic activity toward oxygen reduction with resistance to methanol oxidation. This was further elucidated by the XPS analysis showing d-band vacancy that is attributed to metal-polymer interaction. From the polarization studies, it is observed that even in the presence of methanol there is no significant cathodic shift in the half-wave potential, revealing that Pd-PPy/C is tolerant to methanol. Rotating ring disk electrode studies show that there is only a negligible quantity of hydrogen peroxide produced in the potential region where its production is expected to be high. This confirms that Pd-PPy/C catalyzes reduction of oxygen directly to water through a four-electron pathway. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3489266] All rights reserved.