Localized Impedance Measurements along a Single Channel of a Solid Polymer Fuel Cell

Brett, Dan J. L.; Atkins, Stephen; Brandon, Nigel P.; Vesovic, Velisa; Vasileiadis, Nikos; Kucernak, Anthony

doi:10.1149/1.1557034

Cited by 103 publications

(69 citation statements)

References 21 publications

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“…As the frequency increases, the wavelength of each pressure perturbation decreases; thus more than one pressure perturbation may be required before a voltage response is observed in the PEFC and the phase shift can exceed -360°; given that the distance between the point of pressure measurement and the point at which the pressure 'front' first affects the fuel cell is fixed, the phase shift will tend to negative infinity. There is potential here to examine how flow is distributed in a fuel cell by examining the localised EPIS phase shift using a segmented current collector or reference electrode array, analogous to localised EIS [24][25][26]. Furthermore, diffusion of gas to the catalyst surface can be examined by comparing the phase shift of a system using air to one with helox, a mixture of helium and oxygen, in which diffusion will be an order of magnitude faster [18].…”

Section: Equationmentioning

confidence: 99%

Electrochemical pressure impedance spectroscopy applied to the study of polymer electrolyte fuel cells

Engebretsen

Mason

Shearing

et al. 2017

Electrochemistry Communications

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The development of novel in-situ diagnostic techniques allows new insight into the internal working of polymer electrolyte fuel cells (PEFCs) so that improved performance can be realised. Electrochemical impedance spectroscopy (EIS) is a widely used characterisation technique that takes advantage of the dynamic relationship between current and voltage to deconvolute critical mechanisms and sources of performance loss occurring with different time constants. Here, we apply electrochemical pressure impedance spectroscopy (EPIS) which examines the transfer function relating reactant gas pressure modulation to the electrical response of the fuel cell. A sinusoidally oscillating perturbation is applied to the cathode backpressure using an innovative loudspeaker arrangement and the resulting voltage 2 perturbation is monitored across a frequency range while the fuel cell is operated in galvanostatic mode. It is shown that the technique can be used to separate the explicit effect of water management from reactant starvation when a PEFC is operated under different reactant humidification conditions. KeywordsElectrochemical pressure impedance spectroscopy; polymer electrolyte fuel cell; backpressure; transfer function analysis; water management; mass transport limitation.

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Section: Equationmentioning

confidence: 99%

Electrochemical pressure impedance spectroscopy applied to the study of polymer electrolyte fuel cells

Engebretsen

Mason

Shearing

et al. 2017

Electrochemistry Communications

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“…As reported by Brett et al [21], the problem when choosing an equivalent electrical circuit is that must suit the bulk EIS results when actually different parts in the PEFC frequency response may be fit to the equivalent circuit with very different parameters or may require a different equivalent circuit…”

Section: Development Of a Generic Equivalent Circuit For CCL Analysismentioning

confidence: 99%

A generic electrical circuit for performance analysis of the fuel cell cathode catalyst layer through electrochemical impedance spectroscopy

Cruz-Manzo

Chen

2013

Journal of Electroanalytical Chemistry

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A Generic Electrical Circuit for Performance Analysis of the Fuel Cell Cathode Catalyst Layer through Electrochemical Impedance SpectroscopyThe new electrical circuit is derived from fundamental electrochemical and diffusion theory. It consists of a transmission line in combination with distributed Warburg elements. The validation of this study is divided into a theoretical validation and an experimental validation. In the theoretical validation the impedance response of the CCL generated from three different circuits reported in the literature was compared with the simulated data from the generic electrical circuit. In the experimental validation, Electrochemical Impedance Spectroscopy (EIS) measurements were carried out in an H 2 /air PEFC and through a three-electrode configuration in the measurement system and were compared with the simulated data from the generic circuit. The results show that the generic circuit is able to accurately reproduce the measured data of the CCL at different current densities and is able to represent the electrochemical and diffusion mechanisms of the CCL in the frequency domain. It is possible to generate a deeper understanding of how and where the chemical energy that is released from the redox reaction is being dissipated and retained within the real physical system.

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“…Discussion.-Only few experimental works report local impedance spectra at low oxygen stoichiometry (flow rate); 31,32,[37][38][39][40] the most detailed study has been published by Schneider et. al.…”

Section: Resultsmentioning

confidence: 99%

A Model for PEM Fuel Cell Impedance: Oxygen Flow in the Channel Triggers Spatial and Frequency Oscillations of the Local Impedance

Kulikovsky

Shamardina

2015

J. Electrochem. Soc.

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A physical model for impedance of a PEM fuel cell cathode side is developed. The model takes into account oxygen flow in the cathode channel. Analytical solution to model equations reveals an effect of spatial oscillations of the local impedance Z loc along the channel coordinate z. The oscillations arise due to interference of the local and transported down the channel perturbations of the oxygen concentration. With the growth of the frequency of the exciting signal, the domain of spatial oscillations of Z loc shrinks toward the oxygen channel inlet; a process, analogous to the skin-effect in classic electrodynamics. An expression for the characteristic width of the skin-layer is derived. The spatial oscillations are accompanied by the oscillations of Z loc along the frequency axis ω. The amplitude of Z loc oscillations decreases exponentially along z and ω, with the characteristic scale of the exponent dependent on the oxygen diffusion coefficient D b in the gas-diffusion layer. This effect enables determination of D b from the local cell impedance measured close to the channel outlet at a real operating stoichiometry of the oxygen flow. Electrochemical impedance spectroscopy (EIS) is, perhaps, the most powerful tool for in situ characterization of fuel cells.1,2 In spite of impressive progress in developing physical models for PEMFC impedance, 3-15 cell and stack developers still routinely use simple transmission line models (TLMs) for understanding the impedance spectra.16,17 A great advantage of TLM is simplicity and fast operation, which enables rapid characterization of the cell components in terms of TLM resistivities and capacitances.18 However, relation of TLM parameters to the physical transport and kinetic coefficients of the cell is beyond the scope of this approach.A much more informative physical characterization of the cell can, in principle, be done with the physical impedance models; however, these models are typically slow for accurate least-squares (LS) fitting of experimental spectra. A core element of numerical impedance models is a strongly nonlinear transient model for the cathode catalyst layer performance.19-22 A linearized and Fourier-transformed version of this model leads to the complex-valued boundary-value problem, which in the general case of arbitrary cell current can only be solved numerically. 23 The presence of the boundary-value problem solver makes the respective fitting code slow for massive processing of experimental results.An alternative approach is based on analytical solutions for the impedance.22,24-26 Based on ideas developed in Refs. 27-29 this approach aims at deriving analytical solutions for the linearized version of the cell performance model. If the cell current density is small, these solutions can be obtained and a closed-form expression for the system impedance Z can be derived. Analytical relations for Z typically include the Tafel slope of the oxygen reduction reaction (ORR), the proton conductivity of the cathode catalyst layer (CCL), and the oxygen diffu...

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Localized Impedance Measurements along a Single Channel of a Solid Polymer Fuel Cell

Cited by 103 publications

References 21 publications

Electrochemical pressure impedance spectroscopy applied to the study of polymer electrolyte fuel cells

Electrochemical pressure impedance spectroscopy applied to the study of polymer electrolyte fuel cells

A generic electrical circuit for performance analysis of the fuel cell cathode catalyst layer through electrochemical impedance spectroscopy

A Model for PEM Fuel Cell Impedance: Oxygen Flow in the Channel Triggers Spatial and Frequency Oscillations of the Local Impedance

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