Impact of ionomer resistance in nanofiber-nanoparticle electrodes for ultra-low platinum fuel cells

Previously, nanofiber-nanoparticle electrodes produced via a simultaneous electrospinning and electrospraying (E/E) process (E/E electrodes) resulted in polymer electrolyte membrane fuel cells with high power densities at ultra-low platinum (Pt) loadings (<0.1 mg(pt) cm(-2)). In this study, E/E electrodes were fabricated at various Nafion contents to investigate the impact of ionomer content on catalyst layer transport resistances and fuel cell power density at ultra-low Pt loadings. Regardless of the Nafion content in the electrospray, the Nafion nanofiber diameters and catalyst aggregate particle sizes are constant in the E/E electrodes evidenced by electron microscopy. Therefore, this study allows for the exclusive investigation of the effect of transport resistances on fuel cell performances at different ionomer contents at a constant catalyst layer morphology, which differs from conventional electrodes. At higher magnifications, changes are evident in the micrographs around the catalyst aggregate particles, where an increase in ionomer thin film thickness is observed with increasing ionomer content. The maximum fuel cell performance and a minimum in catalyst layer resistance for E/E electrodes is observed at a total Nafion content of 62 wt%, which differs from conventional electrodes (ca. 30 wt%). (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.