Electrolyte Resistance Measurement in the Catalyst Layer of Polymer Electrolyte Fuel Cells using Electrochemical Impedance Spectroscopy

Abstract

In this paper, Electrochemical Impedance Spectroscopy is used to resolve various sources of polarization loss in a pure hydrogen-fueled polymer electrolyte fuel cell (PEFC). Experimental impedance data are fitted to a fuel cell model in which the catalyst layer physics are accurately represented by a transmission line model. Extracted parameters include cell ohmic resistance and catalyst layer electrolyte resistance and double layer capacitance. For a given MEA construction, similar results are obtained for two operating methods, in-situ (H2/O2) and ex-situ (H2/N2), and for two cell active areas, 5 and 50 cm2. The measured electrolyte resistance increases with decreasing ionomer concentration in the electrode, as expected. We also observed that the real impedance measured at 1 kHz, often interpreted as the ohmic resistance in the cell, can include significant contributions from the electrolyte in the catalyst layer. Our results show that the catalyst layer electrolyte resistance can be a significant source of PEFC efficiency loss, and it is therefore important to accurately characterize it using methods such as those described here.