Polarization Losses under Accelerated Stress Test Using Multiwalled Carbon Nanotube Supported Pt Catalyst in PEM Fuel Cells

The electrochemical behavior for Pt catalysts supported on multiwalled carbon nanotubes and Vulcan XC-72 in proton exchange membrane (PEM) fuel cells under accelerated stress test at 1.2 V was examined by cyclic voltammetry, electrochemical impedance spectroscopy, and polarization technique. Pt catalyst supported on multiwalled carbon nanotubes exhibited a highly stable electrochemical surface area, oxygen reduction kinetics, and fuel cell performance under highly oxidizing conditions, indicating multiwalled carbon nanotubes have a high corrosion resistance and a strong interaction with Pt nanoparticles. Further analyses were conducted using Tafel slope, ohmic resistances, and limiting current density were conducted for the multiwalled carbon nanotube supported Pt catalyst from the actual polarization curve to differentiate kinetic, ohmic, and mass-transfer polarization losses. It was found that kinetic contribution to the total overpotential was the largest throughout the stress test. However, during accelerated stress test, the fraction of kinetic overpotential decreased, the fraction of ohmic overpotential increased, and the fraction of mass-transfer overpotential remained relatively constant. The increased fraction of ohmic overpotential suggests increased proton transport limitation in the catalyst layer. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3530843] All rights reserved.