Understanding single-phase water-management signatures in fuel-cell impedance spectra: A numerical study. (1st August 2020)

• Record Type: Journal Article
• Authors: Kosakian, A.; Urbina, L. Padilla; Heaman, A.; Secanell, M.
• Is Part Of: Electrochimica acta. Volume 350(2020)
• Publication Date: 2020-08-01
• Subjects: Polymer electrolyte membrane fuel cell -- Proton exchange membrane fuel cell -- Electrochemical impedance spectroscopy -- Inductance -- Inductive behavior -- Electrolyte hydration; Electrochemistry -- Periodicals; Electrochemistry, Industrial -- Periodicals; 541.37
• DOI: 10.1016/j.electacta.2020.136204
• Languages: English
• ISSNs: 0013-4686

Abstract

Abstract: Electrochemical impedance spectroscopy is a powerful technique used in fuel-cell diagnosis and characterization. A low-frequency inductive behavior may appear in the fuel-cell-impedance spectrum and is believed to be related to the electrolyte-hydration dynamics. Since water management plays a crucial role in achieving high performance, understanding the electrolyte-hydration-related signatures of the impedance spectrum may help better interpret experimental data and design future fuel cells. In this work, an open-source, transient, single-phase 2D model is presented that is suitable for analyzing impedance spectra of proton-exchange-membrane fuel cells. Special care is taken to compare the model to transient polarization, ohmic-resistance, and impedance data measured in-house. The model reveals that the low-frequency inductive phenomenon is related to the finite-rate exchange of water between the electrolyte and the pores. Two inductive phenomena are observed, at 0.1–200 mHz and at 0.2–5 Hz, that are attributed to the water-transport dynamics in the electrolyte phase of the catalyst layers and the membrane, and just the catalyst layers, respectively. This work also shows an ohmic-resistance breakdown study that demonstrates that the high-frequency resistance is comprised of the ohmic resistance of the membrane and the electronically conductive components of the cell, but does not include protonic resistance of the carbon-supported catalyst layers. Highlights: A multi-dimensional, physics-based transient fuel-cell model is used to study EIS. Low-frequency inductance is related to finite-rate water uptake by the electrolyte. Inductive loop strongly depends on water-transport mechanisms within the electrolyte. Weak back-diffusion of water may transform the inductive loop into a capacitive arc. HFR is shown to not include the ionic resistance of carbon-based catalyst layers.