Study of Cathode Catalyst Layer Parameters for HT-PEMFC Using Electrochemical Impedance Spectroscopy

Abstract

We investigate the effect of platinum loading, cathode catalyst layer thickness and the phosphoric acid doping level on the performance of a polybenzimidazole based HT-PEMFC MEA. The objective is to characterize the cathode catalyst layer, which is known to be the limiting factor for PEMFC performance due to the sluggish kinetics of the oxygen reduction reaction. The range for each parameter is chosen carefully to investigate cell performance. Impedance measurements at four current densities (10, 20, 50 and 100 mA cm-2) with high cathode stoichiometry are performed. These operating conditions minimize the mass transport losses and therefore, the impedance data can be fitted with a simple equivalent circuit model to extract electrochemical parameters related predominantly to the cathode catalyst layer. These parameters are presented for eight membrane electrode assemblies and the cell performances are discussed. Finally, a comparison between the parameters is made and directions for improvement are suggested.