Characteristic Time Constants Derived From the Low-Frequency Arc of Impedance Spectra of Fuel Cell Stacks

2018 ◽  
Vol 15 (2) ◽  
Author(s):  
Stefan Keller ◽  
Tansu Özel ◽  
Anne-Christine Scherzer ◽  
Dietmar Gerteisen ◽  
Ulf Groos ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Time Constant ◽  
Characteristic Time ◽  
Gas Flow ◽  
Electrochemical Impedance ◽  
Air Flow ◽  
Low Frequency ◽  
Impedance Spectrum ◽  
Gas Diffusion ◽  
Electrical Circuit

Electrochemical impedance spectroscopy is used during operation of different polymer electrolyte membrane fuel cell (PEMFC) stack assemblies at various conditions with special interest given to the characteristic time constant τlow-f derived from the low-frequency arc of the spectra which is typically in the range of approximately 15–0.5 Hz. This was done by fitting an equivalent electrical circuit (EEC) consisting of one resistor and two RC-elements to the data. Parameter variation performed on a 90-cell stack assembly suggests that conditions leading to different air flow velocities in the flow channels affect τlow-f while other parameters like humidity influence the impedance spectrum, but not τlow-f. Comparison of the stoichiometry variation between short stack and locally resolved single cell shows similar results with the stack's time constant matching that of the cell's segments which are located off-center toward the outlet. However, a nonlinear dependency between gas flow velocity and τlow-f especially at low stoichiometric values is obvious. Results from stoichiometry variations at different pressure levels suggest that this could be attributed to the different steady-state oxygen partial pressures during the experiments. Comparison of the stoichiometry variation between different stack platforms result in similar dependencies of τlow-f on air flow rate with respect to a reference oxygen partial pressure regardless of size, flow field, geometry, or cell count of the stack. The time constant caused by oxygen diffusion through the gas diffusion layer (GDL), τGDL, was approximated and compared to τlow-f. While it was found that τlow-f ≫ τGDL at low stoichiometric values, τlow-f decreases toward τGDL at very high gas flow rates, suggesting that τGDL offsets τlow-f and becomes dominating if no oxygen concentration variation along the flow channel was present.

Numerical Modeling and Experimental Analysis of Air-Droplet Interaction in the Channel of a Proton Exchange Membrane Fuel Cell

2010 ◽  
Vol 7 (3) ◽  
Author(s):  
Angelo Esposito ◽  
Aaron Motello ◽  
Cesare Pianese ◽  
Yann G. Guezennec
Keyword(s):  
Fuel Cell ◽  
Water Transport ◽  
Gas Flow ◽  
Air Flow ◽  
Gas Diffusion ◽  
Mean Value ◽  
Proton Exchange ◽  
Computational Time ◽  
Droplet Growth ◽  
Experimental Apparatus

An accurate low order model (mean value model) that captures main water transport mechanisms through the components of a PEM fuel cell was developed. Fast simulation time was achieved through a lumped approach in modeling the space-dependent phenomena. Evaporation and capillarity were assumed to be the predominant mechanisms of water flow through the gas diffusion media. The innovative features of the model are not only to simulate the water transport inside the porous media with relative simplicity, but also to simulate the water transport at the interface between the gas diffusion layer and gas flow channel. In order to preserve a light computational burden, the complex air flow-droplet interaction was modeled with several simplifying assumptions, and with the support of measured data. The physics that characterizes the single droplet-air flow interaction was analyzed with an experimental apparatus constructed to study the droplet growth and detachment process. Furthermore, the experimental findings were exploited to feed the numerical model with the missing theoretical information, and empirical submodels to guarantee accuracy. Thanks to the followed fast computational time of the mean value approach, the model is suitable for fuel cell design and optimization, as well as diagnosis and control strategies development studies.

Numerical Modeling and Experimental Analysis of Air-Droplet Interaction in the Channel of a PEM Fuel Cell

2009 ◽  
Author(s):  
Angelo Esposito ◽  
Aaron Motello ◽  
Cesare Pianese ◽  
Yann G. Guezennec
Keyword(s):  
Fuel Cell ◽  
Water Transport ◽  
Gas Flow ◽  
Air Flow ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Mean Value ◽  
Computational Time ◽  
Droplet Growth ◽  
Experimental Apparatus

An accurate low order model (MVM, Mean Value Model) that captures the main water transport mechanisms through the components of a PEM Fuel Cell was developed. Fast simulation time was achieved through a lumped approach in modeling space-dependent phenomena. Evaporation and capillarity were assumed to be the predominant mechanisms of water flow through the gas diffusion media. The model innovative features are not only to simulate the water transport inside the porous media with relative simplicity but also to simulate the water transport at the interface between gas diffusion layer and gas flow channel. In order to preserve a light computational burden, the complex air flow–droplets interaction was modeled with several simplifying assumption and with the support of measured data. The physics that characterizes the single droplet-air flow interaction was analyzed with an experimental apparatus constructed to study the droplet growth and detachment process. Furthermore, the experimental findings were exploited to feed the numerical model with the missing theoretical information and empirical sub-models to guarantee accuracy. Thanks to the fast computational time of the mean value approach followed, the model is suitable for fuel cell design and optimization as well as diagnosis and control strategies development studies.

