A model for mesoporous carbon-supported platinum catalyst/electrolyte interfaces in polymer electrolyte fuel cells

Abstract

Mesoporous carbons (MPCs) have recently attracted much attention as catalyst support materials for polymer electrolyte fuel cells (PEFCs). In this study, we systematically investigate the effect of the particle size of MPCs on the performance of membrane electrode assemblies using MPC-supported platinum (Pt/MPC) as the cathode catalyst in PEFCs. The highest hydrogen/air polarization performance is obtained using the MPC with an average particle size of 695 nm. The oxygen reduction reaction (ORR) activity of the Pt/MPCs at 0.9 V increases with the MPC particle size. Observation of the cross sections of the Pt/MPCs reveals that ionomers are abundant in the region up to 40 nm from the external surface of the MPCs and then their content rapidly decreases in the inner region of the Pt/MPCs. The relationship between the ORR activity and MPC particle size is readily explained by a model in which the Pt particles in the ionomer-poor region have an ORR activity about three times higher than that of the Pt particles in the ionomer-rich region.