Optimization of Nafion Ionomer Content Using Synthesized Pt/Carbon Nanofibers Catalyst in Polymer Electrolyte Membrane Fuel Cell

In this study, carbon nanofiber (CNF) was used as a support in which 47.5 wt% Pt/CNFs catalyst was prepared by a modified polyol method. The platinum particle size and dispersion on the CNFs are approximately 2-4 nm as determined by X-ray diffractometry and transmission electron microscopy. The specific surface area was approximated as 55.90 m(2)/g by BET analysis. Electrodes were prepared by the spray method and have a size of 5 cm(2). A commercial catalyst (TKK, 46 wt% Pt/C) was used as the anode and the cathode was Pt/CNFs. Different amounts of Nafion ionomer (Aldrich, 5 wt% solution, in the range of 0-20 wt%) were coated on a membrane (Dupont, Nafion 212) with 0.4 mg/cm(2) of Pt catalyst at the cathode side. The resulting polarization, ohmic and mass transfer resistances changed significantly based on the Nafion ionomer content. Optimum Nafion ionomer content in the 47.5 wt% Pt/CNFs was 5 wt%. The well-dispersed Nafion ionomer was observed on the catalyst surface area using SEM-EDAX analysis. A sufficient triple-phase boundary was formed by a small amount of Nafion ionomer due to the BET surface area of the Pt/CNFs.