Influence of Cathode Catalyst Layer Ionomer on Air-Cooled, Open-Cathode Fuel Cells

Reducing considerable ohmic resistances is paramount for improving open-cathode fuel cell voltage and power production. We study the influence of catalyst layer ionomer equivalent weight in open-cathode fuel cells operated in a range of challenging environmental conditions. Reducing catalyst layer ionomer equivalent weight (850EW vs 1100EW) substantially lowers proton transport and ohmic resistances for the MEAs not under active load. However, these implied advantages do not translate to higher cell voltage and power when a load is drawn from the cells. MEAs with catalyst layers bound by 1100EW exhibit significantly lower ohmic resistances during operation at three diverse environmental conditions, pointing to improved cell water management. Cell voltage is insensitive to ionomer equivalent weight at low current densities (<0.15 A/cm2). Increasing the catalyst layer ionomer equivalent weight from 850 to 1100 improves cell voltage and power by 20% at higher current densities, where cell thermal and water management and ohmic losses are more critical. MEAs featuring 1100EW catalyst layer ionomer operate at lower cell temperatures (by up to 2.9°C at 0.4 A/cm2), display lower mass transport resistance ascertained from oxygen gain experiments, and improve cell hydration as determined from electrochemical impedance spectroscopy.