PEM Fuel Cell Characterisation by Means of the Physical Model for Impedance Spectra

A recent analytical solution of the physical model for the PEM fuel cell impedance [A. A. Kulikovsky, J. Electrochem. Soc., 162, F217 (2015)] is used for least–squares fitting of experimental impedance spectra. Ten spectra are collected in one experimental run of a cell with ten segments operated at a current density of 100 mA cm− 2 under high stoichiometry of the oxygen flow. The model impedance is fitted to the spectra and the resulting physical parameters of the cathode side are discussed. Of particular interest is a low value of the oxygen diffusion coefficient in the cathode catalyst layer ( ≃ 0.45 · 10− 4 cm2 s− 1), a parameter, which has not been measured in situ so far. This low value, as well as a high value of the cathode catalyst layer (CCL) proton conductivity σp ≃ 0.054 Ω− 1 cm− 1 is attributed to a large amount of liquid water in the CCL

Understanding the distribution of relaxation times of a low–Pt PEM fuel cell

Distribution of relaxation times (DRT) is calculated from fifty local impedance spectra of a low–Pt PEM fuel cell. 48 out of 50 DRT spectra contain three peaks. Evolution of the peak frequency positions and resistivities with the cell current density are analyzed. The analysis allows us to attribute the low–frequency peak to oxygen transport in the gas–diffusion layer (perhaps, including transport in the channel), the middle peak to unresolved processes of charge–transfer and oxygen transport in the ionomer film, and the high-frequency peak to oxygen transport in void pores of the catalyst layer. Comparison of DRT spectra of low–Pt and high–Pt cells suggests a method for measuring ionomer film transport resistivity in a low–Pt cell

Distribution of Relaxation Times: A Tool for Measuring Oxygen Transport Resistivity of a Low–Pt PEM Fuel Cell Cathode

Oxygen transport resistivity of the cathode catalyst layer in a low–Pt PEM fuel cell has been determined using two methods: the first one is fitting of our recent physics–based impedance model to the experimental impedance spectra of the cell, and the second is calculation of distribution of relaxation times (DRT) using the same spectra. Comparison of the two methods shows that the DRT peak with the characteristic frequency on the order of 500 to 1000 Hz describes oxygen transport in the open pore and in Nafion film covering Pt/C agglomerates in the catalyst layer. This result makes it possible using experimental impedance spectroscopy and DRT calculation for routine measurements of cathode transport resistivity in low–Pt PEMFCs

A Model for Local Impedance: Validation of the Model for Local Parameters Recovery from a Single Spectrum of PEM Fuel Cell

A physics–based numerical model for fitting local impedance spectra (local impedance model, LIM) of the segmented PEM fuel cell is developed and used to validate our recent model for recovery of local parameters from a single spectrum of the whole cell (cell impedance model, CIM). Shapes of the local parameters along the cathode channel resulting from the two models are compared. Overall, the CIM quite satisfactorily describes the cell local parameters provided that the oxygen transport impedance in the channel is not small as compared to other impedances in the cell

Correction: Nafion film transport properties in a low-Pt PEM fuel cell: impedance spectroscopy study

Correction for ‘Nafion film transport properties in a low-Pt PEM fuel cell: impedance spectroscopy study’ by Tatyana Reshetenko et al., RSC Adv., 2019, 9, 38797–38806, DOI: 10.1039/C9RA07794D

Oxygen transport in the low–Pt catalyst layer of a PEM fuel cell: Impedance spectroscopy study

A model for PEM fuel cell impedance taking into account the pore size distribution (PSD) in the cathode catalyst layer is developed. Experimental PSD is approximated by pores of three sizes (small, medium and large) and in each kind of pores, the oxygen diffusion coefficient is allowed to have a separate value. The model is fitted to experimental impedance spectra of a low–Pt PEM fuel cell. The oxygen diffusivities of small and medium pores exhibit rapid growth with the cell current density, while in large pores, this parameter remains nearly constant. We show that oxygen reduction occurs mainly in the small and medium pores, leaving the large pores for mass transport only. This effect explains the discrepancy between small effective oxygen diffusivity of PEMFC catalyst layer measured in situ in operating cells by limiting current method, and much larger value of this parameter determined from ex situ experiments using Loschmidt cell

Two States of the Cathode Catalyst Layer Operation in a PEM Fuel Cell

We measure impedance of a standard Pt/C–based PEM fuel cell for a series of current densities from 50 to 400 mA cm− 2. Using our recent model for extraction of spatially–resolved data from impedance spectra, we plot the dependence of the oxygen diffusion coefficient Dox in the cathode catalyst layer (CCL) and Db in the gas–diffusion layer (GDL) on the distance along the cathode channel. While the GDL oxygen diffusivity is fairly uniform over the cell active area, the shape of Dox indicates that the cell is separated into two domains with high and low water contents in the CCL. We attribute this effect to the positive feedback loop between the rates of oxygen transport and liquid water evaporation in the CCL, leading to local CCL flooding

A Model for Extraction of Spatially Resolved Data from Impedance Spectrum of a PEM Fuel Cell

We report a novel approach to processing of impedance spectra of a PEM fuel cell. We split the cell into N virtual segments andlet each segment to have its own set of transport and kinetic parameters. The impedance of a single segment is calculated using ourrecent physics–based impedance model; the segments are “linked” by equation for the oxygen mass balance in the cathode channeltransporting the local phase and amplitude information from one segment to another. Thanks to this transport, the total cell impedancecontains information on the local transport and kinetic properties of the cell. We show that fitting the model cell impedance to theexperimental spectra yields the parameters of individual segments, i.e., the shape of the cell physical parameters along the cathodechannel