scholarly journals The Effects of the PEM Fuel Cell Performance with the Waved Flow Channels

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
Yue-Tzu Yang ◽  
Kuo-Teng Tsai ◽  
Cha’o-Kuang Chen
Keyword(s):  
Fuel Cell ◽  
Pressure Drop ◽  
Gas Flow ◽  
Gas Diffusion ◽  
Flow Channel ◽  
Proton Exchange ◽  
Electrical Performance ◽  
Wave Number ◽  
Gap Size ◽  
Fuel Cell Performance

The objective of this study is to use a new style of waved flow channel instead of the plane surface channel in the proton exchange membrane fuel cell (PEMFC). The velocity, concentration, and electrical performance with the waved flow channel in PEMFC are investigated by numerical simulations. The results show that the waved channel arises when the transport benefits through the porous layer and improves the performance of the PEMFC. This is because the waved flow channel enhances the forced convection and causes the more reactant gas flow into the gas diffusion layer (GDL). The performance which was compared to a conventional straight gas flow channel increases significantly with the small gap size when it is smaller than 0.5 in the waved flow channel. The performance is decreased at the high and low velocities as the force convection mechanism is weakened and the reactant gas supply is insufficient. The pressure drop is increased as the gap size becomes smaller, and the wave number decreases. (gap size)δ> 0.3 has a reasonable pressure drop. Consequently, compared to a conventional PEMFC, the waved flow channel improves approximately 30% of power density.

scholarly journals The effects of operating conditions on the performance of a direct carbon fuel cell

2013 ◽  
Vol 34 (4) ◽  
pp. 187-197 ◽  
Author(s):  
Andrzej Kacprzak ◽  
Rafał Kobyłecki ◽  
Zbigniew Bis
Keyword(s):  
Fuel Cell ◽  
Flow Rate ◽  
Gas Flow ◽  
Air Flow ◽  
Operating Conditions ◽  
Cell Performance ◽  
Fuel Particle ◽  
Air Flow Rate ◽  
Direct Carbon Fuel Cell ◽  
Fuel Particles

Abstract The influences of various operating conditions including cathode inlet air flow rate, electrolyte temperature and fuel particles size on the performance of the direct carbon fuel cell DCFC were presented and discussed in this paper. The experimental results indicated that the cell performance was enhanced with increases of the cathode inlet gas flow rate and cell temperature. Binary alkali hydroxide mixture (NaOH-LiOH, 90-10 mol%) was used as electrolyte and the biochar of apple tree origin carbonized at 873 K was used as fuel. Low melting temperature of the electrolyte and its good ionic conductivity enabled to operate the DCFC at medium temperatures of 723-773 K. The highest current density (601 A m−2) was obtained for temperature 773 K and air flow rate 8.3×106 m3s−1. Itwas shown that too low or too high air flow rates negatively affect the cell performance. The results also indicated that the operation of the DCFC could be improved by proper selection of the fuel particle size.

scholarly journals Optimization of Perfluoropolyether-Based Gas Diffusion Media Preparation for PEM Fuel Cells

Energies ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1831 ◽  
Author(s):  
Riccardo Balzarotti ◽  
Saverio Latorrata ◽  
Marco Mariani ◽  
Paola Gallo Stampino ◽  
Giovanni Dotelli
Keyword(s):  
Fuel Cell ◽  
Electrochemical Impedance ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Cathode Side ◽  
Porous Substrate ◽  
Materials Properties ◽  
Electrochemical Tests ◽  
Electrochemical Parameters ◽  
Diffusion Media

A hydrophobic perfluoropolyether (PFPE)-based polymer, namely Fluorolink® P56, was studied instead of the commonly used polytetrafluoroethylene (PTFE), in order to enhance gas diffusion media (GDM) water management behavior, on the basis of a previous work in which such polymers had already proved to be superior. In particular, an attempt to optimize the GDM production procedure and to improve the microporous layer (MPL) adhesion to the substrate was carried out. Materials properties have been correlated with production routes by means of both physical characterization and electrochemical tests. The latter were performed in a single PEM fuel cell, at different relative humidity (namely 80% on anode side and 60%/100% on cathode side) and temperature (60 °C and 80 °C) conditions. Additionally, electrochemical impedance spectroscopy measurements were performed in order to assess MPLs properties and to determine the influence of production procedure on cell electrochemical parameters. The durability of the best performing sample was also evaluated and compared to a previously developed benchmark. It was found that a final dipping step into PFPE-based dispersion, following MPL deposition, seems to improve the adhesion of the MPL to the macro-porous substrate and to reduce diffusive limitations during fuel cell operation.

