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

Abstract

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�. The CCLs fabricated with 10�20 wt% of the Aquivion� ionomer displayed a similar morphology to the Nafion�-based CCLs. Electrochemical surface areas (ECSA) and double layer capacitances of all the Aquivion�-based samples were similar to those of the baseline. The oxygen reduction reaction (ORR) kinetics in CCLs with 20 wt% and 30 wt% Aquivion� 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�-based samples at low current densities. Relative to the baseline, CCLs containing 20 wt% Aquivion� ionomer demonstrated an improvement in fuel cell performance under operating conditions of 95 �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.