Electrochemical pressure impedance spectroscopy applied to polymer electrolyte membrane fuel cells for investigation of transport phenomena

Abstract

The performance of proton exchange membrane fuel cells (PEMFC) is partly governed by complex, coupled transport processes at high polarization which usually occur in the low frequency region. Electrochemical impedance spectroscopy (EIS) is a powerful tool to extract valuable information about ohmic, charge and mass transport processes but fails marginally below 1 Hz as limited information on mass transport can be extracted. In this work, electrochemical pressure impedance spectroscopy (EPIS) was performed by applying fluctuations of the gas pressure at the fuel cell cathode outlet in the frequency range 1 mHz to 1 Hz to peek into transport processes. An experimental bench was designed and setup for reliable EPIS measurements on a single 100 cm2 FC. Conditions of pressure modulation in the test bench were thoroughly examined, leading to a standard protocol of operation. Two cases were studied in an attempt to better understand and differentiate the various transport phenomena occurring in fuel cell operation. Sensitivity of impedance modulus to mass transport control by the presence of liquid water could be shown for frequency below 0.1 Hz. Moreover, EPIS spectra exhibit striking profile differences in both modules and phases, with variations of the oxygen mole fraction in the cathode gas fed, evidencing gas diffusion phenomena in particular over 0.1 Hz. EPIS has been shown here to become an attractive complementary technique to EIS, even if further work is required for full beneficiation of this promising tool.