Synthesis of perfluorosulfonate ionomer-stabilized platinum colloid and its application in direct methanol fuel cells

Abstract

Pt colloid was synthesized by the reduction of hexachloroplatinic acid with formaldehyde in the presence of a stabilizer (a cation-exchanged polymer - perfluorosulfonate ionomer (PFSI) or Teflon) or without any stabilizers. The average size of platinum particles with a stabilizer, characterized by a transmission electron microscopy and X-ray diffraction, is in a nanometer range in comparison with the particle agglomeration without any stabilizers. Highly dispersive 40 wt. % Pt/C catalyst obtained from the PFSI-stabilized Pt colloid shows much better performance than its counterpart with Teflon as a stabilizer or without any stabilizer according to the cyclic voltammetric (CV) characterization and the single direct methanol fuel cell (DMFC) performance testing. It is strongly suggested that the proton-conducting ionomer could smooth the reaction pathway by facilitating the proton transport, while Teflon inhibit the active sites, though both of them can inhibit the particle growth. The improved fuel cell performance is attributed to the small particles and the unhindered transport of protons/electrons ascribed to the intimate contact of Pt and proton-conducting ionomer.