A Kernel for Calculating PEM Fuel Cell Distribution of Relaxation Times

Abstract

Impedance of all oxygen transport processes in PEM fuel cell has negative real part in some frequency domain. A kernel for calculation of distribution of relaxation times (DRT) of a PEM fuel cell is suggested. The kernel is designed for capturing impedance with negative real part and it stems from the equation for impedance of oxygen transport through the gas-diffusion transport layer (doi:10.1149/2.0911509jes). Using recent analytical solution for the cell impedance, it is shown that DRT calculated with the novel K2 kernel correctly captures the GDL transport peak, whereas the classic DRT based on the RC-circuit (Debye) kernel misses this peak. Using K2 kernel, analysis of DRT spectra of a real PEMFC is performed. The leftmost on the frequency scale DRT peak represents oxygen transport in the channel, and the rightmost peak is due to proton transport in the cathode catalyst layer. The second, third, and fourth peaks exhibit oxygen transport in the GDL, faradaic reactions on the cathode side, and oxygen transport in the catalyst layer, respectively.

Characterization of a Commercial Polymer Electrolyte Membrane Fuel Cell Stack by Means of Physics-Based Modeling and Distribution of Relaxation Times

“…In this work, the K 2 kernel was used for DRT calculation . With this kernel, the basic DRT equation has the form where α is a step function of the frequency f = ω/(2π) H ( x ) is the Heaviside step function and ϵ = 10 –10 is a small parameter to avoid zero division error.…”

“…With α → 0, this factor tends to unity: and hence, at the frequencies above f * , the K 2 kernel reduces to the standard Debye kernel. Equation better captures DRT peaks due to oxygen transport in channel and GDL, while the ORR and higher-frequency peaks are described in a usual way using the Debye kernel.…”

“…In this work, the K 2 kernel was used for DRT calculation. 17 With this kernel, the basic DRT equation has the form…”

“…Further, we calculate DRT functions from the experimental and fitted model impedance spectra. The DRT spectra are calculated using a novel K 2 kernel, which better captures low- and medium-frequency transport processes in a PEM fuel cell as compared to the classic Debye kernel …”

“…The DRT spectra are calculated using a novel K 2 kernel, which better captures low-and mediumfrequency transport processes in a PEM fuel cell as compared to the classic Debye kernel. 17 DRT spectra of a Ballard stack at the current densities of 150, 250, and 400 mA cm −2 exhibit five peaks. We attribute the peaks (in ascending frequency order) to (1) oxygen transport in the channel, (2) oxygen transport in the GDL, (3) oxygen reduction reaction, and (4,5) proton transport in the catalyst layer.…”