Development of conducting polypyrrole as corrosion-resistant catalyst support for polymer electrolyte membrane fuel cell (PEMFC) application

摘要

Three polypyrrole (PPy) samples were synthesized via in situ chemical oxidative polymerization to study their applications as an alternate cathode catalyst support material for polymer electrolyte membrane fuel cells (PEMFCs). The electrochemical stabilities of the PPy samples and commercial carbon supports (Vulcan XC-72) were examined by cyclic voltammetry (CV). In contrast to the carbon supports, only a small anodic current was observed for the PPy samples up to 1.8 V, indicating their resistance towards oxidation under high positive potentials. Among the PPy samples synthesized in this investigation, PPy-3 showed the highest electrical conductivity (1.67 Scm~(-1)) and BET surface area of 69.6 m~2g~(-1), and therefore was selected as a catalyst support for further studies. The wet reduction method was chosen to prepare supported platinum catalyst (50 wt% Pt/PPy) by using sodium formate as reducing reagent. Transmission electron microscopy (TEM) image showed finely dispersed platinum crystallites with a diameter of d_(pt) = 3.6 nm on the polypyrrole support. The potential cycling experiment revealed that Pt/ PPy is electrochemically more stable than the Pt/C electrocatalyst. The oxygen reduction activity obtained from Tafel plots indicated twofold higher activity for Pt/PPy catalyst than that of Pt black catalyst at 0.9 V. Comparison of ORR activity and fuel cell polarization curves demonstrated good oxygen reduction reaction kinetics and comparable fuel cell performance with that of commercial E-TEK Pt/C catalyst for the Pt/PPy catalyst.