Low equivalent weight short-side-chain perfluorosulfonic acid ionomers in fuel cell cathode catalyst layers

The morphology and fuel cell performance of cathode catalyst layers (CCLs) using low equivalent weight (EW) short-side-chain (SSC) perfluorosulfonic acid ionomers have been investigated in this work. The results were compared with those for a baseline CCL containing 30 wt% of the conventional ionomer 1100 EW Nafion (R). The CCLs fabricated with 10-20 wt% of the Aquivion (TM) ionomer displayed a similar morphology to the Nafion (R)-based CCLs. Electrochemical surface areas (ECSA) and double layer capacitances of all the Aquivion (TM)-based samples were similar to those of the baseline. The oxygen reduction reaction (ORR) kinetics in CCLs with 20 wt% and 30 wt% Aquivion (TM) were lower than the baseline under 100% relative humidity (RH), yet similar to the baseline at 70% RH. in situ electrochemical impedance spectroscopy (EIS) measurements suggested that the lowered ORR kinetics at 100% RH may be attributed to the large mass transport resistance in Aquivion (TM)-based samples at low current densities. Relative to the baseline. CCLs containing 20 wt%Aquivion (TM) ionomer demonstrated an improvement in fuel cell performance under operating conditions of 95 degrees C and RH values of 30, 50 and 70%. The greater hydrophilicity of the SSC ionomers is believed to account for the improved fuel cell performance at the relatively higher operating temperature and dry conditions. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.