scholarly journals Electrochemical Performance Measurements of PBI-Based High-Temperature PEMFCs

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Javier Parrondo ◽  
Chitturi Venkateswara Rao ◽  
Sundara L. Ghatty ◽  
B. Rambabu
Keyword(s):  
Fuel Cell ◽  
Electrochemical Performance ◽  
Electrochemical Impedance ◽  
Gas Diffusion ◽  
Cell Polarization ◽  
Membrane Electrode ◽  
Performance Measurements ◽  
Transfer Resistance ◽  
Warburg Impedance ◽  
Overall Resistance

Acid-doped poly(2,2′-m-phenylene-5,5′-bibenzimidazole) membranes have been prepared and used to assemble membrane electrode assemblies (MEAs) with various contents of PBI (1–30 wt.%) in the gas diffusion electrode (GDE). The MEAs were tested in the temperature range of140∘C–200∘C showing that the PBI content in the electrocatalyst layer influences strongly the electrochemical performance of the fuel cell. The MEAs were assembled using polyphosphoric acid doped PBI membranes having conductivities of 0.1 Scm−1at180∘C. The ionic resistance of the cathode decreased from 0.29 to 0.14 Ohm-cm2(180∘C) when the content of PBI is varied from 1 to 10 wt.%. Similarly, the mass transfer resistance or Warburg impedance increased 2.5 times, reaching values of 6 Ohm-cm2. 5 wt.% PBI-based MEA showed the best performance. The electrochemical impedance measurements were in good agreement with the fuel cell polarization curves obtained, and the optimum performance was obtained when overall resistance was minimal.

An Impedance Spectroscopy Study of a Micro PEMFC With Different Flow Fields

2006 ◽  
Author(s):  
Sheng-Huang Yang ◽  
Shou-Shing Hsieh ◽  
Chih-Lun Feng
Keyword(s):  
Fuel Cell ◽  
Impedance Spectroscopy ◽  
Electrochemical Impedance ◽  
Low Frequency ◽  
Flow Fields ◽  
Operating Conditions ◽  
Operational Parameters ◽  
Impedance Spectroscopy Study ◽  
Flow Geometry ◽  
Parametric Effects

The H2/air micro PEMFCs with three different flow fields were designed and fabricated in-house through a deep UV lithography technique. SU-8 photoresist was used as microstructure material for fuel cell flow-field plates. Different operational parameters were examined by electrochemical impedance spectroscopy (EIS). The operational parameters include cell operating temperature (25°C, 35°C, and 50°C), back pressures (1atm, 1.5atm, and 2atm) of reactant gases on anode site, and three different flow fields configurations (mesh, interdigitated, and serpentine). The effect of the above parameters on high frequency, medium frequency, and low frequency arc were found. The influence in terms of impedance on dynamic response of the present H2/air micro fuel cell under different operating conditions and flow geometry can be quantitatively measured. Results are presented in the form of the polarization VI curves, PI curves, and impedance spectra under different operating conditions. The possible transport mechanisms associated with the parametric effects were discussed. In addition, it was found that, among the three flow patterns considered, significant improvements can be reached with a specified flow geometry.

scholarly journals Research on an Artificial Lateral Line System Based on a Bionic Hair Sensor with Resonant Readout

Micromachines ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 736 ◽  
Author(s):  
Yang ◽  
Zhang ◽  
Liang ◽  
Lu
Keyword(s):  
Flow Velocity ◽  
Lateral Line ◽  
Gas Flow ◽  
Air Flow ◽  
Low Frequency ◽  
Lateral Line System ◽  
Least Mean Square ◽  
Line System ◽  
Canal Neuromast ◽  
Air Flow Velocity

Inspired by the lateral line system of fish, an artificial lateral line system based on bionic hair sensor with resonant readout is presented in this paper. An artificial lateral line system, which possesses great application potential in the field of gas flow visualization, includes two different sensors: a superficial neuromast and a canal neuromast flow velocity sensor, which are used to measure the constant and oscillatory air flow velocity, respectively. The sensitive mechanism of two artificial lateral line sensors is analyzed, and a finite element simulation is implemented to verify the structural design. Then the control circuit of the artificial lateral line system is designed, employing a demodulation algorithm of oscillatory signal based on the least mean square error algorithm, which is used to calculate the oscillatory air flow velocity. Finally, the experiments are implemented to assess the performance of the two artificial lateral line systems. The experimental results show that the artificial lateral line system, which can be used to measure the constant and oscillatory air flow velocity, has a minimum threshold of 0.785 mm/s in the measurement of oscillatory air flow velocity. Moreover, the artificial canal neuromast lateral line system can filter out low-frequency disturbance and has good sensitivity for high-frequency flow velocity.

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